My 2001 Rodeo 3.2 v6 was overhauled (bored 0.020) about 20,000 miles ago, but one day it started running rough, got a check engine light, and shows cylinder #3 random misfire. The Chevy dealer will analyze for $115, but other than them telling me I have a broken piston ring, are there any suggestions for other possible (probable) reasons for this to occur.

 

hey al,

was there any work done to it that "one day" or was it totally random?

 

Thanks, just noticed a "miss"--engine overhauled (.020) at 100,000; happened at about 125,000. Parts store analyzer showed "random misfire." I checked compression, found #3 lower, but came up substantially when added a little transmission fluid into the cylinder. One mech says it is broken piston ring, but that's $3,000 to drop piston out bottom, etc. The Isuzu (Chev) dealer says about 6 things can cause it. I've swapped coil units around, but trouble stays at #3. Is the comshaft position sensor a candidate? What else do you recommend. I have not been working for a year and very limited funds. Al

 

sorry i never posted back, saw the email and you cleared my suspicion... thought someone may have put the #6 coil in the #3 cylinder. #6 coil should be just slightly shorter and would cause a misfire in any other cylinder. how stupid is that...

i was hoping it was just a matter of rearranging the coils. i wouldn't suspect the camshaft position sensor. i'm pretty sure that has its own code and the problem probably wouldn't be local to one cylinder.

why did the mechanic say rings? based on the compression? have you been consuming oil since the problem started? you could try running heavier weight oil and see if the compression improves.

 

look at fuel trims and miss fire

short plus long <10% is a spark problem
short plus long >10% is engine / fuel

 

Thanks OOrodeo: Does the "short plus long" test require a trip to the dealer and is it performed only on their analyzer (or another shop that has that capability)? Sorry to confess but I am not enough of a backyard mechanic to know. Can you reply back to educate me a little please. Big Al

 

you could go to a dealer but they would charge alot, all you need is a scan tool that reads engine data, a local shop should have one, there are four pids bank one short and long and bank two short and long, compare the four, also look at oxygen sensor data and see how fast b1s1 and b2s1 move they should be the same but if one moves faster then the other you may have a fuel problem to that cyl, but trims will help you the most,

let me know i have alot of spare parts, and also a engine

 

Thanks, I will get on it.

 

I learned a pretty simple trick the other day, let your engine idle and spray water from a spray bottle at the exhaust headers. If a cylinder isn't firing then the runner won't steam. If one doesn't that means no spark. I'm not sure low compression will set a misfire code, but then again I'm still a greenhorn tech.

 

was there any work done to it that "one day" or was it totally random?