Screw car shutting off under power

After 6 blower belts we figured out that the ignition on the car is shutting off and coming back on when the car launches...sometimes it looked like a bucking bronco or the driver pedaling like crazy. After a couple cycles the belt breaks. The car was running very strong until 100ft out. Once it made it to 400ft. This is not rev limiting the ignition is totally on and off.

The data logger died on the first hit.
I made a fresh file for the 8973. It was corrupted at the last race.
By passed the mag kill solenoid
Ohmed crank trigger
Changed point s box
Inspected all the wiring
Everything except the 8973 went out for inspection 1 race ago.

Thanks
Mike

 

power

no switch for triggers
8973 runs off a fused switch in a dedicated switch panel

 

batt

I have a small lith ion battery for electronics. On some old data I saw the volts drop to 11.8 when the brake was on. Is this an issue?

 

check your battery connections could have a bad battery
are you using a capacitor for the power

 

cap

yes have a capacitor and checked connections

 

Cutting off and on

We had the same problem and the Coil was bad. Put another one on the car and went rite down the track. Sent that one to MSD and sure enough it was bad!

 

power

I have the capacitor inline which should stabilize voltage swings?
I was going to run on nothing but mag and internal trigger for the final but I convinced myself the kill solenoid would fix it. It didn't. 150ft feet of the best run ever and then the worst belt destruction ever for the final.

 

Mag Kill switch

Hi Mike,

Be careful on that, Kenny's car got stuck at full throttle and his 8973 would not shut off when the regular switch was turned off. It may just be how it was wired or something but long story short it made a 280 mph run and stopped a 1/2 mile off in the sand...no joke (Youtube Ken Cruz crash) I put one in for additional piece of mind.

Best wishes,
Trevor Sherwood

 

On the kill switch/solenoid thing, when we took the kill solenoid out of the system I figured killing the power to the 8973 would shut the car down. My normal routine is to pull the fuel shut-off then pretty quickly hit a big kill switch which I have wired to the kill solenoid and also to the air shifter to so it will dump the air at the same time. After disabling the kill solenoid for troubleshooting purposes I wanted to make sure I could kill the ignition so when we test fired it in the pits I killed the power to the 8973. Eventually it did shut down but it took a long time and I'm assuming this is because the capacitor continued to power the 8973 for a bit. This normally probably wouldn't be an issue but I like not having the delay. Maybe wiring the switch between the capacitor and the 8973 would eliminate this delayed shut-off? As I'm thinking through what could be causing this I'm thinking it's probably not just a straight power problem because with this capacitor in the system I don't think that the power could be shutting off and then back on to the 8973 rapidly enough to cause the symptoms we are seeing. This problem was first noted after we broke an old belt near the top end and it did smack the points box and the coil. We did change the points box but not the coil so it could still be suspect. Thanks for any ideas.

Joad Donnelly

 

The switch needs to be after the capacitor for instant shutdown.

 

I had a similar issue and found that the fuse block i was using to protect the grid had its fuse shake loose enough to make and break contact to the grid when i launched the car it shut off and then the nose dropped it took off again, i thought when i had the big dead spot and my foot was to the floor i was going to launch my top end sky high but it just turned back on and away it went, so if you have any check the simple things like fuses and connections first