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

[MrBurgundy]

I had an issue similar before where the DME would not wide open the ICV when stomping on it.

Makes a big difference. The DME itself was bad. Continuity at the TPS tested fine.

If injectors aren't working properly in my experience you'll have a misfire before loss of power.

I'm almost certain that's the issue

You're getting that surge when stopping because the DME cannot send an idle signal at a stop and cannot send a WOT signal when stomping on it.

Try this bro I swear. Remove the canister valve hose from under the throttle body and see what the car does

Should have a lot more power and idle like a champ if what I said is in fact true.

[NathanR]

I had an issue similar before where the DME would not wide open the ICV when stomping on it.

Makes a big difference. The DME itself was bad. Continuity at the TPS tested fine.

If injectors aren't working properly in my experience you'll have a misfire before loss of power.

I'm almost certain that's the issue

You're getting that surge when stopping because the DME cannot send an idle signal at a stop and cannot send a WOT signal when stomping on it.

Try this bro I swear. Remove the canister valve hose from under the throttle body and see what the car does

Should have a lot more power and idle like a champ if what I said is in fact true.

I should have noted earlier, this car has the charcoal canister deleted from previous owner. The port on the throttle body is capped.

[MrBurgundy]

un cap it

we are trying to introduce the air that is missing for idle controll and wot control

To also test my theory, open the ignition and see if the ICV is slammed shut

If it is slammed shut the DME might be bad

[NathanR]

Since I have the rail off already and it’d make me sick to put these injectors back in the car, I’m gonna send to Race German and get them flow tested and rebuilt for at least piece of mind, though I’d be sad if they tested fine before the rebuild. In any case, once they’re back if I still have issues I’ll give the ICV/DME test a try.

[82eye]

Since I have the rail off already and it’d make me sick to put these injectors back in the car, I’m gonna send to Race German and get them flow tested and rebuilt for at least piece of mind, though I’d be sad if they tested fine before the rebuild. In any case, once they’re back if I still have issues I’ll give the ICV/DME test a try.

i upgraded to a modern style open 4-pintle which increases efficiency, smooths idle, and helps the power curve a little. the injector tech back when the cars were built is in the stone age. mine are paired to the build and chip but there are alternatives for stock as well.

[MrBurgundy]

i upgraded to a modern style open 4-pintle which increases efficiency, smooths idle, and helps the power curve a little. the injector tech back when the cars were built is in the stone age. mine are paired to the build and chip but there are alternatives for stock as well.

I second this.

I was messing around w "rebuilt" injectors, which means nothing outside of resealing and apparently flow matching.

Went with the 4 pinel bosch 62415 injectors. Way better performance and way quieter too. They're new, so you wont have to think about injectors for many many miles.

[NathanR]

So I’ve sent the injectors off to be rebuilt and flow tested. This morning I measure ignition coil resistance and got 0.7Ohms on the Primary and 9300Ohms on the Secondary. These are both out of spec but from what I’ve seen the spec can vary wildly. Does anyone think these measurements are of concern?

[TobyB]

If the spark at the plug looks healthy and you're not getting misfires at WOT, I would wait for
the injectors to get back... coils very rarely fail, and when they do, it's often something annoying
like a connection that only opens when they get really hot.

It IS worth checking your plug wires, tho, as they do degrade with age, heat and vibration...

t