Stumbling at 20% load? Found solution.

[Dojo2000]

Developed a miss today on my way to work, I'd get on the gas and it would start to chock and stumble. So I hooked up my laptop and OBD 2 software, and I started watching the load. As soon as it hit 20% the engine would start to stumble. It continued until I reduced the load (let off the gas). As long as I kept it under 20% it ran fine. If this was just some loose wire or something I don't think I would be seeing it happen right at 20%. My first guess is one of my coil packs is going. I have two original coils and one that was replaced 6 months ago (the 6 and ? cylinder coil). It also seems that it doesn't start to happen until the engine and the engine bay heat up, maybe the coils are getting heat-soaked? Could it be that a coil is starting to go bad and then the heat makes it worse? I do know how to check the coils, but I want to get some input before I go through the trouble of taking them off.

I have the scan log, but I don't know what I could read off of it to help me out. I'm not getting any kind of mis-fire code when it happens either. I do have these codes on and off though:
P0102-MAF sensor circuit, low input
P1406-EGR valve system performance
P1561-PSP switch input faliure
P1562-IAC monitor disabled because "PSP switch input faliure" on

Any kinda help would be appreciated.

[ July 14, 2002: Message edited by: Dojo2000 ]
[ July 24, 2002: Message edited by: Dojo2000 ]
[ July 25, 2002: Message edited by: Dojo2000 ]
[ July 28, 2002: Message edited by: Dojo2000 ]
[ August 01, 2002: Message edited by: Dojo2000 ]
[ August 07, 2002: Message edited by: Dojo2000 ]

[ August 08, 2002: Message edited by: Dojo2000 ]</p>

[Silver3800V6FBodyKY]

This has happened to me on a number of occasions. It feels like the car has burned a plug wire or something of that nature, but I know it hasn't. It will choke down and not get above 3000 RPMs. I'm not sure the problem, but I'm guessing it's electic. I'd sure like to know what's going on with it though, so I'll keep checking in case you get some answers.

[Cale]

That happened to me yesterday.

A spark plug was very loose and was shorting out on a header bolt.

Not that it's your problem... but it could be something as simple as that.

[OneQuickV6]

Mine did the same to m when I had bad wire. Couldn't see that it was bad, and it was a new set of wires, but one was sure enough bad. It would idle fine, but around 40% or 50% throttle, it would bog down, choke, or just hesitate like a mofo. If you have autotap, put together a misfire chart. You can select each cylinder, and it will count the misfires as they happen, and only the bad one will show a misfire at all. That way you can narrow it down and fix it easier than the hit and miss method.

[Dojo2000]

no no, RPM's don't affect the stumbling. I can almost redline and it won't stumble or miss unless the load % shown on my laptop raised above 20%. This is not from high RPMs, this is from heavy acceleration.

Cale, it could be as simple as a short, but it doesn't seem like a coincidence that it starts stumbling at 20% load

OneQuickV6, wouldn't I get a misfire code or something if that was the case?

I've been at work all day so I haven't had a chance to look at it. Right now I still think its a coil cause it seems like one of the plugs is just not firing.

[Cale]

Dojo -

The car was running just like you are describing... was fine if I kept it under a small amount of load, and it could rap up to redline just fine, but whenever (at whatever RPM) I would put more than a small amount of load on the engine, it would react.

It's something with spark.

Go unplug and replug all your spark plugs, check for loose ones. Might as well hope for something simple.

[OneQuickV6]

I never got a SES light from mine. It was fine at idle and very light acceleration, but under load on acceleration it was TERRIBLE. If you have stock wires, change them for some new ones, maybe an upgrade. You can get a new set of wires for as chap as $15....but while you're at, if you have a little cash, upgrade. I would right at bet that's your problem, your symptoms are the same as mine were.

[Dojo2000]

Sounds like you guys are probably right. Still haven't checked it out though. Right now wire 6 is still stock because when I changed the wires 25k mi ago it got burnt up, too lazy to change it. And wire 1 is sitting really close to the heat shield, but its been like that for months. I knew these could be the cause of the problem, but it just kinda through me off that it started stumbling exactly at 20% load.

I really wanted to wait to change the plugs/wires again till when I get the tubular manifolds on there. Its a major PITA to change em on a 96 3.8! :mad:
I appreciate the help guys!!

[Magnus]

Look at the codes your throwing. They are all around the TB..

Check your fuses and check the ground wires. Make sure your sensors have power.

[Ironman24]

<blockquote>quote:</font><hr>Originally posted by Dojo2000:
P1406-EGR valve system performance
<hr></blockquote>

If your EGR valve is sticking then it will throw hot air in the intake and cause a stumble under load, usually around 2-3K. I had this problem a long time ago, thought it was spark but found out there was a recall on the EGR units because of the sticking valve. Maybe 20% load is when the computer opens the EGR valve up. It's usually under cruise with load, never at WOT or high rpms.

Have you had your TB off lately or been messing with it? Almost sounds like you have the sensors pluged in backwards. Check your sensors like Keith said. From there I would go to plugs/wires/coil packs.

[Fat_kid_in_little_camaro]

Sounds like what most are saying. mine did the same thing and it was the plug wires, and that is related to the RPMs. The more rpms you turn the more power your coil packs start pumping to the plugs, which is when mine started stumbling. Anything over granny style acceleration and it stumbled.

[Dojo2000]

I finally got off my but and went out there and checked it out. Replaced the # 1 wire that was touching the manifold - had two big cracks in it. Then I checked all the posts on coils, and on the front coil and middle coil each had 1 post that was corroded. From what I remember corrosion means the coil has gone bad, right? I cleaned them, the rest were nice and shiny.

So I drive to work thinking I might have fixed the problem... but NO. SO then I was thinking one of these codes must be the source of my problem. But NO, as soon as the car starts stumbling my SES light goes OFF. Car continues to stumble under load...

Then halfway home from work the SES light comes back on, having no effect on the stumbling. So now I'm going with bad coil. :mad:

[ July 16, 2002: Message edited by: Dojo2000 ]

I've been trying to host my OBD II log files so that someone can look at them for me, but NO
:mad: Stupid ****ing AOL, deleted my website, now I can't even access stuff I have stored on my server space! Does anyone know anybody that offers free, private(not Angelfire, geocities) server space mainly for f-bodies

[ July 16, 2002: Message edited by: Dojo2000 ]</p>

[Jason McCallister]

<blockquote>quote:</font><hr>Originally posted by Dojo2000:
Does anyone know anybody that offers free, private(not Angelfire, geocities) server space mainly for f-bodies <hr></blockquote>

http://www.fbody.com/

[Dojo2000]

Aaarrrrrgggg! This is driving my up the walls! [img]graemlins/crybaby.gif[/img] Now no SES light, but car still stumbles. Changed one of the coils, rest are good. Checked all wires, replaced any that even looked old! I even went to Firestone but they didn't have a clue. Still stumbles,,,

My thoughts: If car stumbles = misfire -&gt; SES light because of misfire code??? I've got no misfire code at all. This could be as simple as a fouled plug, but that = 4 hours work to find one or two fouled plugs. Then I'm installing tubular manifolds which = &gt;4 hours. So if I change plugs then install manifolds 4 + ~4 = 8 hours work! But I could install manifolds then change plugs ~4 + 30 min = 4.5 hours!! I just want my car to run right till I put on the manifolds in a week or two [img]graemlins/crybaby.gif[/img]

Back to the codes:
What exactly could be causing MAF sensor circuit, low input? Could this fix it?
What do I do about EGR valve system performance?
What could be causing Power Steering Pump input failure?
What does the Idle Air Control monitor do?

For the love of F-bodys somebody help me!!
My only other alternative would be to take it to the dealership :( and have them charge me 3 arms, two legs, and my first born to replace everything [img]graemlins/crybaby.gif[/img]

[ July 24, 2002: Message edited by: Dojo2000 ]

[ July 24, 2002: Message edited by: Dojo2000 ]</p>

[Mogobs30th]

I have been having the same problem. My car will get up to speed if i give it little gas, but as soon as I step on it, it bogs down. This happened today leaving work, but this time not only did it bog down, it made a loud popping noise, I believe somewhere around the TB. Can't figure it out for ****. I have replace all the coils, wires, and plugs within the year. It also made my "security" light come on. The only time that light ever comes on is when I first start the car, but light was on the whole way home today.

It almost sounds like the EGR valve. Its the only thing I haven't replaced and it is near the TB, where I heard the popping noise. Might have to go check it later. As for the "security" light, I don't have a ****ing clue.
[img]graemlins/bs.gif[/img]