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Cylinder 1 misfire

Kejtar

Kejtar

PostMaster General
NAXJA Member
Location
Westminster, SoCal
Back to square one..... Spent some time with the jeep again today and here's what I know:
1. Compression is good (Within norm)
2. Got spark
3. Got fuel
4. Comp is also good (tried a different PCM that I got with same exact results)
5. Popped the valve cover off and all the springs are functioning and valves are going up and down as appropriate...

WTF?
oh yeah, manual transmission, 4.0, 97XJ about 200K+ on the ticker... ideas?
 
Any ideas of what the fuel trim #s are?

Have you had the injectors cleaned? (in tank products work but I'm referring to an on car system.)
 
four_shot said:
Any ideas of what the fuel trim #s are?

Have you had the injectors cleaned? (in tank products work but I'm referring to an on car system.)
Click to expand...

I moved injectors around, I rerouted the wiring for the electrical, I tried different injectors. Btw, what's the fuel trim #? Oh yeah if it's a pressure thing, keep in mind that injector 1 is closes to the high pressure input so it can't be that as then I'd most likely have #6 issues....
 
Single cylinder misfires; gotta go through everything related to that particular cylinder.

If you have swapped injectors and the misfire remains, that pretty safely eliminates that.

And if compression is in the 120-150 range, you are good there.

Pretty basic, but don't see any mention of below parts. Even a little degradation in any of these can cause a misfire.

*Spark plug
*Spark plug wire
*Distributor cap
 
Since you have swapped parts between cylinders and replaced the other possible parts that can cause this problem then I need to ask.
Does this problem occur when the engine is cold, warmed up or ALL the time?

Have you checked the fuel injector connector for that cylinder to ensure it is attached snugly and the terminals donot have oxidation?

How long does it take for the CEL to reappear after it is RESET?

Charles
 
When the head gasket went on my 97, it threw a cylinder misfire code and confumed coolant. Does it comsume coolant? In my case it was the number 1 cylinder and when you pulled the plug with the engine hot, you could see steam coming out of the plug hole...
 
CharlesS said:
Since you have swapped parts between cylinders and replaced the other possible parts that can cause this problem then I need to ask.
Does this problem occur when the engine is cold, warmed up or ALL the time?

Have you checked the fuel injector connector for that cylinder to ensure it is attached snugly and the terminals donot have oxidation?

How long does it take for the CEL to reappear after it is RESET?

Charles
Click to expand...

The problem occurs when engine is cold but it takes a while for CEL to occur every so often though sometimes it happens almost immediately. You can feel/hear the engine running rough.
I've bypassed the orignal connection with a different one and checked for oxidation
 
o-gauge-steamer said:
When the head gasket went on my 97, it threw a cylinder misfire code and confumed coolant. Does it comsume coolant? In my case it was the number 1 cylinder and when you pulled the plug with the engine hot, you could see steam coming out of the plug hole...
Click to expand...

No steam... already checked for that.
 
Maybes---

-next time its running bad, IN THE DARK--do a real good visual check of spark system. Be carefull of course! (Looksee only.)

-the propane test for leaks on intake manifold area.

-Check spark plug cable ohms.

-try different brand plug on #1

Good Luck,
Orange
 
orange said:
Maybes---

-next time its running bad, IN THE DARK--do a real good visual check of spark system. Be carefull of course! (Looksee only.)
Click to expand...
Did that: I actually have spark tester that hooks inline. When it's failing I do have spark.

-the propane test for leaks on intake manifold area.
Click to expand...
Would the intake leak cause a misfire?
-Check spark plug cable ohms.
Click to expand...
Tried new cables, moved cables around
-try different brand plug on #1
Click to expand...
Tried champions, bosch, moved plugs from hole to hole.....
 
Did you put a Noid light on the fuel injector plug and make sure the injector is firing?
 
Kejtar said:
Btw, what's the fuel trim #?
Click to expand...

Fuel trim #s are a value in the computer that gives you an idea as to the air fuel ratio. 0 is perfect -15% to +15% is normal.Anything at or above 15% in either direction is a sign of poor fuel control. #s in the twenties usually set lean or rich codes. You need a scantool capable of retrieving data to get these values. Positive #s are a lean condition(adding more fuel) and negative are rich (pulling back fuel)

A high negative number can indicate a fuel injector sticking open. (but If you've swapped injectors the miss would have followed, so the point is moot)
 
Thank you four_shot!!
So thats what them little numbers mean, wow!

------
Just thoughts-----

Misfire usually is ign or mixture being close and 'more or less' (varying).
so thinking intermittent leaky intake or barely ign would do that. Could a bad hyd. lifter and/or cam lobe cause a problem?
("carbon on the valves")

The dark test and propane test are cheep, fast and easy, - just fishing for clues. Gotta be clues !!!

If you have a timing light might test # 1 And say #2 or other, watching for #1 varying more than the others. (Trying to narrow it to ign or mix.)

Good luck,
O
 
hows the spark-plug wires?

also just to add how the pcm detects misfires


MISFIRE DETECTION
With misfire detection, the MIL lamp may come on during the first episode if the OBD II system determines the rate of misfire is really high. On most applications, the MIL lamp will blink once per second while the misfire is actually occurring. After that, the MIL lamp may go out unless the engine had been misfiring before.
OBD II will chart the rate of misfire for each cylinder along with other data such as engine speed, load and warm-up status when the first misfire was detected. It will also set a temporary fault code that will become a hard code if the same problem happens again during the next drive cycle.
50234a.gif
If the engine runs fine during the next drive cycle and does not experience any misfire, the temporary misfire code will be erased. But if the same problem recurs on two consecutive drive cycles, the temporary misfire code will become a hard code and turn on the MIL lamp.
OBD II misfire codes will tell you which cylinder is misfiring. A code P30301, for example, would tell you cylinder number one is not hitting. But OBD II does not tell you why it is misfiring unless there are additional codes (such as a bad fuel injector or a lean fuel mixture code). If the misfire is ignition-related, OBD II can't tell the difference between a fouled spark plug or a grounded plug wire. But it can tell you if a distributorless ignition or coil-on-plug system has an open or grounded coil.
When diagnosing misfires, it is important to use tools that allow you to actually see what is going on. A basic scan tool that reads serial data spit out by the PCM cannot tell you what the firing voltage is or what the ignition pattern looks like. Nor can it tell you if the serial data is accurate or correct. For that kind of information you need a scan tool, DVOM, graphing multimeter or oscilloscope that can look at sensor voltages directly, and/or a scan tool or scope that can also display primary and secondary ignition patterns. If the vehicle has a distributorless or coil-on-plug ignition system, you'll also need the appropriate inductive pickups to get a good ignition pattern signal from the coils.
A random misfire problem (code P0300) means the misfire is jumping around from cylinder to cylinder and that multiple cylinders are experiencing a misfire problem. This is usually due to a lean fuel condition which, in turn, is being caused by a vacuum leak, an air leak in the intake manifold, dirty injectors, low fuel pressure or an EGR valve that is stuck open and leaking exhaust into the intake manifold. If a random misfire code is also accompanied by a P0171 code (cylinder bank 1) or P0174 (cylinder bank 2), it will help isolate the lean fuel condition to one side of the engine or the other. If you find any codes in the P0400 to P0408 range, it indicates an EGR-related problem.
Copyright AA1Car.com
 
Last edited:
Hmmm...

In the dark, engine running, use a kitchen spray bottle to hose down the plug wires, plugs, distributor cap, coil with the spray bottle nozzle set on "mist"--watch for a light show.

As you replaced the distributor and the issue persists I don't know if aligning the synch sensor would do you any good, but it is quick and free so why not give it a shot.

There was an issue with the 4.0 and the valves not rotating properly, trying to remember the symptoms and the fix. I will do a little searching.
 
I had to do that to a yj at work once. Can't remember the symptoms either. I believe it was a rough idle concern.

I can't remember enough to be more specific. Correct me if I'm wrong but I don't think that applied to a single cyl miss.

(Edit: Just looked it up and although the TSB you're referring to is directed at a P0300 code It says that single cyl codes May also be present. the TSB # is 09-003-03.

The cliff's notes version is to take an on car valve spring compressor and release the tension on the exhaust valve spring just enough to turn the valve 90 deg. theoretically freeing it up to rotate again.)
 
Last edited:
four_shot said:
The cliff's notes version is to take an on car valve spring compressor and release the tension on the exhaust valve spring just enough to turn the valve 90 deg. theoretically freeing it up to rotate again.)
Click to expand...
Now... in English? :) which way would I rotate teh valve? Does it matter? Oh yeah out of the two which one is the exhaust valve spring?
 
four_shot said:
I had to do that to a yj at work once. Can't remember the symptoms either. I believe it was a rough idle concern.

I can't remember enough to be more specific. Correct me if I'm wrong but I don't think that applied to a single cyl miss.

(Edit: Just looked it up and although the TSB you're referring to is directed at a P0300 code It says that single cyl codes May also be present. the TSB # is 09-003-03.

The cliff's notes version is to take an on car valve spring compressor and release the tension on the exhaust valve spring just enough to turn the valve 90 deg. theoretically freeing it up to rotate again.)
Click to expand...

Thanks for following up on that. Son and I are opening a new shop together and my fat old butt has been working too damn hard lately.
 
joe_peters said:
Thanks for following up on that. Son and I are opening a new shop together and my fat old butt has been working too damn hard lately.
Click to expand...

No problem. I'm an insomniac, and the leg work helped pass the time last night.
 
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