I have a 5.7 TPI engine and I am receiving low voltage at the fuel pump. I traced the tan wire from the fuel pump to a connector on the passenger side next to the ECM, I also traced the wire up to the harness in the engine compartment, I tried to check continuty to wires that were similar under the hood ( tan and white) and could not find where the wire goes to. I have voltage at the relay and the tan and white wire at the relay has 12 volts when the key is turned to accesory. I am losing the voltage somewhere. I checked the diagrams everyone has posted and they say that the voltage goeas from that relay directly to the pump. I check all of the wires in the harness under the hood and found that one of the tan and white wires ( 3 total) has 12VDC momentarly and then goes to 0VDC. Very frustrated, but still determined to resolve the problem with everyones help. Thanks in advance

Hello smeds!!

Are you getting this low voltage while the car is running, or are you getting the low voltage after turning the key to prime the fuel pump??

The fuel pump will shut off if the engine doesn't start after 2 seconds, and will not turn on again until the engine is running!! This could be the wire that you momentarily have 12VDC, then 0VDC!!

Tell us more!!!

Thanks for responding.

I am receiving the low voltage at the pump ( 6 volts ) with the key turned forward in the accessory position only.

After I installed the wiring harness and motor I began testing all the components, I have spark, lights work etc... The fuel pump would not prime, so I removed the plug from the connector and ran wires directly from the battery to the pump plug and the pump worked.

I then tested the voltage at the fuel pump connector as follows: turn key to on position and listen for the relay to engage and measure voltage ( I am receiving only 6 volts and it is constant with the key in this position). I should receive 12 volts and then the voltage should drop off.
I then started to try and find the wire to check for a short circut. the wire that is suppling the 12VDC and then 0 is not the same wire that goes to the fuel pump, I check this by disconnecting the battery using my meter and checking continuity. The wire that connects to the pump is receiving only 6 volts. The relay is working fine, I check the tan wire at the relay and it has the 12 volts and the drops off when the key is turned forward, I am losing it from there to the pump.

I appriciate any help or suggestions.

Your ECM is failing to prime.

Scan for codes.

◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!

Nina thanks for responding

I checked the ecm for codes and found none, I also checked the tan and white wire at the ecm (position B2) and have 12 volts with key forward and then the 12 volts disappears. I also have 12 volts which also disappears at the green and white wire at the ECM I think the position is A1.

I removed and checked the plug that is below the fuel relay on the drivers side and found that several of the male pins on the 1989 IROC 5.7 harness do not have matching female connectors on the plug mounted in the firewall, is the 1986 wiring within the car compatible with the engine harness from the 1989 IROC?

Also will the 1989 ECM work withoit something to bypass the VATS?

I made some drawing and will post them tommorow, kind of a homemade schematic of sorts.

Any suggestions welcomed

Hello smeds!!

I've seen on these forums something to the effect of certain years engine wiring harness's don't necessarily match up with the firewall connectors of other years!!

You will have to search that out!!

The VATS is another problem unto it's self!! Two ideas here with VATS, 1) disable via custom prom, 2) find resistor value, and wire into circuit!!

The VATS solution can be had via these forums also!!

Sorry I can't be anymore helpful than this, at this time!!

Obviously , that is the relay control wire from ECM

If you have low voltage at pump but 12V at relay ( from batt ) I would be looking for faulty wiring/ bad connection from relay to pump.
Meter ( Ohms ) between relay output and pump and see what resistance is.Should be close to zero resistance on that wire
Check fuel pump fuse and terminals also, may be getting resistance there also.
Meter from fuse terminals to relay and to pump, may determine which section is faulty
Typical GM pump wiring shown,

Vats doesn't affect fuel pump; only injectors and cranking

The fact he is seeing 6V at the pump , key on shows ECM is priming pump correctly.He is losing voltage somewhere

vetteoz thanks for responding.

I checked resistance between the relay output which appears to be red in your drawing and found open circut, I searched for a fuse and found nothing at fuse block. I did check the fuse next to the battery 20 amp and it is good.

The following wires are at the pump relay:

wire A is a tan and white wire
wire B is a black and white wire
wire C is a green and white wire
wire D is a orange wire
wire E is a larger orange wire

The red pump prime wire is not in the harness or connected to the plug or relay. I attached a picture.

I found the following socket connections are not in the C100 connector (car 1986 IROC TPI 5.0, harness is 1988 IROC TPI 5.7)
mounted to the firewall:

A1- Foglights
A7- cold start ( 9th injector?)
C2-Foglights
C3-Foglights
E6-Fuel Control
E7-Transmisson clutch
G4-Fuel Control

Can someone tell me if this is the root of my problem. If anyone has some suggestions I would appreciate it. I have enclosed some pictures of the tan and white wires that am talking about, if I jumper the wire marked 6 volts ( which traces back to the fuel pump power wire) to the tan and white wire which comes from the ECM and provides the prime to the pump, the pump will prime, but if I crank the engine to start the pump I have no voltage at the fuel pump hotwire (tan) to ground.

Thanks guys!!!

Low voltage suggests a poor connection or a short

A is 12v output to the pump
B is grd
C is 12v call from the ECM
D is the prime connector
E is battery 12v input

If possible do a continuity test from pin A on the relay plug to the tan/wht wire in the fuel sender connector near the tank. High resistance or open means your problem is somewhere between. Lucky for you there is another inline connector for fuel at the C207. IIRC its pin D, but it should be the only large tan/wht wire in the connector. Test between the C207 and relay connector and again between the C207 and sender connector. Not a huge help, but it cuts out half of the wiring. A last ditch effort to solve the problem is to run a new wire. Be sure its 16ga or better

If the tan/wht wire is fine (no/low resistance) try the same process above for pin E. It is a direct connection to the battery and has its own fuse near the batt. The ECM also uses the fuse, so function suggest the circuit is good

If both wires check out, replace the relay

Hi Pocket, thanks for the info.

where is the C207 connector located?

I will test tommorow.

Thanks again

Pocket how about those missing connectors in the bulkhead connector C100, also my power windows do not work and the feed wire that goes to them at the fuse block has no power, are these items connected in some way?

Thanks

C207 is located near the ECM. Engine side is clear, dash side is black and divided into two halves

Not sure about your missing wires, but they shouldnt be fuel related for your year

Is the diagram posted above even for a Fbody? Neither the C100 or C207 are listed and depending on the year one of the in line connectors was used

No power for interior functions suggest a blown fusible link. The pump isnt fed by a link, rather a fused direct connection to the battery

I checked position "A" on the fuel pump relay plug to the C207 connector and found the circut is open, I then checked from the connector at the fuel pump to the C207 and I am good to pin D on the C207, I have 0.00 ohms. If I follow that wire from position "D" it traces back to the altenator ( tan and white wire ). I removed the wire from the harness and it goes to the altenator in a sealed plug.

This seems wrong, the diagram does not show the pump running through this circut, but it defintely does.

No other pin showed resistance on the C207 connector to the "A" position at the relay plug.

Getting just a little confused, any suggestions

Fans and alt share the same fuse. Pin D changed purpose over the years and is the same color as the fuel wire. Is it the largest wire in the connector?

Took a picture and used my calipers to measure wire it is about .020 larger than the other wires which are .097 thick.

I took some pictures of the wires at the C207 connector.

tell me what you can see.

Thanks!!

Its none of those. The wire should be the size of a 12ga cable, but the jacket is extra thick for some reason. Copper wire is actually 16ga. Not sure why they the older cars did it that way

Check the C100

Older fuel wires connected with the fuel relay, MAF relay, burnoff relay, oil pressure bypass and whatever body connector it went through

If you still cant find it, run a new wire

I checked and found a C207 drawing at ATGO from 1985 that makes sense, the car is an 1986 IROC and all the numbers and digits check out with the vin decoder. The wire that is in the D position in the drawing is the fuel pump to fuel pump relay.

Check this out and tell me what you think

1985 C207 connector pinout:==========================Pin A: Air select valve (brown wire)Pin B: Fuel pump relay to ALDL (orange red/black wire) VIN F Pin C: Light driver module (white/dark green wire)Pin D: Fuel pump control fuse (black/orange orange/black wire)Pin D: Fuel pump to fuel pump relay (white light blue wire) VIN FPin E: ALDL connectio (white/black wire)Pin F: Engine ECM fuse (pink/black wire)Pin F: ECM IGN fuse to ESC module & ECM (pink/black wire) VIN FPin G: MAS module & emissions (pink/black black/pink wire) “Automatics only”Pin G: Back-up switch (dark blue wire) “Manuals only”Pin H: TCC to ALDL (tan/black wire)Pin J: Crank fuse to fuel pump relay (purple purple/white wire) VIN GPin J: MAS module to ALDL (orange wire) VIN FPin K: VSS (brown wire)Pin L: Fuel tank to fuel pump relay (tan/white)Pin M: Engine ground (black/white wire)Pin N: Park/Neutral switch (orange/black) “Automatics only”Pin P: Brake switch (purple wire)Pin R: Crank fuse to cold start switch & injector (purple/white purple wire)

Dont count on it. 85 harnesses were special. 86-88 are pretty close. 89s are special and 90-92 are identical

I had some time today to continue with the ongoing fuel pump wiring problem.

Found out today where the wires in the harness at the C100 connector go to:
E6-Fuel Control is the orange wire that goes to positon "D" the prime connector on the fuel pump relay.
G4-Fuel Control is the tan and white wire that goes to position "A" on the fuel pump connector.

Since these wires are from an (1988 IROC 350 TPI) harness and the female plug mounted to the firewall is an (1986 IROC 305 TPI) and does not have corresponding connectors, I had to removed these wires from the harness in the hope of running a new wire to the fuel pump directly to the tan and white wire at the C100 connector.

I ran into the following problem:

When I turn the key forward I have 12 volts for about 2 seconds at the tan and white wire at the C100 connector, but when I crank the motor I have no voltage at the same wire.

Does anyone have any suggestions as to why I would not be recieving 12 volts at this wire when cranking the motor?

Any suggestions appriciated.

I did some more testing today and found that the fuel pressure /oil pressure switch may be stuck in the open position, even after cranking the engine for some time the fuel pump wire ( tan and white) had no voltage other than the prime voltage ( 2 seconds ).

I jumped the switch using a paper clip and I had voltage (12.1) volts.

Has anyone had this happen, where the switch remains open?

Thanks in advance.

Switches go bad, nothing new

Hey Pocket. I've got your LT1 harness (in case you forgot), and I'm getting a Racetronix wiring kit along with my new fuel pump, to avoid low voltage problems and fuel delivery issues.

My question/guess is this:

The Racetronix kit comes with a new relay, and I am guessing I will just have to find the old fuel pump relay and switch it out with the new one and then just follow the instructions from Racetronix for the rest of the wiring, just as if it were a stock third gen Camaro?

Let me try to word this better...ONE more try...

...I guess the upgraded Racetronix wiring just runs from the fuel pump, through the cabin, and then to the inside of the firewall underneath the driver's side dash or something, to a plug or pigtail, then I just have to switch the fuel pump relay on the LT1 harness and also run a wire to the alternator??

How close am I??

Ive posted over and over again how the hotwire kits are snake oil for almost all intank pumps

If you are starting with a car that didnt have a fuel relay to begin with (carb car) or are using a pump that has a higher than stock amperage draw (Aeromotive 340, most large external pumps) then the kit is worthwhile, but bear in mind, ITS A RELAY plain and simple. Something you can pick up for $5 most anywhere

The expensive kits generally run in tandem with the old relay, which is another reason I dont like them. If you're not maxing out a walbro 255, dont bother with the kit

My car was a 305 tpi.

So, for a 500+ horsepower engine, just slapping a Walbro 255 in there will work?

And does the fuel pump wiring have anything to do with the engine harness (for example..where is the fuel pump relay?), or will I just plug the harness in everywhere and slap the Walbro into the tank, and the pump will work?