94 DOHC to 97 SOHC swap from HELL no voltage to PTU

**Amphiron** · 06-17-2016, 03:15 PM

I am having a HELL of a time getting spark on this thing. I'm not getting any single to the dizzy telling this thing to fire. This is what I've done (oh god what have I done?):
94 DOHC ATX chassis with a 97 SOHC engine, 97 SOHC wireharness and 97 SOHC ATX ECU.
Areas of concern:
- Possible bad ground on the fuel pump harness, I had to rig this up because the old fuel system had failed. Do the grounds on the fuel pump need to be connected for the ECU to tell the car to SPARK? The car is getting fuel.
- The chassis wire harness, it includes a engine fuse, so there is some sort of connection between the engine and the chassis wire harness. I'm just not sure where and I am not sure if it is different on the SOHC.
- There are a million 4 pin orange connectors for o2 sensors. I believe I have them all hooked up correctly but I could be wrong. Could this cause a no spark condition?

I've read many conversion threads for SOHC to DOHC and I don't see anything on the chassis harness. Nothing on this swap because why the hell would anyone else do this?
I want to avoid swapping the chassis harness because of the differences between SRS systems on the 97 and I'm not sure if the dash wiring harness is even compatible. I can swap all this but it's becoming a pain and it would piss me off it it was something else.

**stealthee** · 06-17-2016, 04:11 PM

I hate to send you over there, but there was a thread on 3si years ago where some did the dohc to sohc swap. I've thrown as many ideas as I could come up with off the top of my head at your direction already.

**Boost4VR4** · 06-17-2016, 04:33 PM

O2 sensors don't matter, engine should still run
DOHC engine harness is a little different than SOHC. The DOHC ECU and SOHC ECU pin out differently. The SOHC uses 88 pins and the DOHC uses closer to 115-120 IIRC. The DOHC harness will need to be modified a bit on the MPI side of things (Distributor, coil, fuel injectors, CAS/CAM, Hall Sensor in the distributor.)

You will need to compare the pinouts between the ECUs and see where you need to re-route wiring. It's probably easier to find a SOHC harness and replace the DOHC harness with the SOHC harness.

**RealMcCoy** · 06-17-2016, 04:34 PM

So you have no power on the black/white wire to the PTU? you realize that's the same circuit that feeds the factory fuel pump side of the MPFI system? You said you had a problem with the fuel pump system, could it be the same issue causing both?

The source is fuse 12 in the underdash box... I'd start there, then the MPFI relay...

**stealthee** · 06-17-2016, 05:12 PM

Originally Posted by Boost4VR4

O2 sensors don't matter, engine should still run
DOHC engine harness is a little different than SOHC. The DOHC ECU and SOHC ECU pin out differently. The SOHC uses 88 pins and the DOHC uses closer to 115-120 IIRC. The DOHC harness will need to be modified a bit on the MPI side of things (Distributor, coil, fuel injectors, CAS/CAM, Hall Sensor in the distributor.)

You will need to compare the pinouts between the ECUs and see where you need to re-route wiring. It's probably easier to find a SOHC harness and replace the DOHC harness with the SOHC harness.

He has the SOHC engine/ECU harness. The chassis harness shouldn't affect the ECU

**Amphiron** · 06-17-2016, 10:18 PM

Im starting to the think the issue is in the chassis harness. The 97-99s have a different harness and the 95-97s have a different ECU. This car is a melting pot. I gotta make sure the crank angle sensor didn't get pinched when dropping in the engine and then check signal from pin 10 on the ECU. If it is outputting single and I'm still not getting spark can I run that somewhere and just manually wire the damn ecu? I also have no idea where the cam angle sensor is on this thing.. I'm sure I plugged it in but where is it?

**stealthee** · 06-17-2016, 10:41 PM

I am pretty sure the sohc doesn't have a cam angle sensor or at least it's part of the distributor. The earlier sohcs didn't even have a separate crank angle sensor. The engine in my 94 came from a 98 and I had to use the 94 distributor because the plug in on the 98 distributor was different.

The crank sensor should be a 3 prong triangle shaped plug in that comes out near the ac compressor. I took my ac off years ago and for years I actually had a cranky angle sensor that was doing nothing plugged into the plug in for the ac compressor. Lol

**RealMcCoy** · 06-18-2016, 12:30 AM

You are talking about no signal, but earlier you said you have no power... which is it? Pretty hard to help if we don't know what the symptoms are...

**Amphiron** · 06-18-2016, 12:39 AM

Going to have to change the chassis harness and probably the entire dash harness too unless I can find a way around all this. I'm gonna end up having to go through every single wire in this car and replacing it lol.
There is definitely some ignition stuff in the chassis harness going back to the ECU on the 94 but not sure. I need to figure out if the fuse junction box is different between the two cars.
Wouldnt be so hard but I cant find the 97 equivalent to this diagram.