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2000 Bonneville 3.8 (VIN K)---- Just replaced power steering pump....and while I was at it replaced some leaky valve cover gaskets. While letting it idle to bleed power steering pump, and it had run about 15 minutes the engine just coughed and died. The engine would not restart.....though every once in a while it will "cough" like it wants to start. I checked for fuel..... no problem..... Checked for spark..... had spark........ What else am I missing?? Ideas of what I can check now.....it was running like a champ! also, I put my Actron scanner on it and it was throwing no codes.........

Unplug the MAF sensor and see if it runs.

Did you double check that nothing got unhooked while changing the valve covers or pump?
Or how about any vacuum lines?

You checked for fuel and spark, how did you go about this?

Unplugged the MAF and it still did not start...... Spayed some Starter Fluid into intake and it still did not start..................I did have spark, but it seemed to be a weaker kind of spark.....could that have something to do with it?

Checked fuel pressure with my fuel pressure gauge and it was to specs and used a spark tester.....flashed on all wires. Even sprayed starting fluid in intake, and it did not start.

So it just keeps cranking? It might be a crank position sensor, given that there are no codes.

If the crank position sensor was not working properly there would be no spark..... my spark tester is flashing just fine...........

What kind of spark tester? Should be able to jump spark over 1/2" gap.

I noticed the spark was quite a bit weak looking so I switched out the module with one from exactly the same engine I had.... when I turned the key I heard a loud bang. Upon observing the engine, it had blown a hole in the back side of the plastic Air Plenum..... I then wondered if the module produced more spark, did raw fuel in the cylinders from my attempts to crank it cause a backfire that blew a hole in the plenum?

Pull the vacuum line off your fuel pressure regulator, this is a somewhat common problem with this engine for a few years, there was a recall on it. The fuel pressure regulator leaks by allowing fuel to get in the vacuum lines and puddles up in the intake, one backfire and BOOM! Sometimes it starts a fire and burns the car to the ground too :(

It is also possible as you mentioned that the fuel from the injectors left enough residual in the plenum to cause this but that is not as likely as it is sprayed right over the valves.

The best way to check for spark that I've found is to simply pull one or more plug wires off the coil and crank the engine over. If all is well you will clearly see the spark jump from the tower to the base of the coil and you will also hear a very pronounced snap noise with it at the same time.

I have a spark tester.....and it was sparking.....but the spark was very faint.....not like what I normally see a bright flash....that's why I switched the module...... then boom...... Well U Pull IT and Pick and Pull have 50% off all weekend....... I know where I'm headed.................

I wouldn't recommend a used plenum unless you can verify that it is newer / recently replaced. The plenums are also a known failure point of the N/A 3800, they degrade around the EGR stovepipe and eventually let coolant into the intake and can hydrolock your engine.

I am well aware of plenum problems...... I found a plenum at the U Pull It that was in good shape..... I'd have loved to have gotten a new one for my daughter's car, but she has very, very limited funds and we are not in a position to help out much...... so this is what it's going to have to be..... I got a plenum for $17....... a new one would have been much much more....... but it dawned on me while out today that in an effort to get this engine running again, I sprayed Starter Fluid into the intake to see if it'd just run a second or two.... THEN when I put another module on it today....I guess with the correct spark, it ignited the fluid I spayed in the intake that was sitting in there....... my bad...... lesson learned.

I replaced plenum, and switched out ignition module...... engine fired right up....but it appears it has picked up a valve tap....... wasn't doing this before the backfire...... help?

How long / how many times did you try to start it between it dying and finally getting it running? It could have pushed the oil out of one of the lifters, if this is the case then running it for a while will pump the lifter back up.

Other then that it is pretty hard to do any actual engine damage from a blow out like that as the plenum is by far the weakest link and blows apart long before any other damage would be done.

That's what I thought, but it continued to clatter.... so I went up to Advance Auto to get some Marvel Mystery oil to add a bit to crankcase to clean it up a bit....when I returned engine would not start again..... this time though it spit, and stumbled, but just would not run but just continued to cough...cough
...... 30 minutes earlier it was running fine (except for the valve clatter)....... This car is beginning to drive me insane.

dandyd wrote:That's what I thought, but it continued to clatter.... so I went up to Advance Auto to get some Marvel Mystery oil to add a bit to crankcase to clean it up a bit....when I returned engine would not start again..... this time though it spit, and stumbled, but just would not run but just continued to cough...cough
...... 30 minutes earlier it was running fine (except for the valve clatter)....... This car is beginning to drive me insane.

Wouldn't valve/valve lifter clatter indicate low/no oil pressure? - BC

my oil pressure gauge was reading just fine when the engine was running.

UPDATE: I pulled a few plugs and all seem to be quite fouled........ will put in a fresh set and go from there.........