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Ecm 6805 and boost related issues

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Old May 14th, 2018, 14:01   #71
aland
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Fuel correction test found - interesting issue - I run VIDA in a Windows 7 VM on a MacBook - the video driver was default and was causing some graphics (like the VC2000 image) to not display properly, hence couldn't see it. Once fixed the image appeared.
Fuel correction test shows an imbalance similar to the values in this post https://www.volvoforums.org.uk/showthread.php?t=236336, with 1,2,3 around 7mm2, 4 at 0mm2 and 5 around 30mm2. I did the same test when the engine is working normally and the results are similar.
It's pretty unlikely cy4 is really perfect on all these engines and that cy5 is miles out also - and the fact that my results didn't change when there is no fault agrees with this.

Regarding the suspected VNT issue, with the engine off, a hand-pump moves the VNT actuator through the range. It reaches the end-stop around 18 in/Hg.
I hooked up a vacuum gauge into the turbo actuator pipe, run into the cabin.
This shows that initially when you boot it, there is around 22 in/Hg vacuum, tailing off to 0 as the revs increase. After a few seconds of 0 it goes into limp mode and the vacuum settles at 6 in/Hg. VIDA shows over-boost (flat-line) a few seconds before limp.
When all is well, it also goes to 0 but no limp (and less boost).
If I hold the release valve on the gauge open (so no vacuum to the actuator), performance is considerably reduced confirming that it needs vacuum to create boost, and that the ECU is correctly attempting to reduce the boost when it's over-boosting, then goes into limp.

So, this must mean that either:
- The engine off VNT test is meaningless, as there is no load on the turbo / VNT mechanism - really need to see if the actuator really moves to the zero position when the vacuum is reduced by the ECU when the turbo is spooled up. Might need a carefully mounted Go-Pro and light to find out!
- Or that the MAP reading is often OTT when cold(er) causing the ECU to believe there is waay more boost pressure than there really is.

As the MAP sensor is cheap and easy to swap, I might start there.

Last edited by aland; May 14th, 2018 at 14:04.
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Old May 15th, 2018, 23:27   #72
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what is the reading of the MAP sensor with the engine not running also show with the atmospheric pressure in vida, they should be very close if all is ok,
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Old May 16th, 2018, 14:09   #73
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Originally Posted by davebb View Post
what is the reading of the MAP sensor with the engine not running also show with the atmospheric pressure in vida, they should be very close if all is ok,
Dave
Good point. It was within 1 digit of the atmospheric reading when I checked that last week.

It's looking like the issue has to be VNT, when under load and anything but HOT.
As my graphs in previous posts show, there is an over-boost issue when it goes into limp, and not when it doesn't.
I can re-produce this at will after a few foot-on-floor > limp cycles. This will cause the turbo to get hotter each time.
I can't see how a fuel issue (eg restricted fuel filter, bad injector etc) can cause an over-boost issue, which goes away when hot. But a worn / sticking VNT when under load could.
The engine is smooth, with no smoke and excellent MPG.

I found this interesting article: https://www.picoauto.com/library/cas...essure-control
Which says: "have found that in each case the VNT mechanism was more prone to failing at cool engine temperatures. Once the turbo had been worked several times the fault occurrence became infrequent"

I've ordered the turbo gaskets from Volvo and will swap over to the spare turbo I have this weekend if dry, to see if it improves things.
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Old May 16th, 2018, 14:24   #74
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Yes I think it is the vnt,
The turbo you are fitting, Have you cleaned the vnt ?
Let us know how it is when done,
Thanks Dave
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Old May 16th, 2018, 14:34   #75
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Originally Posted by davebb View Post
The turbo you are fitting, Have you cleaned the vnt ?
Not yet, but I may as well before fitting, and it's done about 70k less miles than mine.
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Old May 19th, 2018, 23:36   #76
aland
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Smile My issue finally resolved

Today I swapped the turbo with my spare one.
Although the actuator moved the VNT through its range, with the actuator removed, and both turbos sitting next to each other, there was a noticeable difference.
The one from the car felt gritty to move the VNT, and if you rocked the lever side to side it got stuck.
The spare one was smooth, and doesn't stick.
The circlip holding the actuator rod is very fiddly, I'd say impossible to remove and re-fit this on the car to test it.

I removed the bolts holding the exhaust chamber VNT together, but it didn't want to come apart, and I didn't want to risk damaging it.
With the replacement turbo, no more limp mode, and the VNT vacuum sits around 10 in/Hg as you hold your foot on the floor, when before it dropped to zero - confirming that the reduced vacuum IS reducing boost as requested now, when before it was over-boosting and the vacuum was being reduced to zero by the ECU as it desperately tried to reduce the boost.

The official procedure to remove the turbo involves removing the RHS driveshaft, but I found by removing the heat shield over the steering rack (gained a few mm) and a bolt from the rear engine mount, by then jacking the engine a little opens enough gap to get the turbo down and out.
A second person to help is really needed with this job, especially when trying to re-fit the turbo, against gravity.

Based on my findings, I'd suggest that the VNT mechanism test with a vacuum pump is only useful to prove the actuator works, but if the VNT is worn / sticking, it won't show it.
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Old May 20th, 2018, 20:34   #77
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Hi that's great news , what max boost are you now making ?
Dave
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Old May 20th, 2018, 21:24   #78
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Hi that's great news , what max boost are you now making ?
Dave
Good question, I've not driven it yet with live data, so don't know yet. Will do that during the week.
It feels a little down on power to before, but if it was regularly over-boosting, that would be expected - because before it was fuelling to match the boost (until limp) = more power.
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Old Jun 15th, 2018, 08:32   #79
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I have been reading this thread with interest.

After another six or eight months without any limp mode issues I have had it twice in the last couple of days.

The only thing I have noticed with mine over the years is that I can tell that it will happen.

By that I mean starting the car for the morning commute and as I drive up our road I can hear a distinct change in engine noise.

Its not a whistle or knock but a kind of induction sound.

Then usually within a mile when I pull a few more revs to get up to speed I get the limp mode.

There is definitely a different sound under the bonnet so I say to myself, its going into limp today, and it does.

Strange thing is, why does the car run fine and then every six months or so it plays up for a few days/weeks then goes back to being reliable again for another long period of time?

Strange.
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Old Sep 14th, 2018, 16:31   #80
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Well the car ran fine since my last post, now has limped twice in the last two days again!

Stuck behind a fully loaded hgv struggling up a hill and just keeping up with it!

Anyway, had a independent mechanic I know run the codes with his snap-on tool and still the same 6805.

Live data showed everything else seemingly ok, pad vac switching fine etc.

Took the pipe from the EGR to inlet manifold off, a good layer of oily gunk stuck to the sides about 1mm thick so not as bad as some peoples photo's on here.

Had a good trickle of oil floating around in the pipe, so mechanic thinks my turbo is leaking oil internally, I guess on the inlet side.

The car does not seem to loose oil on the dipstick level between services, and it does not have any visible smoke.

Now checking out options on where to go next.
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