My 1990 2.0l Sierra failed its MOT on high emissions (among other things) today. I can sort the other fails but how do I diagnose or treat a high emission problem? It's the DOHC injection engine. All I can think of is taking it for a thrash with injector cleaner in the tank.
TIA
Antony
Yep and make sure the car is fully warmed up when testing.
Other things to check are the coolant temp sensor, (should have a very low resistance when hot and 2000ohms or so when cold. I'm generalising here as I'm not sure of the Sierra specifics.
You could also try cleaning out throttle body/Air Mass Meter with carb cleaner, and check any crankcase vent pipes for blockage.
You can adjust the emissions,on the brivers side wing near the bulkhead theres whats called a map sensor,thers a tiny screw hole for adjusting the emissions. HTH Simon.
Can I adjust this without having some kind of sensor to check the emission? Which way do I turn for weaker and which for richer?
Antony
Rearly need to put it on a machine,regarding which way to turn the screw,i arn't 100%sure but either way i know you have to wind it alot to make a differance,if you put it on a machine and give it 2 or 3 complete turns either way you will know which way it's going. HTH Simon.
ain't got any sort of air flow meters on them mate, but to clean the throttle body you need to remove it and get at it from both sides, remembering to clean the throttle butterfly as well as the insides of the housing this means a new gasket and possibly a reset on the position of the throttle position sensor
as sierra says, there is a screw on the MAP sensor but this only provides a minimal amount of adjustment
how high were the emissions anyway? out by loads or just a little? if it's loads then it may mean a sensor out, but if it's just a little then it could just do with a thrashing make sure the idle speed is at the correct position as well, too high and it screws them up as well
"nooneyouveeverheardof" wrote: how high were the emissions anyway?
I called the guy at the garage that MOT'd it and he said its emissions were measured at 7 (he didn't say what units). He said they should not be over 3.5.
That sounds like loads, eh?
Antony
I'd guess he's talking about the C0 percentage. But I'd say it would be nearer 1.5% if everything is correct. First thing to check is the airfilter, and engine temperature and or the ECU engine temperature sensor. In old fashioned terms, it's running rich.
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