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Thread: misfiring help
11-10-2011, 09:13 PM #1
my truck has been misfiring for about 2 months now and i cant figure it out,
i just had it at a mechanic yesterday and thought my problems were solved, family friend mechanic so i know hes not screwin me, he pulled out the ignition control module and tested it and it was bad. popped in a new one and problems are still there...
i have 2 new crankshaft position sensors in the last 6 months, new cap, rotor, plugs, wires, fuel filter, fuel pressure is good etc. i have a strong feeling it is something electrical due to a DTC (U1255) for a class 2 communication malfunction. if you ned more info and think you can help please let me know, this is a very bothersome problem for me..
kyle2000 Chevrolet Silverado
4.3L V6, 4L60E, 2WD, Single Cab
Poweraid TB Spacer
Flowmaster 10-series exhaust (dumped)
Edge CS insight monitor
LS-1 Dual Electric fans
Corvette tranny servo swap
Head Unit: Alpine
Speakers: Alpine SPR-60C 6.5" component set, 4X6 Infinity Kappas
Subs: 2-12" Kicker CVT's
Amps: Alpine-M1000 (subs), Alpine MRX-F65 (Speakers)
305/70R16 NITTO Terra Grapplers
16" PROCOMP 7089's
2" leveling kit
3" Fabtech Spindle Lift Kit
Front/Rear-Bilstein 5100 shocks
35W HID Low Beams
RECON LED smoked roof cab lights
HELLA LED taillights and 3rd brakelight
HELLA FF-75 Aux. Reverse Lamps
RIGID dually D2, flush mount, wide beam
Hawk HPS Brake pads
Russell braided steel brake lines
Powerstop-red powdercoated brake calipers
Powerslot Cryo brake rotors
EGR in-channel window visors
11-11-2011, 09:13 PM #2
Anytime you get a code beginning with U, your not going to be able to get a true diagnosis without a tech 2 unfortunately. What I would do is track down another computer for your truck, they're all over ebay for $75. Your ICM might not have been bad, the ECM controls all of the spark tables and it can do funny things. Basically a class 2 fault is a grounding issue, meaning there is a short somewhere in the engine harness.
11-14-2011, 05:29 PM #3
Thanks for your input.
also i just installed some stainless steel braided brake cables on friday in the front and (im sure this has nothing to do with it) didnt get to finish bleeding my brakes entirely, still spongy. drove it around it to feel the brakes did its normal (noticeable to me on the inside) misfiring came back parked in front of my garage and had to leave to go to a formal. then the next morning had to go to san antonio for a marathon, came back sunday night, woke up monday morning for work and my truck wont start...
cranking, cranking, cranking had to leave in our back up CR-V.
came home same thing but i got it to start a few times
horribly rough idle, shaking, vibrating when pushing the accelerator, and dies randomly, in no condition to drive...
any help for that? or do you think this may be all due to the ECM?
this is frustrating...
Last edited by reggiecab2000; 11-14-2011 at 05:31 PM.
11-14-2011, 07:37 PM #4
Well there is a free test you can do that is about 50% reliable on the ecm, since there is no difinitive way to check an ecm 100% other than replacement. Take a 1/4" drive extension and tap on the top of the ecm lightly while the truck is stumbling and messing up, If it changes in any way then the ecm is bad. I got this tip off of my firebird club, It actually lead me to find out my ecm was bad before I spent a lot of money on nothing. Worth a shot....
11-15-2011, 12:43 AM #5
sounds like an easy test... is the ecm the box beside the battery?
11-15-2011, 01:29 PM #6
2002 Chevrolet Silverado 1500 z71 1985 Chevrolet Silverado k10 2006 Chevrolet Silverado 2500hd 6.6l LLY Duramax 6.5" BDS Suspension Lift Key'd to 9" Edelbrock Carb & Polished Intake Manifold & Valve Covers NAPC Race Transmission & NAPC Built Transfer Case EFI Live Comp Cam and Valvetrain Snow Performance Methanol Injection 35" Toyo Open Country Mud Terrain on 18" Ion Alloy 179's Headman Long Tube Headers and True Dual Exhaust FASS 150gph Titanium Series Pump AirAid Cold Air Intake with K&N Dry Filter & AirAid PowerAid Throttle Body Spacer 2" Suspension Lift 33x12.50r15 Tires PPE Tuner until i tune it with my EFI Live Pacesetter Long Tube Headers with Cats Gone True Dual Exhaust FlowPro 3.73 Gears Yukon Grizzly Locker with Mag-Hytec Cover & Traction Bars NGK Iridium Tips & MSD Ignition Plug Wires Baja Spare Tire Holder Leveling kit & 34.5" Nitto Grapplers 18" XD Rims Innovate LC-1 Wideband o2 Sensor x2 HID's all around LED taillights and 3rd brake light BDS Dual Steering Stabilizers Pioneer Double-DIN Touchscreen Navigation with Two 10" Subs under rear seat Electric Fan Autometer Pressure, Boost, and Pyro Gauges 4.56 Gears AFE Stage 2 Intake
11-15-2011, 04:01 PM #7
i believe that is the box i was referring to, i just re read my post and i look dumb it looks like i was referring to the fuse box lol but i think i meant the same as you, that angled weird shaped one. ill give it a few taps and see what happens...
---------- Post added at 03:01 PM ---------- Previous post was at 02:19 PM ----------
okay so i tapped all over the ecm, jiggled all 4 of the connections, tapped all over the maf sensor wire, any and almost all other sensors i could see engine related, and pulled and tugged on as many wires as i could, and nothing.... it still only starts up when it feels like it, but anything on the accelerator and the whole truck starts shaking, horrible misfiring...
11-15-2011, 06:05 PM #8
Well that sucks that it didn't work...
I don't know what else to say now, that would be something I would have to see. Hopefully someone else can shed some light into this. Sorry I couldn't help more..
11-26-2011, 09:44 PM #9
okay so my truck still has its on and off days on starting but once its started it idles just fine, anything over 1000 rpms and there goes that earthquake feeling, why does it not do it at idle but at any point on the gas?
11-29-2011, 03:29 PM #10
UPDATE! and i really need some input on this guys...
took my truck to chevy this morning and they ran a diagnostic with their tech 2 ...
sooo my distributor is bad and i also have a leak from some coolant in my intake manifold (which ive known for a while now not a big leak)
but they said for the distributor:
parts labor blah blah
for distributor and fixing the leak (which involves removing intake manifold and new gasket and new fuel pressure regulator)
I know that the dealership charges high prices but can someone please let me know asap if this is ridiculously high or if it is comparable
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