Diagnostic strategies - intermittent fault

I have a motor home based on Fiat Ducato. Chassis/engine is probably 2001; a crossover year with a new engine in an old chassis. Pre ODB II.

Over the years it has had an intermittent electrical fault which then became a hard fault twice so far.

The first time it was tracked down to the throttle control (once diagnostics could be read; that generation Fiats seem to be a bit cranky about this). Wiring connections cleaned up and all fine.

The second time it was tracked down to damage to the wiring loom behind the air filter.

Both are known irritation faults with Fiat Ducato; I think that they aren't a more widespread issue because most 2001/2002 Ducatos will have long gone to the great recycler in the sky. Only ones in motor homes or other low mileage applications will survive. One issue is that very few Fiat mechanics will have any experience of working on 15 year old Fiat vans.

To cut to the chase; at the moment the fault seems to appear (for a short time) every 200 miles or so after a stretch of bumpy road and then clear soon after (although in the outside lane doing 60 mph in heavy traffic "soon after" is still not a comfortable thing). Seems to go into "limp mode" and not respond correctly to the throttle pedal until it clears.

I have a converter from 3 pin Fiat to ODB II and a BlueTooth ODB II reader plus some PC software so I can (with a lot of luck - not tried it yet) monitor the engine until a fault occurs. However the fault will clear from the ECU warning light quickly, and presumably from the ECU soon after.

So (assuming my limited abilities can't trace the fault) what is the best strategy to diagnose and fix the fault?

Auto electrician to test all the wiring?

Commercial vehicle garage?

Small independent garage where the labour rate may well be a lot less?

Specialist diagnostician?

It isn't a good idea to use the motor home on long trips waiting for the fault to harden up.

[Learned this when the second fault appeared on Jura about 6-7 miles from the ferry. RAC lady asked where we were. "On Jura. Where abouts? About 6 miles from the ferry on the only road." This didn't seem specific enough. "What can you see around you? Rutting stags!" "O.K. we will get someone to you in the next couple of hours.". Yeah, right. I think it took over 4 days to get us relayed off the island. Couldn't put us on a low loader because we would have been too high; hitting trees and bridges. A heavy vehicle rescue truck came out from Glasgow eventually. But I digress.]

General advice on the most cost effective way to diagnose an intermittent fault most welcome.

Cheers

Dave R

Reply to
David
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Box of matches, insurance claim. ;-)

Sorry I can't be more constructive. Good luck with finding the fault. Hopefully Mr Cheerful can be more helpful.

Tim

Reply to
Tim+

Jiggling a fuel filter full of crap can make it run rough, when was it last changed?

Reply to
MrCheerful

In message , David writes

I know virtually nothing except that I have now bought several OBD II Bluetooth readers and many of them are rather limited. I must get back on to trying to identify sources of the ones that work well.

The other problem is the way all Windows versions handle the BT to USB to serial port communications. It's very easy to get lots of phantom serial ports. I've been using Device Cleanup and the Com Name Arbiter Tool to try to deal with this

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The other problem in my tour of shaking heads in garages with my Jeep, is that many garages don't trust anyone bringing in a vehicle with a diagnostic report that their SnapOn device can't see.

Reply to
Bill

Can't tell without looking it up, but AFAIK serviced as per schedule.

Good point, though, I am assuming an electrical fault due to history but it could also be a fuel flow fault.

Cheers

Dave R

Reply to
David

Find someone who has an expert knowledge of that vehicle - especially when old. An owner's club of some sort would be the best bet.

Reply to
Dave Plowman (News)

The notion that diagnostics can pinpoint every possible fault is fantasy. Especally ODB which is only really concerned with emissions.

Fault finding requires knowledge and skill - especially with obscure and or intermittent faults.

Sadly, the more people rely on diagnostics, the less skills they acquire.

Reply to
Dave Plowman (News)
[...]

I worked as an industrial electrical technician. I was forever being asked to 'just plug your laptop in and tell us what's wrong with this machine'. I always wanted to beat then over the head with the laptop!

Chris

Reply to
Chris Whelan

In message , "Dave Plowman (News)" writes

On the other hand, I had no idea that my vehicle had a swirl valve, but it gave me something to put into Google. Finding a garage that seemed to know about such things pointed me towards someone with some knowledge and skill.

The more tools, the better.

Reply to
Bill

Update - got a diagnostic lead to support my ODB II reader, and MultiECUscan software (free) to read codes.

The codes are associated with sensors - throttle and speed, clutch and brake.

The throttle sensor is the only one which causes the warning light to come on.

Cheers

Dave R

Reply to
David

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