Timing with SnapOn Luminousity Probe

[jayro88]

Okay, So on Friday I am going to take my '88 E250 in to have the timing checked/adjusted. I found a shop locally that was recommended by a forum member. I spoke to the person who would be doing the timing. He used to own an IDI and will be using a Snap On Luminousity probe that screws into the #1 GP hole. It then attaches to his timing light....kind of like the Ferret meter. My question is:

What should the timing be set at with this type of a probe?

I know that when using a pulse timing meter (like the Ferret), you set it to 8.5* BTDC.

With the Luminousity probe that is detecting the actual detonation I have found mixed info. I found anywhere from .5-1* ATDC to about 5* ATDC. Does anyone have experience with this type of meter that can shed some light on the subject. The shop seems to know what they are doing, but I always like to be educated on the subject before I walk through the door. Thanks

Jeremy

 

[jaluhn83]

I'll check tomorrow when I get home, I believe it's ~4.5* ATDC but I'm not sure if I'm remembering it correctly. The spec does officially depend on cetane, but the variation is about 1*, so I just go for a middle of the road ballpark.

 

[riotwarrior]

Great question, one that bears asking and a quality answer, I'm sure one of the other timing guru members will slip in n leave you unequivocal info but for now, IIRC it's 1.5 ATDC again cetane dependant!

Please don't quote me on this as it's my memory and it's ok some of the time .....

 

[jaluhn83]

1.5 is too advanced, I'm 95% certain I've got mine set to ~3.5. I'll see if I can upload that page out of my manuals tomorrow when I get home. I've got an 85 Ford Facocty manual set that I know has the info.

 

[jayro88]

Hmmm. Now I think (drawing conclusions from my reading) there are 2 types of items that can be used with the luminousity probe......

One is a timing light adapter (like the feret meter) that you can hook the timing light upto. It picks up the rpm from the fuel ignition rather than the pulse of fuel though the line. I read that when using this type of timing method that .5*-1* ATDC is equal to about 8* BTDC with a Ferret.

Two is some kind of a magnetic pick up that is attached to the crank pulley. When this one is used with the luminousity probe then the timing should be set about 4.5* ATDC.

This is from me reading a bunch of different threads. I couldn't find any definative answer....it's all kinda murky.

 

[riotwarrior]

I'll try copy my manual page in a photo tomorrow for ya....that's gotta have it!

 

[jaluhn83]

Hmmm. Now I think (drawing conclusions from my reading) there are 2 types of items that can be used with the luminousity probe......

One is a timing light adapter (like the feret meter) that you can hook the timing light upto. It picks up the rpm from the fuel ignition rather than the pulse of fuel though the line. I read that when using this type of timing method that .5*-1* ATDC is equal to about 8* BTDC with a Ferret.

Two is some kind of a magnetic pick up that is attached to the crank pulley. When this one is used with the luminousity probe then the timing should be set about 4.5* ATDC.

This is from me reading a bunch of different threads. I couldn't find any definative answer....it's all kinda murky.

Good point. My experience is with the magnetic pickup type. Snap on MT480, I think?

 

[jlwoods99]

So why exactly wouldn't you time it the same as with any other timing meter 8.5 or 9 degrees?

 

[jayro88]

So why exactly wouldn't you time it the same as with any other timing meter 8.5 or 9 degrees?

My understanding is this....

With the Ferret meter you are detecting the pulse of fuel through the line headed to the injector. This event happens slightly prior to the fuel being injected so it needs to occur earlier in the combustion process.....8.5* BTDC.

With a luminousity probe you are detecting the actual combustion in the cylinder. This event is later in the the combustion process.....after top dead center. The question is "How Much ATDC?"

You wouldn't want the combustion to occur before TDC as it could cause damage to the engine (or atleast this is what I know about a gasser, not 100% it is the same on desiel)

 

[stumiister]

This is how I timed my truck I used the test and tune meter jj38000 I think that is the meter with the adapter on the #1 injector line and the magnetic pickup on the crank I set the timing at 8*BTDC at 650 rpm with the high cold idle set at 900rpm, which I belive icanfixall told to do I also borrowed his meter on a rental basis.

 

[FORDF250HDXLT]

7 - 5 DEGREES ATDC (PLUS OR MINUS 1) @ 1400 RPM
1.yes,this is how the 6.9l was originally timed.with a timing meter that read the rpm of the engine via a crank sensor probe,as you called it a "magnetic pickup" and senses the actual combustion chamber event time via a small glow plug with a glass window,known as a luminosity probe.
this method if done correctly is always at operating temps,all accessory loads off,engine at 1400 rpm,and always only somewhere between 7 ATDC through 5 ATDC depending on elevation and fuel cetane.
as you can see in the chart there,1 degree either way is still whiten limits,but one degree only from your elevation and cetane rating ok.
whenever you see someone post ATDC numbers that contradict this chart for the 6.9l and 7.3l,they are basing their numbers on noting at all that im aware of besides their guesses,and i feel they simply haven't educated themselves in the method properly.
use extreme caution if you decide to listen to others who post ATDC numbers outside this chart.particularity lower numbers.severe engine damage can result! fair warning!

8 BTDC (PLUS OR MINUS 2) @ 2000 RPM
2.using a timing light,there is no reading of the combustion chamber at all.therefore no lumy probe is used in place of a glow plug for reading engine timing.
instead your reading the engine timing event via the fuel pulse before the fire event.this fuel pulse through the fuel line (#1 of truck or #4 of vans.whichever is easier to get to) is then transferred into a "spark" event so the meter or light can then flash correctly for you to read the O mark on the ballancer.using a light with advance,or your timing meter to set the timing.this method if done correctly is always at operating temps,all accessory loads off,engine at 2000 rpm,and always only 8 BTDC.
plus or minus 2 degrees is within limits.meaning 6 BTDC - 10 BTDC.


attached below is a timing meter capable of timing via both methods with instructions for you to look at for more details.
link:
snapon mt1480 timing meter instructions pdf

 

[icanfixall]

I have not used the luminosity probe type timing method because I don'y have the cetane hydrometer needed for that. Plus I don't want to remove a glow plug and risk any extra work doing so. Is the lumi probe type timing as good or better than the clampon type timing??? I really don't see it being better or worse.. Just a little more work to do. Now if you are to get the cetane reading and time the engine... Then get a tank of lower cetane reading fuel will the timing change... Possibily. So how will the timing change if you use the clampon probe timing method and the cetane changes... Not one bit because your using the pulse method of timing and its not dependant on cetane reading at all. At one time the lumi timing was all we had but things change.. I really am not able to positivey state what the lumi timing should be set at but some of the postings here are very correct. The 1400 rpm is right on a warmed up engine. The cetane reading is a must have too. And finally the degrees of timing doing it by the lumi method is defiently in the after top dead center reading of timing... Ot atdc.... Not the before top dead center or btdc...

 

[jayro88]

Thanks guys. So it looks like there is not a Luminousity Probe/timing light set up that is used then? Only the probe with the magnetic pick-up.

 

[stumiister]

Use the magnetic pickup with the timing adapter on the #1 or #4 injector line.