Stumble in higher rpms

T

"Turbo-T"

V6 on steroids
Joined
Jan 10, 2007
Those of you following my thread of http://www.turbobuick.com/forums/ge...01-so-heres-update-how-my-car-runs-track.html will recall I am having issues with trap speed drop off. Some of you have said to check the cam, a few of you thought maybe the valve springs were at fault.

I still don't know for sure what the cause of my trap speed drop off is, but I think I may have found one of the reasons why my car keeps dropping trap speed at the track, as last Sunday it felt like the car was stumbling when it hit about 5000 rpm.

Tonight I decided to do a test. I took the car out and put it in 2nd, and let the rpms go up to 5000. I just let it gradually build rpms, I didn't even get into boost.

At 4300-4400 it started to lightly stumble, and at 4800 it was stumbling pretty good. it would still continue to climb in RPMs if I pushed it.

Then I did another test where I put the car in 3rd and I got it up to 4300....didn't really feel anything....then 4400....didn't really feel anything...car was still pulling strong...but right about 4900 it started stumbling like crazy. I did get ito the boost a little on this test.

All of my RPM readings came off the Scanmaster. I did an ohms check of the coil right after the run....I got readings of 12,200 on two of the coils and 11,970 on the other....I read the coils should be between 11,000-13,000 ohms. So I will presume my coil is good.

What about the module? Does this sound like a module issue?

I have a powerlogger...will it display if the ignition is the cause of the stumble?

What else should be checked for a stumble at 5000 rpms?

I wonder if this is why my trap speeds kept gradually dropping off...?
 
What spark plugs do you normally run? How old are they? Maybe start there. It's simple and cheap.

RL
 
They're the AC Delco ones everyone recommends. I can't recall the p/n at this time...R43TS maybe? And they're at least 4 yrs old but have only 10k that I know of (were in the engine when i got it 4 yrs/10k mil ago). I pulled them out the summer before last and cleaned them and gapped them at .032
 
87Regal3.8SFI said:
I have a powerlogger...will it display if the ignition is the cause of the stumble?
Click to expand...

it would look like this:

bad coil.png
 
Hey kidglok or anyone else, I don't know if this matters or not but on my powerlogger I have a wideband set up so the graph shows wideband readings.

Also this morning I unhooked the wastegate and took a few runs and logged them in.....of course I was able to still build just a little boost...guess I should have wire tied the wastegate puck wide open?

Anyways the runs I did were in 2nd gear and 3rd gear starting at 4k rpm until after 5k rpm...again with he wastegate unhooked...will these suffice? LMK, I want to get this problem diagnosed and fixed.

Thanks in advance
 
A wide band will show the miss as well. Do you have a log?

Did you put some new plugs in?

RL
 
NGK-UR4 001.jpgNGK-UR4 002.jpg

I pulled all 3 of the plugs from the right bank of the engine. I was wrong about the plug type....they're NGK-UR4 plugs. The plug on the right is #2 and the one on the left is #6 with #4 in the center. I can see they're pretty dirty.

I cleaned and gapped them to .032 once before, except #6 b/c it was a bitch to get out. This time I chanced breaking it off and managed to get it out, albeit it was in there like you wouldn't believe. I'm going to anti seize them.

Judging by the pictures, you think I should just clean and regap these? Or toss them? I do have a box of CR43TS's never used I read are a good plug for these engines.

Also has anyone taken a look at my powerlogger files I posted in this thread?
 
NGK-UR4.jpg

And here's the left bank removed. The #1 cyl is on your left, the #5 on the right and #3 in the center.

All of these have the chocolate brown power like look, as opposed to the others with the dark oily look, except for #4.
 
UPDATE: I put in all brand new CR43TS plugs and gapped them to .032, yet the same problem persists. I get to 4300-4900 and it starts stumbling.
 
I had this same problem a couple of years ago. My car would miss at the top of each gear. I changed plugs, tried different gaps etc. I kept thinking that the car was too rich and this could be causing the stumble. I ohmed the coil pack and always read between 11k-13k. I believe it was Razor who informed me that taking a coil reading is an important step, but does not tell the whole story of what is the coilpack is doing under a load and when it is hot and under a load. I considered buying the casper coilpack tester, but for the money decided to just go ahead and replace the coilpack. Have not had a problem since. Also when I had the stumble, my gain from the 1/8 to the 1/4 was only 17-18 mph. After fixing the problem, I had a 23-24 gain which is more like it. Just food for thought. Good luck with your issue.
 
no options said:
I had this same problem a couple of years ago. My car would miss at the top of each gear. I changed plugs, tried different gaps etc. I kept thinking that the car was too rich and this could be causing the stumble. I ohmed the coil pack and always read between 11k-13k. I believe it was Razor who informed me that taking a coil reading is an important step, but does not tell the whole story of what is the coilpack is doing under a load and when it is hot and under a load. I considered buying the casper coilpack tester, but for the money decided to just go ahead and replace the coilpack. Have not had a problem since. Also when I had the stumble, my gain from the 1/8 to the 1/4 was only 17-18 mph. After fixing the problem, I had a 23-24 gain which is more like it. Just food for thought. Good luck with your issue.
Click to expand...

Thanks for this info....funny you say that about the increase in trap speed at the track....my car currently only picks up roughly 17-18 mph from the 1/8 mile. It used to get about 20 mph but it's been getting worse. Did your car also start losing trap speed?
 
I had the stumbling when I bought the car. I knew I had a lot to learn about tuning (and still do),but I thought my problem was my tune. I thought my turbo was a TA49, but it turned out to be an old stage ll garret which means it had a bigger compressor wheel, but stock turbine with an .82a/r. My goal was anything in the 11's with the stock motor. So I bought a TE44 when they dropped down to $599. I also went from a 26" tire to a 27" along with replacing the coilpack. So I can not really answer your question because I made these 2 additional changes. For what its worth, my best with the old garret was 109mph. First pass with the TE44, tires, and no stumbling was 116mph at the same 23psi.
 
reset the crank sensor ensuring the ring is in the middle of the slot and if it persists after eliminating the coil/module as the problem replace the crank sensor
 
Did you ever get this resolved?

I recently replaced an ignition module to fix a stumble in my car similar to yours, but mine was happening in the 2200-2500 rpm range and at a steady highway speed of around 70 mph. Acceleration was fine with no stutters, but noticed the car would start acting up later in the day as it was warmer. Seemed to get worse at lower speeds and I'd get a code 41 as well. After verifying coil pack and cam sensor were still good (as well as fuel pressure, ECM, grounds, sensors, plugs/wires)...replacing the ignition module cleared it right up. My car also seems to run better at higher rpms too.

Anyways just thought I'd throw that out there.
 
Rodney87GN said:
Did you ever get this resolved?

I recently replaced an ignition module to fix a stumble in my car similar to yours, but mine was happening in the 2200-2500 rpm range and at a steady highway speed of around 70 mph. Acceleration was fine with no stutters, but noticed the car would start acting up later in the day as it was warmer. Seemed to get worse at lower speeds and I'd get a code 41 as well. After verifying coil pack and cam sensor were still good (as well as fuel pressure, ECM, grounds, sensors, plugs/wires)...replacing the ignition module cleared it right up. My car also seems to run better at higher rpms too.

Anyways just thought I'd throw that out there.
Click to expand...

Thanks Rodney. No I never did figure out why. I've been wanting to find out if anyone near me (central MO) had a Caspers coil tester, and if I could have mine checked. I read that sometimes the coils are known to act up in the upper rpms when they get older. But I will keep in mind about a possible ignition module issue.

larry33kc said:
I didn't see how much boost you are running but I think I would close the gap to 28-30
Click to expand...

Larry I have it set for 23 psi as of now. I'm presuming you recommend a tighter plug gap to prevent spark blow out? Can you put in a hotter coil so you can keep the gap more open?
 
Not sure about that. I had a issue like you are having and that was what it was for me. It's easy to try
 
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