The Dreaded Mid to High RPM Cutout

[It's Soda Not Pop]

assuming this is an M20 on motronic 1.3 - With a coil or fuel load related break down the needle will still match the engine rpm and lower as the engine looses power unless its loosing signal to spark entirely from the DME. A complete loss of RPM feedback on the dash is a loss of crank position or rpm input from the DME which only requires a singular feed from the DME for engine speed if I recall. The engine position sensor is as reliable as they come as so long as you're seeing a voltage output from the sensor when you put a metal object against it you can confirm the sensor to be ok generally speaking. The feedback to the cluster seems quite erratic

looking at your video my first hunch is you have some form of interference in your electrical system, especially seeing its effecting your temp gauge which is measured by resistance at the engine.
First thing I would be doing is ensuring the ground strap on the tower is sound, as is the one from your battery to chassis and sump to chassis rail strap. Add jump lead if you have it to see if giving these points a better earth improves your symptoms.
nearly everything in the engine harness goes to the star point grounding strap on the tower so its important its mickey mouse.

what's the charge rate from your alternator out of interest when its running and revving? make sure the crank sensor wiring is well away from the alternator. Its almost as if as RPM increases so does the interference

failing above I would be doing resistance check on the following wires when cold and when the car is at operating temp (when its failing) as with older wiring resistance increases with temp

Pin 8 on DME - Black - CYL ID SENSOR DME INPUT - FROM H/T LEAD
Pin 1 on DME - Black - TIMING CONTROL EARTH TO COIL AND O2 SENSOR
Pin 37 on DME - RD/BU - ECU SWITCHED POWER FROM MAIN RELAY
Pin 31 on DME - Yellow - CYL ID SENSOR INPUT
Pin 48 on DME - Yellow - Engine speed (-) from crank position sensor
Pin 47 on DME - Black - Engine speed (+) from crank position sensor

If that all checks out as consistent I would be applying my own fused power input to the DME to rule out a weak power supply issue.

Also wouldn't hurt to do a voltage check between the cylinder head to chassis to check there is no stray voltage there from the alternator

Thank you. My last alternator was over charging. I checked the voltage at the battery with the car running and it was around 13.5-13.8. I didn't check while reving. I did restore the fuel pump to the factory setup. But again the car was acting up. I'll check my grounds. I have issues with the ignition switch sometimes. Meaning the starter will spin, but not engage the flywheel. But if I leave the key in the on position and jump pins 11 and 14 in the diag plug the starter engages everytime. Could my ignition be cutting out briefly causing this issue? Like it's turning the car off. Again I believe I'm losing a ground or something for a split sec.

[moatilliatta]

Injector harness connector free of corrosion?

[bangn]

assuming this is an M20 on motronic 1.3 - With a coil or fuel load related break down the needle will still match the engine rpm and lower as the engine looses power unless its loosing signal to spark entirely from the DME. A complete loss of RPM feedback on the dash is a loss of crank position or rpm input from the DME which only requires a singular feed from the DME for engine speed if I recall. The engine position sensor is as reliable as they come as so long as you're seeing a voltage output from the sensor when you put a metal object against it you can confirm the sensor to be ok generally speaking. The feedback to the cluster seems quite erratic

looking at your video my first hunch is you have some form of interference in your electrical system, especially seeing its effecting your temp gauge which is measured by resistance at the engine.
First thing I would be doing is ensuring the ground strap on the tower is sound, as is the one from your battery to chassis and sump to chassis rail strap. Add jump lead if you have it to see if giving these points a better earth improves your symptoms.
nearly everything in the engine harness goes to the star point grounding strap on the tower so its important its mickey mouse.

what's the charge rate from your alternator out of interest when its running and revving? make sure the crank sensor wiring is well away from the alternator. Its almost as if as RPM increases so does the interference

failing above I would be doing resistance check on the following wires when cold and when the car is at operating temp (when its failing) as with older wiring resistance increases with temp

Pin 8 on DME - Black - CYL ID SENSOR DME INPUT - FROM H/T LEAD
Pin 1 on DME - Black - TIMING CONTROL EARTH TO COIL AND O2 SENSOR
Pin 37 on DME - RD/BU - ECU SWITCHED POWER FROM MAIN RELAY
Pin 31 on DME - Yellow - CYL ID SENSOR INPUT
Pin 48 on DME - Yellow - Engine speed (-) from crank position sensor
Pin 47 on DME - Black - Engine speed (+) from crank position sensor

If that all checks out as consistent I would be applying my own fused power input to the DME to rule out a weak power supply issue.

Also wouldn't hurt to do a voltage check between the cylinder head to chassis to check there is no stray voltage there from the alternator

[It's Soda Not Pop]

[QUOTE=moatilliatta;n10112981]AFM flapper for getting full swing?

Cap, Rotor, plugs, plug wires all new?

Flapper moves all the way. I even swapped out to another AFM to test. All new ignition. New cap, plugs, rotor, wires, and coil.

[moatilliatta]

AFM flapper for getting full swing?

Cap, Rotor, plugs, plug wires all new?

[It's Soda Not Pop]

I would expect a standalone ECU to have a high-speed crank/cam trigger log.
I know for sure the MS3X can do this, because that's what's on my E30.

You'd be able to see missing pulses straight away.


But I wouldn't swap to a standalone just to address this issue.

I was planning swapping anyway. This is just the issue that's come out of nowhere for me. Reading through this forum I've seen that others were having problems similar to mine and swapping to a standalone fixed their issues. Like I said I'm going to wire the pump back to factory. Right now power comes from the battery directly. There is another relay that clicks over when the original FP Relay gets power from the main relay. This (new) relay then sends power to the pump. I still use the factory ground to the pump.

[Panici]

I would expect a standalone ECU to have a high-speed crank/cam trigger log.
I know for sure the MS3X can do this, because that's what's on my E30.

You'd be able to see missing pulses straight away.


But I wouldn't swap to a standalone just to address this issue.

[It's Soda Not Pop]

I'm going to undo my fuel pump wiring and restore it back to factory. That's the only other change I made.

[It's Soda Not Pop]

So I haven't driven or messed with the car in probably a week. Today I swapped the service interval back to the original. Shocker.......not fixed. I have a brand new harmonic balancer I can put on the car. But I'm still at a loss of why I'm losing timing data or fuel pressure or split sec power loss to the DME. Idk what happening to be honest.
I hope going full standalone will resolve this issue. I hate not knowing what's causing this.

[It's Soda Not Pop]

I appreciate the help and advice fellas. I will update as I try things.

[It's Soda Not Pop]

It sounds dumb, but I had a car doing very similar issues, and the O2 sensor ended up fixing it. The car had a newer sensor installed, but it was the wrong one for the car and it would miss under load with a tach drop and a CEL flash.

I thought about it being the sensor. That's the only sensor that hasn't been changed since 2016.

[It's Soda Not Pop]

Anything is possible. Remove the new board and see if it makes a difference.

I wonder if a short to ground on your tach signal going to that SI board would kill spark.
Maybe it's a shared ECU output to the tach and coil?

Still recommend the earlier advice:

I'm going to swap the board back out. Because the coolant temp needle is also jumping. I'm hoping that this is the fix. I've checked all my connectors. They all look really good. My harness is really good considering the age.

[It's Soda Not Pop]

Harmonic balancer tight? Big and small bolts?

I tested to see if they were tight. They are. I did find a NOS one. I order it just in case.

[It's Soda Not Pop]

consider the TPS being full of oil through the throttle shaft bearings. i know you said you replaced it, but it's worth looking, along with the C191.

a friend had a customer car that came in to his shop for the infamous 4k hard cut. he swapped every single engine component (harness, DME, sensors, etc) off a known good, running driving car, including the goddamn chassis harness, to no avail. what eventually "fixed it", was converting it to a PNP Megasquirt controller.

hope your situation ends better than that.

I'm going with Jake's Turkey and Cheese PNP. Also I put a hole in the TPS for that reasoning.

[E30SPDFRK]

It sounds dumb, but I had a car doing very similar issues, and the O2 sensor ended up fixing it. The car had a newer sensor installed, but it was the wrong one for the car and it would miss under load with a tach drop and a CEL flash.