This past weekend a dyno test proved to me that my stock TBI 55lb/hr (yes, the infamous 40's) injectors would not cut it any longer. . . They were going static as low as 3800 RPM's . . .if you consider anything 85% DC static, then it might be as low as 3600.

Excel file here : Warning dont look if you've got a weak stomach !! those injectors were close to locking and burning -- exceeding DC's of 130%

Ran some calcs on the numbers I got and figured 85 lb/hr should keep me free and clear of that problem. So I ordered the advertised 75lb/hr injectors from turbo city . . . due here this afternoon. Plan to run them about 17-18 psi.

I intend to modify the bin by changing base pulse width, and re-tuning the lower VE table.
Are there any other tables or changes that I might look into making ?

 

Actually, thats better then stock. In my stock cal. they had the injectors skirting static after around 3600 rpm. Most likely done as a trade off for reasonable PWs at idle.

 

. . . thx, I needed to hear that -- so, can you think of any other tables or values I should look into changing besides bpw or the lower ve table ?

 

The BPWc should probably cover most of it. Tailoring the main VE as well as the extended VE adder values above 3200 rpm should cover for any inconsistancies.

 

AE is affected by injector flow rate. It is not affected by the base pulse term.

RBob.

 

oops.. forgot about that. You may have to change how much TPS and MAP AE PW you have to get it not to bog down when you tip in.

Edit: The AE added in with the IAC might have to be looked at as well. I had throuble with my car wanting to stall when the IAC started opening. Too much gas.

 

Some codes have a base PW for cranking.
If you run a cold plug, it might be of concern, if you have an initial richness, when the engine first lights, you might need to shorten it.

 

At the time of production, idle emissions testing was a high priority. Also early TBI was probably designed with a lot of fail safe options like flirting with static injectors to get the best control of idle fuel. Personally I've been very happy with my ??# injectors at 28psi. The idle is smooth and it does take a bit of movement of the 0 and 400rpm VE2 table values to make the idle lean or rich in open loop. Closed loop it's even harder to get it to go too rich or too lean , I wonder why.
Adam, try a lot of fuel pressure and don't look back. Yes the tuning of the VE table will be course but by no means will it stop you from getting the AFRs the engine wants/needs. It might however stop you from getting 128BLMs across the board, that's one thing I've just given up on and settled for closed loop BLMs between 124 and 132, lol. This brings up another good question but I won't hijack this thread.

 

??
A static injector at idle will have raw gas dripping out the tailpipe.
Even at 100% VE that's just metering fuel for 100% cylinder filling of air at X RPM. 14.7 at 600 RPM at 100% VE, isn't much fuel.

VE isn't to be confused with DC.

 

We can resume changes for larger injectors?:
(It depends of codes)

1.- VALUES:

- Injector constant
- Injector flow rate
- Idle fueling BPC
- BPC for N-Alpha fueling
- AE
- BPW for cranking

2.- TABLES:

- Injector constant v/s EGR airflow
- VE tables

Other opinnions??????

Denis V.

 

I was trying to imply that they were trading off idle pulse width control with static injectors at high RPM high load. Not that they were static at idle.

 

Hello,
I'm about to upgrade my Injectors so I'm trying to get a handle on what actually is my Injector constant and what I need to change it too. Ive seen you need to change this in various posts when you change your injectors but I don't have any such constant in my bin called "injector constant" so apparently it must be called different things in different ecm's or different ways of looking at your bin, but I'm not certain.
btw I'm using Tuner Pro
746 ECM $61

From what I gathered the "injector constant" was the BPW constant but after reading this post I'm now not so sure.
My BPW Constant is 134.0

If I upgrade from 55lb to 85lb injectors is that what I need to change? and what should I change it too?

I'm about to put a new 350 crate egine in and I would like to get it close before I start it up.

thanks

 

yes, im am almost certain injector constant and base pulse width constant are the same thing.

theres no way anyone will tell you what these numbers should be. For instance you say you currently have 55'ers . . . well at what psi ? and how about for the 85'ers ? Tubo City rates thier injectors at 15psi -- but stock our cars can have anywhere between 11-13 psi . . .

if you read this post you would already know what else besides bpw you might need to change.

im still pretty green at all this but my calcs would go like this:
(old inj const/new inj const) * current bpw = new bpw
(55/85)*134 = ~87
now do a calc for the increased displacement
(new cid/old cid) * bpw = new bpw
(350/305)*~87 = ~100

- shoot me down if this info is wrong.

 

"J" how are you able to run the injectors at that high a fuel pressure?
I think my GM 1985 pump was measured at 19 lbs max b4 injector. are you using a walbro? what is the pressure at which the injector fails ? i see 80 and 90 lbs GM injectors mentioned. maybe the 85 lbs referred to is Holley or TC. I did blow a new FPR diaphragm with GM VAFPR at startup at high initial FP. still dont know how it happened. TWICE. I assumed due to high FP induced by that reg when i rev'd engine in neutral.. now i have aeromotive reg so maybe better suited for high FP.

 

Ronny, I had the Holley injector pod and the spring was only good for 16psi before bottoming out. So I asked my friends father that works at Princeton University if he had a some closed and ground springs I could borrow. I was shooting for 25psi but when I installed the only spring that was big enough, it went to over 30psi, so I had to remove the adjustment shim which gave the spring a little more height/room and got it to 26-28psi.
Yeah, I have a walbro 255lph pump that's good for about 800hp at the fuel pressure I'm running, lol. Yeah it's big but my stock pump was dead headed at 11psi, the regulator wasn't letting any fuel into the return line. The stock pump is just THAT pathetic.
I like the higher fuel pressure because it gives a better fuel mist and I'm able to run VE tables that aren't at 100% in the 80kpa low engine speed range, lol. Obviously these injectors aren't as big as I thought so I've had to use fuel pressure to crutch it into working for me.
I don't see these injectors failing because they're delphi units, not the crappy Chrysler injectors they had used >5 years ago. I bet these injectors could go to 40psi without a hitch (other than strain on the ecm injector drivers). The GM injectors were tested to operate at 50psi!!!

 

Thanks everyone for all your help and suggestions.
This is exactly where i am after a few weekends of getting the idle and part throttle tune back to 128's.
If I quickly depress the pedal to about 50% tps with the stock AE vs. Diff TPS values I get a momentary bog -- too much gas ?

Accel. Enrichment vs. Differential TPS
%TPS / usec Added
0.0 = 549
3.1 = 610
6.3 = 854
9.4 = 2197
12.5 = 3906

If I use the same values as I was with my 55lb injectors I get a bog that almost stalls the engine. -- way too much gas ?
0.0 = 977
3.1 = 1953
6.3 = 3906
9.4 = 5859
12.5 = 7813

If I reduce the stock values by 33% I get a pop from the TB. -- too little gas ?

Am I right in thinking that the 'magic numbers' will be somewhere between the stock values and the 33% diminished values ?

 

your ae/tps table only goes to 12.5%. so i will assume it is only practically functional for small TPS changes. i made error thinking for some stupid reason it went beyond 12.5%. anyway in my tunercat it shows 0-12.5%. as a result i went overboard on AE/TPS. my stumble was cured by adding at ae/map. i had both ae/tps and map at about 250%. so i upped the aemap to 275 and then 300% and all is well as far as pedal to metal load on engine. the small adjustments(50 mph to 60 mph) caused a stumble but that was cured with ae/tps. the final issue was the PTM wack on throttle or standing stop smoking rubber that the AE MAP cured. for whatever reason i needed triple stock bin or 150% depending upon the starter bin i looked at. i bet you are too little gas based upon my issue but i am no expert.

 

At 0x220 in the prom there is a %TPS threshold to double the AE term. I found on mine that it caused a vicious momentary bog when I opened the throttle past 50%. Try setting that to 255 and see if it still bogs down. I havnt tried my car yet with that disabled (car doesnt run too well when its in pieces) but I suspect itll probably solve the bog problem.

The momentary bog may also be a sign that there is too much TPS AE. Ive found that I at least need some TPS AE to avoid momentary hesitation but too much will cause it to bog since both the TPS and MAP AE may be too much when theyre added together.

 

oh, as for the TPS AE, youll only use the first two cells since its %TPS change over a very short time. Ive seen from datalogs that ts possible to get to almost all the cells but you have to be intentionally trying to.

 

i think my situation was a bit different due to mods. i could flow a lot of intake air quickly and the xram plenum confiscated much of the pumpshot on plenum walls. car runs much better as far as AE when plenum is heat soaked(ie. summer use).

 

you called it
I changed the %TPS threshold to 255 and it really helped. no more bog when i punch it.
can you explain this.
if i make a tps change larger than 13%, wouldn't the ecm use the value associated with the 12.5% tps diff ? why only use the first two cells.

 

The 8746 ecm uses the current tps as well as the previous tps value that was stored on the last pass through to calculate the delta %TPS for the lookup. The ecm cycles through the fuel loop 80 times a second so there will be 12.5 milliseconds between the two tps values. The current value - the old value is the delta tps, but since theyre so close to eachother in time there wont be much of a difference between the values so there will only be a small delta TPS for most throttle openings. In order to get to anything more then the first two cells, you really have to be trying. Unless you have a very bad temper youll never really use more then those first two cells on a throttle opening.

 

Dim, nice find, I never even looked at that threshold. I read it but never bothered to do a search for it in the code . I'll have to try the same thing and see what results I get. I've tuned everything on the car so well but at really low RPM the throttle responce isn't perfect, this might be the issue.
BTW, here's the code;
Location LD220 is the %tps, 128 = 50%

 

recently wired a WBO2 to aid in tuning. . .
heres a screenshot during a few quick pedal depressions over a thirty second time period. Initially this looked to me like the mix was getting quite lean before the ecm 'caught up' and added in the AE. The AF ratio would then dip way down to ~12 then come back and then run way lean for a moment or two before returning to 15's. But the RPM's seem to be really lagging. . . major changes in AF ratio and TPS but RPM's seem to be only affected minimally ?

Does this graph look like correct behavior ?

 

Stab the pedal and hold it there rather then just letting off while doing a log. Youll get a better picture of what its doing at higher loads. Jsut as an observation, I noticed that without any TPS AE my car would just about shut down momentarily after I hit the gas. A lean spike as soon as you hit the gas may be caused by this. Just a guess but thats what I observed, anyway.

 

I thought I would try to resurect this rather than start a new one.

My 90pps injectors have been in about a week and so far I have just been working on idle in fuel table one. Slowly I have increased idle AFR from the 11AFR range to the 13AFR range although it does fluxuate quiet a bit.

Drivability is very good but I still have to work on rich blms at cruise and wot AFR which is now in the 10AFR range. (runs good at wot though)

I notice in reading this thread that my 8746 does not have PW for cranking, or injector constant vs egr airflow etc.
So I am going to work with fuel table 1, fuel table 2 , AE vs TPS and AE vs map.

Jon, grumpy, rbob, dimentented et al, given I have the 8746, are they any other tables I should consider specifically related to the injector change?? especially as it realates to rich idle and AFR fluxuation at idle?

I noticed that I do have a bpw constant VS vaccum egr but don't if that will help with any of this.

as always ,thanks again for any comments..................bob

 

Proportional gains. They are PW based.

RBob.