electrical problem
04-08-2002, 11:30 AM
#1
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electrical problem
My 84 has an electrical problem I haven't been able to solve--going crazy:
Cold engine. Turn the key and all proper instrument lights come on--everything is fine, but fuel pump does not always come on. You have to turn the key back and forth a couple of times before the fuel pump will come on. I know what you're thinking--ignition switch, but I have already installed a new one and it did not solve the problem. The plot thickens--after I get the pump on and start the engine, everything is fine--volts are up, oil pressure is up. Let run 5-10 minutes and then shut it off. When I go to restart and turn the key, now the volt meter light doesn't come on and the oil pressure light flashes on and then immediately goes off. Fuel pump acts the same as before. I understand the circuit excites the alternator field. If you start the engine now, the alternator is not excited and the volt meter reads 11 or less volts. Rev the engine to 3200 RPM and the alternator self-excites. I had the alternator tested in a shop and it is in good working order. I have also replaced the circuit board on the back of the instrument cluster. When it is working properly (cold engine), with the key on and engine off, I read no voltage on the exciter terminal on the alternator (like it should be). Warm engine with the key on (engine off), oil pressure light flashes, no volt meter light (fuel pump may or may not be running). Now I read 9 volts on the exciter terminal on back of alternator. Remove the wire from the terminal and I don't read voltage on the exciter terminal of the alternator, but I do have voltage on the exciter lead. I go to the multi-pin connector by the jumper terminal and unplug. I read the voltage coming from the car harness (engine harness lead to terminal passes continuity test). I also checked continuity on the harness to the fuse board and it's OK. This is as far as I got with the fuel pump not coming on every time seems to complicate the problem. I would appreciate any help--I do not have any wiring diagrams to follow.
Cold engine. Turn the key and all proper instrument lights come on--everything is fine, but fuel pump does not always come on. You have to turn the key back and forth a couple of times before the fuel pump will come on. I know what you're thinking--ignition switch, but I have already installed a new one and it did not solve the problem. The plot thickens--after I get the pump on and start the engine, everything is fine--volts are up, oil pressure is up. Let run 5-10 minutes and then shut it off. When I go to restart and turn the key, now the volt meter light doesn't come on and the oil pressure light flashes on and then immediately goes off. Fuel pump acts the same as before. I understand the circuit excites the alternator field. If you start the engine now, the alternator is not excited and the volt meter reads 11 or less volts. Rev the engine to 3200 RPM and the alternator self-excites. I had the alternator tested in a shop and it is in good working order. I have also replaced the circuit board on the back of the instrument cluster. When it is working properly (cold engine), with the key on and engine off, I read no voltage on the exciter terminal on the alternator (like it should be). Warm engine with the key on (engine off), oil pressure light flashes, no volt meter light (fuel pump may or may not be running). Now I read 9 volts on the exciter terminal on back of alternator. Remove the wire from the terminal and I don't read voltage on the exciter terminal of the alternator, but I do have voltage on the exciter lead. I go to the multi-pin connector by the jumper terminal and unplug. I read the voltage coming from the car harness (engine harness lead to terminal passes continuity test). I also checked continuity on the harness to the fuse board and it's OK. This is as far as I got with the fuel pump not coming on every time seems to complicate the problem. I would appreciate any help--I do not have any wiring diagrams to follow.
04-08-2002, 12:01 PM
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hi
i had a very similar problem. the power feeds to the various ignition parts go thro several relays.
check out '928 specalists' they have relay/fuse panel diagrams online.
i had a faulty ignition relay that would work when cold, then drop out as it warmed up. replaced all the relays in the chain (3 i think) cleaned all the fuses, and the fuse holders. actually removed fuse board from the car...easier to work on. unplugged, and then plugged back in, all the cable harness connectors at the base of the fuse board several times (wiping action cleans contacts)
no further faults.
when mine cut out, if you switched the ignition switch on/off a few times the tacho needle would go full travel!
from memory - three relays....power to fuel pump, power to injection/ignition ecu's, third one was inline with above.....i think. crazy system!!!
regards
johnb
i had a very similar problem. the power feeds to the various ignition parts go thro several relays.
check out '928 specalists' they have relay/fuse panel diagrams online.
i had a faulty ignition relay that would work when cold, then drop out as it warmed up. replaced all the relays in the chain (3 i think) cleaned all the fuses, and the fuse holders. actually removed fuse board from the car...easier to work on. unplugged, and then plugged back in, all the cable harness connectors at the base of the fuse board several times (wiping action cleans contacts)
no further faults.
when mine cut out, if you switched the ignition switch on/off a few times the tacho needle would go full travel!
from memory - three relays....power to fuel pump, power to injection/ignition ecu's, third one was inline with above.....i think. crazy system!!!
regards
johnb
04-08-2002, 12:05 PM
#3
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In this case, having the wiring diagrams in the Workshop Manual wouldn't be much help - the diagrams for the '84 are virtually useless. They don't even give any wire colors!
Some comments:
1) The fuel pump should NOT come on when you turn the ignition switch on. It should only run when you hit the starter, or when the engine is running.
2) The alternator exciter voltage runs from the ignition bus (bus 15) to the warning lamp in the voltmeter, from there a blue wire runs to terminal L23 on the central power panel, out to terminal M13, and from there to the 61 terminal on the alternator. There is a 68 Ohm power resistor in parallel with the warning lamp, mounted on the back of the voltmeter. You should get voltage on the exciter circuit anytime that the ignition switch is turned on. If the alternator is slow to start producing, there may be a bad connection somewhere on the blue wire.
Check the wires on the ignition switch - they sometimes can get loose.
Some comments:
1) The fuel pump should NOT come on when you turn the ignition switch on. It should only run when you hit the starter, or when the engine is running.
2) The alternator exciter voltage runs from the ignition bus (bus 15) to the warning lamp in the voltmeter, from there a blue wire runs to terminal L23 on the central power panel, out to terminal M13, and from there to the 61 terminal on the alternator. There is a 68 Ohm power resistor in parallel with the warning lamp, mounted on the back of the voltmeter. You should get voltage on the exciter circuit anytime that the ignition switch is turned on. If the alternator is slow to start producing, there may be a bad connection somewhere on the blue wire.
Check the wires on the ignition switch - they sometimes can get loose.
04-08-2002, 10:25 PM
#4
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Corroded relays, fuses and bad grounds cause electrical phantom problems.
Below is one of my previous posts I hope this helps.
Low battery voltage or bad grounds, overcharging and undercharging alternator can cause an erratic computer control. Any input sensor, example, TPS, CTS (coolant temperature sensor), relay can malfunction or give a wrong reading under these conditions. With the ignition off turn on the headlights for one minute after one minute turn the headlights off; connect DVOM set to DC volts, negative lead to negative post, positive to positive. A fully charged battery should read 12.6 volts. Anything lower than 12.3 volts, you will need to charge the battery, with the main cables disconnected. With the meter connected to the battery positive-to-positive, negative-to-negative, start the engine; turn on the headlights, heater fan, and radio. This puts a load on the system. You should see 13.5 volts to 14.4 volts. Anything under 13.5 volts could be a bad alternator, bad diode, bad ground or high resistance in the positive cable. Anything over 14.5 volts is an overcharging alternator. With the car still running, lights and accessories still on, place the negative lead of the meter to the negative lead of the battery post, place positive lead of the meter to all of the ground wires. No more than 0.10 volts should read on the meter. A good ground is 0.00 or 0.01 volts. If you have 0.20 or more you have a bad ground wire. You can use a jumper wire for the negative lead of the meter to the negative lead of the battery post, so you can reach the engine compartment. Just be careful and use common sense when working in the engine compartment when the engine is running. You should check the alternator output directly at the alternator with the car running and all accessories on.
Make sure you have the decimal in the right place on your meter.
Good luck,
Steve C
The Great White <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
Below is one of my previous posts I hope this helps.
Low battery voltage or bad grounds, overcharging and undercharging alternator can cause an erratic computer control. Any input sensor, example, TPS, CTS (coolant temperature sensor), relay can malfunction or give a wrong reading under these conditions. With the ignition off turn on the headlights for one minute after one minute turn the headlights off; connect DVOM set to DC volts, negative lead to negative post, positive to positive. A fully charged battery should read 12.6 volts. Anything lower than 12.3 volts, you will need to charge the battery, with the main cables disconnected. With the meter connected to the battery positive-to-positive, negative-to-negative, start the engine; turn on the headlights, heater fan, and radio. This puts a load on the system. You should see 13.5 volts to 14.4 volts. Anything under 13.5 volts could be a bad alternator, bad diode, bad ground or high resistance in the positive cable. Anything over 14.5 volts is an overcharging alternator. With the car still running, lights and accessories still on, place the negative lead of the meter to the negative lead of the battery post, place positive lead of the meter to all of the ground wires. No more than 0.10 volts should read on the meter. A good ground is 0.00 or 0.01 volts. If you have 0.20 or more you have a bad ground wire. You can use a jumper wire for the negative lead of the meter to the negative lead of the battery post, so you can reach the engine compartment. Just be careful and use common sense when working in the engine compartment when the engine is running. You should check the alternator output directly at the alternator with the car running and all accessories on.
Make sure you have the decimal in the right place on your meter.
Good luck,
Steve C
The Great White <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
