Misfiring at high boost+RPMs
Guest
Posts: n/a
Misfiring at high boost+RPMs
Well I'm having a hell of a misfire and it's robbing the ---- out of my horsepower.
I used to run 7 psi of boost on my .48/.60 and have no problems. I upped the boost to 9-10 psi and now it pulls harder, but at about 4000-4500 RPM it starts to misfire and I just lose power. Ocassionally I can get a full pull without misfire and it just ------- rips, but most of the time I get the misfire. I am running uberdata and have tuned my map as well as I can with the misfire, when it does misfire I get erroneous lean readings so I can't really tune that. I am confident that this problem is not with my map.
I don't think it is plug wires because they look just find and don't misfire under any other conditions that high boost+high RPM.
Thought about it being the distributor cap, I actually had an almost new distributor that I was using on my old setup working perfectly. I just swapped that one over and I still have the problem.
I reused the spark plugs from my old setup, NGK BKR7E gapped at .030, I also tried .028. They did get a little black around the edges (not the electrode) from when I was running rich on the basemap but I don't think that should make a difference as long as they are gapped right... or would it? I have ordered a new set of plugs just incase, because that is the only thing I can think is wrong besides....
My base timing. I don't have a timing light and haven't set my base timing. Could this cause a bad misfire if it's too advanced or retarded? I am going to rent a timing light to check that.
Help !!
I used to run 7 psi of boost on my .48/.60 and have no problems. I upped the boost to 9-10 psi and now it pulls harder, but at about 4000-4500 RPM it starts to misfire and I just lose power. Ocassionally I can get a full pull without misfire and it just ------- rips, but most of the time I get the misfire. I am running uberdata and have tuned my map as well as I can with the misfire, when it does misfire I get erroneous lean readings so I can't really tune that. I am confident that this problem is not with my map.
I don't think it is plug wires because they look just find and don't misfire under any other conditions that high boost+high RPM.
Thought about it being the distributor cap, I actually had an almost new distributor that I was using on my old setup working perfectly. I just swapped that one over and I still have the problem.
I reused the spark plugs from my old setup, NGK BKR7E gapped at .030, I also tried .028. They did get a little black around the edges (not the electrode) from when I was running rich on the basemap but I don't think that should make a difference as long as they are gapped right... or would it? I have ordered a new set of plugs just incase, because that is the only thing I can think is wrong besides....
My base timing. I don't have a timing light and haven't set my base timing. Could this cause a bad misfire if it's too advanced or retarded? I am going to rent a timing light to check that.
Help !!
0.0 BAR
Joined: Nov 2004
Posts: 0
Re: Misfiring at high boost+RPMs
I have a similar problem with my new setup but its mainly cause once I hit 10lbs it gets insanels rich, goes from 12 to 1 to nearly 9 to 1 in 2000rpm 
I would just run some cheap *** copper plugs, thats what I'm running and they work great. I would think if your base timing is off than it would have issues at lower rpms as well as lower boost levels. I would look at the map sensor you may be overloading it.
I would just run some cheap *** copper plugs, thats what I'm running and they work great. I would think if your base timing is off than it would have issues at lower rpms as well as lower boost levels. I would look at the map sensor you may be overloading it.
3.0 BAR
Joined: Dec 2002
Posts: 3,829
Re: Misfiring at high boost+RPMs
put some fresh plugs in and slam the gap down to like .025 or something rediculous. If I fixes it, keep working your gap back up. For 9-10psi though, stock gap sould give you no problems. Do you have a spare set of plug wires your can toss on? Old old *** plug wires can easily do what you describe when in boost (the more boost, the harder it is to jump the gap, and if there is any weak spot in the ingnition path, it will jump there)
Guest
Posts: n/a
Re: Misfiring at high boost+RPMs
Holy crap maxing out the map sensor... I never thought of that. When I datalog in uberdata I get values up to the 10.41 column, maybe I am maxing it out and that's why it's shitty. But wouldn't I get a CEL if I was maxing out the map sensor? Anyways, here's a screenshot of my timing map:
3.0 BAR
Joined: Apr 2004
Posts: 9,790
Re: Misfiring at high boost+RPMs
sounds like ignition.
i had a t3/t4 setup with a z6 in a crx that i tuned a while back. at 10psi it started cracklinup on me.
gapped to 028 and all was happy.
try some new plugs, inspect your cap/rotor.
i had a t3/t4 setup with a z6 in a crx that i tuned a while back. at 10psi it started cracklinup on me.
gapped to 028 and all was happy.
try some new plugs, inspect your cap/rotor.
3.0 BAR
Joined: Apr 2003
Posts: 11,057
Re: Misfiring at high boost+RPMs
it's not your map sensor, i've boosted well over 11.xx psi on stock map sensor many times. timing in your maps looks fine, don't see any sudden changes or anything that should cause a sudden loss of power. my guess would have to be plugs/wires, i too have had some problems with shitty/old wires causing misfires at certain times.
