Oh no! Injectors are staying open!

[ForceFed420a]

Hi all,

Car is a 97 eclipse 420a with a turbo. Car was running just fine for several years. MSII board, just fuel control. The battery is in the trunk with a 0 gauge wire going to the front. Last week, I was driving along when the car suddenly died. I found out that the battery wire had fallen out. Wouldn't start, so I converted it back to the stock computer to drive it home. Concerned that I had damaged the MS through a voltage spike, I hooked the MS back up. It DUMPS fuel into the cylinders now. Like to the point where the car won't turn over unless I pull the spark plugs and then it SHOOTS fuel out of the cylinders. I unhooked the injectors at the injectors and the problem went away so I know it's not my injectors. I have the MS board in the car hooked to a the relay board in the engine bay. When I disconnected the two computers (relay and MS board) the problem was still there.

I checked the fuses on the relay board and they are all fine. I hooked my laptop up to the MS board and it's reading normal values and responding to throttle changes. It just seems that when the injectors get power they are constantly open. Any thoughts??

Thanks for your time.
Brian

[Matt Cramer]

Could be damaged injector drivers. Do the injector LEDs stay stuck on if you test the MS on a Stimulator?

[ForceFed420a]

Matt,

Thanks for your help. I cracked open the MS box yesterday to find the top of the U7 transistor completely blown off and rattling around in the case. That's probabaly my problem! I pulled out the transistor and hooked up the stim and my laptop and everything still worked. I'm getting pulses on pin 2 and 4 of U7 and all the inputs were recording fine when viewed with the laptop. I'm going to order another U7 today and the two FET drivers (in case they are blown too) and hopefully that will solve my problem. Can you see anything that I'm missing?

Thanks again,
Brian

[Matt Cramer]

Yikes! Glad to hear it's solved. I don't think there's anything else you are likely to need.

[Heribert]

Ff 420 A
Make sure that verify the flyback circuitry once you have injector channel problems.
Sometimes the smoke breaks out in an obvious manner, like popping the MOSfet open,
but sometimes it is more of the silent type that just dies without fuzz
The injector driver and the flyback ctrl are very much cooperating!
Ohming the circuits with a DVM that has a diode test function will tell you a lot.
Also check that traces have not wrinkled, overheated or turned into copper oxide !

Best of luck

[ForceFed420a]

Heribert,

Thanks for the advice. How would I know that the flyback control isn't working? Let's say I plug another U7 in and the injectors start working properly. I still have my oringinal msq so that shouldn't need any modifying. What would I be looking for to indicate the flyback wasn't working properly?

Thanks again,
Brian

[Heribert]

Ff
I would first of all verify the PCB and all components visually, which at my age means with the aid of a 10x lens and real good
illumination. Look for miscolored, wrinkled PCB traces. Also look for solder joints that are kind of grey, and often have a rough surface.
Then onto components, look for miscoloration and hairline cracks.

Then it is time for a DVM with a diode test option, most have this. Verify that all diodes are indeed diodes , that transistors are OK and that resistors
have the correct values. This takes some electronics skills, you may want to find a geeky electronics buddy who can help you out.

Just to replace the obviouly failed parts and then fire it up is another option, but with power circuits this may not be your best bet. There is a
significant risk that some part of the flyback circuitry is fried, especially if you run LoZ in PWM mode .


If you have a scope , the final verification is to run the car and scope the injector drive voltage

Are you runing HiZ or LoZ? If lo Z PWM or resistor mode

Best regards

Heribert

[ForceFed420a]

Heribert,

Thanks for all the great info, very much appreciated! Sorry it took a while, computer didn't want to work this weekend.

I have low Z injectors with PWM. I looked at the MS this weekend and didn't see any visual problems like you were describing. I was dealing with another problem. I turned the car on to see if my amplifiers were fried (MS not hooked up) and I smelled fuel. Concerned, I went to the front where I saw gas leaking from the injector. I pulled the rail out and did it again and on 2 of my injectors (2 & 4) there was gas spraying from the body of the injector, at the seam where the black electrical piece and the main body of the injector come together. So now I have to replace those as well. The other two injectors were dry. Fortunately, the amps were OK

When I ordered my U7 chip, I also ordered the two FETs that the U7 drives, in case they were bad. Also, I ordered the parts for the flyback board according to the website where it says:
"If you are replacing your flyback circuit because of a failure, you should replace the FETs (2 @ IRFIZ34N-ND - $1.20 each) and FET driver (1 @ IXDI404PI-ND - $1.68 ea.). You also may want to put a socket in for the FET driver, use AE7208-ND - $0.35. " taken from http://www.megamanual.com/fbbom.htm Does this seem right?

My electronics buddy is out of town for a little while, so I did a little research on how to test Mosfets and here's what I came up with. http://www.electronicrepairguide.com/mo ... sting.html

Does that seem right? Honestly, they are so cheap, I was wondering if I should just go ahead and replace them.

Unfortunatly, this has gotten me pretty down. I was hoping that I wouldn't do any extensive damage, but I got a few things to fix before I'm up and running. I suppose it could have been worse. Thanks so much for taking the time to guide me through this, I was awfully nervous about trying to fix this MS but I think I can do it.

Thanks again,
Brian

[ForceFed420a]

Heribert,

Okay, an update. I got the shipment from DigiKey today, and I put the new U7 into the board, hooked up the stim, crossed my fingers and fired it up. Lo and behold, it worked! I have nice pulsing on the stim which responds to RPM nicely. So I know my injector driver is up and running and so are the FET's that it drives. I also shut it off after a few minutes and (after grounding myself) touched the driver and FET's and nothing was hot, so that was good.

So it looks like the only thing that may be still of concern is the flyback circuit. I do have the seperate flyback board installed, which according to the website is beefier that the on board flyback circuitry. I don't see any visible damage. I'm leaning towards putting it in the car and seeing if it runs normally. According to the website, if the motor won't run without the PWM being higher than 75%, then it's not working correctly. This leads me to believe that it could run for a few moments to test it and if it runs normally without changing anything, the flyback board is working OK. If not, then I go and replace components.

One last thing. I think I misread the website before. I forgot that there was on board flyback circuitry and the seperate flyback board. I have the on board disconnected and the flyback board installed with the heat sink. I'm hoping that it was beefy enough to take what I through at it.

What do you think?
Brian

[Heribert]

Thats a new one!
Injectors leaking from thru the body. Never ever heard of. Makes me nervous. Could be that it is a result of
overheatin by applying 12 V cont.Another excellent reason to not use LoZ Injectors leaking down on the
ex manifold is a major fire risk.

The flyback board is not really stressed until you connect up the injectors and start operating them in
PWM mode. Masuring the components is a good step as described, and then maybe trying them out for
a few secs only. If the drivers and IC get hot, switch off and continue troubleshooting.

Best regards

Ola

[ForceFed420a]

Heribert,

Good news! I borrowed a set of injectors from my buddy and put them in the car. Without changing the PWM, I fired it up and it purred like a kitten. After a few seconds I shut it off and touched all the transistors--they were cool to the touch. So I did it for a minute and touched again. Just fine. Then I ran it for a few minutes, revved the engine a little and it ran great. Shut it off and touched them again. Not hot at all! Woo hoo, we are back in business!

Thanks so much for your expert advice. It is much appreciated, and is keeping one more Megasquirter on the road!

Thanks again,
Brian

[Heribert]

Brian,
thanks for the feedback, we learn all of us as we dig in .
Leaking injectors that send fuel out thru the body has got me thinking.
Good luck with the car!

Heribert