wjc1947

I am new member with a 1986 pace car. broke down when driving it after few days at 100 miles per day ran great, Determined fuel pump problem and replace pump, had no power to pump at back , even when straight wireing it found short in wire in tank and repaired, pump runs when hooked sgtraight to battery , replaced all relays up front ,pump, maf burn off, maf power, new engine control module in distributer , new oil presure switch, no poiwer to fp relay, orange wire is dead no power to fp fuse in pannel, or vat fuse. cannot find where relay picks up 12v, can I cut orange wire and put new fusable link in or does it join with another wire back in the harness, where is the fuseable link for relay picking up its 12v from battery?any asistance would be appreiciated

gerardvg

Hi

See the image below, its from my 85 shop manual however most early
C4's have the same wiring. Check you have power on the orange wire at teminal E.

Note the wiring connector can melt and not connect to the fuel pump relay properly, most likely the fuseable link has blown so run power to terminal E and the fuel pump should run. Do not forget to check the fuel pump fuse.

You can also connect 12 volts to the acld connector to test the fuel pump, i do not have the under dash connector info handy though.

Corvette central has repair kits, see the link at bottom of page.









http://www.parts123.com/parts123/yb....5Z50000050F~~~

wjc1947

thanks a lot that helps I notice in fig 8 the fuel pump relay shows pins as ABCED, I have found the same reference in other manuals, however on the car mine is ABCDE with orange wire as last in e.. I have checked the one marked d on car and it seems to be dead, and am unable to ohm it out in any sequence, when power applied to it i do get clicks from the maf power supply relay. and when i apply power to my e terminal get something running on front of engine for fe seconds as if building up presure, not sure which is which , I have made pump run by direct wireing and it supplies presure to rail about 50 on meter

Hooked on Vettes

Are you sure you're looking at the fuel pump relay?

When you turn the ignition On, the ECM will enable the fuel pump relay. If
there are no reference pulses from the distributor the fuel pump runs for 2 seconds and shuts off.

While the engine is cranking or running, the ECM will continue to enable the fuel pump relay.

The wire colors at the relay socket are
Pin A is a Red wire and is the output of relay
Pin B is a Black/White wire. Ground for relay coil
Pin C is a Dark Green/White wire. Relay coil
Pin D is a Red wire from pin G of the diagnostic connector.
Pin E is a Orange wire 12 volts from fusible link H

There are three ways to provide 12 volts to the fuel pump fuse.

1) The ECM provides 12 volts on Pin C Dark Green/White wire of the fuel pump relay. The relay closes and 12 volts from Pin E Orange wire goes to the fuel pump fuse.

2) If the engine oil pressure is greater than 4 psi, 12 volts from the Orange wire passes thru the oil pressure switch to a Red wire that goes to the fuel pump fuse.

3) If you apply 12 volts on pin G of the diagnostic connector the 12 volts goes thru the normally closed contacts of the fuel pump relay to the fuel pump fuse.

In your case it appears you're missing the 12 volts to the Orange wire which is a 20 gauge fusible link.

At the battery positive cable there should be a cable that leads to two fusible links as shown in the first schematic.

One of the fusible links (H) is for the Orange wires. Most likely it's blown.

As mentioned also verify the fuel pump fuse is good.

The other fusible link is for the radiator fan relay which is mounted below the front of the brake master cylinder on the wheel well housing.

Cliff Harris

This is the fuel pump circuit diagram from the '86 FSM, so it should have the correct relay pin letters and wire colors for your car. I have tweaked it to correct several errors in the FSM version:



This is the fuel pump relay. If you have the 4+3 transmission then the overdrive relay is in the same area:



When you first turn on the ignition the ECM turns on the fuel pump relay for 2 seconds to prime the fuel rails for starting. It then turns off the fuel pump relay so the fuel pump will not run continuously if you turn on the ignition but don't start the engine. The ECM will turn on the fuel pump relay when it sees DRP (Distributor Reference Pulses) from the ignition module in the distributor. The ignition module puts out DRPs any time the engine is rotating, whether cranking or running.

wjc1947

I have locted the fuseable links thanks to your information. It even says fuseable link right on the wire , I was looking for a totaly different type of link one with a glass or regular spade type fuse in it , these are just a wire with a black insulator jacket about 6" back from eyelet connector, I am not sure where the fuseable part is , can i just get regular link and replace it? one with a fuse. do i replace the wire from the black insulator foreward or how?

wjc1947

I did find one fuseable link with orange wire that seems dead ohm'd it out and never got any reading .all the others seemed ok,assuming it was the bad link replaced it , after cutting out the link tested it and found it ok and still had same problem with new, apparently problem is further down the harness than the link. so i put a new 12 link in and connected to orange wire at fp relay severing the remaining old wire and had 12v there but still did not work, tied in old wire from harness and tested pump works comes on couple of seconds when key turned the off pressure reads 45+ at rail for few seconds then drops fast if i don't continue turning engine over. but engine will not start, now when i plug in the code reader at test port the cooling fan runs and i get 23, there has to be a short somewhere between relay and original fuseable link, i cannot find, and if i disconnect original wire from relay pump does not work. somehow the original wire must tie into some other wire between relay and terminal and beyond that must be the short, All this was caused by a dead short in the fuel tank which fired the relay. which i have corrected. any ideas how i can bypass the old wire and what other wire should i connect to it to make the circuit comepete

Hooked on Vettes

Read this thread. The fusible link for the Orange wire should be coming from this connector along with the
fusible link for the radiator fan relay.

http://www.corvetteactioncenter.com/...r-battery.html


You've replaced a lot of items. Are you sure you have the correct fuel pump relay installed? I doubt a short
in the fuel pump wiring would burn out the fuel pump relay. I'd reinstall the original relays for the fuel
pump, MAF and MAF burn off.

Have you verified the wires at the fuel pump relay socket are in good condition and the insulation of the wires
hasn't shrunk back?

Remove the fuel pump relay from its socket. Use your volt meter Red probe to the Orange wire at the socket
which is Hot all the time. Black probe to the Black/White wire. Should measure 12 volts.

If no 12 volts, there is a problem with the Orange wire back to the Positive terminal of the battery.

Should read zero ohms of resistance from the Black/White wire to the negative battery terminal.
That verifies the ground wire for the relay is good.

Pull the vacuum hose off of the fuel pressure regulator and verify there is no gas in the vacuum hose.

For the code 23 (Manifold Air Temperature sensor) The sensor is screwed underneath the bottom passenger
side of the intake plenum near the fuel pressure regulator. It has a two pin connector plug. I believe a
Tan wire and a Black wire. Make sure it's plugged in.

Have you verified you have spark when you crank the engine?

wjc1947

I have checked spark I have none the decoder says no signal from distributer to ecm. I replace the icm in distributer as advised earlier I am not confident that the guy at the parts store gave me the right part as it was only $26. I have since had the original one tested and it tests good. I am not sure if i made an error when replacing it. I plan to put the original back in distributer this evening. since I used the tube of silicone lube in first install is there anything I can use on second? may be enough residue left from first as it has only been in two days. I also have one disconnected vacuum line from the right hand rear of injection manifold and am having trouble finding where it should connect should be simple as line is only so long and the port must be within the distances it can reach. I have gotten the pump to come on as needed but pressure drops to dquickly after intial cut off. have found evidence of small electrical fire around harness with fuseable links.Now am not sure I have correct fuel pump relay as I got it from the same parts house o rileys that i got the icm.