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LBZ Larger Injector Idle (smokey) tuning

Practical Diesel Tuning

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I have an LBZ with compound turbos and dual CP3s. It had 60% over injectors that we sent out and upgraded to 100% over and tested. I have it running great except it's a little smokey for my liking at idle (it was not like this with the 60 over injectors, at least not noticeable). I see a lot of people, in other forums, get hazing with 100 over injectors but then I see other people say they have 100s that are not hazy. With the LBZ I don't have as much control over the MAF as the LLY does. The only MAF setting I have in EFILIVE is {B0201} MAF Flow Rate, Analog. For reference: At idle, engine warm, the MAF currently reads about 45g/s.

I haven't played around with it too much. Where do you think I should start? Should I reduce the scaling on the MAF a bit to bring that down to 38-40g/s (I believe those numbers are normal for a stock lbz) or is that just a bandaid? or should I reduce pulse width a bit at idle? Or my last thought is to try advancing the timing a little at idle to see if that creates a cleaner burn? or a combination of all.

I'd like to hear others' thoughts are on this.

Thanks in advance!


The MAF scaling will not effect idle haze. MAF adjustment and lambda control are only useful at reducing smoke when the engine is under load. You're experiencing a lean haze. The truck has enough air to burn the fuel, fuel is just not being injected efficiently which is causing the haze.

My suggestion would be to add timing and potentially some fuel pressure at idle. That should help. Verify your changes are working with the scan tool.



Thanks for the response! That was exactly the info I needed, that all makes sense now. I will give timing advance and Fuel pressure a try.

Thank you,



Thank you very much! I just wanted to follow up in case others find this helpful. Rail pressure was the problem. I initially bumped it up from 0-10 mm3 and from 400-800RPM after getting the car warmed up and doing some data logging, I realized it was fueling 10-12mm3 at idle and my changes didn't do a lot. Since it was interpolating between 10 and 15mm3 I bumped the 15mm3 row in the same RPM range from 30 to 42MPA and now it idles super smooth and doesn't smoke us out (it was even cold ECT). Now I need a warmer day here in upstate NY to get it up to normal ECT and see if it's smokey when warm. This is a Duramax swapped 1957 Chevy Townsman wagon, so it may be a bit before we get a nice day again lol

Also for other's reference, a good starting point for 100over injectors:

I advanced timing to -2.7 at idle (600-800 rpm),

my rail pressure at idle 0-800rpm is 0-10mm3 =60MPA (i know 60 is high but that was stock. engine came out of an express van, I believe a stock truck is 30 in this area.), 15mm3 = 42MPA.

The pulse width is very close to stock in that area (0-20mm3, 40-60MPA).

Runs super smooth and clean. I will probably play with the pressure a bit more once we have nice weather but figured I'd share my progress and starting point. Not a lot of good info out there about tuning larger injectors.

I'm also going to play with the Lambda limiting table (B0795 Main Injection Mixture Limit) to see if I can work on a faster spool time, Nick do you have any words of wisdom on this table? I've been told it is the key table to get a clean (less smokey) and faster turbo spool.


Glad to hear you've achieved the results you're looking for at idle. Nobody likes breathing half burned diesel at a stop light. ha.

The lambda limit or mixture limit table as it's called in the LBZ defines the richness limit the ECM can command. So, even if you push your foot further to the floor the ECM will only allow enough fuel (mm3) to match the measured airflow (axis reference) to the specified mixture limit (table data). Raising values in this table will lean the truck out and lowering them will allow more fuel. You can shoot from the hip to get started, if you go too lean the truck will feel lazy and unresponsive. If you go too rich, you'll see smoke out of the pipe.

The more articulate approach is to fit the vehicle with a WB02 sensor and log a histogram against this table. Review of the histogram (after a 'varied-load' driving session) will reveal which cells should be raised or could stand to be lowered.



That's exactly right! We are trying to do as much as we can but keep it a "clean diesel".

I do wish EFI Live would log lambda correctly, it just reads .625 all the time but I do have RPM and the g/cyl to go by so I think I should be able to dial it in based on that and the engine responses.

Also, that was excellent info! Thank you very much, I really appreciate it. I will play around with it as I get a chance (weather dependant).

Thanks again for your help and I really took a lot away from the class... Mostly that I need a DYNO! $$$$$ haha

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