No start, appears to be thermal failure of something

Jeep: '97 XJ, 4.0, AW-4, NP-231. Tune-up parts are all fresh (<5K miles).

Symptoms: After driving for 10-15 minutes, jeeps starts to run rough and will die, it can be restarted once or twice, but then it is dead for at least an hour. Eventually it can be restarted but it will still only run for a short time. The other weird part is that while driving the speedometer will randomly peg, then come back down. This part is really bothering me.

Codes: these are all pending but I got P0351, P0300, P0302, P0304, P0306.

Thinking P0351 is key, as the rest are just misfire codes, and I didn't need the computer to tell me that there was a misfire...

P0351 is Ignition Coil A Primary/Secondary Circuit, but some searching tells me that few people actually had a problem with the ignition coil.

So far:

-Fuel pressure is good (48 PSI)
-CKP is good (replaced w/my trail spare that was removed from a perfectly good part-out, same issue)
-Swapped ASD and fuel pump relays, no change

On my way to pick up a new Camshaft position sensor and Ignition coil now, but in the mean time does anyone else have suggestions? That speedometer issue is really bothering me and I'm worried it suggests more than just a sensor.


Thanks.

Update: Threw the new Camshaft Position Sensor and ignition coil in, no change. Cranks and cranks and cranks but won't start.

I pulled a spark plug and held it against the block while cranking it over and the spark was intermittent. I haven't done that test before so am I correct in assuming that there should be very consistent, regular spark? It would appear that whatever the issue is, remains intermittent.

Also, since it died the last time (after running for a bit after CKP replacement) it has not restarted again. It has now been about 3 hours. As of right now I'm going to call it a night. Does anyone see any reason for me to pick up some noid lights to verify that the injectors are firing?

You should have a BRIGHT BLUE AND SNAPPY SPARK. Fix that before working on something else.

Ok. HARD RULE in our shop with any driveability issue--including no crank or no start--is to start with the battery. Load test, then check static voltage and cranking voltage, and if it does start check the voltage with the engine running. Now some may ask "why", well, in today's autos when available voltage drops below 9v things go WONKY fast.

Post up what you find.

You can/could have tested the resistance values of the ignition coil for the primary and secondary windings.

joe_peters said:

You should have a BRIGHT BLUE AND SNAPPY SPARK. Fix that before working on something else.

Ok. HARD RULE in our shop with any driveability issue--including no crank or no start--is to start with the battery. Load test, then check static voltage and cranking voltage, and if it does start check the voltage with the engine running. Now some may ask "why", well, in today's autos when available voltage drops below 9v things go WONKY fast.

Post up what you find.

You can/could have tested the resistance values of the ignition coil for the primary and secondary windings.

Click to expand...

The coil was an aftermarket MSD (installed by the PO) so I didn't test the resistances thinking that they would be different than an OEM coil. When the spark was there, it was bright blue, and what I expected... but while cranking it was in and out (while sparking the motor sounded like it might catch, but then it was completely dead and the spark went away). So whatever is wrong is preventing spark from happening.

I can load test the battery and check the voltages tonight, but it was replaced at the same time as the rest of the tuneup parts less than 6 months ago (I know its possible to get a bad one...). It is a mid grade O'Reilly's battery.

Also, started the jeep up first thing this morning before I left for work and it fired right up and ran normally for a few minutes. I didn't have time to do more than that, but it does start and run still...

That fading away of the spark MAY be due to the cranking voltage dropping below 9v and that will foul the PCM--killing spark.

OK, so I knew that all that cranking was draining the battery but I figured since it was still cranking it was fine. But I threw a float charger on it overnight anyway just as a precaution. Well tonight it runs fine. This is with new coil and cam position sensor installed. It wouldn't start after installing either one alone last night so I assumed that neither fixed the problem. Got home this afternoon and after being on a small HF float charger for about 20 hours, the voltage on the battery was 12.6 V. Fired up easily and ran for a total of about 45 minutes.

And now I can't replicate the problem.

Possible that all the cranking pulled the voltage too low to run the PCM, thus killing spark after i replaced whichever component was the issue?

I looked up the specs for the MSD coil that was installed and tested it. It's with spec while cold (although not by much). It's in the oven right now and I'm going to re-test shortly. If it goes out of spec I'm going to swap it back in temporarily to see if I can replicate the issue. Same basic plan for the Cam Position Sensor if the coil doesn't test bad.

Joe, thanks for all the help so far.

Yeah.

Starters like amps, PCMs like volts.

You can have enough amperage to crank but lack volts to run.

Good luck, and keep us posted up on your progress.

OK so I've swapped the old Cam Position Sensor back in as well as the old coil... and it runs fine :flamemad:


Tested the coil. MSD spec is 1.2 Ohm primary, 13.7K secondary (MSD 8228 here: http://www.jegs.com/i/MSD/121/8228/10002/-1 in case anyone is interested)

Tests cold at 1 Ohm primary, 14.5K Ohm secondary
Tests hot at <.5 Ohm primary, >16K Ohm secondary

Which looks like a bad coil. Got excited when I saw that, figured I had found the problem.

But it runs fine now... and has been running for about an hour. I even let it it sit to get a good heat soak and restarted/drove around with no issues.

So I swapped the old Cam Position Sensor back in as well. Still no issues.


So I'm at a bit of a loss. I was really hoping that when I put that coil back in the problem would re-appear. With those numbers, I don't think I'll leave the coil in but I don't understand why the problem isn't coming back.

I also tried wiggling/pulling on the wires and connectors to both the coil and the cam sensor. No effect.

And a little bit of context: I have a budget boost (shocks/spacers/bastard pack) sitting on the shelf that was supposed to go on by tomorrow night so the fiance could take the jeep to visit her parents in Cincinatti. Then this issue came out of the blue so I've been working on it instead, and until I can verify the bad part, this thing isn't leaving a 1 mile radius from my house much less making a trip out of state!

http://www.jegs.com/i/MSD/121/8228/10002/-1

I work in camp 8 days at a time, come out to a dead battery a few times as a result. When the battery is dead, even with a jump the XJ will not run on it's own until the battery is up to proper voltage. I can get it to start with a jump, but I have to keep my foot on it to keep it running. Once I have enough voltage to start itself, it still wants more and won't stay running on it's own. Being an automatic, makes trying to get out of the parking lot an ordeal when it does happen. Usually after I hit the next town (1hr 20min hway drive) it's charged up enough to be able to shut down and restart without issues. I've never had a CEL light up though, just the usual check gauges when it's running rough. Might be the coils code was just happenstance and the battery being low was the primary issue? Seems the charged battery cleared the problem ... might wanna test that battery AND the alternator. Sounds to me like your alt may not be keeping up the battery and it runs down over time.

I've just always though the late models wouldn't run without the battery hooked up like other cars (mine never has). Just always figured the alternator wasn't big enough to meet demands (I'm sure there is another reason but I'm not smart enough to know it) and planned the 136A or 160A swap down the road.

Devilfrog said:

I work in camp 8 days at a time, come out to a dead battery a few times as a result. When the battery is dead, even with a jump the XJ will not run on it's own until the battery is up to proper voltage. I can get it to start with a jump, but I have to keep my foot on it to keep it running. Once I have enough voltage to start itself, it still wants more and won't stay running on it's own. Being an automatic, makes trying to get out of the parking lot an ordeal when it does happen. Usually after I hit the next town (1hr 20min hway drive) it's charged up enough to be able to shut down and restart without issues. I've never had a CEL light up though, just the usual check gauges when it's running rough. Might be the coils code was just happenstance and the battery being low was the primary issue? Seems the charged battery cleared the problem ... might wanna test that battery AND the alternator. Sounds to me like your alt may not be keeping up the battery and it runs down over time.

I've just always though the late models wouldn't run without the battery hooked up like other cars (mine never has). Just always figured the alternator wasn't big enough to meet demands (I'm sure there is another reason but I'm not smart enough to know it) and planned the 136A or 160A swap down the road.

Click to expand...

Battery will be load tested tonight but I don't think it's the issue. I've had plenty of dead batteries (and a few bad alternators) and this acted nothing like any of them.

When I can finally get it to start, it runs like a top instantly. No gas required, no worries about it dieing if I don't hold the gas pedal, etc. It either cranks but won't start, or runs perfectly. No inbetween. While running, the alternator is putting out around 13.5 volts.

BTW, on the alternator with no battery thing - I've got a 160 amp alt in my other rig, and can say definitively that if you have the battery go bad but can get a jump start, you can run on just the alternator... Not recommended as I believe it's bad for the alt, but it'll do it.