2nd eyes<Wiring experts called to HELP

[WhalePirot]

From my signature, you'll see that I have changed my '84 to a TPI'd 406. My harness was modified by Jim's Perf. in VA to run a '90 Camaro ECM in the stock mounts, with a custom PROM.

It recently developed a problem that I am using my '84 wiring diagram to track down, but I'd appreciate input to speed the process from U guys who have and can use a wiring diagram.

My fuel pump does not kick on for the 5 sec. or so, when I turn on the key. I get battery voltage at the fuse and at the 'hot' pin on the relay, but it decreases to GND as I check it with my DVOM. What is strange is that I can jump the fuse to BATT and start the car, which will continue to run with the jumper removed. It will also restart for many hours, following shutdown. I believe this to be a result of the fuel rail holding residual pressure.

The 'hot' pin on the fuel pump relay has two feeds. One is through the oil pressure switch, the other from the ECM. I am trying not to make a major project out of this, as y'all know how tight the workspace is. It seems I have an electrical 'leak'(short) that is preventing, then draining the kick-on signal, but am unsure how to easily find it. I could separate the two leads and check for GND. I know I have had heat issues and might have a compromised, shorted wire in the rear engine area or a bad oil pressure switch.

The ECM must feed battery voltage, not GND to the relay, right? Maybe this side is bleeding off the BATT voltage when shutdown?

As the car will keep runing, once started, I think I can figure the oil pressure switch side is fine.

I will appreciate input from a second set of eyes. Thanks. mike

 

[geekinavette]

Mike, I'll pull up the diagram here in a few minutes and try to help you out.

BTW...what model ECM did you put in it?

Bill

 

[geekinavette]

Check the voltage at the orange wire of the relay...if it does the same thing then it would seem that you have an open fusible link. Follow the lead from the + battery cable, there should be a splice that splits out to 2 red wires. Follow the smaller one and it should go through a single-wire connector. After the connector the wire should turn orange and there should be a fusible link right after the connector. Check that fusible link. That wire provides power directly to the oil pressure switch and to the FP relay. The ECM energizes the FP relay via the green/white relay wire.

That "other" red wire that goes to the ECM is an input to an A/D converter in the ECM that tells the ECM when the fuel pump is engaged.

Bill

 

[WhalePirot]

Thanks, Bill. Seems like I have to get into that tiny space behind my intake.

I spent more time coloring and tracing on the wiring diagram. I have a 'hole' in my mental image of the circuit; partially illed by my eforts today and moreso by yer eyes.
The HOT relay post does go dead.

 

[kingman]

A little help here!

Hey Geek

While you are pulling out tose secret wiring diagrams could please help me locate a hot wire on the drivers side by the fan relays.

Thanks

Alan

 

[WhalePirot]

help>Alan

hot wire on the drivers side by the fan relays.

The orange wire into the fuel pump relay is battery; always hot. This relay has five connectors; one end connector has two larger red wires; the other end is an orange wire.

The red wire in space 2 (there are two reds, space 1 being unconnected) on the fan relay is battery, also, from the starter solenoid. The fan relay has 4 wires, but 5 connectors. One end connector has no wire to it. I am arbitrarily referring to it as space one.

The third relay is for the overdrive.

A simple tool, the test light, has an alligator clip on one end, a pointed metal probe, and a light inside the handle, can verify that you are sourcing 12vdc.
mike

 

[geekinavette]

No secrets here!

http://misterbill.homeip.net/vette/wiring/



Bill

 

[WhalePirot]

I have good, unswitched battery voltage at the orange wire. That explains the continued running aspect.

 

[geekinavette]

Ok so see if I have this right:

1. Fuel pump does not run for 5 sec when ignition is turned on.
2. Pin A (red) of relay shows 12V briefly, then dwindles away to nothing (when ignition is turned on? how long does it take to dwindle away?)
3. Voltage at Pin E (orange) looks good, 12V batt all the time.
4. Bypassing relay will start the car, and will stay running after electrical relay bypass is removed.

If these are all true...then either your relay, or the relay driver in the ECM, is toast (check for 12V at green/white wire at the relay for 5 sec with ign on). The car will stay running after removing the relay bypass jumper because the oil pressure switch is providing voltage to the fuel pump.

Bill

 

[WhalePirot]

Thanks

Ok so see if I have this right: (all checked with the plug off the relay)

1. Fuel pump does not run for 5 sec when ignition is turned on. True.
2a. Pin A (red) of relay shows 12V briefly, then dwindles away to nothing when ignition is turned on? No. It is at zero; measures 3 ohms to GND until it starts up.
2b. How long does it take to dwindle away? When I shutoff the engine, it falls from charging voltage to battery, in 2-3 seconds, then quickly falls to zero.
3. Voltage at Pin E (orange) looks good, 12V batt all the time. True.
4. Bypassing relay will start the car, and will stay running after electrical relay bypass is removed. I just tried this at the relay for the first time (having previously jumped 12vdc to the fuse). Both are true.

If these are all true...then either your relay, or the relay driver in the ECM, is toast (check for 12V at green/white wire at the relay for 5 sec with ign on true, but for less than 5 seconds). The car will stay running after removing the relay bypass jumper because the oil pressure switch is providing voltage to the fuel pump.

Bill

Seems the issue is in one of the red wires. I got minor sparking, perhaps due to the fuel pump draw, as I heard the pump run and the rail pressurize. I fiure the falling voltage is due to the oil pressure drop at engine shutdown. The car will start for quite a while, probably due to residual fuel pressure in the rail. Nice distraction, 'eh?

 

[geekinavette]

Do you get battery voltage at pin A of the relay (or the FP fuse) for approx. 5 seconds when the ignition is turned on?

Bill

 

[WhalePirot]

Do you get battery voltage at pin A of the relay (or the FP fuse) for approx. 5 seconds when the ignition is turned on? Bill

I had to go check the wiring diagram to see which was Pin A (the double red wires). I had BATT the first 'on' cycle, but not subsequent ones. Aha, methinks; I'll swap relays with the O/D. Now the fuel pump runs with each IGN cycle, but only for about 2-3 seconds, which seems to be enough to pressurize the fuel rail, starting the car.

The first relay was original; the O/D relay was newly replaced.

Thanks so much, Bill. I think we got her; very nice or me, as I am headed out to Asia for a stint, and it nice to have one less thing hanging o er me when I return.

Part of what others have said has come around for me, too; that is, help from a great bunch of guys, not hung up on car-guy-ego, as is sometimes expressed at shows and other forums. Ken and others know the frustration that can sour the ownership experience of a modified Vette. It is nice to have offered help to others, but quite nice to get a hand from guys like Bill. A thousand domos, amigo.

The beast roars again! mike

 

[kingman]

Eureka!

Thanks Whalepilot

I will be home tomorrow and l will look for the fuel pump relay.

It's been about 5 months since l picked up the daylight running lights and l was eager to put them in.

Again Thanks

Alan

 

[WhalePirot]

It's been months since l picked up the daylight running lights; eager to put them in.

YW, Alan. I understand the slipping of Vette projects in one's priorities; the inherent frustration.

For the DRLs, you will want an ignition-switched source of power; perhaps a hot battery lead, too, feeding a relay for those lights. Hopefully the instructions that came with them are complete and detailed. Someone else might want to chime in with comments on whether the fuse and wiring of the fuel pump or another source can handle the added current draw of the lights.

The test light I mentioned should be well under $10 and serve you well in ensuring you get the wires that are powered as you require. Virtually any auto supply place should have them. Hope your install goes smoothly.

mike