79 vacuum diagram and EGR dead spot

[dkmcgowan]

I know there are a million threads about this, I've read tons. So I am setting my vehicle back up with factory settings, it's a 79 49 state Wagoneer with 360 and auto transmission.

I did not have the original EGR, but I went with 32187391 which had the 881 stamped on it because I found many people who said that is what would be on a 79 Wagonner for 49 state, so I went with it.

So I went with the ACDelco 2141428

http://www.rockauto.com/catalog/moreinfo.php?pk=533321&cc=1184385

I got two new CTO's and installed them, hooked all new vacuum lines up correctly.

I got a new vapor canister, hooked it all up correctly.

I set my timing to 8 degrees, maybe it was closer to 9 degrees, but it was below the 10 degree mark.

I set my idle pretty close, wasn't all the way warmed up so ends up it probably was not perfect, need to do it better later, but it was 600 RPM in drive, just when it was a little cold.

My idle mixture screws and choke are probably not perfect, but I'm rebuilding another 2150 that I plan to put on this weekend, so I will get it perfect then, but I think it's all really close.

So when driving, from a stop, there is an immediate dead spot. It is not bad enough that the engine would die or anything, but it's noticeable. It's also not there every single time, you have to start really slow and you can feel it. If you hit it hard you don't feel it as much.

So I verified the CTO for the EGR was working correctly, no vacuum at idle and once warmed up, ported vacuum.

So today I added a vacuum delay valve, the black/purple kind the newer Grand Wagoneers used.

That got rid of the dead spot and I do not have any pinging.

My question is the 79 and engine sticker does not have the vacuum delay and I was trying to match it.

Is there any tuning I can do? Would idle mixture screws not being perfect effect the take off from stop?

I used the orifice washer that the EGR said to use for Jeep, but could one of those being too large cause this?

Thoughts?

I plan to just leave the vacuum delay for now. They added it in 80 but that EGR was the fancier one with the back pressure sensor and regulator thing that 79 did not have.

[Tinkerjeep]

You sure its not the CTO converting the distributor's vacuum advance source from manifold vacuum (always present at idle) which is normal source for cold starts, to ported vacuum (not present at idle but present shortly after throttle blades move open) which is normal when engine is hot?

You will feel a slight hesitation when accelerating from a dead stop...at minor to moderate accel.

Bear in mind your vacuum advance will be all gone if you floorboard the loud pedal from a stop, so you wont feel the hesitation.

[dkmcgowan]

With the 79 there are two separate CTO's. I got two brand new ones from RockAuto.

There is one two port CTO. It has the bottom port going directly to the EGR port on the front of my 2150. The second line on the top goes to the EGR.

I verified that when the engine is cold, there is no vacuum at idle or when the throttle plates open.

Once warmed up, there is still no vacuum at idle, but only when the throttle plates open.

The second CTO is a 3 port. I run the bottom port directly to the ported vacuum on the passenger side of the 2150, the middle port goes to the distributor and the top port goes directly to the manifold. When the engine is cold, the distributor gets manifold vacuum, when the engine warms up, it gets ported vacuum.

The newer GW's have that 5 port CTO which is where things could get crossed, but in my setup it should not be possible.

[dkmcgowan]

Also, I do not have the air pump installed or the catalytic converter. I plan to put the catalytic convert back on, but I need a new one, but plan to not do the air pump right now, so my plan was to go to factory setup only minus the air pump. I do not believe either of these two items would cause my issue though.

[dkmcgowan]

You sure its not the CTO converting the distributor's vacuum advance source from manifold vacuum (always present at idle) which is normal source for cold starts, to ported vacuum (not present at idle but present shortly after throttle blades move open) which is normal when engine is hot?

You will feel a slight hesitation when accelerating from a dead stop...at minor to moderate accel.

Bear in mind your vacuum advance will be all gone if you floorboard the loud pedal from a stop, so you wont feel the hesitation.

I just realized what you were saying. You were not saying that the EGR was getting the wrong vacuum, but the issue could be that I installed the CTO to the distributor again so once it's warm it's getting ported vacuum instead.

I can try to do manifold vacuum all the time to the distributor and remove the vacuum delay to the EGR and see if it's different.

The vacuum delay to the EGR did stop the issue though, which implies the EGR coming on is the cause of the dead spot. The question now is how should I best tune it out and still keep try to get everything hooked up correctly.

[Tinkerjeep]

I don't run EGR and never have, so I avoided that portion of your stuff.

I just know that there is a slight hesitation when the Distributor advance is running off ported vacuum versus manifold. Its designed in. Nothing you can do but run it on manifold all the time, which I have found causes a backfire and lean miss at hot idle.

[FSJunkie]

EGR inevitably creates a bog when it operates simply by the way it works. It doesn't work at light throttle or heavy throttle, so you only feel the bog between about 1/4 and 3/4 throttle.

All EGR does is take a 300 cubic inch engine and fill 100 cubic inches with inert exhaust that does absolutely nothing, leaving you with basically a 200 cubic inch engine. EGR is quite literally variable displacement. This increases fuel economy and cools combustion to lower NOx emissions, but it cuts power while doing it because you literally have a smaller engine.

EGR can be smooth and seamless if operated perfectly under all conditions, but these older EGR systems do not work perfectly under, quite frankly, most conditions and you feel the EGR operate. Especially so in the late 1970's when the engines were running the max exhaust dilution they could handle without backfiring. It's a reality of early EGR systems. Automakers played with the ignition timing and carburetor jetting to help mask the bog, but there is only so much they could do.

Aside from removing the EGR entirely, which sometimes requires a revision of ignition timing advance, you can find ways to reduce the EGR dilution rate to a level that drives nicer:

Freeing up the exhaust flow will reduce EGR on engines that use a positive backpressure valve, such as yours. You can also put bleed holes in the EGR vacuum line to reduce valve opening.

[Tinkerjeep]

Good summary, Junkie.

Another issue with EGR is it can introduce carbon into your intake manifold and gunk up your intake valves and then exhaust valves by cutting the heat in the combustion chamber.

If the local laws do not require you retain EGR, it is possible, and can be profitable to remove the EGR and retune the engine.

Once tuned, you should notice better drivability and make better power at some throttle settings. The engine should last longer and run cleaner.

If you have to retain it, there are aftermarket parts makers that offer various EGR valves.

[dkmcgowan]

The vaccum delay I added pretty much made the issue go away. I figure this is why they added them in 1980. I'm rebuilding the carb, will try after its tuned to see if delay is still needed, if so i will just leave it.

[vacaisle]

I went the way of no EGR or emissions at all. I think that more power and throttle response means better gas mileage because you lay into it less trying to get up and go. These old emissions control systems are primitive. It seems like there's always a bandaid needed to cover up some issue caused by them. Next thing you know, the engine is filled with vacuum lines, delay valves, solenoids...and you don't know what's going on. When there's a problem it could be a dozen different systems not up to spec.

[dkmcgowan]

I figured out one difference and I believe I got the wrong EGR. I thought there were only two types, with backpressure sensor and without. I thought all backpressure sensors were external, so when I got the OEM numbers I thought I only had to pick between two because in all diagrams I knew that in 79 49 state 360 with auto did not have an external backpressure sensor, so I assumed that meant it did not have a backpressure sensor at all. So I got an EGR without backpressure sensor, which is wrong for 49 state 360 in 79, according to FSM they all had a backpressure I believe. I think the only thing that did not have backpressure sensor in 79 was a 258 manual CJ.

The big difference was integral backpressure sensor is internal and it looks just like an EGR without the external extra thing, so the vacuum diagrams and such will look the same for no backpressure sensor and integral backpressure sensor.

So here was OEM numbers.

less back pressure sensor:
3223980
3218739
with back pressure sensor:
3230175
3230180
3230181
3230183
3230186
3230188
3230839
3230842
3230846
3231162
3233596
3234967
3235450

So my theory is without the backpressure sensor it is opening too much, that backpressure sensor lets it leak some of the vacuum.

So I found a NOS AMC 3230188 EGR on eBay that I ordered so I don't have to deal with washers. I don't think my vehicle had that specific one but cannot be sure, I believe it would have had 3230186 just because that one shows up more on the internet with people talking about it, but they might just be alternate part numbers for a similar EGR I hope, I know many of the part numbers in the above list with backpressure sensor are all alternate part numbers of the same EGR according to some parts sites.

If that one does not work I will just get the AIRTEX / WELLS Part # 4F1062, which is the one with washers for 3230186 with positive backpressure sensor.

Here are details from a 79 FSM that explain some stuff for others in interested.

[Tinkerjeep]

I went the way of no EGR or emissions at all. I think that more power and throttle response means better gas mileage because you lay into it less trying to get up and go. These old emissions control systems are primitive. It seems like there's always a bandaid needed to cover up some issue caused by them. Next thing you know, the engine is filled with vacuum lines, delay valves, solenoids...and you don't know what's going on. When there's a problem it could be a dozen different systems not up to spec.

Good point. But today's vehicles are no different in complexity. They just use electronic signals sent to the actuator by a processor which decides when to send the signals according to programming which depends on sensor input.

The vac lines, check-valves and CTOs are simply a non-computer control system that operates on mechanical signals versus electronically interpreted signals.

[vacaisle]

Good point. But today's vehicles are no different in complexity. They just use electronic signals sent to the actuator by a processor which decides when to send the signals according to programming which depends on sensor input.

The vac lines, check-valves and CTOs are simply a non-computer control system that operates on mechanical signals versus electronically interpreted signals.

If you take all the emissions controls off a modern car it probably wouldn't run at all. Which is why we all love our old trucks and cars, right? If something breaks, take it off, you didn't need that anyways.

[Tinkerjeep]

Today's control systems are more integral. Ours were added on top of the normal controls.

If you just blindly remove all the 1970-80s smog-crap, the engine won't run well either...but it can be retuned to do so quite well.

[dkmcgowan]

I installed the NOS Jeep EGR I got from eBay this weekend.

I was able to remove the vacuum delay and use the NOS factory EGR and everything works.

I have no pinging, temperature looks good, and I have no more stumble.

Most likely it is due to the factory one having integral back pressure sensor so it does not come on as fast or as often, the aftermarket one I had had no back pressure sensor.

I also do not have a cat converter right now, but solid exhaust and new muffler, but I probably create a little less back pressure so it might not be coming on as much and therefore the stumble is removed.

But no pinging and my timing is pretty much factory (10 instead of 8 degrees), but within range. So I know it's working some or it would ping under load.

I hit a huge hill hard yesterday and I can hear the engine running, but I don't believe any pinging, I assume it would be an obvious different noise.