'98 Rodeo 3.2L V6
P0306 - misfire on cylinder 6, verified
I've replaced the fuel injector. I swapped the coils around. Fuel pressure was 33 lbs. Replaced the FPR and the filter. Haven't checked pressure since. I changed the spark plugs (which all looked good). Compression is good. Small bit of coolant in the #4 and #6 plug tubes. No evidence of oil in the coolant or vice versa.

The engine runs perfectly when it is first started for the day with the miss occuring after warm up. It doesn't always miss after warm up. Sometimes it runs perfectly at normal op temps. Sometimes the miss comes and goes.

No effect when disconnecting the lead to #6 coil when it is missing. Big effect on any other coil.

I'm going to remote the coil and run a conventional spark plug wire so I can get an inductive timing light on the wire. I want to see that I actually have fire to the plug when it is missing.

I remember once replacing a weak valve spring on an engine to cure a miss. Could this be my problem? I'm unconvinced due to the hit or miss nature of the misfire.

I'm open to opinions as to the cause of this misfire. It's driving me crazy. Seriously f'ing crazy.

Thanks,
Lonn

compression and leakdown test - it is possible you have a broken valve spring -

Hate to say this but.........
possibility that the wire bundle that runs under the intake area has a broken wire,I remember another zu fella had the same problem and it was traced to a broken wire.He ended up replacing the harness w/ JY on instead of figuring out where it was broke.

Don't take that to the bank,but try to wiggle the wires when it's missing.
Good luck.

2xs what bansil said
what kind of spark plugs do u have in there now

yea, don't over-analize this (ha, I said anal), could be a mechanical prob (compression test) or electrical ("good" coil not getting juice).

K, you said good compression, and intermittent problem: electrical supply to coil. Check input voltage there while "jiggling" wire.

Hate to say this but.........
possibility that the wire bundle that runs under the intake area has a broken wire,I remember another zu fella had the same problem and it was traced to a broken wire.He ended up replacing the harness w/ JY on instead of figuring out where it was broke.

Don't take that to the bank,but try to wiggle the wires when it's missing.


Good luck.

THAT WIRE HARNESS CRACK OR BREAK IS USUALLY RIGHT ALONG THE FRONT EDGE OF THE CYL HEAD RIGHT AS THE HARNESS BREAKS ACROSS TO GO UNDER OR ALONG THE EDGE OF THE INTAKE MANIFOLD ,AND IT CAN BE TOUGH TO FIND, QUICKER AND EASIER TO FIND A J/Y HARNESS AND REPLACE THE WHOLE THING , CHANCES ARE THERE IS MORE THAN ONE FRACTURED WIRE IN THE BUNDLE, JERRY

THAT WIRE HARNESS CRACK...QUICKER AND EASIER TO FIND A J/Y HARNESS...

Hi Guys, I'm facing something similar with my '96 Trooper 3.2 with 80K miles. I bought it last spring and put about 7k miles on it since. No check engine light, but occasionally it'll misfire for a while and get a little better. I mostly notice after a few minutes or more of cruising and then come to a stop and let the engine idle (traffic light at the bottom of a freeway exit ramp, for example). It idles rough, the way an engine idles when there's a constant miss on one cylinder. Sometimes after a minute or two of idling and a couple of tags at the gas pedal, it seems to improve, but since I've owned it, it's never idled very smooth, or at least not as smooth as my old trooper ('90 w/ 2.8 V-6) did when it was running right. It doesn't use any oil or coolant. I too was thinking like NEVROVR, that it might be a bad injector or ignition coil.

I'm going to take a look at the plugs to see if I can narrow it down to a particular cylinder misbehaving. However, I do have 4 questions. If I get the right gadget to connect to the OBD connector, will I be able to monitor as I drive and will it display which cylinder # is misfiring when the misfires happen? What gadget should I get, is there any particular brand/model that's universally loved? Also, what is meant by "J/Y harness"? And, finally, it's completely stock with 4.56 gears w/ manual trans, and gets 16-17 MPG on California gas. Is this typical?

Thanks...

Hi Guys, I'm facing something similar with my '96 Trooper 3.2 with 80K miles. I bought it last spring and put about 7k miles on it since. No check engine light, but occasionally it'll misfire for a while and get a little better. I mostly notice after a few minutes or more of cruising and then come to a stop and let the engine idle (traffic light at the bottom of a freeway exit ramp, for example). It idles rough, the way an engine idles when there's a constant miss on one cylinder. Sometimes after a minute or two of idling and a couple of tags at the gas pedal, it seems to improve, but since I've owned it, it's never idled very smooth, or at least not as smooth as my old trooper ('90 w/ 2.8 V-6) did when it was running right. It doesn't use any oil or coolant. I too was thinking like NEVROVR, that it might be a bad injector or ignition coil.

I'm going to take a look at the plugs to see if I can narrow it down to a particular cylinder misbehaving. However, I do have 4 questions. If I get the right gadget to connect to the OBD connector, will I be able to monitor as I drive and will it display which cylinder # is misfiring when the misfires happen? What gadget should I get, is there any particular brand/model that's universally loved? Also, what is meant by "J/Y harness"? And, finally, it's completely stock with 4.56 gears w/ manual trans, and gets 16-17 MPG on California gas. Is this typical?

Thanks...

JUNK / YARD YOU SHOULD BE ABLE TO FIND A GOOD SCAN TOOL FOR ABOTU 100.00 OR SO THAT WILL PICK UP A MISS FIRE , BUT YOU NEED TO CHECK YOUR SPARK PLUGS AND SEE IF THEY ARE SITTING IN A PUDDLE OF OIL IF SO YOU NEED NEW VLV CVR GASKETS AND A SET OF PLUG TUBE SEAL , AND OR A NEW UPDATED S ET OF SPARK PLUG WIRES THAT HAVE A RIB ON THEM TO KEEP OIL FROM THE PLUGS. MILEAGE IS ABOUT TYPICAL, FOR A VEH THAT WEIGHS CLOSE T0 4700 LBS AND HAS A 193 CU, IN ENG, JERRY

pull your plug wires...if there is any oil on them at the end, then you are leaking oil through your valve cover spark plug hole seals....Ihave the same problem as you described, and if I pull the plug and wires spray cleaner down in them they are good for another few weeks. I have all the gaskets to do the valve cover and spark plug holes seals, but haven't found the time to do it....

Hi Guys (& Gals?),

(BTW, I hope I'm not hi-jacking this thread)

I did pull the spark plugs and took a look at them.
Aside: In the process, I did find a few drops of oil at the bottom of some of the spark plug holes, but all of the spark plug boots were clean and dry, so I think I'm good for now WRT oil shorting the spark away from the spark plug. However, I guess the few drops of oil at the bottom of some of the holes means the day is coming when I'll have to see about replacing the valve cover-spark plug hole rubbers. Also, on the left bank, two front coil exteriors had a cruddy film (engine oil seepage from the filler cap, which didn't have an O-ring when I bought the truck + dust, etc.) Not exactly wet with oil, but not exactly clean either. They are clean now, however.
Anyway, none of the spark plugs stuck out as a real fouled up trouble maker, but they were all quite well worn, so I replaced them with a set of plain Bosch platinums (not the multi-electrode kind), gaps carefully checked with a wire gage.

Results of this: Improved smoothness and very noticeable performance improvement. The problem I had where it seemed like I'd get a dead miss from one of the cylinders at idle after a good cruise seems to be gone...At least for now. I figure I might have even picked up an MPG or two.:flipoff2:

However, it still idles rougher than I care for. The warmed up idle speed seems normal, like 600-800 RPM (don't recall exactly), but is rough enough that I can feel the vibration and it makes the gear shift (manual) wiggle left-right. I think it could be better.

Also, now that I'm paying more attention to the engine operation, I think I hear the faint sound of detonation from about 2600 or 2800 RPM on up if I accelerate moderately or harder (light acceleration through the same RPM range doesn't make the detonation sound) as if the timing's too advanced. BTW, I'm using 93 California pump gas. Perhaps the PO's previous mechanic set the timing while these worn out plugs were installed? But, doesn't this engine have a knock sensor that would retard the timing and prevent detonation?

Anyway, how do I check the timing if I can't clamp my timing light sensor to the spark plug wire? And what should the timing be at idle, and how much advance should I see at what RPMs, etc.? Is it even possible to set the ignition timing?

BTW, the CEL comes on when I turn the ignition switch on, but goes out as soon as the engine's running = CEL works, but no error codes. Since changing the plugs, perhaps it would be a good idea to clear/restart the ECM by disconnecting the battery for a few seconds, so it can "re-learn" its variables, etc? I used to do this back in the good ol' days. I don't know if it helps to do this with the controller on this engine. Anybody know?

Thanks...

Following up on the plug change, in a 60 mile MPG test (mixture of surface street and freeway driving) I got 20.9MPG. I picked up about 3.5MPG, just for changing the plugs.

Now if I could just figure out the detonation sound (mentioned above).

How do I go about getting the official factory repair manual? Do I have to go through Isuzu? Or is it available direct from a publisher?