Strange misfire/stalling especially under load issue

Ok, you had the misfire and replaced the plugs--what type of plugs did you have in there, and what plugs did you replace them with?
 
5-Speed XJ: What about the Cam position sensor in the distributor? It works in conjunction with the crank sensor to ensure the injectors are being fired in the right order.
FWIW my crank sensor has gone 3 times. twice it did not die right away but had intermittent problems, the other time it completely croaked and no crank.
Another idea is the MAP sensor. If that baby goes the the engine will run on the cold engine cpu settings and dump fuel when the engine is actually hot which causes erratic behaviour. -B
 
5-Speed XJ said:
i replaced the map earlier this year and just replaced the cam position sensor so all thats left is the crank position sensor
Click to expand...

Well can't hurt to have a spare crank sensor for the jeep if it turns out not to be the problem, thats the bright side anyway.

what type of coil did you replace the old one with? reason i ask is i put in a new accel coil and it failed within 1000km which is what i get for buying "made in china". at least my msd lasted 5 years before going tits up, and am now back to my original mopar coil. -B
 
Ok so I broke down and replaced the CPS... and it made no difference whatsoever. Whoops. Oh well, I was pretty sure that's what the problem was based on the way it was acting.

So I programmed my Scangauge to watch my O2 sensors and the upstream is ALL over the place. Bouncing around between .10 and 1 volt in a matter of a few seconds. The downstream however is very steady at .44-.46 volts.

So what on Earth is going on??? Unplugging either O2 sensor makes no difference at all.
 
Oh, and also I managed to get my CEL to start flashing. It could be because of the misfires I suppose but if the misfires caused it you would think that it would then at least leave a code but it didn't. The CEL just stopped flashing, turned off and left no codes whatsoever.
 
The o2 is supposed to bounce around like that, that means it's constantly adjusting the mixture between rich and lean, from my understanding. Just out of curiosity, have any of you checked your fuel pressure. And also isn't there some adjustment that can be made with cam position sensor with a tooth pick. You might want to look into that as well. That's all I can think of to check.
 
I don't think that's correct, the O2 isn't supposed to "bounce around". It's not supposed to "do", or adjust anything. It's just supposed to read the amount of O2 in the exhaust stream and let the PCM do the adjustments. So the only way it should "bounce around" when working properly is when the O2 in the exhaust stream itself is actually going from rich to lean etc.

And I just thought of this, the PCM is supposed to bypass the O2 sensors anyways during open loop and I've sat and watched my Jeep go from open to close loop during warm up with no noticeable difference in how it's running. Also, when I open the throttle all the way to bring it into open loop it still misfires.

So what would cause the primary O2 to be reading such large, constant swings from rich to lean??
 
Umm, actually IH392 is correct to the best of my understanding. It's called a feedback loop - the ECU puts a little less fuel in since the exhaust is a bit rich, then the exhaust gas goes lean, so the ECU puts a little more in, and the cycle repeats. So the O2 sensor output will reflect the rich/lean/rich/lean cycle.
 
0.35-0.6 volts is about the range a normal operating O2 sensor should stay in, not 0.1-1.1 volts. And shouldn't the PCM go into open loop as soon as the primary O2 is disconnected? Also, if it were a bad O2 then I should be fine at WOT since the O2's aren't read during open loop anyways?

I think I have an o2 laying around here anyways, I'll throw that on and see what happens :dunno:
 
K so I replaced the primary O2 and nothing changed at all. Also I haven't checked the fuel pressure with a pneumometer but I primed it then hit the schrader valve and it squirted to the fender so it didn't seem low at all, not to mention the fuel pump is pretty new. I tested my MAP sensor and it was fine. So about the only sensor left that is used to meter fuel is my CMP. And I don't know how to test it without an oscilloscope, any ideas?

There seems to be absolutely no rhyme or reason to when or even how it runs the way it does. Sometimes it idles beautifully and sometimes it "lopes" like a drag car. Sometimes it slowly slows down to maybe 100 rpm or so low that you can't even tell if it's running or not then it dies and sometimes it just turns off just like I turned the ignition off. About the only thing that is consistent is that it never runs well and misfires pretty bad under load above ~30% throttle. Below ~30% throttle it runs like a champ, no problems at all.

Oh, and I noticed after my engine dying on me while diagnosing/test driving that when I turned the key back on there was no beeping from my instrument panel like usually happens when you turn the ignition on.

I also noticed that after every time the engine would die all I had to do was turn the key off, wait 15-30 seconds then crank again and it would fire right up like normal. If I tried to crank without turning the key off first, even if I had waited 15-30 seconds, it would just crank and crank and not even act like it was going to fire. And I should note that this doesn't seem to be a thermal failure issue because it's done the same thing just after leaving the driveway long before heat soak would set in.

And lastly, my Scangauge has been having trouble "connecting" to my PCM. Normally it takes a couple seconds but now it doesn't seem to want to connect at all. I just wanna cover all of my bases before I go buy a $150 PCM that I don't need and won't fix my jeep.
 
Last edited:
Don't drop 150 on a PCM, you can get them at most yards around here for 50. Second... not sure what is wrong at this point. Sounds like CPS or PCM with the scanner difficulties, but I am not sure.
 
You must log in or register to reply here.

Similar threads

B
TPS troubles
Replies
2
Views
199
Blaines2399
B
R
No Start Issue
Replies
10
Views
163
rtd16
R
T
High Idle Issue
Replies
1
Views
198
Tim_MN
Tim_MN
A
95 4.0 RHD (UK) crank no start
Replies
9
Views
263
ahyland
A
A
T-Case Problems?
Replies
7
Views
226
Ol Blue
Ol Blue
Back
Top