The Project Pad

OK, to make a long story short....I have a VEMS V3 ECU running a 40v V8 in my 4kq. Was running fine for about a year then I started noticing my variable intake runners werent swtitching(has 2 that are controlled by steppers). Then a few months ago while on my way home from my parents house the car died. The digidash was still on but the VEMS LCD was off. Found the 5 amp ECU fuse blown. Put in another and it instantly blew like there was a short to ground. Then I put in a 10 amp fuse(no more 5 amp) and it didnt blow. Car started up fine and i drove home. Ever since then the VEMS ECU will shut off by itself after 30-45 minutes of run time. I disconnected the power to the intake manifold vacuum switches that are controlled by the steppers(steppers are inverted to control the ground side) and the problem still occurs. I verified that when the ECU shuts off it still has 12v to it. Ground is good. Also, after the ECU shuts off by itself I can instantly restart it and it will run for a few seconds and then shut off again but if i let it sit for a few minutes it wont shut off for another 20 minutes or so whick leads me to believe it may be something getting hot and or building up resistance and causing the ECU to shut off.

Yeterday I was at derracudas house with the car and started poking around. Found the ground wire from the ecu to one of the intake cavuum swtiches to be open. Checked for shorts and found none in any of the ECU wiring. I still need to do a little more checking, but before I drove home(vacation home ) I disabled both steppers. I drove the car about 25 minutes and then let it sit and idle for another 15 and the ECU did not shut off by itself. Thils leads me to believe it has something to do with the steppers.

My question is, is there anything i can do to check the steppers? maybe open up the ECU and look for something burnt or melted or discolored? Any help on this would be welcomed. Thanks.

Any luck Dan?

What does Marc Say about it?

He's sent me logs on it, but its tough to say. shows up as a disconnect which can mean either an internal or an external problem (meaning, the ecu shutting off because of some internal overload or an external power load). it is possible the stepper is getting overloaded. if that turns out to be the case we can work around it by using a relay control on a p259 to drive some of your high current loads currently driven by the stepper (such as the variable intake runner drive).

LOL, i dont know who sent the logs, but it wasnt me. When this all started my laptop was doing the Blue Screen Of Death, so it spent over a month with Best Buy getting fixed so i wasnt able to make logs. Im going to drive the car tomorrow and see if it doesnt die again and then try enabling the steppers and see if it will die.
Marc, is it easy to open up the ECU and look for damage? When this all started the variable intake runners were not working even though everything still had power/ was hooked up and the steppers were enabled, so im thinking the steppers may be burned up or the like. And thanks for all the help.

40v4kq wrote:LOL, i dont know who sent the logs, but it wasnt me. When this all started my laptop was doing the Blue Screen Of Death, so it spent over a month with Best Buy getting fixed so i wasnt able to make logs. Im going to drive the car tomorrow and see if it doesnt die again and then try enabling the steppers and see if it will die.
Marc, is it easy to open up the ECU and look for damage? When this all started the variable intake runners were not working even though everything still had power/ was hooked up and the steppers were enabled, so im thinking the steppers may be burned up or the like. And thanks for all the help.

take off the back cover plate (opposte the EC36 and EC18 connectors)

the stepper is near that side. if you let the magic smoke out, it will have a horrible acrid burnt smell to it.

when the stepper chip goes, it usually does so in reasonably spectacular fashion. the chip will physically be in pieces or otherwise have a big hole in it.

Will do.

Today we used the car as derracudas "work car" to drive from jobsite to jobsite to see if we could get it to act up and make some logs. Even with the steppers disabled it still starts acting like it has an ignition breakup and then the ECU shuts off. I was able to make a few logs of it although it seems that the logs end when the breakup happens. Everything on the main view freezes and com between the ECU and my laptop is lost.
Marc, I sent you the config file and two of the logs. Look for the email from jettacoupemk2

what does Dereks ECU do in the car? that could rule out something in the car versus something in the ECU no?

When I burned up my stepper chip the ecu would blow the ecu fuse whenever power was applied.
Just a thought...

Speeding, trying his ecu was an idea of dereks. I think he wanted to check with Marc about if it would work or what would need to be done to make it work.
Phil, Originally the fuse did blow, but i've been running it with the 5 amp fuse back in there for the last cuople days and it has not blown. Gonna pull the back cover off the ecu tomorrow and have a look inside.

So... maybe the stepper is burnt up?

maybe. I hope to find out tomorrow. The question I have is... even if one or more of the steppers are blown would the ecu still have the issue that mine is having even with the steppers disabled?

I pulled the ECU today and removed the back cover but couldnt see anything that looked bad in any way so I pulled the whole board from the case to take a better look. Everything looks normal although it did smell like overheated/burned electronics a little. Not sure if the smell is normal or not, but either way there was nothing that looked abnormal to me. No signs of melting, overheating, burning, etc.
I put it back together and reinstalled it with the steppers enabled and power reinstated and the intake control valves do not click. I didnt have accsess to a DVOM or test light so I couldnt test to see if the steppers were supplying ground like they are supposed to. I head back to cali with the car tomorrow so i'll probably have ot wait till sunday to do more diag.