Dyno Run Crazy A/F Ratio

#1

Well I put my car on the dyno to see what I bought this year. My A/F ratio is real lean and dead flat. Looks like something is wrong as I have not seen another stock M20 line like this. Most I have seen fatten up around 5 grand. Any ideas.

Plugs, wires, cap, rotor, fuel filter, air filter, coil are all new. Found a slight vacuum leak to the left of the throttle body after the runs.

A/F
[file name=E30_AF.jpg size=80581]http://spece30.com/media/kunena/attachments/legacy/files/E30_AF.jpg[/file]

#2

HP Numbers [file name=E30_HP.jpg size=77648]http://spece30.com/media/kunena/attachments/legacy/files/E30_HP.jpg[/file]

#3

That’s messed up. Ask dyno guy if he was at WOT the whole time in that graph. It would be good to know if the messed up A/F ratio exists for both partial and WOT.

Test your TPS (Throttle Pos Switch), procedure in Bentley. That tells the CPU that you are at/near WOT. Swap out ECU and make a run. Then swap out AFM and make a run. Flap door in AFM tells ECU how much air is getting thru.

Your mixture is so lean that the resulting heat could damage the motor.

#4

That doesn’t seem right. Almost like the sensor wasn’t reading correctly. The slight variation is just noise in the system.

#5

I second the TPS. The plot is almost exactly 14.7 to 1 and that is what the ECU will try to do when the TPS is not registering wide open. Chuck (BTW…that is burn pistons lean!!!)

#6

I second the TPS. The plot is almost exactly 14.7 to 1 and that is what the ECU will try to do when the TPS is not registering wide open. Chuck (BTW…that is burn pistons lean!!!)

#7

Thanks for the comments. Yes its alarmingly lean. The motor did not burn down last weekend at Watkins Glen. The Dyno guy thought the check engine light should be on and could not check for codes since he mostly does domestic drag cars vs German running gear and dd not have our strange plug adapter.

I will check TPS and AFM. Not sure if there is a procedure for checking the AFM but I will look through Bentley for one. Anyone know of a diagnostic procedure for AFM.

I have a second ECU I can try next trip and will try to source a good used AFM for a try also.

Thanks again.

#8

Use the “stomp test” to check engine codes, but if the CEL isn’t on, I don’t know that I’d bother. Look up the procedure on e30tech.

If you can’t borrow an AFM and ECU from anyone up there, give me a holler and I’ll send you a loaner.

If Chuck Baader thinks it’s the TPS, then it probably is. When I was checking my TPS, I had 2 spares. Of the 3, the only one of 3 that worked was the one on the car.

#9

I will look up the stomp test. I will also pull the dash cluster to see if my Check Engine light is burned out or disconnected.

Thanks for the offer on the AFM. I spoke to one of my buddies today and he has access to 2 e30s. We will barrow a AFM from the one e30 that is not in use that day for the Dyno retest after I get the TPS checked out, small vacuum leaks corrected and a new fuel pressure regulator in the car.

Just to confirm when you did your pulls you do them in 4th gear to get 1 to 1 ratio?

One cool toy the Dyno guy pulled out after seeing my way lean numbers was a smoke machine. He hooked it into my vacuum lines and filled the intake with slight pressurized smoke. Then you see where your leaks are. My car had a small leak coming form the throttle body throttle cable action. I guess where the pin goes into the body to control the flap. Anyone know if theirs has a small air leak also? Or could this be common and acceptable for these cars. He did mention it was very small at best. Had some larger leaks where the hoses go into the sides of the throttle body. They need to be sealed up and a hose replaced since its a bit dry and inflexible now.

#10

No need to pull the cluster to check the CEL bulb, should light up when you first turn the key to the ON position, at least mine does. Also might have an extra TPS if you need one to test things out.

#11

I think that my pulls were in 4th gear, but I can’t be absolutely certain.

My dyno guy also used a smoke machine. That found a vac leak for me too. Nice. Your vac leak might be a factor for parital throttle, but not WOT. Once TPS indicates WOT, which is actually about 10deg of throttle rotation before WOT, the CPU quits measuring intake air and just uses internal maps.

Throttle side hoses. If you mean the ones that go into 90deg fittings, do yourself a favor and remove those fittings, clean the metal surfaces that mate with the throttle, and then use some JB Weld to permanently fix them to the throttle body.

One of the guys showed me that last Feb and it’s a great tip.

#12

That is actually excellent power considering how lean it is.

I had similar issues earlier this year (mine was making about 132hp). TPS was bad and once replaced it helped but my car was still lean. The fact that your lines are so smooth tell me your TPS is OK but I am not an expert. When my TPS was not working my fuel ratio lines and power/torque lines were jagged (meaning the ox sensor was sending correction signals to the ECU) Chuck - Any comment about this?

My proplem was fuel injectors. I had a set that were allegedly recently blueprinted but they sucked. I put the old stock injectors back in the car (after it was already off the dyno)and was able to race but it is still no optimum.

I have the re-rebuilt injectors sitting in the garage. Haven’t had time to re-install them yet.

Good luck and let us know the outcome.

Don

#13

Good point on the O2 sensor. I would think one or both of them are dead. Since the TPS is easier/cheaper, I would replace that first, or at least check it with a DVM. CB

#14

In general, a bad O2 sensor will make the engine run richer than normal when the DME is in closed loop mode. But once the WOT switch closes and the engine exceeds about 4k rpm, the O2 sensor is out of the picture.

#15

Good point, Jim. Now that I have my head back on straight, when the TPS goes wide open, the ECU goes to the map. There may be a threshold RPM, but I believe it to be lower that 4k…perhaps 3-3600? Chuck

#16

I’ve been told from a tuner that the transition happens at about 4k, which is when the AFM signal hits the rail. But I could see the DME reverting to map data before that and the spike in the dyno data that we frequently see could be evidence of that shift.

#17

Sean,
My check engine light must be bad as it does not light up when I cycle the key on at start up. I think I have a few bad lights. Need to pull the cluster, confirm and fix.

Scott,
When you ran the smoke test did you have a slight leak from the shaft that goes into the throttle body. The smoke would come through the spring that returns the throttle linkage to full closed. I had a slight leak there but am not sure if that can be 100% leak free.
Yes, the other leak is in the 90 degree bend aluminum hose fittings that go into the throttle body. I fixed the hose fittings on the other side that goes from the power brake booster by cleaning them and adding a little gasket maker to keep that sealed. Found them just laying disconnected after race and my brakes felt like they had no stopping power. Guess I had non power assist brakes after that fell out of the throttle body.

Chuck,
I will check the TPS via the procedure in the Bentley manual. Seems pretty straight forward. If that is OK I will look towards the O2sensor.

Since I will be sliding down the slope of “While I am In There” I may pull the injectors and send them out to get rebuilt. I saw a few guys recommended places and the price was not too steep. I think Carter and 87isMan recommended places.

Hopefully can get this sorted in the next month or so and get back to the Dyno and see if that corrected the situation. I will keep you posted. Thanks for the input.

#18

No leaks at throttle body. I had a leak on the intake manifold where the vac line to the fuel pressure regulator connects.

Those 90deg fittings were a constant problem tho until they got JB Welded in. Everytime I removed my intake manifold they would come loose.

#19

Wanted to give an update on this. Was back at the Dyno on Monday.
What I did:

  • Replaced most if not all hoses related to intake or could cause a potential vacuum leak.
  • Got a good used throttle body
  • Checked TPS and it was good. Used spare I had that came w/ used throttle body was bad.
  • CEL and ABS light were just floating behind the clustter so they are all reinstalled and working fine.
  • Tested Air Flow Meter and found a dead spot. Replaced AFM.
  • Had injectors rebuilt.

Results:
0 vacume leaks after smoke test.
Run 1 it had a AFR in the 12s - 13s vs high 14s. Also looked like all the other E30 AFR graphs I have seen. Even made a few more HP and Ft lbs of tq.
Run 2 it broke up at 4500 and then just shut off.

Crap what happened. After a lot of parts swapping and relay jumping and many more abbreviated runs we traced it back to the crank sensor. It had a wire breaking off. So we had to push the car back in the trailer as it would not start at all ofter we touched it and I guess broke the wire the rest of the way. Not a great way to end a dyno test but better then at the track. The new crank sensor should arrive in a few days along with all new relays. If the car starts I am back in business. Then back to the dyno for some more exercising to confirm all is well.

#20

sounds like you are on the right track, but I would invest in a cheap Harbor Freight fuel pressure test kit so you can watch fuel pressure while on the dyno…