Losing spark at around 2500rpm

[Brady]

SO I have a newly built 70 406 with an 88 7.4 TBI 4speed system on it.It starts and runs fine.Idles at 800 no jumping.But It won't rev past 2500.It seems to shut the spark off then fire back up when the rpm drops a touch.Getting plenty of fuel.Pattern is nice and even in both injectors.I verified I am losing spark with a timing light.The light quits at 2500 then lights up again when rpms drop.What could this be?I am thinking maybe coil is giving up the ghost at the higher rpms.

 

[Fordum]

Sounds like a rev limiter gone haywire.
But, unless you have an aftermarket ignition system, I doubt its that.
If it was a mechanical advance dist. I would say that the internal wire is broken and opens when the plate moves.

In this case, I suspect either the pickup coil or the ignition module. First, pull the cap and see if the shaft might be loose in the dist. Doubt that too, but its a cheap and easy check.

 

[diesel4me]

An HEI module can lose its dwell advance curcuit,yet still start and run the engine,up until a certain RPM,when it'll fall flat on its face....I've heard of some cheap generic modules that lack the dwell advance curcuit!...how they run the engine at higher rpms,I dont know,they must have fudged it to work somehow................................a pick up coil (If your engine uses one) can cause loss of spark intermittently,but its only on distributors with vacuum advance that it happens on mostly,when the advance moves the breaker plate to advance the timing by moving the pick up coil................................later HEI's with the "EST" module can have problems similar to a bad pick up coil when the electronic advance curcuit starts failing or croaks completely too..

 

[Brady]

This has the stock 88 TBI dist. Looking online I haven't found much info but did read that the TBI dist ignition module has a low rpm and high rpm circuits.I am thinking this may be the problem. Since it runs perfectly below the 2500rpm range.

 

[Brady]

Just do if someone has this same problem.Yes it was the ignition module.Napa tested it as being bad.Replaced it and it runs great now.