94 JGC Hard Start - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 11-12-2001, 10:33 PM
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94 JGC Hard Start

I6-4L Starts fine in warm weather.. doesnt stall.. colder it gets.. longer it takes for fuel pump to activate.. thought it was a pump problem but the delay exists between the ignition switch(in run pos-not cranking) and the relays ..relays are good so is the box.. ignition switch is also good.. again the length of the delay depends on how cold it is. for example when i try to start.. just cranks.. but if i just turn to run and wait eventually you can hear the relays click then pump activates immediately after.. I get code 12 with the turn key diagnostic.. battery is new and connections clean... any ideas?...thx

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post #2 of (permalink) Old 11-17-2001, 07:12 AM
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Re: 94 JGC Hard Start

You might ask this Q over at the Mid-Sized board. Kind of confusing, but your Grand Cherokee is actually a mid-sized (YJ I think). This board is for the Full-Sized Jeeps such as the J-trucks, 84-91 Grand Wagoneer, 69-83 Wagoneer/Cherokee, etc. (SJ)

I could take a guess, but the guys over on the other board are pros on the 4.0L six. They will fix you right up. I wonder if Autozone or Parts America would have a code reader that you could borrow to get the Comp. analyzed. Just a thought. Sorry I'm not more help.

Phillip J. Van Why
1985 Jeep Grand Wagoneer
post #3 of (permalink) Old 11-17-2001, 04:42 PM
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Re: 94 JGC Hard Start

Thank you for your response...I originally posted here then realized I posted in the wrong place...Any ideas from anywhere are appreciated..I have posted in several forums around the net but havent solved this irritating problem yet ..I am hesitating to take it in for $ervice because the dealer says "$$pump$$" right away... just dont trust those guys after they broke my shifter trim panel and tried to charge me for a replacement... anyhoo thx again

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post #4 of (permalink) Old 11-18-2001, 03:15 AM
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Re: 94 JGC Hard Start

Any chance it might be some condensation in the computer or relay box? It would make sense that it only happened when it was cold. If you can put a volt meter on it, you could make sure that the relay was getting voltage instantly and that the pump had power to the feed side of the relay. You could probably (if you wanted to stand out in the cold) even measure the time from key activation to relay activation. That would give you some good ammo against the pump theory and maybe give you enough info to get a new relay. I don't know how much those relays cost though (if it was inexpensive I would almost replace it anyway). The other thought I had was maybe a clogged fuel filter. It would cause an intermittent problem maybe enhanced by the fuel being thicker? (I'm reaching there, but if you haven't changed it in a while, it sure wouldn't hurt).

Is the fuel pump controlled by the ignition switch or the Engine Management System? I know GM systems the fuel pump isn't controlled by the computer. That would sure simplify trouble shooting (and make repair possibilities less expensive).

Have you bought the TSM yet? If you can spare the $100.00 it would give a listing of the engine codes, that would help analyze the source of the problem. Maybe one of the guys on the Mid-Sized board has one, or you could call another dealer and ask one of the service guys to tell you what it means (they might not tell you, but it never hurts to ask).

Have you ever had the fuel sytem cleaned or do you use premium gas? I know you said you could hear the pump start, but extremely dirty injectors could cause a computer fault especially during ethanol months. If its a throttle body type injection, it might not be too hard to pull the throttle body and clean it. I don't think I would mess with a port fuel injection system as there is a lot of possibility for leaks, but if you're comfortable with it, you could pull and clean the intake, fuel rail, and replace the injectors (depending on cost). Even if this isn't the source of the problem, it is a good idea on a vehicle that is getting on in years, might help you narrow down possibilities.

Just some thoughts. I hope that helps.
Phil

Phillip J. Van Why
1985 Jeep Grand Wagoneer
post #5 of (permalink) Old 11-19-2001, 12:37 AM
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Re: 94 JGC Hard Start

Havent considered condensation...not sure which system would be causing this delay. As far as testing under conditions I have tested voltage to the relay box and the delay was there, thats how i narrowed it down. The code 12 means pwer to the PCM(powertrain control module) was lost during the last 50 ignition starts. I have given it a major tuneup so things like fuel filter dirty injectors etc.. are not the problem... fuel pressure to the injectors checks out once the vehicle is running.. as I said I have narrowed it down to something between the ignition switch and relay box...(note when I did the volt test on the box there was a delay as expected I immediately plugged in the relays and the vehicle fired right up)... As far as the computer goes.. could a faulty sensor be causing the delay of power to the relay box?... now that I think of it... power is only delayed to the automatic shutdown and fuel pump relay recepticle. Well you have given me a couple of ideas to try. Thx again...your help is very much appreciated!

post #6 of (permalink) Old 11-24-2001, 01:25 AM
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Re: 94 JGC Hard Start

I was just thinking about the TPS (throttle position sensor) when you mentioned that. I seem to recall this being a weak point of the system (GM at least). Oxygen sensors aren't expensive either.

The other thought would be the code that you are recieving, and that is a bad battery or connection. I know it sounds almost too simple and stupid, but if the computer was re-initializing it would take it a few moments to cycle through it's check-out/initial power up and then it would activate the relay. You would also notice it running rough until you shut it off and then on again (presuming it didn't lose power in the interim)as the computer would be re-calculating the fuel ratios.

I hope that helps.
Phil

Phillip J. Van Why
1985 Jeep Grand Wagoneer
post #7 of (permalink) Old 11-24-2001, 03:51 AM
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Re: 94 JGC Hard Start

I got a reply on another forum from a person having the exact same problem as me... said he replaced the computer and problem was solved... Your suggestion RE the code twelve sounds good (and less expensive!) will be double checking the connections and test those sensors you suggested before taking it in...Thanks again

post #8 of (permalink) Old 11-27-2001, 10:35 PM
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Re: 94 JGC Hard Start

I have a 96 GC with the 5.2 but i have suffered similar cold weather related problems. I also get code 12 all the time and I know there is nothing wrong with battery or connections (all brand new). I agree with the other person about the PCM being the problem. I have not replaced mine yet but it is on my list of to do's. I suspect that there is some sort of internal flaw with them and intend to get ahold of the manufacturer and discuss it with them, who knows maybe recall is in order if there are lots of these out there causing problems. Good luck.

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