5&6 cylinders have a bad miss

[Angie]

Extremely confused on this one. After a blown gasket replacement for the 5&6, the engine has what feels to be 2 dead cylinders.

From the start... when I bought this truck it had a strange miss,so I just replaced the engine with a good 1 I had from an explorer that I scrapped (kept engine as it was very low mileage). after replacing the engine I rechecked all the wire harness and the engine ran tip top till last week when I cooked the head gasket on the driver side, hence the tearing off the heads to replace a new set of gaskets.

After the original heads went back on, the engine had the same bad miss back in the last 2 cylinders.

OK thinking something not 100% correct decided to take off the head again and double check it and block; everything was A-OK. However, I decided to place another head that I have back onto the engine. ( I knew it is a good head) After bolting everything back up and doing everything humanly possible to get the engine running, still is bad miss. can pull either plug wire and the engine makes no difference.

what I have done - tested so far.

Compression tested the 2 pistons, both hit 150 PSI

Spark plug tested great spark, tested the electrical for the injectors, test light lit up in flashing for fire.

No oil is being burnt in the compression chamber, no steam from tail pipe either.

My guess is this is some ghost in the electrical system. what sensor(s) should I test or replace from my parts trucks)?

Any ideas? i am all ears. (1992 4X4 OHV style block)

 

[Dirtman]

Well if you can be certain it's not a compression issue then you have 2 options... no spark or no fuel.

Simple test is to run the engine, stop and pull the plugs on the offending cylinder(s) if they are wet with gas then you have a spark issue. If they are bone dry you have a fuel issue.

 

[Angie]

Hi, ya I understand that concept, and I can see this problem if only 1 cylinder was acting up, but to have 2 dead cylinders isn't passing the sniff test. I have checked every wire, and connection. plugs etc. cheers

 

[Angie]

well not to sure whats next. leakdown test coming up and will probably pull the engine and see if it should be rebuilt i guess. Nothing I have looked at or done has fixed this problem. My guess is that the rings were cooked into the pistons and this has given the engine a strange misfire in the 2 adjoining cylinders. cheers

 

[Angie]

ok, Fixed this problem..... (over last couple weeks as time allowed)

Pulled the engine, re-ringed the 5&6 pistons and new con bearings. Re-honed the holes, returned all parts and placed the engine back into that gaping empty bay ...

Started it back up today... VRRROOOOM

My guess is the cylinders were washed clean as the walls were smooth with no cross-hatch. hence zero compression.

cheers

 

[sgtsandman]

Glad you got it fixed and posted the fix.