Why...

I read the other post, why do you say the fuel pump is cutting out?

Because the engine falls flat on it's face?

What is the fuel pressure when these things happen?

Does it do it when the gas tank cap is off?

This looks like a shotgun approach. There is not that much in the circuit. Do you have a multimeter? Do you know how to use a multimeter if someone gave you test points to hook to and monitor when driving...

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

Yes... The engine falls flat on its face basically...

When it happens (can happen at any given RPM range, but revs less and less each time) the fuel pressure gauge drops, and is so irratic it's hard to read. Drops to ~0, jumps back up, then down again.

I haven't tried it with the gas cap off... I'll go do that now and see what it does. No I do not have a multimeter, sorry.

Someone told me to bypass all the relays and see what it does, so I hard wired the pump to come on when the key is in the on position and it STILL DOES IT... The only think left that I can think of is the ECU, or the Main FI Control Relay...

But then again, I wonder if the TPS can go bad... I was having a similar problem when the TPS was out of adjustment (wouldn't rev above so many rpms, but it didn't get less and less)... I don't know... this is mind boggling for me.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

**** with the multi meter, get a fuel presure gauge on the feed line before the FPR and see what happens to the fuel pressure when it dies. if the pressure is constant up until the point it dies chances are the fuel pump is not the problem. Heck if you wanted to get real technical, then get a ball valve, and hook that up to the fuel line after the fuel pressure gauge you already have installed.
Measure off 3000 cc's or so. Run the pump and with the vacuum/boost line on the FPR increase the pressure to your maximum boost level. so 14.7 + boost psi =
Then once you get the correct pressure set, by adjusting the ball valve, start again, and time it for 60 seconds and measure the fuel. If you have a pump that is sufficient for your application, meaning when you calculate the total fuel flow of all of the injectors combined, your pump should be able to deliver that much fuel at the specified fuel pressure, and have some headway, say 15% flow rate.
If you dont get those readings, get a new pump!

The fuel pump relay, you can take it apart and clean the contacts to fix it. But first, get that multimeter Tony mentioned and go across the two pump wires and see if you get a voltage on the meter. You should be dropping very little voltage across the relay contacts. If you do get a good drop of voltage, then fix the relay, you know .5 volts less voltage at the fuel pump, can make quite a difference in the amount, and at what fuel pressure a fuel pump can deliver. Check it out and figure out what the heck is going on.
You know, also, if you go really lean, the car will eventally just run out of fuel and misfire because of lack of fuel. Keep that in ind , and also you might want to regap your plugs to a smaller gap. That will cause the car to fall on its face also.
Let us know what you find.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

Ok just went out and ran it without the gas cap on... The pump is still hard wired, so no relays are involved with it. Took it out on the street, ran fine upto 5.5k then cut out, shifted to 2nd, ran fine up to 4k and cut out, shift to 3rd, ran to 3.5, then on the way back home it wouldn't rev above 2.5k...

When it cuts out, it's like the someone shut the car off, you can hold the pedal to the floor and it won't run (it will throw an occasional pop or fart out the intake), but as soon as you let off the gas, it comes right back to life again.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

My $ 0.02 is to check the security and mounting of the AFM.

I had the exact symptoms as you discribe on a newly aquired Z. While I was removing noted parts to clean & inspect the TB, I noticed the AFM loose, connection corroded, missing bonding strap and NO attaching hardware.

My guess is that the AFM flap was moving about under acceleration due the load changes during or between shifts, and that the follower on the potensiometer was following suit to change F/A mixtures ....bamm.

Stall!

Lift off the pedal, and she would recover ????????




Check it out !

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

hmmm.... what about the pulse eliminator (after the pump... under the car near the pump).

If the fuel pressure is dropping to 0, then either the FPR is sticking (I had 3 go bad within a month of getting them... one of them never worked) or the pump is sucking air, not sucking anything, or the pump is shutting off.

the AFM has no effect on the fuel pressure unless the AFM has the fuel pump safety shutoff switch in it(The pump will not run on this setup unless the AFM flap has air pushing it open at least a little bit... like while cranking). If the '78 does have the switch and I think it does.. it could be intermittently losing connection.

The ZX AFMs will still hook up to the older Zs, but the fuel pump will not run because they took the switch out and changed to a different system in 79. However, if you have a remanufactured AFM, chances are that it does have the switch in it, since it is cheaper to just make one type of AFM that will cover all years from '75-'83.

Have you tried clamping off the fuel return line? If this fixes it, then it is the FPR. It will run dog rich if you do this, but it is a sure fire way to definitely elimintae the possibility of a bad FPR.

In any case, if the fuel pressure is dropping to 0, the problem can't be the ECU or the ignition circuitry(dizzy) or the TPS as that only controls the spark and the injectors. The fuel pump is on a circuit all its own, and has no idea whether the car is gettiing spark or if the injectors are working.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

You have to put a fuel pressure gauge on the engine so you can monitor the fuel pressure while driving and see how it responds. If you don't have a multi meter, then you can also put a test light on the green wire going to the fuel pump. The wires are located under the carpet behind the passenger seat. Real easy to find.
It sounds like you may have a plugged fuel tank pickup, but the gauge will prove or disprove it, one way or another. FYI, the 78 ecu is not year specific to a 78, a 77 will also fit.

 

or...

A torn boot between the AFM and the throttle body.

You will not figure this out shotgunning it. Until you get a multimeter, I can be of little more help. if you can't tell what the electricity is doing, you cant fix it...

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

If you think about it though, there is no way for the pump to loose power now since it is hardwired, and it's still loosing pressure at given RPM ranges. Everyone says that there is a bunch of crap in my tank that's clogging the pickup... Makes sense... right?

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

The tank is THE problem.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

If you think about it though, there is no way for the pump to loose power now since it is hardwired, and it's still loosing pressure at given RPM ranges. Everyone says that there is a bunch of crap in my tank that's clogging the pickup... Makes sense... right?

The tank is THE problem.

Or the pump in the first place could not, or was not designed to provide that much fuel. I know the stock has a max pressure of 65psi

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

Drop the tank and check it. You probably have a damaged pickup or crud in the line. The fuel pressure will do exactly what your describing if the pump is grabbing air or if there is a blockage in the line. It doesn't have anything to do with the electricity going to the pump. The relays, coil and ignition box were not the problem. The pump works it just isn't pumping. Find out why.


It always amazes me when people blame a problem on the electricals first before testing anything. The &*^%ing manual and get a multimeter. It has a step by step procedure for testing EVERYTHING.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

Sorry I'm to podunk to own a multi-meter! I should just off this thing on some poor soul and spend all the money on my Chevelle.

So here's todays update...

The tank is clean, nothing in the lines (unless somethings stuck in the fuel rail). The fuel pump was hard wired, so there is no reason for it to loose power (thus eliminating my need to test the wires for it with a multimeter). It still does it!

So I've changed the FPR, the Fuel Pump Relay, I put a zx dizzy in thinking that it might be the old ign box, changed the fuel pump several times. Also changed the coil, and the fuel filter.

So today I changed the ECU. STILL does it...

There are no cracks in the AFM to TB boot, the contacts on the ecu are clean.

The only thing that I haven't changed is the Fuel Pump Control Relay (shouldn't matter because the pump is hard wired right now), and the Main FI Control Relay...

What else am I missing? I'm wracking my brain!

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

have you tried clamping off the fuel return line? If that fixes it, then it is a bad FPR.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

OK... I just clamped off the return line, and it ran up to 6k in every gear, both on the trip home, and the trip back... Wouldn't do it. But fuel pressure gauge was up at around 55-60 psi... Is it really the fpr? I tried earlier pulling the vacuum line off it, and that bumped the pressure up to about 41psi, and it still cut out... Wouldn't that have that have the same effect?

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

hmm.... O.k.... the fuel pressure stock is supposed to run about 30-35 at idle and go up when the vaccuum decreases.

If the pressure has to be that high for it to run properly, it sounds like either the injectors are clogged or they are not getting enough voltage or not a long enough pulse.

When the pressure goes up, it will make more fuel shoot through the injectors than it would with lower pressure.

You stated earlier:

"When it happens (can happen at any given RPM range, but revs less and less each time) the fuel pressure gauge drops, and is so irratic it's hard to read. Drops to ~0, jumps back up, then down again."

Id it still doing this without the return line clamped off? Did it still do this when you took the vaccuum line off?

Are you reading the fuel pressure at idle or when you are driving the car?

If the pressure is fine now, without the return line clamped off, I would say that maybe the injector plugs aren't getting a good connection to the injectors. Have you taken the plugs off the injectors and cleaned the crud off of them and off of the injectors?

The only other thing that I an see causing the problem, is maybe the dropping resistor pack for the injectors is almost dead. I'm not sure what the symtoms would be, except that I really don't think the whole unit would die all at once... It seems like you might lose power to one or two of the injectors, but the engine would not fall flat on its face unless it was totally losing power to the pack.(This resistor pack should be located under the drivers side access panel near the window washer bottle and the brake master cylinder).

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

OK... Just changed the FPR and it's STILL doing it. It does it when the vacuum line is pulled, but it doesn't do it if I clamp the line off. I just changed the injectors a couple of months back, and I upgraded the connectors to the quick disconnect type connector. I soldered each one on, and shrink wrapped them.

I read the fuel pressure while driving the car when it cuts out.

I haven't changed the dropping resistors... I wonder if they could be the problem? That might explain why it revs less and less each time I get on it, if they're slowly overheating and burning up or something.

I don't know... I'm growing tired of this.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

This is very educational thread. Please tell more as you find out. You've narrowed the problem down with clamping the return line. It's a fuel delivery problem some how. How many FPRs have you tried? Are they used or brand new? You've complained about spending $50 on a relay, so I'm guessing you're swapping on used. Is that true? If so, how do you know the FPR you're swapping on there arn't bad, too?

Keep is informed.
Alex

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

How do you KNOW the pickup in the tank is good? Given you can't see it, there is no way to actually test them. I've seen this problem DOZENS of times and every time it's something wrong with the tank.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

hmmm... try this... disconnect the fuel line after the filter, and stick the line in a nice large empty jar. Have somebody turn the key on so the pump turn on.

If a good stream of gas comes out, then that means the pump is most likely not sucking air... but if a non-consistent or bubbly stream comes out, then the pump is sucking air(probably means that the in-tank fuel screen is clogged) This happened on my bro's '83. As soon as I took the screen off it fixed the problem... Only his fuel pressure was never real low, it just took too long to build up so it was very deceiving.

So yeah, it could be the fuel pickup... if you are whomping on it, it could be sloshing the gas so that the pump is sucking air.. if it is messed up.

Since the fuel pressure is still dropping to 0.. it could be that clamping it off is just making the sucking air problem not as evident.

Does it rev fine when the car is sitting still, or does it mess up even then?

The dropping resistors would not be making the fuel pressure go to 0, so that seems to not be the problem.

 

Re: Where can I get a "Fuel Pump Control Relay" (different from

It revs fine when the car isn't moving.

 

Using that Logic, then...

"The fuel pump was hard wired, so there is no reason for it to loose power (thus eliminating my need to test the wires for it with a multimeter). It still does it!"

FOR CHRIST'S SAKE THEN IT'S [iOBVIOUSLY [/i]THE PUMP GIVEN WHAT YOU HAVE SAID ABOUT THE TANK, SIMPLY SHOTGUN ANOTHER EXPENSIVE PUMP ON THERE AND THEN POST THE RESULTS!

Of course, if it's still doing it, then you either aren't "hardwired" correctly, or you are wrong about the tank...

Gee, wonder how you will find out if you are hardwired correctly?

 

Hmmmm...

"If the pressure has to be that high for it to run properly, it sounds like either the injectors are clogged or they are not getting enough voltage or not a long enough pulse."

Gee, I wonder how one would verify such a condition?

And the obligatory "clean the injector and ECU connections was done according to EVERY search topic on "cuts out above..."

But we don't need no stinking $15 Mulitmeter, we need extra shotgunned parts layingaround that are far more expensive...

 

BOOOM!

Why don't we all yell "Pull" before you shotgun the next part onto the pig?

 

$50 Relay...

And a Multimeter at Radio Shack is like $15....

Wow.