TitaniumTT's I hope I make it to DGRR '09 Build

[NoDOHC]

Just a question: Are you running a returnless fuel system, because if not, the fuel flow rate is fixed by the pump, it either goes in the injectors or through the FPR, but it always flows the same from the pump at a given fuel pressure. With the engine off, the pump should see load equivalent to 0 psi boost. Under boost, the pump has to make 13.75 psi more fuel pressure.

I think that you are on to something, but maybe not exactly as you described it above. I think that your fuel pump is overheating, which is decreasing the available fuel throughput of the pump and is starving your engine for fuel. You can boost for short spurts just fine, but the pump can't handle the 57 psi for very long without drawing more current.

One more thing, it is likely a multi-stage impeller-type pump, which means that under boost (when the pressure is higher) the flow will actually decrease due to limitations of that design, without factoring in the change in coil resistance due to temperature. (Look at turbo-map speed lines for an idea of the curve shape).

You should have a fuel pressure correction map in the Motec... If not, you can set up an inverse trim to the 0-5V input. Maybe that will avoid going lean in the future.

[TitaniumTT]

Originally Posted by NoDOHC

Just a question: Are you running a returnless fuel system, because if not, the fuel flow rate is fixed by the pump, it either goes in the injectors or through the FPR, but it always flows the same from the pump at a given fuel pressure. With the engine off, the pump should see load equivalent to 0 psi boost. Under boost, the pump has to make 13.75 psi more fuel pressure.

Nope, it's a return system. -6 Stainless return hardline. The all the pulls up till the last three showed about 55 psi of rail pressure. The filter that plugged last week, after we replaced it I drove around for 600 miles without an issue at all. I'm starting to think that the contamination is the pump disintegrating.

Originally Posted by NoDOHC

I think that you are on to something, but maybe not exactly as you described it above. I think that your fuel pump is overheating, which is decreasing the available fuel throughput of the pump and is starving your engine for fuel. You can boost for short spurts just fine, but the pump can't handle the 57 psi for very long without drawing more current.

I agreee. Which is why on my 20 minutes communtes there is no issue or when I drive 150 miles to Daves and cruise down the highway at ~36psi of rail pressure and very little flow, there is no problem. But pull after pull after pull just over works the pump.

Originally Posted by NoDOHC

One more thing, it is likely a multi-stage impeller-type pump, which means that under boost (when the pressure is higher) the flow will actually decrease due to limitations of that design, without factoring in the change in coil resistance due to temperature. (Look at turbo-map speed lines for an idea of the curve shape).

Not sure of the type of pump that it is. Same as all the others I'd imagine.

Originally Posted by NoDOHC

You should have a fuel pressure correction map in the Motec... If not, you can set up an inverse trim to the 0-5V input. Maybe that will avoid going lean in the future.

I do, I've looked at it, and I've already started working on some sort of correction MAP. The only problem is, and admitatdy I haven't spent a great deal of time on it, if we see down to 31 ish psi, there isn't a problem, when under decel. So I'm still pondering how to input the table to account for the needed fluctuations in boost. It'll come to me one night at 3 in the morning when I can't sleep.