Hello-


We have a '98 Chevy 6.5 with 148k on it. At about 100k it had PMD problems and an S&S diesel FSD was installed. Frame mounted fuel pump was replaced (died) about 20k ago. Other than that it is stock.


About a month ago it developed a problem where it would randomly shut off while idling at a traffic light, or coasting to one with no foot on the pedal. No codes etc. Replaced the crank position sensor just as a precautionary measure. The shut off did not go away.


I have checked all the electrical connections I can see to check. Batteries are 6mo old, alternator has 13.8 volt output. Ground connections to the engine at the back on the passenger side are good. Battery grounds are good. All connections to the underhood fuse and relay block are good, everything I can get my hand on is plugged in tight and no corrosion.


I have driven it with an actron scan tool monitoring what you can, which is RPM, calculated load, coolant temp, IAT, vehicle speed, coolant temp and BD2 status. Nothing unusual there.


When it shuts off, all the accessories stay on (radio, defrost blower etc) so I do not think the ignition is killing it. The engine starts right back up.


I don't think it is something fuel related like low fuel pressure as it would sputter and run poorly,(we are a marine diesel shop and have seen plenty of those type of problems) however I do think something is interrupting electrical power to the fuel system.


Where would you recommend checking first in this case? I am hunting up an electrical schematic of the fuel system now to find out where I can back probe a power supply to see if we have an interruption.

 

Check grounds especially the one on the rear passengers side cylinder head if it's not a ground issue it could be any number of things, sucking air into the fuel system, optical sensor, bad crank shaft position sensor any codes?

 

Thanks for the reply, Mayhem.


1. No codes.


2. I found a wiring diagram, and back probed the pink #439 which runs from the ECM 1 fuse to the ignition positive voltage on the fuel solenoid (in this case, the S&S PMD on the inlet manifold) and put my fluke meter on the dash, drove around until it stalled/sputtered. NO voltage loss.


I will move on to checking power supply to the fuel pump on the frame, and fuel pressure.


The reason I doubt air in fuel is simple. Much experience with diesels having air in the system is running rough and surging. Hard re start. This doesn't act like that. Does not mean that couldn't be the problem, but is not acting like that.

 

That's good about the voltage then and you are probably right about the fuel supply one good thing to do I've done it to the few 6.5/62's I have owned is take and put a piece of clear fuel rated hose for the supply line to the IP/ injector pump this will help on determining fuel going to the IP and or air leaks in the system, and take a look at the crankshaft sensor if it's easy to pull and not heat stressed a simple continuity test will rule that out if it fails use only a
A/C Delco for replacement as with any othe electronic parts on these trucks it will save you headaches in the long run.

 

I teed in a fuel pressure gauge, 4.5 psi at idle and 2 on hard acceleration. Still randomly dies. Did not check voltage to the fuel pump but if it is pushing that pressure it is working.


Contacted SS diesel who we got the PMD from, sent it back for testing. Re connected the old Stanadyne remote PMD that preceeded THAT in life, it started and ran in the shop a couple times. And died a lot!


At this point, we have power to the PMD, we have solid fuel to the PMD. I have no means to test signal OUT of the PMD, or the actual injection pump. Of course it could be the harness from the remote SS PMD to the pump, but I have to pull the injection manifold to test that.


Crank sensor is new but not sure what brand.

 

4.5psi and 2 psi isn't enough fuel pressure so it sounds like a weak LP or maybe a obstruction of some sort plugged sock in tank maybe and if that crankshaft sensor looks anything like the one in the link I provided it is completely wrong and that maybe the loss of power problem you are describing.

https://imgur.com/a/FZozt

 

Not having a "loss of power" per se, when it is running, I can powerbrake the thing and leave 40 feet of black rubber. When it dies, it just cuts right off. Same as if you pulled the ECM 1 fuse, killing power to the pink 439 ignition to the PMD.

 

Turn on the lift pump (might have to straight wire a switch to it) and check the flow at the drain valve. Should fill up a red solo cup in less than 30 seconds, if not then you got some sort of blockage and the injector pump is tiring out trying to keep the motor runnin'.

Could be a bad OPS which is turning off the lift pump intermittently.

If the truck ever 'sit up' for a long time then there is a good chance the sock is clogged and crud is in the tank.

 

If sticking with an OEM style lift pump use only ACDelco EP158 or GM.

EP158 is listed for a 93 and has higher flow. I am a believer in the Feed the Beast mod - do the Feed the Beast mod and add a T for a fuel pressure gauge at the same time.

Walking J sells a Feed the Beast kit and may now have one that includes a fuel pressure T

https://www.amazon.com/ACDelco-EP158...cm_wl_huc_item

 

This is the Fuel pressure gauge I ordered for my Tahoe.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

If you search the forums, I had problems with my 1994 K3500 a couple of Decembers ago. On the threads on a few forums, I posted links to how to, diagnostics for return from the PMD to the injection pump.

I have taken to changing the engine harnesses as a matter of general maintenance.

They are all getting to be 20 years old and have various spots that do not look so good.

Your problem could be a pin in a connector that is losing connection randomly.

Get you PMD out of the engine bay if it is still mounted on the intake. I mount them in the bumper with one of the license plate mount bolts. Sometimes I have been able to just add a nut to the back of the license plate mount - Which you may not have in some states.

For good reliable PMD's and PMD extensions - Make your own or order from leroydiesel.com or someplace else that sells Made in the USA PMD extension cables.