cpt_koolbeenz

Hi Guys-
Having a problem diagnosing my 951's newest problem. I just noticed 2 days ago... Under hard acceleration in 3rd gear, up hills, the car basically feels like the fuel gets cut off - it jolts once pretty bad then rpm's fall. I thought it was overboost because I recently installed a reliaboost (running at what Danno sent it at), but just for kicks, once after it happened in 3rd, I shifted to 4th and gave it WOT and at about 4000 RPM it did it again... but the stock boost gauge wasn't even past half. I tried to get it to do it in 3rd on a flat road and it didn't do it (only got up to about 4000 RPM - cops were out). I have premium in her so don't think it would be the knock sensor. I will try to get it to do it tomorrow then check the DME diagnostic port with an LED to see if it tells me anything. Does anyone know what maybe happening?

Thanks

MHT

4TH GEAR, 4000 rpm and WOT should be seeing max boost, if your gauge said only .5bar then I would say the gauge was off. What you describe sounds like overboost protection. Try removing the "reliaboost" and see if the problem goes away. It might also be a good idea to hook up a real boost gauge and see exactly how much boost you are running.

cpt_koolbeenz

Well, I didn't get to 4k in 4th... It wasn't at full boost when I was in 4th but it still did it. I tried again to get it to do it today - I got it to do it twice - about 10 minutes or so after I started it. Then I forgot to leave the engine running to check the diag. codes and turned it off. (Damnit!!) So I went back to the hill to try it again and it didn't do it any of the 4 times I tried. So would boost or knock conditions be different just after I start the car than after it has been running for about an hour? I will try later tonight whn the car has had time to rest... In the meantime, does this sound like overboost to anyone else?

Yan

I have exactly the same problem with my 951 and I haven't been able to identify it yet. Hard cutoff under full boost in third - fourth - fifth gear, then cutoffs at below 10 PSI when flooring it back.

It really sounds like overboost protections, but it began to occur a full year after I had purcharsed it and I hadn't changed anything to the car. Good luck!

cpt_koolbeenz

That sums it up perfectly... Yan have you tried to read the diag codes from the DME port? I am still trying to get them.

Can anyone confirm that it is overboost?

Oddjob

Your symptoms sound like the overboost protection.

If youre running a mechanical boost controller (set to run higher than the stock boost level) with the stock chips in the car, you will hit the overboost protection. Most/all aftermarket chips increase the load limit required to trigger the fuel cut off.

cpt_koolbeenz

Okay guess it is overboost... I'm getting my GURU chips next week so I'll see if that is it. I still want to read the diag codes though...

Yan

No, I didn't try to read to codes yet. It's a good reason to calm down my 80+ mph highway accelerations (less tickets).

Keep us updated!

cpt_koolbeenz

Haha! Well... I do that, but usually not on the highway
I'll try the codes again tomorrow.

Oddjob

If youre just hitting the fuel cutoff without causing the KLR to run in the safe mode (1.3 bar max boost w/ 6 deg retarded timing until you shut the car off), you wont be able to retrieve a fault code from the KLR. It is two separate safety modes/protections.

I had an intermittent overboost fuel cutout problem up to about a month ago. It never tripped the KLR to identify an excessive boost condition or give the blink/fault code.

cpt_koolbeenz

Ah the safe mode explains why I stall it after I've come to a stop and try to accelerate again... Not the power im used to. That would also explain why it did it in 4th at half boost. Thats too bad about the codes... I'm going to try it out though. I'll be getting my chips on Mon or Tues... YAY!

Oddjob

>"safe mode explains why I stall it after I've come to a stop and try to accelerate again"

Actually the dying after the first stop is still part of the DME fuel cutoff, not the KLR safe mode (mine did the same thing and I learned this the hard way). Once the car is shut off and started again, the protection cutoff is reset.

>"That would also explain why it did it in 4th at half boost."

The stumbling cutout at mid to 3/4 throttle position, after you hit the initial fuel cut at peak boost/higher rpms, is also normal for the overboost protection. This is why it dies at the stop signs - I think the DME is still cutting the fuel when you open the throttle to move from a dead stop.

I believe the fuel cutoff will continue for around 60 seconds after the overboost protection is initially triggered, so if you drive the car at a steady throttle position/coasting for a few miles, it will reset the fuel cutoff protection itself, and drive normal until you exceed the peak boost/load condition again.

CPT in Co Springs, are you at Ft Carson?

>"it began to occur a full year after I had purcharsed it and I hadn't changed anything to the car."

I had the same problem, overboosting with a stock powered car. Check for intake system leaks first. I also swapped out the air flow meter and the problem has not reoccurred, but Im not convinced that the AFM was the fix.

Yan

I really worry about a strong leaking problem. If the fuel cutoff only occurs occasionally (once every day or two days) when driving it hard, does it mean that I'm not boosting enough to blow my gasket and that it just sometimes peaks at the limit? That I know, I don't have any manual boost controller and I don't know if there's a wastegate shim or not. I'm sure of one thing: I have a stock DME.

Today, I pulled a carlenght or so on a 911 Carrera 2003 (newer models with the turbo headlights) on a 60-110 mph acceleration. It's not something normal for a mostly stock 951. Do I have to worry about the excessive boost?