Fuel delivery problems with a '90 L98 5.7L TPI in a '77 280Z

[sstallings]

Guys,

I'm still trying to get to my first drive after a long build.  Last week I had an electrical issue that a few of you posted replies, and "rsicard" identified the issue.  Thanks to everyone.

 

So now electrical issues are behind me, I think.  And I'm having a fuel delivery issue.

 

The stock '77 280Z fuel pump is supposed to be good enough for TPI according to the JTR EFI book, but if I read between the lines I think it is marginal.  No matter, my stock pump developed a slight leak between the halves of the fuel pump body, so a few weeks ago, I replaced it with a new 280Z pump "Airtex E8312" from Autozone.  After getting the timing close (more work to do there later) it idles smoothly and pressure (measured at the shrader valve) stays between 35-40 PSI at idle.  But as soon as I tip in the throttle, the pressure starts dropping until it dies at or below 25 PSI.  Even if I try to go back to idle, once the pressure starts dropping, it can't seem to recover.  No matter how careful I am, and I'm talking about barely 2000-2200 RPM, I seem to get fuel starvation.

 

I talked to the parts house, and the Airtex E3210 is the replacement 5.7L Camaro pump, which is rated at the same max. pressure, 5 PSI less minimum pressure, but about 40% more flow rate.  Flow rate sounds like my problem.  However, the E3210 is an in-tank pump that won't physically mount like the external Datsun pump without modifications.  I'd like to avoid all the mods to go in-tank if its possible.

 

I didn't find anything in the FAQs, so what have you guys found as the best/right pump for this combination?

Thanks,

Steve

 

And for those of you that keep requesting pictures, I will be posting them soon for anyone interested in this combination, my suspension mods, my Vintage Air AC install, or anything else of interest.

[NewZed]

It might be flow rate, but it doesn't seem like a pump problem.  That pump is rated to ~90 psi and 30 gph.  Have you checked for restrictions between the pump and the rails?  Fittings, tubing, filters, etc.  Clogged filter, funky brass fitting, teflon tape chunk.  something like that. You might have 90 psi before the fuel filter, but 25 psi after, for example.  In other words, the pump is fine, it's just working too hard to overcome restrictions.

 

A simple check is to disconnect the line before the rails, after the filter(s), and measure flow rate.

[hcarrickz3]

Did you change the stock fuel line that runs from the fuel tank to the front of the car? I just finished with a 94 LT1 swap and went the same route that you did using the stock fuel pump. Runs great. I did go to a 3/8 fuel supply line.

[rsicard]

Steve:

 

Not all that familiar with responding to Email on this forum.  Two things to try.  First disconnect the fuel line at the output of the pump and connect flexible 3/8" long line directly to the fuel rail on the outside the car as a temporary trial basis.  That should eliminate any fuel line restriction issues.  If the fuel pressure still drops, likely it may be a voltage drop from the fuel pump relay to the pump itself.  This can be verified by attaching another wire at the fuel pump for test purposes and extend the test wire to the drivers seat or wherever.  Then get a voltmeter on that test wire and the other meter lead to a good frame ground.  Then try the test over again to measure the voltage at the pump when the pressure dips.  The voltage should stay within reasonable limits and not significant drop.  If there is a drop in voltage, go over the pump source voltage wire connections to make certain they are good.  Also make certain there is a good frame ground on the electrical negative side of the pump.  Could be just a faulty ground.  If so, bypass with heavy gauge wire to better frame ground.  Give it a try and lets us know how you made out.

 

Rolly

[sstallings]

Guys,

Thanks for all the great information.  Here's an update.  I did replace the existing 5/16 fuel line with a new 3/8 line when I did the original swap, so its all new from the pump to the fuel rails.  I'm using the original 5/16 line as a return to the tank after the regulator.  Also, before I installed the engine, I did replace the original injectors with new stock parts so their flow rates would be matched.

 

I checked and cleaned my Summit inline 10 micron after-pump filter, which wasn't very dirty, so I'm getting fuel to the rails.  I did go to the extra work to replace the fuel pressure regulator last weekend in case the old one was sticking or worn out.  While I had the main plenum off I checked all the hidden vacuum lines and electrical connections.  They all looked okay.  And I used new gaskets to put it back together.

 

I have a 1/4 tank of fresh 91 octane gas (best I can get here) that is less than 30 days old, and after a couple of weekends of rain, I started it again last Sunday.  It runs better, but not yet well.  I can blip the throttle occasionally and it will recover and idle.  But I can't stay on the throttle at 2500 RPM for 5 second yet without it stumbling every time, and dying half the time.  So I'm closer, but not finished.  I also realized a couple weeks ago that I have to leave the gas cap off or it builds a lot of pressure in the fuel tank.  That's not safe.  I don't recall if the '90 Firebird had a sealed or vented gas cap, but I need to find out because it ran fine.  But that also means I need to check the return line and the carbon canister line, which I haven't done yet.  I'll also check the voltage at the relay to make sure its not dropping.  And I'll replace the original Datsun ground at the pump to the chassis just because its easy and good insurance.

 

With your help, I'll get there.  Can't wait to drive it   I'll post more results soon.

Thanks.

Steve

[sstallings]

Okay,

It's been months since I posted on this forum, but I'm still trying to find a fuel pressure issue.  I have replaced everything.  And by that I mean all fuel line, return line, fuel pressure regulator, fuel filter, in-tank Aeromotive Phanton Stealth fuel pump, ECM, relays, and on and on.  I still have to wait about 30 seconds for the pump to get the fuel rails up to 40 PSI, then I can start it, and it will run between 30 seconds to 5 minutes before stalling due to no fuel pressure.  After start-up, pressure immediately drops to about 20 psi, and continues to drop each time I blip the throttle.  The warmer the engine is, the faster this all happens.  Each time the fuel pressure drops drastically, I hear a rapid chattering from under the hood.  I've isolated that to the fuel injectors, at least 5 of them.  All of them on the driver's side, and at least one or maybe two on the passenger side.  These are a matched set of (rebuilt) injectors I bought from Rock Auto last year when I noticed that my original injectors were not all the same (the engine had just under 100K miles on it when I bought the 1990 Firebird it was in.  But it ran fine.)  Now I'm concerned that these rebuilt injectors may be shorting out, which is causing the chattering and loss of fuel pressure.  My fuel pump gets a constant 12.6 Volts on cranking and 13.6 to 14.0 volts in run.  Has anybody had any experience with this issue?

Thanks.

Steve

 

Specs:  1990 5.7L TPI with MAP and all stock emission parts in 1877 280Z, JTR conversion, WC T-5 manual trans, and suspension/brake upgrades.

[NewZed]

I checked and cleaned my Summit inline 10 micron after-pump filter, 

I quoted this post just to illustrate.  There are two sides to building pressure - what the pump puts out and what the regulator holds back.  You said that you've replace many things but it's not clear where those things are or what they're rated to do .  For example, your 10 micron filter might be designed for a low rate carb pump.  ?? Who knows.

 

But, what you want to do is break the whole system in to parts until you narrow things down to the source of the problem.  You've spent enough time and money to justify some simple experiments, like maybe running a line with a gauge and your FPR directly back in to the tank without the filter.  That will isolate the most basic elements, the pump and the FPR.  If everything is fine, pressure jumps and holds to where it should be, then insert the filter and see what happens.  Or just take a leap and remove that filter for a test.  A few particles for a short while won't hurt anything.

 

This is basically what rsicard was saying.  Isolate the components.  Your injectors can't lower pressure unless they dump a ton of fuel, so they are not likely the cause.  The chattering might actually be some sort of power loss.  Maybe that's the problem.  Regardless, you have to isolate the pieces.  

 

The fact that you have to wait for pressure to rise indicates a restriction.  If I had to guess, I'd say it's your 10 micron filter.  Why not just run the big ugly paper filled can?  It's big to allow high flow.  And the injectors have their own screens.