Competition Engine quit after hard run!

[JTroiano]

What about the fuel having to come to a dead stop in those little lines. Maybe we are all wrong and the fuel is cavitating in the lines and causing air in the lines?



Jon T

 

[Huff N Puff]

Hey Guys

Its plausible that high cylinder pressure is causing the air lock. What is puzzling me,is the irratic operation of the fuel pump. By the way Greg I have the fuel Preporator on my truck. My theory is the ECM is having a logic issue. Or the VP44s electrical drivers are over heating because we are operating them at there absolute limits. There is a way to limit the electrical curret to the drivers. I am going to try a few things. By the way Greg how did the switch work on by passing the fuel pump control. Merv

 

[Lsfarm]

Cavitating and Bypass Switch

Hi Merv, the bypass switch made the pump run, even during the times when before, the pump would have been erratic, but it also back-fed 12v to the ecm which caused some surging during normal driving. So the bypass switch had to be used only when we thought we may be running it hard. It is not a blanket cure. Maybe a diode in the line would prevent the backfeeding to the ecm?



Hi Jon, as for cavitation, my understanding is that cavitation is created on the suction side of a high pressure pump, or at the inlet side of a pump. The air we are experiencing is in the injector lines down line of the injection pump and on the high pressure side of the pump. So I don't think we have cavitation in the lines, there could be cavitation at the VP pump inlet if it wasn't getting enough lift pump pressure or volume.



In aircraft applications where a high pressure pump is needed for hydraulic pressure, the supply side or the resevoir is pressurized to provide enough head pressure so that there was no cavitation of the high pressure pump. Usually the resevoir is pressurized with air pressure which also reduces foaming of the returning high pressure oil. Sort of like our lift pumps provide steady [we hope] head pressure to the VP44.



We installed the FASS, and it sure runs better, but we still aren't satisfied that it won't stall if we lift abruptly. Snowy roads are keeping us from more testing.



Take care, Greg L. TheNoiseNazi



Great Lakes Diesel Works

DTT transmissions

Performance Shop

 

[FreeBMW]

what about a blow off valve (BOV)? I know a vendor had posted a few pics of a test setup they were working on. It was throttle activated like a exhaust brake.

 

[Lsfarm]

Ecm voltage fluctuations

Just as a follow-up to the intermittent running of the lift and pusher pumps.



On my '01, I have had a digital read-out fuel pressure gauge for about a year now, and it often showed a drop to about 9 psi after a hard run and then lifting way off the pedal. [normally shows 16+psi] I always thought it was a bad ground or loose connection at the pressure sender causing the short duration low reading.



But today I installed a few new fuel lines and a new set of injectors. So while I was in there I hooked up the pressure sender nice and secure, verified all the connections were clean, corrosion free and tight. The test drive showed the same drop to 9psi when the throttle was let off after a WOT run. So I hooked up a temporary direct reading mechanical gauge, and road tested it again, same thing.



So for some reason the ecm is dropping the voltage to the lift pump or is giving it short pulses of current during this 'let-off' scenario. I can't hear the lift and pusher pump in my truck, too much noise insulation, but the readout on the gauges pulses. But on the twin-turbo instalation on a customer's truck that I mentioned earlier, we could clearly hear the pumps pulse.



I haven't a clue why this was designed into the ECM, Any ideas??



I'm running a single PDR HX40 turbo, so I'm not getting the stalling that is discused at the begining of this thread.

But I am concerned that it could stall so I'm trying to remember to let off the pedal slowly.



Greg L The Noise Nazi

 

[BillGotthelf]

My first run at Moroso with the new twin setup at the end of the 1/4 mile I let off abruptly and as I turned off the track the engine was not running. Could not restart until we bleed injectors. My FASS pump was running the whole time. Only thing I could guess was air from cavitation of vp44 because of the sudden change in fuel pressure or blowoff from the 75lbs of boost pushing fuel back up injectors. Next couple of runs I let up throttle slowly and had no more problems. It never did this with my hx40 and DDIII's.