Miss only under load
01-09-2014, 10:11 AM
#1
Miss only under load Symptoms started all at once. It runs fine at any RPM under light load, but as soon as I give it any gas it won't even accelerate. Car does it hot or cold, at pretty much any RPM. No check engine light either.
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01-09-2014, 10:26 AM
#2
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check fuel pressure and injectors. Also make sure all wires are on good and tight. I had a misfire problem around 2-3k rpms and was the opti. However i'd check fuel first, always go for easy items before blaming opti.
01-09-2014, 03:43 PM
#4
Should the fuel pressure drop at all with a free rev? Gauge is too short to tape to my windhshield, and I'm getting about 4 psi of drop with the vacuum line off with reving it in neutral.
Last edited by speed_demon24; 01-09-2014 at 03:51 PM.
01-09-2014, 04:13 PM
#5
a stumble/misfire "under load" can be a bad plug wire arcing. Certainly other things but look very close at night while engine is running at each plug area for any arcing. can be hard to see sometimes. I discovered mine while car was on stands, engine running, from underneath. it was arcing between plug heat shield and plug wire boot
does your FP drop 4psi and stay dropped with sustained throttle? a 4 psi drop should not cause a misfire...assuming it started 38-42 psi in the first place
does your FP drop 4psi and stay dropped with sustained throttle? a 4 psi drop should not cause a misfire...assuming it started 38-42 psi in the first place
01-09-2014, 04:23 PM
#6
a stumble/misfire "under load" can be a bad plug wire arcing. Certainly other things but look very close at night while engine is running at each plug area for any arcing. can be hard to see sometimes. I discovered mine while car was on stands, engine running, from underneath. it was arcing between plug heat shield and plug wire boot
does your FP drop 4psi and stay dropped with sustained throttle? a 4 psi drop should not cause a misfire...assuming it started 38-42 psi in the first place
does your FP drop 4psi and stay dropped with sustained throttle? a 4 psi drop should not cause a misfire...assuming it started 38-42 psi in the first place
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01-09-2014, 05:49 PM
#9
..well if you jumped in to buy a opti than go ahead and swap....although no guarentees that is it. 50k is not high milage on a opti but not a bad idea to at least inspect/replace cap & rotor
...and use dialectic grease on connections both plug & opti
since opti is coming off, inspect TC seals as wp drive is prone to leaks. FelPro TC gasket kit will have all of the seals/gaskets you need for $10
...and use dialectic grease on connections both plug & opti
since opti is coming off, inspect TC seals as wp drive is prone to leaks. FelPro TC gasket kit will have all of the seals/gaskets you need for $10
01-11-2014, 06:38 PM
#13
ICM is more heat sensitive since it is a semiconductor with a heat sink, the secondary ignition is what is load sensitive if insulation is breaking down somewhere between coil, coil wire, distributor, wires or spark plug. People forget the coil wire gets 8x the sparks of the other wires and it would affect all cylinders. That needs to be replaced more often. Engine/coil also needs a good common, don't forget. 15kv or whatever it is firing at has to return somehow. Also if old plug wires get damp from the car sitting outside, that can do it, but it sometimes cures itself when it warms up. Also there is the old corrosion in the opti connector problem.
01-11-2014, 08:16 PM
#16
If it misfires when lugged, even at low RPM, it won't be the ignition module or fuel pressure. 90% chance it's a plug or wire. Old trick that works very well is water & denatured alcohol mixed in a spray bottle. In the shade or kinda dark area spray the plugs & wires with that mixture. Water alone just beads up, won't sheet & cover the whole surface. The alcohol breaks the surface tension, and the water will completely cover the wires, their boots and spark plugs. AC & NGK plugs have resister problems that won't show up like this. Spark leaks will you will be able to see the spark jump to ground in the shade or dark. Possibly hear it. Depends on how bad it leaks. My tune up shop had way too many of the afore mentioned plugs come back in a month or less. We found Autolite plugs to give us fewer problems like that.
Good luck.
Good luck.
01-11-2014, 08:51 PM
#17
If it misfires when lugged, even at low RPM, it won't be the ignition module or fuel pressure. 90% chance it's a plug or wire. Old trick that works very well is water & denatured alcohol mixed in a spray bottle. In the shade or kinda dark area spray the plugs & wires with that mixture. Water alone just beads up, won't sheet & cover the whole surface. The alcohol breaks the surface tension, and the water will completely cover the wires, their boots and spark plugs. AC & NGK plugs have resister problems that won't show up like this. Spark leaks will you will be able to see the spark jump to ground in the shade or dark. Possibly hear it. Depends on how bad it leaks. My tune up shop had way too many of the afore mentioned plugs come back in a month or less. We found Autolite plugs to give us fewer problems like that.
Good luck.
Good luck.
01-11-2014, 09:14 PM
#18
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man i could of sold you a hardly used gm opti for like 100 bucks. Another problem it could to be honest is the o2 sensors. My buddy welded in subframe connectors on my car and i guess forgot to unhook the battery. Needless to say having my h/c/i lt1 getting passed by inivan as i missfire and hardly make it up a hill was rather emberassing.
01-11-2014, 10:00 PM
#20
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Im just speaking from personal experience, my o2s were maxed car missed like crazy, only thing I replaced and it fixed it. However I do agree with checking wires and thats one of the first things I do along with fuel pressure.