JakeS2

Hello,
I tried to find article to locate issues with 928 32V engine running rich problem. But did not find it. Let's do one, eh?

- Symtoms:
* Blows black smoke after 5000 rpm: (fun part starts at 1:40)
* Runs rich on all the rpms, but esp. after 4500 it really dives ; lambda drops to 0.90 and at 6000 it's almost 0.85.
* When releasing throttle it bangs in the pipe quite often
* Sparkplugs are black
* MPG is bad (euro consumption 14-15l/100)
* There is not as much power like f.ex last summer (on butt-dyno)
* On real dyno it pulls 208kW at wheels but the mixture report tells that basically after ~5000 nothing significant happens anymore.
* One can really smell the unburnt fuel
* Emissions report tells that HC is over 200 so it won't pass emissions test
* Idle rpm dwells from 650 to 750, being sometimes at 900 (after driving)

- Changed
* MAF was refurbished by John Speake, really appreciated.
* New wires, plugs, distributors and -arms
* New wires to coils
* Disconnected airpump & sealed it's terminals
* installed X-Over
* replaced O2 sensor last summer

- Checked
* fuel pressure seems to be at 3bar on idle (with a bit leaking meter. I'll try to get better results there)
* no errorcodes on LH / EZK
* spraying carburetor cleaner on vacuum pipes does not alter rpm so guess they are ok
* With sharktuner's adaptation test I can hear clicking sound on ICV
* Sharktuner tells that we have 0-position on throttle body and WOT as well
* Cylinder pressures measured at 200psi per cannon
* temp sensor (NTC II) reading with SharkTuner runs at ~85C when engine is warm.
* coding plug value - matches '89 ROW manual with cats.
* Sensor analysis with sharktuner - all values seem ok.
* Ran the car with another LH and EZK - same results

- Not checked/replaced
* injector wash
* condition of ICV hoses

- Known issues:
* exhaust leaks a bit, will address that when I am under the car next time

- Happening next:
* More testing of FPR with better meter
* Opening a can of beer as driving's off anyway
* ?

SeanR

Temp II sensor/connector would be first step.

John Speake

An exhaust leak could be fooling your O2 sensor, and causing the rich running..... have you tried another LH ECU ?

Bill Ball

Have you checked the fuel dampers for leaks? (Pull of vacuum lines and sniff for fuel). Are you sure the O2 sensor is plugged in correctly?

JakeS2

Thanks for the comments, here is little update.

Car spent today in sensitive care of vilhuer as day turned to evening we ran the car with another LH and EZK with SharkTuner + opened my LH and EZK this is what we found:
- Temp II sensor is operating nice, exactly right on the target with temp values
- Sniffed the fuel damper's vacuum tube - no smell of fuel
- Nothing seems to be "wrong"
- Car accelerated and performed similarly with the other LH + EZK
- ECU has been re-worked my John Speake in 2004 :-) The 'brick' was changed at least
- Car has right type selector plug (i.e. '89 manual with cats)

Next:
- Check all exhaust leaks
- Re-check that O2 is of correct type and connected correctly
- Re-measure fuel pressure (last 3bar idle was measured with a heavily leaking meter)

Question(s)
1. If it blows black smoke at WOT, shouldn't O2 sensor be irrelevant at that point?

John Speake

Well, there's nothing wrong with it :-)

You are correct that at WOT the O2 sensor isn't involved, but the car is obviously running rich when the O2 loop should be in control.....when you had it on Sharktuner, did you monitor O2 adjust at idle ?

These cars always run rich at WOT, that's how Porsche set them up (for safety). Your car seems worse than most because something seems to be making it rich all over the range.

the flyin' scotsman

are all spark plugs black?

what condition are the injectors?

Hilton

Lambda 0.85 is around 12.5 AFR. Which sounds about right for an S4 under WOT.

However, running rich through the range and having black plugs is definitely not normal.

If your idle steady? My most common "runs rich" problem on a cat car is the O2 circuit isn't connected, or has shorted the sensor wiring by rubbing on the heat shields.

I did recently have a lot of issues getting my '87 to pass emissions locally - it turned out that the LH was in the process of dying, until it eventually failed completely (about 2 minutes after I *finally* passed the emissions test, oh the irony! I couldn't drive it out of the test room, but I was still happy).

From everything you've said, I'd measure the Temp II sensor and compare the resistance values of each terminal to the workshop manual.

Then I'd check the O2 sensor wiring carefully, although that usually gives a hunting idle in my experience.

Then I'd borrow an LH off another S4 (preferably not from a GTS or GT), and try that.

Mrmerlin

what spark plugs are you running?

JakeS2

currently we have Bosch wr7dc+. I tried with ngk bp6es but it made this worse.

we tried another LH and EZK and ran '89 S4 software on them with Sharktuner (man, gotta give big THANKS to John Speake for this tool, it's absolutely brilliant) and testdrove the car. I think there was a little change in the car's running but nothing big.

The clutch is about to blow as well so I'm going to tear her a bit apart on sunday. I'll post findings from exhaust department then.

We have not looked at injectors at all. Propably I will rip the throttlebody off as well so then we know more.

The Forgotten On

What could be happening is you could have a injector leak. Air could get sucked into the engine on one cylinder and then the Lambda circuit tries to compensate for it by adding more fuel leading to the rich running. You could also have a vacuum leak anywhere which could cause rich running, even a leak in the A/C system can cause rich running but not as serious as yours. I would definitely recommend changing all of the fuel injector O-rings. It will help to narrow down your possible problems.

John Speake

Most of the smoke at WOT on that dyno run looked blue to me.....oil smoke.

However black plugs aren't right. Suggest you have another ST session and carefully look at "O2 loop adjust" on the system monitor screen at idle and small throttle openings under steady (closed loop) conditions.

Hilton

This is a good point too - a misfire on a cylinder can cause it to run rich due to the excess O2 detected by the sensor leading to the LH adding more fuel.

Checking plug wires, carbon build-up, spark plug gaps, leaky injectors etc. are all to be advised.

You can check for a leaking injector by monitoring fuel pressure after shutdown. It should hold more than 40psi for about 30 mins or so from memory - the exact spec is in the workshop manual. Of course, if it doesn't hold pressure, you need to eliminate the Fuel Pressure Regulator and the fuel pump check valve as possible causes, but if it holds, then you know all three of those are ok.

JakeS2

John, I was there right behind the car. I was carefully looking whether it's blue or black but it was all black. It's supprising to see that on video it actually shows blue. I don't have sharkvent in yet so that might cause some smoking as well. But as I saw how easy it's to tweak the 928's brain with your stuff I'm going to order couple PEMs from you soon

One symptom to add here ; after heave acceleration there is smell of oil in the cabin for a little moment (esp if sunroof is open) but it's not burnt smoke, it's like someone has a fresh oil can at the backseat.

The Forgotten On & Hilton, thanks for the pro-tip on injector leaking. I'll do that next, I need to figure out how to seal my fuel pressure meter properly but that's surely on the next things to do.

So avanti poppolo! Next ; more fuel system analysis and then I jack her up and disassemble exhaust system as I need to put in another starter and clutch.

Hilton

I just read your original post again.

Some European countries didn't get O2 sensor from factory until 1990. Its possible your O2 sensor is being ignored due to the LH coding plug.

Its definitely worth taking a few minutes to disconnect the battery and check the pins on the coding plug. If you've replaced the MAF with one from John, and the coding plug is one for a non-cat car, it would explain the rich running.

Page 24-222 of the factory workshop manual has the different coding plug pin configurations for 89-95 cars. Its (probably) attached to the same frame that holds the ECU's. (I say probably because I haven't looked at LHD cars )