Motor Stumble/No codes

[HHDLea]

Ole girl is giving me fits... Driving with minimal skinny peddle the motor is stumbling. It only last for a second or two and then recovers. If I lay into it it will recover. No real power loss noticed. Mainly happens once the truck is warm and in the higher gears. Starts and idles fine. No codes thrown and LP pump seems to running fine, no low flow light. The no codes leads me to believe it is a fuel issue, maybe my cp3? I have about 160k on the OD. Any help would be greatly appreciated!

 

[Got HO?]

Mine is doing the same thing. I know my lift pump is weak, dips below 5 psi on full throttle. Putting in a FASS 95 gph pump this weekend and will report back. Possible APPS symptom too, not ruling it out, but am going to do what needs doing first. Fuel filter is new.

 

[JJPage]

The OP only shows a Smarty in his sig...

My truck had similar symptoms twice. 1st when my EZ crapped out, 2nd when the TST started failing. Removed the EZ, all issues ceased, until the TST acted up, sent it in for upgrade, no problems since.

HO, once your truck is running, even a failed oem(BD not sure) lift pump will not cause a stumble, the CP3 has the ability to pull the needed fuel to remain running.

 

[Bob4x4]

Depends on how the pump fails if fuel can be pulled through it. Remove the lift pump and yes the ip can pull fuel

 

[Got HO?]

The OP only shows a Smarty in his sig...

My truck had similar symptoms twice. 1st when my EZ crapped out, 2nd when the TST started failing. Removed the EZ, all issues ceased, until the TST acted up, sent it in for upgrade, no problems since.

HO, once your truck is running, even a failed oem(BD not sure) lift pump will not cause a stumble, the CP3 has the ability to pull the needed fuel to remain running.

Still driving it, pump hasn't failed but low pressure warning light comes on under acceleration. I have a 5 psi pressure sensor at the CP3 inlet. I bypassed my TST and the symptoms were still there. I currently have a BD frame mounted lift pump, and I'm on the 3rd one. They don't seem to last very long, so I've decided to try a FASS. Could possibly be a CP3, mine has 281k on it, injectors replaced with new Bosch about 5k miles ago though.

 

[cerberusiam]

Even a worn out fialing CP-3 can make enough pressure to handle the requirements at low speed low throttle opening. Now, if it is grenading internally and spitting metal into the injectors that is a different story. If you have ANYTHING on the TST hooked up it can throw noise into the system and cause problems.

 

[Got HO?]

Even a worn out fialing CP-3 can make enough pressure to handle the requirements at low speed low throttle opening. Now, if it is grenading internally and spitting metal into the injectors that is a different story. If you have ANYTHING on the TST hooked up it can throw noise into the system and cause problems.

I disconnected the system completely for testing. Odd thing is, it's not all the time. I want to ensure a good constant fuel supply to the CP3 first and then see what it does. Was wondering if the potentiometer on the APPS wasn't simply wearing out.

 

[cerberusiam]

Was wondering if the potentiometer on the APPS wasn't simply wearing out.

Yep, it is possible to have them do that and not throw codes. Fan starting to short out or seize, AC wire rubbing, corrosion in the ECU connectors are all possible with intermittent glitches like you describe.

 

[HHDLea]

What baffles me is that its not triggering a code. I should get a HP gauge and a LP gauge but I am hesitant to spend the $.

 

[HHDLea]

My Air Dog is piped directly to the CP3.

 

[cerberusiam]

My Air Dog is piped directly to the CP3.

That is why I doubt it is the CP-3. Anything is possible but if you are only seeing problems at low speed low throttle opening, your power is still good and EGT's not excessive, I doubt it is fuel related.

 

[jgillott]

I had an issue a couple of years back with my '07 where I had a similar stumble without a code. It turned out to be the connector on the fuel rail pressure sensor. No Idea if you have a similar issue, but it is worth checking that connection also.

 

[SierraRam]

Could also be the FCA sticking/failing.

 

[Got HO?]

Replaced the lift pump this morning and drive it. No more low pressure warning light on hard acceleration, but the light throttle stumble/surge was still there. I had a spare APPS from years ago in my shop that I purchased when troubleshooting another issue I had (turned out to be the PCM), so I bolted it on and drove it again. So far so good, no sign of the surge. I'm hoping that was it.

 

[HHDLea]

I am going to swap the APPS out with one from a friends 04. We will see what happens.

 

[Got HO?]

I am going to swap the APPS out with one from a friends 04. We will see what happens.

After the install, turn the key on and slowly depress the throttle to full throttle and back to idle, engine not running. This initializes the idle and full throttle parameters.

 

[Got HO?]

Update. Have put about 1k miles on the truck since the APPS and lift pump replacement, no stumble or surging evident at all.

 

[HHDLea]

Sorry that it has taken so long to reply. I travel all the time for work. Today I had a friend that has a shop monitor the truck going down the road on his computer. The apps spikes between 14 and 16% throttle. He joked and said I should just keep it in 5th gear... . I ordered a new TPS from Geno's today, looks like thats it. Thanks for everyones inputs!