poor acceleration under load... spark missing?
06-22-2005, 07:36 AM
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poor acceleration under load... spark missing? I just finished a cam/headers project and everything went off without a hitch...almost.
Some exposition first: SPEC stage 3, 230/242 cam, PCMforLess tuning, Taylor 8mm wires w/ngk-tr55 plugs .050 gap.
When I give it gas, it stumbles and basically accelerates like crap up until around 2000 rpm where it abruptly changes to the acceleration you would expect, smooth and pulling. I say abrupt because it's definitely NOT just entering the cam's effective rpm range. It's as if under load it's missing. When I really give it gas, normally I can pull it out of the "bogging" phase. Do I need an MSD or equivalent spark booster? Fuel pressure checks out at 45 psi, so that doesn't seem to be the problem. IF spark is the problem, why would it be weak? All components are brand new. Notice that the higher gears are nearly useless, as they're under load most all the time and just make the car shudder as it misses. Any ideas???
Some exposition first: SPEC stage 3, 230/242 cam, PCMforLess tuning, Taylor 8mm wires w/ngk-tr55 plugs .050 gap.
When I give it gas, it stumbles and basically accelerates like crap up until around 2000 rpm where it abruptly changes to the acceleration you would expect, smooth and pulling. I say abrupt because it's definitely NOT just entering the cam's effective rpm range. It's as if under load it's missing. When I really give it gas, normally I can pull it out of the "bogging" phase. Do I need an MSD or equivalent spark booster? Fuel pressure checks out at 45 psi, so that doesn't seem to be the problem. IF spark is the problem, why would it be weak? All components are brand new. Notice that the higher gears are nearly useless, as they're under load most all the time and just make the car shudder as it misses. Any ideas???
06-22-2005, 12:57 PM
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Originally Posted by 1970judge
i had the same problem under load at first my car wouldnt go nowhere but kind abe held back..then snap out of it..it was my cat
06-23-2005, 12:45 AM
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i am having the same problem although I have new wires,plugs,opti,coil,o2s,map,harness,basically everything but a new maf ...what you could try if it isnt spark is disconnect the maf and see if it goes away or gets better...then you know its bad or needs to be cleaned
You really should check 02s and map and maf those are the most common stumbler causers besides opti...But yeah I havent figured mine out yet
You really should check 02s and map and maf those are the most common stumbler causers besides opti...But yeah I havent figured mine out yet
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06-23-2005, 03:53 AM
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Any fbody obd1 or 2 will run without maf thats how the 93s are..It uses speed density mode which relies on your map sensor to do fuel/air mixture you cnat unplug it while running but unplug it before you start... u may have to give it a lil gas to keep it running for a few seconds but after that it should idle and not die
06-24-2005, 02:02 AM
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It sounds exactly like what my car is doing; loss of high resolution optispark signal. But you said all components are new, does that include the opti??
Have you scanned it for any codes?
Have you scanned it for any codes?
06-24-2005, 06:37 AM
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Originally Posted by John95Z28
It sounds exactly like what my car is doing; loss of high resolution optispark signal. But you said all components are new, does that include the opti??
Have you scanned it for any codes?
Have you scanned it for any codes?
06-24-2005, 09:19 AM
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I've got a miss but mine's up top. I'm getting impatient as well. Does the car stumble in the lower RPMs in open loop only or both closed and open loop? You will reach closed loop about 175F coolant temp.
06-24-2005, 09:32 AM
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Originally Posted by dhdenney
I've got a miss but mine's up top. I'm getting impatient as well. Does the car stumble in the lower RPMs in open loop only or both closed and open loop? You will reach closed loop about 175F coolant temp.
06-27-2005, 02:15 PM
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i have a real similar problem to this as well. but it typically happens on the highway if i have the car around 2500-3000, i did splice my o2 sensors when i did the header install though and i think thats my problem.
