DIYPNP Parallel Installation On A Previously Automatic Car?
 

Ok, to kick things off, I just built a DIYPNP and was stoked when I got it working and flashed on the laptop. Then I hooked it up to the car, and my enthusiasm quickly waned.

After plugging it into the vehicle, I noticed that my Charge light was on the dashboard, and no CEL light. The car would crank but wouldn't start. It fires right up with the stock ECU put back in.

My buddy and I started going over the wiring and the diagrams on the DIYAutoTune site, and everything checked out.

After more thought, we realized that the wiring diagram is for a manual transmission, and mine is an automatic car with a 5 speed swap.

So, I've spent all morning searching, trying to find possible solutions and the only thing I can come up with is running it parallel with the stock ECU, but I am finding little to no information on how to pull that off.

I've shot DIYAutoTune an email, awaiting a response still, but I wanted to come to some of the experts here to see if ya'll can't send me down the right path to get this figured out.

In case my signature doesn't show, it's a 94 1.8L, with a GT2860 churbo, stock injectors. Not sure what else ya'll might need for this specific situation, but I appreciate any help and guidance you can throw my way.

DIYPNPs normally don't have a check engine light output.

When it's on the car, does it connect to TunerStudio? Can you get a data log of a failed attempted start?

Hey Matt,

I can get it to connect to TunerStudio through the car, but it doesn't stay connected. The furthest I've gotten with it connected to the car is grabbing the TPS signal.

When I make it grab the no throttle signal, it will accept it, then disconnect. Then reconnect long enough for me to set the full throttle signal, then disconnect again. By the time I hit the "Accept" button, it's disconnected for a 3rd time, and won't go back online until I disconnect it from the car, and reconnect it again.

It repeats this process every single time. Looks like it tries going online 3 different times, then shuts itself off. I haven't been able to do any type of logging on it.

I also replied to that email, if you're the same Matt, noting that I don't have 5V on VREF.

Will it stay powered up if you test it on the bench instead of on the car?

Yeah, it does. On the stimulator, there's no problems.

Check to be sure nothing VREF is wired to is shorted to ground.

What did you and your friend find different on the ECU wires between the auto and manual? I dont seem to recall there being any at the ECU. upload some pictures of the inside of your ECU. Sometimes we can look at it and see something right off the bat thats incorrect. What are you using to connect to the MegaSquirt?

We didn't actually find any wiring different. Looking into the parallel installations through the DIYAutoTune site they mentioned that some automatic cars have a voltage regulator inside the ECU, and assumed that was the issue.

Matt's been helping me diagnose it through email, too -- that's when I realized that the auto ECU isn't the issue, but my soldering / wiring probably is.

I appreciate the help figuring this out! I've attached a few pictures. Try not to beat me up too bad on the solder job. ;P

Testing for continuity on the VREF circuit, I didn't get any. I did notice that I removed the R14 and tied it into 4S and 1J. The trace on the top of the board leads from VREF to one of the legs on the R14.

I didn't have continuity between the two legs on R14, though. Not sure if that makes a difference, but from what I can tell it's not grounded out anywhere.

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