Hey guys, I have installed new injectors and a AFR on my 85/L98. It runs great and I have good fuel pressure while it's running. When I shut it down I can watch the fuel pressure fall off completly within a minutes time. Slow starting too. I suspected the fuel pump in the tank. I did a pinch test on the line and confirmed my suspicion. With the Mild Comp cam, Edelbrock heads and intake, Heddman hedders, dual exhausts, ported plenum, chip, 24lb injectors, and the AFR, should I buy a stock replacement or can someone suggest a good aftermarket pump? I appreciate any help.....thanks,

Troy

 

a stock pump in good working condition should be able to support those mods. if you decide to upgrade (for future mods), Walbro makes a great pump.

 

Which line did you pinch, the feed or the return? Was the hose totally closed? Just double checking.

RACE ON!!!

 

I pinched the feed line after I had pressure on the system. It seemed to be completley closed. The pressure held which would indicate that the valve, (Shreader ?) in the pump was no longer able to hold pressure. I used needle-nose vice grips to pinch the line. To check the regulator pinch the return to the tank. Pinch both to check injectors.

 

I was just making sure. It seems a shame to replace the whole fuel pump for a check valve. I wonder if there might be an independent check valve you could install?

RACE ON!!!

 

I'm not really sure but chances are the pump is the original. I would just as soon replace it with new stock or better. Got any suggestions? One dude said Walbro....not familiar with them. Have you heard of or had any experience with aftermarket pumps designed for TPI systems?

 

Walbro is really good stuff. They are higher volume pumps. Based on your opening post, you'll be fine with a stocker. With the Walbro, you'll spend more money and gain nothing.

RACE ON!!!

 

Thanks for the info man. Stock it is.

 

Go over that one more time, something got lost in the translation (or my brain's not hittin' on all 8).

When you pinched the return line what was the result?

When you pinched the feed line, what was the result.

Jake

 

I pinched the "feed line"......"after", not before, I pressurized the system. The pressure held in the system "above" the pinch, indicating that the fuel pump no longer has the ability to hold pressure. I did not pinch the return. I had just replaced the regulator and injectors with new stuff. After the pressure held for a few minutes I removed the pinch....fuel pressure went to zero. Some people pinch the line and then apply pressure. Since the pressure guage is attached to the fuel rail, the pressure wouldn't reach it if the feed was pinched. I used the guage to tell me the rest of the system was holding pressure and it was. The only thing left was the fuel pump....after making sure there were no leaks in the lines.

 

Did that make any sense? I just approached the problem from a different direction.

 

Here's what I've done in the past.

There are four general areas which would cause the pressure not to hold once the pump shuts down: At the pump, one of the lines/connections leading to and from the pump, the FP regulator or injector(s).

The ones at the pump can be ignored if you choose; the check valve and pulsator. But if it's the regulator, line, or injector(s), well that's a different matter; gotta fix them.

First, I use the flexible hoses that are in the engine compartment, on the passenger side, front of the block down low where the mechanical fuel pumps use to be installed. I don't use the lines at the back of the car near the fuel filler. My shop manual shows the ones at the front are the ones to use for the 86'.

I energize the pump, then pinch the return line while watching my fuel pressure gauge. After the pump shuts down, if the pressure holds, then I know the cause of the pressure not holding HAS to be downstream of my pinch. From my pliars back toward the tank.

Why do I conclude that? Well, because the pump is only activated for about two seconds, then it shuts off. So if the pressure holds, and I know the pump is not applying pressure (since it's off) then everything on the pressure side from the tank up to my pinch has to be sealed up tight. Otherwise the pressure wouldn't hold.

So that would eliminate the regulator or injector(s), and the pressure line/connections since all of of them are upstream of my pinch. So from the pump, through the pressure line, up to the fuel rails, to the regulator and injectors then - on the return route - to my pliars; all are good to go.

That leaves me with the return line/connections (from my pliars back to the tank) and the pump. If there is no return line/connection leaking, all that's left is the pump.

Now, since it has to be the pump check valve or pulsator, I call it a day and go have a cold one. I ignore it because neither has caused any drivability problems for me.

The reason I don't use the pressure line is that with me pinching it, once the pumps shuts down and the pressure drops, I wouldn't know if it's the regulator, injector(s), return lines or the pump; too many possibilities.

What I mean is, I energize the pump and my FP gauge jumps to 40 whatever. I then immediately pinch the pressure flex hose; then the pump shuts down. The pressure immediately drops - well what caused it to drop? Could be the regulator, injector(s), one of the lines going to the back to the tank, or the pump.

See what I mean?

Hope this helps.

Jake

 

If the pressure is dropping under normal circumstances, it could be the regulator, the injectors or the check valve in the pump. If the pressure drops, when the return line is pinched, you know it is the injectors or the pump. The return line isn't supposed to hold pressure, so pinching the return line only tests the regulator. After the regulator is proved good, pinching the pressure line, with the system under pressure, tests the injectors. If the system holds pressure with a good regulator, then the injectors are good, too. That leaves, by the process of elimination, the check valve.

I wouldn't be important which line you pinched first. However pressure has to be established before pinching the feed line. If the pressure drops with the feed line pinched, it can only be the injectors or the regulator. We just found out how to test for the regulator. If the pressure maintains with the feed line pinched, well we've covered that.



You flip flopped in the hoses, here. You are correct, except not the line going back to the tank, it's never pressurized, or the pump, which is ahead of the clamp. The clamp prevents pressure from bleeding back to and testing the pump. The pump is only tested by the process of elimination, after the injectors and regulators are proved good.

Absolutely!

RACE ON!!!

 

you might look into the racetronix wiring upgrade. pump voltage makes a big difference in both pressure and volume. They sell a plug and play kit with a walbro pump.


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