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YJ Sputters with accel at operating temp

2K views 16 replies 10 participants last post by  jguitar1 
#1 · (Edited)
Hi all,

New to the forum and new to owning a Jeep.

I bought an 89 YJ a few months ago and got the mod. bug.

I can't wait to upgrade suspension and install a lift and new tires and wheels, but I have an engine issue I need to address before all that.

Specs:

6 cyl 258
Nutter bypass completed
New D.U.I. w/ 8mm wires (newer) and plugs set to .050 (New)
Timing is correct.
Advance is 10-12
New Weber 38 bought from Redline. Not a Spain model.
Holley fuel pressure regulator set to 3.5 PSI

The issue:

Starts and runs fine. Yesterday I got it up to 65 with no issues. I can tell there is improvement after the new carb and DUI install. Acceleration is decent, but it's not a race car.
After it gets to operating temp. and I've been driving it a fair distance it will cough and stumble but not die. The problem seems to intensify gradually and it will sputter more when I give it fuel. I can limp home as long as it's not to far.
After which the idle seems to cycle between smooth and sort of rough idle.
But still not die...
My next moves are to pull the Weber and check the mount plates for flatness though I've drenched it in carb cleaner and can't really tell if it stumbles or not as it seems to cycle between smooth and crap idle by itself. Also, when I get time I'm going to pull the timing chain cover and check the deflection. But, I installed the DUI, everything was aligned ok.

Any ideas will be welcomed.

Thanks guys.
J.
 
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#2 ·
Check your CTO valve in the intake manifold. It is the gizmo with 4 connections sticking out the side of the intake manifold. That vacuum valve only opens when up to operating temperature. If you have a bad EGR valve or a leaking vapor canister, it could be a vacuum leak that only appears when the engine is hot.

I would just disconnect and plug the vacuum source to that valve and see if the problem goes away. If it doesn't, you've eliminated that system as the issue. If it does go away, figure out which component has the leak.
 
#3 ·
When you did the nutter did you clean up the vacuum lines? What, if anything did you do with the charcoal canister lines? That is the gas tank vent. Quick test to see if anything is wrong there is to just drive with the gas cap loose.

When I plug up the vent's air filter on mine with a mud run, it will bog at speed and idle rough. Crack the cap open and away I go. The filter is a $2.00 part.
 
#6 ·
Update,
So I found there was a bolt missing on the EGR and no vacuum line from the CTO valve to EGR at all. So I pulled it off and replaced the gasket and put it back on. I also hooked a new line from the CTO.
I drove it to work this morning and sputtered one time while accelerating onto the freeway, temp was over 150 at that time.. When I got close enough to work (So I knew I could limp there if it got worse) I tried to really romp on it but couldn't make it do that again. The temp was under 150F by then.
So next steps: I'm going to check all the vac hoses as you suggest Mike and replace the canister filter and PCV valve. I may even replace the EGR and see if there's any build up in that pipe between the manifolds just cause I know how much that stupid valve can affect things. I think it's mostly reliable now...except for that one sputter.
Thanks guys. Any other input will be appreciated.

J.
 
#11 ·
Check all the vacuum lines by spraying them with a little carb cleaner when the engine is up to temp, if there is a leak the engine revs will increase. also remove the spark plugs and look at them, check that they are not black and sooty, mine were as the engine was running rich caused by a leak on the map sensor vacuum line.
 
#12 ·
Yeah, as mentioned definitely check plugs and look for fouling either from rich mixture or oil fouling (more carbon). I have two cylinders that foul quickly with oil burning and it had me chasing carb problems that weren't there. Skipping and hesitating accelerating off idle; run pretty smooth at cruise but progressively worse every few hundred miles. Gas mileage dropping steadily as the plugs foul and the motor gets jerkier coming off idle.

Now I just have to chase the source of the oil consumption - guides or rings.
 
#13 ·
Over rich condition will not sputter except near idle speed. It will run totally flooded if you floorboard it.

Vacuum leaks are first suspect before you start jacking adjustments around on your carb. Set the carb and ignition to spec and go from there. You might want to back the initial timing to 9 or 10 degrees BTDC till you find the problem. Too much advance, or too rapid advance in timing can cause bogs and flat spots in acceleration.

Many of these engines develop vacuum leaks at the intake to head gasket area, check torque.

Same for the carb baseplate and any adapters or gaskets used.
 
#17 ·
Yep. It was the EGR. It's so easy to miss little things like that. I may take the advice to just plate it off and simplify. Probably do that when I get around to unfubaring the wiring after the dui install.
Now I'm chasing a new issue that sounds like an exhaust leak. My jeep was running just fine for a week or so, now seems more rough without any loss of power. Rpms are the same at idle....
Anyway, if I can't figure it out I'll start a new thread.
Thanks everyone for your ideas and help.
 
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