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Injector Flow Rates


geoffbeaumont
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In persute of setting up my Megasquirt correctly, I'm currently trying to figure out the correct REQ_FUEL setting (how many milliseconds it fires the injectors for each pulse). Mostly this is pretty straightforward, but I'm a bit stuck on what flow rate to use for the injectors.

The rating for the Hotwire injectors seems to be 18.25 lb/hr at 43.5PSI, however the fuel rail on an RV8 runs at a lower pressure than this. TomG asked about this a while back, but none of us had an answer for him. He calculated the corrected flow rate at 16.37 lb/hr - I came up with 16.6 lb/hr at 36PSI (so I guess TomG used the minimum pressure).

However... Hybrid_from_Hell found that his fuel rail was at 30PSI when the engine was running. Now, I know HfH has a looney engine with some high flowing Jaguar injectors which might throw the pressure out a bit, but...what fuel rail pressure should I be using? :unsure:

The Megasquirt is now recased (lovely tidy job - photo's when I get hold of a new interconnect for my camera :rolleyes: ), and after a bit of playing around and knicking bits from Dan's config file (thanks Fridge) we got her to fire up. Had a couple of wiring issues; master relay wasn't switching due to a dead microrelay on a daughter board Jonathan had built (new relay), and my left lambda sensor is dead as a dodo - probably a dodgy connection. Swopped to use right hand lambda same as the LPG kit - this is a better arrangement anyway, as the Megasquirt has the extra circuitry to use a second lambda sensor and we can mess around with it without affecting the gas kit.

She fires up beautifully (much quicker than on hotwire), and starts off at about the right mixture but gets steadily richer until it's chucking smoke out the exhaust. Still no idea why :unsure:

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I used 35PSI for the calculator, from what i understand the fuel pressure regulator drops the pressure of the rail by about 7 psi when there is a high vaccuum in the plenum (e.g. around 30 kpa) at idle when when the throttle is opened (towards 100kpa) raises the pressure to 35-37psi. I think this is done to give a smoother idle and gives the injectors more range. So 30psi at idle on HfH's engine would be right. If the injectors are higher output putting in more fuel, Megasquirt would compensate with a shorter pulse width (lower req fuel or lower values on VE table) to get correct fuelling. As long as the fuel pump flow can keep up with the demand, the pressure should stay as regulated

If the fuelling is going too rich after starting, try reducing the fuelling valves in After Start Enrichment and Warmup Wizard in Megatune, the changes will happen in real time so should be able to get it accurate.

I'm very much a Megasquirt newbie, feel free to correct if i'm talking nonsense :)

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geoff, injector specs are not something you should be obsessing about as they are just a means to an end - coming up with a REQ_FUEL value. As long as it runs it doesn't matter what the numbers are as when you tune it right it will be right.

If you really need to know then there are whole tables posted on the MS website:

http://users.erols.com/srweiss/tableifc.htm

http://www.telusplanet.net/%7Echichm/tech/injectors.pdf

http://www.merkurencyclopedia.com/Fuel/fuel_injectors.html

http://www.powerpage.dk/produkter/pic/injectors.pdf

http://www.msefi.com/dload.php?action=file&file_id=86

http://www.project56.com/Injectortech.htm

http://www.autospeed.com/cms/article.html?...;A=0102&P=1

Stock RV8 ones are Bosch 0-280-150-105, 18.1 lbs/hr 190.2 cc/min rated to 43.5 psi / 3.00 bar flow 18.10lbs/hr @ 43.5psi, Low impedance.

The later 3.9 ones look like Bosch 0-280-150-556 @18.25lbs/hr High impedance..

One type (part#ERR722) were used from late 3.5/3.9 all the way to 4.6 with the same specs.

There is some info on the tuning page of how to set everything up, basically you're aiming to get the numbers (REQ-FUEL, squirts/cycle, and fuel map) so that you keep a low but usable pulsewidth at idle and never hit more than 80% duty cycle on the injectors. What numbers you use to get there really don't matter and you can re-scale the fuel map to suit new injector specs any time with the click of a mouse.

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The correct pressure is 38psi and it drops by 0.5bar (7psi ish) at MAP pressures of around 40Kpa ……………..a worthwhile investment is a rising rate adjustable regulator. The only way to adjust the OEM version is by squeezing the case, and that is very hit n miss

The settings that Fridge uses (Req Fuel = 20) seems to work rather well, although it is a little above the calculated figure. I guess that slight difference is no real issue other than the VE values will be slightly lower.

I now have MS Extra running EDIS and fuel on mine ………… the difference between MS and flapper is like chalk & cheese. The low end torque and top end driveability are very much improved. I am expecting further improvements once I fit the WB Lambda sensor and run some data logs.

:D

Ian

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It strikes me from this that there could be some merit to disconnecting the vacuum pressure regulator completely, so that the amount of fuel injected is entirely under the control of the Megasquirt? It seems like a bit of a bodge to get round an inadequacy of the 14CUX system?

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It strikes me from this that there could be some merit to disconnecting the vacuum pressure regulator completely, so that the amount of fuel injected is entirely under the control of the Megasquirt? It seems like a bit of a bodge to get round an inadequacy of the 14CUX system?

I think most vehicles run the same system TBH. Rising-rate ones are a bodge IMHO to save re-tuning a stock system as they up the pressure at higher loads thus causing more fuel to be injected so they're a crude way of running richer on a stock ECU, of course you can just adjust the fuel map with MS.

If you want to cvhange the req_fuel you can put new numbers in and then use the "scale VE table" function which moves the whole fuel map back in proportion to how far the REQ_FUEL value has shifted. At the end of the day it's all just numbers, provided it runs OK it doesn't matter what they are - you could have a REQ_FUEL of 1 or 100 and scale the fuel map to give exactly the same actual amount of fuel injected.

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I am expecting further improvements once I fit the WB Lambda sensor and run some data logs.

Ian

Ian,

I have emailed you a new msq file, from a tuning session on Saturday using a wide band sensor, and boy has it made a difference, top end is a massive improvement. Im now ticking over at 500rpm and when drive (auto) is selected, she wants to go, on the old lucas system. selecting drive on revs below 600rom used to stall out!

Geoff, just one little snippet, you say you start great and then richen up and die, are you not too rich to begin with? The lambda sensor will eventually give false readings, thinking its lean, so requesting more fuel if you are far too rich to begin with.

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The lambda sensor (if it's heated) takes a good 30secs to get up to the correct reading. If it's un-heated or the heater is broken it will only read correctly when the engine is above ~1500rpm and chucking nice hot gas down the pipe.

Geoff - is the MS richening itself up through lambda correction, false coolant temperature readings or inlet air temp readings?

- If it's false lambda readings you should not have the O2 correction on below ~1200rpm and ~70deg CLT anyway or it will never idle properly. If the sensor is dead/suspect just set the O2 adjustment to 0% to disable it.

- If it's false CTS readings it could be going into warmup enrichment (or staying in it) as the engine warms up. Compare your CTS sensor resistance to the CTS values for the RV8 sensor.

- Similar story with the IAT sensor, if it thinks the air is really cold it will chuck in more fuel.

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I think most vehicles run the same system TBH. Rising-rate ones are a bodge IMHO to save re-tuning a stock system as they up the pressure at higher loads thus causing more fuel to be injected so they're a crude way of running richer on a stock ECU, of course you can just adjust the fuel map with MS.

I still think it's a bodge :lol:

If you want to cvhange the req_fuel you can put new numbers in and then use the "scale VE table" function which moves the whole fuel map back in proportion to how far the REQ_FUEL value has shifted. At the end of the day it's all just numbers, provided it runs OK it doesn't matter what they are - you could have a REQ_FUEL of 1 or 100 and scale the fuel map to give exactly the same actual amount of fuel injected.

I know...just seems wrong to me to fudge a base setting. Always makes things more confusing down the line!

Geoff, just one little snippet, you say you start great and then richen up and die, are you not too rich to begin with? The lambda sensor will eventually give false readings, thinking its lean, so requesting more fuel if you are far too rich to begin with.

I had read about that one, and it's a possibility, although if the AFR readout is to be believed (in MS and from the same lambda sensor via the LPG kit) then it's starting at about the right mix. We've tried playing around with both the map and REQ_FUEL, if we drop it too much it won't start but as soon as it'll start it goes rich.

Sounds more like the enrichment settings?

Might just be needing to get this running tonight - I've just walked home from Longbridge. Lost all power to the old ignition coil. EDIS still has power but the lucas ECU is in at the moment (MS isn't drivable yet) and both that and the LPG take their timing pulse from the old ignition :(

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Sounds more like the enrichment settings?

Just reading through the manual for other reasons, and spotted the following, its a very low level but simple double check I suppose. My motor is running a fuel ve value of around 45 at 600rpm tickover with me running a fuel requirment of 22. Which might seem high, but it registers good on the wideband.

If the Req_fuel is too small all it means is the VE table will be full of large numbers and if its too big the VE table will be full of small numbers. The max VE value is 255, try to keep the value around 200 as a absolute maximum so you have some head room, generally 150 is the max value you would expect to see for a NA setup and an idle value of around 30. If your idle VE table value is around 80-100 then your req_fuel is too low, if its around 5 - 15 then its probably too big. As can be seen from the fueling equation, to get the same fuel PW you can increase the Req_Fuel and decrease the VE table values by the same percentage.

This is my coldstart....

post-400-1174301329_thumb.jpg

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The OEM fuel regulators are prone to failure and will give all sorts of odd symptoms.

I don’t know that the rising rate regulator is a bodge ………… they are available for most vehicles that use this type of fuel regulation system to MAINTAIN A CONSTANT DELIVERY from the injectors.

When accelerating the OEM regulator lifts the pressure by a proportional rate over the 0.5 bar (ish …. actually 10psi) variance from tick over to full chat …………. this issue with this is that the reaction time is slow and can lead to a lean mixture under certain conditions when using the OEM ECU’s. The rising rate regulator is proportional just the same, but the reaction time to full rail pressure is 1.7 times quicker than that of the OEM. Also the after market regulators are fully adjustable in terms of delivery pressure.

For a full understanding of how the regulator works and the design fuel rail pressures, here are the words from Rover Lucas L factory manual. ;)

Fuel Pressure Regulator

The fuel pressure regulator is fitted to control the pressure of fuel delivered at the injectors by sensing variations in manifold depression; this is to ensure

that the actual quantity of fuel released by the injectors is governed by one factor only - injector 'open time'.

The pressure regulator is fitted in the excess fuel return pipe (E), close to the injector fuel rail with its fuel supply (F) as seen in Fig.2.2. It has two chambers

separated by a diaphragm (R1); one chamber contains fuel from the supply line (F), the other is linked by a pipe to the engine side of the throttle butterfly to sense manifold depression. In the rest position the spring (R2) holds the, diaphragm valve against the fuel return pipe.

gallery_269_31_26059.jpg

Fig.2.2 Fuel Pressure Regulator

T Throttle butterfly

D Manifold depression

E Excess fuel return

J Injector

R1 Regulator diaphragm valve

R2 Regulator spring

F Fuel rail (pump supply)

Under conditions of low manifold depression, e.g. full throttle (Fig.2.2A), the spring continues to hold the diaphragm on its fuel return pipe seat. In these

circumstances, pump pressure must reach approximately 36lb/sq.in to move the diaphragm valve against spring pressure and allow excess fuel to

return to the tank.

When manifold depression is high, e.g. idle and overrun (Fig.2.2B), the diaphragm valve is drawn against spring pressure. The fuel return is opened

and the fuel pressure falls to 26 Ib/sq.in. Any intermediate depression will regulate fuel pressure between the minimum and maximum.

In this way fuel pressure varies according to manifold depression and ensures the amount of fuel delivered by the injectors is governed only by the

injector 'open time.

When manifold depression is low (Fig.2.2A), fuel pressure needs to be high to ensure sufficient fuel is forced through the injector for a given injector

'open time', say 0.003 cc of fuel per 10 millisecond period.

When manifold depression is high (Fig.2.2B), the depression will try to 'suck' fuel from the injector nozzle. Therefore the fuel pressure needs to be

reduced by the action of the regulator to ensure the same 0.003 co of fuel will pass through the injector in the same 10 millisecond period.

Rog ............... Thanks .............. got your email OK .............. I will respond by email today ;)

:)

Ian

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Have you faffed with the after-start enrichment at all? It ups the fuel for a number of cycles after starting, could be too high. Also check your MAP connection, if it's disconnected/leaky it will start but then be very rich.

After-start enrichment is what I suspect. Hadn't thought of the MAP connection, although it's worked okay for the EDIS timing for months and looks okay in Megatune. It does run from the vacuum advance nipple, and uses a tube which I suspect could do with being larger all the way to the Megasquirt under the drivers seat.

Thinking about it, it can't be an over rich fuel mixture causing the O2 sensors to read wrong, as we tried disabling EGO correction and it made no difference.

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So...if everything's working correctly the Fuel Pressure Regulator should cause the actual amount of fuel delivered for a given injector opening time to be constant, by compensating for the pressure differential across the injector?

Okay, they makes a whole lot more sense :)

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Correct - and my gripe with rising rate ones is that they are adding a variable (injector flow rate) where you could just use the fuel map / acceleration enrichment to achieve the same thing rather than relying on a mechanical device.

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It does run from the vacuum advance nipple, and uses a tube which I suspect could do with being larger all the way to the Megasquirt under the drivers seat.

Geoff,

That is a ported vacuum take off point and will not read the true manifold depression. As fridge has pointed out you need to take it from the plenum ....... the point FF refers to was used on RRC's for the heater control ............ or you could get a T piece (available from any good car accessory shop) and T into the vacuum feed to the regulator.

The size if pipe is nor important

:)

Ian

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Correct - and my gripe with rising rate ones is that they are adding a variable (injector flow rate) where you could just use the fuel map / acceleration enrichment to achieve the same thing rather than relying on a mechanical device.

How very true ............. but.......... it was found that on most vehicles that used this type of regulation, the reaction time of the reg was not fast enough and the injectors were going slightly lean under certain acceleration conditions............ I guess that is where some clever sod worked out that a rise rate of 1.7 times over standard was required. One theory is that the manufacturers designed it that way in order the to stay within EEC emission regs at the time ........ but that may be just a theory.

The OEM regulator is notorious for running glow pressure with old age, and an OEM replacement is serious bucks, whereas the rising rate regulator famiy (even from the likes of Merlin or Demon Tweaks) are resonable money at about £90 each.

However, be wary of terms like 'preadjusted'............... when mine cam from RPI I was getting a lot of exhaust popping ................ I can definately confirm that the injectors drip at 55 psi ! :blink:

As a point of interest, I popped into the local Lucas place and got them to place an EFI pressure gauge on the 9th injector, I then adjusted the the reg and gave the guy a drink (or two) ....................

:D

Ian

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it was found that on most vehicles that used this type of regulation, the reaction time of the reg was not fast enough

You can correct for that with the accel_enrichment / MAPDOT settings which are the equivalent of a throttle pump on a carb setup. I still prefer setting things in software rather than adding mechanical things to the equation, and the ECU is always going to be faster to respond than a mechanical device. ;)

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Well, she managed to limp home. Took the Megasquirt down to Longbridge, loaded up my latest guess at the config, swopped the HT leads onto the EDIS coil packs and then tinkered until it was just about drivable.

Decided the ignition amp had gone, but swopping in the spare dizzy hasn't cured it (that said I've no idea if the spare dizzy works - think it came off an old engine in Robhybrids yard). Really annoying when I probably only needed it to work for another few days :angry:

The megasquirt now seems to be holding a reasonable mixture, but it's still got a pretty horrible idle. Gets much smoother above 20mph, but pretty gutless. The MAP was pretty lousy - it's now connected via an interference fit into the heater vacuum pipe and is much improved.

Since I've no timing pulse for fuelling on hotwire now, best plan seems to be to get the MS running well enough to at least drive a couple of miles and warm the engine up so it'll switch to gas. Also need to rewire and configure the LPG kit to take its timing pulse off the EDIS controller. That and buy something reliable to drive to work in...

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The dead ignition turned out to be a broken spade connector on the coil - it had snapped inside its plastic sleeve, so wasn't obvious until the wire came off in my hand. Must have been making a connection some of the time, too, as we checked the 12V supply to the coil when we went out to recover the truck.

Been plugging away trying to get the Megasquirt set up, but not making great progress so far - still haven't got it idling nicely. At the moment we're running on EDIS fixed at 8o advance. EGO correction, warm up enrichments and cranking PWM are all switched off. Tinkering with REQ_FUEL and the map we can either have a stable idle at close to 2000rpm or a seriously lumpy one at about 800rpm. Rereading the Megasquirt manual the only causes for excessive idle speed are:

  • Throttle stop too high
  • Vacuum leak
  • Idle air bypass valve open

Since it idles at a sensible speed on LPG and on the hotwire ECU the first two are unlikely, so my current theory is that the hotwire ECU is 'parking' the idle stepper motor in the open position when it is turned off. Does anyone know if this is the case?

Next time I've got the Megasquirt plugged in I'll try kicking it over to LPG - if it is the stepper motor that should be affected too.

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cranking PWM are all switched off.

Geoff, you shouldn't have PWM on anytime, it's only if you want to run low-impedance injectors without a resistor pack. The default values IIRC are PWM disabled. SimonR tried PWM on low-Z injectors with no resistor pack and for whatever reason it just wouldn't play.

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