Random Misfire Problem
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Random Misfire Problem Recently one of my dad's work trucks started running terribly. It runs alright when cold but once it warms up it progressively gets worse to the point where it's stumbling bad enough that it won't be able to haul chemicals around, which is why we have it. The truck is a 1998 C-3500 with a Vortec 454. I know it's not an LSx but the same principles will transfer over to my engine. I've changed the spark plugs, cap, rotor and spark plug wires. After I installed those parts the truck runs the same. I've picked up EFI Live for two other GM vehicles that I have but I can read the Vortec 454's PCM. It's throwing the Random Misfire code (P0300). I've got a playback file that has the parameters when the truck is running bad that I'll post up when I get on my other computer. I'm thinking that I'll get a playback file this afternoon of first startup all the way until it's stumbling bad.
Any help will be much appreciated.
Any help will be much appreciated.
Last edited by xXxSilveradoxXx; Jun 2, 2011 at 04:37 PM.
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Here's a screen shot midway through the log when it was running bad. I'm still very new to EFI Live and tuning my own stuff in general. The Commanded A/F Ratio is disturbing at 0.28, I believe that it should be closer to 14.7. The long term fuel trims also are odd at -18%.
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I cleared the DTCs and drove the truck around and logged everything. Evidently I've got a #6 cylinder specific misfire.
The average misfires per 200 revolutions per cylinder are;
#1-0 V #2-13
#3-2 V #4-7
#5-1 V #6-67
#7-0 V #8-0
According to EFI Live the average misfires per 200 revolutions should be less than 25.
I'm hoping that my problem is my injectors. Tomorrow I'm going to pull the upper intake manifold (damn Vortec 454 injection!) and switching around the injectors and see if the misfire relocates.
The average misfires per 200 revolutions per cylinder are;
#1-0 V #2-13
#3-2 V #4-7
#5-1 V #6-67
#7-0 V #8-0
According to EFI Live the average misfires per 200 revolutions should be less than 25.
I'm hoping that my problem is my injectors. Tomorrow I'm going to pull the upper intake manifold (damn Vortec 454 injection!) and switching around the injectors and see if the misfire relocates.
Last edited by xXxSilveradoxXx; Jun 2, 2011 at 04:36 PM.
You may well see that the injs are leaking, even to a point of washing the manifold clean....
Last truck I worked on, had them leaking so bad, after I cleaned them for several cycles on the bench.. Still leaked. Threw them away and put in a new set...
Last truck I worked on, had them leaking so bad, after I cleaned them for several cycles on the bench.. Still leaked. Threw them away and put in a new set...
