New fuel pump, still having nightmares

[Guest the_dj]

Well, I ordered a new MSD 70gph fuel pump on May 31. After a long long long backorder, I received it yesterday and installed it last night. After removing the stock 280Z pump and finishing the installation, I opened up the computer and took it for a drive to try and tune the fuel injection.

 

Results: The car started running 10+ percent leaner than with the stock pump, and my WOT is leaner than before even with the injectors opened as far as possible.

 

Lines are 3/8" inch stainless send from tank to rails and 1/4" or 3/8" return (not sure). Injectors are Accel 24#. Regulator is the stock regulator from the TPI setup I have on the motor.

 

Any ideas? I'm about to head out and put the pressure gauge on the rails to examine things. I'll post results from that later today.

 

It's been a real disappointment trying to get this thing tuned. I should make some progress as I get more things examined.

 

Thanks,

Sam

[Guest the_dj]

Results from preliminary examination:

 

Fuel pump primes (before trying to start) for 4.9 seconds. Pressure holds at 45psi. After prime, pressure drops to zero in about 15 seconds.

 

When starting, pressure jumps back up, then holds at 35psi at idle. Disconnecting the manifold vacuum line raises pressure to 45 psi. When throttle is gunned, pressure jumps to 45psi. (I did this in driveway not driving.)

 

When car is turned off, pressure is lost again in 15 seconds.

 

Sam

[Owen]

I'm experiencing the same thing! Pressure goes up, then back to zero. There was one time when the engine was hot and pressure held at 20psi for a couple of minutes, but that was abnormal.

 

Is it the fuel pump? Adjustable fuel press regulator? My guess would be that the regulator is somehow bad, like it's stuck open.

 

Owen

[SleeperZ]

It sounds to me like the pump has no anti-drainback valve in it. If your regulator regulates pressure, and it sounds like it is, it will hold the pressure when the pump is off. So the fuel pressure must be bleeding back through the pump.

 

Find out what the fuel pressure is doing when you are driving, or with a load on it - that will tell you if the pump can keep up with the fuel demands of the engine.

 

70gph huh? What head pressure and battery voltage is that 70 gallons measured?

[Guest greimann]

DJ,

 

It sounds like the pressure regulator is working properly. It references manifold pressure and at idle (high vacuum, no load) the pressure is reduced. At low vacuum conditions, it delivers full pressure. You really need to be able to monitor the pressure while driving to see if things are working properly.

 

Also, I have had a lot of experience tuning the original Holley 4Di system. What values are you looking at when you say the system is lean? Can you put your fuel map in a spreadsheet and send it to me so I can take a look at the numbers?

[Guest the_dj]

ALLLLrighty. I'm going to get the computer and try to give this in real detail. (map of spreadsheet)

 

For now: No matter where I put the numbers at WOT, I can't get the O2 sensor above .70. It should be at .80. At other times, idle, cruise, etc, I can hit .85+, so I know it's reading proper numbers.

 

When the WOT area is around 170 on the map, I get readings around .67. When it's around 225 on the map, I get readings around .67. No matter what I do, I can't get it to raise at WOT. No clue what the problem is yet.

 

Sam

[Guest the_dj]

What should my timing look like in various areas? Max timing? I have 36 degrees dialed in by 3500rpm (max).

 

Stock 300hp crate motor + 350tpi intake.

 

Sam

[Guest greimann]

Yep, The spark curve should be about 36 degrees at 3000-3500 at WTO. Lesser loads can take more spark to boost fuel economy, but it is not necessary for smooth running.

 

Check something in the advanced setup. There should be something called "duration offset", what is that value? Also, what is your temperature compensation at operating temperature?