Think my injectors are too small?
Moderators: jsmcortina, muythaibxr
Think my injectors are too small?
Engine Specifics:
-Chevy 350
-1.94 heads, RV cam
-DUI HEI distributor
-NOT a race engine by any means
-Holley 2Barrel Projection Throttle Body
-85lb per hr Injectors
-MS2
Problem:
Most of the time engine stumbles and pops around 4800-5200 RPM. On some occasions I've gotten it to 6000 RPM without a problem. In the attached log see duty cycle around 1372, 1435, 1478, 1487 Seconds. Just checking to make sure you agree or if there is something else to check. Unfortunately my fuel pressure gauge is under the hood so I can't view that when the error happens.
-Chevy 350
-1.94 heads, RV cam
-DUI HEI distributor
-NOT a race engine by any means
-Holley 2Barrel Projection Throttle Body
-85lb per hr Injectors
-MS2
Problem:
Most of the time engine stumbles and pops around 4800-5200 RPM. On some occasions I've gotten it to 6000 RPM without a problem. In the attached log see duty cycle around 1372, 1435, 1478, 1487 Seconds. Just checking to make sure you agree or if there is something else to check. Unfortunately my fuel pressure gauge is under the hood so I can't view that when the error happens.
-
- Super MS/Extra'er
- Posts: 1341
- Joined: Mon Sep 05, 2011 1:20 pm
Re: Think my injectors are too small?
Yes I do, you are technically out of injector at 4200 rpm.
Graduate of EFI University.
I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
Re: Think my injectors are too small?
Just to be sure... Megatune calculates duty-cycle based on the actual physical time the injector driver is open and closed irrespective of the injector characteristics settings in Megatune such as "req fuel" correct?
-
- Super MS/Extra'er
- Posts: 1341
- Joined: Mon Sep 05, 2011 1:20 pm
Re: Think my injectors are too small?
Duty Cycle is strictly the percentage of time the injector is squirting fuel, correct, and once you get to 85% and above you are loosing the ability to reliably control fuel. Doesn't matter what ECU is being used, OEM or MS, the calculation is not a function of injector size. In your log you hit 85% around 4200 rpm and it maxes out above 120% at 6 grand or so.
Graduate of EFI University.
I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
-
- Site Admin
- Posts: 39614
- Joined: Mon May 03, 2004 1:34 am
- Location: Birmingham, UK
- Contact:
Re: Think my injectors are too small?
It does sound like the injectors are too small. If the duty shows above 100%, then that's just not happening.
James
James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk
My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
-
- Super MS/Extra'er
- Posts: 6828
- Joined: Sun May 15, 2011 11:41 am
- Location: Walnut Creek, Calif. USA
Re: Think my injectors are too small?
I have no argument with the DC discussion, of course, but am surprised the 85# injectors aren't big enough. I think of an "RV cam" as being pretty mild, intended for good torque at lower speeds. Considering that, a 350 cid engine (this one is up to 360 now?) making the 300+ hp that the 85's could provide fuel for seems about reasonable. Is this engine using gasoline, or E10, E85, something else? I would hate to see the OP going to the trouble to change injectors if the problem is fuel pressure or simply the tune.
-
- Helpful MS/Extra'er
- Posts: 122
- Joined: Mon Feb 07, 2011 1:57 pm
- Location: Montreal, Quebec, Canada
Re: Think my injectors are too small?
Well, if you switch from 4 squirts to 2, assuming your deadtime is correct, you will gain 2ms of headroom on the injectors, which would bring you down under 100%.
But we don't know what AFR you're achieving. We can see the target in the msq, but no AFR data in the log. If you're running way too rich, you may have lots of room with those injectors when it's tuned correctly.
Your VE table looks a bit odd too. As mentioned above, 300hp should be doable on that injector setup.
More tuning, and more complete logging are needed before we can tell if injectors are too small.
But we don't know what AFR you're achieving. We can see the target in the msq, but no AFR data in the log. If you're running way too rich, you may have lots of room with those injectors when it's tuned correctly.
Your VE table looks a bit odd too. As mentioned above, 300hp should be doable on that injector setup.
More tuning, and more complete logging are needed before we can tell if injectors are too small.
Cheers, Brady
Audi 4kq MS1E,
Audi Quattro, 034 IIc
Audi 200qa20v
Audi 5ktqa
Datsun 240Z
Audi 4kq MS1E,
Audi Quattro, 034 IIc
Audi 200qa20v
Audi 5ktqa
Datsun 240Z
Re: Think my injectors are too small?
You can always get a little more flow by upping the pressure. I think those old projection throttle bodies have an adjustable regulator.
65 Cobra replica, 427W, MS2
71 Vette, 383 with shitty chinese 8 stack and no dizzy
71 Vette, 383 with shitty chinese 8 stack and no dizzy
-
- Master MS/Extra'er
- Posts: 643
- Joined: Sun Nov 06, 2005 12:31 am
- Location: NORTHERN CALIFORNIA
Re: Think my injectors are too small?
I was looking at your required fuel calculator settings, shouldn't you have 170 lb/hr. 85 x 2 or should it be 170/8 = 21.25lb/hr? I am used to my ms1 and ms3 fuel calculators. your required fuel just seems hi to me. 6.7 (13.4ms) I put in the injector flow rate of 85lb/hr and it gave me a calculation of 5.4 (10.8ms) you could be flooding the engine with the current settings, the ve table at idle and 100 kpa shouldn't be that large a number... but a rich miss fire using autotune will add fuel where the engine cant burn the fuel it already has. the highest ve values in your table should be at the max torque rpm 100kpa bin. but your tables seem to be reversed.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.