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Discussion Starter · #1 ·
I've been a member for a while now, and I've been banging my head against the wall with a cylinder misfire issue on my '01 Tundra V8. The truck has a tick over 380K miles on it, and has been an exceptional vehicle. I first encountered a misfure issue earlier this past April when I was driving home from Kansas (I live in Indiana) after picking up a replacement bed for the truck. I was just outside of Columbia, MO when the engine began running incredibly rough and my check engine light started flashing. I was able to get the truck to the local Toyota dealer where they diagnosed a bad #5 coil, replaced it, and I was back on my way with no further issues. Once I got back home, I went ahead and replaced my plugs as well as the other coils. The plugs had a little over 100K miles on them and the coils were still original.

In late May I was driving home from work when the rough engine operation reappeared. Again it showed a misfire in the #5 cylinder. Since the original repair had been done at the dealer in Missouri, I took the vehicle back to the local Toyota dealer here in Indy. They said they would honor the warranty if it did indeed turn out to be another issue with the coil. They were unable to replicate the issue, and only offered the advice that I go back with Denso spark plugs due to a different temperature rating of the Denso plugs. I went ahead and replaced the plugs and was good for the next couple of months.

In early August I encountered the #5 cylinder misfire once again and replaced the injectors with rebuilt Denso versions. The overall operation of vehicle seemed to improve substantially (at least to the point where the engine simply "sounded" better), and my idle jumped from around 500 rpm to around 650 rpm. I thought at this point that I had addressed the issue, but that was not the case.

This past week, I fired up my truck after work and the rough idle as well as the flashing check engine light had returned. This time the scan indicated multiple misfires as well as specific misfires on the #1 and #8 cylinders. Digging further on this forum as well as elsewhere, I decided to replace the fuel filter as well as clean the MAF sensor. I also ordered a cylinder compression test kit. After replacing the fuel filter and cleaning the MAF sensor, I started the truck and this time it threw the #1 and #3 cylinder misfire codes :mad:.

I was able to check compression on the cylinders earlier today. Based on what I see, there seems to be something going with the driver's side bank. My readings were as follows (I tested #7 and #5 twice after the low initial readings):

Cylinder 8: 185 psi Cylinder 7: 110 psi (120 psi second test)
Cylinder 6: 180 psi Cylinder 5: 145 psi (155 psi second test)
Cylinder 4: 180 psi Cylinder 3: 145 psi
Cylinder 2: 190 psi Cylinder 1: 190 psi

My understanding is that Toyota indicates 142 psi is the bare minimum acceptable value for cylinder pressure. Obviously cylinder #7 fails this criteria, and #3, #5, and #7 fail the 14 psi difference between cylinders criteria (at least when compared to 1, 2, 4, 6, and 8) that I have seen noted in other threads. My question is whether it's safe to say that I'm seeing some type of valve or piston ring issue here, or if something else is going on. I had considered the possibility of a head gasket issue, but I'm seeing no loss of coolant as well as no loss or burning of engine oil. Plus, it would seem somewhat odd that the issue would manifest in the #8 cylinder if it were indeed a head gasket issue.

The other thing that I found interesting was that the original problem arose in cylinder #5 and now the problem has seemed to migrate elsewhere. Would a piston or valve issue in the #7 cylinder cause misfiring in cylinder #5? I've been taking care of the majority of my own maintenance and upkeep for the last 250K miles, and I'm fearing I may be at the limit of my capabilities. If nothing else, I'm frustrated at the intermittent nature of the problem and my inability to track it down. Any thoughts or suggestions would be greatly appreciated.

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