Ahhh! Frustrated by our 6.5 (stalls, no start, etc.)

[Fossilfreefuel]

Here goes, to begin the truck is a 1995 Tahoe 6.5 with 95,000 miles just filled with diesel but previously was running 100% ASTM spec biodiesel... Last week while driving, the vehicle was driving very jerky as if it was not getting fuel. Then it would stall out. I'd crank it for a few seconds and it would fire up. This was totally sporadic and seemed to have no rhyme or reason. So it was due for a service and we changed the fuel filter, glow plugs and oil/filter. Drove alright for a day and then we stopped to fuel up and when we tried to leave the it would start and immediately stall... Checked the electric lift pump and it was providing fuel, So we had it towed... While we were waiting we disconnected the harness to the PMD and that changed the startup from cranking and firing for a second to just cranking. Figured maybe it was the PMD. I'll also note the PMD was remotely mounted in the glove box, with no heat sink, when we bought the truck... So had it towed and ordered a used PMD, SS Diesel Heat sink and a number 9 resistor. When we went to install the new PMD we tried starting the truck and it fired up fine. Drove it into the shop, mounted the heat sink and new PMD and moved the remote mounting location from the glove box to under the bumper (Aftermarket aluminum bumper with winch)... Ok first start with the new setup it started and stalled immediately, the same problem we had before. Then the 2nd start it ran fine for the next 5 or so starts. So its starting fine at this point and i leave the city to run an errand. I drive the truck for about 40 minutes without an issue. Arrive at my destination, do my errands and as im going to leave it wont start. Fires but stalls immediately! So it gets towed back to the shop... Swap out the PMDs just to see if by chance it would work (remember the old PMD fired up earlier before we swapped them)... No luck. So then we jumpered to OPS to ensure the lift pump was getting 12v. The lift pump kicked on but it did the same thing, start then stall. then we jumpered the fuel shutoff solenoid at the top of the injection pump. We could audibly here the solenoid actuate. And maybe once of the 10 times we tried starting it it fired up... So at this point we pulled codes. 13 19 32 and 33... 32 and 33 had been there previously and we assumed 13 was because we disconnected the solenoid. So we cleared the codes and gave up for the night. This morning when i went to start it it started fine, and i drove it around the block! Then shut it off and it continued to do the same thing its been doing start, stall instantly. So beyond frustrated i pulled the codes because the light came on when i drove around the block and now all im getting is 33! I let it sit for a little while and tried starting it. Now it starts every time and can idle for as long as you'd like but as soon as you rev the engine it stalls at 1800 RPMS every time! Haven't tried driving but in park rev'ed to 1800 stalls every time! (tried 6 or 7 times in a row) From what I gather the optical sensor may be an issue however it seems that that will not make the vehicle stall, just run it in a default LIMP mode? Is this correct or should we explore that? Troubleshooting procedures for the optical sensor? I've also read the ignition switch can cause stalling issues but would think that it would not cause the vehicle to shutoff at 1800 RPMS??I have searched goggle and elsewhere, for some reason every time i search these forums it returns nothing, no matter what i search! I searched words that were in the titles of post on the first page and it still brought back nothing, I'm assuming the search is down at the moment... Any suggestions are appreciated.
~Colin

[moondoggie]

Good Day!

Since no one who actually knows anthing has responded...

"Last week while driving, the vehicle was driving very jerky as if it was not getting fuel." What were the operating conditions? If it operates like a gasser with an ignition miss (runs fine, but misses under load), that generally points to the LP system. "Checked the electric lift pump and it was providing fuel..." How did you check it? The LP is powered by a relay when cranking & through the OPS when running - you need to check each system separately.

"Then it would stall out." "This was totally sporadic and seemed to have no rhyme or reason." Stalling while running is classis FSD/PMD.

"...and ordered a used PMD..." When you're in this kind of trouble, it might be better to consider starting with a brand new FSD/PMD; the others might become spares after this gets sorted out.

"...and moved the remote mounting location from the glove box to under the bumper..." Excellent!

"From what I gather the optical sensor may be an issue..." Disconnect it - it will run in limp mode with it disconnected. If your problems go away (I doubt it), you've found the culprit.

I'd PM every ground & electrical connector I can find. I've also read here of folks having similar trouble due to the ignition switch; I don't think there's a good way to troubleshoot it, & 95's have more than average trouble with these (yeah, I've got two of them).

Let us know how it goes & Blessings!

[Robyn]

You need to check to be sure the lift pump is running when the engine is running and that it is delivering fuel then too.
With the engine at idle you should get fuel out the drain line up front if you open it.
You should be able to fill a pint fairly quickly even with the engine running.
If you see issue here, either the LP or possibly a plugged sock in the tank.

Also install a clear plastic line in series with the fuel feed to the IP. if you see any air you got troubles. Air is a no no.

Check these things as well as be sure the vented cap is not having issues so that you get a vacuum in the tank that prevents fuel flow and or causes air induction into the system.

Good luck and keep us posted

Robyn

[Ramster21]

Just a thought, change the fuel filter, realistically, they are only good for 10k to 15k max life. You'd be surprise of the results of changing the filter.
:cool:

[HH]

Agree with all of the above. Since you were running Bioiesel, what kind of shape are your rubber fuel lines?

[Robyn]

Is your Fossilfreefuel your own home cooked biodiesel or purchased at the pump?

The mention of the filter is a good thing.
The factory filter is a 10 micron filter and can and will let far too much crud through to the IP.
I have heard testimony that the Bio stuff will clean the system and send all the junk its rounded up to the filter/filters. (TANK SOCK)

If you check flow at the IP inlet with just the LP running you can certainly se if there is an issue. The LP should be able to push a pint of fuel very quickly and maintain 2-5 PSI even with the engine running. If you are not getting good flow and little pressure you have delivery issues, be it filter ot LP.
A plugged tank sock can kill you real quick.

Check delivery then if pump is working but flow is low or low pressure replace the filter and if no change, out with the tank and inspect the sock.

The optical sensor, if bad will usually set a code.

If all these tests reveal nothing of substance then it may be time to get the IP to the shop for a go through.
If you mark your IP with a scribe line prior to removal you can reinstall it and it will go right back to work for you and your TDCO will be very close.
Never hurts to check such though after you get it going.

One note here andIt gas been mentioned.
USED PMD

The shop I use here for IP and injector repairs offers used PMDs for Grab bag prices BUTT they sometimes turn out to be duds.
I bought two, one was good and onw was junk.
The owner let me pick another from the barrel of used ones. It was fine.

Your used unit may be a junker.
A lot of IP's go to the shop that are just fine, except the PMD and they get rebuilt and a new PMD, Then again some PMD's are good and the IP has other issues so if you buy a "USED ONE" its the luck of the draw.

Good luck with your gremlin

Robyn