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.
I see no one has answered and I think your thought as to the reason(s)
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
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.
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.
Yes, but didn't you say in original post that 4 and 6 misbehaved
sometimes? If it is all the time have you done a fuel pressure test?
When you say no spark measurement - do you mean it's saying you are
getting no spark? If so, my comments below will not make much sense.
Yes but can it still be defective? I know it sounds crazy but you gotta
I think fuel pressure must be relatively constant, because if it could
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
Hey let me know how you make out.
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