I think my fuel pump is defective. :/

[KDMatt]

I recently had my gas tank boiled/flushed and recoated. I took the opportunity to replace the pump, but now I'm only getting 9 psi. :sick:

I used a cheap/offbrand pump that is supposedly the appropriate modern replacement (which I'm now regretting).

The question I'm wondering though, given that there's a small strainer sort of "built-in" to the tank, is there any likelihood that any coating process could have accidentally obstructed/covered over this and is now preventing enough gas from getting the pump, or is this truly just a case of "you get what you pay for?"

I'd like to know who I should be annoyed at tomorrow: the tank refinisher, or the fuel pump manufacturer.

Oh, and in case this doesn't show elsewhere, car is a '76 coupe, stock EFI. Thanks!

[FastWoman]

I *think* there's an intake screen in all these tanks, but there are some variations from year to year. I know my '78 tank has an intake screen. That said, if you acid-washed the inside of your tank, that could have eaten up the intake screen. Also if you coated an intact intake screen with epoxy, that could clog it up. So you could have problems either way.

Some of us have inserted coarse inline filters between the tank and pump as a pre-filter. I'm running one on my system, and it seems to flow quite well. In hind-sight, I'd probably have installed one of those clear, decorative polycarbonate bodied fuel filters of a type that's popular in an American muscle car. That would give you a good view of what's in your fuel line. I think fuel flow would be adequate for EFI, so long as the filter is a coarse one and not some fan-folded paper filter.

It sounds like your fuel pump MIGHT be for a carbureted system, and hence lower pressure. You can still get the OEM fuel pumps. I bought mine from a local Nissan dealer. It's an excellent pump that will be hands-down better than anything aftermarket you'll find.

[Zed Head]

Actually, you should be annoyed that you don't know for sure what the problem is. Is it a clogged inlet, a bad pump, a clogged pump outlet, a blocked fuel line, an open FPR, etc. Dig in a little and determine what's happening, or not.

To FW's comment- what is the brand and model number of the pump you bought? Were you getting 36 psi with your old pump (and dirty tank)?

[sblake01]

Sounds like he got one of those Airtex or Delphi fuel pumps. Never heard anything good about those. The two I helped people put in their cars both failed, the replacements failed and they both ended getting OEM pumps.

Edited June 6, 2011 by sblake01

[KDMatt]

@FastWoman

I've been keeping one of those clear, small filters between my pump and my tank for a number of years now, "Just in case."

Right now I can see that gas is flowing from the tank to the pump, but I have no way of measuring how much.

@Zed

I intend to do quite a bit more digging, but I tend to lose a bit of motivation when the clock strikes 12 AM and the JuneBug frenzy has commenced (i.e. millions of the dumb beetles swarming my work light).

Blakey's hit it right on the head. The fact that he could tell it was an Airtex pump without my having to say anything presumably speaks volumes about it.

I was getting pretty decent pressure with my original setup, it was just struggling a bit under load/running a bit lean. This is what initially prompted me to drop the tank/replace the pump (given that I tested my EFI pretty extensively by the book, and everything seemed to come back okay).

I initially skipped an OEM pump just because they're so spendy... perhaps this wasn't the wisest decision... :tapemouth

I'll swap the inlet and outlet hoses around on the tank though, just to make sure it isn't blocked.

EDIT: On a total side note, when I yanked the old pump out, the electrical terminals for it were excruciatingly corroded, I'd be amazed if it were getting full voltage. So I suspect this, in conjunction with a dirty tank, were giving me the problems I was experiencing last fall.

Edited June 6, 2011 by KDMatt

[Zed Head]

June bugs. I remember those guys. They're the big ones, like giant Japanese beetles. Don't have them in the PNW.

For what it's worth, I have had an Airtex E8312 (the high pressure FI pump) in my car for 1.5 years and have had no problems. Bought it new at Schucks. Have you pinched the return line to see if pressure rises? It might give you more clues on fuel flow versus weak pump.

You can break these problems in to pieces and get to a point where you're more certain what to fix.

Edit - changed some stuff.

Edited June 6, 2011 by Zed Head

[KDMatt]

That's the same pump I've got Zed. Is yours pretty loud?

Mine's making this horrendous racket.

[Zed Head]

I can hear it but it's just a smooth "whir", no racket. I insulated the mounting points with some thin rubber sheet to keep it a little quieter inside. I can barely hear it from outside the car. It sounds like I imagine a good pump should sound.

If the "racket" is an erratic, grinding noise maybe you do have a bad one.

[FastWoman]

If you want to look at your return fuel flow, just get a long, clear vinyl tube, and connect it to the return line on your fuel rail. You can watch what comes out, and you can either pour it into a gas can or return it directly to the tank through the filler neck. When my pump was just starting to fail, I found there was no return.

[darom]

The PO's Airtex E8312 on my 76 showed all healthy signs (good pressure at idle and with a starter solenoid wire disconnected test), but under load I had some extreme lean conditions and engine bucking. I replaced it with a MSD2225, although a word of caution - this pump is a pusher and shouldn't be used as a puller. I found it out later after reading MSD forums. Mine works fine for now (I will keep my fingers crossed). MSD techs advise people to properly mount them below the fuel level of the tank. I guess it works due to a relatively low fuel pressure in stock Datsuns (under 40 psi).

KDMatt, put a voltmeter on your fuel pump electrical wire leads, remove the starter solenoid wire, have your assistant turn the ignition key to START and see what voltage you are getting at the pump. It should be almost exact as the battery's one.

[KDMatt]

So ... an odd turn of events... the car is running now.

I drained the tank and disconnected the pump... I then just hooked up a long hose to the inlet on the tank and stuck it into a container filled with gasoline, when I gave the pump some power I got a few 'spurting' and whirring sounds before it then silently took up the "slack" and my pressure gauge slowly rose to 37.

I thought this was odd (and also grew concerned, worrying that my tank was, indeed, at fault) ... but I hooked my pump back up to the tank anyway. This time, when I turned the key, it started flowing like it was supposed to... and voila, the car starts!

This just strikes me as odd... nothing has really changed, except maybe now the pump is primed or something?

... also darom, I'd be curious to know your setup, and where/how you had issues with your car under load.

EDIT: I'm mostly curious because the E8312 is also listed as a replacement for the turbo models. That being the case, I imagined it being more than adequate for a N/A car like mine.

Edited June 8, 2011 by KDMatt

[FastWoman]

KDMatt, your pressure should rise higher than 37 psi static pressure -- more like 45 to 65 psi, as I recall. It sounds like your pump might be failing the same way mine did. It would pump just enough pressure to pressurize the fuel rail and provide some return, but the pressure would start to sag as the pump warmed up, leaving my engine in a lean-running state and with no return fuel flow to the tank.

You're going to find out a lot more by hooking up your fuel pump, pulling off the return hose from the fuel rail, and hooking up your long hose there. Put your fuel pressure gauge on a "T" fitting between your fuel filter and fuel rail. Then leave your engine off, but hot-wire your fuel pump. If you do this for a long time, then also put a battery charger on your battery. Now fire up your fuel pump, and watch the gauge. You should get 36.3 psi with the engine not running, as I recall, and you should get a healthy return fuel flow. (Mine reached this pressure, but the return flow was meager.) Then just let it run for a while. Take a break, and come back to it a half hour later. It might look a lot different. (After 15 or 20 min, min was down to 25 psi, with no return fuel flow.)