Buick 3800 stumbling

550Doug · Oct 16, 2019

My 2003 Buick Park Ave Ultra is now stumbling on load/acceleration. A few weeks back it was throwing a code about cyl 6 misfiring but by swapping out the ignition control module and one coil pack it no longer throws any codes and seems just fine while idling. It even runs fine as long as no quick acceleration/load occurs. When changing the coil pack I did several swaps on the coil pack and it always threw the same cyl 6 code. That's why I changed the ICM. So maybe the used ICM is too old (from a wrecker) or maybe the problem is spark plugs. They look hard to access. Any suggestions?

Mike M · Oct 16, 2019

When I worked at the dealership I remember the techs pulling the throttle bodies off and giving them a good cleaning. They get really dirty on those GM's for some reason ?
How many miles do you have on it ?

leroy in ne · Oct 16, 2019

I had one a little older that had a similar problem. After changing one coil pack with no improvement I changed plugs and solved problem for about a thousand miles, then
it returned, wires checked OK with ohm meter then I found carbon tracking on inside of wire boot, new wires and 1 new plug, end of miss under load. Your results may be
different but I would look at plugs even if they have been changed recently. Also some engines are sensitive to brand of plugs.

Steve@Advance · Oct 16, 2019

Go ahead and change the plugs just to say you did.

Check the fuel pressure and pressure regulator function.

Look for vacuum leaks, especially near #6.

37chief · Oct 16, 2019

My 05 F150 was doing about the same thing. I changed the cats after doing a check on them. One pipe felt hot going in, but cold coming out for a few minutes. After a short time the same thing was happening. It would not take full throttle. I finally took it to a shop. The coil pack was bad causing a miss fire. I think this is what plugged up one cat anyway. The other one may have been ok. Things were so simple years ago. Stan

Determined · Oct 16, 2019

When I read in your post that the plugs look hard to get at it tells me you have not changed them before, it also tells me others may have avoided the job in the past.

It always looks worse than it is, put in new set of plugs before throwing a bunch of expensive parts at it.

Running it too long with a miss will lead to converter and O2 sensor problems.

dhermesc · Oct 16, 2019

This sounds typical- old plugs with old wires can cause a lot of misfire issues. If the wires are old enough that you don't remember them being replaced its probably time. I would also check around on what plugs work best with the 3800 engine. I am about to change plugs and possibly wires on a 2005 Impala I bought for my son to drive to school. A mechanic warned me years ago that the individual coils (COP) for each spark plug are more susceptible to failure if the plugs are old, worn and dirty. The coil works harder getting the spark than if the plug is in good condition. The cost of replacing the plug is minimal compared to replacing the coil - or multiple coils.

GregInCo · Oct 16, 2019

I have had a few of those engines and I?m with the others. Plugs and
wires time. I also like to clean the throttle body, MAF and if it has one
clean the air idle motor. You won?t believe what all that does for those
and how much better they run. It?s so gradual you don?t notice it.
There is a procedure for changing the back plugs. Hit YouTube and
check out a couple of videos. The engine rolls forward in the engine
bay making room in the back to get to the plugs.
Greg

daisyman · Oct 16, 2019

(quoted from post at 06:46:17 10/16/19) My 05 F150 was doing about the same thing. I changed the cats after doing a check on them. One pipe felt hot going in, but cold coming out for a few minutes. After a short time the same thing was happening. It would not take full throttle. I finally took it to a shop. The coil pack was bad causing a miss fire. I think this is what plugged up one cat anyway. The other one may have been ok. Things were so simple years ago. Stan

Amen to that !! I put plugs and injectors in my 97 f250 with a 4.6 and that dog on #4 (back under the firewall/dash on the right side) will really test your patience. The one's with a 5.4 on some years, they tell me, had a nasty habit of breaking off in the middle. :evil: No wonder some mechanics won't even work on them!!

Stephen Newell · Oct 16, 2019

I don't know if this pertains to that new of a model but I've got an Oldsmobile with the 3800 engine in it and it was doing much the same thing. I would change the ignition module and it would work alright for
a couple weeks and then start acting up again. Mine had a timing gear that they coated the teeth with plastic to supposedly make it quieter. As the plastic started breaking off the ignition started going nuts.
Eventually it jumped time and changing out the ignition module didn't help anymore. When it jumped time it bent valves so I nearly had to do a complete engine overhaul but it's fixed now.

Buick 3800 stumbling

550Doug

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Mike M

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leroy in ne

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Steve@Advance

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37chief

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Determined

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dhermesc

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GregInCo

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daisyman

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Stephen Newell

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