GT40 Ignition Timing

[dwsa]

GT40 owners, I suspect my harmonic balancer has slipped as I have engine vibration. Question: When you set your timing using a strobe light, does the pointer on the block align with the graduated scale or with a single index mark, a grove abot 3mm wide that is cut into the damper / harmonic balancer. Appreciate any help Gents.

[dwsa]

RE: GT40 Ignition Timing

Does anyone do their own timing???

[AirTool]

RE: GT40 Ignition Timing

I don't know about your GT40, but most (maybe all) engines that have an ECM and a crankshaft position sensor DO NOT HAVE ADJUSTABLE TIMING.

Typically, the distributor can still be loosened and turned but the proper location is at some indexing point and about 2 deg slop either way is allowed. Outside the slop, the engine will still run but the ECM will usually throw a code.

Do you have a cranshaft position sensor?

AirTool

[M3Fan]

Re: RE: GT40 Ignition Timing

I don't know about your GT40, but most (maybe all) engines that have an ECM and a crankshaft position sensor DO NOT HAVE ADJUSTABLE TIMING.

Still, the baseline timing must be set. Spark advance is controlled by when the coil is fired by the computer rather than any type of physical advance, thus the baseline must be set the same way it is set on a non-EFI motor. The GT40 manual even states that "base timing can be adjusted by rotating the distributor when the SPOUT connector is unplugged". The same holds true for any EFI motor with a distributor.

[2gofaster]

RE: Re: RE: GT40 Ignition Timing

It's been a while since I've had a GT40 powered boat or truck, but I believe the index mark signifies TDC. When you pull the spout connector, you should see the timing light stabilize on the graduated scale at 5 degrees BTDC.

[AirTool]

Re: RE: GT40 Ignition Timing

I don't know about your GT40, but most (maybe all) engines that have an ECM and a crankshaft position sensor DO NOT HAVE ADJUSTABLE TIMING.

Still, the baseline timing must be set.

AT - Yep. That is what I meant by indexing. Some are set with a light, some with an index mark, and some with an HMI.

Spark advance is controlled by when the coil is fired by the computer rather than any type of physical advance, ...

AT - Yep. Controlled by the ECM....using the Crank position sensor as a reference and other engine operating conditions like speed, TPS, knock, etc as a basis for calculating desired advance. No parts of the distributor control timing or advance. (Although some GM IGNITION Control modules have a low RPM mode that controls timing advance until control is handed over to the ECM after the engine speed exceeds 400 rpm.)

thus the baseline must be set the same way it is set on a non-EFI motor.

AT - really you mean non-ECM

The GT40 manual even states that "base timing can be adjusted by rotating the distributor when the SPOUT connector is unplugged". The same holds true for any EFI motor with a distributor.

AT - not true for "any" ...Indexing an OBD2 GM is set by rotating/indexing the distributor as I said and you described...but it is not base timing set with a light.

[bobchris]

RE: Re: RE: GT40 Ignition Timing

airtool your a little out in left field in this topic. Call it what you want but it is not indexing of the distributor it's setting the base timing which won't be 0 it will be what ever the spec says it should be in the manual or on the valve cover if it is listed there. You un plug the connector so that the advance is disabled while base timing is set which requires either a timing light or a magnetic probe if the engine is designed to use that type of timing devise where a small magnet is inbeded into the harmonic balancer and has a holder beside the timing mark on the front of the engine. don't have a clue what a HMI is put it's not what you need to set base timing.

Also the ECM, ECU what ever you like to call the computer that manages the engine functions may not control the timing the module can control this, it depends on the manufacture and how the engine is designed some are in the ECU others are in the module.

The only engines that do not require timing to be set is a distributorless ignition system that does not have a distributor or DIS system as they are called. the protech system falls into that catagory most all late model cars and trucks allso fall in to that catagory as well.

[AirTool]

Re: RE: Re: RE: GT40 Ignition Timing

The only engines that do not require timing to be set is a distributorless ignition system that does not have a distributor or DIS system as they are called. the protech system falls into that catagory most all late model cars and trucks allso fall in to that catagory as well.

bobchris, can you tell me how to set the timing on my 2006 PCM 5.7L Vortec?

It has a regular 'ol looking distributor thingy with a cap, coil wire, and 8 plug wires. There is also a distributor hold down clamp/bolt that when loosened allows the distributor housing to be rotated.

[bobchris]

Re: RE: Re: RE: GT40 Ignition Timing

The only engines that do not require timing to be set is a distributorless ignition system that does not have a distributor or DIS system as they are called. the protech system falls into that catagory most all late model cars and trucks allso fall in to that catagory as well.

bobchris, can you tell me how to set the timing on my 2006 PCM 5.7L Vortec?

It has a regular 'ol looking distributor thingy with a cap, coil wire, and 8 plug wires. There is also a distributor hold down clamp/bolt that when loosened allows the distributor housing to be rotated.

it's not adjustable but go a head and loosen that clamp and rotate the distributor and see how well it runs slick?

[dwsa]

RE: Re: RE: Re: RE: GT40 Ignition Timing

OK, thanks for all the input... I bought a new damper from DIM and fitted it, my vibration has gone and when setting base timing with the bypass connector removed my pointer now aligns with the graduated scale as expected. My old damper had indeed slipped causing the vibration and mis-alignment of the graduated scale. Engine runs smooth now. Greg