4.2 carb to 4.0 FI swap - starts, won't run - Page 2 - JeepForum.com

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post #16 of 35 Old 01-20-2013, 07:49 AM
Que89YJ
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Did the fuel pump run and stay running?

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post #17 of 35 Old 01-20-2013, 09:26 AM Thread Starter
JunkyardJeep
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Yes. When I jump pins 87 & 30 from the fuel pump relay, the fuel pump comes on stays running. When I crank it over during that time, it doesn't start at all.
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post #18 of 35 Old 01-20-2013, 12:55 PM
Que89YJ
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Tps will not keep it from starting. Fault codes?
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post #19 of 35 Old 01-20-2013, 01:19 PM Thread Starter
JunkyardJeep
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Quote:
Originally Posted by Que89YJ View Post
Tps will not keep it from starting. Fault codes?
Unfortunately, I don't have a plug for my code scanner. My YJ doesn't have one because it never had a computer, and I didn't use the dash harness from the ZJ. It's exempt from testing for inspection because it's pre-1996, so it doesn't matter in that respect, but it screws me by not having it at times like this. I'm probably going to have to get one from the junkyard and wire it in myself.
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post #20 of 35 Old 01-20-2013, 01:38 PM
Que89YJ
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You can still do codes. Connect a test light to the wire for pin 32 of the ecu and the battery positive and it will act just like the cel.
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post #21 of 35 Old 01-20-2013, 02:10 PM Thread Starter
JunkyardJeep
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Quote:
Originally Posted by Que89YJ View Post
You can still do codes. Connect a test light to the wire for pin 32 of the ecu and the battery positive and it will act just like the cel.
Nice, I had no idea, Thank you. I'm going out to do this now. Thanks again.
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post #22 of 35 Old 01-20-2013, 02:54 PM Thread Starter
JunkyardJeep
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Ok. Checked codes the way you said and here's what it showed.

code 12: Direct battery input to PCM was disconnected within the last 50 Key-on cycles.

code 55: Completion of fault code display on Check Engine lamp.

The code 12 is expected and I don't imagine it's the cause of my problem. The code 55 I have no idea. I'm looking it up now.

If I'm understanding it correctly, It just means it's done reading codes. Is that right?

Last edited by JunkyardJeep; 01-20-2013 at 06:38 PM.
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post #23 of 35 Old 01-20-2013, 03:11 PM
Que89YJ
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Totally normal. Ok so the ecu thinks everything it's ok. You jumpered it so fuel was supplied. You said that you were able to dump fuel with the old ecu into the tb and it would start. What about this one?
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post #24 of 35 Old 01-20-2013, 06:37 PM Thread Starter
JunkyardJeep
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Well, I just spent the last 3 hrs. out in the garage trying to figure this out. I filled a water bottle with gas and poked a small hole in the cap. If I spray the fuel into the throttle body, it stays running. At first, you can hear a loud vacuum sound from the throttle body while it's running. Then it gradually loses power and the vacuum sound goes away. As soon as I stop spraying gas, it stalls.

Frustrated as can be, I decided to pull the fuel rail off. Since it's getting proper pressure to the rail, I wanted to see if the injectors were doing what they are supposed to. I left the injectors in the rail and plugged in. I disconnected the coil wire and cranked it over. All of the injectors are spraying fuel when they are supposed to. I put everything back together and it still stalls after a second or two.

It's getting spark and fuel while cranking, running for a moment, and right up to when it stalls. I want to put a hammer through the windshield right now.
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post #25 of 35 Old 01-20-2013, 07:45 PM
Que89YJ
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You proved it's a fuel issue by supplying the gas and out ran until it runs out. With the fuel pump jumpered you should have a constant supply. I am confused too.
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post #26 of 35 Old 01-20-2013, 07:55 PM Thread Starter
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I know it was probably a waste of time, but I had to see what the injectors were doing so I could rule that out. I'm hearing bad PCM alot, pricing them up now.
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post #27 of 35 Old 01-20-2013, 08:08 PM
Que89YJ
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It's the only thing I can think of. I do know some people that part out jeeps and should have one. I wish you knew someone that had a jeep in your area so you could put your ecu in and try it out. Let me know if you need parts help.
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post #28 of 35 Old 01-22-2013, 06:42 AM Thread Starter
JunkyardJeep
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Well, I'm going to try getting another PCM. From what I've read, They are not available new anymore. Makes sense since it's 20 yrs old. I've also read that most rebuilt units fail prematurely because they are not really rebuilt at all. They will fix whatever is not working and call it rebuilt while leaving every other part of the decades old unit alone.

I found a company called A1 Cardone through Summit racing who claims to completely rebuild all units. They charge almost $200 plus a $100 core charge.

I also found them from Standard Motor parts through Rock Auto for just under $150 with a $125 core charge. I can't find any info from Standard on whether they completely rebuild units or not, but I would imagine a well known company like that would.

Does anyone have any experience with PCM's from either company? Naturally I would like to use Standard because they are cheaper, but if A1 Cardone is better, I don't mind spending a little more.

Any info on personal experiences with changing PCM's like tips, cost, or where to purchase, will be greatly appreciated... thanks, and thank you to all who helped me out on this!
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post #29 of 35 Old 01-22-2013, 06:50 AM
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got anyone near you with a 4.0 Jeep you could borrow an ecm from? I personally have used one ecm from autozone (which sells cardone) and actually still have it in the running jeep. Same deal.. gotta give them back a core.

1998 ZJ 5.2 Auto

1989 Wrangler Black Bone Stock 2.5l 5spd
/l , [____],
|---L--[]lllllll[]-
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post #30 of 35 Old 01-22-2013, 07:07 AM Thread Starter
JunkyardJeep
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Quote:
Originally Posted by Mark05059 View Post
got anyone near you with a 4.0 Jeep you could borrow an ecm from? I personally have used one ecm from autozone (which sells cardone) and actually still have it in the running jeep. Same deal.. gotta give them back a core.
Ahh, exactly the kind of help I was looking for, thanks. Autozone is usually really good on price. They'll probably have to order it, but at least I won't be paying for shipping, lol.
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