Ok so I need a very basic question answered and some help. I had a 2.4 LE5 GM Ecotec turbo motor running on E85 in my baja bug. It ran way to much power for the car to handle and I removed the turbo kit. I left the 80lb injectors in the car and ran it on E85 and it ran fine. I put pump gas in it and it ran as you would expect like crap very very rich does run though. I am not a modern car guy. E85 is extrmely hard to find here and no delivery options that I have seen yet.
I had the ECU shipped to a tuner who found that it had been encrypted in some way and he could not modify the tables which he found. The tables reads the boost levels and adjusts fuel which explains why no boost it ran decently on E85.
He found me a replacement ecu and put a standard performance tune on it and shipped it out the door. Unfortunately it does not work on the car, no spark and no fuel pump activation. We are going to fix this.
So my stupid question, if I put the OEM injectors back in the car will the motor get less fuel because I swapped from a 80lb injector to a 24lb injector. Or are injector to deliver. IE they will always deliver the same amount of fuel but the bigger ones can deliver more. IE can I just tune the car with smaller injectors and use the ECU I have that I know works.
It will run just fine with 24lb injectors if those are the injectors that the computer is calibrated for.
Injectors are just valves that are on and off. The amount of fuel they CAN flow is dictated by their internals, the amount they DO flow is controlled by on time vs. off time. So if you need, say, 20lb/hr of fuel at a given power level, the 24lb injectors will need to be operating at 83% duty cycle, while the 80lb injectors will only need a 25% duty cycle. The tune is calibrated for the injectors first.
It's a little more complicated when you get down to the physical tuning, but that's the gist.
Ok then that makes sense on what we are seeing on the ecu. It looks like the maps are very close to stock when not in boost and they just used 70% bigger injectors to make up for the increased fuel requirements for e85.
I know the owner used to swap between e85 for street and pump gas for off-road so he likely just swapped the injectors back and forth and it was close enough.
wish I could run the ecu myself but it's a big dollar investment for something I almost never do. Wish there was something open source or a friend local who could help.
JBinMD
New Reader
2/5/21 11:04 a.m.
If he is switching from e85 on 80lb injectors to gas, on the same ecu and assuming the same fuel pressure (i.e. the only changes are e85>gas and injector size) then wouldn't he need injectors more like 55lb, not 24lb? Am I missing something here?
In reply to JBinMD :
Sounds like he's going NA as well as swapping off the e85?
If the object of this exercise is a cheap injector swap, this will be a fail. There is little chance of hitting the tuning window by just juggling injectors.
On pump gas that motor will not need more than 30# injectors. 30# X 4 = 185hp @ .52 BSFC
You would have to buy multiple different size injectors until you found a size and pressure that will work with the tune. Seems like a lot of work and expense to get around tuning it which it really needs if you want it to last. Flogging a motor in a dubious state of tune rarely ends well. You can't tell the state of the tune by the way it runs
If it was mine I would replace the injectors and swap the ECU for a Megasquirt or equiv.
Or
We have been running E85 for 3 years at the drags https://www.thunderboltracingfuel.com/about-us-2 We buy this fuel by the drum and it ships all over the US. Can't beat the price, and the quality is far superior to pump E85 due to minimal water content. This Ethanol is double distilled to eliminate water. Pump E85 contains an amazing amount of water. Ethanol for pump gas is fast distilled for maximum productivity, water is free volume, also pump Ethanol is not stored properly. It is stored in VENTED BLACK rail cars parked in the sun until it is blended at a distribution plant. There is little regulation regarding pump E85, the emphasis is on not being able to drink it.
Plan is to tune it properly on the stock injectors. Based on what I am seeing on the stock tables the 80lb injectors cannot go low enough to idle cleanly. Not tune by injector size. I just want it to run well enough so we can get it out to the shop that is going to dyno tune it.
if I had the software I would totally love to do it myself. But I do not have a obd2 port on the harness. Though I guess I could add on with a little work.
Pete. (l33t FS) said:
It will run just fine with 24lb injectors if those are the injectors that the computer is calibrated for.
Injectors are just valves that are on and off. The amount of fuel they CAN flow is dictated by their internals, the amount they DO flow is controlled by on time vs. off time. So if you need, say, 20lb/hr of fuel at a given power level, the 24lb injectors will need to be operating at 83% duty cycle, while the 80lb injectors will only need a 25% duty cycle. The tune is calibrated for the injectors first.
It's a little more complicated when you get down to the physical tuning, but that's the gist.
Just to add to this. I agree completely, but it's possible that you can oversize the injectors. It's true they are on/off valves, but they have trouble remaining accurate at very short duty cycles. If you oversize too much they are trying to accurately deliver fuel with micro-second pulse widths and it can cause rough/rich idle if you go way too big.... which may be the case with 80lb injectors on a 2.4L. Just for perspective, my 160-hp V6 uses 18 lb injectors, which equates to 4 injectors at around 25lbs
Think of it like trying to put an inch of water in a bucket with a water hose vs using a fire hose. Its easy to get just the right amount of water with the garden hose, but nearly impossible with fire hose. By the time your hand gets the valve open and closed again on the fire hose you might have 1" or 6".
In reply to Curtis73 (Forum Supporter) :
That's where we get into where it gets a bit more complicated... 
In reply to Pete. (l33t FS) :
Leave it to me to open the complications bag 
You also may need to check if they are low impedance or high impedance injectors. Most cars use high impedance, but many larger injectors are lower impedance. Two reasons- 1) Low impedance injectors can open and close faster, and may be okay at idle on a small engine. My Galant VR4 uses slightly smaller injectors (74lb) on a 2.0 liter engine. It idles like stock. Is does run a lower fuel pressure than most cars though. 2) If they are low impedance injectors, that likey means that there are resistors installed in the circuit if stock is high impedance- you would need to remove those to reinstall install stock type high impedance injectors.
Ok extra dump question time.
I have a fuel pressure regular that allows between 20-90psi. I know that factory is 45psi. How much doeS fuel pressure really effect delivery.
ie at 40 psi I get x fuel. At 50psi I get x + 10%. Just trying to understand
Answering my own question. A lot. Like way more then i expected. ~20% in total. That's some swing. Going to throw on a friends wideband and see how close we can get just for science.
Ok spent some of the night readying up on some of this stuff still rattling it around in the brain.
So first off if I have boost maps and my ECU is reading boost then as I see it it adjusts fuel to the boost it see.s IE when I removed the boost and ran on E85 it ran just fine because its running on a no boost mapping.
So current injectors are at a 1.35-1.39 multiplier at the 65psi that they are set to run at. They run at that pressure I assume to allow for more fuel when under boost and the off boost rpms just had to deal with the extra pressure by turning down the injectors. If I were to switch to a 55lb/hr injector it would adjust for the E85 fuel increase required over pump gas. (Timing is only 1 degree different on the maps so not really a thing to worry about)
I can make my injectors run at a 55lb/hr injector rate by dropping the fuel pressure to 26psi based on the multiplier that I have off the spec sheet. So I have done just that, I dropped the pressure down and it idles and revs great. Not perfect but more then enough to drive it around with a wideband and see what else is going on with the motor.
So my fuel pressure regulator has a T in for motor vacuum and I am going to leave that in for now but it only raises the pressure by ~12 psi which is what the boost level was supposed to be originally so I assume that is to counteract the increased pressure in the cylinders from the boost. I may need to disable it or maybe not. I will see with the wide band.
80# injectors should idle decent on pump gas.
I have a project 2.3L with 20# boost on pump gas and RC750's (71#) injectors and no idle issues.
Lowering fuel pressure works to a point, you will loose atomization and they will slobber at small openings.
Just got back from a drive. It's way better then it ever has been. Still stalls when cold but after that it runs great. Now I keep thinking you guys were right about inconsistencies in my e85 supply.
found a few threads where guys have measured as low as 55% at the stations near me.
