No Spark at crank, but fires in the run position? SBC conversion with HEI, Help? (1 Viewer)

[oldracerguy]

I have a small block conversion that was done, (professionally?) by a shop in Idaho. The engine will not start when I am in the crank position with the key. However it fires as soon as I let off the key and is in the run position. I checked the voltage to my distributor in the run position with the engine off and it was 10.5 volts, it dropped to 9.5 volts when I turn the key to the start position? I have 12.8 volts at the battery. The new distributor is wired into the factory wiring harness. I am loosing some voltage somewhere?? This is a 1978 FJ40 that I just bought. Any thoughts? Thanks..........newbie.

 

[Plowboy]

The problem may be in the key switch. The brass connectors wear down and will cause just what you are describing. It is a small wire harness on the left hand side of the steering wheel. Remove the plastic cover and you will see where the harness attaches. Replacement are available from ccot, maf and sor.

 

[oldracerguy]

I am going to try and run a dedicated wire that is switched from the ignition to the distributor. I think you are on to something. I may have a few other electrical issues to sort out from the PO and how the new engine is tapped into the factory wiring harness. I'll let you know whatr I find. Thanks!!

 

[76FJ55]

the factory wireing at least on my 76 has a second wire running to the coil that powers it during cranking, by passing the ballast resistor. it does this because during cranking there ias a significat amount of voltage drop caused by the current draw of the starter, and leaving the ballast resistor in the circuit causes low voltage at he coil, and therefore week spark on cranking. during the conversion this line was possibly not reconnected as they probably where just checking for a hot line in the run position. I had a simalar issue with mine after converting to an after market ignition. I don't have my manuals on hand but can check for wire color code on this particular wire when I get home this evening if you like. Hope this helps

 

[oldracerguy]

Found It, Fixed it.......

I forgot to mention that with the Marks of Australia adapter in there I did not have clearance for the fan up front behind the radiator. So the option was to use an electric fan. This was turned on with the ignition in run or crank and was drawing hte voltage down too much at startup. Once this was disconnected the engine fires up immediately. I am putting a relay in for the fan so it is on a separate circuit than the feed to the distributor at startup.
Thanks for all the replies!!

 

[bsmith123]

Time delay relay

get a time delay relay that way it won't even put a demand on the system until the engine is already running