Blown Injector FETs

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Where does the flyback connect to with regard to the relay?  If it goes to the battery then its possible that when the engine speed falls below 100rpm after running there's a few injector events that have no flyback path...

[Sprocket]

Flyback is connected at the fuse that supplies the injectors, fused side

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and what side of the relay is that?

[Sprocket]

Its the switched side of the relay, so when the relay drops out so does the 12v to both flyback and injectors, as per the recommended drawings ;)

Battery - Relay - fuse - flyback/injectors

[[email protected]]

Cool stuff - it always pays to check these things :D

[Sprocket]

No worries mate, i am open to suggestions ;D

[Sprocket]

All this effort and a FET still died >:( >:( >:( >:( >:( >:( >:( >:( >:( >:( >:( >:( >:(

HAMMER TIME!!!!

I have since calmed down and replaced four good NEW FETs with four IGTBs and it seems to work.

I have no faith :(

[gunni]

Since the FET´s are these
http://www.fairchildsemi.com/ds/FQ/FQPF20N06L.pdf

I can´t even see a reason they should crap out.
Maybe there is problem with the voltage to turn it on?
http://en.wikipedia.org/wiki/Power_MOSFET

Maximum drain to source voltage

Power MOSFETS have a maximum specified drain to source voltage, beyond which breakdown may occur. Exceeding the breakdown voltage causes the device to turn on, potentially damaging it and other circuit elements due to excessive power dissipation.

I´m just not good enough to actually make sense of the datasheet to figure out a potential problem to why they fail.
Maybe an electrical engineer could really discover the problem and consult on a possible solution so that the FET´s are protected at all angles?

[lugnuts]

I didnt know that IGBT's could be used instead of fets. Also, I agree that something needs to be looked at.
I work with many brands of commercial ECU's and on none of them did I have to run a flyback wire to the ecu. Also I did not have to lie sleepless in my bed at night worried that a strand was going to break on one of the 5 ground wires.

This product is a very powerful tool with some great features. It would be great to match that with the same level of support and reliability. Thanks to Bob for this forum, hes spending a great deal of his own time helping people out.

[[email protected]]

The Nissan's I've done the plug and play harness adaptors for have, in all but one case, flyback wires, I've seen it on other OEM ECUs too.  The ones that do not seem to have some built-in power controller that allows the ECU to latch its own power.

The reason for the ground wire setup (and the flyback) is to keep the sensor signals clean, when the injectors are firing, and the coils discharging, with a mass of extra current load (relays, wideband etc...) the small resistance in the wires, and the high current load result in a rise in potential - which will send all your analog readings up the chute.

[Sprocket]

I too know that the Rover ECU has a flyback path, as the ECU is fed with a live from the same source as the injector.

Anyway, I really dont know where I would be without this forum, as the Wiki is so bad. Big up for Rob ;D

[GintsK]

Since the FET´s are these
http://www.fairchildsemi.com/ds/FQ/FQPF20N06L.pdf

I can´t even see a reason they should crap out.
Maybe there is problem with the voltage to turn it on?
http://en.wikipedia.org/wiki/Power_MOSFET

Maximum drain to source voltage

Power MOSFETS have a maximum specified drain to source voltage, beyond which breakdown may occur. Exceeding the breakdown voltage causes the device to turn on, potentially damaging it and other circuit elements due to excessive power dissipation.

I´m just not good enough to actually make sense of the datasheet to figure out a potential problem to why they fail.
Maybe an electrical engineer could really discover the problem and consult on a possible solution so that the FET´s are protected at all angles?

Some additional background. I knew ECU where http://www.irf.com/product-info/datasheets/data/irf7380.pdf is used for injectors. With no additional flyback protection. Driven with logical level AFAIK. And with no single damage. It is local (Latvia) construction ECU based on same Atmega128. One-men project from hardware up to GUI. Wise man! Scientist in nature.

Here is some description in Latvian:
http://www.elfa.lv/forum/viewtopic.php?f=32&t=1984&st=0&sk=t&sd=asf

Gints

[Sprocket]

well the forum has been down for over a week and a lot has happened ;D

It took me two days to tune the idle and then to get it to a point to drive, all be it with the aid of the wideband and EGOC ;D

Engine idles at 850 - 900 rpm

Been for an MOT today and passed. Emissions of 0.6% CO and 222ppm HC ( basic test, its only a Mini)

Only managed to get it to 49 % throttle but I really dont think I need any more for general driving  :D

It growels under acceleration, that'll be the ITBs ;D

Dyno booked for next tuesday, just going to put some miles on it this week, nice gentle driving as the map is rather rough and the wideband is working alot, but its driveble without damage to the engine as long as you take it reasonably gently. Its difficult to hold back though :D

http://uk.youtube.com/watch?v=sqbJhBPS6-w

This topic is now closed, and I still have no idea what the problem really is :-\ but it works, I couldnt have done it with out help on here, Thanks.

Sprox

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Sounds nice and smooth.

Glad that you got it sorted, shame it took as long as it did and that you didn't get to the bottom of why.

[Sprocket]

This is the resulting carnage ;D