5 replies to this topic

[AW33COM]

I purchased a used alternator and I can't start the car. The fuse box in the engine bay has no ground. The ground wire from the fuse box goes to the alternator. The ground from that wire does not work.

When I tested for voltage at the fuse box and I grounded to the chassis directly the fuse box had correct voltage.

The alternator itself has a ground bolt that sticks out. When I connect one lead to the bolt and another lead to the engine block it does not conduct any electricity. When I connect one lead to the alternator cover and another lead to the engine block it conducts electricity.

What am I looking at here? Should I pull the alternator and inspect the ground? Why would ground not work at that location?

[DES4]

The engine needs to be grounded to the chassis/body of the vehicle... it sounds as if it is not. Check the heavy ground straps that connect the powertrain to the chassis.

[Jim Boemler]

My recollection (old, admittedly) is that the alternator only has one "bolt that sticks out" -- but it's not a ground, it's the alternator output. Any chance that's where you're measuring? DES4 is right, the ground connection is to the engine, which is in turn connected to the chassis by a braided wire near the left rear of the motor.

[AW33COM]

I think I understand my mistake, but I need to go to the garage and check it out. What you're saying is this: the white thick wire coming out of the alternator is the power. Great, that means the black thick wire going to the engine bay fuse box is also power, but that's the power when engine is not running. If I'm correct, the fuse box does not have a ground, and I have to look there.

Btw, the engine is ground to the chassis. I tested it and that works. What does not work is there is no voltage at the engine bay fuse box if I connect both of the leads to the fuse box. When I connect the ground to the chassis and the hot lead to the fuse box then it's all good.


Update, the fuse box has ground. I have some other problem that stop the power from going into the fuel pump. I exchanged the fuel pump relays and I bypassed the relay in the diagnostics, but that did not help.

[DES4]

Still sounds as if there's a ground issue somewhere. You need to do voltage drop checks, preferably while the vehicle is running (electrically loaded; circuits consuming current). Easy to do: Set your volt/ohm meter to measure DC voltage, and probe your ground points... for instance, put one lead probe on a good chassis ground point, and another on the engine block, or any other ground that may be suspect. You should read 0 volts; should you read anything beyond 1 volt, you likely have a ground that is not on the same plane as your battery and/or charging system. What that means that somewhere between those two points is a high-resistance path that is consuming current. Another means of doing this is one lead on your battery positive, while probing other grounds with the free lead; in this case, the ground that reads the lowest voltage is the ground with a resistance issue... all grounds, ideally, should read full system voltage.

Resistance checks on a static vehicle are of little value; once the car is running and consuming current, an electrical path that looks okay with an ohm meter check may be overwhelmed by demand, and then becomes a high-resistance circuit once its capacity to move current is exceeded.

This ultimately may not be the problem you're dealing with, but should be eliminated first, as these checks take about 5 minutes.

[AW33COM]

Well after few more tests and ripping everything apart I realized the white/red wire at the Fuel Pump relay has no power. The same wire goes to the Diagnostics connector and it has no power either. This wire is in the main relay and it has power there, so I'm sort of stuck now as I have no idea where the splice is (I have a bad feeling it is under the dashboard).

According to the Haynes manual the white/red wire comes from the ECM, gets spliced twice, the first splice goes to the main relay, the second goes to the fuel pump relay, and than it continues to the Diagnostics connector.

The "gets spliced twice" in the manual does not show the actual location. It is somewhere under the dashboard I think. Maybe some of you will know, but it's not an easy thing as the whole dash is assembled.