1980 924T is too lean

Guitarsmith · 08-21-2001, 07:43 AM

I had some overheating problems a week ago and stopped out of town at a Porsche/BMW mechanic. He "set the specs" (timing, CO) and did a pressure test. Car ran a lot better after his work and my Huntley gauge read good numbers.

After a 100 mile run back from a gig, the next morning there was a puddle under the car. Turns out the heater valve was leaking. I walked to a local FLAPS and got a thru pipe and put it in--heat on all the time.
I bled the system, filled it, all OK as far as temps go. No overheating, runs about straight up.

THE PROBLEM: The car runs lean (left red light on the huntley) at idle and till WOT AND the car doesn't want to start. Runs great when warm, but if I can get it started it runs like crap and then when warm it's way to lean.
The mechanic DID set the AFM and I haven't touched it because it was a fine mixture. I have been fiddling with the idle air bypass---which way will make it richer at idle and just off idle? Is there a way to "fool" the car to thinking it's warm?

tia
Nick

3sonfather · 08-21-2001, 07:57 AM

Nick,
Turning the Idle Air Bypass scew clockwise at the throttle body will lower the amount of air into the intake at idle, hence making the fuel mixture richer.
The fact that your car will run better when warm suggests a faulty cold start injector or aux. air flow regulator.

By the way does anyone have the magic formula, either by use of a a/f monitor or CO monitor as to the combination of adjustments: airflow meter bypass, airflow meter wiper position (at the potentiometer), and idle air bypass. How are all 3 of these adjustments made for optimal performance? I think we all could use this info.
Thx,
Scott

Guitarsmith · 08-21-2001, 08:02 AM

Thanks.
If I make it richer at the idle bypass, will it richen it across the RPM range?
I noticed last nite that it goes rich when I let off the throttle (changing gears), so I know the 4 wire O2 sensor is good. The rest of the time it reads full lean.

3sonfather · 08-21-2001, 05:52 PM

Given your last response, the answer to your first question is no, or at least probably very insignificant. With the throttle open, the volume of air delivered past the throttle plate would be much greater that the bleed hole of the idle bypass.
What do you mean: "The rest of the time it reads full lean." ?? And how long does it run crappy?

JonA · 08-21-2001, 06:13 PM

When you replaced the heater valve did you disturb the temperature switch right beside it? I believe this switch holds the oxygen sensor out of the loop until the car warms up(lets it run richer until warm). I think the switch is normally closed, it opens when warm, so if you jumper the leads together with a piece of wire you can simulate a cold engine.
Good luck,
Jon Aborn
82/924

drew1 · 08-21-2001, 09:25 PM

I think that pulling the little plug on the sensor for temp (not sensor for guage)would make the car think it was hot.

Do you have a duty cycle meter to check duty cycle of that valve that sends gas back to the tank? A dwell meter will work. It should be around 50% idling (45 degrees on 4 cyl dwell), I have heard. If not adjust the flapper thing.

Another thing, ohm out the coil of warm up regulator on back of manifold near firewall, & make sure it's plugged in.

drew1

Guitarsmith · 08-22-2001, 06:39 AM

I drove it up to the mechanic (who really is a nice guy)and he came out and decided that when it got to hot or low on coolant it must have been enough to set the AFM out of whack. We richened it up there and now it runs fine.
As far as the cold start problem, he thinks (like Scott) that it probably is a faulty cold start injector and said he noticed that when I brought it in last time.
I adjusted the idle air bypass to up the RPM's at idle and it does run full rich for a second when I change gears (normal, I guess). But no more backfiring and hard starts!
I did pick up a heater control valve ($10.86!) that I will put in as soon as it stops raining (Seattle).
Thanks for quick accurate replies
Nick

Guitarsmith · 08-24-2001, 03:53 PM

Latest version:
Another cooling pipe burst and so I replaced it. No more leaks. They seem to be like light bulbs in the house--when one goes, the rest are soon to follow.

But the car is still lean in gear going down the road. Idle is fine--the Huntley A/F gauge cycles at idle, so I know the O2 sensor is working. Lift the throttle after reving or when changing gears and the meter goes to rich and then back to lean.
I've adjusted the AFM to make it richer---Clockwise with the allen key then plug back the hole.
Maybe I need to go farther?

drew1 · 08-26-2001, 01:35 AM

Guitarsmith,

With motor off & fuel pump relay jumpered to run the pump gas should barely be coming over the top of the injector port on the fuel distributor (or whatever that flapper thing is called), with injection line removed.

You might want to check this & adjust if need be.

drew1