Carb'd LS wont crank
 

A friend of mine cant get his high compression LS motor to crank. Aparently it doesnt spin fast enough to give the MSD box enough of a consistent reference to fire. If they take the plugs out it will spin fast enough to work the MSD box and fire the ignition. But otherwise the motor doesnt spin fast enough I guess.

What can be done to get this thing to crank over fast enough?

Its in a late model dirt car. Its a carb'd LS1 with 3.75 stroke and 13:1 compression.

check/upgrade the battery, power and ground cables, and maybe the starter. it's not getting enough juice to overcome the load of the high compression. also make sure all cable connections are clean and bare metal, no corrosion, no paint etc

It may have carb rejection syndrome. It 's common with LS engines.:engarde:

Also its a Bert trans with the special flywheel.

They said its still getting 14v during the crank cycle.

but its probably not getting enough amps. like how a battery charger has different amp settings but the same voltage for each. having undersized wires/corroded connections increases the resistance and decreases the amps. another example, every try jump starting a car with cheap jumper cables? same principle.

Ok we will

Make sure you're running a thick (I like 4, 2, or 0 gauge) start wires, starter ground, engine ground, and chassis to battery ground. Might give the starter the extra juice it needs.

I had a friend that called me for the same problem as your are descripting for his 88 Trans Am.

He tried Jumping the car with jumper cables and attached to his other truck. still not go and could not spind it fast enough... i pulled my battery out of my Nova and jump it with that.., still no go. we tried a few more configurations..

Then replace his battery with my Nova battery, connected it up and man did it spin...!..

Bottom line, just check everything to be correctly connected, clean and charged. Your cheap K-mart jumpe cables, econo Kragen/Autozone replacement cables may not be able to carry the amps.

good luck.

Thanks :)

They're the type that spend $50 more if it might be better so I have confidence the battery is good but i'll suggest a new one for this season if they havent bought a new one already.

if he is running a gear reduction starter that might be the issue, also get it cranking then flip on the ignition if they have too much advance in their msd box at low rpm that would be cranking speed.

The MSD has removable chips in it but im not sure which specific chip is in the box at the moment.

Also they are running a gear reduction starter but there arent any other options with the specific flexplate for that stock car trans.

Pull the chip out and create a timing map with the MSD software. All of the chips have way too much timing in them for an LS engine. I have seen the same problem (too slow cranking speed) a couple of other times. Your friend may have to figure out a way to get away from the gear reduction starter. I don't think he will ever have much luck with it. Have him call MSD and see if there are any updates that can be done to the box. I believe I read a post a few days ago about the newer boxes having slightly different wiring that might eliminate the problem.

If battery,cables, and connections check ok. Good bet it is too much timing like post before me states....

That is what i was thinking... 18-20 degrees and 13:1 make it hell on a starter. Hook the laptop up an plot a curve. use 6-9 degree on the inital timing till at least 1200rpm or so. Call me if yall need any help....

i made my curve start at 8degrees at zero rpm and climbed to 22 degrees at 1000rpm, this way while cranking and around 200rpm for instance the starter isn't fighting anything. Still start cranking it first then flip on the ignition to see if it'll fire that way. I'm pretty sure though the gear reduction starter might be too slow of a crank speed as well, hook up a laptop and see what the crank rpm is and report back after trying these things.

hook the laptop up and ck the cranking rpm

Aight.

For what its worth this is the second box. MSD said this was an updated version or whatever. I may just take a field trip to Alabama in the next couple of days.

Thanks again so much!

Third box comes back and still the same result....


However!!!!!!!!!!!! They push started the car with a 4-wheeler and it started. And whats even better is, apparently, once the box fires the motor the first time it will fire it every time after, lol.

Maybe MSD boxes learn what to do with a little encouragement? lol

(edit: sucks for the automatic guys I guess)

i had the same issue. msd do have a new box which will fire at very low rpm when cranking a new motor over first time. i got mine swapped and the new box fired first time.
i also got it to work using the old box by direct jumping the starter at 24v for a brief instant (direct wired to 2 batteries and not to any car loom wiring). this cranked the engine over much faster and the msd box worked.
slow cranking and high ignition timing wont help. 12-15deg max we found at cranking speed off a custom map.