Not really sure where to go with this problem the 88 is having.

My fuel system is as follows: Racetronix Walbro 255 pump into a Racetronix wiring harness which connects to the battery negative cable as a redundant ground and another wire to the alternator. The racetronix harness has an additional in-line fuse and I believe a relay, but I was not the one to install the harness - it was done when the whole engine was swapped from the 86 - so I'm not sure entirely how it works and Racetronix doesnt seem to be helping. It was done in 2013 and now I don't remember everything about it.

This leads into a TPiS AFPR and 42lb injectors (from FIC), with a FP setting at 44psi. All of this equipment has less than 20K miles total on it, 7-8 K on the 86 before the accident and 12K on the 88, the Walbro pump has only 12K.

2 weeks ago, I pulled into a gas station to fill up. Filled the tank, car would not catch over. When it did, it stumbled badly, then died. Tried several times. No amount of throttle body opening seemed to help it. Had no scanners or anything with me to troubleshoot. Thought it may have been water in the gas, but store owner showed me his printout showing no water in his last tank test. Towed home.

As soon as I get it off the rollback, car fires right up and is running fine. Scantool shows everything is nominal. Let it run in the garage 10-15 minutes without issue. Later that evening, I attach the FP gauge to the rail and its behaving exactly how it should. Primes to 44psi, fires, and runs. Heavy throttle input will make the pressure drop a couple psi for a second until it recovers.

On shutdown, pressure drops from 42psi to 20psi within 30 seconds, indicating a couple leaky injectors. Figured it may have flooded and refused to catch, but I've suspected leaky injectors for awhile and never had a real problem getting it to turn over.

So I drive the car another couple weeks without any problems at all. Left the scanner in the car, but the FP gauge at home.

Two days ago I drive into work, no problem. 1/4 Tank left. I head out to leave at 530, and the engine cranks and cranks without threatening to catch. Starter spins it, gauges read normally, I can smell some gas, but wasn't listening to tell if the pump primed or not. She won't catch. I pull a plug wire, try to fire it and see nothing. Thought to myself, "maybe Ignition module?". Scanner shows everything is normal from the ECM's data stream. Pressed the nipple on the FP fitting with a door key (no gauge with me) and no hissing or anything else, but may not have pressed it far enough.

Towed home again, get a gauge on the FP fitting and I have zero pressure. I don't hear a priming, figure it must be the pump or a wire to it. Too tired, sweaty, and pissed off to deal with it and decide to look the next morning.

Next morning, of course engine fires right up, FP reads 44psi and scanner showed everything is just nominal. Last night and today, the engine fires consistently, FP always looks normal. I let it get hot this morning, hoping its something that shows up only when hot, and of course saw nothing. There is no FP relay code setting, nor any other codes.

So now I'm stuck. I cant drive it, and if its intermittent in the wiring I don't really know how to start troubleshooting it. I could throw parts at it but don't like doing that.

Any ideas before I pull out the AK and start shooting the SOB?

 

Have you replaced the fuel filter lately? Did it have any water in the filter?

 

No but the fuel filter is on the list to do either way.

 

My hunch is that you have a grounding issue.

BTW... when you experience the no start, can you HEAR the pump whirling around? You should hear the pump spooling up everything you turn the key. If not, you have a pump issue.

From your write up you have made some modifications, so lots could have gone wrong including a grounding issue inside of your tank on the pump assembly.

Now... curve ball... I have no idea how the security system works on the 88 but on later models VATS is often the culprit.

 

Thats the first thing I check when the LT1 is dieing with fuel issue. Ethanol in the fuel attracts moisture from the air. It will attract as much moisture as is ethanol. It gets hung up in the filter which is at the lowest point of the fuel system. If moisture circulates through the filter to the rails, of course the engine will die. While the engine is not running, the moisture will settle back to the filter. It creates an intermittent dieing situation. And the fuel pump turns off when it dies. Check the filter. If it has any moisture, replace it and at least blow the lines to and from the fuel rails and tank. And maybe even clean the tank.

 

Problem just showed up again, Ignition key to Run, no priming at all, zero pressure at the rail. Battery connections all tight as well as the visible connections to the battery and alternator from this wiring harness addition.

Its my understanding that the ECM will kill the pump if it sees no reference signal from the HEI system, but that it would let it prime initially for 1-2 seconds and then kill it. If I understand correctly then it should prime but the pump would be shut off, eliminating any Ignition module issue?

Chart A-7 on 6E3-A-19 in the FSM says to "power 12V to the Fuel pump test terminal", is that referring to the FP Relay terminal that goes to the pump, or is that on the pump itself?

 

Fuel pump "test terminal" I thought is G in the ALDL -

 

Check the wire harness at the relay. My 87 pretty much melted that harness. Not sure what year maybe 88 or 89 they upgraded the harness to eliminate that problem. I spliced in about 6" with the terminal from a newer car to fix it.

 

So then it would be best to come off the cigarette lighter socket with a powered probe

 

The racetronics wiring harness uses the factory wiring harness to supply power to the relay on the racetronics harness which then supplies power to the fuel pump. See if you have 12 volts and ground at the factory fuel pump harness and the racetronics harness. My guess is the relay on the racetronics harness is starting to fail but do some trouble shooting and you will be able to track it down. Work backwards from the from the connection at the fuel tank until you find power.

 

Note that the fuel pump relay uses the NC (Normally Closed) contacts of the relay with ALDL pin G. The ignition must be off (the ECM can't be commanding fuel pressure through the relay).

 

I had similar problem with a 96, mine ended up being a cracked wire in the wiring harness (to fuel pump). Sometimes it would make contact and have normal power, sometimes (if vibrated around) it would not make contact and have no power to pump.

I could hardly find the problem because the wire insulation hide visual clues unless you slightly bent the wires to find the break, insulation held it together.

Just a thought.

 

Dealing with fuel pump issue in my other car as well and some other things over the last couple days I have not checked everything on the 88.

FP 10A fuse is fine.

Thus far I have inspected the racetronix harness from the alternator back to the pump, it appears just fine to the eye, the shop that installed used zipties and its snug but not pinched anywhere that I can see.

The racetronix relay is mounted on the rear crossmember just above the spare tire and has a firm chassis ground there. Only one area I cannot see is just above the shock mount on drivers rear.

I removed the racetronix redundant ground connection (simple wire from the negative terminal to the frame where it catches the hood, this is in addition to the factory chassis ground there just behind the battery) and changed the battery since they had monkey'd up and stripped the battery nuts so that the car would intermittently lose ground connection on the battery and go dead. When I disconnect the wires to the pump at the fuel filler, I got zero voltage between the black and red wires, with ignition set to run (I don't know what the purple wire is?)

 

I applied +12V to ALDL terminal G, with ignition off, no pump prime.

Measuring the voltage between the black and purple wires on the 3-wire connector at the pump, I get 11V with ignition to run. Is purple the sender? I'm not seeing it in the FSM. Fuel gauge in digidash appears to work fine, and from these diagrams that it shares the same ground as the pump itself.

I have 0 V between the black and red wires on the 3-wire connector with the ignition set to run. ~11V between the black and purple.

Audible click from the FP relay on start, and another weak one a couple seconds later. Causes me to suspect Racetronix relay.

 

RX relay has a hot wire coming in directly from the alternator, and ground is there at the rear cross member. Two wires come out, a gray wire and another hot wire to the tank inlet.

RX said to apply +12 to the gray, which made no sense to me, and nothing happened when I did. I applied +12 to the hot, pump primed up. Car runs.

Bolt the relay back in place on the crossmember, put everything up top back together, and the car won't fire up. Take it back apart, do everything over again, pump primed up again, and car runs. Put the relay back on, car fires up.

Bolt relay back in place and its now running. Doesn't make sense to me.

 

Have you tried to apply 12 Vdc directly to the fuel pump itself?
You have probably seen my mentions about my "Power Probe" tool and this is a perfect application for one. There are many ways to do this but preferably a good fused way...

My 1988 Coupe would not pressurize the fuel lines so I started looking around. I was able to supply the 12 Vdc and ground right into the pump wiring and the pump ran just fine. When I was trying to get the ignition switch to start the pressurization process it would not work.

My ignition switch was not powering the fuel pump relay "on". After testing the relay it turned out to be fine. I was getting low voltages (~7-8 volts dc) at the relays power wire when it was activated and calling for fuel pressure. On my car the fuse "looked" good for the fuel pump but when I measured it's resistance I was surprised that the fuse had corroded and would not conduct current. I put in a new fuse and then I heard it prime the system when I first turned the key on.

The main reason for most of my trouble (IMO) was one of the connections to the oil pressure sending units mounted near the firewall (a PIA to get to) was physically loose and after I replaced the connector my car started right up with just the key.

One of those sending units cuts off fuel if it doesn't see a certain oil pressure during cranking.

With your Racetronix system that should not be an issue since you are probably avoiding these "built-in" lockouts. I would check your grounds out really well, my fuel pump was attached to the ground at the fuel tank which is not a great place to do it. I ran a new wire supplying a solid ground to my power antenna and the fuel tank. Now everything is working on my car.

On your car I am surprised that they would go to the alternator for power like that. Yes it works okay, but it is not the optimum place for a lot of sensitive electronics to get power from. The battery acts like a big buffer allowing all that electrical noise and voltage ripple from your alternator's output to go away silently. Taking the power from the battery directly would be the best way, I would use that little post behind the battery where the fusible links get power from.

Where do you get the signal to activate the fuel pump relay? Is it connected to any of the car's original wiring? You should check the voltage that is going to your RX relay to activate the pump, that would be a likely place for possible issues.

Relays like the one in the picture should last for years, I would be surprised if it was bad. How old is the alternator? If it was bad or going bad it might have sent more noise than the relay could tolerate.

I hope that I didn't miss any answers from your previous posts but this sounds very familiar to what my coupe was doing.
I wish you the very best of luck in getting this sorted out!

 

I am using a Power Probe III tool now, I applied +12 to the hot wire coming from the RX relay to the pump, and the pump primes. Something is up with the wiring within the relay, or something is grounding that out that I cannot see.

Alternator is a CS144 that is about 5 years old, less than 25K on it I believe. Always supplies good voltage that I can see.

 

I am glad that you have the Power probe, that is a great tool for times like this. I now have both the 3 and the 4, I find that they are both frequently used in my garage.

When you turn on the car, what energizes the relay to power up the fuel pump?

Where does the signal come from to activate the relay?

Before I cleaned up my power lines I found less than 10 Vdc on my relay trying to keep the relay in the "run" (energized) position. After the fuse block was cleaned up I had a smaller voltage drop and I saw very close to full battery voltage at the relay energizer coil.

Are you still using the ignition switch to turn on the fuel pump via the relay?

I am assuming that your RX relay is simply drawing it's 12 Vdc power from the alternator connection. That is okay for power but what are you using to turn on (Activate) the fuel pump relay?


When I first started working on my car I noticed that the relays were not seeing sufficient voltage to hold or stay connected. What I mean is that the power wire was okay, it was close to battery voltage. The voltage used to activate the relay was too low in my car. This is where a voltage drop would slowly kill the relay, as the voltage goes down the current would go up causing heat as a byproduct. It does not take much to power a electromagnet but over time this is a typical failure mode for relays.

If you are using the original relay to drive the secondary Racetronix relay that could work. But a relay has to have sufficient voltage to remain "on" while you are driving the car.

My sneaking suspicion is that you have a ground issue or a voltage drop someplace that we need to find.
I hope that I have been some help to you in your quest! I want to see this come to a conclusion and your Corvette back on the road reliably!

 

I see now how its running, the RX harness has one line from the RX relay to the pump 3-connector, but two connectors there. It has the 2nd connector to connect to where the factory harness normally plugs into the pump, that factory signal goes back down to activate the relay, and the relay sends the juice up to the pump wires. That way its slaved to the factory Fuel Pump relay, giving it final control the function of the pump. It just has extra juice directly from the alternator when the relay activates.

So the question is if I can just change the FP fuse to a 20A and run on the factory harness and bypass the RX without causing any problems to the car.

 

Should be fine to change the fuse.