please help ZJ! 93 Jeep GC Laredo dies/bogs when warm - JeepForum.com
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Unread 01-26-2014, 01:33 PM   #1
tj707
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please help ZJ! 93 Jeep GC Laredo dies/bogs when warm

hey everyone , new to jeep and the forum , any help or info would be greatly appreciated.

model
1993 5.2 jeep GC laredo 4wd
157,xxx miles ,
stock

I bought this jeep 3 months ago after it just passed smog. it ran great until recently. I backed out of my driveway fine , went to put it into drive and it bucked and kicked on me so I through it back into park and the idle raised back up, when I went to go in reverse to park it across the street from my house (on a hill) it bucks and kicked , died on me , wouldn't start. came back 20 mins later to avoid flooding. and it started up and drove right up my steep driveway fine. let it run for about 10 mins with alternately putting it into drive /neutral/park/reverse to try and get the problem to happen again and nothing. tried it one last time before I called it quits and sure enough. it didn't buck on me ever again, just sputters and dies out when put into gear or when I kick the throttle.but only seems to do this right when temp starts to register on the gauge

It sputters out and dies but (never bucked again) and when I go out and mess with it cold it seems to be fine , starts fine , revs up fine , idles fine , goes into gear and will even drive when cold, but after a few mins of idling and just starting to register a temp on the gauge it drops idle , wants to die when put into gear ,and wants to die after a rev of the throttle


test results had low fuel pressure of 28psi and was stoked because I thought that was the main problem. and guess what. same problem after new fuel pump.

sense it seems temp related (as it only seems to be a problem when starting to register temp on the gauge) thinking it may be temp sensor to pcm?
and that wasn't it either.


I NOW HAVE THE FALLOWING NEW PARTS
NEW FUEL PUMP AND FILTER
NEW CPS (I managed to replace it without removing anything but the cps)
NEW TPS
NEW IACV
NEW TEMP SENSOR TO PCM

I have good spark before, and after the problem.

any info would be greatly appreciated.
please help!

thanks.
tj with the dead zj


Last edited by tj707; 01-26-2014 at 01:54 PM..
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Unread 01-26-2014, 01:59 PM   #2
nnovickzj
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if it only happens when warm the up stream o2 sensor sounds like a good place to start if you replace use ngk brand bosch doesnt work
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97 zj 5.2 40,000mi
locked front and rear, 242, 3.5 iro lift, 32x11.5 kenda klever, 28 laredos for the road
4x 130 watt 6" spots on the roof rack, h3 leds in stock fogs, 2 40w leds on the grill
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Unread 01-26-2014, 03:17 PM   #3
ZeeJay1997
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considering all the stuff you have replaced, i would also suspect the O2 sensor. Disconnect it, stow the connector and drive it. If the problem ceases, change the sensor.

You may need to suspect the coil also
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Unread 01-26-2014, 09:29 PM   #4
tj707
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damn you guy's sure are snappy on here. nice!

ok I'll be checking into the map and o2 tomorrow. starting with the o2 of course. I will also check to make sure it's not jumping over 0.9 to be safe. I've always liked NKG. never really had a problem with bosch. but being both about the same price I'll definitely grab the NGK. wish me luck.

and I have good spark at the wires / and coil before and after this problem happens. But was looking into a MSD coil as part of a good tune up just before this happened.

thanks for the input guy's I'll keep the post updated.
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Unread 01-27-2014, 02:32 PM   #5
tj707
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ok so I unplugged the o2 and it still happened. right when it started to warm up and drop the cold idle it still bogs and dies out after a rev, or after put into gear.


so again:
it starts right up first try when cold , revs fine , idles fine, goes into gear fine.
but as soon as it starts to register temp and minimum the problem is back,
and with a good rev it revs back down right passed idle and bogs out and dies.
or bogs and dies when put into drive. (ONLY WHEN IT STARTS TO GET WARM)

I'll be going to get a vacuum pump to check my map next. any other idea's or info would be greatly appreciated.
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Unread 01-27-2014, 02:34 PM   #6
tj707
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and just to add. after the problem happens. it doesn't want to start back up until I let it cool down. and it I can get it to fire right back up after it dies it just chokes out black smoke until it eventually dies again.
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Unread 01-27-2014, 07:43 PM   #7
ZeeJay1997
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have you tried the key trick to see if a no light code is hiding in there?
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Unread 01-27-2014, 08:12 PM   #8
tj707
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yep I tried for codes and got NADA.
all I got back was 12 and 55. witch is (12 direct power disconnected in last 50 cycles) because I charged the battery ,
and 55 for end of codes.

even when the 02 was disconnected and the map I still didn't get any cel's or codes.




UPDATE!!!!!
(NEW MAP AND SAME PROBLEM)

SO IT'S NOT THE:
TPS
CPS
IAC
MAP
FUEL PUMP
OR 02
AND STILL HAS SPARK.

I'm starting to think PCM since thats about the only thing I haven't tried. just weird it only happens when starting to register a temp on the gauge.
I don't have tons of money to throw into this heap of jeep. only parts that stayed on are the cps and fuel pump. all the other parts were taken back when the problem still happened after install. So being lucky enough to have a buddy at the shop to let me do that. I still am down to the end of the line.

what else could it be?

and does anyone agree on the PCM next? or anyone had similar problems with a bad PCM?

please help! this is supposed to be my work horse. even though I really liked the jeep (when running) it's hard not to miss my chevy's right about now haha.
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Unread 01-27-2014, 08:30 PM   #9
ZeeJay1997
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Quote:
Originally Posted by tj707 View Post
I don't have tons of money to throw into this heap of jeep.
you've already wasted quite a bit. if you think it's the PCM, find some dry ice and pack it around the pcm to see if it helps the problem. does pcm feel hot to the touch? have you checked all the wiring connectors in the engine bay? contacts expand when they warm up.

honestly, if you have a warm place to work, go through the list of things i recommended earlier.
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Unread 01-27-2014, 09:25 PM   #10
tj707
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you've already wasted quite a bit. if you think it's the PCM, find some dry ice and pack it around the pcm to see if it helps the problem. does pcm feel hot to the touch? have you checked all the wiring connectors in the engine bay? contacts expand when they warm up.

honestly, if you have a warm place to work, go through the list of things i recommended earlier.



I only bought the pump and filter witch was needed due to 28psi , and a $40 CPS to prevent it later. all other parts went back to the shop. so I only have 150 into it. got a good deal on a walbro pump. not a cheapy.

I already did what you recommended earlier.
(check coil) witch I already did before/after the problem happens ,
(disconnect 02) I did that and still had the problem.
(check codes) I have been every so often and still have no codes or cel
(check connections) I went around wiggling the wires while it was running to see if I could get it to die out and nothing. also all the connectors look really clean , with a snug fit. but I haven't checked the entire harness with a multi or anything yet.


new motor mounts so there's not a big jerk when dropped into drive or when I rev it. even with a slow soft rev (without jerking) it still will bog and die out (as long as it starting to warm up). so the movement/jerking when put into drive or from a rev of the throttle doesn't seem to effect it at all as it only does it when warm and runs great cold.


what does the dry ice do?
kinda like the old school computer hard drive trick? I checked the pcm connections after it happened and it didn't seem hot. but I will double check that. think I can get away with using a freezer ice pack on it?
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Unread 01-27-2014, 09:51 PM   #11
ZeeJay1997
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oh sorry, you must be on a phone. see this write up

http://www.jeepforum.com/forum/f13/1...l#post14045654

additionally, if you use regular ice, be sure it's sealed good to keep water out of the connectors.

also consider changing the caps in the pcm. see #1
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Unread 01-28-2014, 06:28 PM   #12
tj707
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ohh that long list! my bad. not sure How I didn't see the glowing green link haha.

ok so I started going through the list cleaning all connections , ecu,pdc,main, ( I did a rinse and repeat on the PCM and PDC ) ect packing everything with dielectric grease and nothing changed.
banged on ecu and no changes,
wiggled and jiggled while it was running and nothing.
cleaned all the grounds I could find, (5.2 doesn't have the one by dipstick)
gauge stays about 14v
wasn't too worried about bad fuel because in most of my cases a car will run on bad gas but won't like to start on it, and it fire's right up when cold. any feedback on this one?
have a little over 30psi on fuel pressure at idle (93 5.2) so that should be good right?
just picked up a new cap and rotor as it looks like the one on there is pretty old. not installed yet but will be going on soon.. but again never had a bad cap or rotor give me a no start problem only at temp. any input here?
as fpr the coil I only checked for a bright spark using a spark tester. is this good enough to confirm a good coil? before and after the problem I still have a good spark. or should I double check with a multi to be safe?
couldn't find any vacuum leaks as I've tried multiple times with so carb cleaner.
exhaust seems to be breathing fine.
swapped relay's.

and after I let it start to warm up and get the problem to come back.
it died out and still held fuel pressure.
never lost any fuel pressure when it died. so would it be safe to assume the fuel pump relay is working correctly? NOPE!
this time it seemed to run a bit longer and start up faster after dying. but still had the issue.


ended up being (2) intermittent relays. I guess why I didn't find it the first time. and a bunch of corrosion found in PCM.
don't think the fuel pump was needed but I wanted to be safe as psi was starting to get a little low.
and after going nuts on the grounds and EVERRRYTHING else , not only does it run better, but no dimming/flickering lights , runs smoother , just all around better.


I haven't cleaned the TB yet (waiting for gasket)
and I will be installing cap and rotor today or tomorrow.

Last edited by tj707; 02-12-2014 at 02:28 AM..
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Unread 02-12-2014, 02:45 AM   #13
tj707
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http://www.jeepforum.com/forum/f13/1...l#post14045654

I've been working on / building up car's for years now and still can be tricky times. especially the dreaded intermittent electrical problems.
hard to find the problem when it goes away by the time you get the hood popped and multi-meter out. (double check those D*** relays)
I definitely recommend this on all auto's with or without problems. it might fix the issue depending on.
and worst case you rule a bunch of stuff out and have clean ground and a better connection throughout.


this was a GREAT write up and very useful. ZeeJay1997 Thank You Sir!
she's up and running happy as ever now.
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Unread 02-12-2014, 05:04 AM   #14
ZeeJay1997
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you are welcome. you are also correct that most everything in there is routine auto maintenance, except the PCM problem which is unique.
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