kamaro

I'm so excited that I just made my first drive in my 1987 928 S4, its been exactly a year since I started. got a couple of questions :

- the car is running VERY rich, the spark plugs got fouled after about 10 minutes between idling and driving around the block. Could the mass air sensor be not working correctly? .. is there a way to bench test it?
- I just can't find the automatic transmission vacuum line, I can't see it even at the transmission side! .. does it have one in the first place?

My car is a Euro spec with no catalytic converters or O2 sensor.

thanks,,,

buccicone

Are you sure there’s no O2 sensor? By 1987 all engines had them.

gazfish

Is it definitely a 928 ;-)
The plastic modulator is on the left hand side of the transmission and the vacuum hose should be plugged into that.

kamaro

Yes I'm %100 sure, its an export car with GCC specs. Basically its a Euro spec with no cats/O2 and with US spec rear bumper. pretty weird I know but that how they export 928s to GCC.

GregBBRD

I certainly would not be running a "rebuilt" engine that runs super rich.
While I'm not sure what a "rebuild" means to you, but in my shop this means new rings (when the bores and pistons are still in tolerance) or new pistons and rings.
And running a "rebuilt" engine even slightly rich is absolute death to these pieces.

Mrmerlin

an S 4 thats running rich means that you should have,
a fresh MAF,
the LH computers rebuilt ,
the temp 2 sensor replaced as well its connector
and smell the vacuum lines to the dampers and the FPR,
if you smell any fuel ,
then its a good bet one of these parts has sprung a leak,
and it would be wise to replace the set of them,
2 dampers and one FPR.
Also you should have put in a new CPS and cam hall sensor,
and rebuilt the throttle body and flappy shaft with new double O ringed bearings,
and put on a fresh TPS and new knock sensors.
also a fresh set of cleaned fuel injectors.
Please let use know whats been done

kamaro

I can't just throw $$$ worth of parts into this car without at least bench testing each of them. I think the best approach is to ditch the stock EZK/LH ECUs and use a Microsquirt with speed density tune. That way at least I can troubleshoot just like a modern world car! .. also its a good opportunity to throw away the silly and expensive group of fuel dampers/regulator and just use a single adjustable one instead.

GregBBRD

We tend to try and keep the stock components.
First of all, we are in California, where it takes an act of Congress to get approval on aftermarket fuel injection.
Second of all, I can be assured that if there is an issue, anywhere in the country, any Porsche shop can (should be able to) work on the stock fuel injection system.
Thirdly, Sharktuner allows us to tune the stock injection, so the advantage of a different injection system is somewhat moot.

I do understand the economics of the stock injection pieces.
A MAF rebuild, an Idle stabilizer, a throttle switch, a hall sensor, a couple of knock sensors, a fuel pressure regulator, two dampers, and some hoses will eat up 5K in a hurry.
However, even with an aftermarket injection system, I'm guessing that you will still need an idle stabilizer, functional throttle switch, a hall sensor, a couple of knock sensors, a fuel pressure regulator and at least one pressure damper.to keep the waves in the fuel rails under control..

Speedtoys

You likely have a fairly simple problem...just tell us what you did/didn't do.

The computers are likely just fine, or it wouldn't even run.

928FIXER

"""I think the best approach is to ditch the stock EZK/LH ECUs and use a Microsquirt with speed density tune. That way at least I can troubleshoot just like a modern world car! ......................................



Back in the 1980's,these were modern cars,well engineered and state of the art in many areas. When they did need trouble shooting when they ran pooly, we got out the O'scope, fuel pressure guage and Ohm meter, tools that I still have to use to this day to properly troubleshoot vehicles with performance problems.

GregBBRD

I don't know squat about Microsquirt or Megasquirt, but I did take the time to visit the website and do some reading.
From what I can ascertain, Microsquirt is batch fired (as is the stock Bosch system.) It appears that one needs to buy a Magasquirt 3, before getting sequential injection.
One of the big issues with the stock Bosch system is that it is batch fired. This requires some large pressure dampers, carefully made for the fuel pressure of the system, to control the pressure waves in the rails, as all 8 injectors open and close at the same time.

If Microsquirt is still batch fired, how does it not still need the same pressure waves controlled?

FredR

Leaded gasoline was not phased out in the GCC countries until 1993 hence the no cat models were imported here.
I am not aware of any differences in rear bumper config between US and Euro models for S4/GTS variants. Maybe I have missed a trick ?

GregBBRD

Doesn't that mean that the car has that handy potentiometer to adjust the fuel mixture, close to the computers?

FredR

It certainly does - both my current and previous 928 have/had that feature albeit it is somewhat redundant in my case given I use ST2.

kamaro

Update :
I have noticed that the engine would run much better with the intake vacuum port open, but still running rich, that may indicate that it doesnt have much air passing through the idle valve. I know that if there is a sever vacuum leak the engine should run lean, but running rich with a major vacuum leak makes me think my problem lays somewhere in the idle valve area. things that I have done so far :

1- tested the NTC II sensor, OK.
2- tested fuel pressure with vacuum and without : OK.
3- smoke tested the intake : OK.
4- checked ignition sparks on all 8 plugs : OK.
5- checked the throttle switch as per WSM : OK.

Now I have two components that I need to bench test and would like to get any help from you guys : the idle valve and the MAF.

Thanks!