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View Full Version : No Voltage to Fuel pump on '97 Deisel Chevy 3500



Hammack_Welding
05-21-2008, 07:59 PM
Guys, my service rig is down and has run me ragged trying to find the problem. It started yesterday acting sluggish with cranking so this morning I put a new fuel filter on it and discovered that my supply pumps are not running. I got under the truck and checked for power, and had none to the pumps. I even ran a jumper to both supply pumps, and they worked fine. They just aren't getting fire. I replaced the fuel pump relay today as well with no change. Anyone have any idea where to start looking for the problem? Would anyone have a wiring diagram of the fuel system on a 1997 chevy 3500 with the 6.5 turbo deisel by chance? any help would be GREATLY appreciated. ~Jackson

MicroZone
05-21-2008, 10:35 PM
There is a fuel shut off solenoid that goes bad on those trucks. I will see if I can find a picture of it so you can test if it has power.

denrep
05-21-2008, 11:39 PM
Hammack,

Will it start when you direct wire the pump(s)?

I may have a schematic for 6.5 GMC close to that year, I'll take a look tomorrow, and post asap.

Fuel pump relay operation is probably controlled by the ECM, and based on input from the PMD and other factors.

All those sick of overly complex electronics on every simple thing, say Aye. :angry:

Hammack_Welding
05-22-2008, 07:06 AM
Thanks denrep that would be great if you had a schematic. I have found out that the fuel pumps get there power thru the oil pressure switch, and that can be a common problem. I'm gonna change it, and hope it helps. If not then it's either a short or broken wire.

Mondo
05-22-2008, 09:24 AM
Before throwing parts at it I would run a temporary wire from the battery to the pumps and start the engine then check for voltage at the oil pressure sensor, or just look at the oil pressure guage. If readings are good then the problem is not the sensor.

I regret I can't offer much more guidence, other than to be persistent and chase the circuits with a volt/ohm/milliamp meter (VOM). Look especially for wires that may have become disloged from the split-loom tubing and may now be chaffed from rubbing on rough or sharp edges and are now shorting to the chassis. (I had that problem with a GMC Jimmy in a previous century. The dealer couldn't find the cause of malfunctioning guages, so I just followed the wires wherever they went.) A second look at all the fuses may be productive. I have missed burnt fuses on the first pass - they don't always "look" burnt.
Good Luck!

-Mondo

denrep
05-22-2008, 11:12 AM
Hammack,
I do have a schematic for, 96-7 C and K typical 6.5, it's four pages!

Fuel control components include:
Fuel solenoid driver (PMD)
Fuel pump relay control
Fuel pump balance relay (dual tanks only)
ECM
Fuel pump/Oil pressure switch
Fuel lift pump


Fuel solenoid driver (at injection pump):
A to pin D3 of ECM LT GRN
B to fuel sol RED
C to closure ground pin A1 at ECM BLK
D to 20a Fuel sol fuse F5 G8 PINK (hot in run or start)
E to Fuel sol closure pin C13 at ECM RED
F to fuel sol BLK

Pump relay (in underhood relay center):
B1 is fed power from ECM B fuse 20 amp F11 G12 ORANGE wire
B2 Pump prime connection RED
A3 Feeds lift pump GREY
B3 From fuel pump relay control pin D8 on ECM GREEN/WHT
A1 Ground at cylinder head BLK/WHT

ECM (right side of insturment panel above blower):
C13 Fuel sol closure 5v signal RED
D5 Fuel pump input GREY
D8 Fuel pump relay control GRN/WHT

Let me know if anything else may help.

denrep
05-22-2008, 12:04 PM
I looked it over, here is the most basic function of the fuel pump circuit:
ECM terminal D8 sends current through GRN/WHT 465, to energize fuel pump relay at terminal B5. Relay contacts close, sending battery voltage through A3 GREY to fuel pump C terminal.

Or simpler yet... Once the engine has oil pressure, oil pressure switch closes and sends current to directly to fuel pump C terminal, from pressure switch B terminal (gray wire).

So... "No Voltage to Fuel pump on '97 Diesel Chevy 3500" can be narrowed down to requiring 12 v battery feed from ECM B fuse, (orange wire), through closed oil pressure switch, to fuel pump C terminal.

Powering the pump up by direct wiring, should have eliminated the pump control circuit as a problem. Seems more likely you've lost ECM or PMD feed or signal.

Notice that oil pressure switch C terminal, (orange wire), should carry battery voltage from ECM B fuse, at all times. ECM B fuse, also feeds battery voltage to ECM C13 terminal (orange wire).

Fuel solenoid driver (PMD at injection pump), and shut off solenoid, are powered by separate "Fuel Sol" fuse, through pink wire, only when key is on.

Good Luck :dizzy:

David R
05-22-2008, 05:30 PM
Jackson,

I hope you have got it fired up by now. I couldn't post yesterday. I even tried to send a PM.

Please let us know what you find.

The fuel pump runs for 5 seconds when you turn the key on, then it runs while cranking. Once it starts, the oil pressure switch takes over.

I would test ALL fuses with a test light first, both sides of each fuse in the drivers compartment and the power distribution box under the hood. I have worked on many of those trucks.

Dual tanks on chevys in that year suck. One pumps into the other and there is a module to keep track of what is going on and control the fuel gauge.

I'll be hangin around tonight playing with the V155 :)

I can be in chat at 8:30 or so EST.

David :)

Hammack_Welding
05-22-2008, 11:41 PM
Denrep, you saved me! I owe ya one. Turns out the Green/white wire was broken, and the relay was not getting powered by the ECM. Truck is up an running, and two more service calls down. I would have posted earlier but I couldn't log in, and now I can't seem to get a post to go thru. Anyone know what's going on? Thanks again! ~Jackson

denrep
05-23-2008, 09:49 AM
You're welcome, glad it worked out.

If you tell us where the wire was broken, we'll check that spot first, if another one quits.

It's really blind mans bluff without a schematic on a newer vehicle. There's a steep learning curve every time; and the knowledge probably won't be used again. But what's your option? If you take electrical problems to the wrong shop, they'll install hundreds of bucks worth of unneeded parts, and generally make things worse.

I bought the book to sort out wiring on an HD3500. It had been wrecked. After being repaired with a different year cab, it wouldn't run. The truck made the rounds through several owners and shops before I bought it. Slowly, -one wire at a time- I got it to run and shift again.

Ahh... pure misery! :laugh:

usmcgremlin
05-23-2008, 03:22 PM
i couldnt log on for 2 days i was trying to get here for you but denrep stepped in and did a good job

Donald Branscom
05-23-2008, 04:23 PM
This used to be a common problem on all porche -audi products.

The fuel pump was GOOD, the relay was GOOD the problem was the fusebox/relay box. It was usually located under the dash down by the feet.
The connecters were crimped on and the humid conditions under the dash
cause corrosion of the crimped on connecters.

The dealer knew about the problem and charged $140 to change out the fuse box. NO FUN! Most mechanics would have the dealer do it because they could not beat the price.

I used to keep a KNOWN BAD fuel pump relay in my toolbox so i could easily eliminate the relay as the problem. Saved a lot of time.