I have a 1988 L98 and it has been hard to start. This is not injectors or cold start injector problem. I used to hear the fuel pump running when put the key in the ignition. Since the hard to start issue I haven't heard the pump running. I have change the fuel pump inside the gas tank so we know the pump is new.

How do I test the fuel pump and/or the relay to know it both work?

TIA

 

If the car runs, the fuel pump works. Check to make sure the fuel pump doesn't run for the 2 second priming period, and/or trouble shoot the relay for proper operation.

RACE ON!!!

 

The car runs so the pump work. I know that the pump doesn't run for two second priming time.
How do I check/trouble shoot the relay and the pump? What equipment do I need? Thanks

 

Since the pump is new and the car runs, you don't have to spend time checking the pump. A DVOM is best, but you may get away with a test light. The trouble shooting is mostly intuitive. Follow a logical pattern of checking the relay. The first thing I would do is check for the priming signal from The ECM. If that is present I would check for good solid contacts at all the connections, then continue on for the proper relay function.

RACE ON!!!

 

If this is a 4+3 car, I think you can swap the overdrive and fuel pump relays to see if that brings it back to life. I'd have to double check that though.

 

No Scorp, its an AT and thanks CFI-EFI

 

http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf
http://members.shaw.ca/corvette86/Fu...l%20System.pdf
Some good info from my 86 manual

 

CFI,

Without trying to hijack this thread, I have an opposite problem involving the FP Relay circuit. I have run through the diagnostics
for the FP Electrical system. My problem involves an FP Relay that stays on with ignition ON but no motor run. My prime pulse continues and the ECM does not shut it off with ignition ON only. I know its not the realy because connecting test light to Relay Harness connector terminals C and B doesn't turn light off after 2 sec. Consequently, when I turn ignition OFF after having run the motor, motor continues to run on with gauges lit. The way to kill it is to pull the gauges fuse or pop the clutch. Frustrating.

 

I agree that the relay isn't the cause of the problem. As long as the engine is turning with the ignition system energized, the fuel pump relay gets the power from the ECM to trigger the relay to run the pump. By pulling the relay harness off of the relay while the engine is running, you are testing and proving that the oil pressure switch is working. The fact that turning the ignition, "ON" seems to permanently power the relay suggests, to me, you may have a bad ECM.

It seems to me that some this problem has to do with the ignition switch and the powering of the ignition system. I would be reluctant to "turn off" the engine by popping the clutch, because I don't see how that would de-energize the ignition system or the fuel pump relay. I find it curious that pulling the gauge fuse kills the engine. If this were my car, I'd be pouring over the schematics to see what sort of component failure would power the ignition system through the gauges circuit. Could that failure be the ECM? If I understand what you have written properly, the fuel pump and the fuel pump relay are both acting as they should, albeit, misdirected.

RACE ON!!!

 

Jump the fuel pump relay and test the schrader valve on the passenger fuel rail for pressure, with key in the "on" positon. If no pressure, follow wires all the way to the pump with a test light, and preferably a battery charger on the battery.

 

CFI,

I have used a test light on the C/B terminals of the relay harness connectors and when the ignition is turned to ON, the light will stay ON. I'm not clear on how the ECM is supposed to control the 2sec prime. Does it interrupt the power coming to C, or does it interrupt the ground at B? From the schematics it appears that B is connected to ECM ground and also a ground on that same circuit that terminates at the intake manifold lid. So I am thinking its C. As for a bad ECM, this is the third one, so I don't think its that.
After engine run, and then shutdown, the electrical shuts off the radio and so on but not the gauges. If I disconnect terminal A of the relay connector, then the relay doesn't energize the pump, it takes a bit to start the motor since I am now waiting for Oil Pressure to close the circuit. In this configuration, the motor will shut down with the key in the OFF position. SO it appears that for some reason, the ECM is acting as if it "sees" DRPs, even if there aren't any, which would be one reason why it would continue to energize the relay. I've spoken to Gordon Killebrew and he seemed to be aware of this situation saying that there is some type of feedback coming through the gauges circuit.
Thanks again for any additional thoughts on this.

 

READ the question before answering.

RACE ON!!!

 

Scorp, that is correct, at least in 85, same part number. I think the wiriing harnesses also reach to either without getting out a wrench.

 

As you noted, terminal "B" is grounded outside of the ECM as well as inside. Ynless you have something crossed or hooked up incorrectly the power to terminal "C" of the relay has to come through circuit 465 from terminal 18 in the white ECM connector.

Disconnecting terminal "A" eliminates all power sourses to the fuel pump, including terminal "G" in the ALDL, EXCEPT the oil pressure switch.

It appears to me that without a doubt, the relay is being energized when the key "OFF" should prevent it. It likely isn't the ECM, if you're on your third. Have you swapped ECM generations? Could there be a problem with your adaptor "pigtail? Some other worn or altered wiring?

RACE ON!!!

 

The 2 second prime is a sort of temperature-based "timed" relay or equivalent.

Current drawn by the fuel pump heats up the circuit and when it reaches a certain temp or resistance, cuts power. I think this circuitry is internal to the ecm somehow. So in theory, if the fuel pump isn't drawing enough current, the priming function will never stop. I don't have my book in front of me... so I don't know the details.

 

Interesting Central Coaster. But wouldn't that cut off the FP even if you had an Engine Run condition? From what I have read in the shop manual, the ECM cuts off the power to the C terminal if it does not receive any Distributor Reference Pulses. It will continue to feed power to the relay if it sees DRPs.

 

As I said, this is all internal to the solid state electronics. There's obviously two methods the ecm uses to send 12v out that wire. I got the jist that it functioned similar to the electronic blinker control module on your lighting system. If one bulb shorts out in the socket, the system won't blink from the extra current draw. Also, if one bulb isn't pulling enough load to heat the circuit, it'll blink slowly. i'm reading the manual right now, don't remember where I got that from (or if I made it up. )


Ok, read a little further... in the test procedure for code 54 it shows using a test light in place of the fuel pump to test the 2 second primer. I'd think a testlight would differ from the draw of a fuel pump... nonetheless, what's hooked up doesn't seem to matter. The ecm will send 12v to that wire for 1.5 to 2 seconds, after which it depends on reference pulses.. throwing this code if voltage there drops below 2V for 1.5 seconds or more (such as with a short in the relay or pump or pressure switch.) Nonetheless, we're way too far into details guessing at what goes on inside the ecm.

I'm looking at page 6E3-64 in my 85 shop manual, that's as good as it gets for explanation of this. I'm probably wayyy off topic by now too. Sorry, I just watched Minority Report and my head is still spinning.

I was confusing this thermal time switch for what actually controls the maximum cold start injector run time.

 

Give me your email address and I'll shoot you some schematics that might help. They helped me.

My problem was a short in the wiring under the passenger side dash. The wire bundle had some issues. I disconnected and slaved in a few wires in the circuit until I found the short.

Welcome to my world

 

Ttt

 

Jr,

Here's an update on my situation. I pretty much have the interior torn apart. At least the dash. My problem seems to be that some other circuit is feeding the Fuel Pump Relay Drive circuit. I completely disconnected the ECM and still had power going to that circuit which is ECM Pin W18 on the 84 or A1 if you're using a 7747. Oddly enough, I ested for continuity on that same cicuit and found that the EST LOW circuit would complete it. That would explain how the motor could keep running since it appears the faulty Relay Drive circuit may be supplying power to both the ignition and the fuel. I ran a direct line from the ECM to the C pin on the Relay Harness connector, and with KEY ON, I get no light at all. Now it could be that the ECM driver is fried if it was getting power from somewhere else.
Originally, I thought that the "feedback" was coming from the GAUGES circuit. With KEY OFF, motor would continue to run until I would pull the GAUGES fuse. So I disconnected everything one by one from that circuit, and still had power going to the Relay Drive. Then I inadvertently blew the CTSY/CLK fuse, and no more power even tho the GAUGES fuse was in the block. SO now I am hunting that down.
If anyone has other suggestions, please send them our way.