ECU wiring hack job

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Evanippolito

Evanippolito

New Member
Hey guys I'm new here so if I posted this wrong let me know.. I recently acquired a 91 civic EF with a b20z block and b16a head. Previous owner "custom wired" an OBD0 to OBDI conversion harness and installed a chipped p28 but things got crazy. Long story short, the car won't start. I have very little experience with anything that doesn't have a carburetor.. Can anybody make heads or tails of what I'm looking at/ tell me where to start? It looks like there are two OBDI harnesses so I tried to diagnose which plugs were which. So far all I can figure out is that no matter which combination of plugs I use, I have fuel pressure. The starter seems to only crank when it wants to, regardless of if the car is being jumped or not.
 

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Previous owner had the yellow harness plugged into the ECU. Also, car is constantly throwing a solid CEL and oil light. pulled the ECU board out and it looks fine to me. I don't know what a fried one should look like. There is a slight black mark on RP18 but that's it. Would this mean it needs a new chip?
 
Do you know for certain if the car is a LS/Vtec?

Also check your ignition wires its a common Honda thing to have a different ignition or walmart security system that someone's cousin likely named "Bubba" wired in with a pair of wire strippers and electrical tape

Try and get another P28 just to confirm the ECU is not the issue

Oil lights are weird I didn't have a oil pressure sensor on the harness of my first Teggy but it would still come on at random times which scared me enough I wired one in.

CEL might mean something it might not it could be something stupid like frayed wires on your MAP sensor it would be good to try and scan it.

To make a car start you need fuel spark and air, if she won't start one of those is missing I'd try and start there and identify whats missing. If you have fuel pressure and spark and air (air is almost never the problem) the next thing to check would be injector wiring sometimes those get crossed so you could have fuel pressure but its not getting injected into the cylinder.

Do some diagnostic stuff and get back to us, I had similar problems on my last two builds but its hard when you cant eliminate variables.
 
Thanks for the quick reply. I had the car jumped to my DD and I put the positive right to the starter and got nothing.. My grounds were definitely good. Taped off the injectors and got no spray. I tried looking up what a solid CEL code was and i read that it was an ECU issue. I'm gonna try to get my hands on another p28. Only question is, if I hook up a fresh ECU do I run any risk of damaging it? Also, how hard would it be to rewire just the body harness?
 
I mean if you have a solder gun and some wiring diagrams I'm sure you could do it just seems drastic.

Did the car run before? If it did hooking up another p28 shouldnt hurt but idk what makes ECUs "cook"

Using a power probe if you can get ahold of one turn your ignition on and test the wires to the injectors you should have one with a constant pulse and one ground. The ground should pulse as it tries to fire. If those are fine make sure your fuel pump is good and that you're getting fuel to the rail
 
Yeah I don't know how ECUs take damage. That's why I'm lost. Previous owner said it ran, just didn't run very well. Then he unplugged the ECU and plugged it back in and now it won't run. I'm going to check out what's up with those injectors tomorrow.
 
Ok bud heres how it works its not likely it can be fixed without physically being looked at and diagnosed , id say start over and get the correct harness and electronics and getting rid of whats there and use a obd0 to obd1 jumper harness to use the p28, if its a dx even more is needed because you have to redo the dpfi to mpfi conversion , this is the downfall of buying a car swapped and hacked up by somebody else
 
Yeah I knew this was probably gonna be a huge headache when I got the car. I basically got it for free though so I can't complain. It's hacked up before the OBD0 harness so would you recommend I run new wires from everything? I think it would be easier to start completely from scratch than to try to figure out what wire is what.
 
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