Hi guys,

The car feels good and strong on boost. But the wideband tells me it is at best 12.9:1 AFR and usually a solid 13.5 at WOT.

I am running Bosch 19lbs injectors
New Bosch in-tank fuel pump
Additional Procharger supplied in-line fuel pump
Supplied FMU

Its only 8 psi of boost on a 2 core intercooled P1SC.

I can't read fuel pressure yet but did wonder if the FMU just wasn't pressurising the lines enough?

Like I say I can feel no spark retard, it runs really strong.

I have my base timing at 4 degrees advanced. If I drop it to 0 degrees will that help richen it up?

I have the 305 btw. With big cam.

 

you'll want to check the ratio of fuel pressure added per lb boost on the fmu and monitor fuel pressure to make sure the pumps are keeping up

 

I have the FMU providing max pressure- all the way screwed in.

 

What's the gauge show at WOT under boost?

-- Joe

 

13.5 AFR and it drops to 12.9 just when I lift off.

 

No, the fuel pressure gauge.

-- Joe

 

Don't have fuel pressure data just yet, I did mention.

I did notice that the FMU vacuum source is Teed from the HVAAC source- could that be an issue as it should be a dedicated source right?

 

the FMU should be all by itself and you have to get the pressure gauge in before any more WOT pulls don't want to hurt anything by leaning it out

 

No one has an issue with the 19lb injectors and 8psi boost? Lol even with an FMU I think they are a bit small and your prob maxing those out. 19s are stock for a 305 and 21ish for the 350 which didn't make a ton more power and we're talking 205 vs 225-235 difference. At 8psi boost even at 200hp stock 305 which I doubt yours is stock if you have a big cam in it that's 40% more hp so your at say 280ish for ***** and giggles.

U need a fuel pressure gauge and that should have been on it from the start. Need to verify FMU is working and should be on its own line from the intake or charge pipe. Can you verify injector Duty cycles?

 

8 psi on a decent 350 will be 320 whp easily well within 24's and 19's at high pressure from fmu can work

But i'd check fuel pressure for sure

 

No. 19# injectors will handle 300hp at 43.5 psi. He's running an FMU, and the booster pump.

Knowing his fuel pressure would tell us if the pumps were failing. More than likely his problem is his tune though. But I always try to rule out defective components first.

-- Joe

 

Without knowing fuel pressure you can only speculate, but even a substantial increase in fuel pressure won't compensate for a modified engine with a kit specifically designed for a stock application, so the bottom line is you need more fuel. Most P1SC users see 75-psi at wide open throttle with the provided FMU, and that is 20-psi over the stock fuel pressure regulator at wide open throttle. Using 19-lb injectors, the injectors flow rate essentially increases to 22-lb's. You are also seeing approximately 7.5-psi of boost pressure, that is about 50% additional power over what you are making naturally aspirated (assuming ambient temperature), so if we speculate that your cammed small block is making 225 horsepower naturally aspirated, at 7.5-psi it would place you at approximately 337 horsepower...

This is where your fueling and fuel pressure comes into play. Using a .60 BSFC, you would need 26-lb injectors at 80% Duty Cycle to compensate for 275 horsepower, and 22-lb injectors at 100% Duty Cycle to compensate for 300 horsepower. Using a .55 BSFC, you would need 27-lb injectors at 80% Duty Cycle to compensate for 320 horsepower as well as 22-lb injectors at 100% Duty Cycle for the same 320 horsepower. To reiterate, your 19-lb injectors should now be flowing 22-lb's with the 20-psi increase in fuel pressure with the FMU at wide open throttle, so it should be just enough to cover 320 horsepower, however if your cammed SBC is making 225 naturally aspirated, and if your are running 7.5-psi of boost pressure, you are now making 337 horsepower, assuming ambient air. You are right on the cusp so to speak...

 

Hi guys,

Well I went ahead and ran a dedicated vacuum line from the rear most barb on the plenum to the fmu. I thereby just left the hardline that runs to the hvac.

Went on a run and I am now hitting a constant 12.5, sometimes even lower so looks like we have found the problem!!!

They do stipulate that the fmu runs from its own source of vacuum and now I guess I can back that up. I also wonder if I have a vac leak at the hvac controls contributing?

Thanks so much for all the replies my blower friends, really appreciate it!

 

Right now we're all guessing and assuming. He needs to be able to record his fuel pressure, his injector duty cycle, and tell us more about the engine.


-- Joe

 

Thank you for confirming my thoughts. He has to have maxed out his injector at this point. Even as fuel pressure increases flow decreases... most likely his stock fuel lines dont have the volume to compensate for the higher pressure reduction in volume. 70psi in a 3/8" line is not the same as 70psi in a 1/2" line. And 70psi has got to be tough on the injectors trying to close it off. Since your essentially 30psi over stock or almost double the injectors are designed for.

I doubt the OPs 305 is making 225hp... as the stock 305 TPIs were making 205ish and he def has a cam... a "big Cam" might have actually hurt power and bled off some boost but I would suspect it was matched kinda for the motor.

To the OP, you need to verify all the specs were asking and i would look into pricing out some 28lb injectors. Even if your system is working perfectly your injectors are maxed out and you won't want to run them higher than 80% DC.

 

Why not?

-- Joe

 

Try running a line straight from the charge pipe/intake to the FMU. Either way 12.5 is a bit lean for boost. Your wanting 11.5ish - 12:1 to be safe.

I think your going to find out that your injector DC are going to be very high and you should be changing them out for something larger. The FMU is a bandaid for an inadequate fuel system. Once thats working correctly then your going to verify fuel pressure and then look in the ECM for injector DC... 3/8" hard line is not going to be a restriction at these power levels and either are the fuel fails. So all thats left is fuel pump and injectors that have to keep up. And boosted 300hp always requires more fuel flow than 300 NA hp.

 

Over heating. Recommended fuel injector DC is 80% max... anything higher and they spend too much time open and they will overheat. More importantly as the heating can be an issue the main reason is that they can't meter the fuel properly at anything higher than 80%, think of it as valve float, never really closing or fully opening. If you cant meter the fuel then they aren't doing there job. Essentially a 100% injector is more like a carb jet or just an office for fuel to pass through. Once you get past them getting hotter than they should, and not being able to meter fuel flow anymore you have to worry about the windings inside failing being open all the time, if they fail the they slam shut and kill all flow. Since the injector is basically open constantly at 100% then that also means your can't increase flow or add more fuel and flow is based solely off fuel pressure. So the ECM can't richen the mixture if the injectors are maxed out, so a boost spike etc could be catastrophic.

What do the terms “static” and “duty cycle” mean?
An injector in an engine turns on and off very quickly to control the amount of fuel delivered. The amount of time an injector is turned on and delivering fuel is known as the duty cycle. This is measured as a percent, so 50% duty cycle indicates that the injector is held open and held closed for an equal amount of time. When the engine needs more fuel, the time that the injector stays on (its duty cycle) increases so that more fuel can flow into the engine. If an injector stays on all the time, it is said to be static (wide open, or 100% duty cycle). Injectors should not go static in a running engine. If an injector is static in a running engine (open 100% of the time), that injector is no longer able to control fuel delivery. This could be an indication that the injector is too small for the needs of the engine. Injector duty cycle should usually not exceed 80% in a running engine at any time.

 

This is great advice, thank-you. The whole reason for going with the 'kit' is so I wouldn't have to run a new chip and bigger injectors. If I fitted say 24lbs injectors I would definitely need a chip right?

This would have been easy when tuned performance was about- who can help on that front now?

 

Larger injectors isn't a huge problem. Basically need to change the injector sizing in the ECM so the ECM knows what injectors are flowing. Other fueling issues will most likely have to be changed in the ECM as well but maybe not. The DC of the injectors will be off as the fuel flow at the same injector cycle is different as one is flow a higher amount of fuel at any given time. Most likely swapping to 24 or 28lb will richen you up alot just about everywhere. While 24's would give you a bump in fuel flow I would suggest going a bit higher to factor in a margin of safety. Perhaps a 26-28lb would be a better choice and allow a little room for growth.

tuning you can do yourself as any mail order tune won't be perfect for you application and the tuning stuff is cheap considering the price of tunes. But its trial and error and a learning curve on your part.

Honestly if you swapped your 19s for 21s and didn't touch the tune it would richen the whole tune up a little but prob not need any real changes. But your still at the very high end of the injector so to do it right would be to upgrade to 26-28s and have it change in the ECM.

 

Thanks Custom. Something like these- http://www.southbayfuelinjectors.com...uel-injectors/

 

Sure, make sure they come with the adapters. But you need to figure out everything before you purchase injectors and verify they are actually maxed out. Once you verify fuel pressure isnt dropping and the FMU is doing its job you can check injector DC and then make the call on the injectors. I would see if you can use a calculator to figure out how much HP your making with your mods and the boost. Then get a estimate of how much injector your going to need. You might honestly need a 26-28 due to boost, boost HP always requires more fuel. Check out Fuel injector connection. IF you call and tell him your mods and a power estimate he can spec you a set, flow matched and ready to go. I recently just got some 72lb flow matched Bosch for my 5.3 Supercharged build.

 

That's not true or possible. Here is the deal,and injector is a solenoid. It energizes and opens, and then it closes when power is removed. Duty Cycle is a calculation of how long it is open vs how much time we can be open for a given RPM.

The injector has no idea what it's duty cycle is. The duty cycle number will be different at different RPM's. For example: On a batch fire Delco ECM at 6,000 RPM we have a 10 millisecond window to fire the injector.

At 3,000 RPM we have a 20 millisecond window to fire the injector.

If the Injector is open 10 milliseconds at 3,000 RPM it is at 50% duty cycle. If it's open 10 milliseconds at 6,000 RPM it is at 100% duty cycle. Will it magically overheat at 6,000 RPM because it's at 100% duty cycle? Even though it's opened for exactly the same amount of time per minute?

You see how silly that sounds? Yet this myth gets repeated over and over on the forums.

No, it has absolutely nothing to do with that. It's because as Engineers, we're taught in school to design everything with an 80% duty load with a 20% overload reserve. Be it an injector, a dedicated circuit for an air conditioning unit, whatever.

And the analogy of valve float doesn't make sense either, because again the injector doesn't know anything about duty cycle. If I command my injector to open for 15 milliseconds at 6,000 RPM it simply will continue spraying fuel into the next ignition firing event. Logically speaking this shouldn't happen. Once the injectors are static (on), they won't turn off until the commanded open time is less than the available firing window. If you go static and continue to increase RPM you'll see the AFR get leaner as RPM's increase.


With that said, his injectors may be too small. Still don't know how much power it makes.

-- Joe

 

He doesn't have a "big" cam. I used to have that cam and it is pretty mild. It's the biggest smog legal cam for a TPI engine.

 

Thats fine, Now to use your math above in the actual formula to calculate DC your not exactly correct.

3000rpms with 10ms pulse = 25% DC
6000rpms with 10ms pulse = 50% DC

But I get what your trying to say, as rpms increase at same pulse width it doubles at double the RPM. The difference is the amount of time that the injector pulse has to fire within a shorter amount of time. At 3000rpms your engine takes 1500 complete firing cycles, at 6000rpms it takes 3000 cycles but the time frame does not change as its still all done in 1 minute or 60 sec. So the injector has to fire the same pulse width but more often in a much quicker time frame. Thus the pulses become so close together at 100% that its effectively wide open all the time. I think what your forgetting to see is that the firing becomes so close together due to the decrease in time to fire that it maxes out and basically hangs open.

Heres a nice little graph to show you what happen as the duty cycle gets maxed out. ( see attached GIF)

Once the injector is maxed out in DC there is nothing the ECM can do to compensate for additional fuel flow and the injector becomes essentially a carb jet, any increases in flow will be directly attributed to the fuel pressure/volume in the lines.

Maybe you miss understood my valve float comment, valve float is when the valve is never fully closed or open... and it kind of just floats between. The Injector wont "float" but it will fire so rapidy that eventually the time its commanded to be open will exceed the available time and thus will just stay open. Thats exactly what valve float is as the valve doesn't have enough time to fully open and then close before its opened again and again and again before it can fully close. Same principle of not enough time but valves use springs to close and thus its called "float". Once DC has reached 100% it never closes and thus is spraying all the time... hence my comment about it being like a jet vs and injector. AT 100% the injectors are open constantly and thus all injectors are spray fuel 100% of the time until pulse width is lowered and their is sufficent time for the injector to close.

What happens when you spray fuel 100% of the time into the next ignition event? Their is possible for self detonation if the plug is hot enough or possible firing in the exhaust etc. None of that is good and a good reason to not have injectors at 100% DC.

Why does a injector at 100% (static) go leaner as you increase RPM? Because the ECM can not control the injector to adjust fuel flow, you have maxed out the ECMs ability to regulate fuel and have exceeded the ECMs ability and injectors ablity to TUNE! Again at 100% DC Static fuel delivery is solely based off fuel rail pressure and volume which is why it leans out as there is no more fuel that can be "reserved" and then added to richen things up.

Its physically impossible to run an injector past 100% DC. Once its fully open "static" the injector is no longer an injector but a "jet" and office for fuel to pass through based on pressure and it being a liquid. Jets are more efficent as pressure is introduced. So increasing pressure at the fuel rail will allow the same injector to push more fuel at a higher pressure. But Fuel pumps decrease in fuel volume as pressure increases. So while his 19lb injectors at 70psi are flowing a calculated 24lbs that doesnt mean that his fuel pump can support the increased pressure and volume. Only way to tell is to put a fuel pressure gauge on where he can see it while doing WOT pulls. If fuel pressure drops then his pumps are also inadequate. ANother thing to consider is that while fuel pressure is at 70psi in the rail that actual fuel pressure is more like 62psi since the 8lbs of boost in the engine is effectively pushing back on the fuel what ever the inside engine pressure is.

Solenoids can overheat, and thus not work correctly or even reduce life considerably. The nice thing about fuel injectors is that they have cool fuel running through them which is a great absorber of heat but couple that with high engine temps, higher than normal IATs from the supercharger and possible fuel heating/vaporizing from the super high line pressures and its possible that they could get hotter than they should. While Ive never seen an injector overheat, it could be why some fail quickly... I would have no way to figure out to tell but I dont like to run electronic devices beyond what they are designed for. Especially something that is as important as the fuel injector on a boosted motor.

Bottom line... you can run injectors at 100%. Is it smart... no. You should keep to the 80% rule so you have the ablity to properly tune/fluctuate pulse width when at WOT for changes. The OP needs more data to make smarter/more educated decision on whats going on. But I know hes going prob going to need injectors and then I would get rid of the FMU as they are just band aids for a inadequate fuel system. Make the adjustments needed for everything to run correctly while maintaining a safe margin for parts failures. Have the FMU fail under boost and kiss that motor and possibly the supercharger. $200 injectors seem like a bargain then lol.

So to the OP, if you verify your fuel rail pressure is actually 70psi at WOT then your technically running a 24lb injector. Then subtract the 8psi for boost and your actually seeing a 22.8lb injector. I would suggest a 28lb injector for your setup so your within the comfort zone for the injector DC. But a more accurate recommendation can be made by someone who sells the injectors. But looking at DC will tell you more accurately what the injectors are doing.

 

In the OP's original post quote "I have the 305 btw. With big cam." I dont see any cam specs so I have to take it how it is. Lots of people think that bigger is better for cams, and they like the "lope". But forced induction is quite the opposite. Hopefully its fine for his application... but I still dont see any cam specs.

 

The 2032 isn't big in comparative terms but big for a lil' 305-


Lift: Intake @Cam 301 @Valve 452 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 310 @Valve 465
Rocker Arm Ratio 1.50
Cam Timing: -- @ ---
Lift: Opens Closes ADV Duration
Intake --- --- 270 °
Exhaust --- --- 276 °

 

That depends on the firing strategy used by the ECM. On a batch fire TPI, using a '165 or '730 it's 10ms at 6,000 RPM. (the injector drivers are hardware not software like an MS, Fast, Holley, etc).

https://www.thirdgen.org/forums/dfi-...-strategy.html


I didn't dispute that. I said it would go static as it would be open into the next cylinder firing event. So if you go static at say 5800 RPM, and increase until 6200 RPM you'll watch your AFR go leaner as your RPM's increase. I never disputed that. I simply disputed the "overheating" statements related to duty cycle.

That's not actually true. This is batch fire. Think about it, the valves are at varying states of open/closed on each cylinder yet the injector is firing anyway. Again, I'm talking about the OP's application, not some fancy sequential EFI setup that has injector timing on a per cylinder basis.

This is 100% correct, but again we're assuming he's running out of fuel. He might be, he might not be. We don't know how much power it makes.

It depends on the design of the solenoid. Switching (turning it on and off) has the highest impact on the solenoid itself. The resistance is highest and it puts the most wear on it when it's commanded on from the off position.

As far as injector "Rating" by the manufacturer, I'd be more interested in seeing a document that specs total open time per minute than DC to determine if the injector is being overtaxed.


I have some accel 24# injectors I'd just give him if he was local to try, but again he needs to collect more data.

-- Joe

 

i had 30lb/hr injectors in my 305 with that cam and the procharger fmu maxed making around 11 afr under WOT with 11PSI boost

got rid of the FMU as i didn't like 90PSI fuel rail pressue.

 

Wow, interesting theories on injectors here.

1) Q: Why is it at 12.5 AFR and 8 PSI of boost?
A: Too small injectors: 19* 8 *.85 /.58 = 223 BHP max
Why: Stock ECM wants to control up to 85% duty cycle
and your TPI engine is only about .58 BSFC under boost.
Do Bernoulli's eqn to see that even an FMU can't fix the bad AFR.

2) Q: Where does 85% duty cycle max come from?
A: Nothing to do with heat. 15volts * 1 AMP = 15 watts per injector.
Fuel cools the injector......so longer open is cooler injector.
85% DC is from ECM control. The 1.5ms -ish open/close time causes
the 85%. It is actually better to go 100% when 85% is exceeded, but
most ECMs don't do this. And no, the spray pattern doesn' t change
from 85 to 100% dc.

3) Q: Is the FMU helping?
A: In your case, the FMU is trying it's best but you need more.
If you keep cranking up the FMU then you are going to max out
the fuel pump and/or cause the injectors not to open. Very bad.


Your injectors are too small even with the FMU. Plain and simple.

 

^^^^^ All True ^^^^^

Between the cam, headers, and exhaust I think it makes about 225 BHP N/A.

 

Stock injectors have 1.5 msec of dead time??

That's pretty wild. My siemens injectors are around .600 msec. I think my Bosch III's are .746.


The biggest problem I had with the stock delco stuff and large injectors was getting a reliable idle. On a blown or turbo car that needs 60lb injectors at 6500 RPM, might only command an idle pulsewidth of .800 msec at idle. Obviously if our dead time is just under or even over that we're in trouble.

Since I've gone aftermarket those problems are history.

-- Joe

 

It is a misconception that the injector alone defines the "dead time". The ECM ckt strongly defines the close time. The Megasquirt ECM guys took a while to get a ckt that had a decent close time and not destroy parts.

The GM ECM ckt is actually quite good and I like it better than the MS stuff. As for other ECMs, I don't know. Overall, it isn't just the injector that defines "dead time".
Have you actually measured the numbers you posted? How do you define dead time? Is it when the injector starts to squirt after the Drain has dropped low? As for off time.......Is it the amount of time for the MOSFET gate going low until the pintle closes?

I am not really big on posting actual times because everyone specs "dead time" different and it is injector and ECM ckt / driver dependent.
I bet if you tested you injectors with your ECM that they have a larger "dead time" than you think.

I have run 56-58 #/hr injectors on a stock TPI engine. Injectors that big on an old GM ECM doing batch fire will put it in single fire mode to get the PWs over 1.4msec. With a one injector driver ECM it gives a bit of a rough idle. Moving to a GM ECM with two drivers allowed for a alternating bank fire scheme which idles nice. Can't beat a set of new 58#/hr injectors for $100. Yeah, they are peak and hold but 1/2 hour worth of work and the GM ECM can handle. Megasquirt ckt still has a hard time with it due to the PWM scheme they use.

Sure, not everyone wants to play with this stuff and just plunking down $400 for some of the latest and greatest injectors is another way to go. With newer injectors and smaller moving parts they open and close faster compared to old designs.

 

This is interesting. With the 30 lb's did you do any chip programming?

 

i was running ford motorsports 30/lb hr. i do my own tuning so yes it was tuned for the cam and injectors, i'm now using 42lb/hr green tops, code59 and no fmu. 14# boost, 420 ft/lb to the wheels my motor is not forged so i shoot for around 11 afr to keep the cylinders cool

 

i have a paxton on my car 6psi all bolt on stock vette motor from a 91 car and 36 psi accell inj and stock ecm no tune makes 400 crank 336 to the wheel and i put this together in the 96 wkith zero issues if you want to make every little bit of horsepower then you would tune and i replaced my fuel system with a mallory external pump with return line and removed my factory reg as this was restricting my pressure and creating problems

 

All he needs is 42 pound svo injectors or bosch 3 and 255 lph or the new areomotive 340 lph and a custom chip and he should be good.

 

I never saw this reply.

Numbers on the injectors? No those are taken from the manufacturer.

As for the injector driver, the board I'm using uses a ST VND5N07 for the injector driver. I'm using high -z injectors. You can use peak & hold using the PWM logic however I don't think anyone does that anymore, most people use the logic-level injector output and use a dedicated peak n hold injector board.
The turn on time is 50 nanoseconds and the turn off time is 40 nano seconds.

Well, total dead time would be the time from when the software turns the circuit up until the injector is spraying, and the time in which the circuit is falling down and the injector closed. I suspect that's up to interpretation.

I think other than TBI guys, pretty much nobody uses that.

-- Joe

 

having melted my first motor trying to use the procharger supplied fmu and stock gm injectors a very very long time ago. I throw my 2 cents behind getting them out if there too.


it was my experience that the gm injectors do not like high line pressure. I should have known better, since few years before that I got my first adjustable fuel pressure regulator, and had it cranked up thinking I was tuning more fuel for the headers and cam I had installed. car ran good to me at the time. stopped after a long drive to get gas, and it wouldn't restart. just cranked over, ended up popping the hood and finding cranking fuel psiwas like 60 something, at the time iI thought it flooded, but turning the fuel down to 50 it fired right up and didn't need to clear out like a flooded car. I think the injectors just wouldn't open against that pressure while cranking. but was find running.
then when I put the fmu on it, I got the same thing a few times but at wot, only did that a ffew times before it killed a piston.

at the minimum I'd get a cheap set of mmotorsport 24s in there. it shouldn't be so far off that it needs a tune to drive. at best I'd give the fmu to ssomeone you hate and tune the car right.

 

I've ordered Bosch 30lb III's which I need to fit. Will see how it goes

 

Hi everyone, so I have fitted Bosch III red tops / 30lb injectors. Car wouldn't run that well until I back the fuel pressure right back. So got a chip burned and it runs fine for now. I really wanted to know what fuel pressure I should run? Stock tpi?

 

The AFR under boost is between 11 and 12 now so that's a relief!