well folks, it looks like the TBI thing just may not pan out for me. I can get the car running great everywhere, superior to the carb in every way... except at 5200 rpm plus

Ive tried everything, Ignition is perfect, same spark map as what i ran with the carb, i even upgraded to an MSD.
Ive retarded the timing
I bought an open plenum spacer, 3/8"

Ive played with the AFR.

Basically, sotp its obvious, it hits a strange sour note at 5200, clears up slightly and then gets bad again around 5600 (sotp observances) it then clears up somewhere north of 5800 and feels normal.

when it happens its most apparrent in third gear and almost feels like im tapping the brakes a little bit

The AFR goes from being rock solid to fluctuating around .3-.5 and the car just runs like crap, probably down 30-40 hp.


I havent been able to do a plug pulling run and in order to do that in this area would be kind of hard. Regardless, i think the fuel may be slamming into the manifold floor at high rpm, engine runs sour and reduces the airflow, then fixes itself, airflow increases and repeats the process. It also happens to be where my fuel demand peaks in my fuel map so theres definately alot of fuel coming out.

I have a victor junior i can swap to but in order to do that I need to have it decked to matchup with my milled heads and such. Alot of cost and work and the improvement is still theoretical. Maybe its nothing to do with that, I dont know.

Im probably going to switch back to carb and maybe get a dbl pumper to fix my launch woes and be done with it unless someone can come up with any ground breaking ideas.

I just picked up an 11 second T type that is demanding attention at this point and its kind of hard to ignore sport bike performance with doors its begging for alcohol injection among other things.

anyways, there may be a possibility that I will be selling my tbi goodies off if I do end up going back to what I had setup so keep your eyes peeled

Pablo

 

What is the injector PW at the troublesome RPMs?

RBob.

 

I dont know, i havent logged that.

They are not static though as i can make it run at 11:1 easily if I wish (if that is where you are going with that)

 

Or approaching static. Usually the highest DC% is lower then the peak engine RPM. This is caused by the VE dropping off even though the engine is still pulling. So the injectors could be going borderline then as the RPM climbs the DC% drops.

The airflow into the plenum floor can be a problem with small 2-bbls. With the large TBI unit I don't know if the air velocity would be high enough to cause problems.

When you changed from the carb to TBI was the fuel pressure regulator routing changed? IOW, is the TBI unit fed first, then with the regulator after the TBI and before the return line.

What happens if the throttle is slightly lifted during the problem area.

RBob.

 

Which is the preferred fuel routing?

 

For FI, as mentioned: from fuel pump, through filter, into rails/TBI, to the regulator and back to the tank via the return line.

This is required for several reasons, vapor & air purge, injector surge, etc.

With a carb setup and an EFI fuel pump the carb gets dead-ended off of the feed line. There is no 'through' path in a carb (and none required). So the feed goes to both the input of the regulator and the input of the carb. The regulator then just returns excess fuel.

Upon a switch from carb to TBI it is too easy to just dead end the TBI off the same routing.

RBob.

 

I had a similar problem way back when. Except mine would run fine sometimes, sometimes not. I'm talking full throttle blasts within minutes of each other.

Try a lb or 2 more fp and bump down the bpw and see what happens.

 

its dead ended

the fp is at 20

bpw is 68

the problem is pretty consistent, I may be hallucinating but it seems less severe sometimes in the first WOT run while the car is still somewhat cool but not cold

when i mean less severe i dont mean that it doesnt take as much power away what i mean is the rpm window that it runs bad in seems to shorten

 

whats your wideband saying when it stumbles? lean or rich?

total advance at the point it stumbles? after and before?

I've felt this same thing before at less rpm when the car is just started and run from cold... "tapping the brakes" feeling.

 

i mentioned above, the afr goes from a rock solid number to fluttering around .3-.5

doesnt matter too much where its at so long as its not too low or too high to just run crappy on the basis of a bad afr,
seems like anything from around 12.5 to 13.0 and it can flutter from 12.3 to 13.2 so its actually a bit more than .3-.5 but i would say its mostly in that range

spark advance is the same as it was with the carb (that ran the times in the sig)35 deg. total. ive also tried retarding the timing and there was no improvement

I tried letting off the gas a little while in a third gear run at that rpm, didnt seem to cure anything, may have even made it worse. Hard to tell since the powerloss isnt so blatant, its there though, makes me want to shift at like 5200 rather than 6 which is what I used to shift at, the engine note changes distinctly too, the sound follows the feeling, of the on at 5200 and then off for a split second, then back on again.

 

youre using the 7747 arent you.... ? I think I remember you saying you made that swap a while back.

anybody else having the same problem with that ecm in that higher rpm range. This ecm wasnt really designed to work that high was it... do the tables go that high, i cant remember... been a while since i looked at tuner cat.

 

The VE table tops out at 3200 rpm, but the adder table goes up to 6400 rpm. I guess it would be enough control for WOT at high rpms, but it leaves a bit to be desired as you dont have total control of fueling at every point when your off the end of the main table.

 

Pablo, you say you're dead ended with the fuel pressure at 20psi, why not try a stiffer spring in the regulator and boosting it up even higher. There are a bunch of guys running pretty high pressure solidly. I know jon prevost is running about 28psi IIRC.

 

How can you be sure that the FP is at 20 psi, and always 20 psi for every rpm & load, if the fuel line is dead-ended (unless I am mis understanding the fuel set up)? The carb setup can be dead ended because the needle valve inside the carb will shut the fuel flow off if/when the fuel bowl is full... and when the happens the elec fuel pump isn't really doing any work (it's like covering up a window fan with a sheet of paper).

If there is no fuel return to the gas tank, then the regulator cannot function as intended and I don't think you can be sure about 20 psi. And based on simple math, 20 psi FP is borderline low for supplying enough fuel to make 310 fwhp nevermind more than that.

You should be able to match the carb performance, at least to the point where the dual bore TBI runs out of airflow (near the equivalent of 310-330 fwhp) and with smoothness at all rpms so Before you give up on your TBI, I urge you to (A) replumb the fuel system so that there is a return line to the gas tank and (B) try raising the FP as BronYrAur suggests.

 

yeah, I think you misunderstood what was meant by dead ended. There is still a return, go look at how your standard 3 port external regulator works and you can see what is meant by dead ended the way rbob is talking about it and the way its setup on my car

 

I kinda ran into the same problem when I was trying to get enough fuel to feed my motor. I was going so static the engine would litterally just hit a wall and throw me forward. As I got closer it would just kinda surge (kinda like the brake tap thing) and then I would only see the oil pressure waver. Once I got is just right the oil pressure quite wavering and it pulls much harder now. You really need to spit your PW out and see whats going on with them, I bet your getting pretty close to static in that range.

 

i think you're running some big **** injectors, i think you said before, not here but.... so i cant imagine you're going static... or getting close...

did you do the vac adjustable yet? i bet if you can get a higher fp at higher rpm you'd be ok...

 

if i were running static and it was affecting my performance because of it i would go lean. I know this because with the stock injectors i was going static. I then purchased the "90" lbers which now are like at 100 since they are at 20 psi which should be good for like 350 hp or some such nonsense.

My bpw is 68 and my ve tops out at like 83% at 5600 with a commanded afr of 13:1,

I assure you, i am not static, im not sure its even possible to go static with a BPW of 68. If I wanted i can drown the car in fuel all the way to redline, i have, ive run it down to about 11:1.

I had hopes that this was gonna work out as hypothesized but unfortunately it didnt. I was wrong, and believe me I tried alot of things. I took it for one last spin today with the TBI and sure enough its still doing it even with the afrs hovering around 12.7. I decided I had enough of the guessing game and converted it back to the carb.

All i did was take the tbi off, lower the FP and bolt the carb on, same chip, everything. The power is back, in a big way, i had forgotten how rediculously quick the car was and its all 4500+. I could still use a dbl pumper as im not getting enough fuel on the gear shifts and launch, but its still fast as hell.

The 305 can be a mean SOB when built right.


Anyways, thats all I have to say about that.

 

A few quick calcs puts the duty cycle at over 100% given your VE and BPW. Cant say its entirely right since its just a quick plug into the calculator to get an answer. None the less, I think you really should have datalogged the PW. I suspect that there may have been the posibility of a surprise as to what the actual PW would have been. Teh TBI injectors fire twice as often as regular MPFI injectors, the pintle in them is really heavy, and the spring that returns it, at least in the ones I took apart, is really cheesy.

There was a post on a gn board a while back showing the flowrate vs. PW of an mpfi p/h(?) injector. At higher pulsewidths, the flowrate actually went up before returning to the static flowrate of the injector when it went static. This shows that the pressure region that forms behind the pintle when it touches down on the seat hasnt had time to disipate yet by the next injector firing. The injector tested didnt seem to mind it much but I dont know about a tbi injector. At high pulsewidths I suspect there isnt much control over the pintle but I cant say for sure. All the more reason to flowtest a set at varying PWs and pressures to see what really happens.

 

Pablo, if you send me your bin, I'll be able to test run it and see what the pulsewidths really where. email is dimented24x7@aol.com

 

sure, ill email it to you tomorrow im about to hit the sack

like i said, i could get it to run extremely rich all the way to 6 if i wanted, and besides, the afr was int the upper 12s when it ran crappy, afr is afr regardless of how the fuel got to the sensor I would think.

Also, consider that 90 lb injectors at 20 psi being static would be a LOT of fuel. Im running a 305 not a 454

 

Pablo,

What size carb you runnin?

 

Holley injectors?

 

600 cfm edelbrock 1405

the injectors are GM 90lb injectors