I recently replaced blown 4.0 motor in a 97 Cherokee 4wd Automatic. Piston Exploaded. Found another motor and retrofitted it in. Started up well but was missing badly while idling and stalling after warming up. Tried to figure it out and finally gave up. Drove it to the local dealer. OBX Chrysler. Over Christmas, they looked at it and said there was low compression on a few cylinders. I could not get it to start anymore at this point. Something they did in their diagnosis, dont know. Had to tow it home.

I took off the head and found that several of the valves were not perfectly sealed. Cleaned up head, replaced 3 valves that were warped and lapped it so it passed the water test. No leaks even without springs. Excited to put it back on and fire it up.

Been a couple of weeks now, me and 3 technicians have not been able to make the car start.....

The Engine Turns over well and seems like it is trying to start. Verified the following multiple time:

1) Ignition Spark. Maybe not strong enough. Replaced Coil, Plug Wires, Rotor and Cap, and Plugs. No change. Still have spark, but not as hot as one tech thought it should be.

2) Fuel. Plenty of fuel coming from the rail. Maybe too much. We did find that the new TPS was not reading right on the computer. Put the old one back in and computer verified it was working correctly. Plugs are getting wet. Dried plugs and blew out cylinders several times. Checked injectors for leaks. No leaks. Output is more of a squirt than a spray. Not sure what to look for.

3) Compression. All cylinders are 125 - 150 on compression.

4) Timing is not adjustable on this model. Computer apparently suppose to advance and retard it based on sensor input and emmissions guidelines. Verified that cylinder 1 at TDC matched the distributor rotor at #1 Plug wire.

5) Tried Starting Fluid. No luck.

- Replaced a broken oil pressure sensor
- Found a sensor at the back driver side of the top of the head that there is no wire hookup, plug...
- Tried to start with no fuel pump, by relieving rail pressure and removing pump fuse. Tried to start with Starting Fluid alone. No Luck.
- Tried unplugging O2 Sensor
- Catalytic converter rattles like it has broken ceramic
- New Oil and Filter
- Checked all fuses for continuity
- Noticed that the ignition will not engage starter in Park. Have to shift to Neutral to turn the engine.

Anyone with any ideas on this. PLEASE HELPPPPPPP. Getting really frustrated now after 6 months of work on this Cherokee.....

 

You're not getting spark, or at least you're not getting spark at the proper time. If you used the flex plate from the replacement engine it may be the wrong one for your year. You may have left the ground off of the rear of the cylinder head. You may have damaged the crank sensor while installing the engine. You may have the distributor indexed wrong. My money is on the crank sensor.

 

Drove it in and towed it out. Thats bs id be right back up there *****in.

 

Yeah the Dealer and his Service Manager, I should have taken a little community feedback before going there...... So bad I am afraid to take it back less they do more damage.

Other Comments:

I am getting Spark. Last Tech who helped me yesterday said he thought it was weak though. He brought a spark tester and kept widening the gap to see the amount of current. Wouldnt fire on ether as well.

1) Flex Plate? How would a mismatch flexplate effect spark timing? I am not too knowledgeable about the functions of the flexplate. But all parts and accessories had to be taken off the blown engine to make the replacement engine work. It was running before I asked the dealer to do diagnostics.....just cant figure out what they could have done to it?

2) Bad Ground or no Ground to the Head. Could be. I will look at the wires again and do some continuity tests.

3) Distributor... With #1 cylinder at TDC the rotor is pointing at spark wire #1. What other timing is there on this non adjustable model? COmputer uses sensors to advance and retard timing electronically.. Diagnostics computer did not detect anything other than the TPS which I replaced.

4) Crankshaft Position Sensor... I will look it up and test it. Last technician who helped me said that the RPM gauge would not be working if this was faulty, and it is working. Could there be more to it than that?

Thanks for your input. I will check a few things and get back to you on the news group.

 

I'll hazard a guess the HO flex plates interchange. 91-99 at least. (but NOT with the 86-90). There may well be a resistance test for that CPS that might verify it's bad, but testing good doesn't mean it is. I'd consider changing it, especially if it was left attached to the housing during the swap. Like said, they get mucked up easily. (I carry a spare because mine will fail on a Friday afternoon)

You guys do know the books and diagrams are wrong, #1 is at 5:00 as viewed from the side? Also if you post up the codes, there are some guys here who are pretty sharp, that might help.

 

OK so after letting it rest while I went to the movies, I came back and unplugged several of the manifold sensors and tried to start it.

1) It continued to crank fast and try to start, then I let off the key and it kept going for the first time. Valve cover was off and the 02 sensor was out of the forward manifold.

2) Stopped the car and put sensors back in place and was able to restart, but with difficulty. Same thing, cranked fast and then started after I released the key. Kind of weird.

3) Alot of backfiring when giving it gas. Put Valve Cover back on and it sounds really good at idle. Alot of sputtering when increasing the throttle. Currently still warming up at idle.

Any of you guys think that this may give some more clues about whats been going on with this engine.?

Thanks so much for responding.....

 

Gads...The coil/ICU is getting low voltage, and when you let the key off start, the voltage shot up,and it sparked and started right there. . I don't know...I did have an old engine with points that did that sometimes though. Wouldn't spark well while running the starter.

 

Was reading a thread about testing the CPS. Risistance is suppose to be infinite between pins B and C........ I get 6.xx M Ohms ??

 

Busy with company...I have the fsm somewhere...

 

Are your wires in the wrong order? If you have spark it should at least start with starting fluid..

 

Note from DJ
Take your VOM meter set on DC voltage scale at the 20 Volts setting and measure your voltage at the battery with no load; post the voltage reading.

Next place your VOM meter set on DC voltage scale at the 20 Volts setting where you can see the screen or have a helper try starting your Jeep; post the voltage reading observer while cranking the engine.

 

I spent over 1/2 hr looking through what I have..got about skunked. I did find terminal 1 should be "open" (no circuit) to terminal 2. #1 might have black/light blue, #2 might have Grey/Black. If those color codes match and there is any circuit, that might mean it's faulty. Idk really.

Also it's ground, presumably harness side, should be good. (5 ohms was mentioned), doesn't sound "good" to me, likewise the wire supplying power from the PCM, maybe orange, should NOT be grounding, (it might have actuality said, "have less than 5 ohms"(to ground) Please nobody quote that...I find those numbers hard to believe at all. Then again...maybe the power wire from the pcm does have some contunity to ground while it's off, Idk

OH! Funny, they mention the "jiggle test". "jiggle the wires while it's running, and if it F-s up, repair the fault" it says.

 

Got it. Doing so much starting that I have battery charger hooked up constantly. I do have a load tester and can test the starting voltage drop this morning. Just got up. New CKP is about $30 so I will put in a new one. Catalytic converter is rattling badly, maybe broken ceramic.... Thanks again for feedback.

 

So, I gave in and took it to a shop. Thank God for talented mechanics! Outer Banks Mobile Engine Repair 252-564-4877 . Within about 2 hours they found that the distributor had been installed incorrectly and was off by one tooth.....

This caused the hard start, weak spark, flooding injectors, etc. etc. Since the car started fine before I took it to Outer Banks Chrysler.... it can be narrowed down to their Service Department removing the Distributor and putting it back incorrectly. Drove it there, had to tow it away.....

Thank you all for your help. Hope this information helps someone else down the line!