I need some assistance in diagnosing an issue I am having. I don’t like throwing parts at something if I can help it. My dragster has started surging after it comes off the transbrake. It does not do this in the pits or during the burnout. I have been told by somebody I believe that they have had a similar issue and it was the coil. In trying to talk with MSD, they deny that it could be the coil, because “you either have spark or you don’t.” I have tested everything I can think of to no avail. The fuel pump is set at 20 psi on the bypass and 5.0-5.5 at the regulator under flow. I see no evidence of fuel starvation. The battery voltage is 16.3 during the run. The coil shows a primary resistance of .3 Ohms and secondary of 33 Ohms. All the plug wires are < 40 Ohms/Ft. New set of NGK R5672A-9 plugs. Crank trigger is 65.3 Ohms. All of the wiring to and from the crank trigger and coil are 1.2 Ohms or less. The car just acts like it is cutting on and off about 6 times per second. The Racepak shows the voltage stays steady and the carb pressure fluctuates less than .3 psi. The engine rpm just bounces about 500 rpm each time it cuts out. Thank you for your help!

7720/7730 Ignition
82613 Coil
MagnaFuel ProStar 500 (Filter was cleaned before last race)
MP-9433 Regulator (New Diaphragm)

The only time I've had surging was due to low fuel volume/pressure. I had set my regulator with a nitrous flow tool and later found out that what I thought was 6.5 psi was less than 1.5 psi. Cranked up the regulator and that fixed the issue. I've also had issues with a magnafuel pump. What are you checking fuel pressure with? It is possible to have pressure but not enough flow. To rule this out, take the supply line off the regulator, get a one gallon container, and see how long it takes to fill it. It should be about 15 seconds or less if I remember right....

Also need to check to see tank is vented properly, that there isn't an issue inside of one of the hoses where it's coming apart and blocking flow, and there isn't something inside your tank blocking the outlet....

Just a few things to look at. I agree with MSD, a coil is unlikely to cause a surge, they pretty much either work or not. I think it's a fuel issue, just need to find it.

Had the same problem last season. After replacing the coil, it made one pass and started missing again. Went home and got out the Ohm meter checked every wire involved with the ignition system. It turned out to be the very thin wire between the digital 7 box and the coil. The wire was broke at the crimp but made enough of a connection it ran fine until until you put a load on it, or the vibration would cause a problem going down the track. BTW that connection is now soldered!

You have Grid. Look at the Ignition IN and Ignition OUT channels in the Data Acquisition of the Grid DA run. For every Ign input you should have an Ign output and they should be sequential not be broken up. RacePak won’t show you this.

If you think/ suspect coil and don’t want to purchase 8261, then replace the coil with anything available to try. Grid will fire it just fine.

You wrote that the problem does not happen during the BO. I would guess it’s because BO doesn’t require wot. Coils don’t function any different between 6k rpm BO or 6k rpm wot.

Had a similar issue as Thurston. The wire from the crank trigger pick-up was broken inside the insulation. The g-Forces following launch would cause it to flex and lose continuity. Complete "bog" at launch ans surging down track. Fine during burnout.

^^^^^ If this is the failure, MSD Grid 7730 DA will display it in the Ignition IN channel.

All good suggestions here.

Have you had bowls off the carb? Check all that stuff its free. Clean and blow everything out and inspect. Again free.

Drain fuel cell and inspect. Could be something moving up against the outlet but would suspect you would see fuel pressure drop. Again free. Suggestion to flow system is a good one to rule out flow - but it will be static so again check cell for debris.

Grid in an out good starting point - if that looks good then it isnt the problem.

I did not hear anyone suggest checking all your grounds. Ask me how I know! Or go back and read it for yourself. In all seriousness double check all that and dont just look - take them all off clean them and use star washers - seal them with battery protector spray. Again mostly free and wont hurt a thing to give them a freshening.

On the coil I am sure you have a buddy or acquaintance at the track that would lend you one to swap out. Drive around and ask or like they do up here at our tracks - have the announcer send out a racer in need. Hell my kids master cylinder went out at the money race. We put out announcement and within 5 minutes I had 3 guys - two of which I never met handing me brand new ones to install.

I have had coils that were "weak" on street/strip car before. The symptom was the same as if the carburetor was too rich. New coil and plugs fixed it right up. I had a bad distributor pick up that acted similarly.

I wanted to take a minute to thank everybody for the suggestions. I definitely wouldn’t have found my problem without the knowledge and experience shared with me. What was ultimately the problem was a broken wire on the plug from the switch panel to the relay board. I just happened to bump the plug as I was going to hook up to the grid and heard a relay click. Pulled on the plug just a little bit and it would lose power to the ignition, but would return as soon as you released it. Pulled the plug apart and found a wire broken at the plug. Soldered it on to make the last race of the year. Plan to replace the entire connector and have a spare for the future. Again, thank you all so much for the helpful suggestions!