Smoked the output circuit MS-1

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zorb847
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Posts: 13
Joined: Thu Jun 17, 2004 6:35 am
Location: NJ - Butler

Smoked the output circuit MS-1

Post by zorb847 »

I had my megasquirt 1 ver 2.2 board with relay board setup and working on the bench hooked up to a 90's era GM 4.3 throttle body sitting there idling happily for over an hour and heard the injectors clicking. I am just using this TB for testing purposes as I have a holley 4 bbl TB that I will use for real.
I was using a fully charged 12v tractor battery (plenty to power it) and an external signal generator for the rpm signal.
I had connected external pots to the relay board to set the IAT to around 140 degrees and the coolant temp to 190.
I had an external vacuum pump hooked up to the MAP sensor and could see it respond in the gauge display of Tunerstudio.
I had followed the instructions to set it up as best that I could for an 8 cyl 350 engine,TBI injection, 4 squirts/cycle, 4 stroke, PWM current limit70% (no fly-back board), even fire, alternating staging.
GREAT - it's working!
Next step- took it out to the garage and connected everything to the car. I have all the sensors connected for coolant, IAT and O2 and have the MAP hooked up as well but the throttle body is connected inside the car so that I can run it on the carb to see how everything will work first. Tack is connected to MSD6-AL tach output.
Hooked up the laptop and started Tunerstudio.
Started car and MAP responding, RPM working, all gauges look reasonable readings and responding, pulse width, duty cycle around 15%.
But I don't hear injectors clicking like they did on the bench and then - OH NO SMOKE!!
Injector pod also way hot.
Shut everything off right away.
Opened case up and smoked the run on the PCB from the center pin of Q2 to the db 37 connector.
It seems like the injector was stuck on continuously.
DIY autotune has a good explanation on how to test the injector output circuit and I am able to repair the board with a jumper wire and replace Q2 and Q7 but am at a loss as to what went wrong.
I'm sure U7 is also fried because it now gets hot when I try running it on the simulator.
Is it possible to damage the injectors by running them without any fuel flowing through them?
Can they get stuck on with no pressure behind them?
Anyone have any thoughts on this?
Thanks in advance
billr
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Location: Walnut Creek, Calif. USA

Re: Smoked the output circuit MS-1

Post by billr »

"Is it possible to damage the injectors by running them without any fuel flowing through them?
Can they get stuck on with no pressure behind them?"


I think the answer to both is generally "no". There have been discussions about whether injectors can be powered up indefinitely and I believe they can be, as long as the current limits aren't exceeded. In you case, with the very-low-Z TBI injectors that would be controlled by the PWM settings. I think the MSQ would be required to check those. That "no fly-back board" has me worried, or confused at least. That fly-back suppression is usually necessary to avoid damaging the injector driver transistors; one of those could be what is "stuck on" and applying full battery voltage to an injector circuit. So, I gotta ask... why no fly-back protection?

I have little clue why U7 is hot. I would take off the MS1 chip and do the basic voltage tests for 5V and 12V and ground at the 40-pin CPU socket.
zorb847
MS/Extra Newbie
Posts: 13
Joined: Thu Jun 17, 2004 6:35 am
Location: NJ - Butler

Re: Smoked the output circuit MS-1

Post by zorb847 »

billr wrote:I have little clue why U7 is hot. I would take off the MS1 chip and do the basic voltage tests for 5V and 12V and ground at the 40-pin CPU socket.
I have done this and U7 does not function properly - stuck on.
I was not able to get these parts locally and have ordered through digikey but now will probably not get them until Monday.
Have also ordered the parts for the fly back board.
The thing that is puzzling to me is that I had it working on my bench and when I hooked it up to the car it fried.
Something weird is going on -maybe something shorted out accidentally .
I will put it back together and try again as soon as I get the parts.

Also, will any components on the MS1 board be damaged by running it with no injectors connected to it?
I would say no but please correct me if I am wrong.
billr
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Joined: Sun May 15, 2011 11:41 am
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Re: Smoked the output circuit MS-1

Post by billr »

The injector drivers will be fine with no load (injector) connected.
zorb847
MS/Extra Newbie
Posts: 13
Joined: Thu Jun 17, 2004 6:35 am
Location: NJ - Butler

Re: Smoked the output circuit MS-1

Post by zorb847 »

Ok - repaired board and working OK on stimulator.
I read somewhere that it is possible to damage low-z injectors by having improper settings.
One of mine is now shorted out.
Question is could I have set something wrong to do this and smoke the pcb?
DaveEFI
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Location: SW London, UK

Re: Smoked the output circuit MS-1

Post by DaveEFI »

IIRC , you can't drive LoZ injectors with a V2.2 board directly. You'd have to use series resistors to limit the current. This is what early EFI systems did - until HiZ injectors came along and the problem went away.

The V3 PCB was specifically designed to drive LoZ injectors directly. Or add an after market board to the V2.2 to drive LoZ.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
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