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1995 4.0 AT rough idle, stumble stall.

shaggybob

shaggybob

NAXJA Forum User
Location
Chattanooga, TN
I've searched and searched and that's what's resulted in testing so many things yet no results.

1995 4.0 Automatic Trans

Well, let's see:
Fuel Pump = Good(pressure checked out)
IAC = Good (was frozen now replaced)
TPS = Good (goofy readings, replaced)
Coil = Good (Resistance checks in spec)
Ignition pickup = good (Checked a little iffy, replaced)
Cap and Rotor = good (Were corroded, now replaced)
plugs = good (A little fouled from issues, cleaned and reinstalled)
wires = good (Checked to be within spec)
CPS = good (Checked against new one, is good)
o2 = good (Replaced a year ago, should be good)
Coolant sensor = good (Checked, also replaced in Harlan)
MAP = good (Tested Good)
Charging system = good (Tested good)
battery = good (tested good)
voltage to injectors = good
resistance across injectors = good

running = Bad, missing at idle, stumbles and stalls with throttle input, runs fine above 1300 rpm, if I can get it above that point.

The only other weird issue is that the ECM quit controlling the e-fan on July 1 of this year. No output from ECM to relay when fan should be on.

Things I haven't tried, noid light on injectors.

Any other suggestions?
 
Run a compression test.

Run a vacuum test.

Post up results.
 
Meant to mention the compression test in the first post, did it last weekend, While I can't find the paper with the actual numbers anymore all 6 were between 153 and 158 psi. Didn't seem abnormal.

When I find my vacuum gauge I will check it several ports across the intake. I have pulled a few vacuum lines while it was running and didn't hear any variance, but I know that is unreliable.
 
Vacuum gauge show between 15 and 18 depending on the port. Only fluctuates when the engine misses, other than that it is steady.
 
So going from the chart on that link I would say that the retarded ignition most closely resembles my results, Left column second row.

So, seeing as we have no control over the timing on obdI and later vehicles, does this indicate that my original fears of a failing ecm would be correct?

For more background info, the timing set was replaced less than 8000 miles ago while replacing the crankshaft.

btw thanks Joe_peters for chiming in to help!
 
How long has this problem presented?

Has the distributor been out? Might be one tooth off.

Did you check the MAT resistance--cold and hot?

What was the condition of the plugs before you cleaned them? Were they all the same condition?
 
Happened for the first time 2 weeks ago tomorrow. Before that, no issue.

As far as the MAT I have no checked it both hot and cold, but if unplugged the ECM definitely knows as it throws a light.

The distributor has never been out so long as I have owned the jeep which is almost 2 years now.

Before cleaning the plugs they were all a bit wet with gas which wasn't surprising considering the missing and stumbles. they were all about the same. none worse than any other. but overall not bad.
 
Wet makes me think ignition (spark) is the issue, which could point to PCM/coil.

Does the problem present both cold and hot?

What injectors are you running?
 
Temperature makes no difference whether ambient or engine temp, it's constant.

Injectors are stock. Been thinking about the 19lb Ford injectors though.
 
Well, that might be your issue.

You can get the Ford or even some Neon injectors (a little harder to locate in the salvage yards). I've been running the Ford (Bosch) organge-tops for a couple years with zero problems. Mine OEM injectors were truly trashed, and I did get an immediate improvement in idle. Mine are the 4-hole disc type nozzles. You can find those in 3.8 V6s up through I think the 351 V8s in F350 vans. Around here a set of eight runs $30 at the u-pull-it.
 
Gonna call this one the ecm. I have tracked one down, I'll get it stalled ASAP and go from there.

Just seems to make sense as it's already been the cause of an issue with my e-fan.

I will say that replacing the injectors would probably help in the long run, but since it does fine above idle, I'm still going with ecm. Guess we will see.
 
shaggybob said:
Gonna call this one the ecm. I have tracked one down, I'll get it stalled ASAP and go from there.

Just seems to make sense as it's already been the cause of an issue with my e-fan.

I will say that replacing the injectors would probably help in the long run, but since it does fine above idle, I'm still going with ecm. Guess we will see.
Click to expand...

Good luck, and please post up the result.

I started to lean to the injectors because of the poor idle, wet plugs, smooths out above 1000+ rpm. If you have drooling injectors (gummed up pintles) the spark plugs will be wet from fuel entering the cylinders without the injector firing pulse or spark present.
 
I thought injectors too, but with how much its missing...who knows. Also it was so sudden. Should have the ecm by the end of the week so I'll know soon enough.
 
Fuel injectors also not the problem.

Insert long string of explicatives here________.
 
after dealing with a simmilar problem ive come to find out that just because the sensors "test" fine (according to the book) doesnt mean that they are. my cps and tps all tested fine but my problem was solved when i replaced them.
 
TPS has been replaced, and it's not the CPS. Swapped a CPS in from a friends XJ last night, no change in condition.
 
Problem solved! Though it tested good the coil was the culprit. The readings on the meter were on the low side of acceptable and kind of as a last ditch effort I replaced it a little while ago. Purrs like a kitten, roars like loin.
 
shaggybob said:
Problem solved! Though it tested good the coil was the culprit. The readings on the meter were on the low side of acceptable and kind of as a last ditch effort I replaced it a little while ago. Purrs like a kitten, roars like loin.
Click to expand...

A heat stress test will often bring out a weak coil. A heat gun is best for that chore.

Glad you got it resolved.
 
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