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RE: E30 M20 motor has Major Hesitation at 5,500 RPM's

alexshch — Sat, 03 May 2008 14:16:39 GMT

Rob, check fuel filter and associated lines? I had similar problem at Oktoberfest in 05 which turned out to be a crack in the fuel hose.

RE: E30 M20 motor has Major Hesitation at 5,500 RPM's

schneller — Thu, 01 May 2008 09:42:35 GMT

In our experience w/ M20 engines of your vintage check for weaknesses in the ignition system as they are the most common causes of hesitation, especially under load. Evaluate these components:

1) Crank Position Sensor at front Harmonic balancer (test using a multimeter & values outlined in your Bentley Manual)

2) Inspect Spark Plugs (tip condition & gap, you can tell how each cylinder is running by the burn pattern), Ignition Cap & rotor for carbon build up & cracks. Replace if you can't ever remember replacing them.

3) How old are the Ignition wires? Test for Ignition wire arcing...mist wires w/ spray bottle , run engine & take a long screw driver w/ a well insulated plastic handle ground tip to valve cover & lean metal shaft over towards individual wires to see if ignition spark jumps from wire to screw driver....BE CAREFUL!!!

4) Inspect ignition & coil wire connectors for corrosion & general integrity. Test resistance of individual wires per Bentley Manual.

5) Test ignition coil per Bentley Manual

This should cover the ignition side of the equation. Most hesitations can be traced to this area. Also, don't forget that clean battery terminals, engine & chassis grounds are
also important to generating a good spark for ignition.

Let me know how you make out ;)

E30 M20 motor has Major Hesitation at 5,500 RPM's

Healy325 — Wed, 30 Apr 2008 17:03:08 GMT

I have been trying to figure this out for about a year now. I have an '89 325is with about 180k on the motor. On occasion the car will cough somewhere around 5,000 rpm's almost as if it had hit the rev limiter. It seems to happen only under hard acceleration and not every time either (at least 90 percent though).

The fact that this happens at the same point on the tach and nowhere else makes me wonder if it's a problem with the ECU. I have swapped out the plugs and the wires are in very good shape. The K&N filter is freshly cleaned.

Any ideas would be greatly appreciated.