Running Rich - Thoughts?

[edh]

I did an oil analysis last week that showed fuel in the oil (1.2%). This is after 2 trackdays & 500 miles approx on this oil. Bear in mind this car spends a lot of its time at WOT.

I'm trying to work out why. So far..

Checked plugs - all 4 are black, electrode ends white. So all 4 cylinders running rich, not a faulty injector (could be all 4 I guess)
Checked fuel pressure - 50psi pump on, engine off; 45psi engine idling. Slightly lower than Clarks garage specs, so it's not the FPR
Checked DME temp sensor and AFM temp sensor - both OK at sensor and at DME plug

What next? I haven't changed anything (apart from the headlights). Plugs probably haven't been changed for a year so this may have been creeping up, or may have just happened. Car seems to go well, no hesitation, plenty of power. DME has a Promax chip, otherwise everything pretty standard. I cleaned the K&N filter recently when I did the oil change.

 

[Monkeythree]

Throttle position switch? If it’s goosed, the DME won’t be giving you the right mapping for WOT.

 

[944Turbo]

Still running with original ariflow metering? If it is similar to the turbo, the spring tension can be increased, if the spring is weak then you are not getting as much air as the brain thinks you are, however more of a part throttle issue than a WOT one. It also should be noted clarkes garage or (fr wilk's) write up (cant remember which!) on the afm says not to play with the spring tension - I did quiet successfully on My car (when it had an AFM) and David's to cure rich running issues at part throttle openings. Much easier with an air/fuel gauge though, I had a narrow band gauge running off some thin leads tucked into the factory lambda sensor connector on my car. I guess if yours has one you could do the same, much cheaper and easier than a wideband, but obviously needs the tune to be close.
That has also made me wonder if the Lambda sensor goes bad will the car run rich? (That is assuming a 90 S2 had a cat / lambda sensor in the first place!). My 90 Turbo did.
Tony

 

[edh]

Throttle position switch? If it’s goosed, the DME won’t be giving you the right mapping for WOT.

I think the S2 TPS is just a switch, unlike the 951 TPS?

 

[Waylander]

My Lambda Sensor went southwest not so long ago, I have the ECL wired up in my car, and that certainly made the the light come on.

since replacing it the fuel economy seems to have improved, or it could just be that its a bit slippery out there so the loud pedal is not getting used so hard

 

[edh]

No lambda sensor on this car

 

[Waylander]

I am not sure about that with the TPS, Check this out

http://www.bosch-classic.com/en/internet/bosch_classic/produkte/motor_1/drosselklappensensor_1/drosselklappensensor___mit_teaser_1.html#

0 280 120 308 >82-89
0 280 120 400 >951

 

[944Turbo]

No lambda sensor on this car

removed or never had one? I think there is a link wire on turbos without one, could that be missing / broken?

 

[edh]

No lambda fitted I think
Clarks garage suggest n/a TPS is just a switch that signals idle and WOT but nothing in between

 

[blade7]

Back in my 2 stroke bike days you had to chop the ignition at speed to do a plug check, don't know if it's the same for a 4 stroke?

 

[blade7]

No lambda sensor on this car

removed or never had one? I think there is a link wire on turbos without one, could that be missing / broken?

I dare say most late turbos narrow band sensors fitted in the downpipe are goosed by now. Bypassing it is usual when chipping anyway. Disconnecting the TPS can show up issues with it, AFAIK the DME then runs a pre-installed look up.

 

[944Turbo]

I think there is a plug at the rear of the head (on a turbo, not sure about s2) that links 2 pins of the plug where the Lambda sensor would plug in if you had one, not sure what the effect of not having it is! There may have also been a connector down by the ECU, there are a couple of fly leads for fuel quality (or maybe that is how they were used in some aftermarket chips) approx 6" from the ecu. in the loom.
Tony

 

[edh]

Next steps i think are to test DME and AFM as per Clarks garage. DME switch for WOT might be activating too early. AFM might be giving too high voltages (Although I'm not sure how easy it is to test this)

I found a thread from last year where George mayson fixed a rich 2.5 by altering the spring tension on the AFM.

That sounds a bit of a bodge though. My AFM is 240k miles old so maybe in need of a refurb?

 

[924Srr27l]

Throttle position switch? If it’s goosed, the DME won’t be giving you the right mapping for WOT.

I think the S2 TPS is just a switch, unlike the 951 TPS?

Yes it's either Open or closed not potentiometer effect like the 952 version

What Oil are you on, thin Fully Synthetic ? The plugs could do with changing 4 sure..
You can get the AFM checked for calibration... I think it was these guys that did mine:

https://www.atpelectronic...ow-meter-throttle-body


R

 

[edh]

The TPS provides 2 signals. One for fully closed, one for fully open.

Yes ATP seems like the place to try for the AFM.

I'll do some more tests next week & then work out where to go next.

 

[Monkeythree]

The S2 TPS switches the DME to a different map at WOT. Unless it’s broken. Then it doesnt. Hence the reason I suggested it.

 

[Frenchy]

I have a good AFM if required.

 

[edh]

OK TPS tested as per Clark's Garage

1. Connect an ohmmeter between terminals 52 and 24 on the DME wiring harness plug. This will test the idle speed contact. With the throttle closed, the ohmmeter should read 0 - 10 ohms. With the throttle open, the ohmmeter should read infinite (8). The switch in resistance must occur as soon as the throttle starts to open (approximately 1°).
2. Connect the ohmmeter between terminals 53 and 24 on the DME wiring harness plug. This will test the wide open throttle (WOT) contact. With the throttle closed, the ohmmeter should read infinite (8). With the throttle approximately 2/3 open, the ohmmeter should read zero (0) ohms.

Unfortunately it checks out OK. i thought at first that it might be faulty as the WOT switch was closing well before WOT, then I read the above again... (for an 8V "The switch in resistance should occur just before the throttle reaches full open.")

So looks like the next step is to send the AFM to ATP for testing

 

[Diver944]

Have you ever done a fuel in oil test before? Maybe 1.2% is fairly standard from natural blow by? Dunno if it is, just thinking out loud

 

[edh]

No I haven't but I don't think it is standard (nor do Millers otherwise they wouldn't have remarked on it the way they did)
This oil is 500 miles old. Plugs are black.
I also tested my 996 - 4k miles over 18 months. No fuel traces. Just out of interest, that oil tested absolutely fine, no need to change it.