Car surging? possible bad ignition box or coil?

pfordamx · 04-06-2019, 11:59 PM

Took our amx to the track for the first time this year with a new engine but same electronics that were working good last October including distributer and ignition box which is 7al2 and a hvh pro power coil. also same plug wires and were used and the same carburetor from last season. the car fired up and showed no signs of issues in the garage it started well and free revved just fine, so we get to the track we unload drove to tech went smooth, and being a new engine i decided to drive up the return road and see if it felt ok and with a little throttle input and load the car stumbled then spring up and stumbled bouncing the rpm from almost dead to 4000rpm so i turned around and drove back to the pits and after changing the cap rotor sparkplugs, jets , pulling the 2 step chips moving timing unplugging the crank trigger and going back to the distributor ressetting up the carb, we could not make it better. we tried to make to passes and you could ease into it and it would feel ok but fast throttle movement or to aggressive and it would stumble and start bucking again. we have a second 7al2 that were installing tomorrow to check that but i'm open to any and all suggestions.

Adger Smith · 04-07-2019, 02:25 AM

Un hook your tachometer

gmonde · 04-07-2019, 08:43 AM

check the fuel,,,race fuel normally will be good for a while but you never know ,
check the voltage going to the 7A box ,,
check alternator voltage

pfordamx · 04-07-2019, 08:43 AM

i forgot to list that but we did try unplugging the tach and it still started bucking i guess you could call it.

pfordamx · 04-07-2019, 08:47 AM

i was curious about fuel thats one thing we did change. the car is on e85 and we always ran pump e that we mixed in the past and we swapped to a premixed with race gas e that we bought in 55 gallon drum i believe its renegade i tested it and it was 88 percent witch is fine. i didn't check check voltage at the box i'll do that today the car is on a 16 volt system and the in car volt meter was reading close to 17. oh and no alternator we just charge inbetween rounds.

gmonde · 04-07-2019, 09:02 AM

you might want to investigate further on your fuel and compression of the motor ,,

MikeMoller · 04-07-2019, 08:31 PM

Could be fuel pressure, needle and seat, float issue, or fuel filter.

gmonde · 04-07-2019, 08:37 PM

Quote:

Originally Posted by MikeMoller

Could be fuel pressure, needle and seat, float issue, or fuel filter.

I am thinking more on the fuel not supporting the compression of the motor ,, I ran aircraft fuel in my bracket car and it did the same thing described ,, except my motor was low compression and the oxetane was way to high and the motor stumbled at the hit ,,

pfordamx · 04-08-2019, 09:34 AM

The motor is 14.5 to 1 what are you suggesting by not supporting i was thinking maybe too much octane and its not able to light it underload.

RKelliher · 04-08-2019, 12:31 PM

Did you make sure the engine is grounded,since the motor was just put in. Also why are you running a e-85 mix ?.try running racing gas only. But I have seen problems with grounds.

04-06-2019, 11:59 PM	#1
pfordamx Member Join Date: Sep 2011 Location: Oklahoma City, OK Posts: 214 Likes: 3 Liked 7 Times in 5 Posts	Car surging? possible bad ignition box or coil? Took our amx to the track for the first time this year with a new engine but same electronics that were working good last October including distributer and ignition box which is 7al2 and a hvh pro power coil. also same plug wires and were used and the same carburetor from last season. the car fired up and showed no signs of issues in the garage it started well and free revved just fine, so we get to the track we unload drove to tech went smooth, and being a new engine i decided to drive up the return road and see if it felt ok and with a little throttle input and load the car stumbled then spring up and stumbled bouncing the rpm from almost dead to 4000rpm so i turned around and drove back to the pits and after changing the cap rotor sparkplugs, jets , pulling the 2 step chips moving timing unplugging the crank trigger and going back to the distributor ressetting up the carb, we could not make it better. we tried to make to passes and you could ease into it and it would feel ok but fast throttle movement or to aggressive and it would stumble and start bucking again. we have a second 7al2 that were installing tomorrow to check that but i'm open to any and all suggestions.

04-07-2019, 02:25 AM	#2
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,348 Likes: 433 Liked 676 Times in 260 Posts	Re: Car surging? possible bad ignition box or coil? Un hook your tachometer __________________ Adger Smith (Former SS)

04-07-2019, 08:43 AM	#3
gmonde Senior Member Join Date: Nov 2007 Posts: 615 Likes: 56 Liked 166 Times in 59 Posts	Re: Car surging? possible bad ignition box or coil? check the fuel,,,race fuel normally will be good for a while but you never know , check the voltage going to the 7A box ,, check alternator voltage

04-07-2019, 08:43 AM	#4
pfordamx Member Join Date: Sep 2011 Location: Oklahoma City, OK Posts: 214 Likes: 3 Liked 7 Times in 5 Posts	Re: Car surging? possible bad ignition box or coil? i forgot to list that but we did try unplugging the tach and it still started bucking i guess you could call it.

04-07-2019, 08:47 AM	#5
pfordamx Member Join Date: Sep 2011 Location: Oklahoma City, OK Posts: 214 Likes: 3 Liked 7 Times in 5 Posts	Re: Car surging? possible bad ignition box or coil? i was curious about fuel thats one thing we did change. the car is on e85 and we always ran pump e that we mixed in the past and we swapped to a premixed with race gas e that we bought in 55 gallon drum i believe its renegade i tested it and it was 88 percent witch is fine. i didn't check check voltage at the box i'll do that today the car is on a 16 volt system and the in car volt meter was reading close to 17. oh and no alternator we just charge inbetween rounds.

04-07-2019, 09:02 AM	#6
gmonde Senior Member Join Date: Nov 2007 Posts: 615 Likes: 56 Liked 166 Times in 59 Posts	Re: Car surging? possible bad ignition box or coil? you might want to investigate further on your fuel and compression of the motor ,,

04-07-2019, 08:31 PM	#7
MikeMoller Senior Member Join Date: May 2010 Location: Raleigh NC Posts: 626 Likes: 27 Liked 242 Times in 72 Posts	Re: Car surging? possible bad ignition box or coil? Could be fuel pressure, needle and seat, float issue, or fuel filter. __________________ Mike Moller NHRA 203 Q-R-T/SA

04-08-2019, 09:34 AM	#9
pfordamx Member Join Date: Sep 2011 Location: Oklahoma City, OK Posts: 214 Likes: 3 Liked 7 Times in 5 Posts	Re: Car surging? possible bad ignition box or coil? The motor is 14.5 to 1 what are you suggesting by not supporting i was thinking maybe too much octane and its not able to light it underload.

04-08-2019, 12:31 PM	#10
RKelliher Member Join Date: Dec 2013 Posts: 140 Likes: 27 Liked 147 Times in 47 Posts	Re: Car surging? possible bad ignition box or coil? Did you make sure the engine is grounded,since the motor was just put in. Also why are you running a e-85 mix ?.try running racing gas only. But I have seen problems with grounds.