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Question on timing post 98 cars

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

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amblerman
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Question on timing post 98 cars

Post by amblerman » Wed Jun 05, 2019 1:10 pm

I have been reading a few posts recently about the timing being off by a tooth or so. It made me reason I don't fully understand how our 99 and later cars are timed.

In some brands of cars with distributors, you could adjust the timing with a timing light and rotate the distributor until you had the timing marks properly lined up by the timing light strobe.

But on the 99+ cars, there is no distributor. So we line up the timing marks on the crank and cams. However there is some variability between what our eyes see when lining up the mark on the cam with the notch in the loosely fitting cover. I imagine that even when we get it right and the teeth on the belt also line up it could be off by a bit. A degree here or there.

In cars where you could adjust timing with distributor rotation, you could make up for the "off by a tiny bit" by adjustment.

How do you do this in 99+ cars and is it ever needed? How do we even check that if we're off by a bit ? Do timing lights still have a use?

-A



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Re: Question on timing post 98 cars

Post by abscate » Wed Jun 05, 2019 3:04 pm

They don't

The timing belt only controls the valve timing - true on all cars, both -1998 and 1999 on

We don't rotate distributors anymore on either car because timing is fired by the ECU based on cam or crank position sensors.

For -1998, the ECU fires the single coil and the distributor sends it to the right cylinder

on 1999- on the ECU just fires the right coil


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amblerman
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Re: Question on timing post 98 cars

Post by amblerman » Wed Jun 05, 2019 4:08 pm

Ah . thanks. I wasn't thinking about the position sensors. Thanks. That clear things up.
Does that mean the ECM makes the system self adjusting in the case of minor variance? Is that the right way of thinking about it?



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Re: Question on timing post 98 cars

Post by jimmy57 » Wed Jun 05, 2019 5:31 pm

The ignition timing will not need any compensation. The sensor reads the perforated surface of flywheel. The divider between the holes are 6 degree spaced with a missing divider to note 90 deg BTDC #1. The flywheel fits only in one postion and with a dowel. The flywheel manufacturing and crankshaft grinding is referenced to the crank throws. The cam sensor determines which crank rotation so the correct cylinder is fired. When points or inductive pickup were in a distributor with vacuum advance and centrifugal advance, all those parts introduced lots of places for errors so the timing had to be adjusted as part of service to make up for slop.



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