random misfire

K

KRanch350

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May 16, 2009
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Here are the mods I have: EGR delete, studs, swamps high voltage and tuned FICM, Gutted cat with no muffler,155cc river city sticks, tunes from Cale. The truck has 107k miles. The truck has had a slight shutter at cruising speeds. I had thought it was the converter pulse but I might be changing my mind now. While driving the truck started to misfire. I made it to work which was about ten miles. After work I change all filters and still no improvement. My three mile drive home was a joke as the truck barly pulled its self and had to be pulled in the last few blocks because it wouldnt stay running it was missing so bad. The scanner says innjector misfire on the the contribution test but they are slightly random and at times just one bank, The truck will eventually die and then has a hard restart. After a few minutes it start much better. PLEASE HELP. Ive spent a ton on this truck and I have to make it last. BTW I have a ICP on the way with a new plug.
 
Is it consistently one injector or random injectors on that side? It could be electrical check connections.
 
How old are the Injectors? What codes are you getting?
 
Bad Moose said:
Is it consistently one injector or random injectors on that side? It could be electrical check connections.
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most of the time the odd numbered cylinders are the lean one but not always. At times at higher rpms they are all perfect! I did wiggle most all the injector plugs and the FICM plugs and saw no change
 
Goose said:
How old are the Injectors? What codes are you getting?
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The injectors just have a few thousand miles on them and the FICM was installed this summer. I have no codes. the only time I got a code was when I unplugged the ICP while running and of course it gave a low voltage code then. The EGR codes are over looked because that is all in the trash!
 
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most of the time the odd numbered cylinders are the lean one but not always. At times at higher rpms they are all perfect! I did wiggle most all the injector plugs and the FICM plugs and saw no change
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If your showing every other cyl in the firing order, replace the FICM. Just had a truck give me fits with a new (rebuilt) FICM. it would cut out every other cyl occasionally, ran smooth, just had no power and sounded like a 4 cyl. turns out there is a circuit in the FICM that can allow this to happen.
 
Hey this is jess from warren diesel. I know your problem give me a call. Shop number 8-5 814-439-0218

Problem comes only when warm right?
 
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I'll call Swamps in the morning and get their ideas. As for only when warm I don't think that is true but I will start it up in the morning and check for sure. Any thought about the check valves in the high pressure rails giving this kind of issue. How does the scanner tell on the cylinder contribution test which injectors are firing or not. Is it by voltage or by some other means? could irregular hpop pressure not firing the injectors be picked up by the scanner?
 
If all else tests out ok. I say its in the injectors. I have seen the same problem before just need a little spool valve work and they are good. Truck we had would miss on any random cyl at any given time no pattern.
 
Here

"How does the scanner tell on the cylinder contribution test which injectors are firing or not"

IDS uses crank and cam sensor signal feedback. As a cylinder fires these sensors see the pressure spikes, if a injector is spitting too much or not enough fuel these pulses are weaker or stronger than they should be. In that case you see fuel being added or subtracted to try to even out the firing pulses and smooth out the engine. Thats why you turn off injector compensation before trying to diagnose injectors.
 
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