Lumi timing results

[rockbender]

I finally got around to hooking up my Rotunda meter on my van, and good news! The meter works! I dialed in the offset to -20, got the tach sensor hole all cleaned up and probe in place, and low and behold everything read like it should.

Now the readings... at 1400 RPM I am reading right around a -3.0. I just want to confirm that this IS an ATDC reading, correct? I don't see how it could be advanced to be BTDC as it really isn't very rattly in my opinion. If this is indeed ATDC, I'm not sure I want to screw with it.

I don't have a hydrometer so can't really pinpoint my cetane value unfortunately, but regardless of that it seems I am in the right zone.

anyone have any comments? Should I actually consider backing it off to around 5-6 ATDC like the old manual recommends?

One of these days I'd sure like to get a 7.3 line and pulse adapter for #1 or #4 and have the ability to test the Lumi and pulse back to back.

 

[rockbender]

Confirmation that the negative number on the meter IS ATDC... I just hotwired my cold advance and the number indeed went towards the positive (and, at 1400 rpm pretty much instantly jumps to 1500 rpm). I haven't ever done this before, but the difference in sound is so subtle that I know for a fact I could NEVER time one of these by ear!

 

[FORDF250HDXLT]

yes the left side of the meter with the - marks is ATDC.
yes you should consider sticking with the book. 3 ATDC is extremely advanced (beyond spec) and engine damage can result. be very careful not to let someone convince you otherwise.

when i timed via the lumy method @ 1400 rpm with my old snap on i had great results with 6 ATDC.

 

[rockbender]

Just the guy I was hoping would chime in! There certainly is no harm in retarding the engine a bit, so I think I might give that a whirl. I read that you were getting a bit better economy running slightly retarded, but I realize that was measured via pulse. Thanks for the input.

 

[dgr]

You might try contacting your DEQ and seeing if they specify a minimum cetane number in the fuel. Or you could come down to California and get some at least 53 cetane fuel. Hydrometer won't help you as the test is designed for straight from the distillation column fuel, not crappy fuel with cetane boosters added. Crazy they have to post octane numbers on the pumps but not cetane numbers.

 

[rockbender]

I wanted to add some more information while I was thinking about it for anyone that might be searching on this topic in the future.

After determining that my timing was at 2.5-3 deg ATDC, I decided that I should try retarding it based upon the factory timing chart and an assumption that fuel these days has a low cetane value. I was shooting for about 6-7 deg ATDC, but ended up with closer to 7.5 or 8 deg ATDC which theoretically is still in spec for me at 3300' elevation. At that timing setting, I noticed a dramatic decrease in turbo lag, but consistently higher cruising EGT's and quite a bit more smoke, especially at start up. Cold starts were not as easy as they could be. I only ran about 5 tanks through, and my trips are varied enough that it is hard to quantify fuel economy but it looks like I was down about 1 MPG.

Fast forward to a month or so ago (yes, I spent Valentine's day evening timing my IDI), I decided that the timing needed to be reviewed again. Since I am working without a hydrometer, I decided to try the other side of the spectrum and shoot for between 4 and 5 deg ATDC. After a handful of little tweaks to the pump, I got the timing settled in somewhere between 4.5 and 4.8 deg ATDC. Since then, I haven't even put a full tank through my rig yet but I have noticed easier cold starts and the engine just seems to be much happier. EGT's are running lower, and as such the turbo isn't boosting nearly as much for normal driving.

I'll try to post more information after I get some longer trips in notes on how it does pulling grades and what effects to economy are observed. I think it will be prudent to also check the timing again this summer (once all the winter fuel is cycled out) to see if that has any effects on the luminosity timing.

 

[bbjordan]

Thanks for the update!

Re: the Valentine's day timing, now that is IDI love.

 

[ToughOldFord]

Give the gift of love, give her an accurately timed diesel.


Roses are fleeting, IDIs are forever.

 

[ironworker40]

Now thats classic stuff. I thought I was bad when I bought tire chains for my girlfriends case 580ck backhoe the day before valentines day and said to her, "here is you're valantines day present". At least I spent $160 on the chains. Okay I did get her a card to go with them!

Give the gift of love, give her an accurately timed diesel.


Roses are fleeting, IDIs are forever.