Starts but backfires, misses, runs rough, won't idle
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2nd Gear
Joined: Apr 2026
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Starts but backfires, misses, runs rough, won't idle
I have a 2013 F250 with 6.2L
Today it will start, but barely, have to work the throttle to keep it running. May die, but will restart. It runs horrible, backfires while at idle an low rpms (below ~1200) out the exhaust and I think a couple of times out the intake. Runs rough, will keep running if held at 2,000 rpm runs is rough, but doesn't backfire. It may idle OK for a minute or so at 750 rpm, then you can hear it tune itself and starts to miss and slow idle to 400-500 rpm. Sometimes I can keep it running by modulating the throttle that gradually brings the rpms up.
Error codes are lean codes and misfires
The symptoms initially were hard starting with miss fire for the 30 - 60 seconds then would run fine. Then occasionally it would make a preignition pinging sound on initial acceleration. Now it's degraded to what I wrote above.
What's been done to this point, its been degrading over time...
Are we reading the right parameter in ForScan for Fuel Pressure, believe I have the acronym right from ForScan, don't have it up right now, FLP.... Fuel Line Pressure?
Starts but backfires, misses, runs rough, won't idle
Today it will start, but barely, have to work the throttle to keep it running. May die, but will restart. It runs horrible, backfires while at idle an low rpms (below ~1200) out the exhaust and I think a couple of times out the intake. Runs rough, will keep running if held at 2,000 rpm runs is rough, but doesn't backfire. It may idle OK for a minute or so at 750 rpm, then you can hear it tune itself and starts to miss and slow idle to 400-500 rpm. Sometimes I can keep it running by modulating the throttle that gradually brings the rpms up.
Error codes are lean codes and misfires
The symptoms initially were hard starting with miss fire for the 30 - 60 seconds then would run fine. Then occasionally it would make a preignition pinging sound on initial acceleration. Now it's degraded to what I wrote above.
What's been done to this point, its been degrading over time...
- All 4 O2 Sensors were replaced
- Replaced COPs, a couple of them had been arching
- Spark Plugs were replaced a year ago
- Thought maybe it was bad gas, tried the E85 trick, that cured the preignition pinging, seem to run better in general for a while
- Ran a tank and half of E85, backed it out of the garage in the driveway, on restarting it it started the heavy misfire and poor idling and rough running above and undrivable
- Sounded like low fuel pressure to us. Hooked up ForScan read the FLP was showing 13 PSI and Desired FLP of 89 PSI. Figured it was a bad pump or Fuel Pump Driver Module.
- Troubleshot the FPDM by direct wiring the 12v to the Fuel Pump. Pump ran fine, no change, still didn't run right.
- Assumed it was the fuel pump, replaced it, still no change
- FLP still showing 13 PSI
Are we reading the right parameter in ForScan for Fuel Pressure, believe I have the acronym right from ForScan, don't have it up right now, FLP.... Fuel Line Pressure?
Starts but backfires, misses, runs rough, won't idle
Last edited by MajHazrd; Apr 25, 2026 at 08:56 AM.
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From: Home Base Nebraska
Take a compression test and you may find a low cylinder or one at 0. If so pull the valve cover and look for a broken intake valve spring. I just went through the same thing and it ended up being a broken spring on #4 cylinder. No code reader could diagnose the problem, open intake valve leaking into the intake manifold did some strange things on the way it would run and only a compression test found the problem. It never made a ticking noise or any other noise just multiple missfires.
Denny
Denny
Last edited by rvpuller; Apr 25, 2026 at 04:40 PM.
Thread Starter
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2nd Gear
Joined: Apr 2026
Posts: 2
Likes: 3
Clogged injectors. We pulled the injectors and cleaned them using the Vice Grip Garage 9v battery method to open the injectors. 
Then we flushed them out with brake parts cleaner, compressed air and WD-40 chaser. Runs great again!
Thanks for the suggestions. I'm glad it just needed a good cleaning!! We must have got some bad gas.
Then we flushed them out with brake parts cleaner, compressed air and WD-40 chaser. Runs great again!Thanks for the suggestions. I'm glad it just needed a good cleaning!! We must have got some bad gas.
Last edited by MajHazrd; Apr 26, 2026 at 01:39 AM.
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