Help with wiring harness swap
 

So a couple years back I had a short fry the wiring in my car and so it sat, until now.

I replaced the engine harness, front and read chassis harnesses, and dash harness. Everything out of an 88 except the front chassis harness, which came out of an 86/87 sport. All the wiring was checked for damage before installation.

I left the charging harness be because its modified to work with my battery relocation.

I decided to test the wiring before putting the interior together and I'm glad I did, something is not right. Most plugs in the harness don't leave a chance to mess up and I looked everything over, didn't notice anything obviously out of place.

As it sits now, the cars getting power, I get one normal beep when I turn the key on followed by a few muffles attempts. The fuel pump doesn't prime, car wont attempt to start, the blower door constantly cycles through positions with the logicon off, the fuel level guage pins past full, the tach pulses when the key cycles to the start position even though the starter isn't turning. Seems like something is way out of place.

I noticed some very minor differences in the front chassis harness (just door harness connectors) but it seemed overall the same. Are there any major differences between 86/87 sports and what would have been in an 88 base?

I'm going to try replacing the charging harness to see if that helps but the problem seems deeper than that.

I know this is not a common problem, probably caused by something i messed up, but im lost. Any advice from someone who has done similar would be incredible. I really want to get my baby back on the road.

Have you checked the main relay?
It sounds like you have a lot going on with the cluster and logicon,it may not entirely be your wiring but the Units themselves,i.e. corroded on the boards and connectors.

The pump is not supposed to prime w/key to on unless you have the fuel check connector jumpered.

Have you checked for spark/fuel?

A fuel gauge which responds such as yours could be caused by a grounding of the wire from the sender unit to the gauge (this would eventually damage the gauge).

I haven't gone though and tested individual components yet, Im hoping I won't have to start specing them all and that there is a bigger underlying issue.

I did have the fuel pump rewired so I guess I was just used to having it that way. I was able to get it to come on by opening the MAF door.

I haven't checked for spark yet, I didn't want to damage anything by playing with it while obviously wrong.

I swapped out the logicon with another unit, same thing.

According to the FSM the wiring for 86-88 should be the same, unless you are mixing NA and Turbo harnesses together.

Rear chassis harness came out of turbo if that makes a difference? Everything else is out of non-turbo cars.

there are 2 plugs at the blower unit that sort of look the same.
Honestly I am not sure what "the other one does"..but you may want to double check that area.
One is held onto the frame of the blower unit and remains unplugged if you have NO A/C...so maybe it is for A/C???

I'll check that out. I have a copy of the FSM so worst case scenario I can go through and check everything over piece by piece. I'm picking up a new charging harness tomorrow so I can atleast rule that out before hand

Couldn't get a new charging harness today so ruling that out will have to wait.

I did find I had missed the dash harness ground(due to using just the harness and not the dash itself) and securing that solved my heater control and gauge problems.

Car still doesn't start or have a tach signal. I tried plugging in a spare CAS and spinning it and got no clicking from the injectors. What electronics could be to blame?

The 86 sport front harness seems to be lacking provisions for power windows so I'm going to remove the need wiring from my old harness and run it into my car if that's feasible.

Making progress! Thanks for everyone's in inputs!

No ground will cause all sorts of interesting problems. Glad to hear you got it sorted out. I'm not sure just spinning the CAS would fire the injectors if there's no MAF signal.

If i recall correctly, when everything is in working order it will. The AFM is atleast seeing power, when the door is moved the fuel pump comes on

I think the mixing of a early s4 n.a harness, a late s4 n.a harness and a s4 tii harness is your issue.

When i bought a 86 years ago it had a blown tii swap/harnesses. I swapped in a s4 n.a harness/engine combo but some of the connectors werent compatible. I ended up using a earlier s4 n.a harness and everything buttoned up just fine for me. You may just need to find the harnesses in one shot all from the same chassis.

Also the fuel pump doesnt prime with the key on. It only comes alive while the key is held to start or you jumper a connector on the engine bay harness then turn the key to on.

The only injectors which would click would be the primaries. When spinning the CAS w/key to on the coils should fire as well. Sometimes the coil clicking can drown out the injector clicking. Also, check the Brown/White wire at any sensor such as the pressure sensor and check for 5 volts w/key to on. If not present then the car cannot start.

its possible that the harnesses arent compatible, however i've seen early s4 body harnesses successfully mix with later s4 engine harnesses and the tii rear harness was indistinguishable from na, they could have changed pinouts, but for now im going to assume that they are compatible.

someone else mentioned the fuel pump, I did have it rewired so i was used to hearing it whenever i turned the key on, now that im back to stock wiring, it doesnt, so thats all correct.

The coils nor injectors, nor anything else was firing when spinning the CAS. any idea what components could have failed to cause this? i kept most of the relays intact with the front charging harness, the car the came from was sitting inside, but for a very long time.

W/key to on the Black/Yellow wire at the lead coil should have 12 volts. W/key to on the Black/White wire at the pressure sensor should have 12 volts. And the good ole Brown/White wire of the pressure sensor needs to have 5 volts w/key to on.

B/y wire to leading coil has 12v
B/w wire to map 1.3v
Br/w wire to map 0v

Unplug the AFM and recheck the Br/W wire w/key to on. Also, w/key to on check the B/W wire found in a Green check connector near the lead coil which also has a few Yellow based wires (4 wires in total). This wire should read 12 volts. Check the B/W wire first (B/W wire powers the ECU and if the B/W wire has no power w/key to on that would explain why neither of the two wires tested at the pressure sensor were w/o voltage).

key on, afm unplugged, at pressure sensor br/w wire still has zero volts

key on, green test connector, b/w wire ~1v.

so no power to the ecu.. what next?

Check the EGI COMP fuse for it could be blown. It powers the White/Blue wire in the 4 wire main relay plug. If the W/L wire at the relay has constant 12 volts (no key) then your relay is likely problematic. If the W/L wire does not relay voltage to the B/W wire, as it should w/key to on, then you could jumper the two wires together temporarily to work on your car (the jumper over time could eventually drain the battery).

egi comp fuse is good and putting out 12v at the w/l wire.

at the main relay end, relay unplugged, the w/l wire is ~1V

what does that leave inbetween the egi fuse and the main relay? ignition switch?

It's looking like my mixing of harnesses could be the cause as felixisgod suggested. I got confirmation from someone else who dealt with similar issues mixing early and late s4 harnesses.

Going to investigate more tomorrow.

The W/L wire should be a straight shoot from the fuse to the relay. Pull the EGI COMP fuse and perform a continuity test of the W/L wire from the fuse box to the relay plug as there should definitely be continuity. If there isn't then the wire must be severed (this wire is part of the front harness).

satch you were spot on! the w/l wire had a break in it! really weird though, the insulation where it was showed no damage, was still soft too. after stripping back the insulation, both ends were heavily corroded.

After you get that issue corrected the relay should now send voltage to the B/W wire w/key to on so now the ECU will receive proper voltage and that should help either to fix your problem entirely or at least get you pointed in the right direction w/respect to getting the car to start.

Yeah, I have power to the ECU and map sensor as it should be. I have spark but no fuel.
however forgot my injectors were low impedance and need to wire some resistors into my new harness still so that could be causing the issue I imagine. Hopefully I didn't fry the ecu or injectors in the process.

Thanks a ton for the help satch

Will update again next weekend when I can work on the car