5.7 V8 Missing at WOT

[ajkolar]

Here is my boat info:

1988 VIP 20 ft w/ recently rebuilt (3 years) 350 (4 bolt main) from rapid-o-marine and OMC cobra drive. Pertronix electronic distributor and flame thrower II epoxy coil (also from pertronix), new ESA compatible with the electronic distributor, high performance plug wires, and new plugs last year.

My problem is that at completely wide open throttle the engine misses about one or two times every second. If I back it off just a hair (literally, move the throttle back less than 1/8") the missing stops. The only other time that I experience this is if I give it to much throttle during acceleration (i.e. if I hit the throttle hard at 3000 rpm or go over 3/4 throttle when coming out of the hole). Like I say, it will run fine at 4500 rpm all day, but as soon as I give it just a little more throttle the missing starts again. The missing under hard acceleration is worst of the two situations just because I don't run at WOT very often. OH, and this condition was the EXACT same prior to the eletronic distributor and new coil (that is same problem with points and original coil). I believe I had the same problem before the plug and wire change as well.

The only part of this engine that has not been rebuilt or replaced that I am suspicious of is the carburetor, which is the stock 4 barrel quadrajet. And I know diddly about carbs so I don?t know if this could be a symptom of carb problems or not.

Any ideas or info would be much appreciated!
Andy

 

[wire2]

Re: 5.7 V8 Missing at WOT

I had the exact same problem once with my 5.7, the plugs, cap/rotor/condenser and wire were all fairly new. It would miss a bit on acceleration, then run fine on cruise, and miss again if I pushed it wot. I changed the whole distributor, same thing. Took the Rochester Q-Jet off & had it checked, was ok. Changed the wires again, still same. Changed all 8 plugs, problem solved. All the plugs looked perfectly clean, just a hint of discolorization.
I tested them with a high voltage source, sure enough, 1 was arcing deep inside some of the time. There was no more than 4 hours on them.

 

[CharlieB]

Re: 5.7 V8 Missing at WOT

Since the condition remains the same after the complete tune-up, electronic ignition kit and the carb reuild, the next step (should have been done long ago) is both a compression test and a cylinder leak-down test. Of the two the leak-down test will be the most reliable indicator of the actual problem (a leaking valve).

 

[ajkolar]

Re: 5.7 V8 Missing at WOT

Charlie

The carb. has not been rebuilt, that is why I was suspicous of it, but not knowing much about carbs, I wasn't sure if that would be a symptom of a carb probably. I did a compression test fairly recently and the compression was right around 165 psi in all cylinders. I have not performed a leak down test. Is it possible the engine isn't getting enough gas under those conditions?

Anyone think it could be the carb. I may replace the plugs just to rule that our after Wire 2's post.

Thanks again!
Andy