So i finally thought my car was in perfect running condition after a new clutch and slave cylinder install, but this is not true. I think the engine is running fine cuz I got rid of all my SES codes and got a full tune but heres the problem.

When i got my car tuned, my tuner told me I had my rev limiter set at 6700 rpms and it will rev that high but when I get on it, the car hits an "early" rev limiter. Its hard to describe but under hard acceleration at around 4000 rpms it sounds like it hits the rev limiter and i let off the gas. When i had my stock clutch, i thought it was cuz it was slipping (it had 74,000 miles on it) so i got the ls7 clutch and a new slave but it still does the same thing! It would also do the same thing when I did burn outs but I haven't done one in a while cuz i'm still breaking in the clutch. what the hell could be wrong with my car??? Could it be the stock master cylinder going bad?

 

BUMP!

Please help! I'm desperate! i just installed a new clutch and slave to solve this problem and i still have it....

 

Bump bump bump bump

 

BUMP! come on, no one has any idea????

 

Hey man, the stock rev limiter is set at 6200, unless your tuner reset it to 6700. The Stock tach is sluggish and in 1st and 2nd gear the engine will be hitting the rev limiter, but the tach will be reading low, usually on the stock rev limit(6200), in first gear, it is between 1000 to 1500 rpm behind at WOT. 4000 indicated seems a little low but who knows. To verify, you could either dyno it or get an aftermarket shift light. I have a Harlan light set at 6500, I dont even really look at the stock tach. Keep in mind too the more mods you do, i.e. the faster the engine revs the farther behind it will be. The Tachometer and the rev limiter are 2 completely separate entities.

Hope this helps have a good day,

Aaron

 

Hmmm i think you might be correct! cuz my tach says i'm idling at 500 rpms. It also hits the limiter around 4500 rpms rather than 4000. So my tach must be off throughout all the rpm ranges. looks like i'll have to get a shiftlight or aftermarket tach. thanks for the help!!

 

after driving the car more i'm not sure if this is my issue. The car still seems like it hits the rev limiter under low acceleration at 4500 rpms in first and second gear. It doesn't do it in third gear and I haven't had a chance to go fast enough to test it in fourth.

 

I also just tried to rev it past 4500 rpms in neutral and it still hits what seems like a rev limiter at that rpm. what could cause this? i just dropped my tank and everythings fine in there and i'm running a brand new fuel filter. Also, my wires and plugs seem fine.

 

I just talked to my tuner and this is what he said:
park/neutral rev limiter is set for 4650 rpms, which explains why it does it in neutral.

In gear rev limiter is 6750. Timing is 27+ degrees at WOT and commanded AFR is 12.7. Your problem is not wiuth the tune, it is something mechanical. Best bet is for your to come down (again) and have me take it for a ride and scan it to see what has changed . I'll be able to see if it is fuel pressure. Stock tach would only be off 100 or 200 rpms, but I will also be able to see that in the scan.

what sort of mechanical problem could cause this?

 

probably your stock valve springs

 

what could have happened to them???

 

I think they are way to weak to spin it to 6700.
I am suprised that if it ever did make it to 6700 that it didn't float the valves and bend pushrods

 

I've never revved it that high... and if the valve springs were messed up wouldn't it act like that in all gears??

 

I'm no expert on tuning, but I have an idea.

Your tuner said the Park/Neutral rev limiter is set at 4650, and this is the RPM that it cuts out. On an automatic trans, I must assume the PCM is getting it's info from the PRNDL (neutral safety) switch.

On an M6, the PCM has no way of knowing which gear you are in, even neutral. Perhaps the tune is ALWAYS applying the P/N rev limiter?

Just a guess.

 

^ scratch that advice, sorry.

I just noticed you are o.k. in third gear.

 

Hey what ended up being the problem I know if you change the rear and calibrate the ecm for it it will think ur in park neutral till third but u didn't say u had gears so what was it

 

the guy hasnt logged on since 2011 lol I doubt he's coming back. Start a new thread with specifics to your issue.

I've changed gears a few times it never messes with anything really except the speed and the shift points need touching up but were talking maybe a few hundred rpm. thats not the problem. The pcm shifts off rpm and mph not just mph.

Anyway I hd a very similar issue, I could redline the car at 6500 in nuetral but if I did it under load it would hit what seemed like a rev limiter at 4500-5000. It ended up being a bad crank position sensor. Never threw a code the only way I saw it was with a scanner. motor ran fine otherwise