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TBI to PF4….wiring

JT88K5

JT88K5

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I have cut down the engine wiring harness and removed the old ECM. May have cut a bit too much, nothing that can’t be undone imo. The method used was to work from the bulkhead connector out. Wiring for Alternator, starter, trans, coolant temp and oil pressure were left intact. The sensors were moved from old engine to new. Any remaining wires were cut with at least 30” of wire remaining from the bulkhead into the engine bay just in case I forked up.

In the process, I ended up cutting all wires from the existing fuel pump relay mounted on the firewall. Looking at the pf4 wiring instructions, I saw where the orange and white wires went to the fuel pump relay, and assumed I would connect those in place of the existing orange and tan/wht wires so I cut those. The DK grn/wht wire went to the old ecm, so it was cut, the red wire has a connector on it, problem is I didn’t disconnect it myself and I don’t know what was connected to it. I assume 12v? If something was connected, I can’t find it. Blk/wht was grounded, only wire I’m sure of.

I have the new ecm mounted under the dash, where the old ecm was mounted. Wire harness is routed into the engine bay, same as old. I realize the fuel pump relay needs to connect to fuel pump some how. Instructions note only to use Bosch jd2912 style relays.

First question is if the existing original relay is Ok to use? I’m compelled to replace it just so I’m following the diagram on the pf4 instructions pin for pin.

Second question is can someone help clarify which wires on the bulkhead connector would feed the fuel pump from the relay? I assume those would go through the bulkhead connector.
 
The red wire is open. If you have a relay issue, you connect 12v to that wire and the fuel pump will run. Is a diagnoses aid. The existing GM relay is ok to use, providing it is in good shape. relay is a relay, some have built in diodes which keep some devices from holding relay closed when powered down.
 
@JT88K5 do you have the wiring diagram for that truck? Presumably so since your gutting it
 
What year TBI? The '90 and '91 are a bit different from the '87-'89 due to the electronic gauge cluster.

I didn't use the factory relay on my '90 PF4 swap. I used a Bosch relay and a dedicated fuse. The tan/white was the fuel pump + wire, pink is the gauge. They run from the tank up the drivers frame rail to the bulkhead connector. I cut the tan/white just before the bulkhead connector, below the brake booster and spliced over to the new relay from there. Be careful, there are a ton of pink wires, like the old coil + wire, which is what I used for the ProFlo4 main relay trigger wire. I also swapped to Dakota Digital gauges later. The gauges didn't work right with the stock fuel level wire (pink) but a new dedicated pair +- made it all work properly. There are also a bunch of pink wires in the charging circuit, which should be fine with stock gauges but if you swap to aftermarket gauges there is some trickery involved for charging.

This diagram was correct for my '90 swap.
1722899211685.png
 
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It’s an 87. I do have a tan/wht, from the relay it was connected to the bulkhead connector. I don’t think it was spliced to other wires. The orange wire was spliced inside the harness with ~4 other orange wires, much like you described your pink wires.

I have a heavy gauge pink wire and a small pink/blk (ignition) coming from the bulkhead connector. Heavy pink went to the dist, which I think contained the coil? I just started to install the pf4 wiring, fuel pump relay was first on the list since it’s on the firewall. Also seemed logical after plumbing the fuel lines and regulator.
Back to the tan/wht wire, is there a reason To bypass the bulkhead and tap into wire coming from the pump? Voltage drop due to extra connections?

Below are the diagrams I’m using

EA672018-DAD8-4CD3-9AA8-C2FA9938322B.png

8C00012F-4507-4C1A-B830-A70E57A88568.png
 
JT88K5 said:
You say that like it’s a bad thing. I would call it gently removing. Though I may have bent a few things along the way.
Click to expand...
bent as in rearrange or Bent as in “something Bent would do”?

I believe when I wired the 77 I went that same route. I had originally ran a TBI system, so I removed all of that, but it was 100% separate from the chassis wiring
 
Mine also retains the chassis wiring for lights. The starter wiring is stock through the column.

The larger gauge pink that went to the distributor is the one you want for the ProFlo4. The ProFlo4 signal wire is also pink in the new harness.

You can retain the stock fuel pump relay if you want. I use the ProFlo4 fan triggers for cooling on mine so I wired up 3 new relays with fuses for the 2 fans and fuel pump.
 
HankScorpio said:
Mine also retains the chassis wiring for lights. The starter wiring is stock through the column.

The larger gauge pink that went to the distributor is the one you want for the ProFlo4. The ProFlo4 signal wire is also pink in the new harness.

You can retain the stock fuel pump relay if you want. I use the ProFlo4 fan triggers for cooling on mine so I wired up 3 new relays with fuses for the 2 fans and fuel pump.
Click to expand...
Did you delete the oil switch circuit?
 
Bent77 said:
bent as in rearrange or Bent as in “something Bent would do”?
Click to expand...

bent and Bent:coolblue:

On the 87, it was more segregated than I expected. 1st year tbi? Aside from the wires I described that were connected to the FP relay, think I only have 2 or 3 other wires that come out of the bulkhead and have no termination point at this time. I didn’t get a picture of the stripped down harness, but this is what she was wearing.

1B48BCE1-2454-4AD4-8078-736D5FC44B57.jpeg
 
For what its worth, I tossed everything, used a new FP relay, and omitted the oil bypass switch at the back of the block
 
Bent77 said:
Did you delete the oil switch circuit?
Click to expand...
Yes. I was swapping to the big block anyway so all the stock oil pressure stuff was eliminated and the Dakota sensor went on instead. Can't remember the wiring on it, must have been one of the "extra" wires I trimmed at the end.
 
JT88K5 said:
I have a heavy gauge pink wire and a small pink/blk (ignition) coming from the bulkhead connector.
Click to expand...
I used the heavy gauge pink wire for ignition power to the efi. I used the pink and black wire also; for the trans controller IIRC.
 
What is the oil bypass switch and where is it located on the back of the block? I think it was swapped to the new motor if it’s just to the right of center, back of block at top and I think has 2 prongs on the connector. There is a single wire that remains connected to sensorport above the oil filter. I was thinking that was to the stock oil pressure guage? I haven’t traced it on the diagram to verify.
 
JT88K5 said:
What is the oil bypass switch and where is it located on the back of the block? I think it was swapped to the new motor if it’s just to the right of center, back of block at top and I think has 2 prongs on the connector. There is a single wire that remains connected to sensorport above the oil filter. I was thinking that was to the stock oil pressure guage? I haven’t traced it on the diagram to verify.
Click to expand...
Plugs to the oil pressure output top back of the block
In the original system, the relay would prime the fuel pump to get the engine to turn over and start. Once an oil pressure requirement was made the switch would close and the voltage would bypass through there to run the pump direct around the relay.
 
It looks like I bypassed the oil pressure switch as well. Got nothing to plug back into it. I’m working on routing the pf4 harness at this point. Running a new relay for the fuel pump. I have two wires that run from fuel tank to up front. One is tan w/white stripe, one is pink. Can anyone confirm that the tan/wht wire is power to the pump and pink is the sending unit to guage?

On another note, I was browsing the instructions and as a result, had the O2 sensor put on the pass side after the header as they warned the O2 sensor needed to be on the same side as the ecm for available cable length. Well… the O2 sensor has 3ft of cable connected, the harness has 3ft of O2 connector cable after coming out of the few, wtf do I do with extra 3 ft? I’m gonna try to run it over the ac box, down to the frame to use the extra length and not have a roll of cable tied to the firewall. The two main plugs on the engine side have enough length to reach the front of the engine. It almost seems like I got a ford harness. I’m wondering what others did to use/hide the extra cable? I mounted the ecm in the stock location btw.
 
For extra harness length, I do like you mentioned and route it circuitously around the engine bay.
 
Yeah, the extra length allows for a broad range of application. I get it. I’m moving the relay to the driver side to use up the fuel pump cable. Probably end up looping the wire for the two larger connections behind the throttle body.
Should anyone want to share a picture of their engine bay with a pf4 installed, feel free.
 
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