924Board.org

[Johnny_Haywire]

As I was sniffing around the car tonight, I figured I'd see how rough it would be to get my O2 sensor out of a rusty pipe as it's certainly due for a change, and... the O2 sensor has been removed and replaced by a plug (and I'll bet it was an SAE and not metric plug...). I don't see any wiring down there, either. The car is an '81 2.0 N/A and is fitted with the Lambda system.

I know the O2 sensor talks with the frequency valve and enriches/leans the amount of fuel headed to the injectors once in closed loop. So... I'm not sure what to do here. There are a couple of orphaned plugs/connectors near the brake booster, and another pair hanging under the dash, but I don't see anything removed from the Lambda unit, which has those two round plugs of wires next to it (right?).

From what I've read, you cannot pull the O2 sensor and expect everything to be just fine because the frequency valve will be working on a default level.

Anyone ever come across this?

A Weber conversion is getting more and more tempting as I continue to find little surprises like this. Ugh... I would prefer to get the CIS working properly, though, and save the Webers for a future project.
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1981 924 N/A 5-speed

[Fasteddie313]

[Rasta Monsta]

Hunting idle is a symptom of poor tune (likely vacuum leak) and has NOTHING to do with lambda.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[Fasteddie313]

The tone of the idle swaying with the dwell meter swing as the lambda crosses your AFR back and forth across stoich is what I mean..
The RPMs don't change much if at all but the idle sound/tone sure does as the needle swings/duty cycle varies.
Lambda hunts back and forth across stoich, its narrowband, that's how narrow band works, and this example is particularly old and slow, I can definitely hear the lambda at work in the exhaust note at idle..

Maybe "hunting idle" isn't the correct term for this, you know what I mean..
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80 Turbo - Slightly Modified

[Johnny_Haywire]

Thanks for the info, Eddie. And for a bit of light at the end of the tunnel. I'm okay with running/tuning without the O2 sensor. Of course I wish the car hadn't been messed with, but if it's surmountable without sourcing the wiring/connector, etc., cool by me.

The main problem with my CIS system is me. I've done several tests so far, but not the important one (fuel pressure test). I've got the parts list and just need to put in the order to build mine. I think I know of a local mechanic that has a CO sniffer, so...mostly me being scatterbrained. I need to just build my pressure tester and watch the youtube video on the system (thanks for that, sir). I'm learning CIS better as I go along and as I test components and replace vacuum hose, etc.

The injectors are working properly (I did your test), but did not measure volume/time. They are consistent in volume, though. The cold start inj. is working, though I was not able to test whether the thermo switch is working because the car wouldn't start with the cold start injector unplugged. My coolant temp guage and fuel gauge are not working. The aux. air regulator seems to be working fine.

Replaced tons of vacuum hose, ran lots of premium fuel and Techron through her, new plugs/wires/cap/rotor. Timing at idle is spot on.

So, here's what happens when I fire her up cold. She fights it a bit, and the warmer it is (75 degrees and up) she sputters until finding idle. Since it's been cooler, smoother starting when cold, instantaneous starting after she's run for a while. Revs nicely while in neutral.

I unplugged the idle stabilizer and it idles better without it. A/C is inop, so not much additional draw on the alt.

When driving, it's kind of boggy with normal throttle application and takes its time to catch up. Seems to be getting too much of something, either air or fuel, and once it revs up a bit and you let off the throttle, it sort of overruns smoothly.

When I go full throttle (WOT), the car pulls really well and screams past 4K no problem. I'm hesitant to do this much since I don't know whether I have my A/F mixture correct.

When going 3/4 throttle, it will slowly build up until around 2900 RPM, when it takes off and runs really well, similarly to WOT. Again, hesitant to wind her up much in case I'm lean.

Which I'm likely not. I've enriched the mixture a bit and it has helped the car to accelerate better, definitely rich by my nose, but planning to pull a plug tomorrow to see where she's at.

Does this throttle behavior sound like low fuel pressure? (I know, a pressure test will answer this question for me : )

The pump is pretty noisy. Likely other things are funky, like the thermo time switch. Warm up regulator screens are probably clogged with crap. I have the bolts soaking in PB Blaster now.
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1981 924 N/A 5-speed

[Fasteddie313]

I'm pretty sure any universal 1 wire o2 sensor will do, and they are dirt cheap. A couple on ebay are less than 6 bucks. IDK about the super cheap ones but I recommend one for tuning with a dwell, its an invaluable feature IMO..
Your frequency valve is running correct?

If your injectors sprayed nice cone patterns I doubt you have poor fuelpump output. Yes a CIS pressure test would confirm one way or the other but this is a bit more complex than just "low fuel pressure", more likely it would be too high control pressure actually..

Your symptoms sound to me like a vacuum/air leak between the throttle body and air flow meter, if your pretty darn sure what is there isn't leaking then double triple check your vacuum line routing. I check for intake leaks by revving and opening the TB while putting my hand over the air flow meter/airplate thing to draw big vacuum post TB/pre AFM but I don't know if you can psychically do that on an NA.

You really need a CIS test gauge setup, almost everything CIS is just guessing without it.

I had a hoffman, but I wanted one always so I made this for my car..

All it really is is a guage to read, and a valve on the WUR side to isolate the 2 systems so you can read both in the same place on one gauge..
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80 Turbo - Slightly Modified

[Johnny_Haywire]

I'm going to order the parts for the pressure tester today and will give it another serious going over for vacuum leaks between the air flow meter and TB.

I've read up a bit on fitting the Bosch universal O2 sensor, but my concern is that the wiring has been removed. I know of a few parts cars that I will try to check out next weekend for the wiring (a 931, which is probably too short of a wire due to O2 location, and two early 944 N/A).

As suspected, she is running very rich (this is the #1 plug). At a setting any leaner, it really bogs and won't accelerate past 3000 rpm, and even that takes a while.

I also noticed this switch on the top of the throttle body yesterday. The set bolt is missing and only the pivot bolt is present. It had slid away from the throttle cam and was basically always open. I moved it back so that it works with the cam and will hunt down a set bolt and nut. What does this switch do? I can't find it in the Haynes manual. This is the type of stuff I keep finding as I go over the car. Little surprises everywhere




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1981 924 N/A 5-speed

[ideola]

That is a microswitch for WOT sensing and should be covered in the supplement, I believe chapter 13.
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erstwhile owner of just about every 924 variant ever made

[Fasteddie313]

From what I know about my turbo. that switch is part of that lambda system, what it does when the switch is activated is shut the lambda down and put it into a default mode, quite like pulling the o2 ensor, but in WOT mode it raises the duty cycle of the frequency valve to a steady reading, no longer uses the o2 as feedback.

What this does is let more fuel through the freq valve by keeping it open a higher % of the time, which lowers the distributor lower chamber pressure, which makes it easier for fuel to get out of the distributor and to the injectors, this in effect enrichens the mixture and gives you your WOT enrichment..

This is the WOT enrichment that still works with the o2 unplugged, and the reason it is very important to maintain your lambda system and keep the freq valve running in default mode even with no o2 sensor..

At idle I believe you should be able to switch that switch with your finger and hear the tone of the frequency valve change..

Your frequency valve is running right? It buzzes/vibrates all the time your fuel pump is running even when you jump the pump right?
On my car atleast, I'm pretty sure jumping the fuel pump circuit also jumps the whole lambda system..
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80 Turbo - Slightly Modified

[Johnny_Haywire]

I think my switch works a different way - when idling the switch is depressed/closed, and once the cam moves away from it, the switch stays open for the rest of the throttle cam sweep. I'll take a closer look tomorrow, there is definitely a WOT switch somewhere, because once that is activated, she pulls hard and smooth. I don't think I can move the switch when the throttle cam is at idle.

I think my frequency valve is working, but like most other things on the car, nothing can be taken for granted I'll jump the fuel pump and see if it's active.

Wasn't able to do anything with the car today, but I will definitely set an hour or two aside tomorrow for some tests.
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1981 924 N/A 5-speed