Fuel starvation at WOT

[JimRockford]

I have a '76 450SL that has fuel starvation at WOT, coughs and the tach goes nuts.

On the high way to pass a truck, my SL will top out at 80 MPH and then has the same issues. Fuel starvation.

Other then that, the car drives just fine. No vac leaks (smoke tested it). Starts and drives off without an issue.

Any ideas what I should start looking at?

[Frank Reiner]

Originally Posted by JimRockford

I have a '76 450SL that has fuel starvation at WOT, coughs and the tach goes nuts.

On the high way to pass a truck, my SL will top out at 80 MPH and then has the same issues. Fuel starvation.

Other then that, the car drives just fine. No vac leaks (smoke tested it). Starts and drives off without an issue.

Any ideas what I should start looking at?

Inasmuch as the tachometer is electrically powered and derives its signal from the ignition amplifier (switchgear in MB-speak), look to the condition of all of the components of the ignition system before suspecting the fuel system.

[97 SL320]

Tach goes nuts as in rapidly jumps up and down not tracking actual engine RPM or the engine RPM is actually going up and down with the tach responding to this?

[JimRockford]

Good call Frank.

Yes 97_SL320. The tach rapidly jumps as if its spazing out once it reaches a RPM range. The engine coughs for life and the tach swings like its loosing a signal.

[97 SL320]

You could be losing the ignition module or ignition coil is flashing over internally.

As engine loads increase, so does the voltage required to jump the spark plug gap.

[JimRockford]

Originally Posted by 97 SL320

You could be losing the ignition module or ignition coil is flashing over internally.

As engine loads increase, so does the voltage required to jump the spark plug gap.

That makes total sense.

[JimRockford]

So I put in a new ignition coil, nothing changed.