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Old 09-20-2017, 02:09 AM   #1 (permalink)
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1987 Crx HF random misfire witch hunt

Hello! Wanted to help someone with the same issue/share my experience

So bought a 87 crx hf for 1000$.

The problems:
High idle
Wouldn't pass emissions (failed really bad supposed to have 220 HC ppm it had 2300 ppm)
Got 35 mpg (suppose to get around 50)

What I did:
Traced all the vacuum lines (there's like 100) trying to find a leak. I did find 1 leak in a major line, driver side most rearward off intake
Reset idle mixture and speed (had hard time setting mixture as it still had a random misfire)

Results:
47 mpg
Failed emissions with 1200 ppm HC
Lack of power at freeway speeds
Lack of power at lower engine speeds
Random misfire I couldn't narrow down to one cylinder. (By pulling of a spark plug wire one at a time and listening to engine speed and sound)

What I did that didn't help:
Checked cylinder compression and it read all good across all cylinders so I wrote off anything that was related to the internals of the engine( valves rings head gasket)
New intake gasket
New egr gasket
New anti after burn gasket(ties into intake)
New spark wires
New distributor cap and rotor
New carburetor isolator
New spark plugs
Tried to troubleshoot all the silonoids in the emission black boxes (where all 100 vacuum lines lead)

Result:
I found nothing wrong and couldn't fix the random misfire.

Rethink and re-engage:
I decided to retest cylinder leakage (I woulda thought any problems would have shown up on the compression test)

Results:
Boom!! After months I found the problem. Number 2 cylinder leaking bad (30%) of air. Others where more like 5%) also air from number 2 was coming out of number 1 spark plug hole.

Initial thoughts:
Head gasket blown and for some reason only leaking one way (#2 to #1 but not 1 to 2) not a bad blown gasket ether ( still had decent compression numbers and random misfire not consistent)

Action:
Pulled head looked for blown gasket (gasket looked good)
Cleaned block looking for crack (to the best of my ablity)
Took head to machine shop to inspect and give valve job.

Findings:
No cracks were found
Machine shop found two bent valves

Reflections:
It makes sense now with just a valve bent a tiny bit it can have compression and even combust at higher engine speeds before the air can squeeze out of the valve seat.

Lesson:
Don't assume because you have good compression numbers that everything is all good. A leak down test should be done as well to confirm.

Currently:
Machine shop did head I now have it back.
Waiting to have some time to reassemble and HOPEFULLY the misfire will be gone.

How did it happen:
All I can think of is that the timing belt must have broken at some point before me. piston came up and bent valve but did not cause total disaster. (As it would have on most engines). Why? Maybe because of such a light lower powered motor the valve was able to withstand the punishment.

Cheers hope someone finds this instead of chasing it down like I had too. Ask if you got any questions.

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JockoT (09-20-2017)
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