I have been having problems with fuel! I had the CP3 replaced and thought that was the problem! It wasn't. Basically it's like the truck is de-fueling especially in 5 and 6th gear. The truck is also makes more noise in the cab when it runs rough. I talked to Larry at Ekstam, he feels it's not the air dog. I know the injectors are ok. The truck runs good for about a mile then it start to run rough. When the truck runs good I can see 43lbs and 1600 egt no problem, when the truck runs rough 30lbs and 1200 egt's. The pedal feels weird from 1/2 to full when the truck is running rough. The truck has also stalled out after running down the road in the morning. It happened when I pushed in the clutch Any ideas????

 

Not that it can’t happen, but your symptoms don't sound like the symptoms others have had when their CP3 started acting up and was replaced. Just looking through the service manual, it doesn't give any procedures for testing the pop-off valve to see if it is opening. Someone here may have a way of checking it though. It is a little thing that is held in place by one banjo bolt and looks to be an expendable item, as in easy to replace for a reason. You may just have to replace it yourself and see if that helps. That little thing can't be that expensive.

How is it defueling? Does it go into sort of a smooth limp and just not want to get up and go, or is it physically spitting/sputtering/cutting out?

Give us some details...which engine do you have, what box(es) do you/have you run? Small detail but important....which intake system do you have on it?

Brian

 

What is your max fuel pressure reading?
What is it when the stuttering starts?
The pop off on these trucks is not always accurate. I think its supposed to open at 17 psi.
Some are opening a lot sooner...defective. If its right at its limit, I can see why it would stutter.
More often then not when a pop off fails...the truck will not start.

Scotty

 

I have the TST box on 2/2 anything higher than 3/3 with these injectors has to much fuel. The best way I can explain the problem is: I start the truck up for 15 min and drive it about a mile, then when I shift into 5th the boost will no longer go any higher. 22lbs was the highest I made this morning coming into work. The truck sat for 2 hrs and then I had to leave, it ran fine for about a mile again. Basically it's like having a govenor on the pedal when the truck runs rough. From 0 pedal to 1/2 it's ok after that you can push the pedal all the way down and it won't go any faster than it already is. It also get's real loud in the exhaust when this happens too. The truck also shut off for a split second and turned back on when it was in neutral, after driving it for 10 miles???

 

Check your codes...sounds like a bad TST harness. Or maybe just too much fuel?

What type and size of injectors?

 

I have a p336, but doesn't that come on when you hook up the tst?
If it's a bad harness, what cwould come up?

 

0336 is the Crankshaft Position Sensor Performance code.

Start by disconnectiing all the connections used by your box(es) and clean the thoroughly with electrical contact cleaner. Apply some dielectric grease and put them back together. See if this solves the problem. If not, remove the TST box and any other box you may have and drive the truck on just injectors. See if this solves the problem. If the code still comes up you may have a bad CP sensor. Hopefully it's just a bad connection... I have seen a little water in a connector wreak havoc on trucks.

John

 

Thanks I will try this tonight and let you guy's know! Thanks.

 

The "pop off valve" is the pressure limiting valve. There is a test tool that requires you to remove the banjo bolt and install a test tool that you attach a hose to and monitor to see if there is any fuel passing the valve. I believe the PL valve runs about $450.00.

 

what Jbody say is correct , there is tools for checking the amount of fuel bypassing the valve and is allowed some leakage , the valve is set at 1600 bars. on the Cummins side we use the Insite to run the CP3 at max pressure and check the leakage at idle into a flask.

 

I removed the TST and still am getting the problem. Has anyone had a CP sensor go bad? Could that be a heat related problem? When the truck is cold on start up and run it for a mile or two it runs fine then after that it runs slugish, could that be the CP sensor acting up?

 

Did the fault come back? If so, you need a new sensor or there is an open circuit in the wiring between the sensor and the ECM connector.

I have seen these fail. Mostly due to the fan eating the fan wiring and beating the wiring against the crank sensor.

Now that I think about it, if it is the performance error, it could also be the cam position sensor. It is there as a redundancy. you should be able to disconnect the crank sensor and still run the engine from the cam sensor (but it will run a little rougher).

I would take it to the dealer (with the TST removed of course) and show them the problem. If only to document it for later.

 

You really need to monitor the fuel rail pressure and set point that the ecm wants to see for psi. Another note on the psi limiting valve is that it will only let high psi fuel bleed by a few times. The high pressures involved will actually cut the seat in the valve and cause it to leak all the time causing some drivability probs. If it gets bad enough the truck won't run at all.

 

Would that explain the truck shutting off after driving 10 miles when you slow down or push in the clutch? After that happens all I do is turn the key off, turn it back on let it go through it's cycle and it fires back up?