1996 Chevy C3500 NO POWER and Codes

[troe3696]

Hello,
I just wanted to start out by saying this page has been a big help to me in the past and I appreciate that.

Well here is the story I just bought a 1996 chevy c3500 with the 6.5 TD. Truck has been sitting for 3 years ( I put a brand new transmission in it 3 years ago and the guy never drove it since)
The truck fired up but was hard starting and only started with the pedal pressed. It through 2 Codes P0251A and P1216D and the truck has maybe half power I can get up to 60 mph on flat ground and hammer down. The truck downshifts and doesnt feel like it has anymore power in a lower gear than in overdrive. The truck is not making power.

Here is what I have done so far......

1. drained fuel and added 20 Gallons of fresh fuel and 2 bottles of diesel 911 additive

2. Found lift pump not working so it was replaced and now I have good flow from fuel filter bleeder and the T water drain valve

3. added inline frame mounted CAT Filter assembly before the lift pump

4. The truck idles well after the hard start

5. The truck blows no smoke besides a few small white puffs during hard start

6. The turbo sounds like it spools up I am not really schooled in these 6.5 diesels ( seems alot quieter than my D max )

7. The truck back peddles when I hit a hill of any sort

8. pmd has been relocated well before I ever seen the truck and does not stall out randomly like most pmd problems

Like I said I am very new to the 6.5 diesel I have a OTC Genisys 3.0 scanner and any tools I may need to Diag this truck (I Hope)

I have been reading about injector timing and optical sensors alot but would like some opinion from some seasoned 6.5 guys

It doesnt seem like anyone local or in this area are familiar with the 6.5 enough to really help Is this motor a real mystery?

 

[btfarm]

Welcome to The Truck Stop troe! :welcome2:

The 6.5 guys here ought to be able to help out on this.
Where are you located?

 

[troe3696]

Hello I hope so,
I am in Pontiac Il.
Pretty cool to see a somewhat local guy on here!
Yea the truck is pretty much just grocery getter at this point would never be able to pull anything the way it is..................

 

[ak diesel driver]

The first code is generally an IP code. I would start by putting a fuel pressure guage on the fuel line right before the IP. there are a couple of screens that could be plugged and that will tell you the health of the system up to the IP. also put a piece of clear tubing on the return line coming out of the IP to check for air.

 

[troe3696]

Thanks AK for the wisdom
That is my plan today to check fuel pressure at the IP and if its bad drop my tank and eliminate my pick up sock since I am running a large inline filter system. Have you ever had your truck act like this?

 

[troe3696]

Also how much pressure should I have at the IP I have heard 5 at idle and 1-2 at WOT?

 

[ak diesel driver]

don't forget there's a screen in the FFM and IIRC one in the inlet to the IP. those pressures are ball parkish

 

[troe3696]

Well here is what got settled today.
1. 6 psi at the injector pump at idle
2. 3 psi at the injector pump at WOT
3. Changed pmd with a known good one NO change in the truck at all....................

Any idea's on the next step? Thanks everyone!

 

[troe3696]

and my lift pumps output at the IP is almost 10 psi not running.

 

[ak diesel driver]

did you check the screen in the IP fitting? Next I would unplug the optical sensor and see if it runs, if it does unplug the crank position sensor and see what it does (don't unplug both at the same time)

 

[great white]

251 is an optical sensor related code. If it's an active fault (ie: check engine light on) it usually means the optical sensor is having trouble being read or it's got over 8 missed counts on the "tone wheel" in the pump. All is not lost though, it can be a s simple as air bubbles in the fuel. The "eye" in the sensor gets confused if it has to look through air instead of fuel since that's what it's calibrated for. A simple clear line on the pump return will tell you if you have air bubbles in the fuel. If you do, you may have a small air leak in one of the old lines somewhere. Fuel that is too dark can also cause issues with the OS (IE: waste oil, etc). Running the truck very low on fuel can also cause this code to pop up (air bubbles again).

The old optical filters used to cause this code also, but I do believe they were not installed on 96+ trucks.

Mine threw the 251 code several months ago and I had to change out the optical sensor. But; my truck was bucking and stalling. Yours seems to be a different type of fault from your description.

1216 is fuel solenoid response time too short. The PCM listens for confirmation from the PMD that the fuel solenoid has closed. At this point, I don't think I would chase that one down until you sort the cause of the 251 code. The response time too short often comes up when something else goes whacky in the DS4 system. That seems to make sense to me because if the OS is having troubles, the PCM is going to have trouble timing the injection event properly or it's going to default to crank sensor timing only.

1 Psi from the lift pump at WOT is not great, but it's also sufficient for normal running. It is possible you might have a small bit of air intrusion behind the lift pump to the tank and that could be the cause of your 251.

I would suggest the clear line on the pump return to see if there are air bubbles. It's quick, easy, cheap and will eliminate air as a cause in short order...

 

[troe3696]

Nice write up Great White I have 3 psi at the the IP at WOT. AK I got the OS unplugged and drove it DID NOT change anything acted like I didnt even do it. I will unplug the crank sensor today and see how that changes things. Great White I am going to do the clear line and check for air in the system today also. I will keep everyone up to date on this mystery! Also AK I am going to pull that fitting out of the IP to check the screen and make sure it is not clogged. Thanks Everyone for all the great advice!

 

[troe3696]

Also the 251 and the 1216 are hard codes when cleared the light blinks and thats it. It is instantly back.

 

[ak diesel driver]

Starting to sound like the OS is bad and is running on the CPS. If the OS is bad it probably won't run when you unplug the CPS

 

[great white]

Also the 251 and the 1216 are hard codes when cleared the light blinks and thats it. It is instantly back.

Oh oh, that's not a good sign......

On a whim, do you have a spare PMD to slave in? I've seen this cure many weird faults.

Unplug the crank sensor as AK suggested. If it dies, the OS is highly suspect.

Do you have a multimeter that does frequency measurements?

If you do you can meter it and find out if it is outputting a good signal. There is a spec value for it, I just can't remember at the moment.

The other thing to check is if your scan tool has enhanced data reading and you can check the missed counts on the IP....

 

[great white]

I've also "salvaged" Optical Sensors before. It involves removing it from the pump, cleaning it and reinstalling. Seems the led "eye" gets "coked up" from just the nature of the diesel fuel it sits in it's whole life. A good blast of strategically placed electrical cleaner freshens them up again. At least it worked for a friends truck when I tried it and he's still going strong a year later. It's not always the problem, but I usually give it a try before installing a new OS, once installed they can't be returned.

They are any where from 300-500 bucks to replace.

You getting close to half the cost of a new DS4 at that point and I would suggest going that way vice changing out the sensor if you plan to keep the truck and have the cash to do it.

I changed mine out (had a spare OS also) because my pump is rebuilt with the newer ceramic parts already and mechanically sound. I've replaced nearly all the 'lectrical bits on the pump (everything except the advance motor), but the basic "roosamaster" rotary pump design is still going strong.

My spare was an old style OS I had in a pump I got a couple years back from Bison.

Stanadyne redesigned the OS a while ago. I believe the explanation was basically better resistance to fuel "intrusion"....kind of a backdoor way of saying "we messed it up the first time" if you ask me.

 

[troe3696]

Hello Everyone!
Great White I have replaced the PMD with a known good one, The truck will not start or stay running with the CS unplugged,
LOOKING GRIM!

NEW UPDATE!
Well I removed the extra radio resistor in inline with the optical sensor and I had removed the upper plenum to do it I found the gasket was broke and about 3 inches of it was not sealing at all.

Here is the result
The truck has a small amount of more power.... ( Very Small )
Codes will not clear and come right back still except now the 1216 turned to 1217
and it still has the 0251a code.

Still very hard starting and without the pedal depressed some will not start on its own at all will fire and die.

Still wondering what this big mystery is........

Also The IP has the green tag on it it was replaced at some point....... I also checked all the grounds yesterday cleaned all of them on the engine chassis and batteries....... I think with the truck sitting so long The IP got plenty dried out I believe they have plungers in them that seal with O rings? I am going to run it for the next few days and see what happens if it improves at all anyway. Any miracle cures I am all EARS LOL!

 

[great white]

So, now you've got the OS code (251) and the solenoid response time too short has changed to a too long.

The truck should run in "backup fuel" with only the OS, if it's working.

Does the truck run acceptably with the OS unplugged and only the crank sensor plugged in?

Just out of curiosity: there's a resistor card in the PMD socket, right?

 

[troe3696]

The truck does run well besides cold start and NO POWER weather the OS is plugged in or not, There is a resistor card in the pmd...........
Thanks for all the help everyone hope I can get this pig back running right!

 

[great white]

The truck does run well besides cold start and NO POWER weather the OS is plugged in or not, There is a resistor card in the pmd...........
Thanks for all the help everyone hope I can get this pig back running right!

Do you have a scanner that can read missed OS counts or a multimeter that can read frequency?