Revving the M42 to it's redline, then boom stuttering/sputtering

[ForcedFirebird]

crank sensor maybe

This.



It's Motronic and they are finicky about the CPS and can act as a premature rev limiter (sounds like making popcorn?). Digital Multi Meter and ohm the pins. Two should be open, two should be 540ohm +/- 40ohm, sensor side of the wiring.

[majdomo]

majmodo I agree 100% on that.. I also got the Bosch part first and my car was no-start whatsoever after that. Once I got the OEM it was 100% back to normal. Unfortunately it has jumped in price, but if you want good reliable performance from your car it's necessary. Worth it for these great old cars.

CPS on ecs 19Mar2019: $232
https://www.ecstuning.com/b-genuine-...r/12141721504/

Right on - wish I’d done this repair myself, but ended up paying the mechanic to hunt down the problem. Almost paid him to replace a perfectly functioning cat, thought it was a blockage in the exhaust.


Ezekiel 25:17

[Nairb]

majmodo I agree 100% on that.. I also got the Bosch part first and my car was no-start whatsoever after that. Once I got the OEM it was 100% back to normal. Unfortunately it has jumped in price, but if you want good reliable performance from your car it's necessary. Worth it for these great old cars.

CPS on ecs 19Mar2019: $232
https://www.ecstuning.com/b-genuine-...r/12141721504/

[majdomo]

Revving the M42 to it's redline, then boom stuttering/sputtering

CPS most likely. Had to replace mine 2x, once with aftermarket and finally with OEM. Hasn’t done it since. Exact same symptoms as the video. OEM was fuck-all expensive iirc.


Ezekiel 25:17

[bmwman91]

Is the AFM referenced during WOT?

Yes, it is still used as the primary input for calculating a base load value. The O2 sensor is ignored.

[Victell]

make sure the AFM tests OK.

Is the AFM referenced during WOT?

[roguetoaster]

Check fuel pressure first.

Then, in addition to what everyone else said, make sure the AFM tests OK.

t

You mean to tell me that this OP shouldn't convert to dual side drafts?

[TobyB]

Check fuel pressure first.

Then, in addition to what everyone else said, make sure the AFM tests OK.

t

[bmwman91]

Yeah, crank sensor, or maybe an ignition coil on its way out. Also if the fuel filter is plugged up you might be dealing with intermittent fuel starvation at higher flows.

Pull the spark plugs and check to see if any of them look odd, either sooted/rich or white/lean.

[fastestbox]

What RPM exactly, and is it very consistent or intermittent?

It happens right before redline, although sometimes it will let me hit redline and it won't bounce, instead it'll just retard the revving and start stuttering/sputtering. So probably around 6500-7000 every single time.

crank sensor maybe

That's highly possible as I had a problem with it before...

[Nairb]

Check this vid, are these symptoms similar to yours? If so, it's crankshaft position sensor.

https://www.youtube.com/watch?v=bPNIZQ5kn3w

[digger]

crank sensor maybe

[bmwman91]

What RPM exactly, and is it very consistent or intermittent?

[fastestbox]

Could be anything, but i would start by inspecting the spark plugs and the fuel filter (replace both if you dont know the history)

I suppose I should have put this in the original post, but spark plugs have been changed recently, along with coils and wires. Fuel filter has been changed as well.

Could it be something to do with the engine ground or a camshaft sensor?

[e30davie]

Could be anything, but i would start by inspecting the spark plugs and the fuel filter (replace both if you dont know the history)