Miss at idle and surging when driving

[Shuff]

2014 Ram 3500 6.7 Cummins HO – 225,000 miles – weight loss done around 95k (original owner)

No codes currently

I’m having an issue with a slight miss at idle. According to my scan tool, I’m seeing about a 15–20 RPM drop, but the tach needle on the dash doesn’t really move. You can’t feel it much inside, but you can definitely hear it in the exhaust from outside. The miss isn’t consistent — it will idle smooth for a while, then miss 2–8 times, then go back to running smooth.

While driving around 1400–1500 RPM, I can feel a light surge, more noticeable when going over mountain passes.

When the problem first started, it would occasionally idle fine at a red light, then randomly rev up to about 1000–1200 RPM, fall flat on its face, and then return to normal. After replacing the FCA on the CP3, that particular symptom hasn’t returned.

Other notes:
· No white or black smoke.
· No noticeable blow-by (oil cap test).
· Truck still gets 15.6–16 MPG around town.
· On a recent 4-hour trip (2 hours each way), computer showed 20.8 MPG, which is normal

Work already done / parts replaced:
· FCA on CP3 (Bosch) – 8/2025
· Fuel filters (frame-mounted + engine) with Mopar – 8/2025
· MAP sensor (Cummins, Geno’s) – 9/2025
· Intake air temp sensor (Cummins, Geno’s) – 9/2025
· MAF sensor (Cummins, Geno’s) – 9/2025
· Checked VGT, moves freely and re-calibrated – 9/2025
· Adjusted valve lash 8/2025
· Exhaust back pressure sensor was replaced after one code early on (code has not returned)

Current symptoms remain the same. Any insight or help would be greatly appreciated!!!

Thank you

 

[06 Dodge]

Are you using any bio diesel? Buying your fuel from a high volume station or local mom & pop? When was the last time you used a good whole system fuel additive, also who did you buy your fuel filters from? I hope you don't buy them from Amazon way to many fakes on that site..

 

[Shuff]

no bio diesel around me i can find. Normally buy my filters from geno’s garage. when this started happening i went to the dodge house and grapped a new set and installed only like 3-4k miles in this set of fuel filters.

Normally get fuel at costco which is top tier near me. plus us opt lube lubricant, and cetane boost. I just put a bottle of hot shot diesel extreme in this fill up.

 

[06 Dodge]

no bio diesel around me i can find. Normally buy my filters from geno’s garage. when this started happening i went to the dodge house and grapped a new set and installed only like 3-4k miles in this set of fuel filters.

Normally get fuel at costco which is top tier near me. plus us opt lube lubricant, and cetane boost. I just put a bottle of hot shot diesel extreme in this fill up.

Well at 225K you might be seeing the start of injector problems, as for the fuel filters were they regular Mopar branded box or was it their after market BPROAUTO brand (FS-1BP00869AA)?

 

[Shuff]

Snap on scan tool you can notice the miss/lope at idle. The command pressure, actual pressure rail pressure spike up, vgt and boost go down.

 

[Shuff]

Low Pressure Fuel Test:
Disconnected from the CP3 had 12–13 psi.
10 second flow test resulted in 600 ml, which seems to be within spec.

Pressure Relief Valve on Fuel Rail:
Removed the banjo bolt and installed the adapter on the front of the fuel rail. At idle, no fuel was coming out.

Performed the test using the scan tool at 1,200 rpm (max rail pressure) — fuel was coming out. This appears to be within spec.

Injector Return Flow Rate:
Not sure if this test was done correctly. Removed the banjo bolt on the CP3 return line and added the adapter with a hose to measure.
Disconnected the return line going to the fuel tank and placed it into a bucket.
Using the scan tool, ran the test at 1,200 rpm with max fuel pressure for 1 minute.
Not much, if anything, came out of the line connected to the CP3.
The fuel return line back to the tank was dumping out steadily.

Other Notes:
When the truck isn’t missing or loping at idle, the commanded fuel pressure graph is a straight line.
When it starts to act up at idle, you can see the misses or loping reflected as spikes in the commanded fuel pressure.

 

[06 Dodge]

Based on all the test you have ran an all is a ok then your left with the following injectors, ECU/PCM or wiring...

 

[Shuff]

Injectors:
Installed new fuel injectors yesterday Bosch brand new OEM with new fuel tubes. No hard start, smoke white or black. Symptoms are still the same as before. No check engine light.

Any ideas???