94 Pontiac SSEi Miss on #5 Cylinder.

The car is showing a miss on the #5 cylinder, occurs only when engine is under boost from the supercharger. Occasionally also shows miss on #4 and less frequently on #6. This was found by using a scan tool.
Have swapped plugs, wires, injectors, injector wires, and coils with those from either #3 or #1 cylinder, but problem stays on #5. Also tried a new ignition control module. Engine runs smooth in the driveway at all rpms. Only misses under load and only under boost conditions.
I'm thinking fuel pressure regulator?? fuel pump??
The fuel filter was recently replaced. I run 92/93 octane.
Problem occured after car was parked for several months with only being started every couple of weeks and idling to operating temp. The car has 177,000 miles. Ran great before parking it.
Any help would be greatly appreciated.
Thanks, Jeff
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Jeff & Carol wrote:

might scare some people off, or then it's early and GM drivers are working hard long hours to pay the highest gas prices in Freaken History. LOL Anyway if you only have this problem in CYL 5 and occasional in 2 others how could the fuel pump work and filter be satisfactory in the other 5 cylinders? Have you performed a leak test in that cylinder? That's where I'd start. I feel the boost from supercharger puts pressure in cylnder to fire and compression may be lacking in #5. Equally, if this engine has the 6 pack coil it may be receiving weak spark sometimes ( I had that trouble only when under load and I have a 1991 Park Avenue 3900 engine. A new coil solved that issue, has never happened again. A scanner should identify a weak spark if you can drive under load with scanner hooked up.
Dan H.
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Thanks for your response Dan.
The reasoning for thinking about fuel pressure is that the #5 injector is the last one on the fuel rail. The others #4 and 6 may be getting marginal fuel delivery. ???
My scan tool only shows miss on #5, no spark measurement.
I have checked the compression previous to this problem just to get a feel of engine condition. I don't know the number but it was very close to the other 5 cylinders.
The #5 cylinder also has the newest coil.
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Jeff & Carol wrote:

sometimes? If it is all the time have you done a fuel pressure test?

getting no spark? If so, my comments below will not make much sense.

find out.

drop in one it would drop the same for all and I thought you did say the 4 and 6 were marginal and I think you indicated this was not all the time? Have you checked that the # 5 ignition wire isn't arching? OHMS test when wiggling it. If no problem there, then even though you say about #5 coil being newest, can it still be a defect? If all these check out it's time to check out costs for new or reconditioned injectors. The spray pattern is effected by wear out over time, lack of motorvac maintenance services has a an effect of the life expectancy, and I'm sorry but those STP fuel inj cleaners we're told time and time again through propaganda to dump in our gas tank has about as much effect as one piece of chewing gum to hide the effect of driving after 6 beer. I don't want anyone one to try it though , surely you must be chuckling a little by now. That's it an Internet comedian who replies to posts in riddles, jokes, and maybe even insults, I'm going to register a company today. LOL Hey let me know how you make out.
Dan
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