94 4.0 not running great, what to do?

Scott86MJ

Scott86MJ

Well-Known Member
Joined
May 3, 2006
Location
Dallas
My Comanche has the engine and harness etc from an XJ. The engine swap was done 20 years ago and just set for most of that time. The engine smokes a little especially at startup and while setting idling. I have checked most sensors and gave it a tune up after I got it running again about a year ago. It has a fuel cell with an Xj fuel pump and new fuel injectors and fuel pressure regulator, while I was at the G2G at uwharrie I had what I believe was heat soak issues so before I took it to the Jeep Jam obstacle course I put heat shield around fuel lines (AN lines from fuel cell) put hood spacers and ran the electric fan the whole time I was on the course. It didn’t cut off but over some of the obstacles it would sound like it would have a little backfire sometimes under load. The engine has 150xxx miles and I’m sure it could use a rebuild but I’m wondering if I have some other issue I could fix before stroking it 😎 Anyone have any suggestions
 
If you know someone with a snap on Brick it would tell you exactly what your sensors are reading. I have one and use it on my 94 when it has issues. I think I have had to hook it up twice in 18 years of wheeling my 94. I've never had heat soak ever. Even when my temps where getting really high. I ended up putting z car vents in the hood. I would question your fuel return not working right if your fuel is heat soaking. Just my thoughts.
 
sounds like to much fuel. ECU, harness and engine from same doner? stock injectors? any codes? exhaust leaks?
 
Jeff B said:
sounds like to much fuel. ECU, harness and engine from same doner? stock injectors? any codes? exhaust leaks?
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Yes, all from same xj. I have aftermarket injectors I believe from rock auto and no codes or the CEL is not working. I have a OBD1 scanner I'm going to check it again this weekend. I do not believe I have an exhaust leak the manifold and pipe is new.
 
Whats the injector size?
 
Jeff B said:
Whats the injector size?
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They are supposed to be the stock re-manufactured, carquest a211-1071. I was able to work on it briefly this past weekend but i didnt try to test for any codes. When i drive it it will bog down at about half throttle and will not build up speed or RPMs. If i give it too much gas it will back fire but not too loud. I do not have a fuel pressure gauge but I think I need to check the fuel pressure and maybe pull the spark plugs and give them a look, any thoughts on my next steps?
 
I would test he TPS, remove it and use an OHM meter. three pins, go across 2 and rotate it, you should have a clean sweep of resistance up and down. if it jumps it's shot. You will have to figure out which 2 pins. will be power and signal
 
Jeff B said:
I would test he TPS, remove it and use an OHM meter. three pins, go across 2 and rotate it, you should have a clean sweep of resistance up and down. if it jumps it's shot. You will have to figure out which 2 pins. will be power and signal
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I tested the TPS today and it is working. I checked for codes with my OBD1 tester and I didn't get any codes. I bought a fuel pressure tester and found that I have 28 PSI at idle and if I remove the vacuum line from the fuel pressure regulator I have 38 PSI. It will not hold pressure when I cut the key off. I believe this would mean that the fuel pump has enough pressure but is not holding pressure properly. Any more thoughts?
 
Here’s a video
 

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That's not to far off. What I read is 31 at idle and 39 when the vacuum is removed.

I would perform a leak down test.

Also check timing, I had a harmonic balancer slip on the rubber and throw the timing off. Would not run for shit. When I put it on top dead center the balancer was off nearly 5*
 
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