car studdering

[TDCRacing]

atached is a scan of what the car is doing. Car does not have the problem with the s/c belt off. car studders at fullthrottle and throws a cylinder 3 misfire code.plugs,wires,coilpacks,maf,have all been changed.


someone please help me out on this...1999 gtp

[MMGT1]

Have you modified the delta flow table for the maf max and min allowable flow changes? Wondering if you are exceeding what you are allowing the maf to see? Just a thought....

[TDCRacing]

No,this isnt on my car but rather a 100%stock gtp

[TDCRacing]

car does not do it with the s/c belt off-but continues to do it with the s/c belt on and the bbv disconected....in the scans car apears to be running lean with o2's in the 930's max in pe.stock car o2's should be in the 960's on the nb o2.Pulled cyl #2 spark plug to compare to cyl # 3 (missfire code cyl) to see if we were getting a possible lean and missfire condition because of the injector not working right on cyl #3 even though the injector is new.plugs looked the same.I would say it has to be the fpr but it's got me confused why i would be getting a cyl 3 missfire if that were the case


any ideas??


I plan to change the fpr on wed.and if that doesent work i am going to change the #3 injector


The way i see it-It has to be fuel related because of the lean condition....the only other possible thing i think it could be besides the fpr and the number 3 injector is the fuel pump.But me personally i have never heard of a fp not working at it's full potential but instead just going out and not working at all.and again why the cyl 3 misfire code?

[PDXGTP]

Yes, this is easy.

One of your idler pulleys are taking a crap on you and when the bearing starts to drag the pully pulls hard on the belt placing a brief load on the engine, the belt slips and the engine lunges free. That's the stumble. Eventually the bearing in the pully will freeze up and you'll know which one it was.
To test, remove the belt and turn the pulleys by hand and see which ones drag a lot, make noise or have play in them.
Or..
Its the SC coupler.
Remove the belt and turn the SC pulley back & Fourth quickly, does it have a ton of play? if yes = replace, ZZP has them cheap, $30. -something shipped.

Good luck. its easy.

[TDCRacing]

Are you joking? I promise that it is not belt or pulley related and in no way could cause what is happening in my scans.

[MMGT1]

Are the IPW's getting high when this happens? Could it be the fuel pump? Again just a guess bud, I'm just stabbing in the dark!

[louvered97gtp]

Definately not enough fuel, and possibly not enough timing. That stock tune is short by almost as much as 10% fuel at WOT from what i can see. That continuous KR isn't helping keep the engine happy. that low timing isn't helping much either. Last... that near 200* engine temp is also not helping with detonation.
Overall, i'd start with fueling and timing correction to see if that helps. Just my two cents on what I see going on. I'm assuming it was maybe a hot day and lots of timing was being pulled.
Good luck.

[PDXGTP]

Are you joking? I promise that it is not belt or pulley related and in no way could cause what is happening in my scans.

No, I'm not joking, but hey, You did say it happens when the SC belt is on right? take belt off it stops right?

- no problem. Good luck. it must all be in your tune.

Just a funny thing, I have a friend.. work... his wife's car had the problem you are talking about. she took it to the stealership and they diagnosed it as a bad trans because they could also feel it just so ever so slightly while driving on the hwy... so they replaced the trans under warranty. Anyway, it was a bad pulley and belt tensioner. $60.00 part.

The human mind is like a parachute, it only works when its open.

Later,

[TDCRacing]

No, I'm not joking, but hey, You did say it happens when the SC belt is on right? take belt off it stops right?

- no problem. Good luck. it must all be in your tune.

Just a funny thing, I have a friend.. work... his wife's car had the problem you are talking about. she took it to the stealership and they diagnosed it as a bad trans because they could also feel it just so ever so slightly while driving on the hwy... so they replaced the trans under warranty. Anyway, it was a bad pulley and belt tensioner. $60.00 part.

The human mind is like a parachute, it only works when its open.

Later,

very intresting

[TDCRacing]

again everyone this is a 100% stock tune and stock gtp!!!!!!! this car never har or ever will be tuned

[Russ K]

I would log the current misfire pids. Check for a weak/broken intake valve spring.

Russ Kemp

[PDXGTP]

The PCM uses the CPS to detect missfires.
If the CPS starts to develope some malfunction the tachometer will drop to zero and 10 seconds later the Low track light will come on providing the ECT is at temp etc, then the engine could shut off.
Do you have any of those indications?

I have the Auto-tap program and its really good at detecting missfires and it will tell you which cylinder is missfiring which is pretty handy.
When a GTP missfires the SES light will blink during the actual time of the missfire. Do you see any of those indications?

What gap on your plugs? what brand and heat range plugs?

Just thinking, I do know someone that bent a stock pushrod on a stock L67.

[PDXGTP]

After the last post I watched your scan.

Did you test those parts before you just replaced them?
If you are thinking about that FPR, you can check it in a few ways.
Put a pressure gauge on it, turn the key into the on position and let the fuel rails pressurize then turn the key off. GM says something like the fuel pressure should remain for 15 minutes, I think 5 minutes is plenty.

Also pull the vac line off the FPR (wile its running is fine) and see if the inside of the vac line is wet, smells like gas. fel pressure should also change when you remove the vac line.
When the diaphram inside the FPR tears it will leak back into the vac line which eventually gets sucked back into the intake under vac but not under boost but the overal fuel pressure is lower.
For some reason the #3 cylinder is always the first one to lean out and chip a piston under the low fuel pressure condition.

Later,

[TDCRacing]

The PCM uses the CPS to detect missfires.
If the CPS starts to develope some malfunction the tachometer will drop to zero and 10 seconds later the Low track light will come on providing the ECT is at temp etc, then the engine could shut off.
Do you have any of those indications?

I have the Auto-tap program and its really good at detecting missfires and it will tell you which cylinder is missfiring which is pretty handy.
When a GTP missfires the SES light will blink during the actual time of the missfire. Do you see any of those indications?

What gap on your plugs? what brand and heat range plugs?

Just thinking, I do know someone that bent a stock pushrod on a stock L67.

yes the ses light flashes. i do not see any signs of the tach acting the way you described and def no engine cut off. stock heat range. brand unk

[TDCRacing]

After the last post I watched your scan.

Did you test those parts before you just replaced them?
If you are thinking about that FPR, you can check it in a few ways.
Put a pressure gauge on it, turn the key into the on position and let the fuel rails pressurize then turn the key off. GM says something like the fuel pressure should remain for 15 minutes, I think 5 minutes is plenty.

Also pull the vac line off the FPR (wile its running is fine) and see if the inside of the vac line is wet, smells like gas. fel pressure should also change when you remove the vac line.
When the diaphram inside the FPR tears it will leak back into the vac line which eventually gets sucked back into the intake under vac but not under boost but the overal fuel pressure is lower.
For some reason the #3 cylinder is always the first one to lean out and chip a piston under the low fuel pressure condition.

Later,

as far as parts testing....that was this guys way of testing the parts to see if they were bad (replacing them)...this was before he had me.



i will hopefully be able to check the fpr and the injector on monday and i will report back monday night about my findings



thanks for the help so far guys

[TDCRacing]

FWIW turned out to be the coil pack....changed all 3 and problem went away

[muckleyj]

atached is a scan of what the car is doing. Car does not have the problem with the s/c belt off. car studders at fullthrottle and throws a cylinder 3 misfire code.plugs,wires,coilpacks,maf,have all been changed.


someone please help me out on this...1999 gtp

Does this mean you changed the coil packs twice?

[TDCRacing]

Sorry I had a similar problem with my personal car. I guess I posted the solution in the wrong post.


The issue with his car. Wich is what this thread contains, Turned out to be a bad plug. The ceramic was cracked. Wich was causing the problem. Even though he told me that he changed the plugs aparently he did not change the all of them.


Hope that helps.

[TDCRacing]

I think the problem with my car through a randowm misfire code. And it turned out to be a Coil pack. Was doing it above 3000 rpm's.