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1996 Chevy C3500, 142K miles on engine. About 3,000 miles ago, it started hiccupping while running, first only under hard throttle and then eventually all the time. I FINALLY got it to bust a check engine code and I got P0251 - Injection Pump Metering Control A. This is not the first time I've gotten that code.
Amusingly enough, when the check engine light came on, the engine stopped hiccupping and started running as smoothly as could be. The change was immediate.
Does anyone here have any idea what could cause that problem, and what the likely fixes are? I really don't want to drop two grand for a new injection pump. The truck is still in good shape but I fail to see why a diesel engine should blow a part that important after "only" 142,000 miles. They're supposed to last much longer than that!
Don't know about Chevy diesels, but my old Ford/International diesel also uses an IP and the consensus seems to be that 150K miles is about when you'd expect to be looking at a new one.
One trick that may be worth trying... Take off the fuel filter, fill it with Diesel Kleen or ATF, then let the truck run for a minute or two, long enough to get the fluid in the pump. Shut it down, let it sit overnight, then drive it like like you stole it. It's supposed to help get the gunk out and always seems to get good results from the gs that try it (haven't done it myself).
Mike
Last edited by whiteboyslo; 01-05-2013 at 05:33 PM..
Don't know about Chevy diesels, but my old Ford/International diesel also uses an IP and the consensus seems to be that 150K miles is about when you'd expect to be looking at a new one.
One trick that may be worth trying... Take off the fuel filter, fill it with Diesel Kleen or ATF, then let the truck run for a minute or two, long enough to get the fluid in the pump. Shut it down, let it sit overnight, then drive it like like you stole it. It's supposed to help get the gunk out and always seems to get good results from the gs that try it (haven't done it myself).
Mike
Would this still work if I just got a new fuel filter put in, maybe 100 miles ago? I thought a clogged fuel filter may have been the problem, and it'd been quite some time since I last had it changed.
Yeah, should be fine. No need to install a new filter for this. Just remove it, drain out the fuel, put in whichever product you decide to run, and put it back on.
THis is typical for them The injection pump control module is mounted on the intake manufold under the center, and gets overheated easily, causing it to miss and sputter like you describe. The fix is to move the control module out into airflow, using a kit to relocate it. You can either move it to the top of the intake manifold with a finned cover, lie was on mine originally, or the best is to use a 6' extension cable and relocate it to behind the front bumper, which is where most of us with the 6.5 TD s move it to.
THis is typical for them The injection pump control module is mounted on the intake manufold under the center, and gets overheated easily, causing it to miss and sputter like you describe. The fix is to move the control module out into airflow, using a kit to relocate it. You can either move it to the top of the intake manifold with a finned cover, lie was on mine originally, or the best is to use a 6' extension cable and relocate it to behind the front bumper, which is where most of us with the 6.5 TD s move it to.
I'm hoping it isn't the PMD. I just replaced it two years / 19,000 miles ago. I had the problem you described, and it has been fixed by mounting a new one in a different place.
I was asking about the "optical fuel temperature sensor", which the shop says I need.
Thread is a bit old, but I'll chuck it out just in case the OP is still struggling with it.
Code P0251 is indeed related to the injector pump optical sensor.
However, it's not always as bad as some think. There can be a few causes for this code. I'll try to put this in as much layman's terms as I can, as it can get quite technical:
In a nutshell, the PCM sees and error in the optical sensor functioning.
The optical sensor functions by "looking" thorough a spinning disc in the IP that has "windows" in it. The PCM uses this signal to properly time the injection events to the crank rotation and in turn the piston's rise and fall.
When the sensor has a problem "seeing" though these windows, the PCM sets a code p0251.
The Optical sensor is calibrated to "look through" clean straw colored diesel fuel. It can't see though air at all and doesn't deal well with water, bubbles or some fuel contaminants that make the fuel too dark. These conditions will cause it's signal to fail and set a p0251.
Causes of these things can be air getting into the system, weak or dead lift pump, water in the fuel, running very low on fuel or running out, etc.
Check out your lift pump and see if it is running and giving you around 7-9 psi static. It shouldn't drop below roughly 4-5 psi at WOT.
Check to see if you're getting air in the system. You can run a clear house on the water drain line and pump some fuel through it. If you see a steady stream of any sized bubbles, you have a pinhole or other sized hole somewhere between the filter manager and the tank. This can be a real bummer to hunt down....
Another possible cause is the optical sensor filter harness. These are notorious for failing. chek the wiring harness coming out of the optical sensor and the filter harness will look like a little box in the wiring. 96+ trucks had this filter incorporated into the PCM so you can just unplug it and toss it in the trash. For some reason, GM kept installing in it in these trucks even though the redesigned the PCM. The wiring harness is still long enough pull it up and plug it directly into the optical sensor and the 96+ trucks run just fine without.
Lastly, it can be a failure of the optical sensor components. If the sensor itself has failed, it can be replaced, but there are some very specific procedures that need to be followed. The optical sensor is set up when stanadyne builds/rebuilds the pump on a test rig. Get it wrong and all kinds of drivability problems can arise such as super sensitive throttle. It's not cheap either, somewhere around 350 bucks.
If the IP disc (spinning thing with the windows) is damaged, you have to replace the IP assembly. This is a pretty good shock to the wallet. Depending on where you get one, it can be anywhere from $500 to $2000. Stay away from anyone who is not an authorized rebuilder (the $500 guys). They almost always cut corners, use old worn parts, don't swap in the updated Stanadyne pieces (ceramic pistons and rollers to better deal with ULSD, etc) and don't have the proper test equipment.
I'll chuck up a picture of my truck just so you know I'm not talking through my hat and that I do indeed work my truck good an hard:
My husband has a Chevrolet 6.5, k 3500 ,1995 stick shift, dully diesel. Upon starting it will not turn over, emits a heavy white smoke and sounds to be missing it can take up to 5 to 10 minutes to get it started, sound is like a bluh bluh bluh bluh, once it starts and clears it runs perfectly and will start perfectly for the rest of the day, but gives the same trouble the next morning. Does some humping or surging while driving sometimes. We have taken it to Register Chevrolet, they hooked it up on the computer ,nothing was found, no codes , nothing. We have sent it to SEVERAL diesel mechanics spent more than the truck itself is worth. He uses this truck for work it is a pump rig, has a boom for pulling out pumps, plus boxes around about 11,000 lbs. This is extremely urgent Question as this is our personal business and this truck is our lifeline. We haven't found one mechanic who can figure out this problem. Have a mechanic now who is confused and says lets start with the fuel pump, fuel filter is new, PMD module is new and relocated, throttle position sensor is new, and a turbo sensor was replaced. Has sat on clean concrete to check for leaks and there are none. Any answers or suggestions from previous experiences?
a few points, given that the truck starts/runs properly once it's been started on a given day:
1) Don't let any "mechanic" simply start exchanging parts to see if they make a difference
2) these engines are known for not starting well if the glow plugs aren't functioning properly, and are a necessity for that first cold start of a day
3) white smoke out exhaust on engine cranking is fuel being delivered but not igniting, this pretty much rules out the fuel pump and related fuel delivery items
4) how many miles are on this truck? if the engine is high mileage, it may be worn to a point where the engine compression is low, which also makes for difficult starting when cold. Perhaps a compression test is needed to diagnose this engine
5) glow plugs are easy to diagnose for condition, any diesel mechanic should be able to "ohm" them and/or remove them and visually check by applying power to them and watch them glow red.
6) the glow plug relay circuit may not be delivering power to the glow plugs. Again, easy to verify by a mechanic
7) if you haven't done so already, try plugging in the block heater overnight and see if that makes a difference in the cold starting the next morning. If it does, it's pointing to glow plugs and/or low compression issues with the engine.
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My Husbands truck.
