Houpty GT

I have a 1981 Targa and I have found that the car will lose power occassionally when the headlights are on (idling or on the interstate). I was able to hear the OXS relay, which turns on the computer, clicking under the rear seat. (When the copmputer shuts off it causes greatly shifts the fuel mixture and the engine loses power) This relay is powered by the fuel pump relay and I found it to be clicking more rapidly under the same conditions. At 13.7 volts in the electrical system the fuel pump relay does not click but at 13.3 volts (high beams and ventilation fan on) it will click. The relay should work fine at 12 volts or more, right? I have 2 brand new Chinese made relay and an old German. The old relay is shot and won't keep the car running and with chinese quality I can't guarantee the new parts aren't either. I have heard of 3 chinese relays in a row being bad right out of the box on this forum. Possably relevant is that I have recently replaced the voltage regulator on my updated 1982 alternator because before the system would run at upto 17 volts.

The fuel pump relay shouldn't click at all when the car is running, right?
Is there anything that could be causing this besides the fuel pump relay?
If not, how can I get a relay and be sure it is good?

Houpty GT

I see in the wiring diagram that the fuel pump relay has wires that run to the airflow sensor contact, the alarm system, and the RPM limiter switch as fuel pump cut offs. I will have to figure out if there is anything wrong with these items. The alarm system does not work and I know it went off one time for some reason.

Houpty GT

Where is the RPM limiter switch located?

I am pretty sure the Alarm system is responsible for this. It does not seem to do it now that I have turned the switch a bunch of times. It is hard to get to the control box because all the ventilation stuff is in the way in the trunk. I will need to make some time to work on this. I know I can just jump the fuel pump relay terminals if it gets too bad.

The relay definitely is not suppose to click either. By default the fuel pump relay is suppose to be in the power on position. It is only when there is no airflow that the airflow sensor contact closes the ground and activates the relay to cut power to the fuel pump. The alarm system will do the same thing as well as the rpm limiter switch.

jakeflyer

What manual are you using for your trouble shooting? It sounds like you have some detailed information.

Houpty GT

I use the Bentley. I have the Factory manual but I finding it a little harder to use. The problem with the Bentley is that it has so many mistakes in it. Friday I used it to replace the license plate bulbs and it said to use 1895 which is wrong. The fixture says to use 1855 and so do the parts store catalogs but no one had those bulbs. I ended up using 5007 which is 5 Watts like the 1855 and is the same size. Pelican parts sells the 5008 which is 10 Watts so I guess they are wrong too.

The Bentley does not say where the RPM limiter switch is and I need to know that.

Friday I found a White/Green wire by the alarm that was cut and wrapped up. There was no sign of where it went but I guess it is for the cruise control which does not work and has a wire of that color shown in the diagram.

Houpty GT

I pulled my ventilation out yesterday. I found that the alarm system switch always reads that the alarm is off. This is generally true but I have seen the alarm go off before. I need to do more electrical testing of the system.

I also found that the OXS mileage counter was disconnected and there was no bulb in the fixture. Is this suppose to light when the ignition is first turned on?

"Friday I found a White/Green wire by the alarm that was cut and wrapped up. There was no sign of where it went but I guess it is for the cruise control which does not work and has a wire of that color shown in the diagram." - I unwrapped this wire and found that is has a piggy back connector on it so that it can plug into one spot and another connector can plug into it. I still don't know where it goes. There are a few white/green wires in the system. The electrical tape was of the cloth kind and I wonder if the car came this way.

Houpty GT

I tested my alarm system and had to fix the switch. I was able to us a chisel and hammer to crack the back cover off of the switch and the problem I found is that some of the soldering had gone bad so I removed the old solder from 2 spots on the resistor on the 'On' position side and resoldered them. After this the alarm passed every test except for one that was backwards from the Bentley manual. Test Terminals 15 and 31 went on with the ignition switch on. By examining the wiring diagram, it would appear that mine operated correctly and that this was written incorrectly in the manual.

wwest

The fuel pump relay is NOT as it would seem to be...

When energized it actually disables the fuel pump power except in the ignition switch start position.

The relay is energized and thereby removes the "normal" power source to the fuel pump (switches over to the ignition switch start position) whenever the RPM limiter trips or the airflow valve "measuring" flap/vane in the engine intake is closed. Like the differential brake fluid pressure detection circuit the RPM limiter is subject to locking/latching up if the batteryr is overcharged, energizes the fuel pump relay and now the engine can only be restarted via the ignition key.

Houpty GT

Where is the RPM limiter?

I think I may have had that problem with the brake fluid sensor but the light is gone now since the brake fluid all leaked out and ran into the smugglers cavity. Yes, this fluid leak is going to be one of my other projects while I have the ventilation out.

Houpty GT

My alarm seems to work fine now but I do need to repair the drivers door contact. I drove the car and could not recreate the problem. I found a note in the Bentley stating the electronic speed control relay cuts fuel at 7,000 rpm and is located under the instrument panel to the left of the turn signal flasher relay. If the issue reoccurs once I get the car back on the road then I will eliminate the wire on the alarm and if that does not resolve it then I will have to investigate this relay.

theiceman

Please don't even get me started about mistakes in the Bentley !!!

Houpty GT

Here is a pic of the White/green wire. Any ideas? It was too hard to trace once it got to the wiring harness.

wwest

Some of the solid state components in this 911 series are unusually subject to latch up under slight over voltage conditions. With slight over voltage the CD ignition will generate extra "sparks", triggering the rev-limiter, which latches up in the RPM limiting state, energizes the fuel pump disable relay and thereby kills the engine until the ignition is cycled off (thereby removing power from the rev-limiter and releasing its latch up state) and then back on.

With a poor, slightly poor, electrical connection between the engine, engine compartment chasis, and the battery terminals, ALL THE WAY UP FRONT, you may have over-voltage spiking, or even actual over-voltage, in the engine compartment but not at the battery terminals. Check all the connections but especailly the ground side connections from the engine to the chasis and from the chasis to the battery negative terminal.

wwest

"..headlights on...."

Extra "work" from the alternator, more current flow from the "REAR" to the front, "high" resistance (somewhere) to that current flow, the alternator output voltage rises to compensate....

Some of the solid state components in this 911 series are unusually subject to latch up under slight over voltage conditions. With slight over voltage the CD ignition will generate extra "sparks", triggering the rev-limiter, which latches up in the RPM limiting state, energizes the fuel pump disable relay and thereby kills the engine until the ignition is cycled off (thereby removing power from the rev-limiter and releasing its latch up state) and then back on.

With a poor, slightly poor, electrical connection between the engine, engine compartment chasis, and the battery terminals, ALL THE WAY UP FRONT, you may have over-voltage spiking, or even actual over-voltage, in the engine compartment but not at the battery terminals. Check all the connections but especially the ground side connections from the engine to the chasis and from the chasis to the battery negative terminal.

And remember to remove the battery post connections and clean and burnish both battery terminals and connectors.

Houpty GT

The RPM limiter switch is mounted on the inside driver's fender and can be accessed through the trunk. It is a rectangular black box with a 4 wire white connector going to it.

I suppose my problem had mostly gone away for a year or so but possibly returned in a differnet form. On cetain occassions the motor will completely cut out at over 3000-3500 rpm and my air fuel ratio gause will show no consumption of oxygen in the exhaust. The motor will no come back to life until I push the clutch in and it drops to idle. I also have a more sporadic problem with the fuel pump relay clicking on and off. The first problem was either an issue with the ignition box or the fuel pump. It tends to be more of a problem when it is hotter or is raining and can also be initiated by increasing load on the alternator by using the power windows. The problem with the fuel pump relay is either the rpm limiter or the alarm.

My security system works perfect after repairing the door switch and the lock circuit.

I have disconnected the rpm limiter switch and will see if it returns any problems related to this or the clicking of the fuel pump relay.

I am also having a problem with the chinese fuel pump relays. They have been fusing in the closed circuit position, leaving the pump running. The good news is that Pelican parts has German made Wittren fuel pump relays. They are twice the price but should be worth it for the quality and reliablity. (Edit: The Wittrin fuel pump relay is made in china and seems to be exactly the same as the relay that is half the price.)