Using fidle as fuel pump trigger

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Using fidle as fuel pump trigger

Postby MrFluffy » Mon Jul 02, 2012 6:24 am

Hi all,
I just wired up my ancient megasquirt onto a project after various misstarts over the years (its from the b&g group buy era!) and on a megastim v2.2 it looked to all be in order.
However I've put it on the bike, and its not triggering the fuel pump relay when it should be, then I went back to the stim and its stopped working on that also even though the megatune indicator shows it as running, could something have blown from over current, although its only triggering a relay and has a 1amp fuse inline.

Also, my fast idle output pin appears to meet the same requirements, it comes on every time the fuel pump light does, even when the motor is not running and its priming, and it doesn't go off with high rpm. Could I just use this as my fuel pump relay driver or is there some odd behavior that will screw up this cunning plan? I don't need fast idle, its done mechanically on the throttle bodies for warm up and I'm happy to rely on a stop screw against the butterflies the rest of the time.

Tia, and I thought it was going so smoothly this time, no engine in a bucket of shrapnel the week before or anything like that...
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Re: Using fidle as fuel pump trigger

Postby MrFluffy » Mon Jul 02, 2012 8:30 am

Someone is going to chime in and say "dont do that, itll cause your megasquirt to fry" or something now...
Excitement got the better of me, so I tried it, and the beast did indeed run, respond to throttle etc, then as I'm wandering around checking oil pressures etc, it cut out suddenly.
Now, when I try to turn it on, the led just blinks repeatedly quite quickly and its cycling the fuel pump, so I guess something inside has died and its power cycling instead of booting...
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Re: Using fidle as fuel pump trigger

Postby MrFluffy » Mon Jul 02, 2012 8:39 am

OR someone is going to say something much nicer, like check your battery voltage hasn't fallen so far it still cranks but doesnt supply +12v to the ms when cranking. :yeah!:
Its running again, and just warmed up, the tune is miles off, but its running!
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Re: Using fidle as fuel pump trigger

Postby MrFluffy » Wed Jul 04, 2012 1:46 am

Ok, no responses, is it the case that none of the above makes sense?

While its running with the fidle pin behaving as a fuel pump pin, and controlling the fuel pump relay, I dont *like* that, its a bodge and doesn't make sense and not how it should be, and things like that always come back to bite at a later point.

Is there some way the fidle circuitry can get messed up and cross talk to the fuel pump stuff with component failure? I have double checked and triple checked my pinouts and wiring, and the fidle pin sink is definitely switching with the fuel pump when I'd expect it to.
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Re: Using fidle as fuel pump trigger

Postby SymTech Laboratories » Wed Jul 04, 2012 2:28 am

When you say the FIDLE pin mimics the behavior of the FP pin, do you mean it primes the fuel pump as well? If not, perhaps you just have the idle control algorithm set to "ON/OFF" and you haven't let the car fully warm up. If so, then there's definitely a hardware problem.

The FIDLE and FP circuits are identical (on both v2.2 and v3.0 boards), so you don't risk damaging an otherwise working FIDLE circuit by using it to drive a fuel pump relay.

Could you post a couple of pictures of the top and bottom of the board?
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Re: Using fidle as fuel pump trigger

Postby MrFluffy » Wed Jul 04, 2012 2:40 am

Yes it runs the fuel pump initially to prime it too, I had a small video of the first start and you can hear the pump prime, then shut off after the delay period. Ill look in the software but I thought I had fidle disabled and idle controlled by bg.
Ill de-case it and take the photos this evening, thanks for the reply.

First fire up :-
http://www.youtube.com/watch?v=9F7ptrNumJY
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Re: Using fidle as fuel pump trigger

Postby MrFluffy » Thu Jul 05, 2012 3:44 pm

Shots, Ill link one top and one bottom as img then the rest as urls as theyre so big. Ive kept the resolution to keep the detail in although at this magnification some of it doesn't look pretty! :-
Image

Image

http://www.fluffycentral.com/ms/ms2.jpg
http://www.fluffycentral.com/ms/ms3.jpg
http://www.fluffycentral.com/ms/ms4.jpg
http://www.fluffycentral.com/ms/ms5.jpg
http://www.fluffycentral.com/ms/ms6.jpg
http://www.fluffycentral.com/ms/ms8.jpg
http://www.fluffycentral.com/ms/ms9.jpg
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Re: Using fidle as fuel pump trigger

Postby MrFluffy » Thu Jul 05, 2012 3:59 pm

I shall follow the checks in this thread http://msextra.com/forums/viewtopic.php?f=4&t=34307&p=232146&hilit=fuel+pump+transistor+q3#p232146
and take a look at the area around the components leading to q3, the board looks a little singed around there in the photos...
Im still confused why my fidle pin is being a fuel pump relay pin though...
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Re: Using fidle as fuel pump trigger

Postby SymTech Laboratories » Thu Jul 05, 2012 5:47 pm

Judging by the pictures, there are no obvious issues. We suggest inspecting pins 33 and 34 of the main socket ("U1") very carefully for shorts. Pin 33 goes to the fuel pump relay driver, and pin 34 goes to the FIDLE driver, so a short could cause the FIDLE output to behave like the FP output.
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Re: Using fidle as fuel pump trigger

Postby MrFluffy » Fri Jul 06, 2012 10:31 am

Firstly I noticed on the megastim again, that fp dimly lights when the fidle circuit goes off. Then while on the stim I tried setting the temperatures way high to see if fidle went off, and it did, so it'd warm up then stop working like you suggested.

I went over the pcb and no shorts around the pins or traces between the two circuits and all the components associated checked out apart from the transistors which I couldn't test in situ, so I went for broke and desoldered the two transistors, and soldered the fidle trans into the pump circuit.
Result? I now have a working fuel pump output. I'm guessing the transistor was bad, maybe I have issues with the megastim too and the crosstalk was coming from that instead. Ill order some more transistors just in case, they don't cost much. Thanks for your help.
Case it back up, get tacho out + a shift light working then go over it with a hot melt glue gun now :yeah!:
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