99 sr5 mis fire issue

twitchee2

twitchee2

Member
My buddy has a 99 sr5 4wd v6 auto. Couple of weeks ago we were in tahoe and it developed a bad misfire. I pulled my scan gauge out of my truck and pulled the codes. Found p0303, p0305, p0306...Misfire on cylinder 3 5 and 6. Fast forward 2 weeks and I said lets change the oil, change the plug and get a vacuum tube to replace the one that fell off.

Pulled the plug and found single electrode plug..great. Put the correct dual electrode in.

Still missing. Got some MAF cleaner and cleaned the MAF off and that made the most difference of anything so far. Its still missing on cylinder 6 and im running out of ideas. Im gonna get some starting fluid and do a vacuum test and see if the rpms hop up when i spray it around. but so far is it doing load better then it was.

Then I swapped the coil and wire from my truck to his and there was no change.

Just wanted to run it by you guys and see if there is anything else im not thinking of.
 
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Ill pull the plug back out again later today when i go work on.

All the plugs are new and the wires/coil has been eliminated by using the ones from my 02 4runner and there was no change.
 
To have that many cylinders missing all at once and all of a sudden, I'm thinking maybe it's a timing issue. Like the t-belt skipped a tooth. The harmonic balancer isn't wobbling is it? Did he have a t-belt service done lately? This can happen if they don't torque down the CS pulley all the way down (217 ft. lbs). Those are just some thoughts.. I hope it's something easier, but since at least 3 holes are missing.. and not just on one head but both.. and all at once, I think it makes it unlikely that it's plugs, wires, valves, HGs/cracked head(s), or injectors. They are usually associated with just one cylinder missing (at least at first).

You might try changing the fuel filter too, a plugged one can cause multiple misses.
 
completely spaced the fuel filter, you might be on to something with that brian. that's next on the list now too. With how much cleaning the MAF helped i have a hard time believing the timing is out but its definitely a possibility.

I was thinking about seafoaming it but I feel like we need to fix whats wrong before that gets done.
 
How long has he had it and what is the level of maintenance? We had one similar case on here a while back where it turned out to be a sludged engine--the valves were having trouble closing due to the crud.

I'm certainly not saying this is the case--but it's something to keep in mind along with the loose harmonic balancer idea.

Just to confirm, do you FEEL the misfire as well as see the MIL and the codes? You said it was 'bad', so I assume you do...
 
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oh yeah you can feel the miss fire. it was really bad at idle shakes thole car etc. where exactly is the harmonic balance and how do i inspect it?

hes had it for a 30k miles the previous owner was a mechanic. The truck has a 3in spacer lift + 2in BL /w 33's the cv axles boots are all ripped so dont think it was particular well taken care of so sludge might be it to. Is there any way to check it without pulling the valve covers?
 
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twitchee2 said:
oh yeah you can feel the miss fire. it was really bad at idle shakes thole car etc. where exactly is the harmonic balance and how do i inspect it?

hes had it for a 30k miles the previous owner was a mechanic. The truck has a 3in spacer lift + 2in BL /w 33's the cv axles boots are all ripped so dont think it was particular well taken care of so sludge might be it to. Is there any way to check it without pulling the valve covers?
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Just take a look at the crankshaft pulley (the harm. bal. is behind it) while it's idling and then rev the engine (just don't run it with the miss any longer than you need to). The pulley shouldn't be wobbling. I doubt it's the timing, but it's a possibility. It could be sludge/valves too. Hopefully it's just the fuel filter. Could be a dying fuel pump too.
 
brian2sun said:
Just take a look at the crankshaft pulley (the harm. bal. is behind it) while it's idling and then rev the engine (just don't run it with the miss any longer than you need to). The pulley shouldn't be wobbling. I doubt it's the timing, but it's a possibility. It could be sludge/valves too. Hopefully it's just the fuel filter. Could be a dying fuel pump too.
Click to expand...

Good summary. I'm hoping a look at the plug will give us a clue if it is fuel starvation (filter/pump or injectors) or compression (valves/sludge). I also think timing is unlikely (remember timing belt controls VALVE timing, not ignition timing). If the #6 plug is wet, I would suggest a compression check.If you fail, THEN we pull vavle covers. If it is dry, focus on fuel/injectors. Look at a random plug or two as well.

Definitely do as suggested on the crank puley/harmonic balancer. That CAN screw up ignition timing because the crank gear can move forward and mess up the sensor signal. But I think you would see really bad vibration with that.

I ruled out spark, because you seem to have addressed that, but if I had the truck I'd clip my timing light induction pickup to each of three wires just to be sure.
 
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So we changed the fuel filter, didnt see the balancer moving around, didnt see anything that was moving like it wasnt supposed to.

When starting the truck up after installing the new filter, it backfired. Now im not sure if this means the timing issue could actaully be true. Its not throwing a code after i cleared it yesterday but its still shaking at idle and stutters and shakes if you rev it real quick.

Im starting to think this is out of my knowledge level and im gonna have him take it in. Seems like its a little more then just needing a tune up issue.

truck has 140k on it he thinks it the timing belt was changed but not sure.
 
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If you are still getting a code cyl #6, crank the 4runner, and then pull the injector connector to the #6 injector.

If nothing happens, your buddy may be looking at a bad injector. If the truck stumbles, etc., then as Brian said, it may be a timing issue.
 
Backfire, huh? Probably one-time related to ECU confusion starting up with no fuel in the line. WAG--don't see many backfires anymore with fuel injection and computer controlled timing. But I've never heard of that happening to anybody else on a filter change. Backfire can certainly be caused by valves not closing or bad valve timing, as well as ignition timing. You are at the stage where you need things like a compression check, timing check with a light, resistance and stethoscope check on injectors. A fancy computer analysis might be informative.

Let us know what happens. Good luck. Did you ever look at that plug?
 
yeah its getting to the point where i dont have the tools to do it anymore. I pulled the plug but they are brand new and i couldnt tell either way. I looked at the oil plugs but i dont know where they came out of any more. there was a one that was rich and and a couple that were lean. im about to take off for the weekend and drive to LA so hes gonna be on his own. until then im gonna go change the oil and plug on my 4runner.
 
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