EFI throttle bodies and injectors

S

SR_Crewchief

Well-known member
I'm sure that this has been discussed to death at some point...but my searches over the last few months on several forums haven't turn them up.


I know that I'm going to over simplify this, but that's do to my not having enough technical background on the subject so please bare with me.

I can understand why just increasing the TB size will gain no net hp/tq gains. Among other issues the air volume delivered exceeds what the EEC is expecting for a given throttle position. Potentially creating a lean condition if the programing can correct for based on O2 sensor feedback.

And I can understand why just increasing injector size also has no net gains as well. Delivering more fuel than the EEC expects for a given duty cycle. Potentially leading to a rich condition....


I presume that it's not practical to increase injector size proportial to throttle body increase without needing to alter control tables to keep a/r in acceptable ranges. Effectively what is done when you swap to a larger carberator. My assumption is that the current combination of twin 47mm(in think) throttle body and 14# injectors are at or near optimal for what the current head can handle, short of forced induction. At least with the stock cam.

I'm currious as to whether a mildly ported head, longer duration cam(240-250 duration range), improved exhaust ( for sake of arguement 3" single pipe behind long tube headers), twin 61mm throttle body and a proportional injector set (19# ?) could be in range of what the stock programming could comensate for. Speed density not MAF.

I've got to be overlooking something obvious, but just don't have the fuel injection foundation knowledge to see.
 
Thanks TJ.

I'm looking into what can and cannot be done with the stock ECU first. MS and others are valid options though.

I'm sure that the numbers I intially plugged in are completely invalid since I basicly pulled them out of the air.

But the idea is simple. If the PCM recieves signal X from the TPS it expects aircharge Y and signals the Injectors expecting fuel delivery Y. If the aircharge is now Y+2 for signal X and injector size has also been increased to delivery the Y+2 A/R balance should be maintained.

The variable that isn't addressed here is whether the head flow can handle the Y+2 aircharge. I think that the MAP signal partially addresses this.

It can't be this simple or most of you with EFI would have been doing long before now. I need to research EFI theory more indepth than searching forums. :wink:
 
The issue isn't the EFI, it's the airflow. Unless you get the head breathing better, a bigger T/B and bigger injectors together will add zero. Once you open up the head then you start processing more air and you need more fuel. At some point the T/B becomes the bottleneck and needs to be upgraded. I cannot imagine ever getting a streetable 300 to the point of needing a 61mm T/B, but the 50MM off a stock 302/351 is a likely upgrade.

The stock programming for the S/D EEC-IV starts to get confused at somewhere around 12-15% above expected values or in the case of the 300, about 168-173 HP. This is incidentally just about where the stock 14# injectors begin to limit out and going much beyond this will require you to move up to the 19# units.
 
Thanks SR, That's what I'm trying to get my head around.

If I'm understanding correctly...

From a programming stand point matching the TB cfm increase to injector size is sort of technically feasible.

The stumbling issue is head. Without improving head flow, with the stock cam, the MAP sensor will countermand the increased fuel request from the TPS. And if the TPS and MAP are roughly 12% or more out of sync the PCM will start having problems with management.

But...If we can get a segnificant flow inprovement, then there is an improved chance of seeing useful power increases without needing override the stock control tables. In theory anyway.


I think part of what's been bugging me is seeing pre-EFI's swapping from log intakes to DP's and such, larger carbs, and openning up the exhaust to get useful power increases. All this while the PCM's for the EFI's are appearently a hinderence. I hadn't fully comprehended that in stock form the head was running so close to max.

Thanks for putting up with my dumbarse brainstorming. :D
 
Except that once you upgrade to 19# injectors you need to re-flash the PCM or add a piggyback chip. The 19s have a much different response curve than the 14s, if you don't adjust the PCM's expectations, the system will constantly be hunting for a comfortable place since the feedback from the HEGO sensor will never match the feedback from the MAP and TPS.

One thing that all this talk about peak power ignores is the "area under the curve." In stock form, the 300 makes something like 100 HP @ 2000 RPM which increases to 150 @ 3500. If you get breathing better to where the stock EFI system limits out at around 170 HP @ 3500, that doesn't sound like a big gain but airflow gains from cleaning up the head are likely to show up at all RPM ranges. That same 20 HP applied all the way from 1800 to 3500 is a very big gain.
 
Really? I won't have expected a segnicant difference between the 14# and 19# since they both are triggered by the same signal strength. At least I assume the same trigger strength. I figured the difference was spray orfice size. I guess I should have expected something like that to be an issue since the HEGO is effectively a 3 position switch(lean, acceptable, rich).

I wouldn't say ignored. Just excessively vague in what I ment by usable power. If you can effect the increase earlier and hold it longer, it's more usable.

Unless I replace the PCM, reflash isn't an option. So it would have to be a piggyback on the J3 port. then it's back around to I haven't come across anyone that admits to having crack the table settings for the 88. I've found plenty that claim to cover "all" EEC-IV's 87-96 but tend to drop it or ask for you program code (valid request). Since I haven't pulled to kick panel to look find the program code on the PCM I'm stuck. I guess I could go the MOATES route, which means I've got a lot more to learn vs pass configuration changes to a vendor.

In the end it's nothing money can't cure, to bad I'm short of that like everyone else.
 
StrangeRanger":zphrkj2f said:
<snip> The 19s have a much different response curve than the 14s, <snip>
Click to expand...

Can you point me in the direction of more info on this. I've only done a quick search so far, but haven't found anything relevent.

It just seems odd that 2 injectors that are supposed to have the same impitous to open would have enough difference in performance to cause an issue. I'm not doubting your knowledge, but want to find out more about it and how it affects my assumptions.
 
Actually, I believe the 14 and 19 lb'rs share the same impedance, so the computer wouldn't know the difference as far as firing the injectors, but all the extra fuel would cause a lot of headaches.

What you are describing in your first few posts is somewhat theoretically possible, but only under WOT conditions.
Anytime you are at part throttle or idle, you would be too rich.

Perhaps the solution for you would be to buy a twEECer ... I don't know if they work with the 300's or not. The guys on the twEECer boards could probably tell you.

I fear you won't get too far with your stock EEC, you would ultimately be miles ahead in the end by converting to Megasquirt. It all depends on just how much modifying you plan to do.
 
IIRC, at least the Accel injectors, 14 - 24 share the same impedance. Which tells me that the difference is in the orfice size. From there it could also be differences is spray pattern as well. I've been doing a lot of research into diesel performance as well and could easily be mixing theories though.

Tweecer would be an option. But...acording to posts on thier boards no one has cracked any of the 300's programs. The solution that has been put forth is to swap to a Mustang A9L programmed PCM and MAF conversion. From there the Tweecer can control # cyl's, firing order, etc so that the 300 plays nice.

Another option is to start getting the MOATES gear. Download me existing programs and take a shot at cracking the tables myself. 2 strikes here. 1) no one on the Moates board claims to have a baseline crack of any of the 300 programs 2) since I'm not currently knowledgable in FI programming it would be a very steep learning curve. Not an impossible task, but one that will take segnificantly more free time investment that I currently have to spend.

Which brings me around to "what I'm planning to do". Like serveral others, I'd like see just what the engine can do. So I've been compiling a parts list of what an extreme build would look like. Currently the price tag is in the neighborhood of $6k!! I take one look at that and go 'this is insane!!'. So then I sift through and pluck out those things that make more sense in a build to make a realiable daily drive that has better perforamce than this nearly 20yr old truck currently has.

Which is what brought me to the question I started this topic with. I was hoping that since with relatively minor changes to the intake and exhaust the gas versions could step up to moderately larger carbs the same principal could be applied to EFI. But since no one has been posting that very thing there had to be something I was overlooking. Strange Ranger provided what I had overlooked, in stock form the EFI head doesn't have the reserve flow capacity to accomidate the increased demand.


I've got serveral things that work for and against me. 20 years of helicopter maintenance. Currently being a mainframe applications programmer. A love of tearing into things to make them run better (engines, programs, etc). Raising and training champion Saddlebred horses, not near enough free time, and an enemic cash flow.

I do the samething with my Cummins. I've mapped out what it will take to make a 500hp/1100tg daily driver. I just lack the funds and time to make it a reality.

Know I'm off to clean more stall while thinking of things to do that I don't have time or funds for. :wink:
 
I can tell you from experience that with the time involved with cracking your own tables etc on the 300, you would be WAY ahead just going with megasquirt.

I've messed with factory EFI computers before, and it works... eventually. It's just a much huger PITA than the aftermarket ones.

so unless you see 0xff and immediately think 255, I would stay away from that option.
 
Strange Ranger, I agree that is a good site. About the best I've found for genral info on the Ford EEC-IV's. My next book purchase is Charles Probst (sp) 88-93 Ford Fuel Injection.

Bort62, I may not translate hex in my head but a translation routine isn't beyond me though.

Seriously, I will eventually have to use aftermarket for ease of use. But the Scotch in me, genetics not liquor, hates to throw away something that can do the job for lack of tools to talk to it.
 
SR_Crewchief":fiajyub9 said:
I was hoping that since with relatively minor changes to the intake and exhaust the gas versions could step up to moderately larger carbs the same principal could be applied to EFI.
Click to expand...

Only if measures are in place to determine volumetric efficiency. That is why everyone went mass air.

What you are theorizing isn't possible with a simple speed density system.
 
so heres a question, ive seen the 5.0, and 5.8L mass air conversions. is it possible to do the same deal to the 4.9L? the 5.0-5.8s use a basic mustang computer with factory mass air...

whats to say you couldnt find an oddball 4.9L that came with mass air (ive ran across one or two) and convert an older style (like his 88 or my 89) to mass air. Id love to do some of the mods he is talking about, but i have to smog my truck also... you guys can just slap me and tell me to shut up too. :lol:
 
AFAIK the only MAF processors for the 4.9 are from the '96 which means they are OBD-II and therefore incompatible with 95-down wiring harnesses and sensor arrays.
 
Damn!!! I hate it when I have forehead contution moments(some people call them V8 moments). Strange Ranger/Linc's 200, it dawned on me this afternoon(while shovelling...) what I was truely overlooking. And SR your did try to tell me and I was too dense at the time to understand it. The MAP sensor is telling the PCM a volume of air is being delivered that is actually segnificantly different that it expecting based on TPS feedback. Which is most likely out of range of what the HEGO feedback can correct for. I was considering only 2 of 3 critical criteria for the computer to deal with concerning the air charge and fuel delivery. As I said in the original post, I was overlooking something obvious. Thanks for the help getting my head around it.


svt150j49

Someone over on FTE, I forget who, did use a Mustang MAF EEC-IV(A9L program code I think), bits of the wiring harness and a Tweecer to convert a 4.9.

As far as MAF 4.9 PCM's go... 95 California 4.9's had EEC-IV MAF/SFI suposidly, and all 96's had EEC-V MAF/SFI. If you can find a 95 Cali PCM your doing better than I have. And the consencis I've come across is to stay away from using a EEC-V to convert from an EEC-IV, it's a whole different animal.
 
When I swapped the '97 explorer 5.0 into my '93 Ranger, I converted it to OBD-II. I had never swapped an efi engine in my life up to that point. It wasn't the end of the world.....it isn't rocket science by any means. Knowing what I know now, I could probably do a post - '95 EFI swap into nearly any vehicle. You just have to solder a BUNCH of wires before the end is in sight.
 
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