hey guys i got a 1998 bonneville se. i got a misfire on cyl #3 that just cant be diagnosed.this is all that has benn done. plugs,wires, coils swapped, fuel injector swapped, swapped ignition control modules and still got a doggone misfire on the same cylinder. what in the world could it possibly be. Its a 3800 series II. also i noticed that my uim gasket is leaking terribly and im loosing coolant. is there an exact tutorial on getting the manifold off? and would by any chance the bad gasket cause the misfire? Please help.

Well I dont have a series 2 and Im not mechanically inclined so I shouldnt really be sayin much, but from what Ive read here on the forum is get your oil drained ASAP and use the tech info article http://www.bonnevilleclub.com/forum/...e=article&k=38 to fix it. Thats really all I can help you with. Best to wait to see what one of the gearheads say as they deal with this everyday it seems like. They know exactly what they are doing.

Sam

What he said is correct, and the coolant being fed into that cylinder is likely what it causing your misfire problem. Also, as Paco said, get the oil drained right away before it starts to destroy your bearings. Then, it'* time for the upper and lower intake gaskets.

Have you done a compression test on cylinder 3? Do that and compare it to a reading from cylider 1.
Here is the procedure:
Engine Compression Test
Testing Procedure

Tools Required
J 38722 Compression Tester

A compression pressure test of the engine cylinders determines the condition of the rings, the valves, and the head gasket.

Run the engine until it reaches normal operating temperature. The battery must be at or near full charge.
Turn the engine OFF.
Important: Remove the Powertrain Control Module (PCM) and the ignition fuses from the I/P fuse block. Refer to Engine Electrical.


Disable the ignition.
Disable the fuel systems.
Remove the spark plugs from all the cylinders.
Remove the air duct from the throttle body.
Block the throttle plate in the open position.
Measure the engine compression, using the following procedure:
Firmly install the compression gauge to the spark plug hole.
Have an assistant crank the engine through at least four compression strokes in the testing cylinder.
Check and record the readings on the gauge at each stroke.
Disconnect the gauge.
Repeat the compression test for each cylinder.
Record the compression readings from all of the cylinders.
- The lowest reading should not be less than 70 percent of the highest reading.

- No cylinder reading should be less than 689 kPa (100 psi).

The following are examples of the possible measurements:
- When the compression measurement is normal, the compression builds up quickly and evenly to the specified compression on each cylinder.

- When the compression is low on the first stroke and tends to build up on the following strokes, but does not reach the normal compression, or if the compression improves considerably with the addition of three squirts of oil, the piston rings may be the cause.

- When the compression is low on the first stroke and does not build up in the following strokes, or the addition of oil does not affect the compression, the valves may be the cause.

- When the compression is low on two adjacent cylinders, or coolant is present in the crankcase, the head gasket may be the cause.

Remove the block from the throttle plate.
Install the air duct to the throttle body.
Install the spark plugs.
Install the Powertrain Control Module (PCM) fuse.
Install the ignition fuse to the I/P fuse block.

ok sorry i forgot to mention but i also had an compression test done also when it was at the dealership. the compression for #3 was right at 130psi.

130 seems a little low, what were the readings of the other cylinders?

Is it a dead misfire? Does it miss all the time or only under load?

You could pull the front valve cover off and visually inspect the valve springs for #3. This is pretty easy to do. I only mention this because it could be a broken valve spring, but I'm not trying to jump the gun here. We need to know what the other cylinders were reading for compression first.

What did the dealership tell you was the problem? I really strongly suggest you not take too much more time before you get that oil out of there. You obviously have the intake manifold leak...a known issue with these engines. All other causes are at best a distant second! Wanna run more checks? Fine...do it after you have taken care of the known problem, and do it before you spin a bearing!

Wow, I didn't even see that he said the UIM is leaking badly! Hey Archon sorry for running off with a compression test and all that. I just now noticed that he said the UIM is leaking! Definately need to fix that first!

Don't worry about it Motorhead. Not like you're the first one to miss something, including myself. Sort of the idea of the forum...the more eyes and minds working on things...the more likely it is that we'll solve the problem.

Now, SmartOJ....have you drained that oil yet?

That'* pretty much what I was thinking too.