intermittent misfire after timing belt.

[B.E. Coyote]

Installed new water pump and timing belt.

A little over my head but used some good videos to follow. Timing marks were lined up perfectly. Pulled the pin on the tensioner. Everything looked great. I forgot to rotate two times around to check, only remembered that after I started having problems.

Truck started right up and ran great. Ran it 10-15 miles no issues.

Next day on the way to work the cel flashed and the truck stumbled. 20 seconds later gas light comes on. Probably just a coincidence but I don't know.

Check with my BT OBD and it was a misfire on cylinder 5. Marked as a pending code. The CEL did not stay lit. Filled up with gas, two more stumbles but no CEL. Cleared the pending faults and drove another 15 miles before it happened again.

All were cylinder 5,

Switched coils , drove another 20 miles with no issue. I was hoping to see that the coil was bad by having the fault on the other cylinder.


So my question is could a timing belt that may have slipped a tooth or two cause an intermittent fault on only one cylinder? I know I am going to have to check it but probably won't have time for a day or two.

Any thoughts appreciated.

 

[Warwicke36]

Doesnt sound like valve timing at all.

Loose connector on the coil or injector seems more likely.

Watch the miss, sounds like you have a grasp of what ti do.

 

[B.E. Coyote]

A timing issue would effect at least 4 cylinders, correct?

 

[importman]

A timing issue would effect at least 4 cylinders, correct?

In theory anyway. I don't see how the timing could affect one particular cylinder. Not familiar enough with the V8 so I have to ask. While doing all this work did you have to move the harnesses around some? if so, maybe you disturbed or caused a connection problem in the harness going either to the #5 coil or injector. In a case like this I think I'd try wiggling the harness on that side of the engine with it idling and see if I could duplicate the misfire. If so, then you just try to zero in from there. One other thing that may or may not hold true here. When I was having a really weird misfire problem on my V6, (long story) I called Identifix and the Toyota expert there taught me something I didn't know about Toyotas. You can't trust the misfire monitors. He said they are notoriously inaccurate. Mine was showing simultaneous misfires on two cylinders on opposite banks of the engine. Turned out, only one of them was actually misfiring. If I were you, I'd verify that the misfire is actually on cylinder 5 before I spend too much time on checking it. It probably is on 5 but I'd wanna be sure after what I went through on mine. Good luck.

 

[B.E. Coyote]

Just to follow up. I switched two coils and never had the problem return. I have 1000 miles on it since the problem. No pending codes etc.

I guess it was a loose connector although I don't think I disturbed them doing the work.

 

[Tunnelboy]

Yeah, definitely sounds like a coil pak. I had a similar issue BEFORE I replaced the timing belt. Replaced the belt (the old one was right on), and for the heck of it bought a set of 8 coils. Did all that and nothing ever happened again.

Glad you got that figured out.