Need Help, barely runs and not drivable.

[signal20gsxr]

Hey Everyone. I trying to help a friend out that just bought a 94 Cherokee with a 4.0L. The thing is kind of a Frankenstein. The person she bought it from said that all it needed was a new temp sensor and crankshaft position sensor. Long story short after replacing those it still is barely running.

It's a 94 with a 89 engine. The transmission is out of a 96 (automatic). The crankshaft position sensor we got from the Jeep dealer.

Here is what it's doing. It starts up and the idle speed is very low (500RPM's) then on its own it will go up to 3000 RPM's and stay there for a 10-20 seconds and then drop down to 500 or lower and stay there for another 10-20 seconds and then back up to 3000. If you foot break it you can keep it running and drive it a short distance but it will die on you at times.

Things I have done. Compression test. All cylinders are between 125-135psi. Distributor cap and rotor, spark plugs and wires. Checked fuel pressure. It has 40 PSI with the vacuum line off. Check the codes. Only getting a code for the MAP sensor which we replace with and OEM one. But its still sending a code for the MAP sensor which I think might be due to such low vacuum. It only has 5inHg when its idling at 500 rpm's.

I've unplugged the IAC and it makes no difference with the RPM's going up and down????? I bought a new one, left the old one installed but plugged the new one in and the pentil does not move at all. The new IAC the pentile is in the retracted position. The original one its in the extended position. The o-ring that seals it I replaced. I've checked to make sure the throttle body is closed. Replaced the TPS. Checked for vacuum leaks. All the vacuum lines are good and hooked up. Brakes work good so its not the brake booster. Checked the injector o-rings. 4 of the 6 fuel injectors have been replaced (previous owner) I checked for power to the IAC. Two of the pins are getting battery voltage which seems to be correct??

The exhaust manifold is cracked. So I will be replacing that so the intake manifold gasket will be new.

What I did notice is that the main ground strap from the back head bolt to the firewall was missing. I made one and ran it right to the - battery post. The other thing I noticed is that one of the wires from the distributor (Black with Blue tracer) has been spliced onto and then goes to the boss on the passenger side of the block where there are a couple of tan or yellow wires bolted to. I traced the black/blue wire on a wiring schematic and it seems that is a ground for a lot of the engine sensors and goes back to the ECU. I have not tried this yet but I am thinking that if I disconnect the splice off of that wire (black w/blue tracer) it probably wont run.

As of right now I am pretty stumped as to why the RPM's will vary so much. If it was a vacuum leak I think the RPM's would be consistently high or low. If the IAC is not working how is the computer allowing the RPM's to change so much?

I did take the ECU out and take a look at it. That gel that its sealed in is cracked in a few places but looks really bad in one particular area. I am thinking this might be the driver for the IAC??

I don't want to keep throwing parts at it. I do feel that the ECU is suspect at this point. :bang:

If anyone can point me in the right direction or offer some test that I can do to figure out exactly what is wrong with this thing would be greatly appreciated!

[bluedragon436]

If the engine is out of a 89, is the IM from the 89 or transplanted over from the original engine?? Is the distributor the 89 or transplanted over?? Also do you know if they swapped the flex plate from the original engine over when they did the transplant?? I would see if you can find those items out the first two you can look at and tell, the other one not sure how you'd be able to tell by looking at it, I just remember reading when I did a 91HO engine into a Renix 90 XJ (the one I now own)... that you and to swap those items over as they were all different between the Renix an the HO ECU setups...

[xj4life2]

Well lets start with the obvious, what year is the engine? what year is the computer? do we have a miss match here ? signal received by the computer may not be right. You may have a vac leak , many times a vac leak will cause a high low condition. Spray around with carb cleaner if the RPMs go up you have a leak in that area. I would take the IAC out and clean it for sure.

Good point brought up by Blue , if that's a renix engine with a non renix computer it will never work right ECM, Dist and sensors are all wrong.

[4.3LXJ]

I agree with the engine mismatch thing. Since you have a Frankenjeep situation, I would recommend checking some part numbers such as the throttle position sensor, temp sensor etc. Good point on the distributor. Also the ground should be good from the engine to the body so if it doesn't have one, better address that. The ECM needs good grounds to function right.

[signal20gsxr]

If the engine is out of a 89, is the IM from the 89 or transplanted over from the original engine?? Is the distributor the 89 or transplanted over?? Also do you know if they swapped the flex plate from the original engine over when they did the transplant?? I would see if you can find those items out the first two you can look at and tell, the other one not sure how you'd be able to tell by looking at it, I just remember reading when I did a 91HO engine into a Renix 90 XJ (the one I now own)... that you and to swap those items over as they were all different between the Renix an the HO ECU setups...

IM? The distributor is out of an 96. At least that is what the person she bought it from said. He did mention that it didn't seem to fit properly. It has a 3 wire connector. The wiring harness end is also a 3 wire connector. But from looking at pics for a dizzy for a 94 it shows it being an 2 wire connector.. ??? I will need to look and see if the connector for the dizzy has been spliced into the existing harness.

The numbers on the computer comes up as being for a 94 when I was looking at a replacement one.

I do not know what year the flex plate is. When I was at the dealership picking up the crank position sensor I asked them what it got it signal from. He went and got someone from the service department and they said that it got it off it off of the ring gear on the flex plate. We actually got the wrong CPS the first time. It wouldn't even bolt up. We needed the VIN to get the correct one which did bolt up to the 96 transmission bell housing.

So the engine is an 89. Intake manifold, TB, fuel rails, ECU seem to be the original 94 components. Dizzy, transmission and exhaust are 96. The engine harness does seem to be correct for a 94. The self test connector is under the hood and is not an OBDII connector.

The Jeep is an hour and half away from me. I will be working on it on Friday. So I will be able to look at these things then.

Thanks for reply!!

[signal20gsxr]

Well lets start with the obvious, what year is the engine? what year is the computer? do we have a miss match here ? signal received by the computer may not be right. You may have a vac leak , many times a vac leak will cause a high low condition. Spray around with carb cleaner if the RPMs go up you have a leak in that area. I would take the IAC out and clean it for sure.

Good point brought up by Blue , if that's a renix engine with a non renix computer it will never work right ECM, Dist and sensors are all wrong.

Renix = Non H.0 and Non Renix = H.O. (High output)? HO motors were not produced in 89?

The long block is from an 89. Computer is a 94.

I've checked for vacuum leaks. Couldn't find any. I wasn't going to spay carb or brake cleaner were the Intake bolts to the head. Since the exhaust manifold is right there. I will be changing the exhaust manifold since it is cracked.

I've have worked as a Ford Mechanic for many years. Never worked on Jeeps before. So I am shooting in the dark

I've had other Frankenstein's before that I have had to work on but it was either a Ford or Chevy and could usually figure out what to do..

Thanks again for the replies.

Just throwing this out there. If the motor is not compatible with the computer. What are my options? She spent everything she saved up to get this thing. Guy said that all it needed was a crank shaft position sensor and a coolant temp sensor. Obviously he handed off his problem off to her.

The valve cover gasket is nothing but orange RTV. I cringe every time I see something like that. It tells me a lot about the person working on it.

[Cheromaniac]

Hey Everyone. I trying to help a friend out that just bought a 94 Cherokee with a 4.0L. It's a 94 with a 89 engine. The transmission is out of a 96 (automatic).

It starts up and the idle speed is very low (500RPM's) then on its own it will go up to 3000 RPM's and stay there for a 10-20 seconds and then drop down to 500 or lower and stay there for another 10-20 seconds and then back up to 3000. If you foot break it you can keep it running and drive it a short distance but it will die on you at times.

Only getting a code for the MAP sensor which we replace with and OEM one. But its still sending a code for the MAP sensor which I think might be due to such low vacuum. It only has 5inHg when its idling at 500 rpm's.

Checked for vacuum leaks. All the vacuum lines are good and hooked up. As of right now I am pretty stumped as to why the RPM's will vary so much.

If anyone can point me in the right direction or offer some test that I can do to figure out exactly what is wrong with this thing would be greatly appreciated!

The fact that you're still getting a code for the MAP sensor despite having a new one means that the old one is probably OK and the sensor is reading an abnormally low vacuum.
You said that it's only 5 inHg when idling at 500rpm so you definitely have a leak. The one place you haven't checked is the composite gasket between the manifolds and the head. Try spraying water there and see if the rpm changes.
You might also want to check the vacuum line from the intake manifold to the MAP sensor and make sure it isn't cracked or perished.

[signal20gsxr]

Well I worked on it yesterday. I think I have it narrowed down. The intake manifold does not line up with the head at all. The ports in the intake line up at the top but not at the bottom. :( The head on the motor has ports are just over 2 inches tall. The ports on the intake are just over 1.5 inches tall. The intake is an 94 (confirmed casting numbers). I read that the HO head had a higher intake port but it looks like the floor of the port is raised and not the top.

I was wrong about the dizzy. 94 and 96 for the XJ are the same part number.

I can't leave it apart at the apartment complex and not in a condition where it can't be moved if need be. So I put it back together with the new exhaust manifold and gasket (for a 94). It did run better with a HO intake/exhaust gasket vs the Non HO intake gasket (which was on there). Vacuum was up to 15 at idle but the RPM's were still going up and down. I think the intake is still leaking but not as bad. I did not get a MAP sensor code this time either.

The picture in the second post in this thread is exactly what the intake looked like when I pulled it off. http://www.jeepsunlimited.com/forums/showthread.php?450854-Renix-intake-on-a-HO-Head-amp-Swapping-4-0HO-into-non-HO-XJ

Can I use a 88 intake manifold if I get/ make and adapter for the TB? If not I guess I will have to change the head? Any other suggestions?? I know I could swap the head later on but I would like to avoid that at this time if possible.

The black/lt blue wire ( that is spliced onto from the dizzy and then bolts onto the ground on the rear passenger side of the block along with two black/tan wires) I disconnected and it died instantly. I repeated this a couple of time just to confirm. This wire (according to the wiring diagram I have) goes from pin 4 on the ECU connector to the TPS, CPS, CTS MAP, Dizzy, speed sensor and O2 sensor. I am not seeing anywhere that it grounds to anything. So is it reasonable to assume that ECU is fried?

Where is the casting number for the head located? I looked but was not able to find it.

Thanks!

[4.3LXJ]

On that intake, I would not want to leave it like that. If it was me I would adapt the throttle body over to the right intake, but I have what is needed to make that happen. And that BK/LT BL wire does indeed to go to pin #4. But my diagram shows TCU, Dizzy and even more stuff. It appears to be a common ground for the ECU for 5 volts to several components

[signal20gsxr]

On that intake, I would not want to leave it like that. If it was me I would adapt the throttle body over to the right intake, but I have what is needed to make that happen. And that BK/LT BL wire does indeed to go to pin #4. But my diagram shows TCU, Dizzy and even more stuff. It appears to be a common ground for the ECU for 5 volts to several components

Thanks for the reply.

Does that wire ground anywhere externally? I'm not seeing that it does. I think it grounds in the ECU someplace. Which its not doing.

No I don't want to leave that intake on there. You have an adapter? Will the fuel rail and power steering bracket pump bolt up to an 89 intake?

Thanks.

[4.3LXJ]

Hmm, not sure on the power steering. I would have to look at the two engines side by side for that. I know there is a difference when it breaks at 00. My wiring diagram says all those wires go to terminal 4, not the body.

[signal20gsxr]

Thanks for confirming the wire. That is what my diagram shows also.

I found a pictures of the non HO and 94 HO intakes. It does not looking the power steering will fit. Also the mounts for the throttle cable bracket and fuel rails are different. :(

[4.3LXJ]

There will be some adapting to do for sure. Check on the power steering pump and bracket. I think you will be able to do some swapping there. And yes, you will have change the throttle body. Aluminum is easy to drill and thread. I sold a motor to a guy that will be doing that shortly.

[signal20gsxr]

Thanks for the reply.

4.3LXJ do you have an Renix intake? PM me if you do and how much you want for it.

I thought about it some and I am not really sure what is going to be the best thing to do. Is an HO head a direct bolt on to that block?

Yes drilling and taping the intake for the TB will not be an issue. However fabricating a throttle cable bracket (it's an automatic and has cruise control) and bolted up might be an issue. What about the fuel rails? Are the factory hard lines up to the flex lines compatible? And the power steering pump- I will have to find brackets for it but will I also need to change the pump as well?

Time wise if just swapping out the HO head (provided the pushrods, rocker arms, etc are compatible) is going to be the easiest and best way to fix it I'm thinking.. I work 6 days a week and I really do not have a lot of time to be searching the u-pull-it yards to find everything I need.

I really wish I still had my TIG welder. I would just weld up the bottom portion of each of the intake ports, get the mounting surface milled flat and that should do it.

I do know that the camshafts are different but with the correct head it should run better because of the head flow and ports matching up. Or is this not really an issue?

Thanks.

[4.3LXJ]

I don't have one, but I have a friend on this forum that I sold a 98 motor to that will be pulling his renix motor out and putting a 98 motor in. You can ask him. Also there will be said bracket on that intake he will not use. PM Blackstar8507 and ask him about it

[signal20gsxr]

Just wanted to give everyone an update.

So we got a used ECU off of ebay for a little over a $100. I removed the old ECU and double checked all of the grounds for it. Also check continuity on the black/blue wire at the ECU connector to the sensors and dizzy. I replace the heavy ground strap that was missing that goes from the cylinder head bolt to the firewall. Removed the splice on the splice off of the black/blue wire. Put the new computer in and it fired right up and idled great! Let it warm up and took it for a short drive. It ran great but the check engine light came on.

Check the codes and it was the O2 sensor reading lean. I sprayed water around the intake. It does not appear to be leaking currently. Took if for another drive and no check engine light on the second drive.

I don't think it had been running properly since the motor was changed out. When the intake was bolted up the gasket was not changed out. You could see were the gasket was compressed from the original intake.

It idles right about 750-800 RPM's. I think its good for now. If the intake does start to leak again I thought about getting two gaskets (one for an 89 and another for an 94) and a piece of sheet metal. I would use the 94 exhaust/intake gasket as a template for the ports and put that between the two gaskets.

Eventually we might change the cylinder head out for a HO one. Maybe this time next year. But as long as it not throwing a code and running good I think we are going to leave it alone for the time being.

Thanks for all of the replies to help me get this figured out!:)

[Rocco83]

Grants man, glad you have it running right!

[4.3LXJ]

Congrats man

[signal20gsxr]

Thanks everyone! She has been driving it everyday since Friday. Check engine light is staying off! :)