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940 LPT Idle Woes... Help!

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Old Jun 8th, 2018, 19:54   #21
TonyS9
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Like I say ECUs are very reliable and they tend to work perfectly or not atall.

The problem is an input or something strange with the throttle body. Possibly something being corrupted in the ECU by bad earth or voltage maybe. It shouldn't latch on if its just noise on the input.

It doesn't make entire sense to me, and feels a bit like a design issue, which happens in some cars and I have exaserbated it with my transplant.

I think I'll try creating the problem then probing around with an earth cable to see if it will reset.
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Old Jun 8th, 2018, 19:54   #22
Laird Scooby
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Quote:
Originally Posted by LPTJoe View Post
Thanks.

Will disconnecting the battery for an hour or so not clear the codes?
It would, yes, i was trying to save you having to reprogram the stereo and/or the alarm as well.
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Old Jun 8th, 2018, 23:37   #23
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It would, yes, i was trying to save you having to reprogram the stereo and/or the alarm as well.
Good advice. You were right, pulled fuse 1 for a few minutes and viola, no more code....

Tonight I've hosed the rad through thoroughly, flushed the system though with two fills and drains of fresh water, fitted the new temp sensor (FAE item, although I do have a Bosch one en route), and then a final fill with deionised water and run the engine up to temp with the new sensor fitted for 15 mins or so...

So far running smooth and no warning light...Also, whilst warming up I had a good spray round all hoses with a can of easy start too with no change in engine note or speed...

We'll see how we get on tomorrow after a couple of more deionised water flushes, new thermostat fitted and a fill with fresh antifreeze.

In the unlikely event the car runs well and doesn't produce warning lights then it's job jobbed, if not then unfortunately it looks like I'm going to have to borrow/buy/beg/steal/build my own diagnostics box *Finger crossed it doesn't come to that*
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Old Jun 9th, 2018, 10:59   #24
Delta66
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I got a loan of a reader, here is the thread which includes codes and its use.

https://www.volvoforums.org.uk/showthread.php?t=279776
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Old Jun 10th, 2018, 09:34   #25
LPTJoe
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Thanks to everyone who has helped/made suggestions etc.

Rather than duplicate everything I've recorded updates of my woes in my 'build' thread here...

https://www.volvoforums.org.uk/showt...09#post2412609
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Old Jun 10th, 2018, 22:26   #26
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In the last few days I've cleaned the ICV, flushed the coolant, fitted a new thermostat, temperature sensor and filled with fresh antifreeze. Today I focussed on the throttle body...


SAM_6791 by [url=https://www.flickr.com/photos/152293344@N05/]


As expected it was pretty filthy....


SAM_6797 by [url=https://www.flickr.com/photos/152293344@N05/]


After some scrubbing things looked much better...


SAM_6800 by [url=https://www.flickr.com/photos/152293344@N05/]


With throttle body out access to the oil separator box was much improved so thought I may as well whip that out too. Some clear evidence that this had been leaking around the base point where the box meets the block...


SAM_6807 by [url=https://www.flickr.com/photos/152293344@N05/]


I've been slowly pillaging parts from a local breaker car and one of the bits I'd knabbed was a spare separator box. Despite the fact that this came from a 1990 NA model the part number was a match to mine and the box looked far less oily than the one that came from my car. I plugged the holes, filled it with brake cleaner and then blasted it through to ensure cleanliness...


SAM_6813 by [url=https://www.flickr.com/photos/152293344@N05/]


The network of pipes that come from the breather box were also removed and cleaned...


SAM_6815 by [url=https://www.flickr.com/photos/152293344@N05/]


No flametrap to clean on this car as it's a turbo model, I did however find the hose that comes from the intake manifold nipple and joins the Y shaped section of the breather pipe was split. I trimmed it and re- fitted it but the hose does seem quite hard with age so I shall look to replace it...


SAM_6817 by Patrick Wright, on Flickr


At this stage I sprayed the TPS and IAC connectors with contact cleaner and re-connected then reassembled everything. I struck me that I should perhaps have had the battery disconnected during all of this? I'm not sure of the ECU's capacity to learn/adjust when changes have been made on these cars?

Either way I'll probably pull fuse 1 for a few minutes before re-starting.


Unfortunately I was called in to attend to Sunday dinner so at this point the car remains untested, we shall see tomorrow how and if the changes I've made have effected running.

Last edited by LPTJoe; Jun 10th, 2018 at 22:29.
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Old Jun 11th, 2018, 12:46   #27
LPTJoe
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This morning I pulled fuse #1 for a few minutes to reset the ECU and then took the car out for a 20 mile jaunt, wow, the change is profound! No more surging at all, nil, zero. Also the idle seems almost locked into 900 rpm with very little fluctuation



I'm not going to utter the 'F' word yet, but the initial signs are very promising indeed. I think the ECU at present will be in a kind on 'learn' mode having been reset too, so hopefully over the next couple of tanks of fuel it will get used to the changes made and settle into behaving itself on a full time basis...



Next steps: Replace lots of the 22 year old hoses, the turbo engine reaches some high temperatures so this seems to be good preventative maintenance. Also, my radiator fan seems to run from the get go and appears to be driven directly from the AUX belt... I'm not sure if they're designed to always be running whenever the engine is on so will have to do some digging to gain clarity on that too.
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Old Jun 11th, 2018, 12:50   #28
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The O2 sensor should reset any trim values after warm up cycle, I don't think it remembers anything too long term. Open loop operation is pretty rich most of the time. Closed loop is used mainly at idle and very low load.

For the oil separator its worth putting a new oil seal (o-ring) in. The old one will be be hardened and not sealing well by now.

The viscous coupled fan will always 'run', but it doesn't push hard. In fact it rarely does except maybe after stilling at idle on a really hot day, then when you rev you can hear it sounds like a bus, but only for about 30s or so until the air flow cools it down.

Last edited by TonyS9; Jun 11th, 2018 at 12:54.
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Old Jun 11th, 2018, 13:50   #29
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Quote:
Originally Posted by LPTJoe View Post
I think the ECU at present will be in a kind on 'learn' mode having been reset too, so hopefully over the next couple of tanks of fuel it will get used to the changes made and settle into behaving itself on a full time basis..

Also, my radiator fan seems to run from the get go and appears to be driven directly from the AUX belt... I'm not sure if they're designed to always be running whenever the engine is on so will have to do some digging to gain clarity on that too.

Quote:
Originally Posted by TonyS9 View Post
The O2 sensor should reset any trim values after warm up cycle, I don't think it remembers anything too long term.

For the oil separator its worth putting a new oil seal (o-ring) in. The old one will be be hardened and not sealing well by now.

The viscous coupled fan will always 'run', but it doesn't push hard. In fact it rarely does except maybe after stilling at idle on a really hot day, then when you rev you can hear it sounds like a bus, but only for about 30s or so until the air flow cools it down.
The ECU will re-learn the ideal trim for idle/low-medium load from the factory map over the next few days. Like Tony says, the trim values aren't set in stone and will constantly readjust, based on your driving style, fuel used and so on.

Good call on the oil separator seal Tony!

As for the viscous fan, there are two schools of thought on this and i tend to subscribe to a different one to Tony. They make the engine take longer to warm up, sap a lot of power and also sound like Concorde taking off at full chat.
In my own experience of removing them from 3 vehicles in recent years, not only does that improve warm up time, economy and performance but means you don't need ear defenders while driving!

In the states, several people have done dyno shoot-outs comparing different kinds of fans, all with similar results to this video :

https://youtu.be/ZXdLgaFXZzs

Watch it and you may well be shocked! Then you'll likely reach for ebay and an aftermarket electric cooling fan!
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Old Jun 11th, 2018, 15:37   #30
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I'll just add my disclaimer to the video, they have not done a proper comparison and I think the results are completely invalid for a moving vehicle.

There maybe a small benefit in warm up depending on how often you are stopped. Noise, I can't tell the difference unless its a rare hot day when you will otherwise see the temperature rise.
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