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YJ Computer/ Engine Swap Help

8K views 47 replies 4 participants last post by  laybackman 
#1 ·
Hey guys, I need help again...

Background...I have a 1994 Wrangler with the 2.5L, 5 speed manual in it. Ran in until ~203k on the clock. New engine time came and I chose to stay with the 2.5L (yes I know some will chuckle) but honestly the four squirrels always did what I asked them to do, it was in my price range, and I was hoping it would be something fairly simple and would be heading back down the road. The last statement is anything but true.

Long story short it's been in the shop for the last two months, they can't get it to start on a regular basis, sometimes it will and sometimes it won't, doesn't appear to be any rhyme or reason to it. The shop has replaced nearly every electrical component on the Jeep, made new grounds, sanded the grounding spots, checked the entire harness out of the loom etc etc.

They are suggesting I may have a bad ECM (I had done the "brain" surgery on my ECM a couple years ago and it has worked great!) Anyways, I'm fortunate to have several Jeepers in the area that are willing to part with their ECM from when they did an engine swap and eliminated it.

My question is (and I searched through over 10 pages of posting before making this one as I don't want to waste anybody's time; so I apologize in advance if I missed it or didn't hit the right crawlers) does the part number on my, currently installed, ECM have to match the one I put in it? Before I purchase one from somebody I would like to make sure it will work... My ECM has a part number of 56028289, the dealer said the only ECM that would work would be this one or 56027575; is that true? Unfortunately those who have offered me an ECM don't have those part numbers.

As always your help and expertise is greatly appreciated!!! My wife may off me if I don't get her on any Jeep rides this Summer and it's coming to an end quick. Heck in Ohio Winter may be here tomorrow, who knows. :confused:
 
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#2 ·
Hey guys, I need help again...

Background...I have a 1994 Wrangler with the 2.5L, 5 speed manual in it. Ran in until ~203k on the clock. New engine time came and I chose to stay with the 2.5L (yes I know some will chuckle) but honestly the four squirrels always did what I asked them to do, it was in my price range, and I was hoping it would be something fairly simple and would be heading back down the road. The last statement is anything but true.

Long story short it's been in the shop for the last two months, they can't get it to start on a regular basis, sometimes it will and sometimes it won't, doesn't appear to be any rhyme or reason to it. The shop has replaced nearly every electrical component on the Jeep, made new grounds, sanded the grounding spots, checked the entire harness out of the loom etc etc.

They are suggesting I may have a bad ECM (I had done the "brain" surgery on my ECM a couple years ago and it has worked great!) Anyways, I'm fortunate to have several Jeepers in the area that are willing to part with their ECM from when they did an engine swap and eliminated it.

My question is (and I searched through over 10 pages of posting before making this one as I don't want to waste anybody's time; so I apologize in advance if I missed it or didn't hit the right crawlers) does the part number on my, currently installed, ECM have to match the one I put in it? Before I purchase one from somebody I would like to make sure it will work... My ECM has a part number of 56028289, the dealer said the only ECM that would work would be this one or 56027575; is that true? Unfortunately those who have offered me an ECM don't have those part numbers.

As always your help and expertise is greatly appreciated!!! My wife may off me if I don't get her on any Jeep rides this Summer and it's coming to an end quick. Heck in Ohio Winter may be here tomorrow, who knows. :confused:
5602 7575 is the only ECM listed for your year/engine/tranny in a OEM parts manual. I can't find what the other number is for.
 
#3 ·
Any 2.5 manual controller from a 91/95 xj or yj will work. Are you able to see codes when you cycle the key? When they say it won't start does the starter always torn over? Does the rail have fuel pressure to it? I can help you figure out what's going on if the ECU doesn't do the trick.
 
#4 ·
Laybackman: If in not mistaking I believe 56027575 is the new number for 56028289.

Que89YJ: To my knowledge you can still see the codes when you cycle the key. I've had it to two shops to no avail. In between the two shops I tinkered with it for a couple days. During that time I was able to read the codes. The shop who currently has it is also able to hook up to the computer via a Snap-On diagnostic tool.

The starter always turns over, and I was told the CEL is cycling every time you turn the key over. When it doesn't start it wants to backfire through the exhaust. Sometimes it will start if you try again directly after that but it runs like crap. If it starts the first time it runs like a champ.

The rail has good fuel pressure and holds it. It's got a new fuel pump, pressure regulator etc. He has noided the injectors and all checks ok. He's also pulled the injectors and rail, primed the system and left them sit with cardboard under them to check for a leaking injector.

I guess my only concern was that I didn't want to buy a computer thinking it would work and if it doesn't fix the problem assume my issue is from something else when in fact I wasn't using a compatible computer.
 
#5 ·
Laybackman: If in not mistaking I believe 56027575 is the new number for 56028289.

Que89YJ: To my knowledge you can still see the codes when you cycle the key. I've had it to two shops to no avail. In between the two shops I tinkered with it for a couple days. During that time I was able to read the codes. The shop who currently has it is also able to hook up to the computer via a Snap-On diagnostic tool.

The starter always turns over, and I was told the CEL is cycling every time you turn the key over. When it doesn't start it wants to backfire through the exhaust. Sometimes it will start if you try again directly after that but it runs like crap. If it starts the first time it runs like a champ.

The rail has good fuel pressure and holds it. It's got a new fuel pump, pressure regulator etc. He has noided the injectors and all checks ok. He's also pulled the injectors and rail, primed the system and left them sit with cardboard under them to check for a leaking injector.

I guess my only concern was that I didn't want to buy a computer thinking it would work and if it doesn't fix the problem assume my issue is from something else when in fact I wasn't using a compatible computer.
That wouldn't be the first time they did the ol' number change snafu...:rolleyes:
I hate it when they print a document then go ahead and alter part numbers listed. It is a source document. Someone needs to get a couple of slaps behind the head at Chrysler.....Oh Yeah :fish: :fish:
 
#6 ·
Do the ECU. If it doesn't do the trick try and get a list together and post back everything electrical that has been replaced. If there is backfiring at all it is a timing issue.
 
#8 ·
Timing issue.... One example I experienced when a timing issue wasn't timing issue, but a short to ground issue that acted like a timing issue.

My nephew had a '96 Chevy Blazer 4.3/auto. It would never start when it was raining out. It would turn over but not fire or pop back through the TB.

At other times it would start and run perfect. BUT later on that week it would fire up and run well then an hour later start to stumble and eventually cough, and die.

He had his friends that looked at it along with a few pros but they found nothing to cause this problem. It got parked.

Then he asked me for my help. I said OK but made no promises. In the back of my mind I'm thinking I'm getting sloppy 25ths at this so this is going to be bad.

But nothing was hacked up.

He had charged the battery so I popped the hood and he hit the ignition. It cranks but won't start. BUT.... I can just about here a spark arc somewhere under the hood.

So I tell him to cut the ignition and I start to 'investigate' The 4.3 has it's dizzy over on the passenger's side of the engine compartment. I find some tracing on the underside of a rubber hose in that area and I also find a small crack in his coil wire which is under this hose with more spark tracing on it.

While eyeballing this spot he hits the key again. Would you believe that the coil wire breach allowed arcing to this rubber hose!?!? Maybe because it was dirty?? I have no freaking idea but I saw it.

I slapped some electrical tape on the coil wire for a quick fix so he could replace that wire.

That 4.3 never did that again. He eventually replaced the wire. I will never assume that a plug wire cannot arc to ground via a rubber hose. Or should I say that a high voltage spark cannot dissipate onto a rubber item.

Listen..... & eyeball everything.
 
#9 ·
Very good example! Thanks for sharing. I hate not fixing/ working on it myself, but I was hoping somebody other than me would have better luck, fresh set of eyes, and actually a mechanic!

I purchased a computer tonight from a '93 YJ, dropped it off to the guy and crossing my fingers for great news tomorrow!!!

I think the guy working on it now is about to pull his hair out, but he doesn't want me trailering it away from his shop.

Thanks again.
 
#10 ·
Those hoses all have carbon and are conductive. Usually 8k resistance so they will act like a plug wire. If it backfires the firing would occur at random and fire through the throttlebody as well as the exhaust. I can think of a few good ideas but I will keep my fingers crossed for the ecu before I put in my .02. Check for codes after replacing the ecu and letting it run for 10 minutes and getting it into closed loop. If the problem comes back immeadiately check for codes.
 
#11 ·
Time for another Que learning experience. There was another guy on her Rivera. His jeep would start up and shut right back off IIRC. It was his ECM we swapped ECM's and mine did the same with his ECM that his jeep would do and his ran great with my ECM.

Don't fret to much op Que and Layback will get you going I may even get a chance to chime in. Its almost always something easy and normally pretty cheap it just takes logical troubleshooting to get to it. This is just bad luck swapping the same engine in isn't always this bad. Eithier that or I got really lucky when I did mine. I had never swapped an engine before. Just get your Jeep back and follow the advice here and you will have it up and running in no time.
 
#12 ·
Thanks for the lessons!! Good to know that you're not always the only one with the problems!!! He threw the new ECM in yesterday and said it fired right up, but I'm still keeping my fingers crossed. He said he didn't get a chance to do anything else to it, or a chance to try it more than once etc etc, but I guess it's a good sign it turned right over. Now I just hope it continues to do that every time you want to start it and resolves all of the issues I was experiencing.

Siva - This was my first motor swap in a vehicle... I've done smaller things like waverunners, but not a vehicle. Kinda got down on my mechanical abilities...I like to tinker, but I'm not a mechanic by any means.

I really hope the ECM solves the issues...however, I stole the computer out of my Mother-In-Laws YJ about two months ago and tried it, but it didn't work. It turns out the remanned distributor that we put in that day too was incorrect so the Jeep would have never started anyways...I could type for pages about this and that; but bottom line I'm getting antsy to get her back home in MY garage where she belongs. I'll keep you guys updated; but I truly do appreciate all of your responses and help!!!!! :D
 
#13 ·
Thanks for the lessons!! Good to know that you're not always the only one with the problems!!! He threw the new ECM in yesterday and said it fired right up, but I'm still keeping my fingers crossed. He said he didn't get a chance to do anything else to it, or a chance to try it more than once etc etc, but I guess it's a good sign it turned right over. Now I just hope it continues to do that every time you want to start it and resolves all of the issues I was experiencing.

Siva - This was my first motor swap in a vehicle... I've done smaller things like waverunners, but not a vehicle. Kinda got down on my mechanical abilities...I like to tinker, but I'm not a mechanic by any means.

I really hope the ECM solves the issues...however, I stole the computer out of my Mother-In-Laws YJ about two months ago and tried it, but it didn't work. It turns out the remanned distributor that we put in that day too was incorrect so the Jeep would have never started anyways...I could type for pages about this and that; but bottom line I'm getting antsy to get her back home in MY garage where she belongs. I'll keep you guys updated; but I truly do appreciate all of your responses and help!!!!! :D
Glad to hear it is alive!! :thumbsup:
 
#14 ·
So here's the latest update...I spoke with, and made a visit to, the mechanic today. Unfortunately, he said it wasn't starting every time again. When I arrived he reached in, hit the key and it fired right up!! It reved up, idled great, sounded like you'd want a new motor to sound. He shut it off, we shot the breeze for about ten or fifteen minutes and he went over to start it again. Sure enough, wouldn't start. It doesn't do any loud backfires anymore, just a little bit of a rumble.

Here is where we are. He is going to tinker with it tomorrow for a little bit and he said if he figures it out he does and if not I think he's throwing the towel in. He said by the time he shuts down tomorrow I should have the Jeep, but may not be completely fixed. He said he's lost and doesn't know where to go really. (I've heard this guy doesn't give up on much from other's who have used him) Anyways, my hope is that he will have some epiphany tonight, and get it all figured out.

Quick question, I've seen my catalytic converter before as I put a clamp on muffler on it. My cat had been hollowed by the PO. I understand that noone is allowd to reccomend running the Jeep without one (I'm not asking for any of that, I use this forum too much to be banned!!) and I'm fine putting a new one on. But my question is can the cat being hollowed create a scenerio where there isn't enough back pressure? I never had a problem with the old motor starting, but was just wondering if something on the new motor may not be jiving with a hollowed cat?

I thought we had it figured out; looking forward to your responses, and thanks again!!!
 
#15 ·
So here's the latest update...I spoke with, and made a visit to, the mechanic today. Unfortunately, he said it wasn't starting every time again. When I arrived he reached in, hit the key and it fired right up!! It reved up, idled great, sounded like you'd want a new motor to sound. He shut it off, we shot the breeze for about ten or fifteen minutes and he went over to start it again. Sure enough, wouldn't start. It doesn't do any loud backfires anymore, just a little bit of a rumble.

Here is where we are. He is going to tinker with it tomorrow for a little bit and he said if he figures it out he does and if not I think he's throwing the towel in. He said by the time he shuts down tomorrow I should have the Jeep, but may not be completely fixed. He said he's lost and doesn't know where to go really. (I've heard this guy doesn't give up on much from other's who have used him) Anyways, my hope is that he will have some epiphany tonight, and get it all figured out.

Quick question, I've seen my catalytic converter before as I put a clamp on muffler on it. My cat had been hollowed by the PO. I understand that noone is allowd to reccomend running the Jeep without one (I'm not asking for any of that, I use this forum too much to be banned!!) and I'm fine putting a new one on. But my question is can the cat being hollowed create a scenerio where there isn't enough back pressure? I never had a problem with the old motor starting, but was just wondering if something on the new motor may not be jiving with a hollowed cat?

I thought we had it figured out; looking forward to your responses, and thanks again!!!
If the cat was absent it would make no difference at all. It is what the sensor send to the ECM that counts.

Just for the heck of it. Take a jumper cable and attach it to the - battery post. Take the other end and scrape it along the frame where the hood latch is. Does it spark a lot? If it does your grounds are not good. Re-check the battery cable ground AND the second ground that goes from the firewall to the engine block.
Next I would remove and clean and lubricate the bulk head connector(s) and the connector for the ECM.
 
#17 ·
Ok. You have a no start. It needs to be narrowed down to the system. If it is a no start then it has to be air, fuel, or spark. The mechanic might have run a bunch of test but if the issue was not present when he ran them then he will not be reading it. The fuel pressure, spark, timing, or air must be at fault. Spark, pressure, and timing are easy to test for any mechanic. Get back to the basics. The first thing I want you to try is a battery reset for a 10 count immediately when the issue occurs. Check for spark and measure the fuel pressure if it is not starting. Reconnect it and try to start. Please list all the components that have been replaced. One of the other tricks it's jumping power directly to pin 87 of the asd relay. If the relay is intermittent it will give you the symptoms you describe. I have a few more ideas but this will get you going.
 
#19 ·
laybackman - When I drove the Jeep home I attached the jumper cable to the negative battery terminal and rubbed it on several pieces of the frame/ metal etc. and couldn't see any sparks. It was bright daylight out, but couldn't see anything.

Que89 - When I went to get the Jeep this morning he cranked it over but no start. Without saying anything he walked to the front of the Jeep with the hood open and I saw him press something and all of a sudden my Jeep was purring like a kitten. He had a push button starter hooked up directly to the battery and the other end down to the starter. He said he had tried this before with my old computer but to no avail, but it will work with this "new used" computer. He said he had the Jeep sitting outside yesterday and it started right up for him several times. He said he brought it inside, let it sit for a while and it wouldn't start, but hit the push button and it takes off. So today I played with it a little bit and it will start probably 8 out of 10 times right off the bat; if it doesn't you can just hit the push button and it generally fires right up???? What would cause this? Also, my wife's uncle has my fuel pressure tester. I need to get that back from him so I can have it handy.
 
#22 ·
The starter relay is getting power then and it is a control side issue. Pins 85 & 86 are control. The issue is on 85/86. I can help you figure it out of you have a meter.
 
#23 ·
So when it doesn't start with the key, even though it turns over, you think it's just not sending some type of signal? Or am I way off here? You're speaking of just a volt meter? I'm not great with them, I usually let a buddy that is an electrician mess with that stuff, but I want/ need to learn more about how to use one and what exactly it's telling me. I've got a very busy work schedule the next two days, but I would love to hear more or study up on what I need to do.

I took the Jeep on a little trip today...did good, I did have to use the push button once though. Acted like it wanted to start, but seemed like it needed a little boost to push it on over the edge of starting. I waited a second and hit the push button and it fired right up.

Is there a meter that I should buy? Sometimes I think all of the choices on some of them are intimidating. May sound crazy, but using the volt meter just isn't something I've got a lot of practice with, so if you guys are willing to tell me what to do I'm more than happy to learn!!! Again, thanks for all of the patience and help, it is appreciated!!! :D
 
#25 ·
Layback is saying what I was thinking about the starter not turning over. The jumper wire the guy installed was for the starter not turning over at all correct? Are you still have the issue with no start even when the starter is working? As far as a meter goes a cheap $20.00 one from Harbor Freight or Radio Shack will work.
 
#26 ·
Layback is saying what I was thinking about tghe starter not turning over. The jumper wire the guy installed was for the starter not turning over at all correct? Are you still have the issue with no start even when the starter is working? As far as a meter goes a cheap $20.00 one from Harbor Freight or Radio Shack will work.
That meter is a very important tool trust me.

Open up (and save) the attached pdf file I posted a link to.

I would open up my PDC and pull the starter relay.

See the brown 14 AWG wire that goes from the starter relay to the starter in that pdf file? That goes from one pin of the starter relay socket to the starter. The other side of the relay is controlled by the ignition switch. When turned to START that circuit closes the relay contacts and allows the voltage to go from the 12 AWG red wire going into the starter relay to that brown wire which fires the starter.

Keep in mind that a relay is a cheap alternative to a high amperage switch.

I would set my multi meter to continuity and then I would touch it to the brown wire at the starter and then probe each socket of the starter relay. One of them should show continuity. If you find that socket remember it.

Now get someone else to move the harness around in that area to include the whole PDC box. If you lose continuity at any time you have a broken/loose wire or a bad splice.

IIRC there is a fuse that protects that circuit also. Maybe it has corroded sockets and poor contact. Or swap out the starter relay with the horn relay. IF it doesn't give you any more trouble the relay was the problem. If the horn only works sometimes that is confirmation the relay was junk.

Corrosion is a hidden nightmare that is often ignored/forgotten.
 
#27 ·
Que - The starter will engage every time you turn the key (knock on wood) it's not that you turn the key and nothing happens. It's more of you turn the key and Jeep almost seems flooded?? It wants to start with the key, it's just something is holding it back. When you do go to release the key from the 'start' position to the 'on' position it's sounds like it was almost started but doesn't get all the way over the start gate. (Make any sense??? Sorry if I'm having trouble putting this into writtenm words rather than voicing sounds) If it does that, and you may try another time, and it doesn't start with the key again, so far, you just hit the push button ignition and the Jeep starts. I've had one time where when it did start with the push button it almost seemed as if it were running too rich; but all other times it has ran great and smooth. So even when the Jeep doesn't start by turning the key everything is still trying, I guess...

laybackman - Thank you very much for the file... I've viewed it, but haven't had a chance to really study it yet due to work. I haven't had a chance to check out all of my wiring yet either. On my starter you have the two main posts which one of them is hooked up to the + battery terminal. The other main post doesn't have anything hooked to it, but there is the smaller gauge wire that is basically linked to, what resembles, a relay. What is that??

I very much appreciate all of your help and apologize that you've recommended action items that I've not had a chance to complete yet, but plan on it unless you guys tell me otherwise when I get a spare second.

Also, I don't have an entire list of parts that have been replaced, I haven't received my final invoice from the mechanic who had it, but he did put a new ignition in it. I know he struggled actually getting my ignition as mine what a white plastic but everything that came in or the stores had was a black plastic, but wouldn't work on mine?? Sound right?
 
#28 ·
OK, So the starter always engages the flywheel and turn this engine over, BUT the engine doesn't always fire and run. Is that correct?

And when it doesn't turn over and run, it can often be started using a remote starter. Correct?

Last but not least BUT.....it doesn't always fire up using either method.... correct again?

If that is the case the problem doesn't seem to be in the starter portion of the ignition circuit because it always turns over...even if it does not start.

One question lingers. How come when it does not start with the key it will sometimes start with the remote starter????
 
#29 ·
laybackman:

The only part of your statement that I would probably add to is this: I've only had one instance where I've had to hit the push button more than once. When this did happen the motor almost seemed to be flooded, or run rich etc. It just seemed a little bogged down, but it ran. (Please keep in mind; I've probably only started it 15-20 times or so since I got it back)

You hit the million dollar question on the head. Question...Will utilizing this push button mess anything up?
 
#30 ·
No it is just bypassing the problem somehow if it always turns over but doesn't always fire up.

I wonder if the issue is the injectors not firing. Maybe the problem is somehow related to the ASD relay? But I do not know how the remote starter is effective to fire this engine up when the ignition won't do the trick? The remote starter needs the ASD relay to do it's job or it won't start no matter what.
I'm tired......going to hit the sack.
 
#31 ·
So the relay jumper is to the starter relay in the PDC and you are pushing it and it is turning the starter correct?
 
#32 ·
Sorry for the delayed response...Work keeps getting in the way :D

laybackman: I've contemplated the fuel injectors too. The injectors have been noided, ohmed, and leak tested and seem to pass. The only thing that can/ hasn't been seen is when are they firing and how well are they spraying?! But I wonder how/ could pressing the button affect this?

Que89YJ: The push button is two wires...one wire is hooked from one prong of the push button to the + terminal of the battery, the second wire is ran from the second prong of the push button igntion to the starter; directly hooked up to the same location that the 'relay' looking device is hooked up to. I haven nothing ran to any fuse box, computer etc. It really is a barbaric setup; you just turn the key on and press the button and it starts???!!!! But, yes it turns the starter when I press the button, but it isn't hooked to any type of relay.
 
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