where is overrun cutoff switch?

[simmo300e]

My 87 300e engine starts to cut out at exactly 4,000 rpm when driving, yet will rev beyond that point with the clutch in or in neutral.

From searching previous posts on this subject, it appears that the fuel pump relay is cutting power to the fuel pump at this point, which I have searched for information on.

In previous posts I have seen the Hall effect sensor identified as the unit which would determine whether the car is in motion, which should remove the rev limiter. However, my car doesn't appear to have a Hall effect sensor mounted on the back of the speedometer, and as it does not have cruise control or ABS, I'm told it would not have this sensor fitted.

Having checked the wiring diagram, I see there is an Overrun Cutoff Microswitch attached to the FPR, which would seem to be the likely culprit.

Can anyone tell me where to find this switch and how to check it is working correctly? If it was connected in reverse, would this cause the rev limiter to cut in when in motion, instead of in neutral?

If the car does have a Hall effect sensor and it is mounted somewhere else on this model, where would I find it?

I have already cured a rough idle/stall problem and in the process have replaced the following: FPR, OPV, 6 x injectors, Fuel Accumulator, ICV, rotor and cap, plugs, fuel filter, vacuum hoses, AC relay and checked the Air Sensor Pot which I believe is sending out the correct signals.

Hoping for help on this as otherwise the car is running great.

[Duke2.6]

The rev limiter on US models is 6650. It sounds like there is a restiction somewhere in your fuel supply system.

Duke

[simmo300e]

If there was a fuel restriction, surely that would apply regardless of whether the car was in gear or not?

I have read that there is a limiter in the fuel pump relay that kicks in at 4000rpm on automatics to stop revving above that point when in park or neutral, The restriction is removed when the car is judged to be in motion.

The restriction was said to be governed by the Hall effect sensor on the speedo, which I don't have. Plus it's a manual.

However, if you're right there is a restriction in the fuel system, where would I start looking? Wouldn't this also cause problems throughout the rev range?

[brewtoo]

Originally posted by simmo300e
If there was a fuel restriction, surely that would apply regardless of whether the car was in gear or not?

The engine will require more fuel under load at 4000 rpm than when simply revving up to 4000 in neutral.

[simmo300e]

OK, let me be more precise. The engine starts cutting out at exactly 4,000 rpm, no more no less.

That makes me think something is set to trigger a fuel cutoff at that point, otherwise the problem would manifest itself in a less precise manner.

On that basis, I am confident it is not a mechanical problem, more likely to be an electrical one.

So, can anyone shed light on the rev limiter system that has been put in place to protect the engine from over revving in park or neutral?

thanks