poor acceleration under load...spark missing?
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Joined: Aug 2004
Posts: 96
From: Tampa, Florida
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. 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. 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???
Registered User
Joined: May 2000
Posts: 249
From: Rochester, NY
Re: poor acceleration under load...spark missing?
Exact same thing was happening to me and new plugs/wires cleared most of it up. I am still getting a slight stumble down low on hot/sticky days but I think that is O2 sensor related. There are some Bosch 02's in there right now which I understand do not do well for our cars so I will most likely be switching to AC Delco's soon.
Thread Starter
Registered User
Joined: Aug 2004
Posts: 96
From: Tampa, Florida
Re: poor acceleration under load...spark missing?
my plugs and wires are brand new...
Also, going beyond spark...my y-pipe contacts the frame--could this confuse the pcm into thinking about spark knock? Would it actually retard the timing THAT much if it sensed it, to where I suddenly have a boost in power at 2000 rpm? Wierd problem...
Also, going beyond spark...my y-pipe contacts the frame--could this confuse the pcm into thinking about spark knock? Would it actually retard the timing THAT much if it sensed it, to where I suddenly have a boost in power at 2000 rpm? Wierd problem...
Last edited by contraststriker; Jun 22, 2005 at 10:45 AM.
Registered User
Joined: Apr 2004
Posts: 103
From: Okinawa Japan
Re: poor acceleration under load...spark missing?
Same problem here I have new pump and FPR and my pressure is 50 so thats not the problem, my y-pipe also makes contact with my frame and I have a scanmaster and I have been getting alot of KR but its not consistent, so I am lost as well. I have a stock cam and my stumbles until almost 3000 then its like all hell breaks loose and it kicks hard except in first gear it pulls all the way.
Registered User
Joined: Jun 1999
Posts: 539
From: Minneapolis
Re: poor acceleration under load...spark missing?
Check your plugs again as its possible you cracked the ceramic on one of the plugs. It has happenned to me before. It might not be you problem, but easy to check. You can also take a spray bottle with water and spray water on every cylinder to see if you have a colder cylinder.
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