Slight misfire no codes . Need ideas.
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From: Westchester NY. ΜΟΛΩΝ ΛΑΒΕ Country>self
Slight misfire no codes . Need ideas.
02 coupe. AnA v3 procharged. Tuned by doug at ecs last summer, only put about 3k since. Ran great. Now I’ve started to get this weird misfire. At idle you can hear it get choppy and it is a little rough. Then while driving with slight throttle it hesitates and chokes. Especially under 2k. I’ve changed plugs, wires, both 02 sensors, Removed and cleaned the injectors. CLeaned MAF Checked fuel pressure at the rail and all seems fine. I’m stumped. I need some ideas on what this could be.
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
bad gas? I had a tank ful not too long ago that I swear made the car run poorly
Last edited by bobs77vet; May 30, 2018 at 01:03 PM.
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From: Cape Coral, Florida
Hi !!
Misfire huh ??... Well, how did you figure out that you didn't have any codes ??...was a scan tool used or through your DIC ??...if you do have one I'd check those misfires counters to get some direction. You said you only changed plugs and wires...I'm fortunate to have a Picoscope so I'd be checking your coil primary and secondary windings. You can pull each plug wire and see if you see a change in RPM...no change...equals dead hole !!... Getting to the injectors did you check for feed and control to them before you pulled them out to clean them ??...getting to fuel pressure was it checked just at idle ??...you have to do a "snap throttle" to make sure the pressure does not drop....if it drops you have a fuel delivery issue. As far as the vacuum leak as someone had suggested you would have to look at your fuel trims...car will run better as RPM is increased and your fuel trims will start to ratchet down at higher RPM's. You can spray brake clean or use propane sprayed around the intake and vacuum lines or even water to see if the engine RPM changes. If the leak is small the misfire will sometimes disappear as the engine is heated up and everything starts to expand...Also something "mechanical" can cause a misfire...AC compressor or alternator binding, a bad pulley...ANYTHING that will cause the crankshaft to slow down... I see you cleaned the MAF too...you did check the MAF wiring ??....3 wires are for MAF and 2 are for IAT. I think that maybe you didn't need to change those O2 sensors but without the right equipment you'll just be firing the "parts cannon"....keep us advised !!...Oh, and make sure you have at least half a tank of gas when diagnosing.
p.s Can you do me a favor...I watched a great 3 hour YouTube video seminar on "misfire strategies" last week and the Instructor said if you put a dollar bill up to your exhaust the misfire will suck the bill into the exhaust...I wanted to see if it was true !!
Misfire huh ??... Well, how did you figure out that you didn't have any codes ??...was a scan tool used or through your DIC ??...if you do have one I'd check those misfires counters to get some direction. You said you only changed plugs and wires...I'm fortunate to have a Picoscope so I'd be checking your coil primary and secondary windings. You can pull each plug wire and see if you see a change in RPM...no change...equals dead hole !!... Getting to the injectors did you check for feed and control to them before you pulled them out to clean them ??...getting to fuel pressure was it checked just at idle ??...you have to do a "snap throttle" to make sure the pressure does not drop....if it drops you have a fuel delivery issue. As far as the vacuum leak as someone had suggested you would have to look at your fuel trims...car will run better as RPM is increased and your fuel trims will start to ratchet down at higher RPM's. You can spray brake clean or use propane sprayed around the intake and vacuum lines or even water to see if the engine RPM changes. If the leak is small the misfire will sometimes disappear as the engine is heated up and everything starts to expand...Also something "mechanical" can cause a misfire...AC compressor or alternator binding, a bad pulley...ANYTHING that will cause the crankshaft to slow down... I see you cleaned the MAF too...you did check the MAF wiring ??....3 wires are for MAF and 2 are for IAT. I think that maybe you didn't need to change those O2 sensors but without the right equipment you'll just be firing the "parts cannon"....keep us advised !!...Oh, and make sure you have at least half a tank of gas when diagnosing.
p.s Can you do me a favor...I watched a great 3 hour YouTube video seminar on "misfire strategies" last week and the Instructor said if you put a dollar bill up to your exhaust the misfire will suck the bill into the exhaust...I wanted to see if it was true !!
Last edited by C5 Diag; May 31, 2018 at 01:10 PM.
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From: Westchester NY. ΜΟΛΩΝ ΛΑΒΕ Country>self
Just ran some data. Every cylinder is missing at some point but cyl 7 has the most. I can’t imagine every coil pack having an issue. I’m lost. I was told the coolant sensor could cause this. Any truth in that?
Last edited by LMFD296; May 30, 2018 at 07:49 PM.
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Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
if its totally random and unpredictable doesn't that point to gas?
why not siphon the gas out to a daily driver and fill up with new stuff?
why not siphon the gas out to a daily driver and fill up with new stuff?
Thread Starter
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Joined: Feb 2009
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From: Westchester NY. ΜΟΛΩΝ ΛΑΒΕ Country>self
As far as posting my tune I only have the dyno sheet and a few other graphs. I can if that is what you’re lookin for.
As far as the fuel goes. That’s an option. I’m at about half tank.
As far as the fuel goes. That’s an option. I’m at about half tank.
Last edited by LMFD296; May 30, 2018 at 10:14 PM.
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From: Cape Coral, Florida
So you do have some type of scan tool and it's saying you have all misfires but your misfire counters are showing more on that one cylinder...since it's not cylinder specific I'd lean towards fuel pressure (higher RPM), MAF, crank sensor (usually throws a code), or vacuum leak...can even be an internal engine vacuum leak...you'd have to block off the PCV system and hook a vacuum gauge to your oil dipsick...should be NO vacuum)....you really need some specialized equipment to make a correct diagnosis and not be changing parts...good luck my friend !!
Last edited by C5 Diag; May 31, 2018 at 01:13 PM.
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Joined: Sep 2013
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From: Cape Coral, Florida