Why is my fuel mixture getting weaker?

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Thu 7 Feb 2002 19:11
Why is my fuel mixture getting weaker? - Danny
I have a 1991 pre-cat Toyota Carina 2.0 GLi Exec Auto with the 3SFE (Fuel injection) engine and 103,000 miles. I have had various intermittent cold starting and cold running problems which the family owned garage I normally use couldn't get to the bottom of and so I took it to my local main dealer for a diagnostic.

The code that came up was"28" which is an irrelevant code -- it shows there is a fault but it doesn't tell you what or where. The dealer did notice the CO% was very weak and adjusted the fuel mixture to the correct setting, thus correcting the CO% and curing the problem, albeit temporarily. For about 5 weeks, no problems but they came back with no obvious triggers.

I had it MOT'd today at my regular garage (it passed) and I asked the proprietor to look at my CO% reading to see if it had slipped from the correct setting -- it had, and is once more showing very weak.

These are my questions -- what is causing the fuel mixture to weaken of its own accord? Is it compensating for a problem elsewhere? Is there anything in the electronics that is giving the wrong information out to the engine management system? Has anybody out there seen this problem before?

Looks like I'll be going back to my main dealer again for more diagnostics -- specialist Toyota ones, my normal garage doesn't have the necessary programs. But it would be good to know roughly where to look. In all other respects the car is spendidly reliable, and I'd rather fix the old warhorse than p/x it for something newer and smarter.

Thanks for your feedback

Danny (Medway, Kent)
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Thu 7 Feb 2002 20:50
Re: Why is my fuel mixture getting weaker? - Adam Going (Tune-Up Ltd)
Danny,

Two immediate thoughts. First, an increasing/developing induction air leak. Second, a faulty coolant temperature sensor - worth replacing as a first move being easy/cheapest option.

If you need some professional help you could call my colleague Stuart Braund on 01634 377804.

HTH, Adam
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Tue 19 Feb 2002 04:28
Re: Why is my fuel mixture getting weaker? - ROBIN
On the same tack,might it be his thermostat allowing the engine to overcool itself?
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