I have read alot on this forum regarding my problem of rough at idle and loss of power with hesitation with my 1994 Pontiac Bonneville. The specifications for my vehicle are:


Body style: 4-door sedan
Layout: FF layout
Platform: H-body
Engine:
3.8L Series 1 L27 V6
Years Used: 1992-1994
•Family: GM 90° V6
•Model: Series 1 3800
•RPO/VIN: L27/L
•Displacement: 3,791 cc (231 cu in)
•Stroke: 3.40 in (86 mm)
•Bore: 3.80 in (97 mm)
•Power: 170 hp (127 kW) @ 4800 RPM
•Torque: 225 lb·ft (305 N·m) @ 3200 RPM
•Fuel Type: Gasoline
•Fuel System:SEFI
•Configuration: 12V/OHV
•Compression: 9.0:1
•Aspiration: Normal - Non-Supercharged
Transmission: 1992-97: 4-speed 4T60-E automatic
Wheelbase: 110.8 in (2814 mm)
Length: 1992-95 SSE: 201.1 in (5108 mm)
Width: 1992-97: 74.5 in (1892 mm)
Height: 55.7 in (1415 mm)
1998-99 SSE: 56.0 in (1422 mm)
Fuel Capacity: 18 U.*. Gal

I checked the coil packs and the spark plugs, the fuel injection, as well as there were no error codes to be had. I also checked all the sensors and computer(*). I even checked the coil packs and spark plugs the "Old Fashioned" way, (pulling a plug wire off the coil pack one at a time while the engine is running), and discovered that even though there was spark and fuel to all cylinders the number 5 cylinder was missing badly and it didn't matter whether or not the spark plug was connected and firing or not.

Then I learned that this engine series has a habbit of burning exhaust valves. The only way to determine this is to perform a cylinder compression check. If there is 1 or more cylinders with low compression, then you can just about bet it is a burned valve.

The tollerance for the compression check between each cylinder is:
100lbs No more than a 70% variance of the highest to lowest readings.

I also learned that you have to replace all the cylinder head bolt each time you remove them since they are "Expansion" bolts.

I hope this helps wth whoever may be having the same issue and has been throught the gambit as I have.

Thanks for all of your advice as well as your different ideas and checklists of things to go over.

Gratefully,
Marc Hoflin

when is the last time you had your fuel filter replaced?

How did the plugs look when you took them out? White coating on any of them?

Actually, All the plugs looked fine. There was a slight white "Dusting" on them, which I always have known to be a good indicator for running right. However, the plug for the cylinder that was bad had a black almost crusty appearance. Another thing to note was that when I took the plug out, I expected to see it wet but in actuality it was dry, which was because the burned valve was letting the fuel/air mixture escape. An interesting thing to note was that when I took the plug wire off the coil pack it acted like the plug wasn't firing, when in actuality it was, there was no fuel to burn because of the leaking of the valve.

I replaced it when the trouble started

I relpaced the fuel filter whenthe trouble started