88 MJ w/ 94 block and head won't rev over 1200 rpm.

Hello,
I have an 88 MJ 4.0, auto, 4x4 with a 94 block, head, and intake on it. But its still running the factory renix system. The previous owner swapped in the motor because the old one toasted the rings. He never finished it, or had it running. I fixed a bunch of little things to get it to run. New distributor, plugs, wires, cap and rotor, fuel pump, water pump, radiator (eliminated the closed cooling system) Removed the c101 devil connector, and some other little things that I'm forgetting. Also rebuilt the head because it had blown a head gasket moving it the 50 feet into my garage, and put a cam and lifters and a new timing chain and rod bearings in it while I was at it.

So when you start it, it will start right up. runs decent. it you crack the throttle open it will misfire like crazy and die. I checked the map sensor, ignition module and coil on a friends XJ with the same set up (90 XJ with 94 block and head, same cam) they work perfectly well. His knock sensor isn't hooked up either, yet runs great.

Any ideas as to what it can be? I refreshed the grounds to help eliminate that and removed the c101 as these are the 2 biggest problems with the renix system. My only thought is to try swapping ECUs around to see if thats the problem.

sounds like the distributor is off one tooth.

checked and rechecked. Did this before the head and cam swap, still does it after.

possible bad cps?

if its too far away from flex plate, the signal is weak.

Is the engine dropping a cylinder(s) before it dies when you crack the throttle or does it backfire through the intake or exhaust then die?

civic50 said:

Is the engine dropping a cylinder(s) before it dies when you crack the throttle or does it backfire through the intake or exhaust then die?

Click to expand...

Yes. With the timing light on the #1 cylinder at idle it sits at 10 degrees and is consistent. When you crack the throttle it starts skipping around and not firing every time like it should.
It back fires out the intake. Ill try and take a video of it today.

oh!

pull your distributor cap and rotor, see if the shaft of the distributor has play in it.

Also while you have the cap and rotor off look at the pick-up coil and make sure the metal pointer that is on the inside of the pole piece (also called a signal generator) and make sure it hasn't separated from the pick-up coil. Even a little separation will cause all sorts of problems. The metal piece kinda looks like a house that points to the inside face of the pole piece. I had this issue with my 87 XJ.

I reset the timing and inspected it. All that looked fine. Pull the crankshaft position sensor off to see if it had build up on it, turns out it had been spliced back together at some point. i cut the heat shrink off (big surprise the PO even used that) and one of the wires was barely hanging on by a few strands and a small dot of solder. Put a new crank sensor on it, and it runs so much better, and revs now. Still has a slight misfire to it, but you could drive it now.

Going to put a door on it tomorrow, wash it and take it for a drive to uncover other problems.
Thanks again for the ideas.

Yay