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6.7 missing/ popping... i need some help

23388 Views 49 Replies 7 Participants Last post by  Alphamax81
looked everywhere on here for other threads with my symptoms with no luck. so here it is... just switched from h and s to efi live from fleece about 3 weeks ago. ran great till a few days ago. was driving to work at a steady speed and it had a little hiccup miss. Didn't think much of it. prior to this (night before) i got a map sensor code two times in a row after deleting them. when i went to leave work i had to give it a little bit of heavy throttle to keep up started missing/ popping. any time i would put a load on the motor as in heavy throttle or go up a hill it would have what i call a little hiccup miss or cut out got a split sec and you can feel the truck jerk back. when i made it home it had the a slight miss at idle but it would happen a random and just barely feel the truck jerk slightly. so i drove back to work and switched out both the sensors on the air intake and that seemed to help it.didnt notice a miss at idle and it feels like i have to really try to get it to miss under a load maybe once you get the revved up to 2800-3000 and get the boost around 40 it will really miss and jerk its worse. rail psi stays between 23-25kpsi. i think its electrical but what do i know. lol doubtful its an injector cause they just got tested a year ago and 5 rebuild by area diesel. has no smoke white at all on start up. any help is much appreciated!!
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Hows crank time?
Watch rail pressure as you crank and take note?
Got a temp gun? Shoot manifold at each cylinder and note temp differences.
Bad connection at harness plug and are loose connection at injector.

A few things to look at and report back.
No that seems normal. Obviously if its running fine at the time you checked the temps, they will show to be within reason.

To completely rule it out I would try to catch it when its running bad.

Does it do this under light throttle as well as wide open? Sorry if noted already, my mind is tied up remembering a bunch of other things at the moment.
What size cp3 are you running?

If its an actual popping kind of noise my guess would be an electrical connection of some sort. Check your wiring, specifically the fuel rail sensor wires. Move all wires and plugs that have something to do with that circuit while the engine is running.

It could still be a fueling issue if it feels more like your turning the key off and on while under WOT. Have you monitored lift pump pressure while this is happening? How about a full tank of fuel versus 1/4 tank?

Happen to notice if its boost specific? Note the psi when it happens, is it consistent? 36psi?

Process of elimination, you'll:thumbsup: find it!
You wouldn't think so. I am a firm believer on if it didn't do this before and now it does it may be the issue.

I would definitely look over your work to make sure all is good on the sump.
The pop backfire noise definitely sounds like electrical though. I chased this on mine back when i built this motor.

Brand new wiring harness had a broke wire in the plug at the fuel rail sensor. every time the engine would torque over under heavy load it would pull on the harness and make the connection issue.
Have you noticed it worse with lights on or lights off. Another scenario to look at is your alternator. Lack of amperage will play havoc with injectors.

Voltage may show ok but running amps may be diminishing. How old is the alternator?

Lots of things could cause this, just have to narrow it down.

Do things like crank and turn all power draining sources off. How does it idle, does it miss when you try to brake boost, at what RPM, whats rail pressure doing.

Do same thing with lights on. Anything change?
At least youve determined you have a rail pressure issue. Now just need to find out whats causing it.

If you've moved all wires and connections while the truck is running and it doesn't act up, it may be an injector acting up.

It would be great if you could get it to act up and isolate the potential bad injector or connector tube leak with temp gun. It would save you the next step of process of elimination.
If you have any doubt about the connector tubes being tight enough, I would start there.

The popping still gets me though. I've had bad injectors and leaking connector tubes and it normally just white smokes, misses and runs bad.

I guess it could still be an issue in the solenoid part of the injector.
No it returns in the same trac as the injectors do. Exits the rear of the head back to fuel tank.

The cooper washer is the seal on bottom and O-ring on top.
There is an allowable amount of fuel that will be returned. Even brand new injectors have return.

Allowable is 1.5 FL-OZ for 30sec crank time. (Dont Start)

Max 6 FL-OZ for 1min Idle time.
How long has the rail plug been installed?
You said this started after the sump instal.

Did you do anything else to the truck at this time? Instal CTS, Tap Any Wires, Rail Plug, ETC...
Beings you've reused the connector tubes 5 times and only rebuilt 5 injectors, I think you need to check for high returns.

This will let you know if its injector/connector tube related.

If returns are normal, then its a good chance the cp3 is your problem.

Connector tubes will develope rings around the tips from sealing to the injectors. Over time and multiple uses the tend not seal properly.

The procedure is to cap the rail for each cylinder until the problem is isolated.

Fleece can test your cp3...
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Part #4918298
Fuel System Leak Tester
Used to cut off injector fuel supply when diagnosing injector leakage
or malfunction. (Used on fuel rails with 18 mm threads).
cap the rail by taking the line off and putting a cap on it? I have never heard of this but ill do whatever it takes to get this unit back up on her feet. what if i did an injector kill test on one injector at a time and drove the truck to see if it quits popping on one of them. would that be the same a capping the rail? also can i visual inspect the tubs and see problems?

Im sure it would help narrow it down.

Yes, just look for a dent are bad groove cut in the sealing surface on the tip. They will most likely have a slight ring around them which is normal, just make sure its not deep are overlapping.

Theres also an edge filter inside the tubes. If you've ever had bad fuel you might consider changing them anyway.
Pretty fair price. I get them a little cheaper but I also spend over 200k a year with these people.

Might check with Jeff at Mumau Diesel, hes a cummins dealer in PA. I buy a lot of things from him as he knows his parts. Its just easier and more convenient dealing with him as long as your not in a hurry for the part.

If i have time to wait for the two days to ship he gets my business!!
Pull your FCA plug and see if it maintains max rail at idle.
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