Thread: 92 Cossie 4x4 Running Rich - MOT Fail
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Old Dec 16, 2008 | 06:23 PM
  #26  
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mercmark
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Joined: Sep 2008
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From: Yorkshire, UK
Unhappy
Hi guys, Just a follow up on my post, I know it’s been a few weeks, but the car actually drove me to distraction, so I parked it up and left it, especially as I had other things to do.

Anyway, I found a bit of motivation and decided to carry on with it this week, and this is where I'm up to. The car is a 1992 bog standard Saff Cossie 4x4, green cam cover N5 Cat by the way, and so far here’s what I’ve replaced:

ECT Sensor
ACT Sensor
TPS (set to 0.0v at rest)
Idle Valve (second hand but works fine)
Lambda Sensor
Phase sensor (gapped correctly)
Distributor cap
Rotor Arm
Spark Plugs (Genuine Ford and gaped to 0.9mm)
CPS (gapped correctly at 0.6mm)
Fuel pressure regulator
MAP sensor (2 Bar as car is bog standard)

...in short just about everything!

Took the car down to the MOT station this afternoon, so I could use their gas analyser (car nice and hot after a good caining) and this is the results I’m getting:

If the CO (circa 0.30-0.50) is ok at idle, then on fast idle, it fails the Lambda test, giving a reading of 1.080 – 1.100, sometimes more, so then if you use the CO pot on the ECU to richen the mixture, to get a Lambda reading of around 1.000, and a CO content of about 0.1 – 0.2 – all is fine then it passes the fast idle test, however when you let the revs drop for the natural idle test, the CO doesn’t drop far enough, stopping around 1.28% (should be 0.50 or less)
......so, adjust the throttle pot at idle so the CO falls to 0.4-0.5 ish, and that’s fine, but then it’s too weak on the fast idle test, failing the Lamda test.

I tried for well over an hour to find a happy medium between the two using both the CO pot, and idle air screw, but over stayed my welcome a little, and to be honest I would have been there all night!

I have to say when the CO content is right at idle it seems to run decidedly lumpy at the top end, probably because of the weak mixture which was almost as low as 0.00 at 3000rpm, which can never be good on a Turbo’d engine. It actually runs better with CO, and hence Lambda set correctly for the fast idle.

One thing I did notice when the CO was high at idle, the HC content went up too, indicating unburnt fuel....could this be down to incorrectly gapped plugs....the Ford ones that are in there are at 0.9mm. I also tried it with the Idle valve both connected and disconnected, but that made very little diference.

It’s a bit frustrating really, as I’ve gone from having a car that’s running too rich, to one that’s running way two weak.

I’m sure now, it’s nearly there, but there's something just not quite right. To make matters worse, while I was messing around at the garage and just to further lay the boot in, the ABS light came on, so that’s something else to sort now!

Please help Stu, Tabetha, anybody!

Mark.
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