Need some opinions on IP diagnosis

[HighSierra86]

Hi guys, long time since I've been on any of the forums but when I hit a road block this is where I find the best information.

I'm about ready to replace the injection pump on my '96, but just wanted to make sure I've exhausted all ideas. At this point I already have myself prepared mentally and financially, just don't want to miss any other underlying problem.

I've been clearing a p0251 and occasionally a p0370 code for quite some time now. The optical sensor code will almost always come back with the first restart of the truck. I always use additive and I've tried the few tanks of a heavy dose with no change. Lift pump is a raptor unit less than a year old which I have running 8-9 psi at idle before the IP. Verified there is no air bubbles in the fuel with the clear hose on the return line. Running the stock fuel filter housing as well as a 30mic pre-filter before the lift pump.

Truck seems to operate normally other than the following conditions: I'm beginning to have harder starts, followed by a stumble (glow plugs good), very occasional stalling, and what seems to be an skip or miss under 2500rpms.

Only thing I haven't tried is replacing the PMD. Current unit is about 8 years old on the Heath plate up front. I also removed the optic sensor filter harness when I replaced the PMD. Injection pump is somewhere in the neighborhood of 12+ years/40K miles old replaced by the dealer still under warranty.

Time for a new pump? Or worth it to try a new PMD first?

Thank you in advance,
Nick

P.S, this is the truck in my signature, 1996 Chevy 133k miles

 

[Will L.]

Removing and cleaning the engine mounted grounds and trying your spare pmd is definitely worth the hassle. I would think slim chance by the description, but not to be missed.

Sounds like you dont have a spare pmd on you, if you get one to try it, I say mounting 2 on a heat sink (or 2 seperate heatsinks) and have a chopped plug filled wih silicone as a plug for the spare. Anytime there is question, just swap the plug over to the spare. If the first one is bad then your rig is still functioning. This came in handy in a large fleet of them and not sending a guy on a rescue mission once every couple weeks.

Leroy sells the lifetime warranty ones...

 

[WarWagon]

10 years is the expected life of trons. 8 Years on a "red hot" PMD is a good run. Will said it best, but, I will X2 and say a spare PMD can't hurt.

I would run a "Wiggle Test" on that old PMD extension cable with the engine running and see if it's starting to fail by stalling or a skip of the engine.

Grounds as suggested and also look at the positive battery cables and connections.

Fuel. What's really in there? Does it smell like gasoline? Is it good "CLEAR" diesel? Cloudy diesel like from bugs, low quality etc. should be verified. Same diesel source?

Is the shut off solenoid working including wiring? The computer will code on wiring to it, but, if it sticks shut or leaks air...

Last the hose to the IP is suspect for kinks etc. Simply covering every possible cause. IMO this would vapor lock and cause bubbles to show in the return.

You can attempt to replace the Optic Sensor and clean the wheel before replacing the IP.

 

[Big T]

10 years is the expected life of trons. 8 Years on a "red hot" PMD is a good run. Will said it best, but, I will X2 and say a spare PMD can't hurt.

I would run a "Wiggle Test" on that old PMD extension cable with the engine running and see if it's starting to fail by stalling or a skip of the engine.

Grounds as suggested and also look at the positive battery cables and connections.

Fuel. What's really in there? Does it smell like gasoline? Is it good "CLEAR" diesel? Cloudy diesel like from bugs, low quality etc. should be verified. Same diesel source?

Is the shut off solenoid working including wiring? The computer will code on wiring to it, but, if it sticks shut or leaks air...

Last the hose to the IP is suspect for kinks etc. Simply covering every possible cause. IMO this would vapor lock and cause bubbles to show in the return.

You can attempt to replace the Optic Sensor and clean the wheel before replacing the IP.

I attempted to clean the wheel, but found a piece of it missing. Honestly, that wheel is paper thin and very fragile. If he's getting P0251 code almost immediately, then he's havin Optic Sensor issues or his wheel is broken like mine.

 

[HighSierra86]

Removing and cleaning the engine mounted grounds and trying your spare pmd is definitely worth the hassle. I would think slim chance by the description, but not to be missed.

Sounds like you dont have a spare pmd on you, if you get one to try it, I say mounting 2 on a heat sink (or 2 seperate heatsinks) and have a chopped plug filled wih silicone as a plug for the spare. Anytime there is question, just swap the plug over to the spare. If the first one is bad then your rig is still functioning. This came in handy in a large fleet of them and not sending a guy on a rescue mission once every couple weeks.

Leroy sells the lifetime warranty ones...

Thanks for the replies guys. I do have a spare PMD that I will try. I think you are onto a good idea to have a full spare setup ready to go. I only have one other DS4 truck left, but it would still be handy only if used once!

Grounds were all cleaned not long ago, but ill re-check the usual culprit areas.

10 years is the expected life of trons. 8 Years on a "red hot" PMD is a good run. Will said it best, but, I will X2 and say a spare PMD can't hurt.

I would run a "Wiggle Test" on that old PMD extension cable with the engine running and see if it's starting to fail by stalling or a skip of the engine.

Grounds as suggested and also look at the positive battery cables and connections.

Fuel. What's really in there? Does it smell like gasoline? Is it good "CLEAR" diesel? Cloudy diesel like from bugs, low quality etc. should be verified. Same diesel source?

Is the shut off solenoid working including wiring? The computer will code on wiring to it, but, if it sticks shut or leaks air...

Last the hose to the IP is suspect for kinks etc. Simply covering every possible cause. IMO this would vapor lock and cause bubbles to show in the return.

You can attempt to replace the Optic Sensor and clean the wheel before replacing the IP.

Diesel fuel is good and clean. I can tell you that from years of fuel system work on all our equipment. We have a bulk tank at the farm that's been filled by the same supplier. And this is my personal truck, so it gets extra attention to filter changes and additive on a regular basis. Even has a newer fuel tank and bio-fuel lines.

Ill have to take a closer look at the shut off solenoid and wiring.

I was actually in the process of looking into replacing the optic sensor, but from everything I've read I'm beginning to think at that point I'm better to just replace the entire pump as the rest of it might not be far behind. Unless everyone seems to think its worth it, then maybe ill give it a shot.

-Nick

 

[WarWagon]

There is always a DB2 conversion... After all if you wind up swapping pumps.

 

[Will L.]

Yeah really, if you end up swapping anyways, db2 makes life easy...
What is smog requirements like in Connecticut?

 

[HighSierra86]

There is always a DB2 conversion... After all if you wind up swapping pumps.

In all seriousness, I would love to do this. However, it was always my understanding this could only be done on OBD-I trucks correct? If I can do this with my '96 OBD-II, then there isn't even a discussion. That is the route I'm going to go. I have the NV4500 in this truck, so that's already one less hurdle to jump around...

Yeah really, if you end up swapping anyways, db2 makes life easy...
What is smog requirements like in Connecticut?

CT emission laws are quite relaxed. I've always passed with flying colors on everything unless a light was on. I have farm plates on the truck now which is exempt from emissions all together. I would have to take the truck to emissions with any other plate. I cant even remember if they used to plug the truck in or just do the tailpipe test with this truck when I first got it.

 

[1994ch]

you would probably have to get the computer re-flashed or live with the SES light on all the time, but I do not know of any reason you could not swap it. Bobby Martin made a great guide on swapping and all that was needed. Most of the work is getting the tranns to work right, but since your truck uses your hand and foot.......should be pretty simple. I still recommend looking up that guide cause I think there are a few things like different injection lines, etc to think about.

 

[1994ch]

Here is a link to that guide http://www.mediafire.com/?4wj51rn22o6z6

Should give you a good idea what is involved.

 

[1994ch]

Link to the post http://www.thetruckstop.us/forum/threads/the-db2-conversion-guide.30127/#post-354769

He does say that the guide is for the OBD-1 trucks but I think the differences would only involve the tranns wiring.

 

[Will L.]

Well... the whole purpose of the ds4 is so the obd2 can monitor the fuel info for the ds4. epa said a fompiter has to read and tell how much fuel is bieng asked for and delivered. (So howcome the db2 is more fuel efficient? Haha).

Before dmv started freaking out here and eliminated doing it, I converted one of mine, hut been so long ago I don't remember what I did about half the rig never "turning on".
I used to get free vdo gauges back then, so I ripped out the dash and did all mechanical gauges. I ran a hot lead from the ignition to a hd solenoid- that powered fss, alternator, fuel pump, etc.
Wish I had an easier answer to make it work for you.

 

[HighSierra86]

Thank you for the above link. I will have some bedtime reading material now. Looks as though the automatic transmission would be the most troublesome with the conversion, which I obviously have no issues there.

I did a little more digging on my current problem today. Need to have the truck operational for the time being while I gather all the parts for the conversion.

Swapped in a used (known good) PMD. I'm instantly back to my quick starts and the truck seems to run noticeably smother at lower RPMS. Maybe its all in my head, but that was my first impression with a test drive. I did however get the P0251 code back on the second start up. The light came on with the key in the run position and stayed on after the key start cycle. Cleared the code and havent seen it back for the last few restarts, so i guess I'll just wait and see what happens...

Just for the hell of it, I ran the truck through the "2000rpm test." Still not sure what exactly indicates a pass or fail with this. Seems to be very spotty information in regards to it. The pedal seems to be very sensitive to any movement where as getting it right at 2000 seems a bit of a challenge. And trying to slowly let it down sometimes leads to a quick drop in rpms. However, with the high idle switch the truck holds perfectly steady at the desired speed. Is it really a pump issue or a sensitive pedal?

Either way I'm getting excited to get rid of these damn electronics and go back to the manual DB2.

-Nick