No power out on ECM fuel pump wire
#1
Staging Lane
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No power out on ECM fuel pump wire
I am experienced with wiring and electronics (I'm an engineering electronic tech with over 20 years experience), but this is got me. I'm thinking it's either the ECM is bad, VATS hasn't been disabled, or some other signal is incorrect going to the ECM.
First, let me give my setup:
'04 4.8L from Tahoe
Wait4Me harness and ECM re-program
Engine runs great when I "hot-wire" 12v to my fuel pump.
Checked fuel pump wire all the way back to ECM, OK.
Checked grounds, all OK, I even connected ECM housing to battery ground to make sure.
Tested relay, it's OK. Tried another relay.
But, the problem is the fuel pump activation wire out of my ECM is not pushing enough voltage/current to power the relay. I checked with a multi-meter, this is what I found:
Getting 6.40V out of ECM fuel pump wire when engine is running (fuel pump hot-wired to battery).
Getting 10.45V out of ECM fuel pump wire when turn key on. Stays there, doesn't change until engine is running.
(Both voltage measurements were taken with the relay disconnected, measured right from ECM wire with no load attached).
This is how I wired up the relay, just for reference:
So, is there something I could be overlooking, like:
missing ground, missing signal to ecm, VATS not disabled??
Any help would be appreciated!
Thanks,
Phillip@maliburacing.com
First, let me give my setup:
'04 4.8L from Tahoe
Wait4Me harness and ECM re-program
Engine runs great when I "hot-wire" 12v to my fuel pump.
Checked fuel pump wire all the way back to ECM, OK.
Checked grounds, all OK, I even connected ECM housing to battery ground to make sure.
Tested relay, it's OK. Tried another relay.
But, the problem is the fuel pump activation wire out of my ECM is not pushing enough voltage/current to power the relay. I checked with a multi-meter, this is what I found:
Getting 6.40V out of ECM fuel pump wire when engine is running (fuel pump hot-wired to battery).
Getting 10.45V out of ECM fuel pump wire when turn key on. Stays there, doesn't change until engine is running.
(Both voltage measurements were taken with the relay disconnected, measured right from ECM wire with no load attached).
This is how I wired up the relay, just for reference:
So, is there something I could be overlooking, like:
missing ground, missing signal to ecm, VATS not disabled??
Any help would be appreciated!
Thanks,
Phillip@maliburacing.com
#2
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these computers dont switch voltage, they switch grounds only. you shouldn't have any voltage comming out of the fuel pump wire from the ecm. When the key is powered on, the fuel pump wire is grounded pulling in the relay to power the pump. it should pull in for 2 seconds and then kick out until the key is in the crank position. i think you have your relay wired wrong.
#4
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well maybe im wrong. I have only wired ls1's and a handful of 5.3's. The 4.8 might be a totally different breed of its own when it comes down to the ecm so i could possibly giving you false info.
#5
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LT1 PCm's are different from LS1 PCM's in fuel pump control.
Go here and scroll down to the 99-02 LS1 schematics: http://chevythunder.com/
Halfway down is the actual BCM, pcm to fuel pump relay schematics.
Noid light should light for 2-5 seconds, enabling the relay to prime the system and start the engine. as long as there are crank pulses the relay will stay engaged. Engine dies/stops, no pulses, relay shuts off pump.
LT1 operates similar but it has a switch in the oil pressure sensor to keep the relay engaged.
No oil pressure, relay shuts off.
Anthony
Go here and scroll down to the 99-02 LS1 schematics: http://chevythunder.com/
Halfway down is the actual BCM, pcm to fuel pump relay schematics.
Noid light should light for 2-5 seconds, enabling the relay to prime the system and start the engine. as long as there are crank pulses the relay will stay engaged. Engine dies/stops, no pulses, relay shuts off pump.
LT1 operates similar but it has a switch in the oil pressure sensor to keep the relay engaged.
No oil pressure, relay shuts off.
Anthony
Last edited by aknovaman; 08-25-2009 at 08:18 PM.
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#9
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all LS....4.8, 5.3, 5.7, 6.0 etc give power out for the fuel pump relay...opposite of old stuff and opposite of the fans and other outputs. gen III does not output to ground for fuel pump relay. Sounds to me like the ECM is faulty if you are certain you are checking the right ECM pin for output.
#10
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It was labeled by Jesse (did the harness for me). I guess it's correct. I have some schematics, I will see if I can determine if it is the correct pin. It's a pretty bad printout, so it is difficult to read. Is there a good quality ECM pinout schematic someone can point me to?
#14
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Thanks Anthony. I've been out in the garage and used my schematics. I had to pull out the "old man" glasses to read it, LOL.
I got it fixed.
It appears that the Jesse had the labels reversed on two wires that were next to each other on the PCM. Pin 9 of the red connector is the fuel pump activation and Pin 10 is the tach output. He had the labels on the wires reversed, so of course the fuel pump was not coming on connected to the tach output wire.
Now the pump primes and operates like it is supposed to. It's amazing how you can fix things if you actually read the documentation....
Thanks guys,
Phillip
#15
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Here is the F-body one.. PCM RED #9, Fuel Pump Relay Control Primary, goes to the Fuel Pump Relay. You have to Ground it to make it work properly. I know this cause I checked it when I wired up my Car.
Glad you got it worked out.
#19
Can I get the ecm plugs diagram