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.

Re: Car surging? possible bad ignition box or coil?
 

Un hook your tachometer

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

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.

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.

Re: Car surging? possible bad ignition box or coil?
 

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

Re: Car surging? possible bad ignition box or coil?
 

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

Re: Car surging? possible bad ignition box or coil?
 

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 ,,

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.

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.

Re: Car surging? possible bad ignition box or coil?
 

Yes we have grounds running from both cylinder heads to the frame this setup was happy last year with a milder engine, and we like e85 for a number of reasons but i'm wondering about this fuel becuase it just happens to be the only real variable in this equation everything else was happy at the end of last season. unless its a internal issue with the engine. we did have a loose ground a week or so ago when we initially started the motor that caused some trouble but we found it and fixed it i'm wondering if that could have damaged the ignition box.

Re: Car surging? possible bad ignition box or coil?
 

Surging is most likely a fuel or carb issue. If it’s popping and sputtering then ignition would be suspect. Could be an issue with your accelerator pump. What carb?

Re: Car surging? possible bad ignition box or coil?
 

Its 950qft convertered to e85 by mark sullens.

Re: Car surging? possible bad ignition box or coil?
 

and maybe a surge isn't the right word it would pop or just act like it wanted to die fall on its face comeback to life and repeat.

Re: Car surging? possible bad ignition box or coil?
 

If the carb. was set up for e-85 then it has richer jets for alcohol than straight racing fuel.May not be problem,still sounds electrical.Are connectors crimped or soldered? Plus box could have taken a hit with the bad ground.

Re: Car surging? possible bad ignition box or coil?
 

there all soldered. the only crimp would be the weather pack connector at the coil i guess that could be it.

Re: Car surging? possible bad ignition box or coil?
 

Just a heads up.......

About 40 years ago I had a similar problem with my MSD-7AL..

Race car would idle and take a throttle snap fine...

Put it in gear and all was OK...

When we went to drive the car it would stumble almost to the point of killing the engine..

Drove me crazy and I almost rebuilt that car from the ground up..

I found that the problem was a high resistance connection in the power circuit to the MSD..

It would light a test light..

MSD ignitions, depending on load such as large plug gaps, suppression plug wires and add to that the engine load of trying to accelerate, can draw up to 15 amps..

The higher the load the more the draw..

The MSD will stop firing, the load is reduced, then start working again..

Using a test light is useless to track this down and you need a Volt-Ohm meter to check the resistance in all of your power and ground connections..

I spent a lot of time tracking this down on our 350 Super Stock engine..

I hope that this helps

Re: Car surging? possible bad ignition box or coil?
 

BOB

Thats very helpful, what would you consider an acceptable ohm reading for a power and ground wire. i did check voltage at the box and its the same as battery voltage but i didn't ohm the power wire or the ground. however i will say we've had 2 other motors in this car before and this one was in in september of last year but couldn't keep head gaskets in. but the half pass and couple hub dyno pulls it made didn't display this issue which really makes me think the box took a hit and or there is a fuel issue but our 7al2 is 22 years old so we decided to go ahead and upgrade and its getting a grid system this weekend with a new hvh 2 coil and we will go from that point.

Re: Car surging? possible bad ignition box or coil?
 

The ohm reading that I would be shooting for is zero...

I'm an old school guy...

ALL of my electrical connections are crimped and soldered..

Do not use the crimp only, insulated type of butt and ring type connectors.

The crimp is the mechanical connection and after crimping the connection should be tested by trying to pull it apart..

If the mechanical connection is OK then it is OK to finish the electrical connection by soldering....

Finish it off with the glue inserted shrink tubing and you have pretty much a lifetime, trouble free electrical connection..