86ttopbird

I saw an option in my bin to set a flag to turn on single fire mode. First, what does that mean? Second, can it be done? I have done the '165 swap and burned a few PROM's already so that is not an issue. I think having a similar style to sequential would be much more efficient. I am wondering what I might have to do to make that work. The 5.0 Mustangs fire their injectors as such. But I am sure there will be much BS involved in making the switch. There is something about having the previously atomized and metered fuel sitting on the intake valve waiting for it to open that erks me. One would think that the fuel would then puddle and thereby defeating atomization in the first place. If it is as simple as programming the PROM, then i see that as no big deal. Any input? bl85?, Rbob?, Mav?

duckmanquacker

86ttopbird

Anyone have some input on this? If this is possible i would like to do it.

bl85c

iTrader: (2)

Just means it will fire once per revolution instead of twice. Really only useful if your pw is so short that the injectors don't have enough time to fully open (below 1msec). So if you have super large injectors on a motor that idles at a very low g/sec and you have an idle problem single fire can clear it up some. Above a certain pw the ecm will go back to double fire.

ttypecamaro

iTrader: (2)

From experience the 3100 motor using $6E code and a medium cam idles right on the threshold for switching from single to double fire. It idles great when it slips into single fire mode (commanding a 1.65ms PW), but if it remains in double fire at idle (commanding .76ms PW) it will be an annoying 12:1AFR. I tried bumping the low PW correction one hex point and it leaned out to 18:1.

oh and 37pph injectors

86ttopbird

I dont have large injectors, i am using the Ford ones. I snarfed a set out of a 3.8 Cougar(these are disk type. That is what i was after.). I am wondering if setting this flag would help my idle anyway. I have no large cam or anything.

ttypecamaro

iTrader: (2)

single fire probably won't change a thing in your case. The minimum base pulse width might have some effect on idle ($03AB) and then the default pw when its below that min ($03AD).

RBob

iTrader: (1)

Double & single fire is used with batch or bank mode. These modes are when either all injectors fire together or each bank alternates in firing. I know of no 3rd gen port system that uses bank fire.

With one exception all 3rd gen port systems use batch mode. The only 3rd gen that uses SFI (sequential) is the '89 TTA (with the boosted Buick 6 cylinder).

As for double fire and single fire:

Double fire is the normal mode of operation. The injectors fire twice per engine cycle. Which being a 4-stoke, the injectors fire once per engine revolution.

Single fire has the injectors firing once per engine cycle. Which, being a 4-stroke, is once for every two engine revolutions.

Single fire mode is an asset. When the injector PW gets small, the ECM will double it and operate the injectors in single fire mode. This provides smoother operation through better fuel control. The ECM code used in the TPI systems from '86 through '92 have this capability.

For the 2.8 & 3.1 MPFI engines, when the injector PW gets too small the ECM will go into what is know as async mode. This is a sputtering of the injectors. And basically sucks.

Note that single fire mode is useful even with stock injectors. And even with a small increase in injector flow, such as going from 16 #/hr to 18.5 #/hr, single fire mode is used quite often.

RBob.

86ttopbird

Thanks for the input. While i have a 2.8, i have done a '165 ECM swap and I am using one of bl85's bin files. Looking at this bin, it appears to be a modified TPI bin. Think my car will run better if i enable single fire mode?

bl85c

iTrader: (2)

Another question, do you know what the switchpoint from single to double is? I'm guessing it's around 1msec.

RBob

iTrader: (1)

I was partly wrong about how the single/double fire modes work in the $32 and $6E code. What I described above is correct for the '90 - '92 $8D TPI code.

In looking for the switch over thresholds I discovered that that isn't any. So I looked further into how the $6E operates, then checked it against the $32 mask.

With setting the single fire option flag, the ECM will use single fire as the default injector mode. The PW will be twice that of double fire mode and injection will take place every other engine revolution.

My $6E hac isn't too well commented, so it took a while to get through it. And not having a test bench for the '7165 I can't try things for verification (unlike the '7730 and some other ECMs).

Back to $32/$6E, the default mode with the option flag set is single fire. When the ECM goes into WOT/PE mode it will revert to double fire. There appears to be other areas that will switch it back and forth between single and double fire. DFCO is one.

The reason to switch to double fire when in PE mode is due to injector duty cycle constraints in single fire. In single fire mode the highest possible DC% is 50%.

This is from having the ECM flip/flop the injection PW from actual to a 0 as each injection event occurs. The ECM hardware doesn't know about single fire mode. To it, an injection event occurs every 3rd DRP (6-cylinder).

The single firing of the injectors is accomplished in the ECM firmware. Every other injector event programs the hardware for a 0 msec PW. With the events in between these having the doubled PW.

So any PW greater then 50% gets truncated via the hardware. As soon as the 0 PW is programmed in, any current remaining PW is immediately ended.

Recall that the purpose of single fire is for better control over short PWs. In this regard the 50% DC isn't really an issue.

But with the way the $32/$6E code handles the use of single fire, this needs to be checked with an running engine and logging. And may be the reason that GM apparently didn't use it in the $32/$6E masks.

Although the larger the injectors vs. engine displacement, the less likely that this issue will occur. So we are back to single fire being usable on the '7165 ECM with $32/$6E.

I would try it, do some data logging, and see how it works out. If it runs out of injector by hitting the 50% mark. Can lower the PE mode threshold. Or, if the engine requires it put the larger injectors in.


In the AXCN mask, $8D, y-body, 6-spd, the cross over thresholds are:

Enable S/F once lower then 0.85 msec.
Disable S/F once over 1.1 msec. (these are double fire PW values).

RBob.

bl85c

iTrader: (2)

That's something I'll have to change with my version of 6E then. As well as having an option for open loop idle.

86ttopbird

That is some interesting facts there. I think ill try enabling it and doing a few datalogging sessions and see what comes out of it. I am thinking that the engine would be slightly more efficient and leanout might not occur at WOT because the ecm will revert back to double fire at that point, most likely to prevent a lean condition. My line of thinking is to not have the fuel sitting on the intake valve any longer than it needs to be so with the injectors firing only 1 revolution vs twice per revolution, it is pretty cut and dry why I might be thinking about it. I am always thinking along the lines of going against the grain and being different as well as getting the most out of what you have. Why not make a great bin even greater?

bl85c

iTrader: (2)

Well fuel on the valve isn't bad. It cools the valve and vaporizes the fuel which means a more homogenous charge. Poor homogenization is the main cause of detonation, that was smoky yunic's theory behind the 'hot vapor' motors of the 70's & 80's.

86ttopbird

Smokey Yunick, I totally forgot about that guy. I have a "How to hotrod small block Chevy's" book written by him. Good stuff in it. Like i said, it is just a theory of mine that efficiency will increase with the single fire mode. Since sequential is impossible without reworking the innards of the ECM itself, close is not bad. I am going to play with this a bit when I get some time here. In theory also, wouldnt the engine be more prone to vapor lock on a hot day? I know my car has a hell of a time when its hot and humid out.

bl85c

iTrader: (2)

Vapor lock is a result of heat soak. Happens when the fuel lines absorb enough heat from the motor to boil the fuel.