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Discussion Starter #1
All,

Could use your help making sense of my leakdown test on my 2.7L.

2001 Tacoma Prerunner, 2.7L 3RZ-FE, 215k miles, auto trans, has run well until recently. Valves have never been adjusted to my knowledge (I've had the truck since 150k and haven't done them and I'm 99% sure they weren't done before that. I know, not good.

Truck has been running a bit rough lately, pending code initially was Cylinder 4 misfire. I swapped in a new plug, didn't get better, swapped the coil pack from Cylinder 1 and the pending code has now shifted to Random/Multiple misfire. Decided to do a leakdown test and the results are puzzling to say the least.

I ran a leakdown test on all 4 cylinders, 3 times each (because I assumed based on the numbers that I was doing something wrong), but all the % losses were +/- 3% each time. I have the OTC leakdown tester. So,

Cylinder 1: 22-24% loss, mostly hearing loss from the oil filler and/or throttle body vacuum port on top of the valve cover. I assume this is air getting past the rings, if there is another reason, I'd like to know.

Cylinder 2: 54-56% loss, again loss is coming from oil filler and/or throttle body vacuum port. This truck doesn't burn any significant amount of oil (maybe 1/4 to 1/2 quart low from full at the oil change which I do at 4k miles), no smoke out the exhaust on start up, hard acceleration, or heavy load. This result makes very little sense to me. Again, I ran the leakdown test on this cylinder (and the other 3 cylinders) 3 separate times.

Cylinder 3: 43-44% loss, same as above, but I can also hear loss from the intake.

Cylinder 4: 10-13% loss. This was the cylinder that originally threw the misfire. This also doesn't make much sense.

Also, no bubbles in the coolant during any of the tests. So, what gives? I'm hoping it's something obvious and I'm just an idiot. Thanks for your help, I appreciate it.
 

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Discussion Starter #3
Did you also run a compression test? What are those numbers? While the leakdown test tells part of the story, you need to pair it with additional diagnostics.
Forgot to post those, sorry.

Cylinder 1: 210
Cylinder 2: 185
Cylinder 3: 195
Cylinder 4: 205

Alldata calls for 178 psi or more (127 psi minimum) and less than 15 psi difference between cylinders.
 

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I don't see this problem being related to compression or leak down. Since the problem moved with the coil pack, you should probably start there. Also be sure your MAF is clean and your TPS is working correctly. That will insure the air flow is correct and eliminates that as a mitigating factor.
 

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Discussion Starter #5
Thanks for the responses ShowStop.

Made some progress.

I was finally able to consistently recreate the conditions that resulted in the misfire (which happened to move back to cylinder 4 for over 10 start ups). Truck would idle and run fine from dead cold through the first full heat cycle. If I cut the truck off, waited 5 minutes, and fired it back up then the cylinder 4 misfire would always show up. Moved coils around (again) and the misfire stayed at 4.

So, I pulled the cylinder 4 injector plug while it was misfiring and idling like crap. Nothing changed, so I figured I would check the injector resistance and it was 2.56 megaohms (spec is 16 ohm max). So, looks like a bad injector. Going to do the fuel filter and clean out the MAF, throttle body, and intake while I'm at it.

Anything else I should do while I'm at it?
 

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I think I can help you a little on the compression test information. Squirt a few pumps of oil into the cylinder between test. If the #'s change it will most likely be the rings as you suspected


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So, looks like a bad injector. Going to do the fuel filter and clean out the MAF, throttle body, and intake while I'm at it.

Anything else I should do while I'm at it?
What were the results? I always wondered if the fuel filter could cause the fuel injector to reduce ohm, which would cause someone to errantly replace a normal functioning fuel injector.
 
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