olddragger

iTrader: (3)

Trying to learn here. I have another thread going on concerning the fuel starvation issues some face. Does anyone know this?
Olddragger

StealthTL

iTrader: (1)

The fuel pump has two relays, one runs the pump thru a resistor, lowering the rail pressure - you could start there....

S

olddragger

iTrader: (3)

Yep aware of that one--- just wondering about the differant parmeters associated. I know cold start up and warm start up stuff, but my real ? is how much does fuel demand play into this--if any? Fuel pumps are always designed to pump more than the engine needs but since the invent of the nonreturn system i have gotten a little confused. I am wondering if our pump is only a two speed because of start up issues?
olddragger

dannobre

iTrader: (3)

According to the Service Highlights book....." the required fuel amount is determined by the engine speed, battery positive voltage, and ECT"

So there is a lookup table in the PCM that looks at what it thinks the engine needs based on RPM, battery, and coolant temps....and will turn on/off the relay.

I'm surprised that load isn't one of the parameters for this. I makes me think that it is very generous in calculating the time to turn it on/off.

olddragger

iTrader: (3)

so load is a constant? The ect is controlling the injectors, but I wonder other than at start up is the ect controlling the pump at all? I have to work this w/e but the next I will hook up the ole ddm and drive her for a while and see if I get any differant readings at differant rpms etc.
olddragger

dannobre

iTrader: (3)

I would think that the ECT calls for more fuel when cold.....so it would increase fuel pressure sooner when colder?

The fuel pump control only gives more potential.....not higher pressure at constant load on the pump...that is controlled by the pressure regulator. They use the differing speeds to lower the stress on the pump unit when it high output isn't needed

olddragger

iTrader: (3)

Ok I get you. High output is used at all start up(turn the ignition on) I think --due to pressure leak down, but switches to low almost at the time the engine starts.
I would think that while on the track the high setting would be on all the time?
What I am getting at is this--voltage delivered to the fuel pump makes a huge differance in the pumps output. A 2 volt differance can make a 30% differance. Now if the pump is switching back and forth on the track then an override switch may solve our problem but adequete voltage has to be insured. If we are only drawing --saying 10.8 or 10.5 volts when we should be at 12 or at least a 11.7 or so then we may need to rewire with bigger wire or something. I need to find out how can i test the voltage being delivered in the highout mode. I dont know if the jumper wire test at the fusebox is activating the lowspeed or the highspeed setting.
olddragger

StealthTL

iTrader: (1)

Sounds like time to run some wires....

Run wires to lights for each relay and test your theories about when it turns on/off.

You could even run a bypass switch to run "high" whenever needed - screw the strain on the fuel pump. I have done things to that pump that would make you weep - it will not quit under pressure.

I had a "weak" pump from new, it was replaced under warranty and the new one is better than the old EVER was!

S