Effect of timing adjustment?

[hitechmechnick]

Picked up a 1990 7.3 with the turbo, runs like a top, but was surprised with really bad miles per gallon, getting about 8 fully unloaded cruising 55. I managed to find a snap on mt480 locally for $40 and a few luminosity probes on eBay, got everything working on the truck and it looks like I have some timing issues.

From what I have seen everything states 8 degrees BTDC at 2000 rpm, but I am currently at 4 ATDC at 2000rpm, which I would think would make quite a big difference.

My question is how much of a difference could this really make? What should I expect both power and mpg difference? I am not expecting a Prius, but 15 would be nicer than 8.

 

[IDIBOBS]

8.5 at 2000 is the correct timing. Some like it a little more and some like it a little less. Some say a little less with turbo. But in general 8.5 at 2000 is about where you want to be. Timing makes a huge difference in power, mpg’s, egts and coolant temps. Also every time you turn up the pump it affects the timing. I’ve got my truck set up just how I person like it. 8deg I can pull my 8500lb horse trailer up the steepest grade in California with no issue at 50mph in 120deg weather and never get over 205 coolant and still get well into the 20s mpg empty.

 

[Black dawg]

Timing spec with pulse style meter is 8.5. I believe the spec done with the lumy probe is around 4atdc....

 

[IDIBOBS]

Timing spec with pulse style meter is 8.5. I believe the spec done with the lumy probe is around 4atdc....

Yup sorry didn’t think of that. I do believe you are correct. In that case ….. is the pump turned way up? How much smoke when you punch it?

 

[hitechmechnick]

Ya I’m using a lumi meter, the timing setting with that vs pulse was somewhat confusing, and how they can be so different.

As well as how some people say 1400 some 2000 and some idle setting.

Pump is turned up a “half” from what previous owner tells me. Smoke isn’t very crazy, will smoke if I want it too, but just normal driving there’s nothing.

 

[IDIBRONCO]

Ya I’m using a lumi meter, the timing setting with that vs pulse was somewhat confusing, and how they can be so different.

The lumi probe detects the actual firing in the cylinder. The pulse detects a pulse in the injector line which is quite a ways from the cylinder, relatively speaking. This means that the line pulse is extremely advanced compared to the actual firing of the air/fuel mixture.

As well as how some people say 1400 some 2000 and some idle setting.

The 1400 is for the original Ford Rotunda timing device.

 

[Brian VT]

I have a pulse timing meter. I got a pump and injectors from Russ (Grhis) about 2 years ago.
I timed it to @ 8. I can't get much more than 11 mpg unloaded (not that it matters much because I don't drive much).
I get some smoke at startup and for the 1st mile or so.
Would Russ have left me to figure out where the fuel adjustment should be? I just assumed he set it close.
And back to the OP, what general effect does advancing or retarding the timing have in each direction?
1987 6.9 N/A, fwiw.

 

[Clb]

Timing
There's a HUGE swing where these will run from -10 degrees (or more) to + 12 ( say g-bye to the glows) but tire size and driving style are bigger inputs for me.
Are you running a taller tire that slows the speedo down?

Play with settings of +6-9 degrees for a tank load of same fuels and same travels and see.

 

[The_Josh_Bear]

If you're getting 8mpgs empty at 55mph and your lumy timing is correct then you've got other issues. I don't remember the spec for lumy as I have a pulse meter...

Yes, timing matters a lot. But with these engines it matters most for power and MPGs. The average driver would not be able to tell the difference between 5* advanced from perfect to 5* retarded from perfect, a 10* swing!

I've never gotten good MPGs(16 best average), but I can tow my 4k trailer with my 2.2k cabover camper(see avatar) through the very hilly PNW at 60-65 keeping up with traffic and really using the power on the hills without going below 10mpgs. That's a LOT more work than your empty rig at 55, though I don't know your terrain in Nor Cal. Just for a comparison.

1. Maybe your speedometer is off? Use phone GPS to double-check.
2. Does it have good compression?
3. It's technically possible for the crank on these engines to slip, making all timing-related measurements inaccurate. It's not common, but possible due to the two-piece but not keyed harmonic balancer.
4. Beware that the average turbo IDI is sold with a clapped-out turbo. A poorly-operating turbo will kill MPGs.

 

[hitechmechnick]

Update for anyone curious, got the timing set up in and it all functions well, from the many sources I have found, average seems to say 2* atdc at 1400 rpm. Initial reading when warm on mine was 11 atdc.

Made a fancy wrench and was able to get it to around 1.5 atdc, while doing this found 4 glow plug that were shattered up top, as well as some very dark and wet injector return lines. Ordered a kit from pensicola with all injectors, return cups and line, as well as the glow plugs.

Gonna throw that all in, retime, and see what it does. If no real change last thing I can think of is to pull the turbo and look at the hot side and see if something’s bad.

 

[Kizer]

Ordered a kit from pensicola

Good luck brother.

See "Hall of Shame"

 

[Old Goat]

You don`t always need to purchase a new return line kit.
Most times the caps can be reused.
Look up McMaster-Carr web site, and you can purchase the Viton "O" Rings in bags of 50 for something like $10 +.
Size 111 .
Then buy the return Hose at the auto supply and cut it to length.
6.9 are 3/16" and 7.3 1/4"

Edit:
o
(
o
)
o
(
o
If the rubber hose has a curve to it, you may need to place them like this to keep them straight.
The Spring Clamps work great. They keep constant tension.

Goat

 

[hitechmechnick]

Got the injector/return/ glow plug kit in, found where my fuel was going, and it isn’t into the engine. Return line under the turbo was completely broken, which would definitely explain the low MPG’s.

Mostly surprised I didn’t smell a ton of diesel or see a trail while it was running.

Got it timed and it’s running like a top.

You must be registered for see images attach

 

[Old Goat]

Great you are back up and running.
Wonder why, with a Turbo, the return Line is run under the turbo?
With the heat from the Turbo, doesn`t seem like a good idea.
That cross over return line can be connected to any of the Caps forward of the Turbo, and easier to get to.

Seems like a good chance for a fire.

Now you need to power wash all the K rap off the engine.
I picked up a Hotsy Pressure washer off CL several years ago for $750. The hot water really cuts through the oil/grease & other crud.


Goat

 

[IDIBRONCO]

Wonder why, with a Turbo, the return Line is run under the turbo?
With the heat from the Turbo, doesn`t seem like a good idea.

That's the way it used to be done. I've seen A LOT of turbos with the return lines running underneath them. It seems like it was mostly Factory Turbos that had the crossover return line running differently. Another example of the lack of knowledge from earlier years.