Poop's out at higher RPM's while accelerating

[pkajohnson]

99 Intrigue was running a bit rough and starting hard occasionally when warm. I cleaned the throttle body and the MAF Sensor and it made a big difference. However, although better, under hard acceleration as it gets up to around 4500 to 5500 RPM it just sort of dies...like it runs out air or fuel or something. I did get a check engine light (the one on the right of the instrument cluster) the last time I did it, but haven't had the opportunity to check any for any codes. Any ideas??

[BNaylor]

Which engine 3.5L or SII 3800?

Have you done the basics like spark plugs and fuel filter?

If the SES/CEL light is on it is best to get it scanned to see if there are any odb-ii DTC error codes.

[pkajohnson]

Sorry...it's the 3.5 litre. I'm taking it in to my regular mechanic today and one of his guys is going to change the plugs for me. It's right at about 80k, a little ahead of schedule, but can't hurt. My general philosophy is to do the cheap stuff first (stuff that'll eventually need to be done anyway) and if that doesn't work get my serious about it. I suppose then it could be the MAF or something else. Anyway, we'll see what happens after the new plugs.

[BNaylor]

Good philosophy!

Let us know how it turns out. Good luck!

[pkajohnson]

OK. I had the plugs changed by my mechanic (he got the "right" ones from GM dealer) along with the fuel filter. He also used some injection cleaner he swares by (didn't ask what it was...trust him) and put a couple bottles of Heet in gas tank too. Well, it does run a bit better, but the original problem is still there. Normal acceleration is fine. It just sort of dies and hesitates when you kick it down into passing gear...like around 50 or 60 and kick it up to about 75 or 80. If you just back off a bit on the accelerator it comes back to life. Essentially, you can't floor it and kick it down to the passing gear...just poops out until you back off to like, maybe, 2/3 throttle. No lights on or anything. Even have stayed in it and let it struggle to maybe get the check engine light to come on. Maybe a dumb question, but if the light's not on may there still be some codes stored in the PCM or does the light have to come on?

[panzer dragoon]

I did get a check engine light (the one on the right of the instrument cluster) the last time I did it, but haven't had the opportunity to check any for any codes.

the check engine light came on = check those codes. Even if the light goes off you should have codes.

When is the last time you changed your air filter. Those oiled type air filters will usually mess up sensors also = use a paper air filter and change it every year or two. <$10 Fram (and others) makes them.

[BNaylor]

Unless the SES/CEL light is staying on I doubt a scan will show anything. And if he has any codes stored it probably will not be relevent to his problem unless his problem is tranny related which I doubt. Probably only class C or D codes, if any. The ones that count are class A and B DTC error codes and there is a high probability there are zero of these since they trigger a SES/CEL light and the light usually stays on until corrective action is taken.

A - DTC = Turns on MIL light after the first failure
B - DTC = Turns on MIL light after two consecutive trips with failure

I would run a fuel pressure system check to make sure it is in specs. Another suggestion is to look closer at the MAF sensor since your problem is occurring in open loop PCM mode during acceleration.

I'm not sure about the 3.5L but on a SII 3800 you can disconnect the MAF sensor for troubleshooting purposes. The PCM will detect MAF signal missing and use pre-programmed MAF/VAF tables.

And certain MAF sensor problems do not trigger any codes or a SES/CEL light.

[LittleHoov]

A sluggish O2 sensor or clogged cat could also be part of the problem.

Unless you have access to something that will give you a live data stream, the only way to rule out the O2 sensor is to replace it.

You can check your catalytic converter, if you bang on it with something hard, and you hear rattling on the inside, its probably clogged.

[BNaylor]

I would not waste my time arbitrarily replacing any of the 02 sensors based on his specific problem. They are only used to control fuel injection in closed loop PCM mode. Mainly at idle after proper engine warmup or while at cruising or a consistent speed. The PCM inhibits the 02 sensors during aggressive acceleration and WOT.

The CAT is a possibility but as bad as his problem is misfire DTC error codes like P3XXX would set or the SES/CEL light would blink. Also, a really clogged CAT normally sets a P0420 efficiency error code. He can have it tested for possible high back pressure at any muffler shop. Must not exceed 1.25 psi. Or he can run an engine vacuum check with an automotive vacuum gauge (0-30 in. hg). A CAT that is clogged will normally fail the 2000 rpm test. Normal vacuum will read nothing less than 15 hg. On a clogged CAT the vacuum will slowly decrease instead of stabilizing at around 18 -22 hg and may even drop below 15 hg.

[pkajohnson]

Hey guys, thanks for all the input. I'm not sure why, but I keep gravitating back to the MAF. I have had one go before on another car and, although much more pronounced, some of the symptoms were kind of the same (a 3.8 LeSabre I used to own). Also, perhaps, because it's only a moderately expensive item within my "fix the cheap things first" philosophy and it's an easy 10 minute fix. I can get one at a local PartsAmerica store for about $150 for a new one...remanufactured for about $125 or less. I thought about doing that, slapping it on and if it doens't cure it taking it back...if they'll let me.

However, before I try that, to make sure I understand about disconnecting the MAF; are you saying just unplug it, drive it and see if it's better? I kind of assumed if you disconnect it, the car wouldn't like that much and probably either wouldn't run or run pretty poorly.

As to the issue of the air filter, no oiled filter in it...just a fresh Fram. That should be OK. Also, no indications I've got a bad cat. I've had them go before too and there was definately some warning there in the form of stuff rattling around in there and that lovely rotten egg smell.

Just for the heck of it, I also picked up a new PCV valve to throw at it. I looked really quickly one day and I didn't see it...where is that sucker? I tend to work 10 to 12 hour days along with a couple of Saturday's a month. So, I don't have a lot of down time to fool with it. So, honestly, sometimes I'll just get a wild hair to do it quick...if it doesn't jump out at me I shut the hood and figure I'll look at it later. I've had that PCV valve about a month now...just to give you an idea.

Again...thanks for all the input...it's appreciated.

[BNaylor]

Originally Posted by pkajohnson

However, before I try that, to make sure I understand about disconnecting the MAF; are you saying just unplug it, drive it and see if it's better? I kind of assumed if you disconnect it, the car wouldn't like that much and probably either wouldn't run or run pretty poorly.

I would highly recommend not getting a remanufactured MAF sensor, specifically A1 Cardone brand. They have a high failure rate out of the box. New MAF sensors like Niehoff and Standard have a bad history too. Although it is expensive the best route is a new GM MAF if you decide it is your problem.

Most odb-ii GM cars will run with the MAF disconnected. Again this is for troubleshooting only. It is part of troubleshooting procedures contained in the GM service manual. Here are the side effects. The idle will be erratic until the engine is properly warmed up. The PCM will detect the MAF signal missing and use pre-programmed MAF/VAF tables and rely on other engine parameters such as TPS settings, engine RPMs and MAP.

I am not sure how a 3.5L will act with it disconnected but the SII 3800 will run all day long with it disconnected. The Caddy Northstar V8 will run with a MAF disconnected. So it is your decision to try it or not. I've run with the MAF disconnected for over a week with no other driveability issues other than the erratic idle until the part came in.

[pkajohnson]

Thanks for the advice and the education on the MAF sensor. How about Beck/Arnley or BorgWarner? Also offered by PartsAmerica. May have some time tomorrow...my disconnect that sucker and we'll see what happens.

Thanks again.

[BNaylor]

Originally Posted by pkajohnson

Thanks for the advice and the education on the MAF sensor. How about Beck/Arnley or BorgWarner? Also offered by PartsAmerica. May have some time tomorrow...my disconnect that sucker and we'll see what happens.

Thanks again.

Not sure about the BA but the Borg Warner should be OK. Good luck and let us know what happens.

[pkajohnson]

Unplugged the MAF sensor. Got the eratic idle you mentioned, but once warmed up that disappeared. The "service engine light has come on and stayed on. However, the car runs great! No more pooping out at under hard acceleration. So, it would appear that that's isolated the problem. I'll order anew MAF sensor this week. Thanks for your input. I appreciate it.

[BNaylor]

Originally Posted by pkajohnson

Unplugged the MAF sensor. Got the eratic idle you mentioned, but once warmed up that disappeared. The "service engine light has come on and stayed on. However, the car runs great! No more pooping out at under hard acceleration. So, it would appear that that's isolated the problem. I'll order anew MAF sensor this week. Thanks for your input. I appreciate it.

You're welcome. Yeah, I forgot to mention a possible odb-ii DTC error code popping up and a SES/CEL light but that will reset either with a scanner or by itself after few drive cycles once new MAF is installed. Good luck and let us know how it turns out.