Injectors flooding engine

[Slave2theBunny]

Hi everyone, I need help,


For a bit of history, I'm running a Version 2.2 (copyright 2001) board, it's for fuel only so I guess it's a MS-1 (it's been so long ago I built this I forget now) It ran great ever since it was built and installed on an 81 vw rabbit T3 turbo, the car was stored back in 2008 and it was running great, I tried to start her yesterday and after priming the engine to build up oil pressure with the plugs off ( it was turning over fine) I cycled the ignition a couple of times to build up fuel pressure then I tried to start her and it was hydrolocked, I pulled out the plugs and they were soaked, I cranked it over a couple of times (big geysers of fuel shooting out) to clear the combustion chambers, I put the plugs back in and took out the injectors thinking they were stuck open with varnish, I had 2 spare ones so I swapped them in and cleaned the best 2 of the original ones (I tested them with a battery and I hear them clicking and holds the carb cleaner I topped off on the top of the injector, I re-installed them and same thing, hydrolocked on all 4 cylinders, so I figured it's not the injectors that was the problem, I disconnected the injector plug (I'm only using one driver for all 4 injectors) I cycled the ignition again to build up fuel pressure and it seems to be holding and I re-cranked the engine to see if I was getting leakage into the pistons. No leaks, engine turns over with 50psi on the fuel rail.

Then I pulled out my multimeter and checked the injector plug, with the key in ignition, I was getting 12v (which was why the engine flooded it was wide open) I just found my stim this morning and will be running tests on the megasquirt, Any ideas why this would happen only after 4 years?? I opened the cpu no obvious blown/burnt parts but my nose does detect a very slight burnt electronics smell, not sure if I'm imagining it, I can't locate where on the board I smell it. Please help me.

[trakkies]

The injectors should have 12v positive to them all the time the ignition is on - it's the ground which is switched by the MS.

In the absence of a Stim, wire an LED with a 1000 ohm resistor in series with it across the injector feed - you should see it flashing at low revs, ie when cranking, if you can't see the one on the MS.

If there is a driver fault be careful not to burn out the injectors if low impedance.

[Slave2theBunny]

Yeah I know there's supposed to be 12v there, what I meant was when I checked both terminals leading to my injectors, I had 12v on one side and constant ground on the other pin for the injectors, so the injectors were getting constant power and ground with the key in ignition. hope that clears things up.

[trakkies]

Yeah I know there's supposed to be 12v there, what I meant was when I checked both terminals leading to my injectors, I had 12v on one side and constant ground on the other pin for the injectors, so the injectors were getting constant power and ground with the key in ignition. hope that clears things up.

Unless a wiring fault, sounds like a driver transistor has failed. Does the injector LED on the MS stay on?

[Slave2theBunny]

okay I get the weirdest symptoms, I tried to check my megasquirt with my megastim, but I think I fried my megastim because I hooked it up to my 12v motorcycle battery, (it's been so long since I built this thing I forgot it was 9v, anyways I finally found a 9v power supply hooked it all up, all the leds on the stim are lit solid, but on megatune all seems fine, pw varies with rpm, my tps pot was defective from day one, anyways I decided to rehook everything up in the car, disconnected the fuel pump relay and the injector harness, powered it up with the key in ignition coolant. rpm air temp all seems normal, pw jumps a bit at ignition power up like before.


right now the tps seems to be doing funky stuff, at closed throttle it sometimes reads 100% I think I have to readjust it.

Funiest thing is that afte I reflooded the engine, I dried everything off, unplugged the fuelpump relay and recranked, with a bit of feathering the gas pedal, it runs(d'oh!???!!!) though roughly it still runs...I think the engine is really flooded the exhaust started billowing out whitish smoke that stinks of gas.

I will probably readjust the tps, rewire the injectors to inj 2 output of the megasquirt (oh btw the LED for the injectors blink on and off during cranking and rough ildling.

[Slave2theBunny]

okay I was working on the car all afternoon, and I realized something, the minute I plug in the injector harness with the key in IGN the injectors all click open which is why my engine keeps filling up with fuel, the led on the megasquirt flashes but I think the outputs are burnt or stuck open, I even changed it from pin 32-33 to pins 34-35 ( Iwas only using pin 32-33 before with no problems.


I measured the impedance on one of my injectors and it was 14.5, but all four of them in paralled (that was how the stock vw G60 inkector wiring harness was) was 4 ohms, you guys think it's what killed my megasquirt? Please help me, what do I need to do or replace on my megasquirt to get it back up and running, when I do repair the unit I am planning on rewiring the injectors to 2 batches and switch to alternating squirts.

[trakkies]

okay I get the weirdest symptoms, I tried to check my megasquirt with my megastim, but I think I fried my megastim because I hooked it up to my 12v motorcycle battery, (it's been so long since I built this thing I forgot it was 9v, anyways I finally found a 9v power supply hooked it all up, all the leds on the stim are lit solid, but on megatune all seems fine, pw varies with rpm, my tps pot was defective from day one, anyways I decided to rehook everything up in the car, disconnected the fuel pump relay and the injector harness, powered it up with the key in ignition coolant. rpm air temp all seems normal, pw jumps a bit at ignition power up like before.

The stim won't be worried by 12 volts.

right now the tps seems to be doing funky stuff, at closed throttle it sometimes reads 100% I think I have to readjust it.

Funiest thing is that afte I reflooded the engine, I dried everything off, unplugged the fuelpump relay and recranked, with a bit of feathering the gas pedal, it runs(d'oh!???!!!) though roughly it still runs...I think the engine is really flooded the exhaust started billowing out whitish smoke that stinks of gas.

I will probably readjust the tps, rewire the injectors to inj 2 output of the megasquirt (oh btw the LED for the injectors blink on and off during cranking and rough ildling.

The LED should flash at low revs as it's following the injectors open time. At higher revs it still flashes but at a faster rate so the eye sees it as being constantly on.

I'd be inclined to look carefully at your loom. Home made or modified ones are frequently the source of problems.

[Slave2theBunny]

I pulled the megasquirt out of the car again, and have it on the bench with the stim hooked up, as I 've said before, the led on the megasquirt for the injectors seem to pulse in relation to rpm but the ones on the stim are stuck on full, I remember that they used to flash in conjuction with the led on the megasquirt speeding up as rpms go up,

My question now is what needs to be replaced on the unit to re enable the injector outputs???

And it's not the wiring, I checked right at the db-37 plug, I also just finished resoldering all the connections on the board. Please help I'm tired of pushing my car up and down the driveway

[trakkies]

I pulled the megasquirt out of the car again, and have it on the bench with the stim hooked up, as I 've said before, the led on the megasquirt for the injectors seem to pulse in relation to rpm but the ones on the stim are stuck on full, I remember that they used to flash in conjuction with the led on the megasquirt speeding up as rpms go up,

My question now is what needs to be replaced on the unit to re enable the injector outputs???

And it's not the wiring, I checked right at the db-37 plug, I also just finished resoldering all the connections on the board. Please help I'm tired of pushing my car up and down the driveway

Not too familiar with MS1, but it's likely something in the driver circuit has blown. You say you're only using one of the two, so doing some comparative measurements between the two output circuits would be a start. If a transistor has failed short circuit it should be quite easy to find.

[Slave2theBunny]

That's what I thought too, but both outputs seem to be stuck open, I might try the procedure on one of the other posts about using an LED to check inputs and outputs on the megasquirt.

[trakkies]

That's what I thought too, but both outputs seem to be stuck open, I might try the procedure on one of the other posts about using an LED to check inputs and outputs on the megasquirt.

As I see it, the LED on the MS looks at the output of the processor which then goes to the drivers. Those on the stim the output from the drivers. But the stim doesn't present the same load to the drivers as the actual injectors, so might not show if they are operating correctly. An LED across an actual injector will show if it is operating and check the loom to it.
If you are only using one drive circuit, it's unlikely (IMHO) both have the same fault in the MS hardware.

[Stag76]

Is the fuel pump turning off after 2 seconds when the MS is powered up. I has a similar situation where the pump stayed on and the injectors (8) were all open (both channels). Re-loading the firmware fixed it.

[Slave2theBunny]

I believe I have found the problem, it is indeed a flyback failure, U7 has a hairline crack. I will try and source the parts locally instead of ordering online, I will keep this thread posted on what happens

[Slave2theBunny]

I've got a couple of questions for the megasquirt experts in here,

1. is there another fet driver I can use to replace the one in U7??? I've been to 2 different electronic shops here and they don't have a MC34151, or a tip42c for that matter to replace Q1
2. is 4 high impedance injectors in parallel considered a low impedance load, low enough to cause my flyback failure? I measure 5 ohms with all 4 hooked up to injector 1 output