Thread: Tuning witout Timing Marks - Petrol Engines

if you use a timing light with an advance dial you can work out what the distributor is doing from the zero TDC position.
The thing to check is total advance and ensure the advance curve is working smoothly. There should be specs for the distributor advance curve some where online . You can also check the vac advance and see if it is working as well with and advance timing light.

Ian
Bittern

Originally Posted by ian4002000

if you use a timing light with an advance dial you can work out what the distributor is doing from the zero TDC position.
The thing to check is total advance and ensure the advance curve is working smoothly. There should be specs for the distributor advance curve some where online . You can also check the vac advance and see if it is working as well with and advance timing light.

Ian
Bittern

Thanks - is a 4.6 so no distributor - normally timing would be controlled by the ECU but I have carbs with a crankshaft sensor that is triggering the Edis 8 - I will ad an ignition ECU shortly but it still needs to know where TDC is.

Hence my question whether modern tuning equipment can tell where TDC is without timing marks.

Cheers

Garry

Sacrifice an old spark plug, weld in an extension, turn motor over till extension touches piston and mark balancer, ditto in reverse direction. Half way between the 2 marks is tdc

Mightn’t be relevant but if motor fires and runs fine tuning timing can be done with a vacuum gauge

Cheers Paul

Originally Posted by 101RRS

For the mechanics with modern tune up equipment in their businesses.

The engine is a Rover 4.6 so does not have original fit timing pointer or marks. Using a technique related piston position up and down and an indicator through No1 sparkplug hole I determined where TDC should be on the crank pully and made a pointer to match that position. Should be OK but not 100% convinced.

I am using Edis 8 in default mode (fixed 10BTDC) to fire the ignition coils (wasted spark) but dont have an ignition ECU fitted up at the moment.

The engine fires up first go and runs OK but is a bit cantankerous when hot so advance may be a bit more than I expected.

So my question is the the experts with modern tune up equipment - can you determine TDC and actual ignition timing from the tuning machine rather than the timing marks via a timing light?

Thanks

Garry

What you did is how it is done and how I learnt along with everyone else decades ago. Trust yourself or do it a couple more times until you are confident.

The crank sensors are not at TDC they vary in position and the factory ecu calculates the spark from rpm and sensor signal based on its programming.

Thanks for all those comments but I still have the question "can you determine TDC and actual ignition timing from the tuning machine rather than the timing marks via a timing light?"

Thanks

Garry

Originally Posted by 101RRS

Thanks for all those comments but I still have the question "can you determine TDC and actual ignition timing from the tuning machine rather than the timing marks via a timing light?"

Thanks

Garry

I know what you are asking but the 'tuning machine' is the ecu which does it on the fly as the engine is running.

What you want is a plug in gadget that tells you when number 1 is at top dead centre on the compression stroke when you want to find it turning motor over by hand and then have a readout when the motor is running that tells you what the timing (advancing or retarding) in degrees is as you rev up and down or hold foot steady .

The first part of the answer is you have already found the TDC by the physical method thru the spark plug hole and you can mark the crank pulley and block to suit yourself.

The second answer is that workshop diagnostic gear actually does that, ie can plot advance / rpm range for you as well as display in real time as that is part of the diagnostics a good automotive technician uses.

When you just turn the engine by hand with a multimeter on the crank pickup you will get a measurement from the pickup but you will then need the specs as to how many degrees the slot in the flywheel is from top dead centre (that blips the pickup) and keep spinning while using a degree wheel to get to a mathematical TDC. Compounded by how many slots in the flywheel so you need to know which is the correct 'blip' to start with.

So use the physical method for TDC and make sure you are on the compression not exhaust stroke (by eyeballing the camshaft) and mark it off. Then you can use a degree wheel to make a plate with markings if you want to check idle timing with light.

But if you just want the dynamic readings on a screen a garage diagnostic machine loaded with your vehicles specs will show you that.

Originally Posted by 101RRS

Thanks for all those comments but I still have the question "can you determine TDC and actual ignition timing from the tuning machine rather than the timing marks via a timing light?"

Thanks

Garry

Even if the computer could determine TDC, you don't have one so you are back to step 1.