XJ Running Bad - Hard Starting & More

Okay, this is going to be a long post that may be hard to read through, if you have any questions let me know, I’m going to outline out what problems I was having at what point during the repair attempt process.

Pertinent information:
1989 XJ – 4.0 – AW4 – 230,000

The original problem had to do with a no start situation, ended up being a bad constant 12V wire to the computer. Here is what I did to try to fix it before I pulled the head out of my ass and diagnosed it right.

Replaced the CPS with a new OEM unit.
Replaced the coil with new Borg Warner from Pep Boys.
Put in borrowed, known good distributor from another ‘89.

On the road to Moab and in Moab I was getting approximately 8 mpg, if I ran the Jeep for awhile at relatively high RPM (3000 – 4500) and let the throttle down it would stall in most cases. Under hard acceleration I would spew black smoke. My exhaust would gas you in five minutes. To try to take care of that I did the following at the campground.

Repaired O2, Knock, and CTS wiring, mine was burnt up.

Didn’t change the running condition of it at all, I drove home anyway. When I got home the problem changed slightly. While I still had the poor fuel consumption (even without towing a trailer), the stalling, and the general running like crap it was very, very hard to start it up when stone cold. It would take anywhere from 5 – 20 minutes of cranking to get it to fire. Here is what I did the other night to try to cure me.

Put my distributor back in with a new stator inside (aka pickup coil and camshaft sensor)
- My stator was aligned differently than Scott’s, when I put the new one in and aligned it how mine was supposed to be (there are two different ways to align it) the engine ran noticeably different, I believe this was half my problem.
New plugs and wires
New cap and rotor

Now it is slightly better. Cold starts haven’t been a problem the past three mornings, there is no black smoke, but at last check I was still only getting 11 mpg. To top it off my hard starting is now happening when warm, same situation, 5 – 20 minutes to get it to start. When it is about ready to start it will catch halfway and die, then eventually start. Today when I started it was missing pretty bad at idle, and at no-load when hitting the gas, but once I started driving it it would react fine.

I haven’t had the chance to have anybody help me so I could check spark, unfortunately I’m always alone when it freaks out.

What about the distributor, could it be one tooth off and that can cause my grief? How sensitive is the Renix system to that?

Any other ideas?
Thanks,
Sequoia

In my experience with the Renix distributor on my 87, one tooth too advanced led to hard starts, feeling almost like intermittent hydrolocking, but no discernible change in running, and no smoke. One tooth too retarded resulted in good starts but it was unable to accelerate or rev at all. I suppose that some misalignment or sample variation that put it the equivalent of a half-tooth retarded on the one I had might be different, but I don't know.

A timing light should answer your question pretty well though. The Renix system can correct a big timing error once it's up and running, and once the error is corrected it should run all right. I'd start looking at fuel injectors. An injector hanging open could be dumping fuel, and that could certainly lead to bad starts, smoke and poor economy. A bad cam position sensor in the distributor would likely result in no start, but I don't think it would mess up the fuel economy, and the "known good distributor" swap makes that unlikely anyway.

Question: does starting behavior vary with throttle position at all? It shouldn't make a difference with a healthy vehicle, but wide open throttle will sometimes help if an engine is flooded.

Have you put a vacuum gauge on it to see if there's anything funny there?

I'd have somebody do a proper check of the injectors. If you're into home repair and diagnostics, you might consider getting a fuel pressure gauge and an injector testor. The pair should come in under a hundred bucks.

When my engine would take more than a minute to start when hot, I found out that it was the injector leaking fuel into the manifold because the hot fuel from the injector rail would boil, and would dump all the fuel out of the bad injector. So I had to hold the throttle down to start it. I noticed when I had the injection assembly removed that one of the injection ports on the manifold was extremely clean because the gas would keep cleaning the carbon off the port. So I replaced that injector and the engine fired right up, and it ran smooth again. I hope your problem is that easy, I have a 90 4.0.

When it feels like acting up the position of the throttle when trying to start makes no difference. I have not yet tested my fuel pressure as I have to pick up my pressure tool from my tool cache.

Matthew Currie said:

and an injector testor.

Click to expand...

Are you talking about a NOID light here Matthew? Just curious becuase I've always just used a hotlight on the connector to check for firing through the wiring.

I'm still suspecting the distributror, I'm goign to re-index it as soon as I have some time. Does anybody know if the gear can be put back on 180º out? Meaning when replacing the stator you must remove the gear from the distributor shaft. That gear is held on by a roll pin, remove the pin with a punch, slide the gear off, when you are putting it back in you slide the gear on and re-pin it. I doubt that'd be it...but this has been enough of a pain for me to grasp at straws!

Sequoia