Misfiring cylinder

DARRENDAVIS10

MEMBER
2004 CHEVROLET COLORADO
3.5L
5 CYL
2WD
AUTOMATIC
175,000 MILES

I replaced the plugs and ignition coils in the truck to try to smooth out a small vibration/rough idle. After installing the new parts, it would barely run. It ran fine before, other than the slight rough idle. The vibration/rough idle had never tripped an engine code. After replacing the plugs and coils, it tripped a misfire code on cylinder three. I had it towed to my mechanic who ran a compression test that showed 150 psi in #3. He stopped there, diagnosed a bad injector and replaced it without further testing.
After the new injector was installed, the mechanic reports that it ran great for about a minute, then started clattering badly. The #3 valves had broken apart and fallen into the cylinder, crushing the spark plug tip and twisting the piston off its rod.
Should a leak down have been done despite the 150 compression test, to be sure everything was in proper working order? My mechanic says no, and won’t accept any responsibility for the ruining of the motor.

3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

I understand what you are saying but if it unlikely that the mechanic caused this to happen.

Yes he should have run a leak test as he was loosing compression but I suspect he didn't think it was low. When I first looked at the fact that he had 150 PSI, I didn't think it was an issue either.

https://www.2carpros.com/articles/how-to-test-engine-compression

However, due to the fact that it needs 215 PSI it is low. This is not going to cause what happened though. If it was low on compression then changing the injector probably did not make much improvement if it made any at all.

It was only a matter of time before this happened. Unfortunately he did not find it before it completely failed but again, it was not his fault as you took a poorly running vehicle too him.

The only thing you can fault him for is not finding this issue before the engine failed but he did not cause it to happen by replacing the injector. In other words, it would be his fault if you could prove that this never would have happened if he didn't replace the injector which means the injector caused it.

Please let us know if you have other questions. Thanks

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Thursday, May 13th, 2021 AT 4:34 PM

DARRENDAVIS10

MEMBER
2 POSTS

I did not mean to suggest that the mechanic was at fault due to the impact of a new injector. I am more interested in whether the shop shares some responsibility for the total engine failure. You say the 150 PSI compression test results would not have raised alarms with you, but also that it was obviously low compression since it really should be in the 215 PSI area. My question is, if he did not inform himself about the needed compression, is he not responsible for the engine failure that resulted from installing a new injector, thereby increasing the combustion in the chamber, which subsequently blew up the valves which may have already been compromised. I feel that the low compression demanded a leak down which was not performed. Seems that the techs ignorance is costing me thousands of dollars more than if he had properly diagnosed the full problem, instead of skipping the leak down which presumably would have led to an inspection of the valves, valves seats and perhaps piston rings. Had he done so, and found the trouble by visually inspecting the valves and seats, is it not likely that I could have then only needed a valve job and a new injector installation performed, rather than now needing an entire engine rebuild or replacement?

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Friday, May 14th, 2021 AT 6:53 AM

KASEKENNY

MECHANIC
18,907 POSTS

Sorry if I was not clear. The compression of 150 PSI would not stand out to me until I checked the spec, like I did. Normally engines compression is 150-180 PSI. However, this is also why you never check just one cylinder.

As for the rest, of course you could blame him for not diagnosing it correctly and the engine ended up failing. You are going to have a hard time proving that he should pay for the engine.

If it were me and I didn't diag it properly and the engine ended up failing, I would charge you my dead cost to replace it. Basically I would not make any money on the job just because of the way it looks, regardless if I feel I did anything wrong.

In essence, I agree with you that he could have prevented this but hindsight is always 20/20.

I try to look at it from their prospective with the information that he had at the time. Based on the 150 PSI, he should have done more testing as he should have known that this was low but there was no way he would have known the engine was going to fail. Even if he knew the compression was low this was less then 30% loss. That is a lot for performance issues but not alarming to think that the engine is going to fail. I have seen engines run for a long time 25% low on all cylinders.

From a legal prospective, you are going to have prove negligence and that is not easy as he just didn't diag it correctly. It is not like he left the oil out of the engine or some other action like this. It was his lack of knowledge that caused it.

What I would suggest is just reasoning with him to see if he will help with the installation.

Hopefully that helps.

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Saturday, May 15th, 2021 AT 5:05 PM