87 TBI Wiring

[Beyond]

Can anyone tell me where the exhaust sensor wire that goes into the drivers side exhaust manifold sensor originates at? I repaired my exhaust manifold this weekend and don't believe that sensor was hooked up. I looked all over the back of the block and around the firewall looking for a female plug to hook the sensor back into but haven't found one yet. Not sure if someone clipped it off somewhere or what. The engine must be running in "default mode" or something with that sensor unhooked and I think it's been that way since I got it a couple weeks ago. Also found that the temp sensor in the pass. head was broken off and not working, I'm kinda surprised the truck runs as good as it does 10mpg.

[Russell]

With the TBI (and I would guess 700r4) you should be getting closer to 18 - 20 mpg with that truck... The sensor from your exhaust manifold is the 02 sensor, but I'm not quite sure where you hook it up....

[Beyond]

Well it's a 454 crew cab dually (ton), with Granny 4-speed. I didn't think 10 was too bad for city/highway driving considering the weight of the truck. If I can find out where to plug that sensor in I'm hoping to gain a little more.

[Jason Spears]

There should be a purple wire with a connector on it coming from a wiring harness behind the engine. Hopefully someone did not clip it off, that would be bad. I have a small block TBI in my truck but I'll try to find out where the wire comes out of the harness tomorrow. Hopefully, they small block and big block are similar.

The temp sensor in the passenger side head is for the auxillary cooling fan.

Good luck.

[Beyond]

Thanks Jason, I'll dig around some more tonight and try and find it. It's probably there somewhere, just having a heck of a time seeing it. Finally got the pass. side exhaust manifold off last night - found out they are impossible to remove without taking off the air injector plumbing first LOL.

[nn2004]

According to the diagram, it originates at the ECM. I'd start pulling off all the plastic wire covering coming out of the passenger firewall and look for a very very light colored purple and see where it was cut at since it's all on the top of the firewall. Mine is almost a whitish purple for some reason.

[Beyond]

Finally found it last night, was hiding on top of the bellhousing. Hooked it back up and the truck idles down quicker now. Still haven't found the miss in it. When I repaired the exhaust manifolds (2 cracked ones) I introduced a miss in it somehow. So far I've replaced plugs, wires, cap, rotor, module and hooked the o2 sensor back up. Still has a miss in it. Only thing left is the coil and pickup, guess I'll try the coil next.

[Beyond]

Finally found the miss, sparkplug was arching to the spark plug heat shield on #6. Run's like a champ now.

[nn2004]

Glad to hear everything worked out for you.

[Grim Reaper]

The sender in the passengerside head is for the AUX electric fan in the grill. It comes on at 225 degrees f

The sensor for the ECU is above the water pump on the front edge of the intake. Driverside sensor is for the gage or idiot light.

[Beyond]

That explains a few things about the aux fan sensor. I was trying to figure why the previous owner had a toggle switch under the dash hooked to a relay on the drivers fender. I bet he was overriding that fan relay. I unhooked his switch setup, had bad wiring job on it. I'll get me a new sensor and try and find a socket somewhere to get that fixed.