Hi All

I have been fiddling with my timing over the past week in my 1987 740 turbo (LH 2.2), and i have discovered a problem with my timing, at normal settings that is 12 degrees BTDC, the car seem to lack power but as i advance the timing to 17 Degrees the car runs great, it seems to be the sweet spot, is this the wrong timing or is the harmonic balancer out, and will it damage my motor, if i keep it at this setting. In the past month i have replaced the headgasket and all other acosiated seals and gasket, and clean everything TB and intake, All wiring was redone. So is it a timing problem or is it just covering up another.

Thanks
87 volvo740turbo 310000
85 volvo740GL 340000
90 volvo740GL 285000

The crank pulley outer ring with the timing marks may have shifted. Remove the number one plug and loosen the others. Turn the engine over by hand until the piston is at the top of it's compression stroke. Should be able to feel the compression by plugging the hole w/ your finger. You should then be able to see the piston by shining a flashlight into the plug hole. The crank pulley should be at the TDC mark. If not you'll need a new pulley.

Another method that I prefer is to put a screwdriver (or something else too big to fall into the cylinder) in the plug hole and observe it moving up and down as you rotate the crankshaft. This makes it easier to determine when you are exactly on TDC, which is important, as you are trying to confirm (or not) a discrepancy of only 5 degrees, so accuracy is essential.

Don't be too concerned about damaging your engine with incorrect timing. You have a knock sensor. If it is working correctly, it will prevent excessive advance, whatever the base setting. If it's not functional (unlikely) you will hear loud pinging, which should alert you to take your foot out of it IMMEDIATELY and figure out the cause. (This is true even if you have no other issues with the timing) In general, with a knock sensor, having the base timing overly retarded is more of a worry. This can overheat the exhaust valves, manifold, turbo etc.

Does the knock sensor need to be bypassed somehow to set timing.
Im told that the 89 740GL B230F ignition timing is run by the ECU
and turning the distributor cap won't advance ignition timing.
Whats going on with turning the cap then? Is it changing only dwell?

Is there no way to tweak the advance for our beloved E10 fuel?
(Advance to just before knock under load)

Thanks, Bill

Dwell is the duration of the points being open. It's a term you don't hear much anymore, as it only applies to points. Electronic ignition is triggered by an instantaneous signal from either a Hall effect, optical, or other sensor in the distributor, or a crankshaft position sensor.

On the 89 and later B230F , base timing is fixed, nonadjustable. The knock sensor will allow more timing advance with higher octane fuels, so if your ethanol blend has a higher octane than regular gas, it will adjust automatically. However, these engines were designed to run on 87 octane, so higher grades offer little or no benefit. Turbos, on the other hand, will run noticeably stronger on premium.

Perhaps there's some slop and/or adjustment in the hall effect
or other sensors that could retard/advance the spark?

If you have a distributor with a Hall effect sensor (LH 2.2 = B230F, up to and including 88, B230FT, up to and including 89) the sensor is mounted solidly to the distributor base plate. This plate can be rotated relative to the head to adjust the timing. If you have LH 2.4, the distributor contains nothing but the rotor, and the timing signal comes from a crankshaft sensor mounted at the top of the bellhousing, that reads holes on the perimeter of the flywheel. This sensor is fixed in place and is not adjustable. Turning the distributor on these cars does not adjust anything, it only makes the spark jump from a different point on the tip of the rotor to the electrodes on the inside of the cap. That's why the electrode on the tip of the rotor is about 1/2" long---so that it will work properly, wherever the distributor is "adjusted"

Thanks Blue Horse,

I'm still puzzled.
The sensor controls the HV switching at the coil.
Then the HV pulse is at the rotor and then the rotor cap to the plugs.
It looks like you can't advance the spark,
but you might be able to retard the spark some with this setup.
Is that right?
How are you supposed to adjust the cap?