TM___

Hi all,
I wanted to start a separate topic on this, because the title of my original topic covered mutliple problems, fuel consumption not being one of them.
Previous post on my troubleshoot

Long story short:
My 84 Euro S (twin distributor car) with 174.000 km (110.000 miles) is a very thirsty car. I average 20,3 l/100km (11.6 mpg) over the 2000 km I drove it. Last 200km were the worst at 23,1 l/100km (10.2 mpg).
I only once got a 14,3 l/100km (16.4 mpg) when I did almost exclusively highway at 125 kmh.
Other highway trips were not going below 18,8 l/100km (12.5 mpg).

It has received new injectors and a revised MAF from JDS Germany, in 2021 before I bought it. I have had it checked out by a 928 mechanic and we have put in new original spark plugs too.
I found a leaky fuel pressure regulator and have replaced both (backside of the engine). The damper in front seemed fine (holds vacuum). There was a brown substance in the air intake neck, below the throttle valve.
Last week I installed a cruise control vacuum servo, and noticed the brown slurry was back in the neck. It smelled of fuel. (pic below) This is within at most 1000km. I suspect the mechanic will have cleaned it out when the airbox was removed too, so I suspect this to be from the last 500km even. If the FPR are brand new, I guess the culprit is the FPD?

My old spark plugs indicated it running rich, though the mechanic found clean plugs when he replaced them. A bit strange, but maybe due to the 100km highway trip up to the mechanic.
I'll check them again now and will report here.
I will also check resitance of the MAF as proposed here Thread: fuel consumption seems high
I have slightly turned the screw in the MAF as well, I can always reverse, based on resistance findings.

I guess my first action should be replacing the fuel pressure damper in front? But if there's this much fuel in the neck, shouldn't I be able to visibly suck fuel out of my damper with the mityvac?

Darklands

Looks normal, this little lake of oil has my car too.

My engine received new piston rings 10.000 km ago. The oil ist from the crankcase and typical for These engines.

TM___

A question on the idle rpm: is the idle speed supposed to change after warm up? Mine is at 700rpm right after starting and creeps up to 800-850 in those first 30 seconds. It stabilizes around those 800-850 after revving the engine.
After it is warmed up, there's no big change in idle speed. Should it drop? There may be a slight increase even, up to 900 rpm.
Could this be related to my fuel consumption? A faulty temperature sensor somewhere?

Darklands

You mean the LH Jetronic has rich fueling all the time? A good explanation for to much consumption.
But if the temp sensor is broken you should have permanent high CO readings on the exhaust tester.

Is your head gasket broken? What‘s the pink stuff in the V and in the middle bottom of the picture?
Or is it the bolt hole?

Mrmerlin

did you readjust the MAF for mixture after the engine gets to running temp.
make sure the temp 2 sensor is good as well as the connector for it.
NOTE you can use your nose for this MAF adjustment to get it close.
I find that the Euro 2.2 needs a MAF ohm setting of about 170 to 185 ohms,
the fresh MAF will come set to 380 Ohms.

TM___

So, I took out the MAF today and measured the resistance between pins 6-3 and 5-3, as the WSM says.
I read 4.1 Ohm between 5-3, which is top end of what the WSM says.
Between 6-3, I only read 0.2-0.3 Ohm, the WSM says 0..1000 Ohm. Is this the reading that should be around 180?

Can I simply adjust through the screw, or should I send it back to Germany? It is a rebuilt unit by JDSPorsche (dated 12/2021) so still under warranty.

Also, If I check resistance on the TEMP I sensor (in the airbox housing), I read infinite ohms (at room temperature). I can't seem to find any spec on this, but infinite does not sound good?
TEMP II sensor reads correct values.

(The pink gunk may indeed be dried up coolant from the head gasket. Should I get those replaced immediately?)

Darklands

If the car don’t loose water yet you should monitor your coolant level regularly.
Dangerous is if one bore is full of coolant if the car sits longer in the garage and if you crank it the water breaks the block.
Better doing the gasket job planed so you can moderate the time frame.

I let my engine refresh after water consumption and the car was month away.

Mrmerlin

you adjust the MAF with the engine running,
make a tool with a 3 MM allen glued into the end of vacuum hose fit this into the adjuster ,
then run the engine,
smell the exhaust to get an idea if its rich or lean,
you should be able to smell.
NOTE an O2 sensor machine is the best way to set the MAF but its not a common tool so you have to make due

TM___

Hmm, my experience with smelling is nihil.
Just to be sure: does the allen pot control the ohm reading on pins 3-6? It's currently reading .3 ohm. Will I screw things up if I start turning it out of the car? Should I get it to a base reading before finetuning it while the car is running?
Can you describe the smell I should be aiming for?


(Is the temp sensor in the airbox broken, and could it affect my fuel consumption?)

gazfish

A bad airbox temp sensor will effect ignition timing, I’ve read here Temp 2 is more important. There’s a modern alternative to the stock sensor that’s worth fitting if you search the forum, I felt a step up in performance especially in cold weather so the airbox sensor definitely does something. For what it’s worth these are my consumption figures for the same model, not necessarily right but definitely less than you’re seeing.




Also check the temp 2 resistance is also correct at the LH connector to eliminate an issue with connectors/harness.

TM___

These are numbers I would indeed expect, thanks for sharing. Mine are much worse. Long term consumption over 2500km is 20.2 l/100km (11.6 mpg). I have also made an excel to keep track, but I wish I wouldn't have included fuel prices, that total is rising quickly. It's not that I care so much about the number, but knowing it's much worse than it should/could be is what bothers me.

The temp 2 sensor measures the same at the LH plug, it's around 3000 ohm with cold engine parked in my garage (I guess around 10°C there now).

But, if my MAF reads 0.3 ohms, would that be the lean side of the 0..1000 ohm setting? I read in another thread that the 1000 ohm is the maximum rich setting. This would not make sense?

IcemanG17

Agreed about temp 2 sensor..... when they go bad, they default to freezing cold, or rich. Granted this was a USA car...but on my 84 lemons racer it wouldn't run.....chased it back to Temp II....jumped it with a piece of wire so near zero ohms (it was a hot day)...ran just fine....pulled the wire, instant stall and won't restart until very cold..

The really good news....a bunch of cars that use Bosch injection-AFM etc use it....we pulled one from a Saab, same bosch part number and it ran great

TM___

I started messing with things and turned the pot on the MAF until the Ohm reading went up. It was at 0.3 ohm to start with and I turned it up to 185. That took a couple of full turns (after the first half turn clockwise, reading was still 0.3 ohm). Right after that, it was smoking a lot at idle. The day after, no smoke at all. It is intermittently smoking and not smoking.
Drove another 330km until the empty fuel tank light went on (from full) and averaged 21.6 l/100km (10.9 mpg), slightly worse than before.

Today, my new airbox temperature sensor arrives (TEMP I) (the newer and faster bosch one), my current one reads infinte ohm so was obviously broken. I will replace it and drive another fuel tank and report back.
I assume my TEMP II sensor is fine, it reads 3000 ohm with cold engine in a cold garage, both from the sensor plug and from the ECU unit in the passenger footwell. I'll check prices and may order a spare, just in case.

Darklands

These cars aren't gas guzzlers. Yesterday I was every time over 130 kmh and had 14 l /100 km.
I reach if I doing trips around my village 550 km with one tank full of gas.

If you can't find the problem I can send you my spare computers for trying.

TM___

I read your thread on your "new" 928. Nice trip to start your relationship!

I'm slowly taking on things, step by step. If I'm sure all parts of the fuel system are working fine, I'll have to turn to the computers. Thanks for your willingness to help me out with those, I'll let you know when I'm at that stage.

Thinking about changing the injectors too, although the set is new since 2021 and has cost 850 EUR. I'll contact the seller and ask which injectors these are specifically (work was done with the previous owner: a car seller in Nurnberg). They might as well be cheap chinese replacements sold for a large profit. I don't know.
Is there a way of testing their specifications for an amateur like me?