engine timing different between automatic and manual tranny?

[stamina]

i read in the a4ld to 5 speed thread in the tech library at the end of it said to make sure to re time the engine, as the manual and automatic use different timing. is this true? and if so why is that? the “auto trans timing” on the 2.9 is 10° i believe.

 

[RonD]

Never read that about the TFI spark system
10deg BTDC is spec for the 2.9l engine with either transmission
Most prefer 12deg BTDC

Engine should be warmed up fully to set timing
Remove SPOUT connector(same as unhooking Vacuum Advance on older engines)
Set timing
Reconnect SPOUT and you should see timing jump up by 10deg or so, that's whats suppose to happen

 

[stamina]

Never read that about the TFI spark system
10deg BTDC is spec for the 2.9l engine with either transmission
Most prefer 12deg BTDC

Engine should be warmed up fully to set timing
Remove SPOUT connector(same as unhooking Vacuum Advance on older engines)
Set timing
Reconnect SPOUT and you should see timing jump up by 10deg or so, that's whats suppose to happen

what is the reason for 12 as opposed to 10? what benefits can this bring for my truck? also what is the correct fluid for the m5r1?

 

[RonD]

The 2deg difference can gain a bit more power, full combustion happens sooner ATDC

M5R1 uses Ford ATF, yes, automatic transmission fluid, Mercon V or similar synthetic



Best Spark timing is when full combustion happens when piston is at about 8deg After TDC
Air/fuel mix of 14.7/1 has a fixed rate of time it takes from Spark igniting local fuel and then "flame front" expands to ignite all the fuel in the cylinder, full combustion
You want full combustion to happen After TDC of course, so the expansion of the "explosion" pushes the piston down adding power to the crank shaft
To close to TDC and explosion doesn't have enough leverage so piston/rod absorb some of the energy
To far after TDC and the explosion has more room in cylinder to expand so doesn't add as much power

So at idle RPMs it takes the piston XXXX amount of time to travel from 10deg BTDC to 10deg ATDC
And 14.7/1 air fuel mix takes YYYY time to fully ignite

As RPMs increase the piston is moving faster, so spark must happen at say 20deg BTDC to account for the faster piston speed
This is RPM based spark advance

The other monkey in the wrench is air/fuel mix
Richer air/fuel mix "burns" faster, so full ignition, YYYY, takes less time
So when you "step on the gas" the spark timing must change, this is called Load spark advance, adjusting spark timing to new air/fuel mix
Its what Vacuum Advance was for and SPOUT is for on TFI system
And, of course, RPMs go up so that also changes spark timing as well at the same time

This is a VERY SIMPLE explanation of spark timing, nothing literal
Loads of articles are available on the specifics of spark timing if you want to learn how it really works down to the degrees

 

[rubydist]

I don't know about the 2.9, but I do know on the 4.0 sohc, the spark timing map for the manual and automatic are significantly different.

 

[RonD]

Yes, but that would be Load spark advance not base spark timing, like with the 2.9l with distributor
With and without EGR also used a different load spark "map"
With or without Knock sensor as well

After 1994 3.0l Rangers the Computer had full spark control, base timing, RPM advance and load advance, distributor less with a Crank Sensor
The 2.9l or any engine with a distributor needed to be set at a Base spark timing manually so spark module and computer had a "known" reference point
Crank sensors were/are a set reference point for distributorless engines