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DTC P0251

MrMarty51

MrMarty51

Well-Known Member
Messages
20,676
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Location
Miles City, Montana
On my way to Sheridan Wyoming and then back to the cabin and the lake.
Made it about 25 miles and this DTC pops up.IMG_3564.jpeg

I emailed QS Tuning a few minutes ago so waiting for a reply from them.
Cleared the code and it pops right back up.
Engine falters when it does but then picks up and runs like nothing is the matter.
I have about five to ten miles to the next exit where I can turn around and head back home.
Anyone think it would be safe to continue on My trip from Miles City to Sheridan Wyoming ?
 
Will L. said:
Is this with that brand new ip?

And no- long potentially danger trips are not advisable with a 251.
Click to expand...
Yup. Brand new not remanned IP.
From where I first checked the code and sent out the distress call to the forum, the truck went to the rest area about five more miles down the road.
Pulled into the RA and rechecked and cleared the code.
Started the engine, fired right up, tripped the SES lamp again and the engine kind of stumbled.
Was going to go about another five miles and turn around to go back home.
Put the truck shifter in OD and the engine killed.
There it set.
Called AAA and once again the roll back came and loaded me up.
I told the owner of that truck that there is nothing the matter with my truck, I’m just trying to improve my fuel mileage. We laughed. 😹😹😹
This is the third time this truck has been on his roll back.
 
I’m getting good at yanking these IPs.
I didnt time it but I’m guessing about two hours and that included hauling the tools from the garage out to the boulevard and street side.
Yank that inner fender and turbo, pipes and manifold and that pump is setting on the bench, trying to get it ready to ship back to Quad Star.
The ground wire that attaches to the top of the pump, I had to clip that in order to install the wire harness from my old pump as the harness on that brand new pump was compatible with only the Stanadyne grey box and not the Dorman or Flight Systems box.
I hope they are okay with that when they get the pump back.
Now I’m going to install that lower mileage used pump I purchased from the Humvee site.
I believe that one will run the distance.
My hopes are that one of these times, this truck will leave the yard and make an entire round trip journey.
 
MrMarty51 said:
I’m getting good at yanking these IPs.
I didnt time it but I’m guessing about two hours and that included hauling the tools from the garage out to the boulevard and street side.
Yank that inner fender and turbo, pipes and manifold and that pump is setting on the bench, trying to get it ready to ship back to Quad Star.
The ground wire that attaches to the top of the pump, I had to clip that in order to install the wire harness from my old pump as the harness on that brand new pump was compatible with only the Stanadyne grey box and not the Dorman or Flight Systems box.
I hope they are okay with that when they get the pump back.
Now I’m going to install that lower mileage used pump I purchased from the Humvee site.
I believe that one will run the distance.
My hopes are that one of these times, this truck will leave the yard and make an entire round trip journey.
Click to expand...
Geez you’ve been through hell on this. I’ve been there on the ‘94 and you helped diagnose it with the loaner IP. Hope you finally get this resolved so you can enjoy the truck.
 
Big T said:
Are you saying the brand new Stanadyne IP which costs $2700 failed on you?

That AC Delco reman I got for $794 is running strong.
Click to expand...
Yup.
Got a reply back from John at QS.
In His reply He included this link.

PO251 and Optic Sensor Troubleshooting

Customer Reports: " Pull out onto the main road, rpms only go to 2200 and no power. Lags at 2200 for a moment finally shifts to second gear. This repe...
quadstar-tuning.frontkb.com quadstar-tuning.frontkb.com
It doesnt really match what My truck was doing.
Even with the SES lamp ignited acceleration was still good.
Then after getting to the rest area and clearing the code again, engine would crank a little longer like a possible optic sensor fault but then putting the shift lever into gear would kill the engine.
I just now sent Him another email asking if there is anything He would want me to attempt to do with this new pump before I install one of the used pumps.
 
I wonder how safe it would be to install an IP and fuel lines, install right side manifold heat shield and turbo them take the truck for a drive before installing the lower and upper intake, inner fender and air filter.
Hope for no road debris to kick up ? ? ? ?
🫣🤷😹😹
 
Sort of holding off to see what John wants me to try next to diagnose this problem.
I hope it doesnt involve reinstalling the pump.
His article on diagnostics kind of leads to a bad optic sensor.
IDK if I have the abilities to replace one of those.
I have read the instructions about that and it seems to be a bit complicated.
 
I’ve had optic sensor issues a couple of times. Most recently was a couple years ago on my newly remanufactured IP. The truck ran ok but, the internal seal failed and was allowing diesel to blow through the connector and into the wild. Apparently, the original sensor supplier isn’t making them anymore either. The exchange isn’t too complicated a procedure but, the devil is always in the details. The most important thing is to ensure the sensor itself goes back in with the same clearances as the one that came out. I was told to scribe a line but, both times I used feeler gauges to get the side wall to sensor clearances set and went with that to install the replacement. No issues.
 
Having to replace an optic sensor in a BRAND NEW ip or even one you buy that is a rebuild is completely wrong.
Buy a long block engine and have to replace an oil pump or oil pan? No.

If a new ip is faulty and has to get replaced by a shop- the distributor pays for a cut portion on labor costs. This is why a mechanic shop never installs parts you bring in. They loose a little money on marking up the part- but more so any problem it has becomes their problem and lost revenue. So when they have to return a part under warranty- they basically get a credit on their account towards future purchases. The distributor won’t do it for tiny shops with low volume, but you better believe dealerships and large shops get it.

Diy guys- it is normal to not get anything because we have no buying power and they wont loose money on one sell to hops they get enough sells later to make up the loss. But to expect you to diagnose then disassemble part of the ip, where if you do it wrong and they mail you the new optic sensor- then the ip still doesn’t work- no. I just never heard of that.
 
Have the used IP I just purchased from off the Hummer forum.
Truck runs and no leeeeks.
I have the heat shield and turbo bolted in position. Coolant is filled. No intake manifold as of yet. Was making sure this was going to fire and run first.
Warmed the engine to about 175*. Installed the temperature fooler device from QS tuning, I really like that little tool, thanks to @Paveltolz for mentioning that device in a thread or post You had submitted.
Although, be sure to sufficiently warm the engine to where it will not need the GPs to fire and run, at least with the tune I have, with a cooler engine mine wont run through the GP cycle. I found that out one morning after I had forgot that it was plugged into the sensor harness.
Anyhow. I been using a stick of angle steel between the rocker covers and thats a big aid in getting the IP close to the proper timing offset angle.
The passenger side of the back of the IP needs to be angled very slightly lower than the left side.
First startup after installing this used IP.
IMG_3569.png

The engine fires right nice.
I am wondering though, without having the intake manifold bolted to the heads and the turbo hooked to it, even with the baro and intake temp wires connect, when revving the engine it seems to cut out and blow a lot of black smoke.
Is that normal when revving without having turbo pressure, even as slight as it is with turbo hooked to intake system ?
 
Also, one other question, is it okay to reuse the intake manifold gaskets ?
I been getting the blue gaskets from NAPA, they always appear to be okay after removing the intake manifold.
Seems I been removing and reinstalling IPs so frequently its been costing quite a bit for intake gaskets, about $39.99a set.
The problem, I get the truck together and it seems to be running just great then something goes the matter with the IPs and it all has to come apart again.
There goes another $39.99 It adds up fast.
I been going through them things so fast that I even have a spare set on order for me to keep on my shelf.
 
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