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Welcome to the 3500HD.com forum created October 2009

Author Topic: 3500Hd 6.5 diesel computer?  (Read 5626 times)

komputatek

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3500Hd 6.5 diesel computer?
« on: May 27, 2010, 12:18:54 AM »
I've got a 1999 Chevy 3500HD with the 6.5 turbo diesel. A guy apparently welded on it without disconnecting the battery and now it won't start. By "Won't start" I mean it cranks over, will fire on ether/WD40 but the in-tank pump doesn't run and there is no fuel in the filter well.  The dash gauges do operate.  I think the alternator is now bad as it drains the battery overnight which it didn't used to do.

  I plugged my OBD2 /CAN scanner into it but my scanner couldn't read ANYTHING. It kept telling me to plug it in. I was told that this year model didn't have a computer. I was also told that the pins are "non-standard".

My questions are:
1.  Does this have a computer?
2.  If it has one should my scanner read it?
3. What is the port pinout and voltages so I can verify that the computer is dead (if it has one)?
4. Is there anything else I should try before getting a new computer?

Thanks in advance.

ED-NY

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Re: 3500Hd 6.5 diesel computer?
« Reply #1 on: May 27, 2010, 07:09:56 AM »
Did you check the fuses for the ecm, pump and relays.  When I use my OTC OBD1&2 CAN scanner on "OBD1" vehicles it also tells me to plug it in if I don't have the external 12v power supply hooked up. Don't know about your 99 but my 95 had the fuel lift pump mounted on the frame rail externally from the tank, so I just had to run a 12v jumper wire to make it work.

Hagemann

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Re: 3500Hd 6.5 diesel computer?
« Reply #2 on: May 27, 2010, 11:26:06 AM »
1996 and up is obd2. The 6.5 uses a lift pump located on the LH frame rail below the drivers door. If yours is equipped with dual tanks, there will be an additional lift pump on the LH frame rail in front of the rear axle.
The rear pump feeds fuel from the rear tank to the front tank, controlled by a fuel module. The fuel module is located near the front lift pump. Stay with me! The front lift pump does the work of feeding the engine, so lets worry about that one for now. When the key is energized the front lift pump will run briefly, after the engine is started the lift pump will maintain 3 - 7 psi as long as oil pressure is present. The lift pump circuit goes though the oil pressure switch to the fuel pump relay to the fuel lift pump. Go to the fuel pump relay, located on top of LH front fender well. The fuel relay should be the front RH. there are 5 pins. Probe pin 87 for 12v +. If you look at the bottom of the relay it should have pin numbers. If pin 87 shows 12v or battery voltage your fuse is good. Now with the key off jump pin 87 to 30. This will energize the lift pump. Its not too loud. if pumps works open bleeder on top of filter housing until fuel is seen. It will take a while for injectors to bleed. Batteries must be up to full charge. You should get a sputter right a way, just remember to allow no more than 30 seconds on your starter before allowing it to cool. If lift pump doesn't energize from jumping pin 87 to 30, leave jumper in place and probe wire at lift pump for power. No power means bad wire from relay to pump or bad ground lift pump to chassis. If 12v is present test lift pump to be safe. One other note, the main injector pump is capable of operating without a lift pump, if your filter was empty this means there is an air leak somewhere. check all hoses for cracking. If lift pump function is restored, and fuel is pumped to filter and then to injector pump and still no start, It is more then likely your FSD (fuel solenoid driver), the black box on the side of the injector pump. This is the box that most 6.5 guys relocate to a cooler area. I also recommend the aftermarket version made by Dtech. hope this helps. Just remember welding usually upsets the grounds, double check all of them. The rear RH on the intake manifold is all your engine to chassis grounds.
« Last Edit: May 27, 2010, 11:29:46 AM by Hagemann »

komputatek

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Re: 3500Hd 6.5 diesel computer?
« Reply #3 on: May 29, 2010, 01:56:15 AM »
I cleaned the ground connections on the back left of the engine (as looking under the hood). I then found 12 volts at pin 87 where the fuel pump relay plugs in. I was also able to jump the relay and hear the pump run. I then purged the filter assembly of air. I had a good flow of diesel fuel to the filter housing. I tried several time both with and without either to get it to start. It would fire under ether, but never picked up on fuel. I made these attempts with the jumper wire in place on the fuel pump relay socket.  The pump never runs with just the relay plugged in.

Does the fuel solenoid driver also control the fuel pump relay?
What powers / controls the FSD?

What next?





Hagemann

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Re: 3500Hd 6.5 diesel computer?
« Reply #4 on: May 29, 2010, 09:39:34 AM »
If fuel is making it to the injector pump the next problem is usually the FSD (fuel solenoid driver). The FSD is the black box mounted on the LH (drivers side) of the injector pump. As for the lift pump not running except only with the jumper wire, the oil pressure has to be above 7 psi to activate the relay. This is for accident safety, if the engine were to stop, fuel is not continually being pumped. At this point you might try cracking loose the injector lines at the head, try cranking with your jumper wire in place and then observe if fuel is making it to the injector. A weak IP (injector pump) sometimes has trouble bleeding air out unless the lines are bleed. It like bleeding brakes. Its not necessary to do all of them, just try what you can reach, once it starts bring the rpm to 2000, the rest should bleed from there. If not fuel is noticed from the above procedure, it is your FSD or the obd2 computer. It would be better to have a Tech 2 scanner at this point. Try this first.

Hagemann

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Re: 3500Hd 6.5 diesel computer?
« Reply #5 on: May 29, 2010, 09:46:02 AM »
One more thing, 6.5s don't like ether. Head gaskets won't take it. if you need a little help try pouring some gasoline on a rag and place in front of the air filter, fumes work the same, but a lot softer on head gaskets.

komputatek

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Re: 3500Hd 6.5 diesel computer?
« Reply #6 on: May 29, 2010, 11:23:57 AM »
" If not fuel is noticed from the above procedure, it is your FSD or the obd2 computer. It would be better to have a Tech 2 scanner at this point. Try this first."

I'm a little confused. I initially connected my automotive OBD2/CAN scanner and it said it I wasn't connected. Is a Tech2 a different type of scanner?  Another posting talked about needing an external power source. I say this so I'm not buying a new FSD when I don't need it. I'm not complaining, just asking for clarification.  It seems to me that when a person welds on a vehicle it could "fry" a computer.


I also want to re-phrase my initial comments about the welding. A man DID weld on it. He claims that he disconnected the battery cables, but we drove the truck to his shop and had to have it towed away!  It now has a steady drain on the batteries just like the rectifier in the alternator is fried.  I think this guy is trying to save his butt because he screwed up.

Thanks so much for your help thus far.  This whole thing is very annoying. I'm just trying to keep it as inexpensive as possible.

Hagemann

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Re: 3500Hd 6.5 diesel computer?
« Reply #7 on: May 29, 2010, 12:21:56 PM »
Tech2 is what GM uses. Its not just a code scanner, it see what the computer sees. Your truck has several issues, just trying to work one at a time. Did we try to start with fuel relay jumper in place and fuel injector lines cracked? This will tell me whether the injector pump is air locked or not. From that, if fuel is not present at the point of the loose injector line after cranking you either have a bad FSD or engine obd2 computer. I live near Atlanta, by any chance are u close by, because I have a Tech2?

komputatek

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Re: 3500Hd 6.5 diesel computer?
« Reply #8 on: May 29, 2010, 03:30:34 PM »
I'm relatively close for someone who lives in Zurich Switzerland. I live near Peoria, IL. so probably a slim chance of us getting together. I checked and that FSD is like $225.00 I'll probably work on it again Monday or Tuesday. Too much happening this weekend. 

Thanks again.

 


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