Occasional Miss - What Part to Change Next?
08-20-2012, 06:34 PM
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Occasional Miss - What Part to Change Next? Guys,
I'm running a 383 M6 with AI heads, a custom solid roller, bosch 42# injectors and a Walbro pump. Car did 427/404 on a Mustang dyno.
I'm dealing with an occasional miss/hesitation at WOT. This occurs only, say, 1 out of every 10 times I take it WOT through the gears...and it only seems to occur past 6K rpm (I shift around 7K). The loss of power is not complete, so I'm thinking this is something specific to certain cylinders (or one cylinder). Of course, I've only experienced this issue while the engine is hot (don't go WOT when it's cold).
I'm to the point where I am just throwing parts at the car, hoping to solve the issue. I have replaced the opti (CMS), coil (MSD), ICM, plugs, and fuel filter. I'm running Taylor wires that have been on the car for 8 years but for only about 2000 miles (car was just parked in a garage), and they appear to be in good condition with no tears or frays. Before I make my way back to the opti (would be AC Delco next time), I want to tackle some more low-hanging fruit. Though I am fairly certain I have an ignition issue, I'm not so sure it's the CMS opti. I bought the CMS opti because I did have a faulty factory opti which caused severe hesitation every time I went WOT beyond 5K (made the tach skip and jump). This issue is only occasional and much more mild, and the tach stays steady.
What you do think of these theories for the cause of the miss?
(1) Wires. Would replace wires with Granatelli zero-ohm wires.
(2) Plug gap. Gap is at .035 now, which might be making the spark too cold for my compression (~11.3:1) or, to the other extreme, might be too wide and occasionally allowing some spark blowout.
(3) Dirty injectors (though I have the injectors out right now and they look clean). I'll probably just toss in some injector cleaner, though I doubt that will change anything.
(4) Detonation. It's hot in Texas in the summer. This miss is occurring in 90-degree, high humidity weather, though it's happened at night too when the temp is *only* in the 80s. I run 93 octane gas. Could that be insufficient? I haven't heard pinging, but the exhaust is loud. Detonation seems unlikely to me because the miss is only occasional, the miss generally lasts a few moments, and the plugs have not shown any specs on them (and they should, because this would be some relatively serious detonation).
Thanks for any help.
-Chris
I'm running a 383 M6 with AI heads, a custom solid roller, bosch 42# injectors and a Walbro pump. Car did 427/404 on a Mustang dyno.
I'm dealing with an occasional miss/hesitation at WOT. This occurs only, say, 1 out of every 10 times I take it WOT through the gears...and it only seems to occur past 6K rpm (I shift around 7K). The loss of power is not complete, so I'm thinking this is something specific to certain cylinders (or one cylinder). Of course, I've only experienced this issue while the engine is hot (don't go WOT when it's cold).
I'm to the point where I am just throwing parts at the car, hoping to solve the issue. I have replaced the opti (CMS), coil (MSD), ICM, plugs, and fuel filter. I'm running Taylor wires that have been on the car for 8 years but for only about 2000 miles (car was just parked in a garage), and they appear to be in good condition with no tears or frays. Before I make my way back to the opti (would be AC Delco next time), I want to tackle some more low-hanging fruit. Though I am fairly certain I have an ignition issue, I'm not so sure it's the CMS opti. I bought the CMS opti because I did have a faulty factory opti which caused severe hesitation every time I went WOT beyond 5K (made the tach skip and jump). This issue is only occasional and much more mild, and the tach stays steady.
What you do think of these theories for the cause of the miss?
(1) Wires. Would replace wires with Granatelli zero-ohm wires.
(2) Plug gap. Gap is at .035 now, which might be making the spark too cold for my compression (~11.3:1) or, to the other extreme, might be too wide and occasionally allowing some spark blowout.
(3) Dirty injectors (though I have the injectors out right now and they look clean). I'll probably just toss in some injector cleaner, though I doubt that will change anything.
(4) Detonation. It's hot in Texas in the summer. This miss is occurring in 90-degree, high humidity weather, though it's happened at night too when the temp is *only* in the 80s. I run 93 octane gas. Could that be insufficient? I haven't heard pinging, but the exhaust is loud. Detonation seems unlikely to me because the miss is only occasional, the miss generally lasts a few moments, and the plugs have not shown any specs on them (and they should, because this would be some relatively serious detonation).
Thanks for any help.
-Chris
Last edited by cmorales; 08-20-2012 at 06:39 PM.
