Fuel starvation over 4000 rpms
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Fuel starvation over 4000 rpms
Hey guys i have a fuel problem. Its in the upper r's. 02 readings mostly around 850 MV's and runs great. At 4000 rpms it drops to 750-800 MV's. At 4500 rpms it drops to around 100-300 MV's. drops to 0 Mv's @ 5000 rpms. My transmission shifts on its own @ 6000 rpms, although the camshaft rpms are 4000-7000 rpms. i run a 7747 ecu (asdu) based. Now, ive messed with PE AFR from 9:1 to 14.7:1 with non-noticable WOT difference in AFR. Ive also messed with Async Multiplication starting at 4000 RPMsAsync Fuel Mult vs. RPM
RPM Mult
(null)
6400 2.67
5600 2.33
4800 2.77
4000 2.77
3200 1.33
2400 1.00
1600 0.67
800 0.33
0 0.00
went from 1.67 to 2.77 without noticable WOT AFR changes, unless that wasnt a very big change. I guess i could try something like 9.00 and see what happens. For the most part i went back to just about a stock bin with my own timing map, seems my car wont idle under 16 degrees. There has to be a way to change the WOT fuel curve. I dont think i have a pump problem although possible, the pump runs 20 PSI without a problem but ive never checked fuel pressure @ WOT. With the stock cam i dont remember it doing this. Anyone know how to change WOT fuel curve? I edit my bin file with TunerPro.
RPM Mult
(null)
6400 2.67
5600 2.33
4800 2.77
4000 2.77
3200 1.33
2400 1.00
1600 0.67
800 0.33
0 0.00
went from 1.67 to 2.77 without noticable WOT AFR changes, unless that wasnt a very big change. I guess i could try something like 9.00 and see what happens. For the most part i went back to just about a stock bin with my own timing map, seems my car wont idle under 16 degrees. There has to be a way to change the WOT fuel curve. I dont think i have a pump problem although possible, the pump runs 20 PSI without a problem but ive never checked fuel pressure @ WOT. With the stock cam i dont remember it doing this. Anyone know how to change WOT fuel curve? I edit my bin file with TunerPro.
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From: Corona
Car: 92 Form, 91 Z28, 89 GTA, 86 Z28
Engine: BP383 vortech, BP383, 5.7 TPI, LG4
Transmission: 4L60e, 700R4, 700R4..
Axle/Gears: 3.27, 2.73
Have you increased the VE in the upper rpms?
Did you log the injected PW and calculate duty cycle?
If you're 100% duty cycle, then no matter how much you add in the ECU, the engine won't get it.
Check your fuel pressure before you go much further at WOT.
Did you log the injected PW and calculate duty cycle?
If you're 100% duty cycle, then no matter how much you add in the ECU, the engine won't get it.
Check your fuel pressure before you go much further at WOT.
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From: Chasing Electrons
Car: check
Engine: check
Transmission: check
'RPMsAsync Fuel Mult vs. RPM': set this back to the 8 cylinder values. This table is only used for conversion of sync PW to async PW.
Changing the cylinder select will change the SA timing, so don't do that. Set it to the proper cylinder value.
OK, I'll bet that the problem is lack of fuel. What you need to do is to estimate the HP the engine is going to produce. Then size the injectors and fuel pressure to provide the required amount of fuel. With TBI systems it is all too common to under-estimate the required fuel delivery requirement. Part of this has to do with what the injectors actually flow at the rated pressure.
Checking fuel pressure at WOT is important. Even the slightest drop off is grounds for a better fuel delivery system.
Back to the injector requirements. Let's just say that this engine will make 400 HP at 6,000 RPM. Using .5 BSFC and 2 injectors, will need 118 #/hr fuel flow from each injector. ((400 * .5) / 2 * .85% duty cycle).
To get this we can choose from a variety of injectors. Let's start with the common 61#/hr 350 injector. To get 118 #/hr will need to bump the fuel pressure to 48 psi. That is a good deal of pressure, but within the limits of that injector.
If we use BBC 80.5 #/hr injectors, will need 28 psi of fuel pressure.
Or, can move to a dual quad manifold and run two 2 BBL TBI units. Or a single quad manifold and run a 4 BBL Holley unit.
RBob.
Changing the cylinder select will change the SA timing, so don't do that. Set it to the proper cylinder value.
OK, I'll bet that the problem is lack of fuel. What you need to do is to estimate the HP the engine is going to produce. Then size the injectors and fuel pressure to provide the required amount of fuel. With TBI systems it is all too common to under-estimate the required fuel delivery requirement. Part of this has to do with what the injectors actually flow at the rated pressure.
Checking fuel pressure at WOT is important. Even the slightest drop off is grounds for a better fuel delivery system.
Back to the injector requirements. Let's just say that this engine will make 400 HP at 6,000 RPM. Using .5 BSFC and 2 injectors, will need 118 #/hr fuel flow from each injector. ((400 * .5) / 2 * .85% duty cycle).
To get this we can choose from a variety of injectors. Let's start with the common 61#/hr 350 injector. To get 118 #/hr will need to bump the fuel pressure to 48 psi. That is a good deal of pressure, but within the limits of that injector.
If we use BBC 80.5 #/hr injectors, will need 28 psi of fuel pressure.
Or, can move to a dual quad manifold and run two 2 BBL TBI units. Or a single quad manifold and run a 4 BBL Holley unit.
RBob.
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Could a stock bin have 100% cycle somewhere in the rpms? I mean ive done some radical stuff with very little effect, but this burn im using currently (ASDU) is very close to stock on the fuel part. where i actually want the added fuel is in ASYNC mode above 4000 rpms. I did raise my fuel pressure to 18 PSI. The car runs a whole lot better. I am going to test my WOT fuel pressure and go from there. thanks alot guys 
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From: Chasing Electrons
Car: check
Engine: check
Transmission: check
A lot of stock BINs have the VE at 100% and higher. The ECM max's the VE% at 100 whenever the two tables add up to more.
Why/how are you in async mode above 4,000 RPM??
RBob.
Why/how are you in async mode above 4,000 RPM??
RBob.
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You know, i think your right about Async @ 4000 and above, it really should be in sync mode, or at least seems that it should be. On a stock bin like the ASDU, is it normal for the injectors to "skip a beat" @ 5000 rpms and over?
Seems like i need do increase fuel flow and decrease my duty cycle. i have parameters for Max Async and Min Async
Max Asynch BPW
Usec
305.00 305.00
(null) 45.75 274.50
Min Asynch BPW
can i control Async mode with this? (on and off)
Injector Bias (added)
Usec
503.25 503.25
(null) 0.00 305.00
BPW Const for EGR off 134.00
i have'nt founf a difference in these 2 settings unless injector bias adds to a certain map.
Usec
274.50 274.50
(null) 0.00 686.25
Seems like i need do increase fuel flow and decrease my duty cycle. i have parameters for Max Async and Min Async
Max Asynch BPW
Usec
305.00 305.00
(null) 45.75 274.50
Min Asynch BPW
can i control Async mode with this? (on and off)
Injector Bias (added)
Usec
503.25 503.25
(null) 0.00 305.00
BPW Const for EGR off 134.00
i have'nt founf a difference in these 2 settings unless injector bias adds to a certain map.
Usec
274.50 274.50
(null) 0.00 686.25
Last edited by escort_ford84; Nov 10, 2006 at 07:13 PM.
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Car: 91 Formula WS6 (Black, T-Tops)
Engine: 383 MiniRam (529 HP, 519 TQ - DD2K)
Transmission: Built '97 T56, Pro 5.0, CF-DF
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From: Dallas, TX area
Car: 91 Formula WS6 (Black, T-Tops)
Engine: 383 MiniRam (529 HP, 519 TQ - DD2K)
Transmission: Built '97 T56, Pro 5.0, CF-DF
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A scan tool as well as a laptop for data logging? How, sharing the ALDL port? I'm confused.... (not the first time, either LOL)
I've just not noticed that data stream value in my 730 and S_AUJP set up. Guess I'll have to go back and look again....
I've just not noticed that data stream value in my 730 and S_AUJP set up. Guess I'll have to go back and look again....
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SYNC must be where PE settings make a difference. My ECU is in ASYNC cold i see. Lowering values in the ASYNC mult @ 800 makes the car not idle cold (from .33 to .28) lol. But i still dont see where i can control WOT in SYNC. I mean, i can set PE @ 3600 RPMs to 12:1, but i still dont see if CFM is increasing how fuel increases with it. I will try raising my VE tables @low vacuum and see what it does.
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From: Hurst, Texas
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Is this the "old skool" solid cammed L03? Not bad for such an old cam profile. But you could have made just as much peak HP and ALOT more TQ with a more modern cam and it would have been much easier to tune.
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Yeah, i realize that. This is the way i wanted my engine to run. Im really just having fun and learing with this. Setting my upper RPM VE as % (FL2) seems to has fixed my fuel problem. I set them all to what the 3600 RPM value is. Im sure with the HP im making the stock injectors will be ok. The thing im wondering about is the RPMs. The pulse would fire 8 times per RPM @6000 RPMS i presume is 48000 per minute. It seems like the injectors would float the pintle at some point. My car is actually running good now. Recently, i did take the swirl port heads of in favor of my ported "416" heads which i used the valves from the 187 (all of them were good) revs alot faster the entire RPM range. The swirl heads were linear in power. If it wasnt for you all, id probably never had found the FL2 and the way the fuel curve was after 4000 rpms. thanks again.
Joined: Jan 2005
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From: Hurst, Texas
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Yeah, i realize that. This is the way i wanted my engine to run. Im really just having fun and learing with this. Setting my upper RPM VE as % (FL2) seems to has fixed my fuel problem. I set them all to what the 3600 RPM value is. Im sure with the HP im making the stock injectors will be ok. The thing im wondering about is the RPMs. The pulse would fire 8 times per RPM @6000 RPMS i presume is 48000 per minute. It seems like the injectors would float the pintle at some point. My car is actually running good now. Recently, i did take the swirl port heads of in favor of my ported "416" heads which i used the valves from the 187 (all of them were good) revs alot faster the entire RPM range. The swirl heads were linear in power. If it wasnt for you all, id probably never had found the FL2 and the way the fuel curve was after 4000 rpms. thanks again.
Let me get that right, you set VE 2 to the 3,600 RPM value through-out? Then you re-corrected VE1? You do know there is a 100% cap in the ECM right. That means that VE1+VE2 will never be more than 100% in the eyes of the ECM, even if you put 100% in VE1 and 100% in VE2, you only get 100%, not 200%.
Ported 416s DO make sense for a cam of this size though. What intake are you running? The stock TBI intake? A performer RPM with a carb-tbi adapter would pull much better over 4,500 than the stock intake. You certainly do not need EGR with a cam of this size.
On a V8, the injectors open every other distributer reference pulse(8 per distributer rotation, 4 per crank rotation), back and forth. One injector at one reference pulse, then the next. That is two times per crankshaft rotation. At 6,000 rpm you are getting 12,000 openings a minute per injector. You have less than 5msec of time to get the fuel you need into your engine. At 6,500 RPM I had even less time, something down around 4 milli seconds @ 85% DC. My 3.1 V6 on the otherhand is able to turn 6,000+ RPM easily on not much injector, the difference is that there are 2 less firings per distributor rotation.
https://www.thirdgen.org/forums/tbi/...ghlight=static
Here is a little clip from RBob on Static Injectors.
Originally Posted by RBob
Static is at 100% or greater. The '747/'8063/'8746 ECMs fire an injector every time a plug fires. There are two injectors. They alternate on plugs firings.
Before I go too much further this is in synchronous mode. Sync mode is sync'd to plug firings. This is the most common mode. I have seen a few cals that are always in async mode, but never an f-body cal.
So for each revolution (V8) there are four plug firings. It takes two revolutions to fire all eight cylinders/plugs. Alternating injectors, that means each injector fires twice on each engine revolution.
At 4,000 RPM (revolutions per minute), divide by 60 for revolutions per second: 4000 / 60 = 66.67 revolutions per second. Invert this value for the time of each revolution (or frequency thereof): 1 / 66.67 = 0.015 seconds. Or, 15 milli-seconds (msec) per revolution.
With each injector firing twice each revolution we need to divide the amount of time in half: 15 msec / 2 = 7.5 msec.
This 7.5 msec is the amount of time an injector has before it is fired again (at 4,000 RPM). The higher the engine speed, the less time there is for an injector to deliver the required amount of fuel.
This is why it is important to keep an eye on the injector PW. Once the PW value exceeeds that given amount of time, no more fuel can be added. The darn injector is on ALL of the time.
At this point the only thing that can be done is to increase the delivery of fuel. Bigger injectors and/or higher fuel pressure is required.
As another data point at 6,000 RPM a TBI injector is static once it hits 5.0 msec of on time. For best results TBI injectors shouldn't be open for more then 85% duty cycle. At 6K RPM this is 4.25 msec's.
RBob.
Before I go too much further this is in synchronous mode. Sync mode is sync'd to plug firings. This is the most common mode. I have seen a few cals that are always in async mode, but never an f-body cal.
So for each revolution (V8) there are four plug firings. It takes two revolutions to fire all eight cylinders/plugs. Alternating injectors, that means each injector fires twice on each engine revolution.
At 4,000 RPM (revolutions per minute), divide by 60 for revolutions per second: 4000 / 60 = 66.67 revolutions per second. Invert this value for the time of each revolution (or frequency thereof): 1 / 66.67 = 0.015 seconds. Or, 15 milli-seconds (msec) per revolution.
With each injector firing twice each revolution we need to divide the amount of time in half: 15 msec / 2 = 7.5 msec.
This 7.5 msec is the amount of time an injector has before it is fired again (at 4,000 RPM). The higher the engine speed, the less time there is for an injector to deliver the required amount of fuel.
This is why it is important to keep an eye on the injector PW. Once the PW value exceeeds that given amount of time, no more fuel can be added. The darn injector is on ALL of the time.
At this point the only thing that can be done is to increase the delivery of fuel. Bigger injectors and/or higher fuel pressure is required.
As another data point at 6,000 RPM a TBI injector is static once it hits 5.0 msec of on time. For best results TBI injectors shouldn't be open for more then 85% duty cycle. At 6K RPM this is 4.25 msec's.
RBob.
Last edited by Fast355; Nov 16, 2006 at 09:27 PM.
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well i dont really think i doubled anything, i could be wrong. ill show you what i did. im pretty sure this was causing my lean out taper after 4000 rpms, this is a stock bin
VE as % (FL2)
RPM %
(null)
6400 0.00
6000 0.00
5600 9.77
5200 17.58
4800 21.48
4400 32.03
4000 35.16
3600 41.02
3200 39.06
2800 39.06
2400 39.06
2000 39.06
1600 39.06
1200 39.06
800 39.06
400 39.06
0 25.00
now after 3600 it tapers of the fuel, all i did was take the value at 4000 rpms and repeat it up the rpms. so the duty cycle hits 85% % 4000 then it should remain the same up the RPMS. i guess
VE as % (FL2)
RPM %
(null)
6400 0.00
6000 0.00
5600 9.77
5200 17.58
4800 21.48
4400 32.03
4000 35.16
3600 41.02
3200 39.06
2800 39.06
2400 39.06
2000 39.06
1600 39.06
1200 39.06
800 39.06
400 39.06
0 25.00
now after 3600 it tapers of the fuel, all i did was take the value at 4000 rpms and repeat it up the rpms. so the duty cycle hits 85% % 4000 then it should remain the same up the RPMS. i guess
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