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Apologies in advance if this doesn't apply; I've been reading this thread to learn about these earlier (than mine) cars.
One of the things that I may have missed in the discussion is anything about an O2 sensor. Does your car have one? If so, has that been checked?
Good luck with all of this, I'm interested in hearing how you fix it.
All the best
Zirconocene,
The 84-86 ROW cars do not have O2 sensors
TM___,
Back in 2007, I drove my 84 Euro to SITM and returned home (around 2000 miles). I didn't measure going to SITM, but noted mileage and fuel returning. I had set my cruise control when I left the Banner Elk city limits to @ 170kph and left it there except for high traffic situations and fuel stops and my car got 21mpg for that 1000 mile trip.
Last edited by soontobered84; 01-12-2024 at 05:28 PM.
Reason: adnl info
There is indeed no O2 sensor in these Euro S2 cars.
What flappy do you mean?
I have no CO meter here. Also no clue as to what I need to smell in the exhaust.
Is there a relatively cheap meter I can get to actually measure the CO?
When I bought the car last year, the MAF was at 0.2 Ohm and passed an emissions test, but I have no measured value.
(The car came with a TÜV report from march 2021, where the measured CO was 0.157%vol, but this predates the installation of a revised MAF, which was invoiced in december 2021. So that is probably not very informative. This was also before new injectors were installed etc.)
There is indeed no O2 sensor in these Euro S2 cars.
What flappy do you mean?
I have no CO meter here. Also no clue as to what I need to smell in the exhaust.
Is there a relatively cheap meter I can get to actually measure the CO?
You can read/SNIFF the exhaust 2 ways. On my custom exhaust that I built, I included O2 bungs on each pipe (true dual system) BEFORE the hi-flow cats! OR you can go to any COMPETENT DYNO tuning facility and they will have a laptop with an attachment to analyze the exhaust gases. Then just dial it in and REtest until you have it right. Use the MAF and 2 adj. FPR to get the level correct! The dyno shop I used WAY back in 2005 could see the A/F number in real time thru the rpm range. You want 14.7 at idle and low rpm's and slightly rich as you approach redline
The Flappy = Remove the center plenum in the middle of the spider. Then look down the Throttle at the plate (butterfly plate/valve) have someone step on the gas pedal. The plate MUST be straight VERTICAL when gas pedal FULLY pressed. IF NOT adjust it at the firewall, where the adjustor is! THIS CONTROLS OXYGEN FLOW, if yours is off that could make it run rich.(with engine OFF of course)
make sure your cam gears are aligned exactly and not a tooth off.
The right spark plugs (heat range) are necessary(NGK V power) , the alignment of the TWIN DIZZY is also important check that, then coils, final stages, 3 temp sensors, 1 other thing
My engine is just back from being rebuilt by a knowledgeable 928 workshop. I would suppose the cams and distributors are aligned correctly.
Not sure if I want to start taking the intake back off, since all of it has just been assembled.
I'll make an appointment to get CO measured and MAF adjusted.
I noticed that my idle is high. At cold start, it goes immediately to 900 rpm (instrument cluster) and surges up to 1100 rpm over the next 30 seconds, at which point it kindof stabilizes.
Once warm (20 minutes of driving) it idles around 950 rpm.
Hot start (after 30 minutes of driving and being shut down for 10 minutes), it immediately goes to 650 rpm and climbs up to 950 rpm over the next 30 seconds. It settles around 950-1000 rpm after revving the engine.
I adjusted the idle screw in front of the throttle body s.t. it idles around 700 rpm warm. It does need a little time now to stabilize again after revving the engine. Like 10 seconds of swinging between 650-800 (all reading from the tacho).
Just to be sure, according to the WSM for CO adjustment, the idle should be set at 750 rpm with warm engine. CO needs to be 0.5-1.5% ROW (no O2 sensor, no cats), ideally 1%?
The WSM says to disconnect the auxiliary air pump hose and to plug the air pipe. This has been deleted from my car, so no action required there?
This will be something for this week.
There are only a handful of men on the planet that really know these cars, most are on this forum. Even they don't know everything about every model.
If you had great 928 mechanics recently work on this, why the thread? I have not read every word, What is the specific problem.
The throttle body valve check is relatively easy as these things go. pull back the 8 blacks sleeves, undo the black tube holding it on the throttle body and pull it off. it's a PITA
I never cared about gas consumption when driving mine, there was no comparison to anything else. More fun than my R1. High rpm's all the time. Well worth every penny.
All I can say is NO euro ran as good as mine. The video is proof, I wish I had driving video's.
The thread was started even before the engine overhaul. Went in for a steering rack and possibly head gaskets, and finally did the works while the engine was out.
The car ran rich before and still does. Numerous things have been gone over. Everything checks out, but the thing is still rich and thirsty.
I shouldn't really care about consumption, but it's way above what it should be. I drive it, a lot, and at €45 per 100km (that is 60 mi), it unfortunately does bother me. I've put in almost €500 in gas during the last two weeks.
That's crazy money. 928 is my dream car, used ONLY for fun not transportation. Back in the day I would take it once a week usually late in the evening when the roads were empty and just drive it like it was intended.
The days when the 928 was a decent daily are long gone. It is simply not economically viable anymore today. With everything in perfect working order fuel consumption goes from poor to just okay.
The days when the 928 was a decent daily are long gone. It is simply not economically viable anymore today. With everything in perfect working order fuel consumption goes from poor to just okay.
Sometimes smiles per gallon are more important that mpg and why I daily mine. I have no interest in driving a Honda Accord Hybrid that gets 800 miles/tankful.
The air pump if installed will dilute the exhaust gases.
Good point and perhaps a good reason I have been chasing a very odd overly lean issue. It may be partially overly diluted exhaust. I need to check if the air pump is present.
So, after half an hour driving around (not treating it gently), I hooked it up to an exhaust gas analyser (fully warmed up).
I had previously adjusted the MAF pot to 169 Ohm (where it was 250 Ohm coming back from the engine rebuild).
The WSM dictates to plug the air pump before adjusting idle and CO. I don't have an airpump anymore, so that is taken care of.
Idle rpm was adjusted to around 775 based on the tacho (no other way of measuring at the local shop).
CO was 7.50%vol to start with (169 Ohm in the pot).
Turned the pot CCW until CO did not further drop and ended up with a CO of 4.81%vol
I checked at home, and the pot is at 0.4 Ohm, so fully dialed down.
I've attached the other values the machine showed.
Now what?
When I just bought the car and had to undergo federal road inspection before registration, the car passed the CO test. I'm not sure if the pot was dialed in at that time by the workshop (I needed a car dealer to do the inspection with the car having a dealer plate, only way to get it registered after importing) but afterwards, I also found the MAF pot to be fully dialed down (+- 0 Ohm resistance).
I filled the car up and had my all-time worst fuel consumption over the last 120km: 25 l/100km. I admittedly drove it like I stole it over a good portion of those kms, but still.
@Darklands I'll pm you to arrange me trying your computers.
I just went over the EZF and LH plugs in the footwell and all MAF and temperature inputs are within spec.
(TEMP I input was 0.8 kOhm, but this was with a hot engine, not running, so it may have gotten hot enough in the airbox (this reading should be 45°C). The sensor is a new bosch part, so it's probably alright.)
01-12-2024, 05:20 PM
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