pinging/detonation

[JRBAMATEX]

Been working on this Cherokee almost constantly since I got it in December 2009 and haven't really been able to drive it much at all. I guess that's Ok though cause it's just a hunting rig. Problem is more me than the truck. I just want it to run right and be semi reliable for it's purpose. I hate it when things aren't right. I can handle old and not perfect. Just have trouble with noises and excessive leaks. (I know it's gonna leak.) But my hunting buddies are going to give me heck about it... I can hear it now.. "Should've bought a Chevy JR..." Yeah yeah OK but I think this FSJ has the best 4X4 out there and if running right should go anywhere.

So here's the deal now. When I run it around the neighborhood test driving it I have what I think is a lifter that clatters like a little jack hammer under certain acceleration conditions. Mostly tourque heavy conditions. Such as.. Hard acceleration from a dead stop or slow roll or if I goose it from about 15 MPH or so. Then it goes away once it get up to speed a little and the tourque condition lessons. Once up to speed and goose it more no lifter noise. Otherwise the engine runs great! No noise at start up. No noise just reving it in park or neutral.

The lifter noise is really a bummer because I was just in there recently. I replaced the intake valley pan and gaskets (cleaned all sludge), timing chain, new chain cover, oil pump, rear main seal, etc. cleaned and painted all parts. Looks great and runs great. Except for the lifter clatter.

Oil psi = 25 - 50 depending on accleration deceleration or idles about 35 psi.

1979 Cherokee, AMC 360, TH400, QT W/Reduction.

I just drained all of the Quaker Stae 10-W30 and put in a Qt of the Lucas thick oil stabilizer and some Castrol 20-W50 in the hope that it would help to keep the lifter pumped up. Might have helped a smidge but not enough to matter.

Any thoughts or ideas before I dig back in to this thing and start changing lifters. That is as for as I want to go. Don't want to have to go back under Timing Chain Cover again. i.e. cam replacement. Wife will freak if I clog up the driveway for two months like that agian.

Sure would be great if there were some kind of additive that I could pour in it to make it quit this. I think the lifter seals (if there is such a thing) must have dried up durring the time I had the engine open while working on the intake and Timing chain cover, etc. Maybe some of the break cleaner I used to help clean gunk in the valley comprimised a lifter. I dried it up as quickly as I could and put assymbly lube on the tops of the lifters to help protect them while it was open but you never know.

JR

[Heavy_Metal_Thunder_81]

You say its a clattering under acceleration? May be the flex plate...Ive gone through 2 on my '79 Cherokee and one on my '79 Wagoneer and both sounded like you describe. Put it in drive and brake torque the engine and see too see if the noise get louder or pull off the inspection covers on the trans, take a flashlight and look up in there all the way up to the crank and look for cracks.

[JRBAMATEX]

Hmmm.. OK I'll check that out. The noise does sound like it is coming from the area of the number 6 or 8 cylinder. So that is in the back part of the engine. (Not far from flex plate I'm guessing.) I have found over the years that noises hardly ever wind up being where you think they are coming from.

I don't know what a flex plate is or does but I will find out. If there is damage to it will it be pretty apparent visually when I look up in there with my flashlight? Also... I bet it's a bear to fix right. Kind of like open heart surgery. I mean why wouldn't it be everything else is.

Have to pull engine?

I'll do some searches on the topic.

many thanks,
JR

[Chris P.]

Also check for an exhaust leak. They have symptoms just like you describe.

[Heavy_Metal_Thunder_81]

Hmmm.. OK I'll check that out. The noise does sound like it is coming from the area of the number 6 or 8 cylinder. So that is in the back part of the engine. (Not far from flex plate I'm guessing.) I have found over the years that noises hardly ever wind up being where you think they are coming from.

I don't know what a flex plate is or does but I will find out. If there is damage to it will it be pretty apparent visually when I look up in there with my flashlight? Also... I bet it's a bear to fix right. Kind of like open heart surgery. I mean why wouldn't it be everything else is.

Have to pull engine?

I'll do some searches on the topic.

many thanks,
JR

Flex plate is a flywheel for an auto trans. Its just a stamped piece of spring steel. All of mine were pretty easy to see but I let them go til they got real bad before lookng at them. You can either pull the trans back a bit to get at it but I found it way easier on the last one I did to pull the engine. Not a bad job to pull an engine on these, coule have it out and back in in a day if youre motivated, weekend at most.

[Heavy_Metal_Thunder_81]

Chris brings up a good point, these rigs are notorious for exhaust leaks...

[Wayne]

Could be detenation, try retarding your timing.

[JRBAMATEX]

What a goof I am. Flexplate is like a flywheel only its for an automatic trans. You know I have always just called that a flywheel. never knew that they had a differnt name if auto or manual. I love learning new stuff..

This sounds like it's going to be a bummer lifter of flexplate. I'll check it out and update you guys.

[xsonmyeyes]

Sounds like Detonation/Spark knock to me??? :confused:

[azpackrat]

X-3 detonation, occurs during hard acceleration, try using some high octane gas if the noise goes away it's detonation, then it's time to play with the timing and fuel mixture.

[JRBAMATEX]

Whooo Hooo!!!!

Based on azpackrat and xsonmyeyes notes I did a little web search on the detonation theroy. I don't own a timing light but I do know how to twist the distributor so I started retarding the timing a little at the time this morning. The test driving between each adjustment. Clatter is all but gone!!! Just a little bit every now and then and it is not as pronounced as before. Don't want to retard timing any more because it starts idling kinda rough if i go any more and the vacuum hose is getting closer to the PS belts. But it runs pretty good now.

Now maybe I should twist the knobs (adjustment screws on the carb.) that's really getting into an area where I can mess something up though and wouldn't even know where to start outside of idle adjustment screw. Mixture and such is an oppty for never run right again for me.

Any advice on MC 2150 carb adjustment? It seems kind of slugish to me. I know its a two barrel on a 360 and some sluggish comes with that but just a touch more jump would be great. Might even eliminate that last little bit of Detonation.

You guys are great. This forum reminds me so much of the time I spent over at SteelSoldiers.com when I had the deuce and a half.

THANK YOU THANK YOU THANK YOU!!!!!

JR

[GearJamsey]

Valve clatter, valve clatter! Mine did the same thing when my distributer spun clockwise a little bit.. spin it teh udder way.. and it'll quit it!

[xsonmyeyes]

Well, I don't mean to get u into a bunch of stuff u don't want to be in but I got rid of all my spark knock with a HEI and edelbrock 4 barrel carb and intake. :eek:

[JRBAMATEX]

Guys this thread has been very helpful but I am still trying to figure out how to get this last little bit of detonation clatter/ping out of my rig.

Based on the advice above I played with my timing and the ping has really improved. All but gone really. Only slight pinging when I really get in to it in a kind of on the gas off the gas back on the gas hard and really trying to make it ping. But still I want to try to make it go away completely if I can. Cause apparently it can be a bad thing and I figure even a little isn't good.

I have adjusted the distributor clockwise as far as I can go withoiut adversely affecting the general idle negatively. Some of the research I have done says that making the fuel mixture a little richer could help with the elimination of the ping. I have done some searching on the site and see some coments that say that the Idle Mixture Screws may not help me with this problem since they are "Idle" mixture screws. Do you all think that any adjustment to the idle mixture screws might help to eliminate this last little bit of detonation ping?

Or is there some other adjustment I could make? I think in my searches on the site I saw something about an adjustment inside the distributor like maybe some type of vacuum or mechanical advance adjustment that might cause the last little bit of improvement I am looking for. If I can get past this I can start working on some of my electrical/lights and heater ducts and interior stuff. Maybe even some grille repair.

Thanks and sorry thread still says Lifter Noise when it clearly isn't.

[kennewick]

Also check for an exhaust leak. They have symptoms just like you describe.

X2 exhaust leaks can make you crazy. 3/8's fuel hose one end in your ear probe the gasket surface with the other end. Nothing works better.
Wasting your time without a time light. Get a count back model and learn how to use it. You need to figure out how to static time, total time (with mech. advance) and calculate vac advance. Then decide if your going to use ported vac or mani vac (I use mani but that disscussion can start a duke).
You would need to be prepared to adjust the idle mix and idle rpms after every diz change. Count back time lights have a tach on them and it makes it easy. About 70 well spent bucks. Get a vac guage, oil pressure guage, while your at it and get a vac troubleshooting chart. Cheap. Last get a good compression guage. Stop guessing and start knowing.
Oh yeah... elk strap rocks!!

[JRBAMATEX]

Still searching and found a post that said a plugged EGR can contribute to ping so thought I would mention that my EGR was not functioning prior to the recent work I did on intake gasket/valley pan so when I put it back toegther I just capped the EGR.

Figured I should add that.

[shimniok]

Yeah, I think EGR could help by lowering combustion temps... maybe there's some carbon deposits in the cylinders that is igniting the fuel due to high comb. temps? Or by decreasing volume (increasing CR) ...

My old motor started to get real prone to spark knock before I pulled it (needed a rebuild anyway at that time).

Also possible that your vacuum advance is advancing too much... It might be interesting to check w/ timing light and applying vac pump to the vac advance on the distr to see how much advance you're getting.

I have a recurved distributor (tuned by an AMC guru) that appears to have a limit screw installed to limit the amount of vac advance possible. Maybe something like that could be done, I dunno.

And also maybe see if you can get a sense of mechanical advance... perhaps you're getting too much mech. advance... test timing at say idle, 1000, 2000 rpm and 3000 ? You may need a timing light that you can enter in the advance settings otherwise you can't see the mark. Plot it on a graph or something and if it is getting advance too much too fast that might be part of the problem. Maybe the advance springs are weak...

Just throwing out some ideas...

[biotex]

Running higher grade gasoline will help with pining. The higher the compression ratio, the higher the octane needed. Do you know if the engine was rebuilt, and maybe someone put 10:1 pistons in?

More than likely you are just one or two degrees off on your timing. Too far advanced will ping. If you are running a stock distributor, chances are your curve is fine. If an aftermarket HEI, the odds are you are running too much total advance. Most aftermarket HEI's are cloned from GM specs. The AMC engine doesn't like as much advance as a SBC.

The stock distributor can be adjusted with an allen wrench, so it is possible someone has moved the advance rate around.

You really need a timing light so you can stop guessing. If you hook your advance up to ported vacuum instead of manifold, then you won't get full advance at idle. How is yours hooked up? Directly to a ported source (base of carb) or to manifold vac?

[JRBAMATEX]

I agree on the need for timing light acquisition. Was just trying to get by on ear and seat of pants. Years ago I had a 1968 Chevy C-10 that I put a junk yard motor in and got it running real good with no T light. Don’t think that’s gonna happen this time. I am going to get the timing light and then run through the Haynes Procedure to set Mech and then deal with Vac. I am running the stock Dist on Manifold advance. I think the last time I filled it up was with 93 Octane. I know that I can’t be far off because it runs pretty dog gone good now that I have turned Dist back clockwise. Still just have that last little occasional ping. But I’ll find it….

Thanks for the encouragement to get the timing light and do it right.

I think I’ll dinker with re-routing some of the electrical patchwork of the PO this weekend and figure out why the front running/signal lights come on when I apply the brakes… Too funny!!!

[threepiece188]

What a goof I am. Flexplate is like a flywheel only its for an automatic trans. You know I have always just called that a flywheel. never knew that they had a differnt name if auto or manual. I love learning new stuff..

This sounds like it's going to be a bummer lifter of flexplate. I'll check it out and update you guys.
The flexplate is not much like a flywheel. A flywheel is made to have mass (weight) in order to store kinetic energy. I would actually consider the torque converter to be much more of a flywheel than the flex plate since it has much more mass.
Dan

[kennewick]

I agree on the need for timing light acquisition. Was just trying to get by on ear and seat of pants. Years ago I had a 1968 Chevy C-10 that I put a junk yard motor in and got it running real good with no T light. Don’t think that’s gonna happen this time. I am going to get the timing light and then run through the Haynes Procedure to set Mech and then deal with Vac. I am running the stock Dist on Manifold advance. I think the last time I filled it up was with 93 Octane. I know that I can’t be far off because it runs pretty dog gone good now that I have turned Dist back clockwise. Still just have that last little occasional ping. But I’ll find it….

Thanks for the encouragement to get the timing light and do it right.

I think I’ll dinker with re-routing some of the electrical patchwork of the PO this weekend and figure out why the front running/signal lights come on when I apply the brakes… Too funny!!!

I have to get going right now but I will supply you some links for educational purposes to get timing down in your mind, Haynes isn't much help. Once you get the good time light and know how to use it your confidence level will go way up.

[biotex]

I am running the stock Dist on Manifold advance.


Manifold vacuum gives you vacuum at idle. Vacuum at idle cause the canister to advance the ignition to the max. You don't need advance at idle.

When you step on the gas to accelerate, your manifold vacuum drops. This drop in vacuum causes you to lose advance, when you need it!

A lot of guys run manifold vacuum, but it is not the best way for engine longevity, and optimal fuel mileage. Not trying to start something, but those are facts than are provable.

I'm not saying that is your problem with pinging, just saying that you can optimize your performance with ported vacuum. It is also easier on your exhaust valve seat (decelerating).

I would cap off your vacuum advance, and set the timing to 6° to 8° BTDC. hook the vacuum advance back up (manifold) test drive, and see how it does. If it still pings, then try setting your initial advance to 10°, and leave the vacuum advance off and capped. Test drive, and see if it still pings. If not, then you know you are getting too much total advance.

Try switching to ported vacuum, and test drive again. If it doesn't ping, then you can reset initial timing to 8°, and leave it on ported. Doesn't cost a thing to try!
It took me 2 hours to get my 304 to stop pinging making minute adjustments, but it sure runs good now! I will add that it is on manifold vacuum curently, since I bought a new CTO switch, and have not hooked it back up yet (being lazy). I am going to switch back to ported soon.

FYI! The factory DuraSpark ignition module has a built in ignition retard (6° to 8°) during cranking for easier starts. This allows you to run a bit more initial advance, and not have starting issues.

Hope this helps you!
Eric

[SamW]

Don't forget to try and eliminate any vacuum leaks you might have, I would do that before messing with the carb settings. Timing light and checking your timing at idle are the best places to start. I have my '89 at 12 degrees BTDC with ported vacuum and I run mid grade octane fuel, mine only pings with the AC on on really hot days at part throttle.

Other things are, as you mentioned, adjusting the vacuum advance on the distributor, also limiting the total advance on the distributor and replacing the mechanical advance weight springs in the distrubtor.

If you pinging is mostly at wide open throttle, my first guess would be too much advance on your timing, I once set mine (by accident) to 16 degrees BTDC and it would ping under a heavy load with lots of throttle.

[kennewick]

I have to get going right now but I will supply you some links for educational purposes to get timing down in your mind, Haynes isn't much help. Once you get the good time light and know how to use it your confidence level will go way up.

http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html
Link above is a write up from a former GM engineer about timing advance. It is also my understanding on it.
Vac advance works best when there isn't any load. The fuel air mix burns slower so advance allows the mix to burn as the piston positions for its down travel. Idle is very low load. As you romp on it you go to wide open throttle and the fuel air mixture burns faster and mani vac goes down for less advance. As vac comes down the speed of the diz picks up and mechanical advance weights picks up the duty all the way to total advance around 3000ish rpms and a total advance of around 35* this is it until red line. As you back off and cruise the load reduces and mechanical starts down but mani vac builds some and the two work can work together at cruise load(depends where the vac diaphram is set) also during cruise the mixture burns slower and thats when you need the additional advance (provided mostly by mechanical as most stock Vac Diaphrams don't advance below 18" ). This is the way it was until emissions came around in the 70's. Less advance at idle ran engines hotter at idle and used more gas along with sluggish performance. EGR of that era is a dog but could reduce NOX and allow higher ported vac advance without ping. It had to be ported to keep the EGR closed at idle when vac is high. But durring cruise the ported vac would operate the EGR. During WOT vac would drop and close EGR for passing power. Cat converters burned up the rest of the incomplete combustion.
Anyway thats my understanding. I could be wrong.

[woodfar]

Figure this strange one out. I just upgraded to HEI. Set timing to 10. Trying to get best bang for my buck I started advancing timing few degrees at a time trying to get pink so I could back it down. 40 before tdc and still no pink. What gives?

[Chris P.]

When you step on the gas to accelerate, your manifold vacuum drops. This drop in vacuum causes you to lose advance, when you need it!

A lot of guys run manifold vacuum, but it is not the best way for engine longevity, and optimal fuel mileage. Not trying to start something, but those are facts than are provable.

Once off idle, ported and manifold vac are exactly the same.

I'd like to see the argument for ported being better for mileage and longevity.

Figure this strange one out. I just upgraded to HEI. Set timing to 10. Trying to get best bang for my buck I started advancing timing few degrees at a time trying to get pink so I could back it down. 40 before tdc and still no pink. What gives?
Maybe the balancer slipped or the timing light is on the wrong wire?

[kennewick]

[quote=Chris P.]Once off idle, ported and manifold vac are exactly the same.
True statement. And they would handle EGR equally once off idle. But one would have to run without egr with mani vac at idle or it would have idle trouble. So if EGR is still working ported is better. Another consideration is a high lift cam. The vac advance would have to operate at a lower vac. A degree or two below idle vac. After market adjustable.

[Chris P.]

EGR will still work fine with the dizzy on manifold vacuum. Just leave the EGR on ported vacuum. Why would you put it on manifold vac?

[kennewick]

EGR will still work fine with the dizzy on manifold vacuum. Just leave the EGR on ported vacuum. Why would you put it on manifold vac?

I said:
"But one would have to run without egr with mani vac at idle or it would have idle trouble. So if EGR is still working ported is better."

I was trying to say that but you said it better. I agree.:)

[biotex]

I'd like to see the argument for ported being better for mileage and longevity.


You asked!:D Please read post #13 for the argument. Grab some popcorn first:eek: .

http://www.jeepforum.com/forum/f8/timing-1055680/

I'm running manifold vacuum on my CJ, and the 304 runs awesome. It's one of those debates that will never go away. There is merit to both sides, so it is one of those personal choice things. Just too many variables, but still worth reading IMO.

[Chris P.]

Thanks for posting the link. That is a great read.

Though I think there is some misinformation there. Just my opinion.

[biotex]

Thanks for posting the link. That is a great read.

Though I think there is some misinformation there. Just my opinion.

No one is always going to be 100% correct on the more technical issues, and personally I'm one of those guys that believes "if it works for you" go with it.

I have run both ways, and to tell the truth, I can't tell any difference between P & M vacuum (on a healthy and tuned engine).

I understand the point about when you deccelerate from cruise, and your manifold vacuum sky rockets, and you advance to the maximum. I just don't know whether to believe it potentially hurts the exhaust valves or not (albeit minutely) by banging them shut harder.

Heck with it! I'm soon going to TBI anyways...

[Ristow]

ah yes. the vacuum discussion. ported is an emissions tactic. nothing more. period. it raises combustion chamber temps by forcing the engine to run in a less efficient state,at idle. manifold is the correct way. why? because lean charges need more time to burn than rich charges. idle is a lean charge condition. so is cruising down the highway.


I understand the point about when you deccelerate from cruise, and your manifold vacuum sky rockets, and you advance to the maximum. I just don't know whether to believe it potentially hurts the exhaust valves or not (albeit minutely) by banging them shut harder.
ignition has absolutely nothing to do with how hard the exhaust valves close. the ramps on the cam do.


the biggest reason for all the debate on this is because 1. an alarming number of people still believe ported vacuum rises as the throttle is opened,and 2. they believe timing should advance for a rich charge (when you punch it).

furthermore,ported vacuum can never be more than manifold,since it is in fact manifold vacuum,only the port is placed just above the throttle butterfly-when it's at idle position-so as soon as the throttle is applied,the butterfly swings up,placing the port below the butterfly,where the vacuum is.

[kennewick]

ah yes. the vacuum discussion. ported is an emissions tactic. nothing more. period. it raises combustion chamber temps by forcing the engine to run in a less efficient state,at idle. manifold is the correct way. why? because lean charges need more time to burn than rich charges. idle is a lean charge condition. so is cruising down the highway.



ignition has absolutely nothing to do with how hard the exhaust valves close. the ramps on the cam do.


the biggest reason for all the debate on this is because 1. an alarming number of people still believe ported vacuum rises as the throttle is opened,and 2. they believe timing should advance for a rich charge (when you punch it).

furthermore,ported vacuum can never be more than manifold,since it is in fact manifold vacuum,only the port is placed just above the throttle butterfly-when it's at idle position-so as soon as the throttle is applied,the butterfly swings up,placing the port below the butterfly,where the vacuum is.

A++

[biotex]

ignition has absolutely nothing to do with how hard the exhaust valves close. the ramps on the cam do.


I'm referring to when you slow down (hooked to manifold vacuum), the manifold vacuum rises, due to the closing of the throttle blades, and that can cause a 'Popping' out the exhaust since the ignition is completely advanced from the large 22+ In.Hg. vacuum signal, and it's causing 'Pre-Ignition'. As a result of the pre-ignition, causing pressure problems for the pistons, valves, bearings, ect.

That 'Popping' can blow the exhaust valve off the seat, and let it slam back into the valve seat. In essence, this is a result of the ignition.

Please keep in mind that I am only beginning to research this, and am by no means any kind of an expert. I'm simply trying to see both sides of the debate, and am forming my own personal opinion based on what i'm learning. I don't have access to a dyno and expensive diagnostic tools, so i can only try to sort out the facts from what I read. What I posted above makes perfect sense to me, so I throw it out here to possibly get another point of view. Trying to learn how to make my Heep perform at it's best.:)

[biotex]

1. an alarming number of people still believe ported vacuum rises as the throttle is opened,and 2. they believe timing should advance for a rich charge (when you punch it).


I'm under the impression that ported vacuum rises due to more airflow. Isn't that a direct result of opening the throttle. More throttle = more airflow = more vacuum = more advance. Is this not correct?

[Ristow]

I'm referring to when you slow down (hooked to manifold vacuum), the manifold vacuum rises, due to the closing of the throttle blades, and that can cause a 'Popping' out the exhaust since the ignition is completely advanced from the large 22+ In.Hg. vacuum signal, and it's causing 'Pre-Ignition'. As a result of the pre-ignition, causing pressure problems for the pistons, valves, bearings, ect.


dynamic compression is very low with the throttle closed. preignition at this point is practically impossible. if it did so in this condition it would also do it at idle,which is again impossible. the popping is not preignition you hear,it is in fact burnt exhaust valves-among other things- putting raw fuel into the exhaust where it later burns.

That 'Popping' can blow the exhaust valve off the seat, and let it slam back into the valve seat. In essence, this is a result of the ignition.

no. preignition happens in the cylinder. any pressure in the cylinder works against the opening of the valves. that scenario is impossible. preignition damages pistons,and spark plugs.

I'm simply trying to see both sides of the debate,
the debate is fact vs. fiction.


I'm under the impression that ported vacuum rises due to more airflow.
no. it is not a venturii effect. it is simply manifold vacuum,obstructed by the butterfly at idle. nothing more,nothing magic.


More throttle = more airflow = more vacuum = more advance. Is this not correct?
incorrect. more throttle/airflow equals less vacuum. the vacuum an engine makes is the pistons pulling air against a closed throttle.an open throttle offers little resistance to the displacement the pistons are giving. that's why diesels don't make vacuum,they don't regulate airflow,the use fuel only as the throttle,the airflow is always open.


keep in mind the vacuum advance is the engine load detector. it detects engine load,regardless of rpm. it changes timing based on that factor,which is very easily-and simply-determined via vacuum.


Please keep in mind that I am only beginning to research this
and by all means continue to do so.but keep in mind there is a lot of bad information given by people with good intentions. there are also those that like to over complicate things so as to sound real smart,all the while being fundamentally wrong.

i am confident in my info,not because i'm so dang smart but because i know the info i give is verifiably correct.

[Eugene 1]

X2 :thumbsup: Ristow helped me out with my old 401 when i had pinging issues

[kennewick]

dynamic compression is very low with the throttle closed. preignition at this point is practically impossible. if it did so in this condition it would also do it at idle,which is again impossible. the popping is not preignition you hear,it is in fact burnt exhaust valves-among other things- putting raw fuel into the exhaust where it later burns.


no. preignition happens in the cylinder. any pressure in the cylinder works against the opening of the valves. that scenario is impossible. preignition damages pistons,and spark plugs.


the debate is fact vs. fiction.



no. it is not a venturii effect. it is simply manifold vacuum,obstructed by the butterfly at idle. nothing more,nothing magic.



incorrect. more throttle/airflow equals less vacuum. the vacuum an engine makes is the pistons pulling air against a closed throttle.an open throttle offers little resistance to the displacement the pistons are giving. that's why diesels don't make vacuum,they don't regulate airflow,the use fuel only as the throttle,the airflow is always open.


keep in mind the vacuum advance is the engine load detector. it detects engine load,regardless of rpm. it changes timing based on that factor,which is very easily-and simply-determined via vacuum.



and by all means continue to do so.but keep in mind there is a lot of bad information given by people with good intentions. there are also those that like to over complicate things so as to sound real smart,all the while being fundamentally wrong.

i am confident in my info,not because i'm so dang smart but because i know the info i give is verifiably correct.

Excellent explanation. I banged my head on this too but the facts are the facts. There are a lot of experianced mechanics militant about useing ported but the science is all wrong.

[biotex]

Thanks for the expanation. I will consider this matter closed, and leave my CJ hooked to manifold!

[Ristow]

if you're running the motorcraft distributor do this.

http://www.ifsja.org/forums/vb/showthread.php?t=84586

[biotex]

no. it is not a venturii effect. it is simply manifold vacuum,obstructed by the butterfly at idle. nothing more,nothing magic.

incorrect. more throttle/airflow equals less vacuum. the vacuum an engine makes is the pistons pulling air against a closed throttle.an open throttle offers little resistance to the displacement the pistons are giving. that's why diesels don't make vacuum,they don't regulate airflow,the use fuel only as the throttle,the airflow is always open.


Ok, I know I said matter closed, but I just can't quite get a grip on this part yet. Sorry! Ok, At idle you have high manifold vacuum because the butterfies are closed, and since the ported source is above the BF's, there is no vacuum at the ported nipple agreed?

Now when you open the BF, your manifold vacuum drops some, but your ported vac increases. If not a venturii effect, then you are saying that the ported source is now able to get a bit of vacuum from the manifold as opposed to creating it's own. Is this correct?

[biotex]

if you're running the motorcraft distributor do this.

http://www.ifsja.org/forums/vb/showthread.php?t=84586

Will do, thanks, but will have to come back to it. Getting ready to move a WagonMaster to my house.

[Ristow]

do you have a vacuum guage? get one. play with it on the motor. it will be educational.


Now when you open the BF, your manifold vacuum drops some, but your ported vac increases.

actually,as the throttle is lightly opened vacuum will increase a little. the added rpm of the engine overcomes the little bit the throttle was opened. the ported fitting to the distributor will be uncovered as this happens.

also,vacuum doesn't just drop off a cliff the minute the rthrottle is touched. nor does it "swing wildly" at the most minute throttle change,as indicated elswhere. it smoothly tapers off as the throttle is opens.

the real kicker is-ported vacuum tapers off as the throttle is opened right alongside manifold vacuum. why? because ported vacuum IS manifold vacuum.

again,no magic involved.


seriously,go get a tuners vacuum guage. it's indispensible for tuning ignition and carburetors.

[JRBAMATEX]

Man you guys have been busy! Lots of good info here and in the links.

JR