Injector flyback shorted

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sdtib
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Injector flyback shorted

Post by sdtib »

MS2 Extra

Car was running great until 2 days ago, I had my laptop connected doing some data logging when I lost the connection, when I check the cable to the the MS, it had come unplugged. when I plugged it back in, the engine immediately began running rough and my idle AFR dropped to 11:1.

For my serial connection, I use a DLP-TXRX internal USB/serial adapter from DIY Auto tune. I have it mounted in the bottom of the case with a strip of Velcro with the connector end poking through a hole in the end plate below the DB9 connector. When I opened the case after this problem occurred, I noticed that it is very close to the legs of Q11 (TIP42) and because it is only held in place with Velcro, it can move a little when the cable is plugged in and come into contact with the left leg of the TIP42. I believe this is what happened when I plugged the tuning cable in with the MS powered and I shorted out something in the bank 2 injector flyback circuit. I read here in another thread that a faulty flyback circuit can cause the injectors to stay open too long creating an overly rich condition. Seems to me that I have 1/2 of my cylinders running rich.

So, assuming I am correct and this is what happened, what needs to be replaced? I already replaced the TIP42 because I found it in stock at Radio Shack but that did not make any difference. I am guessing the next most likely suspects would be the diodes, either the rectifier diode in D7 or the Zener diode in D20. the only other component in the flyback circuit is a 1/4w resistor in R33, could this be it? Anybody know which way I should go or how I go about testing to see what is blown?

Thanks
jsmcortina
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Re: Injector flyback shorted

Post by jsmcortina »

Change the TIP125 for that channel too. Beyond that it is a bit tricky without an oscilloscope, unless someone else has some good diagnostic ideas.

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sdtib
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Posts: 56
Joined: Mon Jan 06, 2014 10:28 pm

Re: Injector flyback shorted

Post by sdtib »

Thanks James!

I have hi-z injectors so I am not using using the PWM current limiting flyback circuit, do you think the TIP125 could still have something to do with this?
Marek
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Re: Injector flyback shorted

Post by Marek »

The good diagnostic idea is to check how much current is being used by each channel - the more channels you have, the better the test.

For example, put the car into injector test mode of say 4mS per 20mS duration and connect voltmeter inline as an ammeter in circuit. If three channels pull (for argument's sake) 1.1amps, but the 4th pulls 1.6amps, then you immediately want to know what is up with the 4th channel as its injector is staying open longer because the average current pulled is higher. (You can then do some calculations given how much current it takes to open an injector, what its average hold current is (in your case, the same) and the duty cycle to work out whether the measured number corresponds well to the empirically found results.)

Obviously, the more channels/cylinders running sequentially, the better. You can then multiplex the connections to isolate where or what the fault might be.

kind regards
Marek
sdtib
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Re: Injector flyback shorted

Post by sdtib »

It's an MS2 so, non-sequential, only two channels. I have it wired to fire each bank alternately so channel 1 fires bank 1(cylinders 1,3,and 5) and channel 2 fires bank 2(cylinders 2,4,and 6). The firing order is 1-2-3-4-5-6 so this made the most sense to me.

I had it hooked up to the Stim last night and the LED's indicated that both banks were firing alternately as they should but I noticed that the LED for bank 2 was much brighter, or more intense. I took that to mean that there was more current flowing through that channel.

I think I am just going to order both diodes and the resistor and replace them all and see if that fixes it.

Thoughts?
sdtib
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Re: Injector flyback shorted

Post by sdtib »

Parts came in today, replaced D20, D7, and R33. Fired the engine and still running rich, back to square 1.

I was assuming the problem was related to the active flyback clamp circuit but now that I have replaced all of the components in the circuit, I'm not sure anymore.

I'm attaching my current msq and the log file of when it happened. The problem began when I plugged the tuning cable in while the MS was powered but the engine was not running,....At record 1460 is when I arrived at my daughter's school and shut the engine off to go get her. you can see the engine is running normally up to this point. When I returned to the car I turned on the ignition but did not start the engine right away, I could see I was offline so reached down and plugged the tuning cable back in and then started the engine. from that point forward it began running rich. does anything jump out at anyone
sdtib
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Re: Injector flyback shorted

Post by sdtib »

okay, a little more information. This is a parallel install so the stock ECU is still in place controlling AC, automatic transmission, idle valve, etc. It also still has the stock o2 sensors connect to it so I hooked up my obd2 scanner today to see what it would tell me. Bank 1 02 voltage was. 04, bank 2 02 voltage was. 9. Bank 1 fuel trims 32, bank 2 fuel trims - 32. I also pulled the spark plugs and all of the plugs on bank 2 are black and sooty so this is definitely an issue with bank 2 only.

I don't think it could be the injector driver (Q5) because it is firing the injectors, just way too rich. Do you suppose I could have damage the processor? I don't see how because everything else is working fine but I guess it is possible. I already tried reloading the firmware.

Could I have burned the traces on the PCB? If so do you think I should use some hook up wire and follow the schematic to make the connections directly?

are there any other components I should try replacing? I am at a loss here and could really use some help.
sdtib
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Re: Injector flyback shorted

Post by sdtib »

Well, since this is my daily driver and I am still driving it daily, I have been a little worried about Bank 1 running too lean. With bank 2 so rich ego control is running at 75% trying to equalize the AFR. I have really been babying it so has not get into boost at all until I can get this sorted out.

Since I can't seem to figure out what is wrong with it at this time I came up with a temporary solution. I set up tunerstudio to run dual tables and I have tuned the VE table for bank to very lean until I got the AFR to around 14 at idle. Bank 1 ranges from 50 at idle up to 120 at 185 kPa while bank 2 is set at 20 at idle up to 110 at 185 kPa. it needs a lot less adjustment at the larger pulse widths to get it to run right.

I'm still looking for some help because I am completely stumped
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