sac45 idle

Vmyrhaug

2003 lb7sac45 35" 20x12 fjallasport flares
Mar 6, 2016
170
4
18
40
Norway
in idle, what fuel pressure and timing are best for sac45?
i have a little fuel smell of exhaust in idle, 5degress timing and 50mpa of fuel pressure.
i wonder if i should bump fuel pressure up to 60?
 

Vmyrhaug

2003 lb7sac45 35" 20x12 fjallasport flares
Mar 6, 2016
170
4
18
40
Norway
2 degress or less it will bee. so 50mpa is too high?
what would cause the small unburnt fuel smell? no haze, only a very weak fuel smell in exhaust.
balanse rates are good, very good also,
are pilot injection too large?
 

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
3,386
402
83
Central OH
50mpa shouldn't be an issue, but IMO unnecessary to clean up a Sac45. Try timing first, what did you change as far as pilot quantity / timing?
 

2004LB7

Well-known member
Dec 15, 2010
6,595
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Norcal
What the main rate in addition to balance rates?

You can also use the DVT tools to manually raise the pressure to see if there is any particular value that it idles good at. Than plug that into the tune
 

Vmyrhaug

2003 lb7sac45 35" 20x12 fjallasport flares
Mar 6, 2016
170
4
18
40
Norway
50mpa shouldn't be an issue, but IMO unnecessary to clean up a Sac45. Try timing first, what did you change as far as pilot quantity / timing?
pilot quantity is stock lb7. maybee should have adjusted that? but not sure if i should doo less or more..
 

Vmyrhaug

2003 lb7sac45 35" 20x12 fjallasport flares
Mar 6, 2016
170
4
18
40
Norway
What the main rate in addition to balance rates?

You can also use the DVT tools to manually raise the pressure to see if there is any particular value that it idles good at. Than plug that into the tune
did raise too 60mpa a day here, forgot too smell at exhaust, was only too check if i got injection rattle.
 

Vmyrhaug

2003 lb7sac45 35" 20x12 fjallasport flares
Mar 6, 2016
170
4
18
40
Norway
and there is no visible haze, only a small smell of unburn fuel at idle. diesel here in norway have 10-20% bio in also.. but are only driving with shell vpower nitro diesel. less smell with that fuel.
 

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
3,386
402
83
Central OH
Dave has a solid SAC injector tune here in the library you can check out, or I can email you one? But yes I would up the pilot quantity a tad to try at first, and revise the pilot timing as well. The pilot timing table I use is based off of Dave's tune, at least I think it was...
 

blueshift

New member
Jan 29, 2024
21
15
3
Raleigh
I recently tuned my own S&S 45% SACs (though life got in the way and I never got it fully finished).

I also have a very slight haze and smell at idle. I did some testing with fuel pressure and timing. I found that they made no difference at all. Had -4 degrees and 35 MPa in tune 1, all the way to +6 degrees and 70 mPa in tune 5. I stood at the tail pipe with a flashlight shining through the exhaust, and had my wife switch back and forth between the two. Couldn't tell one bit of difference in the smoke (though it was noticeably louder).

I've briefly played with the pilot timing. I switched over to an LLY pilot timing table. Switching between that and the stock LB7 table on the DSP5, I can tell a small, but definite, improvement in the haze with the LLY timing. Gives me hope that tuning the pilot can get it mostly cleared up. Still need to do some more testing.

I haven't played around with pilot quantity yet. That's basically next on the list.

If any of y'all smart people want to give a heads up on where to start there......😁
 

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
3,386
402
83
Central OH
Sorry but I don't believe that a 10deg swing in timing made no difference, especially at -4 it should start smoking heavily. Did you datalog it to ensure it was actually commanding -4 and not hindered by a limiter or multiplier?
 

2004LB7

Well-known member
Dec 15, 2010
6,595
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On top of that, I thought I remember a bug in the DSP tunes where it ignored the pilot tables and didn't change them when switching tunes. Might extend to other areas too
 

Vmyrhaug

2003 lb7sac45 35" 20x12 fjallasport flares
Mar 6, 2016
170
4
18
40
Norway
did dave share a sac tune?
that 175+ tune for voc he shared was awesome💪
 

blueshift

New member
Jan 29, 2024
21
15
3
Raleigh
Sorry but I don't believe that a 10deg swing in timing made no difference, especially at -4 it should start smoking heavily. Did you datalog it to ensure it was actually commanding -4 and not hindered by a limiter or multiplier?

Why would it smoke at -4? -4 is the stock timing in my OS. It has a very slight haze and smell (can only see it at night with a light), but definitely isn't heavily smoking. Main mm3 is 7.5, and all balance rates are +/- 1.5. I shut off each cylinder individually and the smoke output never changed, so it seems to be a system-wide issue rather than an individual injector.

I just checked my tune and realized I slightly mis-spoke earlier: the max timing was +4, and the max fuel pressure was 75 MPa. I did the timing at -4, -2, 0, +2, and +4, the fuel pressure at 35, 45, 55, 65, 75. Did each variable independently, and both together. All at 175+ ECT, in neutral and AC off. I datalogged and verified everything was changing as expected. It got very slightly louder with each timing advance, and noticeably louder with the higher pressure. But if the haze output changed, I couldn't tell it.

Again, it's very slight, but the fact that it hasn't responded to timing or fuel pressure changes tells me either:
1. The orifice size/angle and/or SAC chamber void below the pintle isn't as optimized for efficiency / clean burns at idle, or
2. There's some ideal relationship between pilot quantity and timing for a smokeless idle, and the stock LB7 tune doesn't match up with that ideal relationship of the aftermarket, oversize SAC injectors

The fact that advancing the pilot timing a bit did make a small, but noticeable, improvement makes me optimistic that it's #2, and I just need to spend a bit more time on it.

On top of that, I thought I remember a bug in the DSP tunes where it ignored the pilot tables and didn't change them when switching tunes. Might extend to other areas too

I remember hearing that too, but I've never seen it. Pilot timing absolutely changes in my DSP5 OS. Pilot quantity is only in DSP2; I haven't gotten around to trying that yet.



I read through all that (and a couple others, too) a few months back when I was getting started on my tune. Was definitely a big help.

The biggest issue is that it seems not all SAC nozzles are the same, and the even same brand may have changed a bit in the last 8 years, so some of the advice / findings seemed specific to the exact injectors and setup being used at the time. I haven't seen much discussion of it in recent years, and had actually considered starting a new thread at some point once I got back to playing with it, but vmyrhaug beat me to it.
 
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Bdsankey

Vendor
Vendor/Sponsor
Feb 1, 2018
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Larsen, Wisconsin
I can say my Dynomite Diesel SAC100% do not haze nor smell of raw fuel at idle. Currently the truck was at around 55mpa the last time it ran. That was on zero run time on a brand new engine as well.

I don't tune but I have a sneaking suspicion looking at the changes between VCO and SAC files from here that pilot is the biggest difference.
 

Vmyrhaug

2003 lb7sac45 35" 20x12 fjallasport flares
Mar 6, 2016
170
4
18
40
Norway
I can say my Dynomite Diesel SAC100% do not haze nor smell of raw fuel at idle. Currently the truck was at around 55mpa the last time it ran. That was on zero run time on a brand new engine as well.

I don't tune but I have a sneaking suspicion looking at the changes between VCO and SAC files from here that pilot is the biggest difference.
what is the diffrence in pilit injection, more/less? more adv?