1996 GMC 6.5L Diesel troubleshooting - Diesel Forum - TheDieselStop.com
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Old 10-12-2005, 10:41 PM   #1 (permalink)
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1996 GMC 6.5L Diesel troubleshooting

I have a 1996 GMC Sierra 3/4 ton 6.5L diesel, and she has 144,000 miles on her, and has a very rough idle. Lately, she's having difficulty starting and even after firing up, I have to rev it several times to prevent stalling out. She's also dropped some torque and power, especially going up hills. Any ideas what's wrong? I'm thinking fuel injectors. The air and fuel filters are fresh.
Also, any info on the engine itself, especially in relation to other engines, cummins and powerstroke, would be very much appreciated. Thanks!
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Old 10-13-2005, 02:24 AM   #2 (permalink)
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Re: 1996 GMC 6.5L Diesel troubleshooting

very possible injection pump getting ready to leave the building...

Josh
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Old 10-13-2005, 07:27 AM   #3 (permalink)
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Re: 1996 GMC 6.5L Diesel troubleshooting

I had a '94 with the 6.5 and had the symptoms you are describing twice. Both times it was a warning that my injection pump was on the way out. The fuel system on those engines are very touchy and tend to go out every 100k-150k. Too much kero in the winter and they die and any form of water and they stop working as well. When it gets bad enough, it will usually spit out a code something like "fuel injection pulse width short". I don't remember the number for it but it is a definite sign. If you need a new pump, it is probably worth taking a sample from the bottom of your tank and cleaning out the entire fuel system if necessary. Good luck.
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Old 10-13-2005, 04:49 PM   #4 (permalink)
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Re: 1996 GMC 6.5L Diesel troubleshooting

FSD/PMD, little black box on the side of the pump. Normally the pumps are fine and they get prematurely changed due to a bad FSD/PMD. They make it very hard to start and stall frequently. Also check your lift pump, the oil pressure switch that activates the lift pump is a royal PITA. Try the dieselplace, they are geared towards the GM and you will get straight answers not trade it in.
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Old 10-13-2005, 08:33 PM   #5 (permalink)
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Re: 1996 GMC 6.5L Diesel troubleshooting

I have a 6.5L with over 180,000 miles on the clock with the original injection pump and injectors, my pump is mechanical and does not have the "PMD/FSD"....I use Power Service with nearly all my fill-ups, and when I don't I notice a smokey start or rougher idle.

Add a bottle of Power Service to your next tank.
Check lift pump operation.
If the problem is only during cold starts it could be related to the glow plugs or glow relay.
If the problem occurs when the engine is warm look to the FSD...
For more ideas go here: www.thedieselpage.com

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Old 10-23-2005, 02:35 PM   #6 (permalink)
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Re: 1996 GMC 6.5L Diesel troubleshooting

Thanks for all the input. I don't think it's the fuel pump, as it was changed right before I bought the truck 6 months ago. Pardon the ignorance, but what is the FSD/PMD, and what is it's function and price? Also, as to the lift pump, how much would the oil pressure switch cost? Thanks!
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Old 10-23-2005, 10:03 PM   #7 (permalink)
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Re: 1996 GMC 6.5L Diesel troubleshooting

Try the dieselplace, there is a lot of good info over there. The FSD/PMD is what energizes the fuel solonoid to control fuel flow to the injectors(not the cut-off solonoid). It is a rather failure prone device in the stock location(the side of the injection pump gets pretty hot), but when properly remote mounted they hold out alot better. The OPS controls the lift pump and is another highly prone failure item but are fairly cheap to relace(less than $50), alot of PMD/FSD failures are also due to bad OPS. As you can see from my sig I drive one, and have went through alot of the 6.5 downfalls. And I have also made the upgrades to make it more reliable, and I now have no problems jumping in it and taking off on a 1,000 mile trip at any time. Got to the http://dieselplace.com/forum/index.php and ask your questions over there under the 6.5 section. It is sort of a self regulating forum and alot of very helpful and knowledgeable people(just follow the welcome notes and update your sig as soon as you register).
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Old 10-24-2005, 10:44 AM   #8 (permalink)
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Re: 1996 GMC 6.5L Diesel troubleshooting

The OPS (oil pressure switch) sends power to the fuel lift pump that is mounted on the driver's side fram rail underneath the cab. When the OPS fails, the lift pump stops operating, causing hard starts, stalling, and poor acceleration. You can check the fuel pump itself by placing the transmission in drive, and turning the key to 'start.' This will not engage the starter, but will engage the fuel pump. You should be able to hear it. Then go ahead and start the engine and place your hand on the fuel pump...you should be able to feel it operating. If not, leave the engine running, and then open the fuel bleeder valve at the front of the engine. The engine should stay running and fuel should be squirting out the drain hose. If the engine dies, the lift pump is not working. Replace the OPS.

There are mods available to prevent this from occuring again (common problem on the Chevy trucks). I suggest www.thedieselpage.com for more information.

Another problem associated with the OPS is that the lift pump is supposed to send fuel through the IP and back to the tank, helping to cool the IP and the FSD= fuel solenoid driver, the little black box mounted on the driver's side of the IP. This is basically the brain of the electronic IP. If the lift pump has been non-functioning for some time, it can cause an early death for the FSD.

I had to replace the OPS and FSD on my '95 when I bought it. I upgraded the OPS with an aftermarket relay harness, and relocated the new FSD to a heatsink mounted off the engine. Now it's very reliable.

Casey
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Old 05-04-2011, 02:10 PM   #9 (permalink)
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1997 gmc bucking/hesitating after driving around for awhile

I got a 1997 gmc with 115,000 miles on it its diesel and have 8 cylinders with 6.5 liter engine.. the fuel injector pump had been recalled back when we bought it and it was replaced a few times and gave us some problems for a few years after we bought it but has been fine since.....

last year after filling up 1 day at hess, i started having problems and suspected the tank had crap or w.e inside of it after filling up because the fuel filter we replaced had lots of particles and stuff...

anyway, yesterday i finally had nice weather to install a new tank, new filler neck, new inline fuel pump and all and everything went well and seemed to work fine today..

the inside of the tank was loaded with crap and stuff so it was overall at least a good idea to of replaced the tank and all drove around today to test it and refuel the tank and stuff and maybe half hour or so after that i had some hiccups and rough riding for a bit and 1 stall but the last 10 mins of driving home it was fine.. i didn't get a chance to replace the fuel filter yet and have plans to do so as well so i have no idea how dirty that might be...

I was hoping i had fixed my problem but i guess i didn't

reading a lot of the comments here and around and all so hoping to hear what might be the problem and how hard is it to repair myself?
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