Multiple random misfires

[rlrnr53]

This has been driving me up the proverbal wall. My daughter's 94 Buick LeSabre started out with multiple codes, P0300, P0321, P0341, P0361 and P0401. Having taken care of a crank sensor, cam sensor, all 3 coils, plugs and wires, I'm still getting the P0300. Scan tool shows random misfires on 1 & 3. have checked every thing, even fuel pressure (36 to 42lbs.). I'm at a loss as to what might be causing the miss. Anyone have any ideas?

[roadrunner]

What engine? If it's the 3.8 is it aluminum or plastic intake?

[killian96ss]

Does this Buick have a DIS (no distributor)? Random multiple misfires are usually caused by problems in the ignition system or fuel system. From what you have done so far, it sounds like the problem could be caused by one or more leaking fuel injectors depending on what type of system the Buick has. Does the car have a MAF sensor, or is it speed density controlled?

Steve

[rlrnr53]

Its the 3.8 with the plastic intake, with DIS and mass airflow sensor. The MAF shows different readings at various rpms on the scantool.

[roadrunner]

You may be experiencing a manifold burn through. There is a weak spot in the plastic manifold where the engine coolant loops around the throttle body rearward of it. More specifically where the egr passage is located. This allows small amounts of anti-freeze to enter the manifold directly (initially) causing multiple mis-fires. As the condition worsens it will leak more mostly during hot-soak shut off engine causing hydrolock of engine. This is a fairly common problem with the plastic manifold on the later model Buicks. The "improved" manifold has more space and heavier material in this area but still will fail. My 98 Park Avenue had this problem for the original owner twice before I bought it from him and I had it once after that. Rather than replace the upper and lower manifolds which is pretty pricey I tapped and plugged the water passage in the lower manifold so the upper plenum would have to burn completely through to fail. Three years ago and it has yet to have any problems. The only downside to this is possible throttle body icing in damp cold weather. Not a problem here where I am but consider it according to your own location. By the way the car had just over 100k on it when I got it from the previous owner and now has over 200k on it. If you use this method for this problem make sure to use plenty of pipe tape on the plugs if you install them. This is my opinion on your problem based on personal experience that mirrors what you've tried thus far up to and including the stated codes.

[HenryJ]

I'll second his prognosis. ^^ I do not have fist hand experience, but a friend down the road had the same problem with his Buick. Coolant leaking into the intake passage. His mechanic replaced the intake I believe.

[rlrnr53]

Intake ordered, will probably be a few days before I can get to it, time to get the girls to college (finally).

[HenryJ]

Does that mean you DID find a problem with it?

[rlrnr53]

With all the other problems and the fqct that the csr won't be here, and thr fact that the short life of the intake, better safe than sorry.

[HenryJ]

A pressure test of the cooling system should be a good diagnostic tool to determine if this could be a problem.

[roadrunner]

Warning!!!!!! The replacement fix requires the replacement of both the lower manifold and the upper plenum. The problem area starts between the two and replacing one or the other may not fix the problem.

[rlrnr53]

Ordered the intake Wed. evening, when we got back from taking the girls to college, the intake was sitting on the porch when we made it back home. I think that I will probably be using 1A Auto again. Fast and cheap too.

[rlrnr53]

Finally got it done. Besides the miss, there were multiple other problems. The old plenum was questionable, leaking oil out from under the lower intake, valve cover gaskets were bad, throttle body was extremely dirty, MAF was dirty, thermostat was corroded to the point of having to use a large pair of channel locks and a screwdriver to pry it out. Both radiator hoses were starting to fail along with the bypass hose. The lower intake was checked with a straight edge and was OK. THe ckeaning of the lower intake and throttle body took the better part of two evenings. THe only trouble I ran in to was losing one of the valve cover bolts, luckily GM keeps them in stock in their PDCs. I was able to get a new set overnight. This has bee a long project but well worth it to have piece of mind with the girls away at college. The next project is to get the engine in the 03 Pontiac mini van.

[F9K9]

Ain't keeping multiple older vehicles road worthy fun? Glad that it might be fixed!

[HenryJ]

[remove cigar from mouth] "I love it when a plan comes together." [/chew on cigar]

[roadrunner]

Ahhhhh, but inquiring minds want to know. Is the multiple miss-fire ghost gone???

[rlrnr53]

All codes gone, running better than it has since we've owned it. You're right Reed its getting to be a full time job, back yard hasn't been mowed in over 2 weeks, guess I'll have to bale the hay when I get home from work on Monday.

[F9K9]

All codes gone, running better than it has since we've owned it. You're right Reed its getting to be a full time job, back yard hasn't been mowed in over 2 weeks.......

You'd need another full time job if, you had to pay dealership prices to diagnose problems by throwing parts at them.