Thread: V8 fuel injectors.

Originally Posted by DAMINK

Are the fuel injectors supposed to pulse when on gas?
I thought the gas system stole the pulse and used that to fire its injectors.
Is both fired i would assume a massive over fueling would take place???

The fuel injectors are cut off by the gas computer, so no unless the computer drives them independently
by software settings. In that case the computer deducts time off the gas injectors to compensate. Great for peak performance.

Originally Posted by bee utey

The fuel injectors are cut off by the gas computer, so no unless the computer drives them independently
by software settings. In that case the computer deducts time off the gas injectors to compensate. Great for peak performance.

Yea thats what i thought. So if a fuel rail (injectors) are sealed and functioning properly they should not fuel when on gas.
Unless the pressure was too high and forcing past the injectors. Or there not functioning properly.

Should the fuel pump turn off when pressure is achieved and no reduction? Ie on gas?
I seem to recall the pump runs constant regardless?

Originally Posted by DAMINK

Yea thats what i thought. So if a fuel rail (injectors) are sealed and functioning properly they should not fuel when on gas.
Unless the pressure was too high and forcing past the injectors. Or there not functioning properly.

Should the fuel pump turn off when pressure is achieved and no reduction? Ie on gas?
I seem to recall the pump runs constant regardless?

EFI fuel pumps are constant displacement and the pressure is set by the fuel pressure regulator not a switch. To turn off the pump makes the injectors run hotter and coke up as they're not fed cooler fuel. That wrecks their spray pattern or just blocks them. Leaks tend to be from o-rings and hose tails, so sometimes cars burn to the ground after being LPG converted.

Originally Posted by peter51

Youve done a lot of testing but cant establish if you have meticulously checked the wiring under load.
This sounds more like a wiring issue - somewhere in the loom between the inputs and outputs is a high resistance point - or I have seen weak earth under load give fluctuating voltage at any point in the system EG fuel pump or ECU or any input output device.
BTW You cannot just check resistance on a wire to establish integrity I.E. Ohms test - the wire must be under load and voltage drops along the path are tested.
It seems illogical that the injectors are at fault or any of the other devices - as it has been yr daily driver.
My suggestion is to inspect every wire in the engine management loop for a rub or break - is any part of the loom rubbing, have scotch locks have been used anywhere, check all pins and terminals to pins for multiple copper strands adrift etc. Be extremely thorough.
Now power up - check battery voltage at the input side of every feed point to Input and output devices. E.G batt voltage at ECU or fuel pump input. A voltage drop of 0.1 V between battery and device is a suspect wire.
Check output voltage from ECU to actuaors or any output from ECU. E.G at flapper or any other device that receives a feed from the ECU. Be thorough.
Now check again as best you can after start - is the voltage at the pump or ECU stable over time?

We all tend to assume its an input or output device first but it is wiring issues that cause most faults - like the body if you have have healthy organs but a restricted vascular system then the system functions poorly.

If its a perfect body and you want to keep it then an aftermarket ECU with wideband would be a good investment - see FAST EZY systems in the USA - however AUD is tanking right now.
Best of luck - I feel your pain.

Peter, yes I have. A lot in all conditions. Including wiggle testing, voltage drops on power connectors and earth's. None of the wiring has been tampered with, except of course for the ignition module mod. With the AFM apart I have tested for a voltage drop between the pins on the harness and the actual components inside.

So my reason for believing the system is ok, not great but ok, is that with different ECUs there are different problems. If the problem was with the greater system, the symptoms would be same or similar between the ECUs. One over fuels, the other doesn't even fuel.

To recap, the original ECU will over fuel and flood the engine when the fuel pump is powered up.

From this I know it runs. The ECU is firing the injectors and there is spark. You could even argue that it is being metered as when you open the throttle, revs lift. Lots of smoke, but it does lift.

I also read in the system description that the over run switch is there to tell the ECU to stop firing the injectors when the engine is in the over run condition, as the vacuum can draw more fuel than is being metered through the injector. I did bypass this switch with no change in conditions.

The new ECU will not run at all. It did initially but for some reason won't now.

Not sure if I had mentioned this before but when it was my daily driver the fuel economy was slowly getting worse.

There were also times I could not start it for a week or so, but after changing the fuel filter it would be fine. I have also changed the fuel pump as that died three weeks before I pulled it off the road.

I do not think this has anything to do with the current issue, as different ECUs have different issues.

I am currently trying to motivate myself to head out on what is already a 33 degree day (top of 40) to just change these injectors to take them off the list. If it isn't the problem, so be it.

I'm not usually a swapnostics sort of guy, but without an osiloscope or other awesome testing equipment, I am limited to a mutli meter and a few bits of reference material.

Thanks..

Oh also, this vehicle is not on gas. Never has been. I am the third owner.

So Il concede, it's not the injectors..

Albeit it does run smoother in all conditions.

Randomly though, the new ECU runs again. It runs lean and off idle there is a flat spot that you need to overcome to pick up revs. Once there it will pop and splutter. Have tried winding up the fuel with no change. Timing is at 12BTDC and anything less or more will cause it to stumble.

The old injectors measured 3ohms and the new ones 2ohms.

Have looked for an air leak, but still can't find one. Adjusted the throttle pot once again with no change.

Not sure where else to go as one ECU is too rich and the other too lean.

Aaarrrgggghhhh!!!

Did you adjust the spring in the flapper to try to make it leaner?
If so you should adjust it back to where it was.

Regards Philip A

There was a procedure to systematically test all the flapper components, I can't remember where I saw that though, maybe Rave. Have you tried the factory pressure regulator with the new injectors and replacement ECU?

Here's a terribly awesome video of the flapper system broken down, seen it yet?
YouTube

Originally Posted by PhilipA

Did you adjust the spring in the flapper to try to make it leaner?
If so you should adjust it back to where it was.

Regards Philip A

I didn't no. I only moved the flap with my hand to see what difference it made while running. Any adjustment there will be held off until it is running correctly.

I haven't seen that video and I will watch it several times to ensure I am over it. And yes there is a test procedure in Rave and on another flapper EFI read through. Both have been exhausted.