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Unread 01-03-2012, 07:45 PM   #1
mike87gta
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1993 ZJ 
 
Join Date: Jan 2009
Location: Prince Albert, Saskatchewan, Canada
Posts: 23
Runs rough when cold outside

Hi.
I have a 93 ZJ with the 5.2.

Heres the problem;

No codes.

When I start the jeep stone cold, and temp outside is 10*f or colder, it will run really rough for about 5 minutes, usually only at idle and sometimes will run rough if I hold the rpms high in neutral. It runs smooth accelerating, and after the engine warms up.

If I have the block heater plugged in, the jeep will run fine, if its unplugged and 10*f or colder it will run rough. The problem here is, well, its still a problem and sometimes I won't be able to plug it in.

If i turn the jeep off when it is running really rough it will be hard to start unless I hold the throttle wide open, then it will start easy, but continue to run rough. (This must enable clear flood mode - cuts off fuel, atleast it does on GMs) So it seems like something is causing it to get WAY to much fuel.

One time I decided to unplug the MAP sensor while it was running rough. It ran worse. I pluged it back and while running and it started running smooth. I tried this on a few more occasions but it didn't work, so it must have just been a fluke.

I replaced the plugs, wires, cap, rotor, fuel filter and did the IAC clean recently.

Any ideas? I don't want to just chuck parts at this thing and hope it fixes the problem... i'd like to diagnose if possible.

If someone has any ideas, or tables with voltage or resistance values to test suspected sensors that would be great...Thanks. Hopefully I can fix this before it gets to -35 here and won't run at all, LOL.

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Unread 01-03-2012, 08:25 PM   #2
Buzz98zj
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1998 ZJ 
 
Join Date: May 2011
Location: Lyndonville, Vt
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My 5.2 does the same thing. I noticed today while it was at a rough idle my voltage gauge was moving up and down just the slightest.
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Unread 01-11-2012, 06:47 AM   #3
mike87gta
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1993 ZJ 
 
Join Date: Jan 2009
Location: Prince Albert, Saskatchewan, Canada
Posts: 23
Ttt...

0°f this morning. Cold enough that it ran rough with the block heater plugged in this morning. The misfiring cleared up after 5 mins of warm up time...

Need to get this fixed before it gets way colder. Any ideas? Thanks!
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Unread 01-11-2012, 12:53 PM   #4
caligiuri87
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1994 ZJ 
 
Join Date: Aug 2011
Location: oskaloosa, iowa
Posts: 535
same proble mhere !!!! i do not have a block heater???? how come u do! gimme! lol but i prime the fuel pump twice then start it after i push down the pedal then it starts just fine rough for 2 sec but then it levels out bit higher idle but that clears when it warms up. its not that cold here yet but since im in the country with flat farm land around me the wind is very cold. but that works for me. im going to replace the cps hoepfully soon when money lets me that should def help im sure. i have 230000 on it and i think it is still original . maybe something to think about
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Unread 01-16-2012, 02:21 PM   #5
mike87gta
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Location: Prince Albert, Saskatchewan, Canada
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-22°f here today.. Jeep was misfiring like crazy until the temp gauge got to 1/4. Anyone?
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Unread 01-16-2012, 02:56 PM   #6
Buzz98zj
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I unloaded my niner last night and it was -9 out and it was running like crap. Stalling and seemed to be misfiring. I did notice a PCM plug was broke and loose. I'm going to try a full tune up and go from there. If it works I'll post.
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Unread 01-16-2012, 03:05 PM   #7
GrilledJeep
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I have come to realize that the jeeps don't like to start clean in the cold like I don't want to go out in the first place.

but when she is warm, purrrrrrrrrrrr.
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Unread 01-16-2012, 05:01 PM   #8
mike87gta
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Thanks.. Keep me updated. I have the day off tommorow and its supposed to be -28f so ill get to check the sensors with a multimeter when its acting up.

Already did a full tune up with no change.

Gas mileage is down to 6mpg now in the city. My last 5.2 zj with 35s got around 12 city in the winter.

I checked vacuum, tps voltage, map voltage and fuel pressure the othere day when it was warmer out and not acting up. Everything was ok. Ill check when its acting up tomorrow and post results. I just cant reach the multimeter probe to the cts to test that.
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Unread 01-17-2012, 09:06 AM   #9
mike87gta
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Location: Prince Albert, Saskatchewan, Canada
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Little bit of an update.
Cold as hell this morning.
Started, misfire like crazy.

I only had time to check map voltage and vacuum before it smoothed out.

Map voltage was 3v (high volt = low engine vacuum) So I put a vacuum gauge on it to see. Vacuum was at 8"hg, then about 30 seconds later the vacuum gauge jumped to 16"hg and the jeep ran fine. A vacuum leak this big would be very loud and obvious, but I can't hear any leaks at all.

Hmm
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Unread 01-17-2012, 09:45 AM   #10
PolkaPower
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Quote:
Originally Posted by mike87gta View Post
Little bit of an update.
Cold as hell this morning.
Started, misfire like crazy.

I only had time to check map voltage and vacuum before it smoothed out.

Map voltage was 3v (high volt = low engine vacuum) So I put a vacuum gauge on it to see. Vacuum was at 8"hg, then about 30 seconds later the vacuum gauge jumped to 16"hg and the jeep ran fine. A vacuum leak this big would be very loud and obvious, but I can't hear any leaks at all.

Hmm
Have you checked your plenum gasket foe leaks?
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Unread 01-17-2012, 11:07 AM   #11
mike87gta
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1993 ZJ 
 
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Location: Prince Albert, Saskatchewan, Canada
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There was no oil pooled in the bottom when I took the throttlebody off to clean it.

UPDATE: The jeep was running fine at the time of the test.

I was able to replicate the exact problem and cause the jeep to run like it does on cold starts.

The egr valve or solenoid seems to be the problem. It is on the passenger side of the intake manifold behind the fuel rail. This only applies to 93-95 5.2 zj's - 96+ have no egr.

The EGR solenoid gets vacuum from the intake manifold, and sends a vacuum signal to the EGR valve when certain conditions are met (not idle).

Test procedure:
I removed the vacuum line going from the EGR solenoid to the EGR valve.
I then ran a vacuum line from the intake manifold directly to the EGR valve, this causes the EGR valve to open - it immediatly started to run EXACTLY like it does on cold mornings. Removed vacuum from the EGR valve and it ran perfect!

So for some reason the EGR valve is opening during cold starts when it shouldn't. My temporary solution was to block off the vacuum line going from the egr solenoid to the egr valve.

Will perform a cold start later tonight or tomorrow morning to confirm that the problem was solved.

Thanks
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Unread 01-17-2012, 07:48 PM   #12
mike87gta
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Looks like the problem is solved. Went out to start it after it sat for 7 hours in -25F. Started up and ran great!
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Unread 01-18-2012, 06:11 AM   #13
dmxsoulja3
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I like that people come back to the forum and post that they got it fixed and don't leave a bunch of open ended threads, for getting your Jeep fixed. I feel bad that I don't want to go work on my jeep when its 40 degrees outside here in FL, lol
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Unread 01-18-2012, 09:56 AM   #14
mike87gta
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Location: Prince Albert, Saskatchewan, Canada
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Quote:
Originally Posted by dmxsoulja3 View Post
I like that people come back to the forum and post that they got it fixed and don't leave a bunch of open ended threads, for getting your Jeep fixed. I feel bad that I don't want to go work on my jeep when its 40 degrees outside here in FL, lol
Yes, its pretty frustrating when you search to find a thread with the same problem, but with no end result.

It started up and ran great again this morning in -29*F and -47*F windchill!
Hard to believe just over a week ago we were at +32F temps..
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Unread 01-18-2012, 10:01 AM   #15
bananaslug
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Being from souther Cali, before this thread I thought our 40* morning was cold
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