czentner

Hi guys,

I have an 88 951 with a Vitesse stage 3 turbo kit (including MAF) with 89k miles. It has manual boost control, but I always run it all the way down (13 psi) as the car makes enough power for me. I am running 94 octane fuel.

I had my first DE event on mon/tues (woooohaa! What fun!) and noticed a problem while on the track that I'm hoping you guys can shed some light on.

Approx once every session, under high engine load, there would be a POP! noise from the engine accompanied with a split second loss of power, then everything would be fine again. Does this sound like misfiring? How should I go about troubleshooting this?

Thanks,

Willard Bridgham 3

Start with the spark plugs......what do you know about them?

czentner

The plugs are supposed to have <10,000k on them.

But does what I describe sound like a misfire?

The car is parked somewhere other than my house, I will pull them and check their condition the next time I'm out there.

User 52121

Honestly aside from the "13 psi" setting it sounds like overboost protection.

Do you have the V-Flex MAP sensor add-on?

czentner

I am not sure - the PO bought and installed the Vitesse Stage 3 kit that was purchased in 2005. Vitesse's website says that their kit includes a MAP sensor, I don't know if it was included in 2005.

Is there an easy way for me to tell if I have one?

It's for sure only running 13psi (I have a boost gauge inside whose needle never goes up over 13). Is overboost protection mode damaging?

fast951

Back in 2005 we did not use a MAP sensor. in spring/summer of 2007 we introduced the V-FLEX software which incorporated a MAP sensor, which enabled the DME to alter the tune based on actual boost.

With V-FLEX we also added the capability to let the user set his/her own over-boost protection and rev-limit (as well as other alarms). The settings are "usually" done via the Piggyback (or 3rd party system such as Zeitronix with Alarms). The Alarm signals were sent to the DME to handle the Alarms.

A couple of years ago we introduced the next generation of V-FLEX, we changed the name to V-MAF+. V-MAF+, which also uses a MAP sensor, is the standard software that comes with the MAF kit for the 951.

Even though the system was purchased in 2005, over the years many customers upgraded to V-FLEX or V-MAF+. So it's worth investigating further.
If running V-FLEX or V-MAF+ you should have a MAP sensor.

The software, even back in 2005, was programmed with 2 rev limiters (one for pump gas, one for race gas or E85). So even if the user did not set the rev-limit, we still limit it.

Did you hit the rev-limiter?

Overboost protection is not damaging, it's there to limit the boost to save the engine.

To get back to your main concern, if you have the old software (2005) or if you have the V-FLEX or V-MAF+ but not setting alarms, then something else is causing the misfire. It could be a tired ignition or fuel component or something totally different. To pinpoint better, if you can reproduce the problem, data log via PB. It may help.

BTW. are you the same person who I exchanged emails with earlier today? Following the instructions I sent you you should be able to access your PB.

Feel free to drop me a note if I can be of any help.

czentner

Hi John,

Yes, I am the person you've been talking to via email today. I will see what I can find out the next time I'm out working with the car (probably this weekend). And no, I was definitely not hitting the rev limiter. As I said, this would happen perhaps once per 20 minute track session.


Thanks for your help!

fast951

No problem, drop me a note if you have any questions. Being new to the 951, there is a good learning curve ahead of you. You're in the right place!

Unless we have additional information, all we can do is guess. With the heat generated in a 20 minute track session, you could have a tired ignition coil or fuel pump.. A ignition misfire, not good, but not as damaging as a "Lean intake backfire".

Do you have a Wideband O2 system on your car? It's almost a must have, be it for tuning or to warn you if things go bad.