97 cherokee Cyl #1 misfire

[xj88superjeep]

Hi everyone, I did search countless threads, and find nothing that I am looking for, so please discuss this with me. I have a random misfire in cylinder #1 on my 97, and it has already had the ignition system replaced from rotor to plugs over a year ago from a previous "no start" issue. I replaced all plugs and the injector, and still same problem so I took it to a shop. They charged me $75 for looking for the problem (but not finding it) and $75 for an engine decarbonization that aparantly did not work since the code is back. They confirmed everything I already knew...
Compression IS lower in that cylinder, but not devastatingly low:
Cyl #1 = 130
Cyl #2-6 = 150
They mentioned that vacuum was slightly low, but came up a little after the "decarbon" but said that low vacuum would affect all cylinders not just #1. They said could be the valve spring in that cyl... but they claim that they checked everything from injectors , and it is all working properly and it MUST be an internal engine problem causing the misfire. I have a little trouble swallowing this because I know how the Cherokee gremlins operate and I know how mechanics dismiss them. I have 2 sneaking suspicions that I can't afford to throw money at. One being fuel starvation (when I did a fuel pressure test, the needle flutters within spec at Idle, but smooths out with throttle input) Can anyone confirm if this is normal or not? The shop said if it was low fuel pressure it would affect all cylinders, not just #1... The other is cracked or loose flexplate, but they also said this would affect all cylinders. Can anyone please point me in the right direction? I can't afford paying another $160 for nothing.

 

[89xj]

you can check for cracked or loose flexplate bolts.

other then the somewhat low compresion, what else indicates that its a miss on cylinder 1?

from what you said, i beleive the mechanic is being honest with you. it could be internal.

have you checked for any stored codes?

 

[kastein]

Have you checked the wiring to the #1 injector? Do you know anyone in your area with a 97 you can borrow/buy the ECU from? I would suspect a bad injector driver in the ECU or intermittent wiring with the description given. My first guess would be cap/rotor/sparkplug/plug wire, but you already tried that.

EDIT: before you try this, do the cheap thing and disconnect your battery then hold the battery cables (NOT the battery terminals, unless you like sulfuric acid and molten lead for breakfast) together for a minute or two, then reconnect it and start it back up. This should force the ECU to relearn the engine calibration curves and may solve the problem.

 

[xj88superjeep]

The cylinder #1 misfire code is the only indication. Runs great... seems to be after a long highway jaunt then getting off the highway is when the engine runs a little rough. Zero overheating, runs at constant 210 under all conditions. Good oil pressure at all times. If it was a mechanical issue, wouldn't it be a CONSTANT misfire?

 

[xj88superjeep]

kastein,
I have a spare ECU left over from throwing cash at the "no start" last year so changing out the ECU was the first thing I did, and the shop cleared it out also after they worked on it... I asked the shop about the injector wiring because I know it is pulled tight where it comes from the loom to the back of the fuel rail, and they said they checked for continuity the entire time it was running, and they claim the injector was firing. I think I need to unwrap and inspect those wires myself, because I am sure they did not go that far and their tests may not have duplicated the circumstance of a fault happening...

 

[kastein]

Hmmmm. If it was other cylinders, I'd suspect heat soak, but #1 on a 97 without the precats should be just fine...

I dunno, this is a really interesting (read: infuriating) problem.

 

[xj88superjeep]

I have never heard of heat soak happening on a 97, so I would never even think that...
The mechanic claims a bad valve spring could cause the problem that it has happened before... Is there any way to know without tearing into the engine, and is that a huge problem to fix if it ends up being a bad or broken valve spring?

 

[birchlakeXJ]

I have a random misfire in cylinder #1 on my 97, and it has already had the ignition system replaced from rotor to plugs over a year ago from a previous "no start" issue..

When you say replaced "ignition system" please confirm that includes plugs, plug wires, distributor cap and rotor. I assume it does but just checking. If that stuff was replaced a year ago, really still can't rule it out. Swapping a plug wire with a different cylinder and seeing if the misfire follows or at least testing the wire for acceptable resistance would make sense. So would replacing the distributor cap.

 

[xj88superjeep]

When you say replaced "ignition system" please confirm that includes plugs, plug wires, distributor cap and rotor. I assume it does but just checking. If that stuff was replaced a year ago, really still can't rule it out. Swapping a plug wire with a different cylinder and seeing if the misfire follows or at least testing the wire for acceptable resistance would make sense. So would replacing the distributor cap.

The entire distributor all the way down to the gear was replaced in fall of 08 with a brand new unit, along with high performance wires and have been on it since then, and I put in brand new bosch platinum +2 plugs about a month and a half ago. I don't know if the mechanic tried swapping plug wires or not, but I do know it is not a constant misfire and it is contained only in the #1 cyl... Going to stop by there agian tonight and talk to him about it some more. I'll let you all know what he thinks at this point. I do want to swap plug wires or replace them, but hate chasing this thing at this point, just want it fixed, and hate to see the mechanic scratching his head about it while I am paying him to do so.... UGH!!!

 

[joe_peters]

I'm tending to lean toward an exhaust valve sticking.

Beg/buy/borrow/rent an vacuum gauge. Don't worry about how much vacuum the engine has, but watch the needle for intermittent "drops" when the condition is present. If it is, then you have a sticky valve.