volvo 940 missfire

[Laird Scooby]

Originally Posted by PCH

You can open the throttle slightly and spray some carb cleaner into the vacuum line going to the intake manifold. If the revs pick up and engine smooths out then you have fuel delivery issue. How is the intake vacuum at idle?

Not necessarily because you've created an air leak by pulling the vacuum hose off - this may also increase the fuel rail pressure as well and then you're correcting it by spraying additional fuel (carb cleaner) into a lean running engine. Sadly not a conclusive test for this reason.

[Breadcom]

Hello,it was the crank position sensor and disk thing I'm not sure what's it called tone ring or flex plate or trigger wheel but idk where I can buy this from ? LH2-4-flex-plate.jpg

Thanks for all the help

[360beast]

Originally Posted by Breadcom

Hello,it was the crank position sensor and disk thing I'm not sure what's it called tone ring or flex plate or trigger wheel but idk where I can buy this from ? Attachment 138751

Thanks for all the help

What is wrong with the flexplate?

I believe TomSaintJames has a spare one as I gave him one and then a bottom end I sold him had one on too.

[TonyS9]

You need to think less about what has been replaced or what to replace, and more about what tests and checks have been done.

There is not usually a 1-1 symtom to cause relationship.

Are all the plugs firing? (easily done with plugs lights)
Are they firing at the right time? (timing light and check plug lead wiring)
Is the fuel pressure correct? (measure it)
Do you have any air leaks? (smoke test or inspection)
Are the injectors all working equally? (disconnect one at a time)
Do you have good compression on all cyl? (measure it)

If your mechanic is doing this, you maybe need to try another mechanic. There is nothing unusual about the 940 engine.

[Laird Scooby]

Originally Posted by Breadcom

Hello,it was the crank position sensor and disk thing I'm not sure what's it called tone ring or flex plate or trigger wheel but idk where I can buy this from ? Attachment 138751

Thanks for all the help

I'd fit a new crank position sensor (fairly cheap on ebay or your local parts factor) as it is incredibly rare the flex plate has problems. It's also a gearbox or engine and gearbox out job to replace the flex plate so worth thinking long and hard about going down that course of action.

[Breadcom]

A new cps was put in and it run amazingly better than ever but then 1h later wouldn't run at all so check it and the ring thing was broken and we found lose bolts in the gearbox which we guessing caused it to be damaged,we have gone over the transmission and can't find any other reason it would brake so almost certainly was lose bolts inside.

[Laird Scooby]

Originally Posted by Breadcom

A new cps was put in and it run amazingly better than ever but then 1h later wouldn't run at all so check it and the ring thing was broken and we found lose bolts in the gearbox which we guessing caused it to be damaged,we have gone over the transmission and can't find any other reason it would brake so almost certainly was lose bolts inside.

I'm guessing by gearbox you actually mean the bellhousing? Round the flywheel and clutch or in your case being auto, flexplate and torque converter?

In that case, i'd make a guess the only place you could get loose bolts from would be those that secure the flexplate to the crank shaft. Engine and or engine & gearbox out job, fit new patch bolts to the flexplate/crankshaft but make sure it's in the right place first - i can't remember exactly but it's something along the lines of the gap in the teeth round the edge for the CPS shoul line up with the starter hole at TDC. Someone else can confirm or correct that i'm sure!

When i say patch bolts, they are bolts with a threadlock compound on, usually blue, red or yellow and this isn't activated until the bolts are tightened and are normally single use only as a result. Old bolts if in good condition can be cleaned up and something like Loctite 243 can be used as a threadlocking compound. Failure to use the right bolts or to use threadlock can cause the bolts to come loose resulting in the problem you've got.

[360beast]

Yep the two missing holes will be in the middle of the starter motor hole when the engine is set to TDC which you can easily do by lining up the timing mark on the crank pulley with the 0 on the bottom cam cover.

[Breadcom]

Thanks for all the help I've learned so much but it's currently at a garage as it stopped working just before an mot.they have diagnosed the problem and want me to sauce a part as they can't get one new or old

sorry if I'm bad at explaining, thanks

[Laird Scooby]

Originally Posted by Breadcom

Thanks for all the help I've learned so much but it's currently at a garage as it stopped working just before an mot.they have diagnosed the problem and want me to sauce a part as they can't get one new or old

sorry if I'm bad at explaining, thanks

That's all very well, we can almost certainly source parts and link to them for you to get but what parts exactly do you need? You've already had a CPS and the 4 loose bolts in the bellhousing suggest they've come from the end of the crankshaft where the flexplate bolts on so i'd guess you'd need the 6 bolts for the flexplate as mentioned before.

No disrespect to you but if you're not technically minded you'll struggle to understand the terminology the garage is using and also to remember exactly what they've said. Do you know someone who has a bit more technical knowledge on cars that can go with you and ask questions and find out exactly what part the garage wants you to get?

https://www.volvopartswebstore.com/p...1/6842012.html

https://www.volvopartswebstore.com/p...88/946379.html

Flexplate and screws (might be 8 screws and not 6, Luke can confirm), not sure on availability but at least you have part numbers now. Prices will be different as last time i checked Cornwall was here in the UK and not in the USA and that's a USA website. Chances are those bits will have to come from gcp.se which is Genuine Classic Parts in Sweden via your Volvo dealer so aren't going to be cheap to buy new!