Running on 4 after overheating

[wilson0279737]

1995 Chaparral Sunesta 220, 350 Mag w/ Carburetor.

Last fall I was running WOT across my lake. Everything was running great until all of a sudden the temp gauge shot up and my alarm went off. I brought the rpms down and it cooled right off but there was smoke coming out of the engine compartment. It was difficult to keep it running long enough to get it on my boat lift as it wouldn't idle. The next day I advanced the timing which kept it running but there was a clatter coming from the port valve cover towards the rear. It seemed to quiet down as I messed with it but the engine is only running on four cylinders. The weird part is that I can take off any combination of four plug wires with no change to the idle. Once I remove a fifth wire it wants to die. I replaced the coil thinking that it might be a weak spark but that didn't help. Any ideas???

 

[alldodge]

My guess is you blew a head gasket if not both. Do a compression test to determine if its one one side or both. Then will need to pull the heads

 

[wilson0279737]

I forgot to mention that I already did a compression test and all eight are around 140psi

 

[alldodge]

Doesn't sound right, that all are 140. At 140 it should be running fine, maybe try another gauge

 

[wilson0279737]

Yeah i know it doesn't sound right. If the compression is good then it's either fuel or ignition but with ability to randomly disconnect four wires without change I'm not sure where to start.

 

[scoflaw]

How did the plugs look ? What was the smoke source ? Got an inline spark tester ?

 

[wilson0279737]

The plugs look perfect and the spark looks good. I used an in line spark tester on each wire coming off the distributor cap and it looked strong.

 

[scoflaw]

I've seen v8's idle very smoothly on 4, like when a batch fired mpi loses an injector and it takes down all 4, But that scenario won't accelerate above idle. So will your engine accelerate ? Doubt it, so do your testing when it falls on it's face

 

[alldodge]

350 carb motor that overheated
Had to advance timing to keep motor running

perfect plug
good spark on all cylinders
good compression on all cylinders
can disconnect up to 4 cylinders with no effect on idle

I have no idea what the issue is, but something listed above is not correct

 

[QBhoy]

Only thing I can think of is that you have blown a gasket or seal. And you’re now letting water into the combustion area. Causing it to run poorly at lower rpm. All you’ve done is try to counter it maybe ?
Still not totally making sense though. Check your plugs for water maybe ?