MSefi.com read only forum (Jan.15,2018)

Sorry to be late to the party, but I KNOW what this problem is. My big block Chevy did almost exactly what your description and datalog report.
Not enough fuel pressure under load.

OK. Lets prove it.
Put a pressure gauge right at the injectors and monitor it right when the problem occurs.
My problem was caused by a bad relay. It didn't allowing enough current to get to the fuel pump, causing the pump to slow down, the pressure dropped and the mixture went real lean. The trigger +/- dropped and the tach signal went all over the place. It took me weeks to find it. All my parts were new!

Just because it's new, doesn't mean it's good.

A defective 5 dollar relay had me pulling my hair out...

See "8 pin HEI Dwell settings".

Good luck and let us know.
Holl

I have not looked at the forum in awhile so this is a late reply. I actually have a fuel pressure gauge on the fuel rail so will give it a look one of these days when i get a chance to run it at high RPMs thanks for the tip, hope this works as it is driving me nuts

I used a 5 foot long fuel line and brought the gauge into the car so a passenger could watch it. Probably not the safest way, but it worked!
Holl

I think we have finally zeroed in on what is causing the hard rev limit, it is in the base ignition settings and is called tach signal masking. This was set at 50% and when I changed it to 20% the tach would go to 11,000 RPM vs the 6,000 limit I was experiencing before. If I set the masking to 10%, the RPM will go over 13,000. This is using the stimulator as the car itself would not run over 7,000. Looking back at when this first started happening is when I installed a new Autometer tach and a wide bank O2 sensor. We chased the O2 sensor circuits thinking this was the problem as I had put my old tach back in after that and still had the 6,000 rpm limit. I don't know why this happened but did not spot it until I loaded the msq in TunerStudio vs Megatune and went through the settings again. Anyone have this experience before with the tach masking signal percent or understand how this works?

Thanks for thinking on this