ForcedFirebird's m20 dyno thread.

[ForcedFirebird]

With typical DIY/mechanic tools (or help of a friend), these are some things to look for.

M20 health checklist:

Blue coolant sensor for the ECU : 300-330ohm at operating temp
TPS switch : Check for pin short at WOT and idle. Adjust/replace if necessary. Don't forget to check cable too!
o2 sensor : .9v at operating temp at idle on the signal wire
CPS : 540ohm +/- 40ohm, .030" air gap (thick business card is a great shim), check chaffing at back of water pump pulley
Spark plug wires : <7ohm, longest ones may be a little higher
Idle fuel pressure: ~43psi with regulator line disconnected and capped
Running fuel pressure : ~43psi at 4000rpm under load (many bad regulators in the past few years, check it)
Fuel volume : >1ltr in 15sec with fuel pump energized
Spark plugs : Stock m20 ignition system works best with single electrode copper plugs. I use wr8lc for stock engines, pbr7es on turbo and high compression (+/- heat per app).

EDIT as of 5/8/18:

When checking your sensor values, use the DME connector, NOT the actual sensor. Happened again and reminded me that if the DME doesn't see the same value the sensor connector does, so, your ECU will obviously be making wrong computations based on input if you have high/low resistance in the wiring, or could have corrosion on the connectors.

EDIT 10/13/22:

Seems as a lot of Spec guys are running into issues with the crank damper and reluctor wheel spinning on the hub. Check the condition of the rubber!

[ForcedFirebird]

Been asked a few times to share some m20 dyno files. Not sure how many are in the folder, the dyno tower PC crashed and lost a bunch, some files where customers prefer to no make public, so will share what I can. Have a ton of files and prefer to be thorough with explanations, guides and hints, so may be slow going.

To start, a bone stock 200k mile 325i, WOT switch on the TPS was inop, so it's weak on power. This is what happens when the m20 TPS goes bad and the ECU does dot receive a WOT signal. The ECU stays in closed loop and reads the o2 sensor, which "should" be ignored at this time. Note the AFR's.



Here is what happens when the TPS WOT switch is functional. Note the power increase and smoothness of the AFR curve.



And overlay for the dramatic effect....



Don't go to the dyno to see how much power your 30 your old engine is making without checking up on it's condition. All to many times we see things like this on "perfect running condition" cars.

So, in the next post, we will go through a checklist to make sure your m20 is in top running condition.