1997 k1500 crank no start.

[99caddymess]

Hi and TYIA.
I have a 1997 k1500 with a 5.7. I am having an issue with crank no start. It has spark, and I replaced the distributor, ignition coil, and ignition control module to no avail. It has 12v to pin 87 of fuel pump relay, but none of the other pins i have confirmed that the fuse is good by swapping it out with another truck. Also, all the fuses are good in the engine bay fuse box/in dash fuse box. When I jump the fuel pump relay from pin 87-30 the pump turns on but it sounds very weak, and the using a fuel pressure gauge it shows 0 psi normally AND cranking. It will start with starter fluid but will die after I stop spraying. Any help would be appreciated.

 

[99caddymess]

Hi and TYIA.
I have a 1997 k1500 with a 5.7. I am having an issue with crank no start. It has spark, and I replaced the distributor, ignition coil, and ignition control module to no avail. It has 12v to pin 87 of fuel pump relay, but none of the other pins i have confirmed that the fuse is good by swapping it out with another truck. Also, all the fuses are good in the engine bay fuse box/in dash fuse box. When I jump the fuel pump relay from pin 87-30 the pump turns on but it sounds very weak, and the using a fuel pressure gauge it shows 0 psi normally AND cranking. It will start with starter fluid but will die after I stop spraying. Any help would be appreciated.

There is 0 resistance between pin 85 of the fuel pump relay and c4 pin one of ecm. So not a broken wire. I am suspect of the ecm being bad. Is there a way I can test it to be sure?

 

[Schurkey]

Download the service manual set for your vehicle from the Sticky threads section of the Engine forum.

Trace all branches of the fuel pump relay socket.

You have "12 volts" at pin 87. I'd have expected somewhat more than that--12.6--12.7. Same as the battery.

Pin 30 obviously leads to the fuel pump, but you haven't checked for voltage on the fuel pump ground wire back by the fuel tank. A poor ground could reduce fuel pump effectiveness, as could bad connections or corroded wire on the supply side. You need to verify voltage on the supply and ground side of the fuel pump, AS CLOSE TO THE PUMP AS PRACTICAL, and with the fuel pump RUNNING.

You say there's no voltage on pin 85; but that pin would only have voltage for two seconds during the prime cycle unless the crankshaft was turning so that the crank sensor signal was informing the computer that the engine was cranking or running and therefore needed fuel. Connect a scan tool, verify that the computer is receiving an RPM signal from the crank sensor when the key is turned to "Crank".

The ground side of the relay coil has not been tested. A break there could disable the relay, too.

 

[99caddymess]

Download the service manual set for your vehicle from the Sticky threads section of the Engine forum.

Trace all branches of the fuel pump relay socket.

You have "12 volts" at pin 87. I'd have expected somewhat more than that--12.6--12.7. Same as the battery.

Pin 30 obviously leads to the fuel pump, but you haven't checked for voltage on the fuel pump ground wire back by the fuel tank. A poor ground could reduce fuel pump effectiveness, as could bad connections or corroded wire on the supply side. You need to verify voltage on the supply and ground side of the fuel pump, AS CLOSE TO THE PUMP AS PRACTICAL, and with the fuel pump RUNNING.

You say there's no voltage on pin 85; but that pin would only have voltage for two seconds during the prime cycle unless the crankshaft was turning so that the crank sensor signal was informing the computer that the engine was cranking or running and therefore needed fuel. Connect a scan tool, verify that the computer is receiving an RPM signal from the crank sensor when the key is turned to "Crank".

The ground side of the relay coil has not been tested. A break there could disable the relay, too.

I verified there is 12.6 volts at 87. The ground at the pump is good. 0.8 ohms. Also, there is no rpm to the scan tool when cranking, but there is to the gauge cluster. Pin 85 has 0 volts during priming cycle. And I have verified that the relay has a good ground.

I did however find that the ecm has a OL at pin 17 of c3 (white/gray plug) to ground.

 

[99caddymess]

Download the service manual set for your vehicle from the Sticky threads section of the Engine forum.

Trace all branches of the fuel pump relay socket.

You have "12 volts" at pin 87. I'd have expected somewhat more than that--12.6--12.7. Same as the battery.

Pin 30 obviously leads to the fuel pump, but you haven't checked for voltage on the fuel pump ground wire back by the fuel tank. A poor ground could reduce fuel pump effectiveness, as could bad connections or corroded wire on the supply side. You need to verify voltage on the supply and ground side of the fuel pump, AS CLOSE TO THE PUMP AS PRACTICAL, and with the fuel pump RUNNING.

You say there's no voltage on pin 85; but that pin would only have voltage for two seconds during the prime cycle unless the crankshaft was turning so that the crank sensor signal was informing the computer that the engine was cranking or running and therefore needed fuel. Connect a scan tool, verify that the computer is receiving an RPM signal from the crank sensor when the key is turned to "Crank".

The ground side of the relay coil has not been tested. A break there could disable the relay, too.

Voltage to the pump when jumping the relay is 12.6. With the relay installed it is 0

 

[Schurkey]

I verified there is 12.6 volts at 87.

Good.

The ground at the pump is good. 0.8 ohms.

Resistance means very little. Get a voltage test with the pump running.

Also, there is no rpm to the scan tool when cranking,

That's why the pump isn't running at first. No RPM signal, computer does not turn the pump on except for 2-second prime.

Faulty crank sensor? Faulty reluctor? Faulty wiring?

Pump should run once the engine has oil pressure, via the oil pressure bypass.

Pin 85 has 0 volts during priming cycle.

Yeah, that's a problem too.

I did however find that the ecm has a OL at pin 17 of c3 (white/gray plug) to ground.

That can't be good.