Hunting down power issue

[NathanR]

I’ve got an M20B25 and my friend has convinced me it’s low on power. This is my first E30 and I’ve always assumed it’s just a slow 30 year old car, but after having it lug a tiny in in 4th up hill, he convinced me to do a 0-60 which resulted in ~12s with a little rolling start to save the clutch. Now I cannot stop thinking about it and I’ve started to tear into the car.

• Symptoms
  • Car is slow
  • When car is at a stop, if RPMs are coming down and throttle is blipped it will surge a bit
  • Found a drop of fuel in the throttle body
  • Smells like gas but has no cat
  • Mpg is like 20 but I have no reference
• Diag
  • Sprayed carb cleaner wherever I could find a vacuum line, no notable changes in idle
  • Water temp sensor seems to be working fine
  • Adjusted TPS idle and WOT to be working correctly (I think)
  • Unplugged AFM while running, car shudders and settles
  • Fuel pressure looks good with key on and also when engine is running. Once turned off it starts to drop, lost 15PSI in 10mins
  • Pulled vacuum line to FPR and pressure raises accordingly
  • No fuel in FPR vacuum line
  • Pulled rail and injectors, none drop fuel after turning pump off
  • Injector resistances are all within spec
  • Injectors look really dirty to me, but the ends are clean? Was considering sending out for a rebuild or purchasing the Bosch Gen 3.
  • Borescope showed a tiny bit of fuel on a couple pistons
  • All cylinders are within acceptable range for compression
  • One of the spark plugs looks like it’s running lean, one other has fuel on it, but could entirely have been from the rail when I pulled it.
  • Spark plugs are gapped at 0.035-0.036 from box, I see spec is lower.

• Questions
  • On injectors, should I do nothing, rebuild, or buy new. If buy new, which ones?
  • Any ideas on where I’m losing fuel pressure? Starting to think this is unrelated.
  • Should I re-gap these spark plugs?
  • Outside of injectors/ plugs, my next steps were
    • Check distributor rotor and cap
    • Check ignition coil resistance
    • Check spark plug wire resistance
    • Check timing
    • AFM voltage sweep
  • Anything else I should look at?

Thank you!

[TobyB]

Start with an injector cleaning. This generation (and earlier) is pretty sensitive to injector flow,
and the injectors do clog- unlike later designs.

Then the tune- up parts are a good idea, if yours are older than 5 years.

I very much like a wideband oxygen sensor- it tells you a lot about what combustion efficiency is.

t