Hello All,
I'm a little new to the forum and I hope this hasn't been covered too many times, but I have a little variation on the problem of poor performance under acceleration that I'd thought I'd throw out here.

OK, it'* a '92 Park Avenue Ultra, supercharged with about 240k miles on it. It'* been quite a good car since I've owned it. Lately though, I have the problem that when I accelerate the engine stumbles and I've got no power, Captain.

Ahem, now when the engine is cold the problem is not so pronounced, but you can feel the lack of acceleration. But when the engine has warmed up and I'm let'* say I want pass another car on a hill, the car really breaks up and doesn't respond. I really have to accelerate slowly.

There are no codes at present and I don't have access to a scanner to see live data. I checked the Idle Air Control and Intake Air Temperature sensors with an ohm meter and they are OK. I can't remember if I checked the MAF. I also changed the spark plug cables. But so far no "smoking gun," so to speak.

I haven't checked the vacuum or compression or plugs. From reading other posts on the forum, I should also get away from the Bosch plugs and O2 sensor I'm currently using.

For some months now, the catalytic converter has been rattling and rumbling and I've been too cheap to replace it. At the moment, it'* my prime suspect and I'm getting it changed tomorrow.

I guess I'm a little skeptical about whether or not it'* going to solve the problem. But if it doesn't, where do I go from here?

--Cheers!

Definitely the cat. I had the same problems you were experiencing. Get a high flow off ebay or performancepeddler.com and you'll be all set. Probably around 100 bucks if you shop around right...

Your rattle-cat will have some bearing on your issues. But not all of it. The fact that you hear rattling indicates there is *some* flow going through it, so your exhaust isn't completely clogged. But changing it will def. help you out.

Yes, Bosch is bad...if they are platinums. Regular Bosch copper-cores will do you fine, though I use Autolites and I have yet to run into issues using them. Bosch 02, no matter how you slice it, are junk. You use a single-wire O2, so finding an AC Delco unit is cake. Costs about as much as a good cake too.

Clean your MAF sensor. Take it out, spray some MAF cleaner on it, and shoot your throttle body down with TB cleaner. DO NOT USE CARB AND CHOKE CLEANER. C&C cleaner is a more potent formulation, but will strip off clearcoat that is internal to throttle bodies, and may also take out a few other sensors. TB cleaner is much more sensor-friendly.

Here'* an update on my prime suspect for my acceleration problem, the Catalytic Converter.

I got the thing replaced today with a Magnaflo/FloMaster CAT. And, drum roll please, it didn't make much difference. OK, so no rattling and rumbling but the engine stumble and loss of power on acceleration is still there.

Now really the idle is a little rough, and in some ways the stumbling is like a mis-fire. But, still no codes. I have to rule out the fuel pump because a year ago or so I replaced it due to a similar problem I was having.

That one turned out to be due to me not remembering to reconnect the IAT sensor.

Still I'm glad to have the new CAT.

But, there'* more to do. Plugs, O2, and clean up of the MAF are all in order. Thanks for the advice! I appreciate the help.

Hello,
Today I got a chance to work on the engine some more. I tested vacuum and got a good reading. So I bought some MAF sensor cleaner and some Throttle Body cleaner (CRC stuff) and had a go at removing the MAF but it was kind of jammed in the TB and I didn't want to force it. So I cleaned it in-place. Also stuck a new air filter in.

Took a test drive and no change still lacking power.

After dinner I braved the chilly Florida winter air and put in new ACDelco plugs I got from Advance Discount AP. I'm using the cheapo 41-601 plug. I thought I'd slap a little anti-seize on them and torqued to 20 ft.lbs.

And.............VROOM!!!VROOM!!VROOM!!! No hesitation, stumble, etc. on the quick test drive up and down my road.

So. We'll see what happens tomorrow. BTW, the old plugs are powdery white on their tips, you know, the little hook thingy. Bosh Platinum. They've been in for a while now. But good riddance!

--Cheers

Hooray! You got it fixed. Crappy Bosch platinum plugs strike again. Could you please edit the title of this topic to add the word "fixed" so it reads: Engine Stumbles on Acceleration - Fixed! This will aid others using the search feature at the top of the page with a similar problem. Thanks!

OK, only one VROOM!!!
I drove the car on the Interstate to work. Changing the plugs did make a big difference, but the engine will still stumble a little under acceleration. Now it'* more like a stutter.

I'm beginning to suspect troubles with the supercharger. When I accelerate hard, there a moment where you should feel the boost of the SC. But, in my case now, there'* acceleration but no burst of movement. The engine stutters but doesn't breakup as much.

I guess it could be several things. But I don't understand the supercharger operation enough, yet. I'm focused on the engine not getting enough air.

I'll continue on the quest. O2 maybe spark plug wires, try and build a computer scan tool interface, Fun stuff like that.

Back to the forums!

Today I got the chance to replace the 02 sensor and spark plug cables with real ACDelco stuff. At first blush, I think there'* an improvement. I monkeyed around with the supercharger especially the Boot Control Solenoid and I noticed that it can be tested using battery voltage.

The electrical shop manual shows the ECM controls the BCS by grounding one of the leads. That is to say one side of the BCS is at 12V and the other side of the solenoid'* coil goes to the ECM and inside the ECM is probably a little transistor in an open collector circuit that in effect grounds that side when it wants to.

So I unbolted it from the boost actuator, pulled the vacuum hoses off, connected a couple of clip leads to the solenoid and started blowing through it. Then I connected the leads across the battery and it air flow through it was cut off. Also, you can hear the solenoid click with voltage across it.

BTW, the coil resistance is about 27 ohms on my meter.

I don't really know what else to do about the supercharger testing at this point. I do notice when the car is off the bypass lever is down and when the car is running the lever is up. When I rev the engine out of gear the lever doesn't move at all.

Now I have become suspicious of the state of the transmission after reading posts from this forum and others. So, maybe my stuttering upon hard acceleration is a tranny problem or just a sign to change fluid. With 239,000 miles on her, well you might say it'* something to consider.

Well more road testing. Where this acceleration thing really rears it'* ugly head is when I'm cruising along turning over 1500 rpm or so and then have to zoom around someone.

Thanks again for all the help! I'm closing this one out for now.

I won't wax mechanic too much on this one. But, by George, I think I've got it fixed!

I went to our local salvage yard and came away with an ICM, a MAF and 3 coil packs.

I noticed I had small cracks on two of my existing coil packs. In both cases, the cracks ran from top to bottom on the side opposite the high voltage electrodes.

I installed the salvaged parts and what made all the difference were the coils!

I'm going to put in all new ACDelco packs and hold the salvaged stuff for spares.

Acceleration under load is very good; no misfires.

BTW, the salvaged coils and MAF cost $12, the ICM $14

Good for you! It is encouraging to see how perseverance pays. You stuck it out, and got'r done.