3.6 rev limiter cutting in early at the track

[WILSPEED]

Hey guys, I run a 993 3.6 motor which recently had a new tuned ECU installed. I was at the track and the rev limiter started kicking in at 5000-5500 rpm or so instead of the usual 6300...... consistently halfway through each session.

I was later told by the guy who prepped my car that I was suppose to mix 110 octane with 91 pump gas 50/50.

I was only able to add 5 gallons of 110 octane (topped off) for the feature race and the problem didn’t start until a bit later, about 3/4 into the session.

Is this issue really from wrong fuel mix or is it a problem with the ECU itself? Anyone else had this issue before?

[stownsen914]

My first thought was that there might be knock sensing set up in your ECU that reverts to a limp mode if it detects detonation. Which it might if you were running 10 octane too low. But then it did it again with the high octane stuff added, which suggests that may not be the issue. Were you able to do any more sessions and replicate the issue again? Knowing as many details of the exact conditions that cause the cutting out can help diagnose.

Unfortunately cutting out can be from a number of things, fuel or ignition. I once had a substantial cutout issue, and luckily recalled that I had just adjusted the air gap of the aftermarket crankfire sensor. Apparently .030" was no good - it needs .060". After confirming the correct setting, I changed it back and voila.

[spyerx]

is your engine stock?
Exhaust or intake mods?

How hot is it getting on track (and which track?)

who tuned it?

Thats not normal, the knock sensors won't kick in the Rev limiter, it pulls timing.

At least in my experience

[WILSPEED]

Stock 3.6L non vario. Tuned ECU. Open custom exhaust setup with Y-pipe outlet. Engine temp around middle of the gauge. I have a front mounted oil cooler with another one on the right fender (Carrera oil cooler). Both from elephant racing. Seemed like the issue kept coming on midway through the session but the car was definitely not over heating.

I was only able to add 5 gallons of 110 octane for the last session (the race). The problem then came back 3/4 into the session so it lasted a bit longer without the issue. The race was my last session of the day. By miracle, I actually won (there was a lot of defensive lines taken towards the end of the race).

The track was Willow Springs in CA (main track).

https://youtu.be/r18DVXeDsEQ <—— video of the race. Scroll to 13:25, problem starts from there. After turn 6 and turn 9 is where it keeps hitting the limiter.

[Tyson Schmidt]

Pop the distributor caps and make sure the rotor advance is working freely. If it’s sticking, it can cause I high rpm misfire that feels like a rev limiter.

[stownsen914]

In the video it does sound like a rev limiter cut. Do you have any data acquisition? Things like AFR, fuel pressure, etc. might give clues to the source of the issue.

[Steve W]

Does your original factory chip/ECU have any early cut out? If it's with this tuned chip/ECU, and cuts out early halfway through your session, then likely the software is improperly programmed/written. The ECU recognizes the chip error(s) and causes an early rev limit at around 5500 rpm about 5-10 minutes in after start up. Who's chip/tuned ECU is it?

[spyerx]

ok so this is a total shot in the dark. First, race car... it would be great if there was other data as mentioned....

What is your fuel cell and fuel pickup?

On my 964 (not a race car, but gets on the track) the fuel pickup is not ideal on the stock fuel tank - at least compared to my 997 GT3 which doesn't have this issue, at all... . Below 1/4 a tank I can get fuel starvation in higher g-load corners that felt exactly like a fuel cutoff.

if you had an AFR reading that would show as a lean condition.

That car looks like a blast.

FWIW I had good luck with Steve Wong doing a custom motronic tune on my car. Took a good 1/2 day on the dyno.

[WILSPEED]

OEM fuel cell and pickup. I don’t think it’s fuel starvation because I started with a full tank and it was happening on the front straight after T9.