Well, I THOUGHT I knew where all of the wires for my TBI system went. It would appear that I do not.
I was looking at how to install the fuel pump in my Jeep (1990 Chev Caprice L05 TBI system, 8746 ECM/ANLU bin) and the wiring diagram is fairly misleading. The wires on the fuel pump are red and green...right? Well, there is one wire that is supposed to feed the fuel pump and according to the wiring diagram, it comes off of the oil pressure switch. That doesn't make a bit of sense unless GM was using the oil pressure switch as a safety to prevent engine damage...but then how would the engine start with very little oil pressure at startup/cranking?
Anyway, the wire from the oil pressure switch is tan and the diagram says it is supposed to go to the fuel pump and that the fuel pump is supposed to be grounded to the frame.
PLEASE HELP!!! This is pretty much the last part I can do without the ignition harness adapter and the AutoPROM.
TIA

 

https://www.thirdgen.org/schematics/...o/ecmVinE4.jpg

The oil pressure switch is there to prevent the engine from stalling if the fuel pump relay goes bad or the ECM has a problem.

 

So I can run that GRY wire from pin B2 to the fuel pump RED and the fuel pump GRN can go to ground. Is there a tap off of GRY/B2 to the fuel pump? I do not remember having seen one and I have been over each and every wire in the harness with a digital multimeter to verify pinouts and the like. I could just splice into it, I guess.
Anyway, sounds cool to me. Thank you, Brent!
This is gonna be cool......

 

yes, well see below.

I don't understand the question.

I wouldn't splice into the gray wire/b2 near the ECM as I believe it is a lighter gauge wire. You'll want to find the heavier gray wire near the relay or pressure switch.

O'course I could be all wet as its been quite a while since I looked at an actual harness......

 

Hmmm...pressure switch? I haven't seen one of those. Did I miss it somehow?
It looks like I'll be pulling a lot of thise wires back out of the gooseneck to track down the fuel pump power splice that should already be there. I am sure I missed it in the mix.
Many thanks!
EDIT:
I just looked at the diagrams again and I see what you are talking about...pressure switch=OIL PRESSURE SWITCH. Duh...
Thanks again. This thing just might be up and running in a week or so...if I could get that ignition harness from Summit to adapt my Accel 300+ ignition to the GM system. Hmmmm....new post time...

 

Okay, this damned thing is still giving me fits...
I have pulled the wires out of the gooseneck and I can't seem to find a point in the wiring that would tap +12V to the fuel pump. My oil pressure switch is wired properly...I have checked the conenctions to the ECM with a continuity tester and all seems to work fine.
My oil pressure switch has three wires going into it...the 1989/1990 wiring diagrams show only two. One of the wires to the press switch goes to B+ volts via C16 and B1 on the ECM plugs. (There is a splice there.) The other lead that I can track goes to the fuel pump relay at port A and to B2 on the ECM connector (12-pin connector). This one is labeled "Fuel Pump Voltage Monitor) and I have verified that it is properly wired (I think). When I got the harness, the fuel pump wiring had been cut out, so I am cobbling it back together as best I can. There was a connection to the ECM 12-pin connector that had been cut and I traced it out using the wiring diagram and a continuity tester. The results of that were to reconnect the TAN wire to that ECM pin. It seems to terminate at the oil press switch with no obvious tap for the fuel pump.
Does that third wire from the press switch feed current to the fuel pump through the oil pressure switch connector?
Thanks in advance. This is really giving me hell!
EDIT:
Forgot another rahter important little detail. There is one connector that has RED and GREEN wires going into it with a blade connector on the both of them. They go pretty much nowhere as far as I can tell. One of them has continuity with the fuel pump relay RED wire, but nowhere else. HELP PLEASE!!!

 

The third wire on the oil pressure switch is for the dash oil pressure gauge I believe. You can ignore it. Don't connect it to the ECM.

Thats correct.

Hmmmm, I think that should be going to port E and B2.
Well, It should be connected to the switched port on the relay.


Anyhow, get your fuel pump power from port E on the relay.

I'm not sure what the red and green wires are for....

 

You have mail
Hope it helps

 

Thanks gentlemen! I think it is figured out now. Here's what I have
First off, the two wires I mentioned earlier (red and green) seem to be for the A/C request signal. They appear to be pretty big wires (12 ga or 14 ga)...seems to me that these are a bit big for an A/C compressor clutch solenoid. The RED wire seems to have a direct connection to GND via the BLK/WHT wire on the fuel pump relay where the GRN wire has continuity with B8 on the ECM connector (labeled "A/C Signal Request"). I figure that leaving them alone should be okay.
Since I know where the fuel pump is supposed to come from the ECM connector and the wires seem to have continuity, I could simply wire the fuel pump from the splice I found (the one that was cut before) and put an inline 20a fuse in the wire. The only thing that concerns me is that the fuel pump seems to have a direct connection to the ECM board. It seems that there could be a potential for bad things to happen to the ECM such as a current spike sending 20amps directly to that pinout...mucho smokeo. Electrically, the fuel pump gets power from the volts monitor wire and then grounds to the chassis. The diagram even shows this as being the case. I am assuming that the diagram is right and that the GM engineers took this into account when they designed the ECM board. One bad current spike could ruin my day.
Thanks again, gents. I'll keep you posted as the rainy South Texas day progresses. Once I have this done, I am going to start testing the system in the absence of the Accel ignition harness. I know it'll probably throw a code of some sort, but I can clear that out later. I can still test the fuel pump and the injector drive.
Thank Gawd for my carport.

 

Well, the fuel pump is plumbed and wired. That was pretty much the last part of the puzzle. I still need to weld a bung in the exhaust pipe for the O2 sensor and wire a light for the SES light. I guess I will remove the oil pressure switch since I have a nice new mechanical oil press gauge to use instead.
I wired the fuel pump to the relay off of pin 'E' and it worked. At first, though, I got squat. It turned out that I had a blown fuse on the B+ side of things/ It was a 15amp fuse, but I suspect it needs to be bigger...maybe 20amps...anyone? Anyway, once I got that figured out, I put the switch in RUN and the pump pumped fuel...right out of the inlet hose to the TB where I forgot to crank the hose clamp down. All is good there and the thing has fuel pressure.
Next, I hooked up my little jumper to the TPS and I got a 0.67VDC reading...needs to be adjusted a bit IMO, but it'll do for now. At least I know the ECM is feeding power there. I moved the throttle and got no gas out of the injectors. Shouldn't they squirt gas even if the engine isn't running? The Holley system would squirt some gas into the TB if you moved the throttle to WOT. I may test the TPS to see if it is actually working right.
Lastly, what else can I test to see if this thing is working right? Is there anything that I can test to see if I need to replace parts before the final crank date in about a week? I have an ALDL cable, but no working laptop to hook it up to. What components can I test for voltage to ensure that all the parts/wires are in the right places?
Thanks again, Bill and Brent. Beers to the both of you!

 

The pump ran for 2 seconds and quit right? If it runs constantly you've got a problem.

20amps is what the factory calls for. Should be fine.

TPS movement shouldn't fire the injectors unless the engine is running.

Hmmm testing....
Ignition on:
TPS, MAP and CTS should all have 5V from the ECM. 12V at each injector (ECM switches the ground).

Other than that.... Your service manual should have a trouble shooting section with flow charts for testing various voltages and resistances.

 

Yep...the pump ran for about 2 sec and stopped after it squirted gas across the carport.
I am happy to hear that the injectors shouldn't squirt gas unless the engine is running. That means that the TPS is probably okay.
I haven't tested the +5V ref signal at the sensors yet. I guess I could do that to make sure they all have voltage. I have the section of the factory manual that shows what the various voltages should be for a lot of stuff, but I haven't really looked at it yet. I was just happy that the thing powered up with the key in RUN and that the fuel pump worked! All that and NO smoke from the ECM!!! That was the best part. IMO, that means that I probably wired it right the first time from the diagrams I had. I guess all that time spent with the diagrams and the digital multimeter paid off after all.
I went junkyard jumping a few minutes ago looking for a VSS and 4-out buffer...no luck. I went to a junkyard owned by a friend of mine (I get stuff free since I give him stuff I don't use on my projects...). I looked in several vehicles and couldn't find ANYTHING with a VSS or a buffer in it. I guess they had all been previously scavenged. While I was there, a cold front blew in and dropped the temps by about 20deg in about 3 minutes. I went home 'cause I was in shorts, sandals, and a t-shirt.
Thanks for the tips, Brent.

 

The regular ECM diagrams have a "Key On" and a "Run" voltage check listed on them. It's a good tool to start with.
If you don't have them check the GM-ECM site.
HTH