Duramax Diesels Forum Truck of the Week
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Old 03-01-2019, 11:41 PM
DIESELMAFIAPER.LB7's Avatar
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Default Sac injectors

So curious if anyone has had issues with sac injectors not wanting to cold start....

I had 80% over exergy injectors with vco nozzles never had a real issue starting the truck below 32* ever

I've noticed dince my new sac 100% overs anything under 25* this ****ing thing doesn't like to start with a couple turns of the key and some extra cranking?

Maybe sac injectors need something im not thinking of ?
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Old 03-02-2019, 07:40 AM
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I've noticed the same thing with mine but not quite as severe as you explain. Mine will start it just turns over a little longer than before, they are Exergy 100% SAC's and I also did a set of Lincoln/S&S 100% SAC's for a friend with the same result. I was going to add a little more cranking fuel to just have not yet. I already bumped the rail psi a little around the idle p/t areas.

Irrelevant but on paper my Exergy's flow more than the Lincolns's I got though.
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Last edited by rcr1978; 03-02-2019 at 07:44 AM. Reason: mispeelr
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Old 03-02-2019, 08:28 AM
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DAVe3283 DAVe3283 is offline
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I have SAC +75% injectors (Lincoln / S&S for what that's worth) and my truck starts great in the cold, down to 13F so far. I never plug it in either, not worth the electricity cost IMO.

SAC injectors take major tuning changes vs. VCOs to be happy in the cold. I ended up using less pilot fuel than VCOs, less timing advance when cold, a hair more fuel pressure, and a way smaller cranking pulse (at -10C, stock was 1600 us, I run 850 us, about half!).

I attached my tune if you guys want to look through. I do my MAF scaling in a funky way vs. most tuners I've seen, so the MAF limit tables might look weird. And I have a big single with a really big cam, so keep that in mind if you see the mid-RPM stuff being funky. It is hard to get on top of this turbo with this cam, so I do weird stuff.

You should be looking at the base timing, pilot timing, ECT timing compensation & multiplier, pilot quantity, cranking quantity, and main pulse tables. In the idle range, those should work on most engines. Mine has lowered compression vs. stock, so a stock motor could be more aggressive with the cranking fuel but might want to pull a little timing out? But this should be a good starting point or reference information.

This is how SAC +75% injectors can start in the cold:
Attached Files
File Type: ctz No Logic 5 BETA r20190202.ctz (327.8 KB, 10 views)
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Old 03-02-2019, 09:59 AM
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Yeah I'll drop pilot and timing a little more see if it helps anything.

And I'll watch main injection I run plenty of rail pressure at idle/cranking for sure once it starts it cleans right up
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2003 GMC CC/SB: billet 66/83mm compounds, dual pumps, exergy injectors, built trans (by me) tuned by me 11.11 @ 124.63mph @ 7100lbs

2012 mega cab 6.7: Tuned and deleted (reliable) sold! (should have kept it)

2016 CCSB custom sport lml ltz deleted with sotf tunes by me
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Old 03-05-2019, 02:43 PM
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I have the smaller 65% SAC nozzles, 16.5:1 compression and mine starts fantastic at 0 degrees a few days ago. And as crazy as it sounds I swear it starts faster than a stock truck. I know it's stupid but just a reminder we're LB7's with no ECM glow plug diagnostics. Back in the day I lost 6 glow plugs over the course of one summer and was having just a slight hard start when winter hit. Didn't even realize. Easy to over think the simple stuff.
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Old 03-05-2019, 06:43 PM
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My 100% sacs will start at 5* no issues. I’ve noticed zero change during starting from stock injectors to these.
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Old 03-16-2019, 06:37 AM
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Yeah mine hates it I dunno never had a issue till the sac injectors with starting in the cold runs fantastic otherwise.

I made changes with a minor change in how it started was 19* I bumped glow plug time up a little as well and it started first try still took bout 6-8 seconds of cranking. Might make a few more changes to it today see what happens
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2003 GMC CC/SB: billet 66/83mm compounds, dual pumps, exergy injectors, built trans (by me) tuned by me 11.11 @ 124.63mph @ 7100lbs

2012 mega cab 6.7: Tuned and deleted (reliable) sold! (should have kept it)

2016 CCSB custom sport lml ltz deleted with sotf tunes by me
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Old 03-16-2019, 06:38 AM
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Quote:
Originally Posted by chevyburnout1 View Post
I have the smaller 65% SAC nozzles, 16.5:1 compression and mine starts fantastic at 0 degrees a few days ago. And as crazy as it sounds I swear it starts faster than a stock truck. I know it's stupid but just a reminder we're LB7's with no ECM glow plug diagnostics. Back in the day I lost 6 glow plugs over the course of one summer and was having just a slight hard start when winter hit. Didn't even realize. Easy to over think the simple stuff.
I put all new in maybe the relay isnt really working correctly either
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2003 GMC CC/SB: billet 66/83mm compounds, dual pumps, exergy injectors, built trans (by me) tuned by me 11.11 @ 124.63mph @ 7100lbs

2012 mega cab 6.7: Tuned and deleted (reliable) sold! (should have kept it)

2016 CCSB custom sport lml ltz deleted with sotf tunes by me
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Old 03-16-2019, 09:12 AM
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Quote:
Originally Posted by DIESELMAFIAPER.LB7 View Post
I put all new in maybe the relay isnt really working correctly either


Highly possible since they commonly die
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Old 03-17-2019, 01:28 AM
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I have some 65% overs and Starlite tuning. I have noticed that the truck will not cold start the first time with the autostart, not enough cranking time.... It always starts the second time the autostart tries. It has not been an issue with using the key, I think the autostarter could use another second or two or cranking and it would be just fine.
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Old 03-17-2019, 05:16 AM
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Quote:
Originally Posted by BlkMax View Post
I have some 65% overs and Starlite tuning. I have noticed that the truck will not cold start the first time with the autostart, not enough cranking time.... It always starts the second time the autostart tries. It has not been an issue with using the key, I think the autostarter could use another second or two or cranking and it would be just fine.
Isn't actuating glow plugs very long I'd bet.
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Old 03-17-2019, 01:58 PM
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With sac injectors I've found pilot timing/quantity are key to making them work. SMALL changes to pilot can completely change the way the engine reacts. I've only got 45 overs, but it starts better now than it did with stockers.
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Old 03-17-2019, 02:29 PM
gmc502 gmc502 is offline
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Quote:
Originally Posted by THEFERMANATOR View Post
With sac injectors I've found pilot timing/quantity are key to making them work. SMALL changes to pilot can completely change the way the engine reacts. I've only got 45 overs, but it starts better now than it did with stockers.
did you add or subtract ?
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Old 03-18-2019, 06:42 PM
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Quote:
Originally Posted by gmc502 View Post
did you add or subtract ?
I subtracted quantity, switched to an lly timing table, and tweaked from there. What I found was even a half a degree change in pilot timing could make the idle fuel rate change 1mm3 of fuel with no other changes.
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1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, little of this, a little of that,
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Old 03-19-2019, 05:47 AM
gmc502 gmc502 is offline
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Quote:
Originally Posted by THEFERMANATOR View Post
I subtracted quantity, switched to an lly timing table, and tweaked from there. What I found was even a half a degree change in pilot timing could make the idle fuel rate change 1mm3 of fuel with no other changes.
very interesting,thank you for the info
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