[mark104]

Hello,

Last year I purchased a 1999 GMC 6.5l TD Bluebird school bus, converted it to an RV, got RV plates, insurance, all that, my blog on the conversion is weboughtaschoolbus.blogspot.com if you are interested in seeing that.

Now on to engine issues. I had some stalling happen 3 or 4 times in a 10 mile area, then I got it home, checked the air filters, they are good, started up again fine.

Got oil change, and a new PMD and relocated it to the front bumper. This seemed to fix the issue, but now it continues to stall but only after running for a while, around 10 miles or so and seems to fail after running hot or uphill for a while. Luckily I have some time and space to troubleshoot.

I ordered a new PMD (lots of research lead me to believe it might be that I got a bad one) - a different brand, should come Wed.

So I have some things to try. Like the new PMD.... but anyone know which resistor or if I should have a resistor in there at all? I put the #9, then the #5 and both stalled, I havent tried getting it to stall w/o a resistor, I will try that tomorrow, but wanted to see if anyone had experience in this engine and knew the resistor I should use or if any.

A few notable notes too:
- When it stalls, there is no misfires, it runs great, then it just stalls, losses power steering, etc a few sec later, have to pull over.
- It is hard to start after stalling but I can get it going after a few tries, 5-10 min, the PMD was NOT warm or hot last time I road tested and it stalled.

Other thing I was thinking in troubleshooting was to try to bleed the air out of the fuel line at the engine right away after stalling and see if it starts up immediately, would that let me know its in the fuel lines? Although from what I have read it seems like I would have some misfires or codes or warnings if it were air in the fuel lines.

Anyway, learning as I go, I appreciate the help. Thanks. :thumb:

Mark

 

[mark104]

Other info I forgot to mention, the IP was replaced 15K miles ago.... and I also replaced the lift pump which I am sure is working correctly.

 

[Glagulator]

If you just let it idle for 15 minutes does it stall?
Any resistor will work, I would use the 5.
You need to have a resistor.

 

[dieselmike1]

Even though you replaced the IP a while back, what your describing seems to replicate a bad IP. Next time it stalls after its warm, take and slowly pour cold water on the IP, and then try to start it. Just because you got a rebuilt pump doesn't mean anything, a lot of rebuilders just put in new seals and call it rebuilt. That's why its important to research rebuilders thoroughly to make sure they do a proper rebuild. Badger Diesel is a favorite on here for injectors and IP's.

 

[nsdtk]

5 is stock, 9 gives a little more fuel. Check your PMD Wire harness. See if you have a loose wire on the PMD side. I lost a PMD and had a bad connection on my last stall episode.

 

[mark104]

Has #5 on now, running it ritht now for 15 min to see if it stalls, then ill drive it around and try the cold water on the IP thing. For what its worh I got the bus from a big wealthy school, so I am pretty sure they used new OEM parts when replacing.

Will let yall know how the tests go, thx for the quick reply!!

 

[mark104]

Well it didnt stall after 20 min of idling.... Put some diesel fuel injector cleaner and filled up the tank, drove it around for about 15 min with cold water bottle in hand, no stall... It was busy and i didnt really feel safe "wanting" it to stall so i decided to wait till i have time at a less busy time.

Thx again, any thoughts are appriciated.

 

[JMJNet]

Glad you get it fixed. PMD can be an issue anytime regardless of whether you like it to happen or not. By moving it outside the hood, hopefully, it help prolong the life. I am not sure what is the situation in bus, I suspect you should have a little more space.

The resistor should not cause a stall unless you happened to be in the time when ECM is asking for a resistor value which should happened once in a blue moon kind of a thing.

 

[Freddyack]

How To Check For Air In The Fuel System

Another thing that can cause stalling is air in the fuel system.

The best way to tell if there is air in the fuel system is by replacing the rubber hose from the IP to the return line system. Use clear 1/4" fuel line. Oreilly's has it in the lawnmower parts area. You may need smaller diameter clamps.

Here are pictures of mine (mine is Tygon fuel line)

Then (tranny in Park with E brake on) start the engine. First check for leaks where you clamped the clear line. Then look for air bubbles.

If there are bubbles, you have to find and fix the leaks.

 

[mark104]

Not fixed yet!! : )

Thx Freddyack! I will try that if the new PMD does nothing. Can I leave the clear tubing in afterwards? Also, would it misfire before stalling if it were air? Seems like it does not misfire at any point.

Thx

 

[JMJNet]

I will check the LP first, although you assume it is working but have you checked it?
Bad LP can cause air.

How is the fuel filter?

 

[mark104]

Thx, Fuel Filters are in good condition, replaced less than a year ago, are clean - tested lift pump and worked but was very old, so I replaced that last week.

 

[VanBoy]

Have you checked your ignition switch? I know on the pickups, sometimes when they go bad, they can stall the vehicle....

 

[mark104]

Well that was fun!

Got the new PMD in the mail, got it installed, started up fine, got about half mile down the road and it stalls. Get it going again and it stalls 20 ft later, at a light where people got extremely angry at me while I switched it back to the old one.

Then it runs fine on the old one home.

I thought it was maybe the resistor I put in there since I switched that too, so I put in the other resistor (known good one) in the new PMD and same thing happened, started ok, then died shortly after. Put the old PMD in again, and it runs fine.

So not sure what that tells me, but at least I know this PMD is bad, I am going to try to return it ASAP.

Would there be anything that would be causing the PMD to overheat?

Or is it possible I just have two bad PMDs on my hands, one just much worse than the other?

Thx in advance. In the meantime I am going to try to return this one not exchange and get it from somewhere else, again... :think:

 

[Freddyack]

Unfortunately some PMDs are bad right out of the box. The PCM picks up a change in resistor value after 50 key on/off cycles (at least in a 1994).

PMD overheating can be caused by not mounting to clean, flat heat sink with a thin coat of heat transfer paste or the heat transfer "gasket" that comes with it. The Stanadyne gray comes with one of the "gaskets"

 

[JMJNet]

The IP harness where the PMD hooked up into can be bad.

I am assuming those PMD are mounted on a good heatsink if they are not on the original IP location?

Where did you get them from? May be the extension cable is bad?

Did you ever check the LP as suggested above?

 

[mark104]

Luckily I can return it for free through Amazon - I just purchased a different one - D-Tech one, hopefully that one works.

Not sure if this is at least telling me my problem IS the PMD.... but at least the symptoms of a bad PMD are the same symptoms of what I am having happen, what happens to me just takes more driving first.....

 

[mark104]

JMJNet - I replaced the LP last week with a new one, works well.... It was night and day when I switched the PMD back to the old one.... so it must be that. Yes relocated with heatsink to front bumper....

 

[mark104]

I got it from APDTY through Amazon....

 

[nsdtk]

I had to replace the end of my harness. The part that plugs into the PMD had gone bad and was making a bad connection. If that connection moves on a bump and looses contact you get a dead engine. There's replacement ends on Ebay.