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Unread 08-11-2007, 02:34 PM   #1
jason1977
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94 Grand Cherokee Laredo NIGHTMARE with staying running

To anyone who at least reads this....THANK YOU..I'm at a loss here.

I've been working on cars and trucks my whole life, and I've never run into this problem, and for months I havn't been able to figure it out.

I have a 94 Grand Cherokee Laredo, close to 270,000 miles on it. Looks great, runs really good for as many miles as it has. When it runs. For some reason, and at seemingly random times, the ignition/fuel system just shuts down. No warning, everything just goes dead. Let it sit for a few hours or overnight, starts and runs (until it dies again). The really weird part....when it dies, the Check Engine light and the fuel pump won't come on. Everything else works fine, sensors on the motor all have voltage where they should, motor turns over, coil has power, etc... The only thing I could think of was a bad ECU, whiich dosn't make real sense, because as stated, when it runs, it runs great. After some reading on the web and talking to a few mechanics I know, I thought it might be related to the security system...but there is none. I checked behind the glovebox and there is no VTSS controller. Interesting, because the serial number on the ECU (56028300) references to a vehicle equiped with a security system.So I tried unlockng and locking and vice-versa all the doors and rear deck, no change. From what I've read and been told, if the ECU is from a security model, it shouldn't run at all if installed in a non-security model. So i tried another ECU from a similar jeep (federal emmisions, no security, 4.0l, automatic) only 1 year newer (serial# 56028026). With that ECU the truck fires, but won't stay running more than 2 seconds. It came from a running but wrecked 95 GC. Im about at the end of my wits with this........

If someone out there has ANY clue what to do besides set the thing on fire, PLEASE let me know!!!!!!

Also kindly send messages to jasonenglish77@gmail.com if possible, or jason@surferz.net. Thanks in Advance!!


1994 Jeep Grand Cherokee Laredo
4.0l
Auto, 4WD
all stock running gear
266,000miles and counting (hopefully)

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Unread 08-11-2007, 02:56 PM   #2
smokestack
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Same problem that alot of us here have. Not sure what to tell you other than start searching the threads here about stalling. But if its like mine it wont really do much good. Mine is a bad board or something in the ecu...if i jiggle the part the wires go into it dies. You can also check to see if there is play in the distributor...i heard that can cause random stalls and non starting issues.

Hope you can track it down. I know how it is
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Unread 08-11-2007, 11:03 PM   #3
zjay
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Ign coils can crap out when hot- and real common for them to die. put a test light between the 2 terminanls and see if it flashes when cranked. if it does and you have no spark, get a coil.
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Unread 08-11-2007, 11:36 PM   #4
Briandl
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Sounds like a crank position sensor, but I don't know a lot about 94's...
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Unread 08-12-2007, 06:20 PM   #5
smokestack
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I woulda said that but i replaced mine and it was good. Didnt solve any stalling or starting issues..
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Unread 08-12-2007, 06:59 PM   #6
jeepunlimited
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mine used to stall out on me, doesnt anymore, i replaced the IAC , TPS, o2 , crank sensor , coil , plugs , wires , everything, even the o2 sensor...no dice

put a new fuel pump in and hasnt let me down yet ....the pump being on its way out would make sense cause when the pump gets hott, it will shut down and not run at all, soo you wouldnt hear it come on...and the check engine light doesnt come on for anything for the fuel pump....at least it doesnt on my 93
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Unread 08-12-2007, 07:08 PM   #7
smokestack
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I know that my fuel pump is getting there but it always turns on..i can hear it anyways. But the sending unit is shot so i never know how much gas ive got. Thats what sucks about it. Im pretty sure mine is the ecu...i just dont have 400 bucks for a new computer.
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Unread 08-12-2007, 07:56 PM   #8
Briandl
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Unread 08-13-2007, 06:01 AM   #9
Bob D.
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Quote:
The really weird part....when it dies, the Check Engine light and the fuel pump won't come on.
The WJ has been known to have a similar problem when the battery terminals become a slightly oxidized - a little resistance builds up affecting the electrical systems voltage and it wigs out - stalling, gauges acting strange etc. Same if the battery is getting flaky.
Don't know if the ZJs are as sensitive but it's worth checking.
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Unread 08-13-2007, 08:17 AM   #10
ezrider327
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--"" So i tried another ECU from a similar jeep (federal emmisions, no security, 4.0l, automatic) only 1 year newer (serial# 56028026). With that ECU the truck fires, but won't stay running more than 2 seconds. It came from a running but wrecked 95 GC. Im about at the end of my wits with this....""--

I didn't think that would work, aren't they "programmed" to the vehicle??

As for the issue at hand, we had a 97 Dodge Caravan ( I know it is a different vehicle BUT it IS the same situation ) that would do the same thing after almost a year of trying to figure out why and switching out different things we found out that the fuel pump was the problem.

Once it was allowed to "cool down" ( scary thought being IN the tank ) it would run like nothing ever happened. This drove us (or not - LOL) crazy, it was a totally random occurance, sometimes it would do it on a long trip & sometimes on a 30 mile trip & then it would not do it for a year or so, driving was always a gamble - will we make it without a tow ????.

When it "acts up" can you hear the pump running? I would check that first
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Unread 09-19-2007, 10:37 PM   #11
andrewkjc
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93 Grand Cherokee stalls, dies, backfires, HELP

I just bought a 93 Grand Cherokee with 252,000 k's on it. When I took it for a test run, it started and ran great. I took it to a mechanic, and he gave it a thumbs up, and said especially that the engine looked and sounded in Awesome shape. It's the V8. Anyway, next morning I go to start it, and it stalls right away. I start it again and it gasps and coughs and stalls. This went on until I put my foot down a bit, and then the engine would obviously miss fire and shake the whole vehicle. And if I put gas on it would backfire when I let my foot off. I took it back to the mechanic, he looked it over, couldn't figure it out. My little screen told me I had a bad coolant sensor, which I replaced. The mechanic suggested the the Hall affect, or Pick-up in the distributor could be affecting it, so I replaced it as well. Meanwhile, it now says that my coolant sensor is bad again. It doesn't say it all the time, just once and awhile. Now, when the Jeep works, it works great. But it takes half an hour of fighting with it, and then leaving it for about the same length of time until it will start and keep running. I don't know what to do, as I'm not really all that mechanically minded. The other thing is that the computer looks like it was replaced in 2002, and the check engine light never comes on for any of my problems. I've been reading here on the forum, and the fuel pump seems to be a popular fix. I hope someone has some insight. I'm really frustrated. The dealership wants 80 bucks just to look at it, and I was really hoping for a dependable vehicle.
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Unread 09-20-2007, 10:14 AM   #12
indept
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Does the fuel rail have a fitting on it to put a gauge, I know my 2000 I6 WJ does. So put a gauge on it when it won't start & see if it has good (> 40 psi) pressure. then see what it reads when it DOES start. A simple check.
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Unread 09-20-2007, 10:40 AM   #13
Upside
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Andrew your Coolant sensor problem is most likely an issue with the vehicle information center (VIC) not the sensor. The solder joints go bad and need to be resoldered. There are a bunch of write ups about that issue, I have a laredo so my VIC isn't a digital screen like yours (it's more of a Playskool looking screen).
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Unread 09-20-2007, 11:00 AM   #14
tjsgrecc
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my moms old 94 Bravada did the exact same thing just shut off like that and then it worked fine for a wile. she got rid of it right away to someone for cheap and a week later the ecu i believe or some other computer on that thing went out for good and cost like that person $1000 or more to fix it (or so they said). so probably the computer is going out or there is a dry solder joint on it some where from being old.

in my old car the headlights used to just turn off randomly (infinity j30t) and i found some little box thing under the hood that had some kinda chip in it and i reheated all the solder joints and they worked fine ever since. i know u cant do this on an ecu but it just makes me think it could be some kinda connection problem on that board.
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Unread 09-20-2007, 12:03 PM   #15
kdavis
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My 94 limited did the same thing, and the fuel pump ended up being the culprit. I'm totally guessing here, but it's possible that the fuel pump is failing, and as it heats up, the electrical resistance increases as the jeep tries to keep it running, which eventually tells the computer it's bad/inactive, and kills it. When you let it sit, it goes away.

The ECU solution from another vehicle probably won't work becuase it isn't programmed for your system, but again, a guess.

You said the ignition system shuts down, does that mean the starter? Could you physically hot wire it if you tried? If so, you're still getting power to the starter, just no fuel.

I'd put a new fuel pump in first, see what happens.
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