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
Hard rev limit all of a sudden
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Read the manual to see if your question is answered there before posting. Many users will not reply if the answer is already available in the manual.
If your question is about troubleshooting, configuration, or tuning, you MUST include your processor type (MS-I or MS-II) and code version in your post. If your question is about PCB assembly or modifications, you must also include the main board version number (1.01, 2.2 or 3.0). For tuning/troubleshooting questions, please attached a datalog and your MSQ file to your post.
If you have questions about MS1/Extra or MS2/Extra code configuration or tuning, please post them at www.msextra.com Such questions posted here will be moved to: a temporary MSextra sub-forum, where they will be removed after 7 days
The full forum rules are here: Forum Rules, be sure to read them all regularly.
Re: Hard rev limit all of a sudden
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
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drholl
Re: Hard rev limit all of a sudden
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
Holl
Re: Hard rev limit all of a sudden
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
Thanks for thinking on this