International Full Size Jeep Association
Home Forums Reader's Rigs Tech Library Trail Stories FSJ-List
International Full Size Jeep Association  

Go Back   International Full Size Jeep Association > Tire Kickin' > General FSJ Tech

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 08-16-2014, 06:43 PM
Eighty3Zwagon's Avatar
Eighty3Zwagon Eighty3Zwagon is offline
I have never been more filthy in my life
 
Join Date: Apr 12, 2014
Location: Middle Tennessee
Posts: 59
Hesitation, and Jerking

When I start up and drive my rig after sitting overnight I will get a hesitation if I give it more gas than it takes to power the rig forward at a slow speed. If I accelerate too quickly the truck will jerk forwards and back with a surge until I let off and ease back into it. It feels like it may be starved for gas, but this will go away after it warms up 5 or 10 minutes of in town driving. It will come back on a decent hill if taking off from a standstill occasionally after warm, but not all the time. Any Ideas before I start digging into it too deeply?

Would a stopped up catalytic converter cause this symptom? Slipping Trans until warm? Not real sure, but I thank you in advance.

Oil pressure remains constant when this occurs too.
360 / 727 trans
__________________
1983 Wagoneer Limited - Stock (AKA - Beauty)
1988 / 35th Anniversary Corvette Triple white
Reply With Quote
  #2  
Old 08-16-2014, 07:12 PM
vacaisle's Avatar
vacaisle vacaisle is offline
snide. snarky. grease covered.
 
Join Date: Mar 18, 2013
Location: Rockaway Beach, NY
Posts: 1,390
Sounds like a carburetor issue. Is this a 2150? Could be a bad accelerator pump. That would cause the hesitation when you give it gas. Or may be a blown power valve. Maybe both. Check to see if there is fuel under the accelerator pump. It's in the front on the right of the carb towards the bottom. The power valve should have manifold vacuum hooked up to it. It's to the left of the accelerator pump on the bottom front of the carb. Pull the hose and see if there's fuel leaking out. It could also be the choke. There's lots of possibilities here.

What's your timing at?
__________________
89 Grand Wagoneer
145,000 miles, TFI, MSD 6a

Last edited by vacaisle : 08-16-2014 at 07:22 PM.
Reply With Quote
  #3  
Old 08-16-2014, 07:42 PM
Eighty3Zwagon's Avatar
Eighty3Zwagon Eighty3Zwagon is offline
I have never been more filthy in my life
 
Join Date: Apr 12, 2014
Location: Middle Tennessee
Posts: 59
Yes 2150

It is the 2150, and I will check the items mentioned. Thanks, and not sure what the timing is at - will check. If carb related, what would cause this to improve as it warms up, fuel evaporation?
__________________
1983 Wagoneer Limited - Stock (AKA - Beauty)
1988 / 35th Anniversary Corvette Triple white

Last edited by Eighty3Zwagon : 08-16-2014 at 07:56 PM.
Reply With Quote
  #4  
Old 08-16-2014, 09:27 PM
cst756's Avatar
cst756 cst756 is offline
Grease Monkey
 
Join Date: Sep 05, 2008
Location: South Carolina
Posts: 394
I have a similar issue that Ive been trying to figure out. One day I will get a tool and adjust the carb properly. Carnuck (I think) mentioned to me about making sure both of the little shooters were shooting gas in the carb. I also had a slight pop coming from the carb. one was not, it was clogged after cleaning that it was ALOT better, but still if I stomp the pedal from a stop (that's when its the worst) or any speed for that matter there is still hesitation. Im sure mine is from poorly adjusted mixture screws, but could be something else. A carb rebuild is never a bad idea if its been a while since it was done. please post up if you come across something specific that makes it stop.
__________________
1983 Wagoneer
360/727/229
Running good!!!
Reply With Quote
  #5  
Old 08-16-2014, 09:38 PM
vacaisle's Avatar
vacaisle vacaisle is offline
snide. snarky. grease covered.
 
Join Date: Mar 18, 2013
Location: Rockaway Beach, NY
Posts: 1,390
I don't know. But based on what you said those are the things I'd check first. Im sure others will chime in with more insight.

Everything I mentioned is related. The choke could explain the cold start issue. The uphill problem could be explained by a bad power valve, timing off. The hesitation could be the accelerator pump.

Also, depending on where your distributor is getting it's vacuum source from, it could be related to the vacuum advance. Maybe the spark CTO isn't functioning correctly and your distributor vacuum advance isn't functioning correctly.

Like I said, it could be a lot of things or a combination.
__________________
89 Grand Wagoneer
145,000 miles, TFI, MSD 6a
Reply With Quote
  #6  
Old 08-16-2014, 09:39 PM
RWrightPhotog's Avatar
RWrightPhotog RWrightPhotog is offline
Gear Head
 
Join Date: Jun 07, 2011
Location: Columbus, Georgia
Posts: 639
Mine was doing nearly the exact same thing.

I was able to replicate the situation by flooring it until it started to hesitate and 'starve'. Then I immediately shut the Jeep off and coasted it off the road. Pulled the top of the carb off and the bowl was empty.

New fuel pump and problem was gone.

Something you might try...
__________________
Rob

1982 Jeep Wagoneer Limited 360
1979 Jeep Cherokee 4-Door 258
1979 Jeep Cherokee Chief 360
Reply With Quote
  #7  
Old 08-16-2014, 09:48 PM
vacaisle's Avatar
vacaisle vacaisle is offline
snide. snarky. grease covered.
 
Join Date: Mar 18, 2013
Location: Rockaway Beach, NY
Posts: 1,390
Quote:
Originally Posted by cst756
I have a similar issue that Ive been trying to figure out. One day I will get a tool and adjust the carb properly. Carnuck (I think) mentioned to me about making sure both of the little shooters were shooting gas in the carb. I also had a slight pop coming from the carb. one was not, it was clogged after cleaning that it was ALOT better, but still if I stomp the pedal from a stop (that's when its the worst) or any speed for that matter there is still hesitation. Im sure mine is from poorly adjusted mixture screws, but could be something else. A carb rebuild is never a bad idea if its been a while since it was done. please post up if you come across something specific that makes it stop.
I think it's a process of elimination. I would suggest starting with a full and total carb rebuild. Make sure you have all the right parts. Then make sure everything is bolted up correctly and torqued properly. Then tune everything correctly. It's not supposed to do what you are describing. Before I rebuilt mine I had to put the accelerator pump arm on the top notch to smooth out the slight hesitation I had. Now everything is set factory and it's smooth as silk and very responsive. Once you do all this you'll "get it" and decide to do it all again and that time you'll make it better than before. I learned everything about my truck from this forum and the not so great Haynes manual I have. So read up.
__________________
89 Grand Wagoneer
145,000 miles, TFI, MSD 6a
Reply With Quote
  #8  
Old 08-17-2014, 12:30 AM
men in black's Avatar
men in black men in black is offline
AMC 4 OH! 1
 
Join Date: Jul 08, 2006
Location: Grand Blanc, Mi
Posts: 3,505
I just had a complete tuneup, rotor,wires,plugs, carb rebuild.

But there was still a hesitation on take off, Addicted told me to preload
the accelerator pump. So I adjusted the plastic trunnion on the end
of the accelerator pump linkage by two threads. This removed almost
all the hesitation.

You need a forked bit to fit inside the backside trunnion.

So Big Thanks to Addicted for the help.
__________________
1990 Grand Wagoneer.. black with sand interior..
Razor grille, Hella H4 headlights, Piaa driving, LED spider taillights, tinted windows.
Full Corinthian leather front and rear seats, custom full length center console with cup holders. 100 sf of Rattle Trap on floor.
Edelbrock intake and 2132 cam, Howell TBI, Ford Distributor Cap, TFI Ignition Coil, Desmogged
















Last edited by men in black : 08-17-2014 at 12:33 AM.
Reply With Quote
  #9  
Old 08-17-2014, 10:36 AM
Tinkerjeep's Avatar
Tinkerjeep Tinkerjeep is offline
Banned
 
Join Date: Mar 01, 2009
Location: Redneck-populated Flyover Country, USA
Posts: 3,662
Understanding Vacuum Advance....

Timing will vary initial rate of acceleration from a stop, a tiny bit - depending on whether you have ported or manifold sourcing your distributor. The reason I say this is because your vacuum signals are the same once the throttle blade opens a small fraction.

The manifold vacuum inlet is drilled on the inside of the carb throat just below the throttle blade when the bade is closed.

The ported vacuum inlet is drilled on the inside of the carb throat on the other barrel, and it is located just above the throttle blade when closed.

As soon as the throttle blade opens a bit, the ported vacuum becomes manifold vacuum since the divider between the two signals, the throttle blade, has moved and now BOTH manifold and ported vacuum inlets are BELOW the lip of the throttle blade.

Manifold vacuum is there at idle.

Ported is not.

If you are sitting at a stop light and the light turns green, when you accelerate while manifold vacuum is plumbed to the distributor, your acceleration will be instant and smooth because you have full vacuum advance there already.

If you are plumbed to ported, there will be a slight hesitation until the throttle blade opens enough to let ported vacuum become manifold vacuum and then your vacuum advance kicks in.

If you accelerate at WOT, from a dead stop, vacuum advance will have very little (if any) input, since at WOT your vacuum signal goes to "0" and so you have no vacuum advance (unless you have the vacuum advance diapraghm on Duraspark distributor adjusted wrong). But under high load, the fuel/air mix in the combustion chamber does not need as much advance to ignite.

High engine load, smaller combustion chambers, and higher compression ratio (as well as unleaded, or low octane fuel) require less ignition advance to ignite the fuel/air mix.

Light load, lean mixture, large combustion chambers, low compression ratio, and high octane fuel require more advance to ignite the fuel/air mix.

Vacuum Advance is adjusted separately but must be considered along side the initial timing advance (set up by loosening the distributor hold down bolt and rotating the distributor housing clockwise (retarding) or counter clockwise (advancing) or centrifugal advance - altered by changing springs and weights in the distributor itself.

On 1978 -1991 FSJs the Motorcraft/Duraspark CENTRIFUGAL ignition system is not very tunable, but the INITIAL advance is. And so is the VACUUM advance. The vacuum diaphragm is tunable so you can insert a 1/8" (IIRC) allen wrench into the vac nipple on the diaphragm housing and turn the screw inside clock, or counter clock wise. this will alter the range of vacuum that the preset amount of advance will come in. I think most factory vac advance curves gave 10 degrees, but don't quote me. Regardless, you can alter the inches of vacuum that the advance range is active. And its a gradual increase.

So, lets say you set it up so you have full vacuum advance in at 15" of vacuum, and its all out by 5" of vacuum. At 10" of vacuum your vac advance will be half of the total. You turn the screw one way or the other a few turns and you change the curve. Set it to be all in by 10" and all out by 0"...at 5" it will be half in. You can make it so your advance is all in at 5" and half out by 0", but that means full vacuum advance is present above 5" of vacuum. You will have all advance under moderate to heavy (not WOT) acceleration and may experience a running misfire or stumble and you might even get preignition ping.

You can adjust your vacuum advance the other way too -all in at 20", all out at 10"...but that's practically no advance during moderate to hard acceleration, so your engine may seem sluggish, and it will be hard to keep running when started cold.

I'll try and do another article for centrifugal advance...Chew on this in the mean time.
Reply With Quote
  #10  
Old 08-17-2014, 10:52 AM
Tinkerjeep's Avatar
Tinkerjeep Tinkerjeep is offline
Banned
 
Join Date: Mar 01, 2009
Location: Redneck-populated Flyover Country, USA
Posts: 3,662
BTW, the reason I just wrote about Vac advance...I don't think thats your problem...

It sounds more fuel related. Advance rarely (if ever) causes bucking or surging unless it is severely out of tune or broken.

Low fuel level in the carb (due to bad mechanical fuel pump) and the choke sticking closed cause more drivability issues on this site!

If its not fuel related, then you can start looking elsewhere. broken distributor is possible.

But the TF727 transmission is a possible cause, too, since loss of pumping pressure may cause the Torque Convertor to not impel power from the driving impeller to the driven impeller in a smooth manner. Clutches or bands slipping due to not enough pressure or volume to keep them engaged is also possible.

I'm not sure what internally causes the "actuate upshift" signal and the "delay upshift" signal. I know they are actuated externally by the throttle rod, but not sure what internally the signal goes through, Never had a TF727 apart.

Any surging above 35mph in 3rd gear may be a bad Lock Up Torque Convertor clutch...but those only came in 1980 to 1985 ish TF727s.
Reply With Quote
  #11  
Old 08-17-2014, 11:02 AM
Tinkerjeep's Avatar
Tinkerjeep Tinkerjeep is offline
Banned
 
Join Date: Mar 01, 2009
Location: Redneck-populated Flyover Country, USA
Posts: 3,662
Plugged Cat.....

If you don't need to pass smog, cut the cat out (it likely has seen better days) and even if it is like new condition, these DID flow poorly.

You can replace it with an aftermarket Ct, make sure you get the same type if you have to keep the engine stock for smog certs. But the modern Cats generally flow much better than older style.

I doubt this is the problem, it would just act like your engine is falling on its face at any throttle input above moderate. And it would be pretty consistently bad whether the engine was warm or cold.

The HEAT RISER VALVE on the passenger side exhaust manifold may be stuck closed too, and that will cause loss of power at higher engine load.
Not sure about bucking though. I'd weld that sucker in the open position, or remove it and cut the valve out and weld the holes the valve-rod went through...or tap them using a pipethread tap and run pipe plugs into the holes.
Reply With Quote
  #12  
Old 08-17-2014, 04:45 PM
Eighty3Zwagon's Avatar
Eighty3Zwagon Eighty3Zwagon is offline
I have never been more filthy in my life
 
Join Date: Apr 12, 2014
Location: Middle Tennessee
Posts: 59
Thanks for all the input guys.

I am going to start with the Fuel pump, and work towards the Carb rebuild after that. I believe it is fuel related at this point, but can't figure out why it would get better the more I drive. I will keep you posted on the correction, hopefully,

I will also check the sticking choke theory on my next outing, and the vacuum flappers on the intake.
__________________
1983 Wagoneer Limited - Stock (AKA - Beauty)
1988 / 35th Anniversary Corvette Triple white
Reply With Quote
  #13  
Old 07-21-2015, 08:14 AM
rwells427's Avatar
rwells427 rwells427 is offline
Member
 
Join Date: Jul 02, 2014
Location: United States
Posts: 28
Quote:
Originally Posted by men in black
I just had a complete tuneup, rotor,wires,plugs, carb rebuild.

But there was still a hesitation on take off, Addicted told me to preload
the accelerator pump. So I adjusted the plastic trunnion on the end
of the accelerator pump linkage by two threads. This removed almost
all the hesitation.

You need a forked bit to fit inside the backside trunnion.

So Big Thanks to Addicted for the help.
men in black could you (or anyone that knows what he is talking about) post pictures of the trunnion and what you are talking about adjusting here? I don't know if I am understanding you correctly. I have been having the same problem except it is all of the time under heavy load. Doesn't matter how long I have been driving. I got rid of the cat, which helped a bit, had it timed by a professional, and I'm still having the choking/sputtering problem of it not accelerating until I ease off the pedal and accelerate very slowly. Any advice would be appreciated. I am running the edelbrock 1406 and have it tuned well. While I am cruising and during idle it behaves fine. Could it have something to do with the transmission kickdown linkage? I have no clue if I have that set up correctly, I wouldn't trust the mechanic who did it. Don't think it would cause the effect I am having, but I have tried a lot with no avail so what do I know!?
__________________
1984 Jeep Grand Wagoneer
70s Style Custom Paint Job
Rebuilt AMC 360 V8 Engine
Edelbrock 4 Barrel Carburetor, Air Cleaner, and Intake Manifold
Super Flowmaster 44 Exhaust System
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 05:46 AM.


Powered by vBulletin Version 3.5.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
corner corner