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Discussion Starter · #1 ·
Hi all,

Thanks for the great forum! Sorry for the book length post, but I thot it might help someone in the future if they have similar issue.

I am new and have a similar problem to Stukey in his thread:

92 wrangler cranks, but won't start. Please help!
http://www.wranglerforum.com/f8/92-wrangler-cranks-but-wont-start-please-help-199368.html

I didn't want to hijack his thread with my sad story so starting a different one. Maybe we will have the same solution though from the sound of it at least.

Problem:

Wrangler cranks fine but doesn't start.

History

The problem started in spring 2012.

It ran great until one day it was hard to start, and took a while of cranking before it kicked in and ran. But once started it ran fine, no problem.

It always seemed to start if I gave it enough time but I was afraid the battery would die after so much cranking, giving it a few minutes for the battery to rest, and then cranking some more. After several rounds of that it would start up fine and go around town and even to the grocery store and back, no problem. After it was started once for the day it seemed to like to start quicker the next time that day. Next day tho it was back to the slow cranky starting. Sitting overnight seemed to be bad for it.

I had the service station come to tow it one day as it was not starting. The guy in the tow truck took off the air filter cover and blew in the filter box. He thot it was flooded. Dang thing started right up when he did that of course. So no tow needed. Next time it got cranky (wouldn't start) I tried his trick of blowing in the air filter box. He must have had sweeter breath than me cause it didn't work for me. I also noticed no smell of gasoline from the air filter box when doing this, so I started to doubt the flooding theory.

So after a few weeks I had it towed in to the station. They checked lots of important things under the hood and other important sounding places. The station manager ended up saying it was a problem with the gas tank. He said the fuel pressure was too high (90 lbs) and it was somehow an issue with the gas tank. So, new gas tank and stuff and off we go.

Except that didn't fix it. It was still cranky and hard to start. I took it back for more diagnosis. This time they said it was the fuel injection system fuel rail. The explanation was a rusty area near the seal with the engine head that let fuel drain out of the fuel rail when it was turned off. This then required a bit of time for the fuel pump to fill up the fuel rail with gas again after the key was turned on. The mechanic said think of it like a toilet bowl filing with water before you can flush it. Sounded pretty reasonable to me. It would start after waiting with the key on for about 5 to 7 minutes.

They said the fuel rails aren't made anymore so I'd have to find one at a junk yard. That didn't happen fast. All summer long it would start after a while. Eventually I noticed that after sitting in t for several minutes with the key on, it would make a clicking noise, kind of chattering. The check engine light would briefly come on when the relay clicking/chattering started, then go out. If I waited a minute after the chattering stopped, it would start pretty darn ok. But it seemed like the clicking/chattering was taking longer to happen over time. I found the clicking was coming from the fuel pump relay under the hood. Turns out the fuel pump relay and the horn relay are the same part number. So I swapped them. Swapping the relays didn't change anything.

So I did get a fuel rail and took it back in for the fuel rail to be installed. That was done but it didn't fix the problem. The new story was that the computer was bad. They explanation being that it wasn't holding it's memory. After the key was turned on the computer would fail to start up so it would reboot and load factory defaults and then it would start. The relay clicking was related to the computer rebooting.

So, this is the third diagnosis of the original problem by the garage. I think they actually are right about it this time. But I can't afford $500 for the new computer and the install costs on top what I already spent on it. So my plan is to try and fix it myself.

So tomorrow Lord willing I will try to get the computer out of the Jeep and take a look at it for any obvious problems. I am first going to look for corrosion on the external connector pins. I might get lucky there and find simple corrosion that needs to be cleaned up. Sometimes connector corrosion can be cleaned up just by pulling a connector and re-seating it several times.

If that doesn't help I plan to dissemble the computer case and check for any chip sockets. Chip sockets can get corrosion on the pins also and the same treatment (re-seating) is often enough to fix that. Getting a chip out of a socket is sometimes tricky but you can do it by using a small screwdriver under one end of the chip (not the socket) and slowly wiggling it upwards. Then pry the other end up. Chips have a small indent or a white dot of paint on one corner to mark pin #1. That matches a small notch or paint dot or sometimes a small impressed triangle on the chip socket so it is easy to install it in the correct orientation.

Static electricity is a big killer of digital chips so I plan to touch a ground before touching any of the computer circuit boards metal contacts or electrical paths. Of course I wil pull the battery cables before removing the computer or it's connectors too. Electrical surges are bad for digital chips too.

I don't know if these car computers actually have sockets in them for the chips tho. It may be the chips are soldered straight to the mother board. That's more reliable in a situation like a car with lots of vibration.

So I may not get anywhere with the easy fixes and may have to replace the computer module. Hopefully I will be able to find out tomorrow.

I found this Youtube (Bleepin' Jeep) video on computer troubleshooting that was interesting. Probably been posted it before but it was interesting to me. I didn't think the Jeep would even run with the shorts he introduced. But it did.


ECU troubleshooting Bleepin Jeep
https://www.youtube.com/watch?v=cdovPxDHcPY

I also saw this thread about a similar problem and it seems the computer was the possible problem there.

Wrangler forum fuel pump relay clicking
http://www.wranglerforum.com/f8/fuel-pump-relay-clicking-on-94-help-140761.html
 

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Founder, ThumbJeeps
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^ ditto, I replaced my PCM back in 2009, haven't looked back.

One note is, if it sits for a few minutes with the key on then the check engine light comes on at the same time as the fuel pump, its def. the PCM. Sometimes it will take upwords of twenty minutes before the fuel pump kicks.
 
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