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Sometimes the fault is seriously hard to find

Fiesta 1.25 1996

Elderly fiesta, even more elderly owners. They complained that especially from cold it was hard to drive. It seemed a bit gutless but still driveable, however when I tried it from dead cold up a hill it was really in trouble, all the symptoms of a very weak mixture. Full throttle and it would barely move, light throttle and it would go gently.

Checked every sensor and every other bit practical including the MAF which showed excatly the readings that Autodata said it should have.

Much internet searching found someone with exactly the same symptoms, disconnecting the MAF gave all the power back, a secondhand MAF fixed the fault, probing the replacement MAF showed that it gave a higher voltage than autodata showed, which, it seems, gives a richer mixture.

Many hours spent, which a donor car could have saved. Still, happy customer.

Reply to
Mrcheerful
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How do you charge for that type of fault? Would you consider that the knowledge gained plus the likelihood of customer retention would be worth taking a loss on your time?

Chris

Reply to
Chris Whelan

In this case I only charged them for the parts, jobs like this are not really common, but I would usually make a nominal charge for labour and put the rest down to personal training expenses, these are elderly friends I have known for 25years and I am going to his 90th next week! Most garages would have turned a job like this away after not finding any fault codes and a quick look around. I like a challenge, and this was one! What I don't understand is why the Autodata info was wrong, they say 0.6v MAF output at idle and 1.5v at 3000. Which it had. The replacement also had 0.6v at idle, but 1.9v at 3000, usually I have found that a faulty MAF just does not alter voltage at all. It would be interesting to know what voltage the ecu assumes when the MAF is disconnected since it went well with it disconnected, I got it round to 95 mph before I had to slow for traffic lights, I am certain it would have got significantly over the 100 mark given a bit more road.

Reply to
Mrcheerful

MAF's are notoriously difficult to analyse with a DVM, and not that easy with a 'scope. Best is a genunine replacement. That said though, are you sure that the coolant temp sensor was giving good readings and that the ECU was seeing it ??

Tim.

Reply to
Tim..

the cts had perfect readings on a meter/temp basis and the gauge showed correctly, so presumably the ecu is seeing the right temp.

the car had always (at least ten years) gone flat at 4500, but had previously run well generally. the cold hesitation had developed this year. replacing the maf has certainly made it go properly and removed the high rpm hold back. I have encountered other fords that go flat a little over 4000, so presumably they have the same problem, but many drivers don't try that hard or notice.

Reply to
Mrcheerful

I had a faulty MAF on my Audi TDI. It still gave a changing output, but logging with VCDS showed it way below expected output. Unplugging it made little difference, a new one dramatically improved things. No codes stored.

Reply to
Chris Bartram

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