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> Trouble Getting Diagnostics To Work.
steve.hall30
post Nov 20 2012, 11:54 AM
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Drives: 440



I've been having a host of problems, but trying to use the diagnostics port isn't helping like it should. This is what I do.
Turn key to off
Put the wire into socket #2
Turn key to on
Press the button (tried all sorts of press durations)
The LED lights up while the button is depressed, but then nothing at all happends, doesn't flash codes, doesn't flash 1-1-1. Absolutly nothing.
Checked the connection to the correct pin on the ECU - fine
Tried a spare ECU - no change.

I'm getting this sudden power-no power jumpyness to the drive, it doesn't stall, but it seems to have two modes.
1) Working normally
2) Under no load, short delay between pressing the pedal and revs rising freely. Under load, press pedal and nothing happens.
The car will just jump back a forth between these two modes with very jerky power as it comes and goes. If you turn off the enginer and start again, it often stays in mode 1 for 30seconds to 2 minutes, but then it'll jump backwards and forwards with a frequency between 0.5 seconds and 10 seconds.

If anyone has any bright ideas why the diagnostic port isn't working, or the engine fault I'd love to hear.
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steve.hall30
post Nov 21 2012, 09:09 AM
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Just a follow up, I've fixed the problem with the jumpy, jerky acceleration.

Bit odd wording at the start as I'm relying to someone else somewhere else:

But for info:


Thanks for the reply. It's hard to explain well how the engine behaves under throttle, but I was able to exclude anything from the throttle, throttle sensor and idle bypass valve from the behaviour.
MAF could have been it, but the switching between high and low power was very fast, so I excluded anything to do with fueling, had to be down to the spark.
The engine never missfired, only high and low power. This got me thinking about ignition timing, because it was just about the only thing that fitted. Bit more thinking and a faulty knock sensor would explain the sudden switching between high and low power as it jumps the ignition advance back and forth.
As a test, I unplugged the knock sensor from the front of the engine, it was a little rough when cold, and when warm it ran smoothly, with perhaps 80-90% power I am used to. Important thing was the power delivery was smooth, no jumping back and forth. So looks like I've found it, new knock sensor will be ordered in due course and I'm looking forward to reliable motoring again :-).

As for diagnostics, I wasn't using a code reader, just the technique where you plug in the wire from the socket and press the button. Still not joy here, but less of an issue now the need is gone.
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grendel1960
post Nov 21 2012, 11:24 AM
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Drives: 92 volvo 440, 91 volvo 940



the diagnostic boxes on the 440's can be a bit tricky to get working, you have to press for just the right amount of time (its been a while but I did have 3 440's)too short or too long and it doesnt work.
one thing I came across was with the maf/ altitude sensor (little box up just in the gutter behind the firewall) was that I tested 3 with no improvement before I found at the fuel injection end of the hose is a restrictor in the pipe(brass plug with small hole through) this had blocked causing the unit to think the car was at altitude thus running the mixture rich to compensate, so worth noting if you get a similar problem.
Grendel
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steve.hall30
post Nov 21 2012, 12:13 PM
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Thanks Grendel,
I'm more a of Toyota man normally, so it's nice to know the querks of Volvos for next time.
I've tried quite a lot of timings on the button, but I may have one more crack at it.
If you mess it up, can you try again or do you need to turn the key off then on again?
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grendel1960
post Nov 21 2012, 12:34 PM
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this was the best site I found for retrieving the codes - http://www.am.torun.pl/~ja/volvo/diagnostic-system.shtml
I dont know if you have to switch off and on again, but it makes sense to do so.
Grendel
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