Car noses over hard at 5K rpms and will not recover until the throttle it lifted?

[NCTURBOS]

Key On, Engine Off & moving the throttle position up and down... What does the MAF signal do?


K.

 

[SlickTR]

Steve any updates? I just went trough as much wiring as i could and checked my grounds and cleaned alot of electrical connections. I pulled the ECM out and there was some buildup/corrosion looking green stuff on the plug so i cleaned that up, pulled the chip and made sure the pins on that were not bent and were clean. I will let you know if it helped when i get the car out later.

Key On, Engine Off & moving the throttle position up and down... What does the MAF signal do?


K.

Mine does nothing, which i would think It should do nothing with the engine off right? Its a Fullthrottle mega maf (the 4inch intake with integrated slot type MAF the new corvettes use.

 

[Steve]

Today I put in new plugs with a tighter gap(.28)but that did not help. I also leaned it out a little more but no change there either. I borrowed a coilpack/module from a buddy and tried that but that did not help either. I did the test NCturbos suggested and I did not get any change on the MAF signal.

Based on what I learned from Eric about the MAF locking onto 255 I don't think it would be the MAF causing the problems because once the MAF gets to 255 the ECM bascially stays at that value and somewhat takes the MAF out of the eqaution. Does that sound correct?

I have a spare ECM so I think I will try that to eliminate that as a possible cause. Any other suggestions? Thanks for the help

 

[Eric Stage I]

Steve, you're right, it shouldn't be the MAF. If you look at the log, the injector pulsewidth is stable and doesn't drop off.
How much boost are you running? If you reduce boost, is there any point at which it stops cutting out?

 

[Steve]

Steve, you're right, it shouldn't be the MAF. If you look at the log, the injector pulsewidth is stable and doesn't drop off.
How much boost are you running? If you reduce boost, is there any point at which it stops cutting out?

I was running 19 psi but I turned it down to 14 to try it and it did the same thing. I have been reluctant to rev it to 5K in neutral but I went ahead and tried it and it did the same thing in neutral-it sounded like a rev limiter or a 2 step. I pulled both valve covers to check the valvetrain and I checked both sides with the engine running and all clyinders seem normal and no sign of a wiped lobe. I did some searching on the board and tried unplugging the cam sensor while it was running like was suggested in another post and tested it that way and it had the same problem. I am going to try my spare ECM now and beyond that I am unsure of what to do next.

 

[tttype]

Pull a couple valve springs & check installed pressure.
My CC980 were down to 50# after 350 miles !

New LT1 springs woke mine up.
But now I am having other high rpm issues.
Arn't hybreds fun.

 

[Steve]

I tried my spare ECM with no change. I had a old RA93 chip for 60's in my spare ECM so I went ahead and tried that with the spare ECM to make sure I had not damaged my TT chip but it was the same problem and even a little worse for some reason. The RA chip and spare ecm would only make it to 4600 rpms before the problem set in. Not sure what to make of that. I am running out of things to try. I will pull a couple of springs and get them checked. This is the 5th different 10 second LC2 I have put together over the years and I have never had any problems like this!

Is the ESC module ever a problem? I have never had an issue with one but I am curious if anyone else has.

Anyone ever have a ground problem with similar symptoms? My car is a hybrid so it is possible something may not be grounded properly. Any suggestions on grounds? Thanks

 

[SlickTR]

I tried my spare ECM with no change. I had a old RA93 chip for 60's in my spare ECM so I went ahead and tried that with the spare ECM to make sure I had not damaged my TT chip but it was the same problem and even a little worse for some reason. The RA chip and spare ecm would only make it to 4600 rpms before the problem set in. Not sure what to make of that. I am running out of things to try. I will pull a couple of springs and get them checked. This is the 5th different 10 second LC2 I have put together over the years and I have never had any problems like this!

Is the ESC module ever a problem? I have never had an issue with one but I am curious if anyone else has.

Anyone ever have a ground problem with similar symptoms? My car is a hybrid so it is possible something may not be grounded properly. Any suggestions on grounds? Thanks

Cleaning up my connections and ECM pins etc did nothing, problem is still there. Didnt really think about the ESC module, i'm wondering now it that is it. Hopefully i can get ahold of one to borrow tonight and see what happens, i'll let you know.

 

[NCTURBOS]

Mine does nothing, which i would think It should do nothing with the engine off right? Its a Fullthrottle mega maf (the 4inch intake with integrated slot type MAF the new corvettes use.

Yes, it should do nothing. I had a car that acted like yours once that I traced to a MAF ground issue. When I did the "test" I mentioned, the MAF signal would move up and down as the TPS signal moved up and down.

I wish I was closer to you to give you an extra set of eyes & hands. I love these kind of issues... Once we figure them out of course... :biggrin:

I'll try and look at your log again for something... FWIW, I remember being at Norwalk a couple years ago and one of the Ohio Gang had an issue with their car that the ESC module being replaced fixed. I just can't remember what the issue was... Remembering that I'd say if you can borrow a known good one, go for it.


K.

 

[NCTURBOS]

Ok... So I assume everyone is looking at the log and scratching thier heads about frames 578-852, correct?

I have questions about what/how the car is acting during frames 136-277...?? How is the TPS showing idle/dropping, but the o2 values and spark advance look like you're going w.o.t.?? Some of the other graphs show this as well. contradicting each other, idle vs. w.o.t...


K.

 

[Eric Stage I]

136-277 look normal to me. Timing for idle is around 25-28 degrees, O2 in open loop idle around 750-800.
However, the idle BLM of 142 is pretty high, usually indicating either a big vacuum leak, or bad MAF.

 

[tttype]

Wouldnt an ESC module issue show up as funny KR ?

 

[NCTURBOS]

136-277 look normal to me. Timing for idle is around 25-28 degrees, O2 in open loop idle around 750-800.
However, the idle BLM of 142 is pretty high, usually indicating either a big vacuum leak, or bad MAF.

Hahhhh, you're right... :biggrin: You know, I never really looked at one of your chips at idle before!! I did just look at a few now though...


K.

 

[gunslinger]

I would check your injector harness to see if you're losing inj pulse. The log looks like it's going full lean when you're losing power. If the fuel pump and pressure are good, then look at the harness.

What you're seeing in the log files it what the ECM is commanding the injectors to do...it's not necessarily what they are doing.

IPW stays stable, but the DC drops with rpm.

The MAF looks goofy to me too, but if Eric says that that's how it should be, I'm not going to argue with him.

 

[NCTURBOS]

I have been reluctant to rev it to 5K in neutral but I went ahead and tried it and it did the same thing in neutral-it sounded like a rev limiter or a 2 step.

This makes me re-think some of it... Can you record a Powerlogger log doing it in neutral?


K.

 

[Steve]

Thanks for the suggestions. I saw that Eric said that the BLM number indicated a possible vacuum leak so I went out and pressurized my intake with shop air to check for leaks and I found a small one around the EGR blockoff but one thing I found that I had not thought about is the VBP-VAC check valve set up I have for my turbo 400. It is a piece made especially for 400's in a boosted application so that the pressure modulator on the 400 does not see any boost and cause run away line pressure in the trans. It has a check ball and should not be a vacuum leak but does vent off boost pressure from the line leading to the transmission so it would be a boost leak. I am going to fix the leak around the EGR block off, then check the injector harness, then I will get a log of the problem at idle like NCTURBOS requested. Thanks again for all of the help!

 

[streetknight]

Mine was doing the exact same thing earlier this year, mine turned out to be valve springs. Good luck.

 

[Steve]

I fixed the vacuum leak at the EGR block off and pressure tested the intake and everything appears to be sealed up pretty good. I tested it after fixing the vacuum leak but the problem was the same. I tried to get a log of the problem in neutral like NCTURBOS requested but when I tried I noticed that the boost was building fast when it started to cut out so I had to lift immediately so the log was unsucessful. I drove the car tonight with my spare ECM and the RA93 in it and it acted exactly same. I am beginning to doubt my new valve springs. I bought the cam and springs from Full Throttle and had the heads ported and put toether by the same guy that built the last 3 10 second turbo Buick engines I have done(all 3 are still together and one has been running 10's for 6 years!). I have complete faith in the builder so I don't expect an issue there. The springs and cam were both from Comp Cams. Anything is possible but I have never had a set of springs go bad in only 1500 miles of highway driving and no abuse.

One thing I did notice that seems odd is that when the problem sets in the 02 reading drops to almost nothing but the car is extremely rich. From what I learned from Eric about the ECM locking onto the 255 gps until I lift off the throttle I am sure it is extremely rich and I can smell the fuel and it stumbles for a few seconds and the black smoke rolls so I know its not lean like the 02 reading seems to indicate.

 

[Slow91z]

One thing I did notice that seems odd is that when the problem sets in the 02 reading drops to almost nothing but the car is extremely rich. From what I learned from Eric about the ECM locking onto the 255 gps until I lift off the throttle I am sure it is extremely rich and I can smell the fuel and it stumbles for a few seconds and the black smoke rolls so I know its not lean like the 02 reading seems to indicate.

When you get any O2 sensor that far out of it's range it's liable to show anything...I would ignore it in my troubleshooting especially if it works fine the rest of the time...Remember at WOT the computer isn't looking at the O2 numbers at all.

 

[TurboBuRick]

Spark, fuel or air. One of them is going south.

For the hell of it, try throwing in batch fire and see if it still does the same.

Unplug the cam sensor while the engine is running and go for a test ride.

We need to get to the bottom of this.