1990 4.0l Engine swap help! - Pirate4x4.Com : 4x4 and Off-Road Forum
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Old 02-25-2009, 03:55 PM   #1 (permalink)
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1990 4.0l Engine swap help!

I bought a 1990 YJ a few weeks ago and need a little help getting it running. I believe motor came out of a 90 xj

The jeep had a 4.0l engine in it when i bought it, the guy i got it from got it from another guy so there isn't any way to get a hold of the original person that did the swap. First problem found was that the bulkhead firewall connection for the wiring harness from the engine was plugged into the YJ firewall and wires did not match up correctly. As of now i have two power sources from the engine harness plugged into the firewall for power inside the cab. I have a yellow wire that powers the PDC ,(4 relays under hood) and various other things like coil and such, that wire is switched on with the ingnition switch. And the only other wire running between the engine wiring harness and YJ firwall is the signal wire for the starter relay. After a day of tracing wires to figure this out i went to a junk yard and pulled a new harness that wasn't hacked up and also got everything hooked to the harness that i thought i would need. ECU, sensors, some metal box that the wires ran through the firewall and was mounted under the glove box? I can't find any good diagrams and the local dealer didn't want to give me the time of the day. I did not pull the distributor or coil from the junk yard XJ.

So after installing new harness i realized that there was no Crank postion sensor installed, but there was a spot in the bell housing for it. I have since installed sensor. Next problem was that the guy tried using a cheap fuel pump mounted under the hood to supply fuel to fuel rail. Well after i took the clamp of the pump i could see the sticker said it was rated for 9 psi. Found a stock YJ tank for a 4.0l an have installed and wire directly to battery with switch temporarily.

Sorry for the long info. just wanted to give all the background info.

So my problem is that when i try to start the engine it turns over several revolutions before starting, each time it sounds more and more like it is going to start till it finally hits a lick. The next and more major problem is the fact that it dies after about 2 seconds. I know your thinking it is a security thing but before you say that, it is a 1990 model engine. Did they have any security devices on jeep that model year? The only thing i have read is on the obd ll engines that have the security feture. The other reason i'm not so sure that is the issue is because i had 2 ecu's that came with the jeep and the one from the junk yard, they all give me the same result.

So is did xj's come equipped with a security device on that year or do i have another problem. I know of about 2 more jeeps in the yard with the same computers but i don't want to spend anymore money on a computer since i have three of them.

Again sorry for the long post, but any info you can give me would be much appreciated!

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Old 02-25-2009, 04:19 PM   #2 (permalink)
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Check your ASD relay, may be getting hot and opening the circuit.
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Old 02-25-2009, 04:20 PM   #3 (permalink)
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do you have a fuel pressure gauge hooked up while trying to start it? sounds like it's running out of fuel.

Last edited by Nukegm426; 02-25-2009 at 04:20 PM.
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Old 02-25-2009, 04:34 PM   #4 (permalink)
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I'm not sure which relay the ASD one is, I don't have any good documentation on the wiring! I have 4 relays all hooked together out in the open, not like the newer ones that were consealed inside a plastic housing along with fuses. I can take the old harness and trace each relay to the end or might try putting a meter on each one and seeing what happens each time.

As far as a fuel pressure gauge goes, that would be a negative. I tried picking one up at the local part store but they were out, just like every other part i have need for this thing. Not a very well run store. I was kinda thinking that might cause it but it seems to run the same amount everytime it starts.

I will try both of them though, thanks and anymore suggestions will be great.
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Old 02-25-2009, 09:28 PM   #5 (permalink)
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Some years of XJ's had an ignition bypass for the fuel pump, it gets full battery voltage when cranking and then goes to a resistor circuit for the pump that runs about 9 volts. If they did not hook up the resistor then you might have power to the pump when cranking but not when running. Also check the signal from the CPS, use an AC volt meter, unhook the cps and read the two wires with the volt meter, it should read .250-.400 volts AC while cranking.
Confidence is that feeling you have right before you fully understand the situation.
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