Rich S2

[Alexw]

Hi All,

I finally found the time to get my S2 on a dyno and its confirmed what I've thought for a while - its running very rich. I'm not sure whats causing it though, I've checked the vacuum lines on the FPR and there no fuel there. I'm not exactly sure what i can do next apart from replacing the damper/FPR. Or possibly take it to Wayne at Chipwizards, but if its a mechanical problem I cna't imagine that would really solve the problem.

Has anyone any ideas as to what could be causing the engine to run so rich?

 

[JamesO]

Was the Dyno run done at full throttle? Not sure about the S2 but the other cars have a set map for full thottle, which I would have thought at least eliminates the Airflow meter.

 

[Alexw]

Yes, it was a power run. I'd be damn impressed if it wasn't at full throttle yet was making 200ftlbs of torque []

It also has an after market MAF on, but I had Hartech check that out a while ago and they found putting the AFM back on made it even worse!

I am looking into ways of testing it is working properly, from what I've seen on the frwilk site it should be getting a steady 5v and outputting between 0 and 5v from idle to full throttle?

 

[PSH]

I wouldn't take it to Wayne until you sought the problem out, but I'd certainly give him a call to see what he suggests you should look for. It would be worth fitting a fuel pressure gauge to see how much fuel is being pumped out. The AFR graph is certainly a mess , not seen an S2 with that much fuel before so be careful or bore wash. Check all of the obvious parts, vac lines,FBR,damper, AFM etc. Also has anyone been playing with the FQS, I don't know how long you've had your car but if new to you I'd certainly check that. When were the plugs last changed? may be worth changing those anyway or at least cleaning them to give them the best chance of burning that fuel.

If I've forgotten anything I'm sure someone else will point it out, I'm more familiar with the Turbo than the S2 so certainly not an expert on the model..


Pete

 

[JamesO]

Has it allways been rich? Has somebody played with the fuel quality switch (assuming the s2 has one)? FPR's do seem to be failing a lot lately.

Is the car running different chips?


Beaten to it.

 

[Alexw]

I checked the FQS and its fine and appears to have the standard chip - it has always been rich, its why it needed an engine rebuild a few years ago - fuel washed the bores clean. I might just bite the bullet and change the FPR and or damper. The easiest way I have of telling if its rich without another trip to the dyno is when the engine has just been started from cold, it misfires at 3k rpm for the first minute or so, which is a rich dip on the graph.

I've changed pretty much the whole ignition system last year, plugs, leads, dizzy and cap, trying to make sure it burns as much as possible as you say.

I am tempted to set the FQS to -3% fuel as a "band-aid" style fix for now, maybe after I've replaced the mechanical bits.

 

[bmnelsc]

Porsche wsm talks about testing the AFM and Lambda sensor. Error code 1123 when mixture too rich or too lean. Possible causes for too rich condition are listed as:
- no partial vacuum on the pressure regulator
- injection valve does not close
- return to the fuel tank clogged

Might be worth checking out....

 

[TTM]

You mean the engine was rebuilt because of bore wash and the exact same FPR, fuel damper, injectors and lambda sensor were used again?

Also check the signal from knock sensors. If knock is continually detected because of a faulty signal then the engine may run pig rich in any condition.

 

[Alexw]

Excellent stuff, thanks very much - how would I go about testing the knock sensors? Are they the same way as on a turbo?

TTM - Yes, I took the car to EMC as it was using stupid amounts of oil and they could see the rings were knackered. I sent the injectors away to be cleaned and tested either just before or after. It doesn't have a lamda sensor AFAIK.

 

[TTM]

Unplug them and check if it makes difference.

I would suggest adding a lambda sensor regardless. All post '85 cars are prewired for one.

Check the vacuum line to the fuel damper, if there's fuel in it the damper is dead.

 

[Eric_Oz_S2]

I might just bite the bullet and change the FPR and or damper. The easiest way I have of telling if its rich without another trip to the dyno is when the engine has just been started from cold, it misfires at 3k rpm for the first minute or so, which is a rich dip on the graph.

Did you find the problem? Are you sure it doesn't have a lambda sensor? To me it sounds like it is running a "lambda" map without the lambda feedback. The fuel will default to rich in this case. If there are no coding or variant plugs in the DME harness, then the DME will be running a lambda map. If there is no sensor for feedback with the lambda map it will run very rich. There needs to be a coding plug installed to run in open loop (non-lambda/no o2 sensor).

If the sensor is faulty it will run in limp (rich fuel) mode.

Check for the presence of a lambda in the exhaust, and if there is one, check the wiring back to the DME. If that doesn't fix it replace it.

 

[Alexw]

I haven't sorted this yet - the lambda connection at the back of the engine is blanked off and has a wire feeding back into itself - I'm pretty sure the ROW cars didn't have lambda sensors until much later than mine. I'll probably get one anyway and see if that can sort it.

Actualy, getting an o2 sensor for it still feels a bit like I'm treating the symptoms and not the cause - cars don't run this rich normally so there is something wrong somewhere, theres plenty of S2's on the road in the UK without o2 sensors that are fuelling themselves just fine...

 

[Alexw]

I'ver finally managed to get hold of a fuel pressure guage and its bang on 3.5 bar at first going down to 3.4bar after a few minutes, which is perfectly normal according to clarks. That leads me to think theres some sort of electrical problem? Does anyone know what can cause the engine to run so rich when the fuel pressure is fine??? I've had the injectors cleaned and "serviced" a few years ago so I dont think they should be sticky.

 

[Hilux]

If the ECU thinks the engine is cold it will enrich the fuel mixture. Whatever is being sensed in my view is telling the injectors to fire for longer.

I am not an expert on the 944 engine management system but must assume the engine temperature sender transmits this information so I`d check it or change it.

Alternatively the MAF is sending a wrong signal in that the ECU thinks its open more than it is but if its idling correctly I`d still look at the temp senders.

 

[Diver944]

The S2 engine temperature sensor is only a tenner from these people:

http://www.123spareparts.co.uk/cgi-bin/atm_shop.pl?dsco=10&language=en&ansicht=autoteile&suche=autoteile102747&zubdetails=ERSA-2899015&FZGNR=2988&pag_goto_page=0&pag_select_items_per_page=10&

Coolant will dribble out as you remove it but you won't lose much if you stick the new one in quickly