injector Timing {B3702}.... when to tune?

[Goldfinger911]

I have been tuning my idle and VE since a recent cam upgrade in my 383. I went to a much more agressive cam and am running lucas 42# injctors. I have noticed that peopler rarely if ever, change the timing offset in B3702. I know the injector timing is an offset in the injector firing based on crank-based triggers.

My question is... is this a constant with all LS1's for example? Let's say you increase stroke and then increase cam duration, and even have some cam advance ground in... shouldnt the injector timing be altered to better match the earlier opening of the intake valve?

I am going to try and play with this... but I dont know what to watch or log to see the effects.... maybe AFR? Richer means a more complete burn?

I am open to suggestions.

[SSpdDmon]

I have been tuning my idle and VE since a recent cam upgrade in my 383. I went to a much more agressive cam and am running lucas 42# injctors. I have noticed that peopler rarely if ever, change the timing offset in B3702. I know the injector timing is an offset in the injector firing based on crank-based triggers.

My question is... is this a constant with all LS1's for example? Let's say you increase stroke and then increase cam duration, and even have some cam advance ground in... shouldnt the injector timing be altered to better match the earlier opening of the intake valve?

I am going to try and play with this... but I dont know what to watch or log to see the effects.... maybe AFR? Richer means a more complete burn?

I am open to suggestions.
Learn how to read your spark plugs...


Then, teach me. LOL :D

[Goldfinger911]

I know how to read the plugs. The plugs are actually perfect when inspected. I am just always in search for perfection. :)

I will be sure and let everyone know what I learn. I am trying to find a way to create a calc PID that will do variance. That will help with tuning for various types of stability. I start geeking out on this stuff and cant stop. Hahahaha

[SSpdDmon]

Just thinking out loud here....

But, if you have a cam with greater duration and let's assume some overlap....is it really going to net you anything to squirt the injector a little sooner? Wouldn't you just be shooting more unburnt fuel into the exhaust?

IMO - messing with this table is not necessary for 95+% of the people that tune their own setup. Unless your injectors are static @ WOT, I don't know if you're going to see any significant gains. And if your injectors are static, you've got IDC problems to worry more about than simply when they're firing.

[Goldfinger911]

Yeah. You're probably right. I just got hooked on the idea that cam advance would equate to a change in injector firing to optimize the intake stroke efficiency. Originally my thought process was...

-1 RPM = 360deg crank rotation
-1000rpm = 360000 deg <---- typical big cam idle and to keep the math easy
-16.67 revolitions per second
-6000 degrees of rotation per sec
-0.0167 revs per ms
-6 degrees of rotation per ms
-Therefore when advancing the intake opening event by 2 deg, this means firing the injector .334 ms sooner.

But, once you factor in LSA and possibly a different ICL, the point becomes moot, I think.

Oh well. Hahahaha. The exercise was fun.

I wondering one more thing.... why... in the stock settings for Injector timing... does the timing offset increase with engine temp? Why would a hot engine need the injector fired sooner than a cold engine? (I am pretty sure the timing offset, it a time "in advance" to compensate for injector lag when fired.) Or.. is a time value AFTER the crank trigger? Hmmm... no must be an advance. to compensate for lag.

[Goldfinger911]

Ok... um... I know i shouldnt :) But I have to post my results. <<GEEK ALERT GEEK ALERT>>

I went back and retested before and after and came up with the same results. I flly warmed up my car to 80*c. I monitored AFR using a gauge on the dash page... because you can enable the min and max needles. With the stock injector timing settings, copied from the stock 20002 FBody LS1 tune, my AFRs bounced around at idle (like they always have) from anywhere between 13.8 to 15.8, giving me an average right about where it should be. I then used my logic above, and altered the timing to essentially fired the injector earlier. I subtracted.334ms from the injector timing because this equates to 2 degrees on the crank. I reflashed and restarted the car. I let it get to 80*c again and started my monitoring. Now, my AFRs bounce between 14.2 and 14.8. I thought I was seeing things, so I put the setitngs back and tested again... back to the way it was. Readded timing to the offset of .334ms and sure enough the AFR's are back to 14.2-14.8.

Hmm... it occurred to me that that 2 degrees on the crank is 1 degree on the cam, the injectors are fired off the crank sensor, so I should actually use more time... so for the hell of it I am going to try to add .668ms and see what happens. I really dont have an explanation.. but I thought I would share. My cam specs are 242/248 .613"/.617" 112+2. This cam with my 11:1 (or higher) compression ratio makes for a rough idle.

UPDATE: I tried lowering the timing offset by another .334ms and see the same result. Maybe slightly more stability but still definitely different that stock timing. Just to make sure, I put stock timings back again and saw the same bouncier AFRs. It is a good Friday.

[swingtan]

Here's a few things I've seen with altering the Injector timing.....


With the E38, the stock timing is very high. 220' at normal operating temps and more when cold. I found that at times, fuel laden intake charge could be pulsed right out of the intake and result in a strong fuel smell inside the car.
Dropping the timing to a little under half the stock values removed the occasional fuel smell and altered the note and feel of the motor. It actually felt a little stronger.
Dropping the timing even further resulted in hesitations at idle if you stabbed at the throttle. I think the injectors were simply firing too late and resulted in a lean spike.
Altering the Injection timing a fair amount will mean you need to adjust the transient fueling as the to seem to go hand in hand. You may also need to revisit the VE table.


Simon.

[Goldfinger911]

Thanks Swing'
Those are awesome observations. I have idled my car and drove it some with my changes... and I actually do have less fuel smell both in the car and in the garage when idling to fully warm. (I always warm it up good before taking off.)

I just found it funny that in almost all the idle and injection troubleshooting threads, no one mentions the injection timing. People always focused on the pulse width(s) and adders.

I came from the AEM world... and on an AEM ECM, even the plug and play ones, injection timing is HUGE in tuning a car with bigger injectiors.

I had 84lb Delphi injectors with twin Walbros, feeding a 2JZGTE (a whopping 183 cubic inches), with a set of mid sized Crower cams, and it idled smooth as glass at 14.6:1 AFR. I just think that there HAS to be more to the black art of LSx injection. :)

Thanks man.

[Sid447]

Agree with your yearning to understand Goldfinger911,

As an aside LS Injectors fire when the IV is closed, am I correct?

We could sure do with someone like David Vizard around here.

[Goldfinger911]

Hi Sid,

Yeah man, I yearn to understand on a daily basis. Hahaha.

If by IV you mean Intake Valve, then I think so. I think the injector firing coinsides with the instant before opening of the intake valve. Ideally, you would want it to fire with a low manifold pressure, maintain atomization, then fully ingest the fuel and air mixture, right? I am guessing here, and thinking outloud. If thats the case... and you have a cam that had advance ground in... then that intake valve is opening sooner... and you should ideally fire that injector sooner for optimal fueling?

Now, if we could only find out when, with respect to TDC, a stock LS1 injector pulse happens.... Hmmm... Maybe the base pulse is actually at TDC, and the timing in the stock tune advances it. So, if the stock injection timing is 5.55ms. then that would be 33.3 degrees BTDC when fully warm?

If thats the case... if I set my timing to zero.. then would fire at TDC? Hmmm.

Off topic... I found a great source for injector info: http://users.erols.com/srweiss/tableifc.htm

[joecar]

Thanks, that's a great site, I added it to our scattered tutorial section: showthread.php?t=2990 (http://forum.efilive.com/showthread.php?t=2990)

Interesting topic, I'm all ears... :cheers:

[SSpdDmon]

Ok... um... I know i shouldnt :) But I have to post my results. <<GEEK ALERT GEEK ALERT>>

I went back and retested before and after and came up with the same results. I flly warmed up my car to 80*c. I monitored AFR using a gauge on the dash page... because you can enable the min and max needles. With the stock injector timing settings, copied from the stock 20002 FBody LS1 tune, my AFRs bounced around at idle (like they always have) from anywhere between 13.8 to 15.8, giving me an average right about where it should be. I then used my logic above, and altered the timing to essentially fired the injector earlier. I subtracted.334ms from the injector timing because this equates to 2 degrees on the crank. I reflashed and restarted the car. I let it get to 80*c again and started my monitoring. Now, my AFRs bounce between 14.2 and 14.8. I thought I was seeing things, so I put the setitngs back and tested again... back to the way it was. Readded timing to the offset of .334ms and sure enough the AFR's are back to 14.2-14.8.

Hmm... it occurred to me that that 2 degrees on the crank is 1 degree on the cam, the injectors are fired off the crank sensor, so I should actually use more time... so for the hell of it I am going to try to add .668ms and see what happens. I really dont have an explanation.. but I thought I would share. My cam specs are 242/248 .613"/.617" 112+2. This cam with my 11:1 (or higher) compression ratio makes for a rough idle.

UPDATE: I tried lowering the timing offset by another .334ms and see the same result. Maybe slightly more stability but still definitely different that stock timing. Just to make sure, I put stock timings back again and saw the same bouncier AFRs. It is a good Friday.
Interesting. I love being proven wrong. :D

I wonder how this would affect my setup. I'm still on the stock cam...but, I'm running Motron 60's.

[Goldfinger911]

Well, nothing is 100% yet... :) I just enjoy the learning and breaking the code of systems like this.
Regarding you car.. the stock cam should be optimal for the stock injector timing.. however I would assume the Motrons do not react when charged exactly like the stock 26lb'ers. So.. maybe some compensation for that is needed. The question is.. are they faster or slower than stock injectors? Disc injectors are usually faster, but I dont know.

I am working on a way to use the Export Log function of EFILive Logging to look at the stability increases and decreases of MAP and of AFR with different injector timings.

I have a cam question... or two... does anyone know what the stock LSx cam's intake lobe centerline is? Would it be the same for all LS cams (aftemarket and stock)? Where I am going with this is... lets say the stock 2002 LS1 cam has a intake duration of 197 deg. Then I install an aftermarket cam with 242 deg at the same lift. Does that mean that my intake valves are not not just staying open later... but opening sooner by the exact same degree? Like this:

242* - 197* = 45* total increase in duration
then 45* / 2 = 22.5* meaning the intake valve opens 22.5* earlier and closes 22.5* later, assuming the ICL is the same?

Given this huge assumption... it is quite possible that the stock injector timing could be spraying fuel on an intake valve that is not fully closed?

[swingtan]

Center line of the cam lobe will depend on both timing and any ground in advance. A longer duration cam will nearly always result in the valves both opening earlier and closing later. Think of it in terms of overlap and the problems of big camshafts having both the exhaust and inlet open at the same time. FWIW, Hymey and I have spoken a bit about this.

We looked at injector timing vs cam timing and what happens with bigger cam shafts. The theory was that for big cams with lots of overlap, you could delay the injector timing to fire when the exhaust valve closed to minimise fuel being lost out the exhaust at low RPM. Then ramp the advance up as the RPM climbs to give the fuel time to fully vaporise for combustion. The issue was that it will probably effect transient fueling a bit and that would need a lot of work to correct for sharp throttle movements. It certainly needs lots of WB use when playing.

In latter tunes, I think GM have gone for very high injector timing to take advantage of the heat in the head / valve to vaporise the fuel in an effort to increase fuel economy. However that also means that the intake charge warms up a lot while sitting in the intake. I think that dropping the timing may allow for some "chemical cooling" of the charge, allowing that charge to be used before it's taken on too much heat from the head. The risk is though, that some of the heavier components of the fuel may not vapourise and remain in liquid form. So the timing needs to ramp up again as the RPM climbs.

Simon.

[Goldfinger911]

11/23 UPDATE: Well, I have been driving, logging and tuning of the past few weeks. The injector settings in my latest pump gas tune are the ones that have given me the best overall performance of my Lucas 42#'ers. You can check out my tune in my signature below.

I have been experimenting with injector timing, IFR, Pulse Width Adjustment, default and minimum pulse width. These settings given me the more stead AFR's while Auto VE tuning and under decel, my AFR's stay around 14:1. Please note, my car has no MAF and runs a full OLSD tune. Questions, let me know. My IFR is set up for a vac referenced reg at 64psi of fuel pressure.

[redhardsupra]

what's your methodology?

[Goldfinger911]

It is actually a combination of a few methods I used.

I started playing with injector timing because my the advance in my new cam, and the erratic nature of my AFR at idle and at light throttle compared to the old one. I calculated how to alter the injector timing to account for x number of degrees advance in the intake valve opening event. This made a definite improvement in the swing/range of AFR's. Then I took some data from AEM on the Lucas 42# injectors that RC Eng resells and incorporated the values from AEMPro/AEMTuner into my Pulse Offset table. (I used to be a big AEM/2JZGTE guy in a prior life) Lastly, I talked to RCEng regarding the minimum pulse of those injectors and dropped my min and default pulse accordingly. On top of that, a lot of logging (I have a folder with 94 log files) and tweaking with driveability being my #1 concern. I know some people laugh at the word driveability when running a big cam but I think it can be done.

My cam swap went from 230/234 .598/.601 113lsa to an XFI lobed 242/248 .613/.617 112+2 and now I have the new cam idling and low-speed driving like the old cam. (until I get to 4000rpm, then the fun starts. :)


what's your methodology?

[jfpilla]

I think this question is in line with the thread.
Can someone explain the attached tables and how they differ in affect? My car has an LS7 engine. I've converted whatever tables I could to the LS7 values. I don't understand these and if I should or how I should change values?

[joecar]

Joe,

B3702 is the absolute timing of each injector wrt to some crank position referenced event i.e. BDC or something (since IVO changes with cam)...
I'm not sure what exactly this event is.

B1205 sets the timing based on ECT.

(I'm sure you already know that... :hihi:<- you, :redface: <- me)

What I don't understand is that the 1st table is in time (ms) and the second is in angle (degrees [is it CKP or CMP degrees...?]),
and it both cases wrt what crank position/event...?

I don't know how to tune those... spraying/atomiztion must occur by the time IVO occurs...
might need to plot some graphs correlating crank position and IVO/IVC.

Joe
:)

[jfpilla]

Joe,
We both don't understand the same thing.:grin:
Each table references ECT. The LS1 table uses MS and the LS7 table uses, what appears to be, some crank position value?
Trying to back into the thought process, the LS1 values increase as the engine temps go up. Do the injectors open sooner or later when the engine is cold? Which ever it is the LS7 values are highest at colder temps. It would seem to make sense that the values are upside down if the LS7 table is CP. But that doesn't help in translating from the ls7 to the ls1 table.
It's interesting to note that if you turn the LS7 table upside down and put a decimal after the first digit the numbers are close.

[joecar]

Interesting observation...

the one must be timing in crank degrees wrt to an absolute crank position,
and the other must be timing advance relative to some cam/valve event
(which is also wrt to absolute crank position since the cam degreed to the crank...
ah, I just went in a circle... :) ...lol).

[jfpilla]

Joe
I think I'll leave it alone. The car tuned easily and runs well, so unless I can find a good reason to change it, I won't.
It would seem that both should be timed to the crank. Cam positions are often changed.
(theory: 2ms before something would be in the same position as, say, 500 degrees of something.)
Thanks for your thoughts
Joe

[NASABlue]

Center line of the cam lobe will depend on both timing and any ground in advance. A longer duration cam will nearly always result in the valves both opening earlier and closing later. Think of it in terms of overlap and the problems of big camshafts having both the exhaust and inlet open at the same time. FWIW, Hymey and I have spoken a bit about this.

We looked at injector timing vs cam timing and what happens with bigger cam shafts. The theory was that for big cams with lots of overlap, you could delay the injector timing to fire when the exhaust valve closed to minimise fuel being lost out the exhaust at low RPM. Then ramp the advance up as the RPM climbs to give the fuel time to fully vaporise for combustion. The issue was that it will probably effect transient fueling a bit and that would need a lot of work to correct for sharp throttle movements. It certainly needs lots of WB use when playing.

In latter tunes, I think GM have gone for very high injector timing to take advantage of the heat in the head / valve to vaporise the fuel in an effort to increase fuel economy. However that also means that the intake charge warms up a lot while sitting in the intake. I think that dropping the timing may allow for some "chemical cooling" of the charge, allowing that charge to be used before it's taken on too much heat from the head. The risk is though, that some of the heavier components of the fuel may not vapourise and remain in liquid form. So the timing needs to ramp up again as the RPM climbs.

Simon.


Awesome info and thread. I don't know if there is already injector timing info in the sticky section, but if not, this should be a candidate...

I have the Lucas and THeres a lot to just to get the correct conversion for the flow rate between pressure and rating with the test solution vs US gas.


:cheers:

[Sid447]

Anyone notice,

The Injection Timing Table {B3702} is different in the LS1-B HSV GTS tunes (see holdencrazy.com) ......when compared to all the other stock tune files?
Especially the 2002 GTS M6 which is considerably different and wonder if it might be a mistake in the tune file. Though {B3703) IT Trim has been adjusted too.

[5.7ute]

Just to try keep this thread going. Has there been any advances on where the reference pulses for the injector are in relation to TDC ( or whatever piston position it uses)?