Odd Fuel Cut, No overboost?

[MazdaspeedSix]

Having all kinds of headaches. Installed high pressure internals, all went well. 2 months later notice idle FP of 190-220, would build slowly under part throttle but die under heavy load. Researched online figured out it was the relief valve. Replaced with a Pt-p unit. Fuel pressure now looked great, 400+ at idle and whatever I command at WOT 1800-2000. I'm getting fuel cut now however, at first would happen somewhat randomly, especially in hard first gear pulls. Checked for boost leaks etc. Got slightly better. Then I put FP settings in ATR back to stock levels and the issue is *almost* gone. Now I only get it at around 6300 rpm. I have no overboost and my AFR's look good until about 1/4 second before the cut. Drops from 11.8 to 11.2 or lower then I have the cut. I was still suspecting a boost leak but my boost is very close to target all through the rpm range I attached a log, you can see at 6.96 seconds it starts to richen then cuts at 7.12 seconds, 6302rpm. Any help would be greatly appreciated.

[MWSpeed6]

You should log other parameters like throttle position, WGDC and spark advance. Anyway, the only thing that seems abnormal in your log is the spike in fuel pressure from 1818.71 to > 2000 PSI at around 6157 RPM. The AFR goes to 29.29 while still in boost and that probably explains the momentary loss of power. I'm not sure what this could be, but it's strange to see the pressure spike and the momentary drastic change in AFR.

[Braden @ COBB]

Having all kinds of headaches. Installed high pressure internals, all went well. 2 months later notice idle FP of 190-220, would build slowly under part throttle but die under heavy load. Researched online figured out it was the relief valve. Replaced with a Pt-p unit. Fuel pressure now looked great, 400+ at idle and whatever I command at WOT 1800-2000. I'm getting fuel cut now however, at first would happen somewhat randomly, especially in hard first gear pulls. Checked for boost leaks etc. Got slightly better. Then I put FP settings in ATR back to stock levels and the issue is *almost* gone. Now I only get it at around 6300 rpm. I have no overboost and my AFR's look good until about 1/4 second before the cut. Drops from 11.8 to 11.2 or lower then I have the cut. I was still suspecting a boost leak but my boost is very close to target all through the rpm range I attached a log, you can see at 6.96 seconds it starts to richen then cuts at 7.12 seconds, 6302rpm. Any help would be greatly appreciated.

It looks like your fuel pump is running away on you, right before the cut you can see the pressure spikes to over 2000psi which would trigger this type of behavior depending on how your fuel pressure targets and max's are setup. I've seen this on the PTP pumps when doing testing and there wasn't any way to control other than slowly ramping in fuel pressure down low and hoping it didn't run away at the top of the power band. This behavior on the dyno resulted in what feels and sounds like spark blow-out.

Thank You,
-Braden @ COBB

[MazdaspeedSix]

Ok I was thinking it had something to do with runaway, as did John at PT-P. He tried helping me with the map to compensate by lowering commanded fuel pressure in the upper range but it didnt help much. Ill try setting it do build up slowly/linearly and see if it helps. Thanks!

[MazdaspeedSix]

Ok so staggering the FP...starting at 1600 +/- building to 1798 for 1k rpm then tapering down to 1600+/- did actually help a bit....was hitting cutoff or whatever it would be called at 6300 or so, made it to 6400 and the cut didn't feel as violent/abrupt. I reflashed with the same map just with a 6300rpm rev limit. Ran a log and everything looks fine. I think I'll just leave it at that and not give the pump (KMD Internals and PT-P Rail Valve by the way) a chance to go overboard closer to redline. Thanks for the help Braden I really appreciate it. And MWspeed it wasn't a momentary loss it was a "face, have you met wheel?" event. Thanks for the thought though of course.

[MWSpeed6]

It looks like your fuel pump is running away on you, right before the cut you can see the pressure spikes to over 2000psi which would trigger this type of behavior depending on how your fuel pressure targets and max's are setup.

Just trying to learn more here... So exceeding the pressure limits of the map actually causes the ECU to cut fuel delivery?

[Braden @ COBB]

Just trying to learn more here... So exceeding the pressure limits of the map actually causes the ECU to cut fuel delivery?

Yes, there are safeties built into the ECU for situations like this. The ECU cannot determine the actual amount of fuel being delivered and so it shuts things down quickly to ensure engine safety.

[MWSpeed6]

Yes, there are safeties built into the ECU for situations like this. The ECU cannot determine the actual amount of fuel being delivered and so it shuts things down quickly to ensure engine safety.

Thanks Braden!

[MazdaspeedSix]

I wanted to make a comment based on my own post. When I reread it it sounded like I thought John (PT-P) wasn't helpful, at least how I read it. He was actually extremely helpful and custom built me numerous maps focusing on the FP settings. When I say that they didn't help it kind of points to the rail valve doing its job so well and just wanting to build pressure.