Inj. Duty Cycle

Sy370

Sy370

New member
I was wondering if my duty cycle wasn't running any higher then 6, using DataMaster, then I turned the fuel pressure down 4 pounds, did another run and duty cycle was at 60, do I then turn the pressure down again to get it at 80? I am confussed and having alittle difficulty with fuel pressure tuning. Can anyone shed alittle light?
TIA
rik
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leroy

leroy

Donating Member
Re: Inj. Duty Cycle

WOT is open loop. There would be no correction in duty cycle as the fuel pressure is changed. There may be a change in duty cycle at idle, cruise, etc.

IMO, it's better to see if you went faster, or had more knock counts. Wideband helps.

HTH,
Jim
 
Sy370

Sy370

New member
Re: Inj. Duty Cycle

on the Datamaster it says I am in Closed Loop, I am still learning here so bear with me, should it be switching to Open loop sometime? thanks for your input
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leroy

leroy

Donating Member
Re: Inj. Duty Cycle

During most driving conditons, the ecm tries to maintain an air/fuel ratio of 14.7:1 to keep the catalytic converter happy. The O2 sensor monitors the a/f ratio, and if the a/f ratio strays for awhile, the ecm corrects it. That's what the BLM is.

When you go wot, the ecm goes into PE (power enrichment) mode. In PE mode, the a/f ratio can be as rich as 11.8:1. There is no BLM calculation in PE mode. However, if the open throttle BLM is greater than 1, indicating lean, the blm correction is used in the PE calculation.

Datamaster may show closed loop. IMO, injector duty cycle is not too useful for tuning. It can tell you that you need bigger injectors, but that's about it.

Is that confusing enough for you? lol

Jim
 
Sy370

Sy370

New member
Re: Inj. Duty Cycle

Yeah, you got me. So I shouldn't worry about the duty cycle at all, as far as running rich/lean? Just make sure that they aren't over 80%, should I try and get them at 80% or no?
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leroy

leroy

Donating Member
Re: Inj. Duty Cycle

Don't worry about the duty cycle. But, if you notice the duty cycle going over 80, consider bigger injectors.

If you want to tune for WOT, it's best to have a wideband. Some folks have good luck with a narrowband, and tuning for a specific O2 mVolt, but I've seen a wide variation in voltage, depending on sensor age, and exhaust temperature. The other tuning aid, and the most definitive, is spark plug reading. There is an art to that, and it's a PITA to remove plugs on these trucks.

Jim
 
Sy370

Sy370

New member
Re: Inj. Duty Cycle

I was thinking of a wideband, but no funds right now for that. I used to work on harley davidsons for about 8 years, so I have done my fair share of sparkplug readings. I was only checking #1 and thought I was running alittle lean, so I richened it up, getting me to this part w/ the injectors. Maybe i am looking into to far or something.
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Loeryder

Loeryder

New member
Re: Inj. Duty Cycle

I think he means if you intend to be able to tune to a very specific level you are going to need the sensor capable of taking those readings.
Experimenting too far off the beaten path could cause permanent damage to engine internals. Datalogging is mission critical to a good tune.
Most of your mail order tuners will want you to provide WBO2 readings at WOT if you are getting what you pay for.
 
cloneman315

cloneman315

Active member
Re: Inj. Duty Cycle

just be easy if u dont have one,the plx m300 for 300 bucks will work fine,once u get one u will wonder how u ever went without
 
SeattleSy#1255

SeattleSy#1255

Category 5 Conservative
Re: Inj. Duty Cycle

you can over 100% DC but it'll take alki to do it...if they are at 80 i'd watch it, but don't think you'll need new injecters unless you have a larger than stock turbo or running high boost. which is a waste of time over 20 in the stocker anyway.
 
leroy

leroy

Donating Member
Re: Inj. Duty Cycle

SeattleSy#1255 said:
you can over 100% DC but it'll take alki to do it...if they are at 80 i'd watch it, but don't think you'll need new injecters unless you have a larger than stock turbo or running high boost. which is a waste of time over 20 in the stocker anyway.
Click to expand...

How can you go over 100% duty cycle? Aren't the injectors static open at 100%?

Jim
 
cheatham2492

cheatham2492

New member
Re: Inj. Duty Cycle

Yes that is correct they are constently open when operating at 100% DC and above. They say 80% dc is safe because they get to close for a period that way they dont stick open and waste the motor.
HTH
Dan
 
cheatham2492

cheatham2492

New member
Re: Inj. Duty Cycle

Yes that is great. anything below 85% to me is just fine.
I have seen #'s of 120% . I think the injector was exhausted amd the motor lucky.
Cheatie
 
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