I'm not sure if these questions belongs here or in Tech/General Engine, so I'm posting them in both.

All questions pertain to a 1988 TPI 350 with a Mass Air ECM.

Question 1: What other relays, if any, besides the Fuel Pump relay, are involved in the fuel pump circuit when you turn the key on?

Question 2: What is the under dash, Fuel Pump fuse rating supposed to be - 20A, 25A,or what?

Question 3: Can old wiring in the FP circuit cause the resistance to go up, thereby requiring more amperage to trigger the FP when the ignition is placed in the on position?

Question 4: If the answer to question 3 is yes, then how can that be fixed?

Question 5: This one's for those of you who really know your stuff - what does it mean when you jump terminals A & E (1st and last) on the FP relay harness, while using a 20A fused jumper wire, and the FP doesn't come on until you tap the terminals together (using the jumper wire) several times?

Question 6: Would it be advisable to bypass the FP relay by installing a toggle switch between terminals A and E and placing it on my dash - switching it on when I want to start the car and off when i turn it off?

Here's some info that might help you in answering the questions above:

*Its a brand new FP relay;

*when I put the key in the on position, I hear a click in either the Mass Air Flow relay, or the Mass Air Flow Burn-Off relay;

*the ECM does activate the FP relay for 2 seconds when the ignition is placed in the on position;

*there are no codes set;

*the FP is a high flow Holley in-tank repalcement;

*when I drive the car, after it finally starts, it seems to run fine and has power;

*all of the circuits are connected and seem to be working fine; and

*when the car is running, I disconnected the FP relay and it still continued to run so I know that the oil pressure switch is not involved in this problem.

Whoever can figure this one out is the all time guru of TPIs as far as I'm concerned

 

I don't know much, but...

I do KNOW the MAF Bur-Off Relay and the Fuel Pump relay are the same PN.

Try switching the plugs, to the opposite relay, then you chould be able to eliminate, or pinpoint, that relay circuit as the culprit.

My MAF Burn Off code 36 kept going off. I switched the plugs, expecting a fuel pump problem, but getting no code 36, and sure enough, no code 36!

 

I am not sure I understand what your exact problem is but I'd guess the fuel pump doesn't run sometimes?

Answer 1: Yes, the MAF relay is activated by the FP relay so I would recommend disconnecting both MAF relays while you're trying to diagnose the FP circuit. They will only draw extra amps and confuse you with their clicking.

Answer 2: There is no FP fuse under the dash. The FP draws from the orange wire under the hood, through the main inline 20A fuse (by the battery).

Answer 3: Sure it could. Bad connections can create extra resistance, same with wiring hack jobs (found too many when I bought my car), old solder connections etc.

Answer 4: You'd need to FIND the bad spot and fix it. Or just replace every wire. I think the first option is easier.

Answer 5: That could mean two things: 1 - bad fuel pump, 2 - bad intermittent wire somewhere by the relay that gives you good contact after it's jiggled a few times.
A good test is to put an amp-meter (on 20A setting) on terminals A and E. Watch the amp reading. If you get amperage, the fuel pump IS drawing current. If you get no amperage, it's a circuit problem.

Answer 6: By all means no. The circuits in the car were designed to run the way they run and bypassing them doesn't solve the problem. What if you get into an accident, the fuel line ruptures and starts pouring gasoline? If you're unconscious, who will shut the fuel pump off? Don't want to lose a fellow 3rdgenner. I strongly advice against the switch.

Ok, hopefully you can keep troubleshooting with my answers.
I think your question #5 says a lot so it looks like you'll find the source of your trouble soon.

Lou

 

Lou, you're the man! Thanks; I'll give your suggestions a try. However, one thing I failed to mention, for brevity, is that the car was once a 2.8 MPFI and is now a 5.7 TPI. I had the wiring harness modified by Leonard Sparks (chevythunder.com) to work with my TPI set up. That's probably why my Mass Air Flow relays are by my battery, in the front of the car and I have a 20A fuse under my dash for the FP.

One question though, with regard to your response to question #5, so if there is amperage and the pump isn't charging, then that's a pump problem for sure, right? There's nothing else in between the harness and the pump that could be sucking up that amperage?

 

Correct, if you measure current going from pin A to pin E but the pump is not running, it's only because it's stuck. And yes, this can easily happen. I learned the hard way when my fuel pump died a few times (may it rest in peace). When the pump is stuck, you should see a slightly higher current going through it than if it is spinning and pumping fuel.

You can perform another test if you wish: block the front wheels, jack up the rear of the car, (might need to remove the heat shield above the muffler), disconnect the fuel pump connector (in front of the tank, on the wall behind the rear seats - from the outside) and give the pump 12V from a battery (not from a charger). If you see the same behavior, it's the pump.

Lou

 

GOD, I hope it's not the pump. It's brand new. The car's been a work-in-progress since 2001, so the new engine and pump have maybe 50-60 miles on then, at best. Several months ago, I had my guy change out the old fuel guage sending unit and that's when this problem first reared its ugly little head. So I'm hoping that it's maybe a loose connection or something. WHAT A NIGHTMARE THIS CAR HAS BEEN!

Thanks for your help; I'll keep you posted.

 

If the car has had the same tank of gas since 2001, I would not be surprised if the pump is plugged up. I know what pain it is to drop the tank, believe me. That's why you need to troubleshoot well before replacing the pump. A friend of mine asked for my help swapping a fuel pump and after we were done, it turned out that he had an electrical problem. You can imagine how much I wanted to kick him!

Lou

 

You're not gonna believe what the problem was. I'm leaving on vacation tomorrow and I stayed home from work to run the errands that I need to run before I go. Instead, however, I started working on the Camaro and I finally figured out the problem - after the whole day had passed!

Anyway, as you know, there's a 3 prong male harness that connects to the pump; it plugs into a female 3 prong connector riveted to the body of the car, behind the rear seats. The harness' power wire (grey) was damaged somehow; probably when they replaced my sending unit. The wire sheath was in tact, but I could see that the it had been stretched a tiny bit and that the wire inside the sheathing, right at the 3 prong weather pack connector, was crimped in a weird way - telling me that it's probably torn on the inside.

So I charged up the pump and wiggled the power wire around and sure enough, the pump would start and stop. To be sure, I isolated the power wire in a position that caused the pump to run and I wiggled the other wires to make sure that they too weren’t damaged; they weren’t.

Rather than rebuild that connector and risk some sort of short from water getting up into there, I twisted the connector around itself until it was nice and tight; wrapped some electrical tape around it for no good reason (just seemed like the right thing to do at the time), then plugged it back in. The pump spun to life and stayed on no matter how much I poked, prodded and wiggled the wires. I figure that it'll continue to work this way since by spinning the connector around itself like I did, I secured the connection in the torn wire.

I tell you, as much as I hate this car, solving these little mysteries really makes it worth while. Thanks for all your help.

 

Thank you for reporting your findings and solution and of course congratulations on finding it.

Once again, it paid off to troubleshoot thoroughly before dropping the rear axle and gas tank. Good job.

Lou