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How to diagnose a misfire....

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Old Aug 28th, 2018, 15:17   #1
Joe H
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Angry How to diagnose a misfire....

So I need some education again.....
Our V70 1999 2.4 non-turbo started a major misfire. One moment fine, the next hiccuping shaking and very rough running at all revs.
The AA decided it needed all 5 coil packs replaced but could only get a single one from the local motor factors so swapped that into each plug in turn without it making much difference.

Back home I put it on VIDA which shows ECM3503 and ECM3502 misfire on Cyl 1 and 2. The misfire count is the same on both if that means anything. It is the same with hot or cold engine
So far I have dug out tools I haven't used since the days of carburettors and:
-Done a compression test (consistent across all cylinders)
-Swapped injectors around. The misfire stayed with 1 and 2.
-Checked spark with a tester that shows the spark jumping a large gap on all cylinders.
-Swapped plugs and also later put in an old set. No difference.
-Swapped coil packs. Engine seemed to get a lot more rough with some swaps but VIDA still reported just 1 and 2
-Removed the wiring harness covering under the cam cover. All looks healthy
-Checked coil pack earths on cam cover, all looks OK.

So......what do I do next??? I'm not forgetting that the AA guy wanted to replace all coil packs but as they are all giving a healthy spark that doesn't seem right. Or can they be breaking down in some other way?
Joe
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Old Aug 28th, 2018, 17:36   #2
volvo again
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Camshaft position sensor??
Had a similar problem on my old 2.0L 10 valve...
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Old Aug 28th, 2018, 22:02   #3
SteveSarre
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Hi Joe H,

Are "ECM-3503" AND "ECM-3502" the only active codes (in VIDA)?

Are you sure it came all of a sudden? No poor fuel consumption, lack of power, hard starting etc?

What make of plugs (current and the spare set) did you test with? Use Volvo. The turbo plugs are different from non turbo.

It seems almost impossible that all coils have failed at the same time. And if they had, surely you wouldn't just get codes on cylinders 1 and 2. (And the car probably wouldn't run at all).

Check that the wiring harnesses to the coils are good, and that the coils are bolted down (I think that is also a ground connection).

Can you clear the codes? If you can, and swap coil 1 and 2 to say 4 and 5, then if those 2 coils are the problem, then when you run you should get new codes which correspond to the two new positions.

Is there any small air hose near cylinders 1 and 2 which has perished or fallen off? I don't know about your particular car, but some of those 98/99 normally aspirated models had a small black rubber elbow underneath the cambelt end of the intake manifold, which perishes and allows excess air in. If you look carefully you might see it.

Also see this old post
https://www.volvoforums.org.uk/showthread.php?t=236453

Steve
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Last edited by SteveSarre; Aug 28th, 2018 at 22:05.
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Old Aug 28th, 2018, 22:04   #4
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Also, see if the misfiring stops if you unplug the MAF .
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Old Aug 29th, 2018, 09:59   #5
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Quote:
Originally Posted by volvo again View Post
Camshaft position sensor??
Had a similar problem on my old 2.0L 10 valve...
Did not think of that one - did it throw errors for just a couple of the cylinders?
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Old Aug 29th, 2018, 10:17   #6
Joe H
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Thanks Steve - answers are:

Quote:
Originally Posted by SteveSarre View Post
Hi Joe H,
Are "ECM-3503" AND "ECM-3502" the only active codes (in VIDA)?
Well...initially they were but then I got one for the interior ultrasonic sensors faulty which was strange. I thought maybe the battery was getting a bit low by then so put it on charge.

Quote:
Originally Posted by SteveSarre View Post
Hi Joe H,
Are you sure it came all of a sudden? No poor fuel consumption, lack of power, hard starting etc? Steve
No advance warning at all. It was running / starting perfectly normally

Quote:
Originally Posted by SteveSarre View Post
Hi Joe H,
What make of plugs (current and the spare set) did you test with? Use Volvo. The turbo plugs are different from non turbo.
The original ones and the older set are Volvo ones and correct for the non turbo

Quote:
Originally Posted by SteveSarre View Post
Check that the wiring harnesses to the coils are good, and that the coils are bolted down (I think that is also a ground connection).
Yes, I stripped the covering back and the wires look fine. I got excited when I found a spliced connection part way along the head for coils 1 and 2 but it is original to the harness and looks fine. Ditto the earth - there is one just for those coils.

Quote:
Originally Posted by SteveSarre View Post
Can you clear the codes? If you can, and swap coil 1 and 2 to say 4 and 5, then if those 2 coils are the problem, then when you run you should get new codes which correspond to the two new positions.
Yes, I can clear them and swap plug / coil around but the codes stay the same.
With coil packs moved to the other end of the engine it did not want to start - coughing and wheezing first but then ran with a similar misfire.
The warning light does not come on the dash btw, although it sometimes flashes.

Quote:
Originally Posted by SteveSarre View Post
Is there any small air hose near cylinders 1 and 2 which has perished or fallen off? I don't know about your particular car, but some of those 98/99 normally aspirated models had a small black rubber elbow underneath the cambelt end of the intake manifold, which perishes and allows excess air in. If you look carefully you might see it.
Good spot - that perished a few years ago and the new one seems fine

Quote:
Originally Posted by SteveSarre View Post
Honestly, that is the kind of thing I was expecting to find here. Wonder what he did to the wiring. Mine looks fine but....

Last edited by Joe H; Aug 29th, 2018 at 10:22.
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Old Aug 29th, 2018, 10:18   #7
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Quote:
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Also, see if the misfiring stops if you unplug the MAF .
Hmm. Also did not think of that - will try it.
Joe
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Old Aug 29th, 2018, 11:25   #8
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Do you have an EGR on your engine?
Ensure it is clean and operating properly

EGRs putting wrong amounts of exhaust gasses in the engine can upset the air/fuel mixture to a point that a misfire can result

I've seen a very interesting video of exactly this on a Ford (I think) which resulted in intake manifold removal, then cleaning of all the EGR lines (some were totally clogged) to resolve the issue

Once the EGR lines were clear and clean, the engine ran perfect with no misfires.

Yes, I know the Volvo has a different EGR setup, but it's something worth checking.
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Old Aug 29th, 2018, 11:36   #9
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The engine coolant temperature sensor can also cause problems with fuel mixture if it is failing.
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Old Aug 29th, 2018, 12:35   #10
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See this nightmare thread
https://www.volvoforums.org.uk/showthread.php?t=61077

with a possible solution from Chris Rogers
https://www.volvoforums.org.uk/showthread.php?t=62631
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