OK - here's the deal - no where can I find fuel system wiring for a TBI car. This page is missing from Haynes, Chiltons, and everywhere else I look.

Seems to me that the following takes place:

1) 12v from battery to Oil Pressure Sending Unit
2) OPSU gets pressure, sends 12v along to the relay (from grey wire on OPSU through to big orange wire on relay)
3) Relay sends 12v to fuel pump (from grey wire on relay)

Tell me if I'm wrong.

Here's where I'm confused:

1) Where does the 2 second pump priming come in at - what tells pump to prime for only 2 seconds?

2) Why so damned many wires on FP relay? There's 5 - FP only uses orange (incoming 12v), grey (outgoing 12v) and maybe another (as an outgoing ground). What's the green/white stripe wire, red wire, and black/white stripe wire for?

3) Why have a relay? What do relay's do exactly? Is it to maintain a constant steady 12v to the fuel pump, rather than a hit or miss voltage that could be affected by radio, power windows, winshield wipers, etc running?

4) Why the 2 second prime? Why not just run FP constantly when key on? Doesn't the Fuel Pressure Regulator and the fuel return line take care of excess fuel?

Here's where I stand:

1) Fuel pump doesn't work - no prime, no run
2) If I jump at the relay the orange wire and the grey wire, fuel pump runs - bad relay right? Wrong - see 3
3) Switched realys (went through 4 relays from my other car that I know are good, since it runs) - still no fuel pump run.
4) Fuel pump relay wiring harness must be working, since I can jump the connectors in the wirepack and fuel pump works.

This is on a 1992 TBI car - that I swapped in 350 carb, using Mallory FP reg and in-tank pump. OPSU is good.

Why can't I just wire the fuel pump so it bypasses the OPSU and the relay, so that it just comes on when key on, and runs as long as key is on? Isn't this what occurs when everyone switches to a Holley blue on the fenderwell, and an in-tank pickup for carb?

 

OK - Autozone.com has a wiring diagram - figures I'd find one after this post - I've been looking for days......anyway.... here it's under repair guides, chassis electrical, wiring diagrams.

Looks like Fuel Pump gets 12v from OPSU AND relay. The red wire on the relay controls the 2 second prime somehow. But according to the autozone diagram, pump should run with or without relay, since hot in run goes through OPSU before the relay circuit. And this would make sense, since a year ago my fuel pump ran constantly - even with key out and in my pocket.

So now I'm really confused - according to the autozone wire diagram, the fuel pump circuit is complete whether relay in place or not, and also is complete whether OPSU is in place or not, but one or other must be there - which we all know that doesn't work either - both must be in place!

So now I'm more lost than ever.

Also, I forgot to mention my ECM is removed - but it's been that way for 6 months and running fine.

 

1 - The ECM controls the relay.
2 - need four wires for Relay operation, the fifth is the OPSU wire which is connected in parrallel to the relay
3 - relay can handle the current draw of the fuel pump. Its just an electrically controlled switch.
4 - You answered your own question. PRIME is the key word. The ECM primes first and then IF it gets igntion pulses from the distributor it turns on the fuel pump. This is probably a safety strategy. If you wreck the car bad enough the engine stalls the fuel pump stops, preventing potentially torn fuel lines from emptying the fuel tank onto the road.

Since you are carbed, just let the OPSU controll the fuel pump. Only problem is if you run the carb dry.

 

ECM must not control the relay or the prime - 'cause my ECM has been in the shed for over 6 months now - and the fuel pump was priming last week.

It was all working fine for months, with no ECM, all other wiring in tact, HEI dizzy, Mallory FP reg, and in-tank pump - then it stopped, and only thing I can see that could be wrong is the relay, but I put working relays inplace and still nothing - I even put the relays back into my 1990 stock TBI car and everything worked.

 

You might have mentioned that the first time......

The relay does nothing without the ECM. Never.

Unplug the OPSU and jumper it. The pump should run. If so the OPSU is failed.

 

Unplug the OPSU and jump it where? From what to what? The orange wire on the relay to the grey wire on relay?

Sorry - I've looked at it all too long and I can't think straight anymore!

 

The OPSU has heavy grey and orange wires in the connector right?

Its down by the Oil filter right?

Place a jumper across the OPSU connector on the harness.


BTW: its page 6-170 in chilton82-92 Camaro

 

OK - so that jump makes it run. So the OPSU is bad huh? Geez, I just replaced it not 1000 miles ago. Have any clue why it's going bad so quickly?

You got a better Chiltons than me - I looked at 2 different Chilton's, and neither had the TBI wiring - had everything else known to mankind, except TBI.

 

The OPSU is a backup in case the relay fails. In the diagram see how they both run in parallel.

The 2sec is to in case you don't start the car, there is no need to keep pumping. When you crank/start pump goes back on. The attached diagram is a typical for several year camaros and is how I wired up my jeep/swap.. Im up in Wake Forest if you need a hand with the wiring.. -mike

 

Well, I just replaced it all dammit! No sense in fooling around! It's not like I have anything else to do with my time or money! LOL

OK - installed new fuel pump, new OPSU, new relay, new fuel filter, new fuel pressure guage. Everything seems to be working fine, except the car! LOL

I've obviously got some carb issue now - stalls on hard turn or hard brake, bogs sometimes when foot in it, other times acts like it's running out of gas. Adjusted float levels, adjusted for best vacuum, have a 6psi fuel pressure, 11*BTDC timing, no backfires, runs good in driveway, wants to leave me stranded on road. Time for me to find a carb guru, as I've done all the damage I can do.