Fuel pump turn on signal - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**michael bustamante** · 08-31-2019, 02:52 PM

2003 dbw.
Blue /green plugs
So now I'm not signal from the pcm to turn on the fuel pump relay when I turn the ignition on. Does anyone know why this would happen?
It's the green plug number 9 dark green/white wire. Should I be able to test with a test probe light?

ls1nova71 · 08-31-2019, 09:44 PM

It should put out 12v to the fuel pump relay, the opposite of all other relays in the harness that are activated by a ground from the PCM. Are you sure its hooked up right?

**michael bustamante** · 09-01-2019, 11:47 AM

Yeah I secured all the grounds, re soldered the connection points I used to lengthen the wire. I tested the wire right at the plug where it goes into the pcm and no voltage

It did start the truck one time and it actvated the pump but now I don't get signal at all. Could I have e damaged the pcm somehow?

88Ironduke · 09-06-2019, 07:10 PM

Modern PCM 12 volt drivers are robust and I'm pretty certain current limited. Unless you hooked it up straight to ground its probably ok. I would start ensuring I have communication with the PCM. If its not priming for two seconds after key on the PCM is probably not powered. ECM power and grounds are the next stop, validate the connections exist and are good. If communication is good, you have spark, injector control is positively identified, cam and crank sensors are functioning then you may have indeed damaged the driver. In that case I would manually control/operate the relay and throw the dice. I'm leaning towards a "No Comm" issue.

Paul

kipps · 09-06-2019, 08:08 PM

Does the "check engine" light illuminate when you turn the key on? It seems that would be the simplest method of confirming PCM power.

Somebody else confirm if I'm right on this. I don't have a LS running yet. I'm just assuming the CEL comes on immediately with ignition.

lutronjim · 09-07-2019, 09:37 PM

It does on my 'connect and cruise' LC9.

Wildkarde · 09-09-2019, 09:52 PM

Yeah, the CEL should come on with the switch on but not started. So you don't get 12v at Green pin 9 for a few seconds after key on or when cranking? Do you have a code reader you could plug into the obdII port to see if it will connect. That would tell you for sure if the ECM is on and working.

**michael bustamante** · 10-21-2019, 06:40 PM

yup looks like I need to hook up the ecm code reader, update to follow

08-31-2019, 02:52 PM	#1
michael bustamante Senior Member Join Date: Sep 2007 Location: Albuquerque NM Posts: 7,862	Fuel pump turn on signal 2003 dbw. Blue /green plugs So now I'm not signal from the pcm to turn on the fuel pump relay when I turn the ignition on. Does anyone know why this would happen? It's the green plug number 9 dark green/white wire. Should I be able to test with a test probe light? __________________ 1967custom

08-31-2019, 09:44 PM	#2
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,119	Re: Fuel pump turn on signal It should put out 12v to the fuel pump relay, the opposite of all other relays in the harness that are activated by a ground from the PCM. Are you sure its hooked up right? __________________ My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html 5.3 swap into my RUSTY '71 C10 http://ls1tech.com/forums/conversion...71-c-10-a.html

09-01-2019, 11:47 AM	#3
michael bustamante Senior Member Join Date: Sep 2007 Location: Albuquerque NM Posts: 7,862	Re: Fuel pump turn on signal Yeah I secured all the grounds, re soldered the connection points I used to lengthen the wire. I tested the wire right at the plug where it goes into the pcm and no voltage It did start the truck one time and it actvated the pump but now I don't get signal at all. Could I have e damaged the pcm somehow? __________________ 1967custom

09-06-2019, 07:10 PM	#4
88Ironduke Registered User Join Date: Jul 2010 Location: Willingboro, NJ Posts: 489	Re: Fuel pump turn on signal Modern PCM 12 volt drivers are robust and I'm pretty certain current limited. Unless you hooked it up straight to ground its probably ok. I would start ensuring I have communication with the PCM. If its not priming for two seconds after key on the PCM is probably not powered. ECM power and grounds are the next stop, validate the connections exist and are good. If communication is good, you have spark, injector control is positively identified, cam and crank sensors are functioning then you may have indeed damaged the driver. In that case I would manually control/operate the relay and throw the dice. I'm leaning towards a "No Comm" issue. Paul __________________ Retired USAF - No rockets, no mortars, no bad guys shooting...No stress!!! My Build Thread: Project 72' Green http://67-72chevytrucks.com/vboard/s...d.php?t=587932

09-06-2019, 08:08 PM	#5
kipps Registered User Join Date: Jul 2014 Location: North-central Virginia Posts: 1,104	Re: Fuel pump turn on signal Does the "check engine" light illuminate when you turn the key on? It seems that would be the simplest method of confirming PCM power. Somebody else confirm if I'm right on this. I don't have a LS running yet. I'm just assuming the CEL comes on immediately with ignition. __________________ 1987 C6P V20 truck, 2010 LMG 5.3, AFM delete, 2010 Camaro exhaust manifolds, 1997 nv4500, 1991 np241c, hydroboost, 2005 14bff axle & driveshaft, drop-n-lock gooseneck, 4.10 gears, stock suspension, rims, and tires. Still a work in progress. Any questions or suggestions are welcome!

09-07-2019, 09:37 PM	#6
lutronjim Registered User Join Date: Dec 2013 Location: Dunwoody,Ga Posts: 443	Re: Fuel pump turn on signal It does on my 'connect and cruise' LC9.

09-09-2019, 09:52 PM	#7
Wildkarde Registered User Join Date: Mar 2018 Location: Ardmore Posts: 100	Re: Fuel pump turn on signal Yeah, the CEL should come on with the switch on but not started. So you don't get 12v at Green pin 9 for a few seconds after key on or when cranking? Do you have a code reader you could plug into the obdII port to see if it will connect. That would tell you for sure if the ECM is on and working.

10-21-2019, 06:40 PM	#8
michael bustamante Senior Member Join Date: Sep 2007 Location: Albuquerque NM Posts: 7,862	Re: Fuel pump turn on signal yup looks like I need to hook up the ecm code reader, update to follow __________________ 1967custom

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