Bad idle, stalling, runs rich, sooty plugs.. wtf - JeepForum.com
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post #1 of 197 Old 12-02-2020, 12:00 AM Thread Starter
variable
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Bad idle, stalling, runs rich, sooty plugs.. wtf

I realized I've been tacking on to other peoples threads - and yes I pilfered the 'things to do when your zj stalls' thread. There was a lot there, so I could have missed something, but I'm killing myself with this so I'd rather look like a tool and get a 'duh' answer that fixes things than not try...

OK... like the title says, idles super rough and all over the place. Snapon diag tool says the LT fuel trim is somewhere in the -30% range... Its too old to have any real misfire detection though I'm boggled that its not throwing any codes or tripping the CEL. Pulled the plugs and they're all sooty and some of them look like they've got some oil on them (sorry, don't have a pic) but I don't seem to be burning oil or using up coolant - not quickly at least. I've cleaned them, checked the gap for the 93 out of the FSM (which has a glaring typo... 0.035in does not equal 0.089mm...). As soon as I try running after cleaning them, it seems to do OK for about 30 seconds and slowly goes down hill from there.

I've reset the PCM multiple times (shorting the disconnected positive lead to ground) and let it go through a full warm up without touching anything.

First some numbers (compression test):
CYL PSI
1 145
2 140
3 148
4 140
5 140
6 148
7 145
8 145

Nothing interesting there. Its not a leakdown, but I'm doing the self quarantine thing and I'm short handed. I also don't think thats going to get me to the source. Meaning, while it might be useful to diagnose if something isn't quite right, I can't imagine the compression test being OK and the leakdown being so catastrophically bad as to result in the symptoms I've got.

Other things worth noting:
Hughes plenum kit
Double Roller Timing set (upgraded timing chain basically - I don't recall why I went with this, was 5+ years ago)

Parts I've replaced in the last 6 months or so (I try to get Mopar where I can, but its getting harder to find new stuff) - I think the only sensor I haven't replaced is the cam position sensor (thats tomorrow - but I don't have a mopar part unfortunately):

(For the most part, 'Generic' is the 'National' brand from O'Reily - mostly just an availability thing)
(This is all 2020 FYI)
December:
Crank Position Sensor (Mopar) - remind me never to replace this again.. my arms look like they went through a garbage disposal..

November:
Intake Sensor (Generic - and unnecessary as it read correctly)
Ignition Coil (I actually picked up one from O'Reily's just to test and compare and then went back to my existing MSD one)
Fuel Filter (Generic - and probably unnecessary)
Water Pump (Mopar - unrelated really, but was leaking)
IAC (Mopar)
EGR (Generic - I'm pretty sure the one I had was good... except for the crack in the vacuum line..)
- Removed the Catalytic Converter just to simplify the equation and remove the possibility of a clogged up or otherwise bad cat.

October:
PCV (Generic - probably unnecessary)
Fixed some potential vacuum issues/leaks - this was more for good measure.
Fuel injectors 0280156162 (K-Suspension - a rebuild recommended in another thread, but probably unnecessary (and a b*tch to install). The originals were mis-matched 710's and 700's (not sure how that happened), but were working fine for almost 5 years..)
* Also redid the wires to the injectors for good measure (also probably unnecessary)
TPS Sensor (Echlin - Napa - probably unnecessary..)
MAP Sensor (Generic)
Throttle valve cable (goes to the transmission - the adjuster button was stuck and it was old anyway)

September:
O2 Sensor (NKG)
Driver side Exhaust Manifold Gasket - minor leak
Alternator - I went through several iterations of this which is a longer story.. suffice to say, 175 Amp, its good.
Replaced the "H" vacuum connector - I couldn't find a good direct replacement so I just used regular vacuum lines
Moved the Charcoal Canister so I wouldn't hit it on a rock (sits under the air filter now on its side - the K&N conical one (its a tight fit))
Serpentine belt (7K896 - it was time)
Power Steering pump (unrelated, but it pissed me off)
Ditched the eFan and went back to a mechanical fan - which I'm pretty sure is why I had to replace the water pump a few months later (just a guess)

August:
Spark Plugs (Champion RC12YC - the "usual" known good plugs last I read)
ECU/PCM - Probably unnecessary.. Long story short, I finally settled on a reman from O'Reily's, but I'm pretty sure the 2 I had on hand already were also good.
TPS & IAC (Generic - yes, thats more than once I've replaced these - for good measure.. or so I tell myself)
Fuel Pressure Regulator (Generic and probably unnecessary)
Alternator (200 amp one from ebay.. that makes a strange noise)

July:
Timing cover & Harmonic balancer - something was leaking, and I had the cover anyway and the balancer's rubber bits were old and warn (another 'for good measure' replacement)
AC Compressor (don't ask)
Alternator (Went for the 160 amp one from a Durango - wanted to upgrade from the 90 amp one I had)

* I don't recall exactly because I forgot to write it down, but I replaced the Cap, Rotor and Wires - Pretty sure they're all Accel, but I'll have to dig up my receipts. I also don't think this fixed anything either.

There's lots of other work done, but its either unrelated or general maintenance - oil changes, drivetrain stuffs, suspension, etc.

I'd say that most of this started probably around the time I replaced the Alternator the first time. Somewhere in there I re-grounded the sh*t out of things and fixed (I hope) a good amount of wiring that looked like it was either becoming one with the borg, or had turned nearly green (on the inside). I'm not totally convinced that there isn't more wire that needs replacing, but I can't source a new harness - only used ones.

As I said earlier, I think the only thing I have left to replace (aside from the whole damn Jeep) is the Camshaft Position Sensor. I feel like there was more sensor goodness that got replaced but I think I must have lumped them into some other replacement...

Thats it I think... I guess I can't totally rule out head gaskets but I don't know if I'm willing to put that much work into it after all I've already attempted.


93 ZJ V8 5.2 - K&N FIPK, lots of headaches

Last edited by variable; 12-02-2020 at 10:26 AM. Reason: Added the year for posterity
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post #2 of 197 Old 12-02-2020, 01:01 AM
USSENTERNCC1701
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Curious about the results after replacing the cam sensor. Aside from it simply being the only thing you haven't replaced, it genuinely sounds like a good bet. Bearing in mind that fuel trim is the computer's response to data, treat running rich not as an observed symptom, but instead as a conclusion. What symptoms cause the conclusion that it's running rich? Are those symptoms significantly different than if the ignition timing is retarded?
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post #3 of 197 Old 12-02-2020, 05:42 AM
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Some thoughts -

oops just realized this is a 93, had to delete.
fix exhaust. leaks can skew o2 sensor readings.
check ECT. What does the PCM see. live data will show.

Have you checked FPR (fuel press reg) ?

Out of an abundance of caution check eng oil for fuel. That -30 fuel trim is AFU.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 197 Old 12-02-2020, 10:11 AM
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Are you still using the ebay injectors? lol
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post #5 of 197 Old 12-02-2020, 10:13 AM Thread Starter
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Quote:
Originally Posted by USSENTERNCC1701 View Post
Curious about the results after replacing the cam sensor. Aside from it simply being the only thing you haven't replaced, it genuinely sounds like a good bet. Bearing in mind that fuel trim is the computer's response to data, treat running rich not as an observed symptom, but instead as a conclusion. What symptoms cause the conclusion that it's running rich? Are those symptoms significantly different than if the ignition timing is retarded?
I didn't mention this earlier because after making some change (I wish I knew which thing...) it stopped complaining about it.. There was a brief period where it was throwing a code for excessively rich air/fuel mixture. The smell of the exhaust would seem to support this conclusion, but currently (other than the exhaust - which obviously smells like all kinds of nasty with the cat removed) the only semi-definitive symptom (conclusion?) is the sooty spark plugs. I realize thats not the only thing that can cause that, but it seems to be a common theme and the air filter is almost brand new.

The snapon tool I have shows me where the current mixture is sitting (generally) in the super specific: Lean/Center/Rich. I would expect during idle, for it to run rich during warm up, occasionally going lean as it takes in data and then eventually doing its best to settle in the center range, occasionally going lean/rich since nothing's perfect. At least, in my head, this makes sense... maybe (probably) I'm off my rocker? I'll try to get some pics of the snapon tool's data. It can "capture" data, but its only method of output is a printer.. I might be able to capture this to my laptop.. I'll have to think about that one and how best to do something useful with that data.

Quote:
Originally Posted by jtec View Post
Some thoughts -

oops just realized this is a 93, had to delete.
fix exhaust. leaks can skew o2 sensor readings.
check ECT. What does the PCM see. live data will show.

Have you checked FPR (fuel press reg) ?

Out of an abundance of caution check eng oil for fuel. That -30 fuel trim is AFU.
Fix exhaust? Unless you're suggesting I stick the cat back on, I'm 95% I don't have any pre-O2 sensor leaks. If I do, they're minor enough that they aren't even leaving a sooty mark on anything. I suppose I could replace the exhaust gasket on the passenger side since I have the gasket (it came as a set when I did the driver side), but I don't have any evidence to suggest its leaking.

ECT - sorry, thats one I forgot to log.. this was replaced as well. As well, I also replaced the connector and a fair amount of the wire going to the connector. This particular year has 2 coolant sensors right next to each other, one feeds the PCM and the other the gauge on the gauge cluster. I replaced the one to the PCM and swapped out the one going to the gauge cluster with a DS18B20 that feeds a MCU with an LCD next to the dash so I can tell what the actual number is rather than relying on a needle indicator. As far as I can tell, comparing it to the snapon which is reading the PCM, they're very close, +/- I'd say 1.5 degrees F (last I checked).

I've got a gauge semi-permanently attached to the fuel rail which is telling me that I'm in range - at least from what I recall, I'll have to take a look to get actual numbers but I want to say ~33 psi while idling(?) and closer to 40 when its primed? I might have that backwards, but it wasn't all over the place anyway. The regulator is pretty new, and I only replaced it to rule it out.

I'm not actually sure how to check the engine oil for fuel to be honest... It looks like its just oil - not something mixed or odd looking, no bubbles or spots of something oddly colored. I could try lighting it... I would imagine if there's fuel in the oil, whats on the dipstick would go up pretty quick but take some time to light if it was just oil. Not the safest test, but unless I was actually replacing oil with gasoline (which I think I'd smell.. amongst other things..), we're talking a pretty small amount. In a controlled environment of course (I don't think there's gas of measurable quantities in the oil )

One thing I noticed - more as an interesting observation - it would seem to store different fuel trims based on the drive mode (Park/Drive). Its one value at idle and immediately jumps to another when I throw it in drive, even before the gears engage. I can see this with the vehicle off as well (key-on). The snapon will change the displayed trim when I shift, so its something stored. Maybe this is well known and I just never thought about it...

93 ZJ V8 5.2 - K&N FIPK, lots of headaches
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post #6 of 197 Old 12-02-2020, 10:15 AM Thread Starter
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Quote:
Originally Posted by HighLonesome View Post
Are you still using the ebay injectors? lol
The mis-matched ones were the ebay injectors (that ran fine all this time..) I'm still not sure how that happened... aside from the numbering and a slight color difference (one set is yellow, the other a little on the orange side), they otherwise looked identical. The new ones from K-Suspension (or rather, the rebuilt ones) are blue.

93 ZJ V8 5.2 - K&N FIPK, lots of headaches
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post #7 of 197 Old 12-02-2020, 10:24 AM
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I wonder if they are rated for 39 psi ('93-95) like you need.

find a set of injectors from a late '95 V8, they outflow all other ZJs
why is swapping them a bear?
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post #8 of 197 Old 12-02-2020, 10:25 AM Thread Starter
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On a side note - I have on order a new throttle-body from hipotek. 50mm. He actually sent me one, but it was for the wrong vehicle (I'm guessing a durango or something as it was very close). It also had a 50mm bore, which after measuring is maybe 0.4mm larger? I doubt this is going to get me anything useful, but its cleaner than I'm ever going to get the existing one and the bore holes are one size (the stock one would seem to have a small change just after the butterfly valve (or before it... I don't remember).

I think as well, my throttle might be a little on the sticky side, but I think that might be my fault - and would have been recent (like over the thanksgiving break - recent (nov 2020 for anyone reading this in the future..))

93 ZJ V8 5.2 - K&N FIPK, lots of headaches
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post #9 of 197 Old 12-02-2020, 10:33 AM
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Quote:
Originally Posted by variable View Post
throwing a code for excessively rich air/fuel mixture. The smell of the exhaust would seem to support this conclusion, but currently (other than the exhaust - which obviously smells like all kinds of nasty with the cat removed) the only semi-definitive symptom (conclusion?) is the sooty spark plugs.
I'd call smelling fuel in exhaust and soot on plugs symptoms. From those we can deduce unburnt fuel. If we assume timing is correct, then unburnt fuel means too little air, might conclude AFR is too rich. But that assumes good timing. Retarded timing could cause unburnt fuel even with an otherwise acceptable AFR.
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post #10 of 197 Old 12-02-2020, 10:38 AM Thread Starter
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Quote:
Originally Posted by HighLonesome View Post
I wonder if they are rated for 39 psi ('93-95) like you need.

find a set of injectors from a late '95 V8, they outflow all other ZJs
why is swapping them a bear?
I don't believe these were intended to increase the flow, just atomize the fuel better, but I could be wrong. It asks for the year on the page, and while assumption is the mother of all f*ckups, I would imagine that if they weren't taking it into account, instead of a year selection, they'd just say, "applies to 93-98" or something.

Here's the site: K-Suspension Fab

They were a bear because I had a hard time getting the rubber seals to fit properly without ripping apart. I think when I rebuilt the engine years ago, I may have bent the mounting brackets slightly which caused them to sit very slightly off or something and the slight angle makes it a tight fit on one side of some of the injectors, and not the other. After much fiddling (and wasting seals), I was able to get them to fit properly. If I replace them again, I'm probably going to replace the fuel rails as well... though I haven't found a good source for replacements..

One other thing worth mentioning, technically the engine thats in here is out of a 92 dodge 1500. As far as I can tell, the differences are almost negligible - I kept most of the Jeep parts for compatibility etc. One of the things that was different was the fuel rails. Unless I've got it backwards, the dodge version had 2 lines connecting the fuel rails that ran on either side of the regulator. I opted to stick with the jeep ones for consistency, but maybe this was a mistake? (or I got it backwards...?) Either way, this was ~5+ years ago, so it couldn't have made that much of a difference...

Oh, one more - that I'll have to add to the first post. I have the Hughes Plenum kit(hopefully thats the right link). Could be a leak in there somewhere, but I kinda doubt it.

93 ZJ V8 5.2 - K&N FIPK, lots of headaches
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post #11 of 197 Old 12-02-2020, 10:43 AM Thread Starter
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Quote:
Originally Posted by USSENTERNCC1701 View Post
I'd call smelling fuel in exhaust and soot on plugs symptoms. From those we can deduce unburnt fuel. If we assume timing is correct, then unburnt fuel means too little air, might conclude AFR is too rich. But that assumes good timing. Retarded timing could cause unburnt fuel even with an otherwise acceptable AFR.
I replaced the timing chain cover recently and checked the timing chain for play and it appears to be in spec. When I rebuilt it, I replaced the stock chain with a double roller set (for whatever thats worth) For as long as its still up on amazon, here's the link: COMP Cams 2103 Magnum Double Roller Timing Set blah blah blah

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post #12 of 197 Old 12-02-2020, 10:46 AM
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Quote:
Originally Posted by variable View Post
I don't believe these were intended to increase the flow, just atomize the fuel better, but I could be wrong. It asks for the year on the page, and while assumption is the mother of all f*ckups, I would imagine that if they weren't taking it into account, instead of a year selection, they'd just say, "applies to 93-98" or something.

Here's the site: K-Suspension Fab

They were a bear because I had a hard time getting the rubber seals to fit properly without ripping apart. I think when I rebuilt the engine years ago, I may have bent the mounting brackets slightly which caused them to sit very slightly off or something and the slight angle makes it a tight fit on one side of some of the injectors, and not the other. After much fiddling (and wasting seals), I was able to get them to fit properly. If I replace them again, I'm probably going to replace the fuel rails as well... though I haven't found a good source for replacements..

One other thing worth mentioning, technically the engine thats in here is out of a 92 dodge 1500. As far as I can tell, the differences are almost negligible - I kept most of the Jeep parts for compatibility etc. One of the things that was different was the fuel rails. Unless I've got it backwards, the dodge version had 2 lines connecting the fuel rails that ran on either side of the regulator. I opted to stick with the jeep ones for consistency, but maybe this was a mistake? (or I got it backwards...?) Either way, this was ~5+ years ago, so it couldn't have made that much of a difference...

Oh, one more - that I'll have to add to the first post. I have the Hughes Plenum kit(hopefully thats the right link). Could be a leak in there somewhere, but I kinda doubt it.
I looked at that site and one of the reviews was from a guy with a '98 5.2 and he said it ran great, so that probably means they are for '96-98 (49 psi).


I wouldn't swap the fuel rail since it ran well at one time.
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post #13 of 197 Old 12-02-2020, 10:53 AM Thread Starter
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Originally Posted by HighLonesome View Post
I looked at that site and one of the reviews was from a guy with a '98 5.2 and he said it ran great, so that probably means they are for '96-98 (49 psi).
I don't think the site is fancy enough to allow for comments to be that specific - sort of like how Amazon reviews are sometimes totally unrelated to what you're looking at because it's a different "color".. Unless they're specifying in the content which is which.. but it's worth an email. The guy is very responsive and helpful.

93 ZJ V8 5.2 - K&N FIPK, lots of headaches
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post #14 of 197 Old 12-02-2020, 10:59 AM Thread Starter
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I emailed the guy and will reply back when I've got someone more concrete than my impression

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post #15 of 197 Old 12-02-2020, 11:05 AM
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early ZJ and late ZJ injectors are incompatible, my money is on the injectors

Quote:
I purchased a set of these 4-Port Injectors for my 1998 Jeep Grand Cherokee with the 5.2L V8. This Jeep is my daily driver, which typically runs over 100 miles every day for commuting. I was starting to get some sputtering problems while traveling at high-way speeds, and I determined I had an injector go out on me. Instead of replacing my stock injectors with another stock-set, I decided to try these 4-Port injectors. I noticed an immediate difference after installing these injectors; Throttle response was greatly improved, seems to shift a little better, no more sputtering at high-way speeds, and it seems like these injectors gave a little life back into my motor (which has 172K miles on it). I would recommend these injectors to anyone looking for an upgrade over the stock injectors. I have also personally noticed a slight improvement to my MPG by about .2 miles so far. Thank you @ K-Suspension for providing another awesome set of injectors for the Jeep community.
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