6.5 Won't start after Biodiesel.

[HUGH429]

I bought a 1996 GMC Sierra Z71 last week. It has the 6.5 and is an extended cab. I have been making my own biodiesel for about a year now and have had no problems running it in my 1982 Mercedes 300TD. I filled the GMC up on Wednesday and took a short trip. The truck ran fine. I made several trips that day without issue. Late that evening when I would try to start her up I would have to try several times before she would fire. Thursday morning------Nothing. What could be the problem?

[JTodd]

Where are you? Is it cold? I believe the gelling temperature of Bio-Diesel is pretty high - mid 30*s. With the snap cold in unusual areas of the country, that might be the problem.

[HUGH429]

JTodd, Im in South Carolina. That MB will crank on B100 homebrew at 27 degrees without the block heater. I just expected to get the same performance out of the 6.5. It was cold wednesday evening and thursday morning (around 35 for a high and upper 20s for a low), but friday it warmed up to the upper 50s. She still will not fire. I think that my problem is related to the bio but I don't think it is a gelling issue----I could be wrong.

[Bnave95]

Make sure all of the glow plug are working. 60g glows will need more time than starting on diesel.
Fuel filter look normal?

[Slim shady]

IS the fuel filter clogged, BIO diesel will clean a fuel system and clogg a filter quickly until you have removed all of the dirt in the system.

[HUGH429]

The fuel filter is a new one. I thought the same thing so I changed it. The old one looked ok, but since it is a new truck to me I figured that it may need changing. I don't want to totally blame Bio for my problem as I see Alternative fuels as an answer to our dependance on foreign oil. I feel like whatever happened would have happened eventually on Petro-diesel. I just think that the problem may have been brought about sooner by the bio. Maybe years of low grade US petro and then a sudden switch to the higher lubricity of the bio. I hate to invest in a new IP if there is something simple like the optical sensor or PMD, but the symptoms do not point to PMD, or do they? Could it be the optical sensor? You know the guys at the Dealership are going to try to make up for Christmas with me so any advice or direction will be greatly appreciated. I would like to document this troubleshooting as someone may, in the future, have the same problem.

Thanks,
hugh

[DmaxMaverick]

Have a close look at your fuel lift pump and OPS (Oil Pressure Switch). If they have issues, it could have been caused by the bio, or just a coincident. The OPS in OEM form is failure prone.

[HUGH429]

The fuel lift pump seems to be working fine. I can hear it hum while the glow plugs are warming and the it will hum again after the ignition is switched off. I have opened the T-valve and there is plenty of fuel. I have loosened an injector line and there is no fuel there. What would cause this? Also you mentioned the OPS. What and where is this and what does it do?

Thanks,
hugh

[redbird2]

OPS stands for oil pressure switch in is mounted behind the left cylinder head if the electric fuel transfer pump is coming on then the OPS is good.
Have you had tried draining the fuel out of the filter housing and filling with diesel and see it the truck will start on straight fuel.
Are you sure the glow plugs are good I would test each plug to make sure there good don't just go by the kight being on telling you the plugs are ok. I made that mistake one time after hour of pulling hair out I went back to the basics and fould the problem

[Slim shady]

If you have fuel pressure in the injector pump and none at the injector, that tells me you have an electrical problem. The electric Injector pump can have all of the fuel it needs but if the fuel selonoid does not work you will not get any fuel to the injectors.

YOU can take a little diesel fuel or wd40 and spray it in the intake, if the truck starts you have an electrical problem with the fuel solenoid driver or the optical sensor. I would think Fuel solenoid driver if it starts and runs a short time with the fuel in the intake.

I MEAN a SMALL amount I cant stress this enough, you just want to see if it will run. WD40 does great when they start and will not hurt the motor like starting fluid.

[HUGH429]

Thanks for the input. I hope we are on-to something with the fuel selonoid. One question. What does the fuel selonoid do? Does it turn the fuel off when the engine is turned off thereby stopping the engine through fuel starvation? If this is not how the 6.5 is turned off then could I remove the "guts" from the selonoid if it is bad? Whould this solve a "sticky" selonoid problem?

thanks,
hugh

[Bnave95]

Thanks for the input. I hope we are on-to something with the fuel selonoid. One question. What does the fuel selonoid do? Does it turn the fuel off when the engine is turned off thereby stopping the engine through fuel starvation? If this is not how the 6.5 is turned off then could I remove the "guts" from the selonoid if it is bad? Whould this solve a "sticky" selonoid problem?

thanks,
hugh
There is a fuel selonoid Driver on the injection pump that is not really a R&R item. This selonoid should throw codes.
Now there is a fuel shut off selonoid on the front top part of the IP.
This must work to fire the Eng. Comes on with the key.At this point I'm sure you have checked fuse's.
The glow light on dash time is a PCM control. My 95 will time out with the first key cycle. If I try to double cycle the 2nd will only glow for a couple of sec. so the first glow time must work. If truck does not start at first than the 2nd time the key must be of for some time to get a long glow cycle.
Even when you jump the glow relay I would pull a plug,ground and watch what it's doing.

[Slim shady]

"There is a fuel selonoid Driver on the injection pump that is not really a R&R item. This selonoid should throw codes.
Now there is a fuel shut off selonoid on the front top part of the IP.
This must work to fire the Eng. Comes on with the key.At this point I'm sure you have checked fuse's."

Very sound advice and my fault for not being complete in my explanation. Thanks

This and the fuel shut off solenoid on top of the IP (injector pump) can both cause a no start.

Sometimes I forget and take for granted that which I ass-u-me (assume), that being said, the FSD (This is the module that drives the fuel solenoid inside the injector pump) will not always throw a code, it can go bad and cause a no start. The vehicle could have run fine and on the next restart the FSD could have failed. I suspect the best way is to plug a new FSD in and see. Kind of like the old distributor mounted Ford ignition module, I know there is a specific procedure (pin check for voltage and the other GM trouble chart checks that always say check circuit for short to ground or five volt reference circuit). (Possible but not likely the fuel solenoid went bad itself) you can use an OHM meter to check the internal solenoid that is driven by the FSD, you will need a wiring diagram for that and I am not sure they give a spec for it.

I believe the fuel shut off solenoid (This shuts fuel off from reaching the inside of the pump) is much easier to check. In my 1995 2500, the fuel shut of on top of the pump should have 12 volts at the pink wire in the connector. The PCM grounds the blue and white wire to energize it. This is for a 1995 model only. I am not sure of the wire color coding for your year truck, once again the solenoid can be ohm checked to see if it is bad.

BOTH of these circuits are run off of fuses. I can't stress enough checking the basics first.

[JohnC]

First thing I'd do is look for diagnostic codes. No point in working in the dark with your eyes closed...

[65TD]

The shut off solenoid is an important part of the IP.

[arveetek]

JTodd, Im in South Carolina. That MB will crank on B100 homebrew at 27 degrees without the block heater. I just expected to get the same performance out of the 6.5. It was cold wednesday evening and thursday morning (around 35 for a high and upper 20s for a low), but friday it warmed up to the upper 50s. She still will not fire. I think that my problem is related to the bio but I don't think it is a gelling issue----I could be wrong.

I, too, have been running home-brewed biodiesel for about 1.5 years. My '95 runs great on it, in any percentage up to B100.

I have been cutting the percentage down during cold weather, though. Usually I run about 75% bio and 25% petro diesel. I found out this past week that it wasn't enough of a mixture, though. My '81 gelled at 27 degrees. Luckily I had nothing but petro diesel in my '95 during this recent cold snap, so I didn't have a problem with that vehicle. I finally got the '81 in the garage and warmed up, and then I topped off the tank with 100% petro diesel (was almost out of bio anyway) and a healthy dose of Power Service. It's running now, but I think I might have to run it a while to get the rest of the gelled bio out.

Casey

[Burning Oil]

If it fires on WD-40 then you might have air in the lines from changing the filter. Did you purge all the air before you cranked it. The original problem could have been the dirty filter and now won't start because of air in the lines.

[Lil Timmy]

Another possible problem could be the biodiesel itself. if it is not well washed and dried it can cause problems with the optical sensor on the electronic injection pumps on the 6.5. Your Mercedes is not nearly as sophisticated and will have fewer issues with home brewed fuel.