breathment

i am getting a good 14 volts at the battery and alternator. and like 13 volts with lights on and most accesories on. but inside the car. according to the scan tool and measureing the voltage at the dome light. im getting anywhere from 10-13 volts. and when the voltage drops down to 11 or so. the engine runs rough. like im not geting good voltage at the coil. or maybe its the ecm getting low voltage. not sure.. so its like the battery and alternator always have good voltage. but from there to the inside of the car. something is screwy.. can i maybe have a short or something going on? cause i can't drive my car like this cause i don't need it to die on me. again..

also, i am having starting problem. where i try to turn the car over. and i only hear a click coming from the starter. so i think its not getting good voltage either.. but i know the engine is well grounded cause i can put the test leads on the alternator, and the intake plenum. and i get the same voltage i get at the battery.. so why isn't it getting to the other parts of the car?

IROCmonkey

have you checked the engine grounds? starter fusible links?

AlkyIROC

I'd also suggest looking for bad grounds. Make sure there's a good engine ground and make sure there's a good chassis ground although with a unibody everything is a chassis.

I had a Freightliner like that. 14 volts at the alternator and 11 in the cab. I chased wiring looking for a voltage drop for hours before finding out that the cab ground strap was missing.

94-6spd

Really check the grounds like previously posted. I redid all my grounds and it made a huge difference. Is there paint on the block in between the starter and the block? Or maybe paint on the starter itself? I put this stuff called Penetrox on all my connections also. It supposedly makes a better contact than just metal to metal. You will probably find this stuff on the net. I got mine from an electrician. I put this stuff between the starter and the block. I have no voltage drop now.

ZZ28ZZ

Is the low voltage causing eng to stumble or
is the eng stumbling causing the low voltage?

If your eng stumbles, your alt output will go down since the alternator slows down. Alternators don't produce much output at normal idle speed, and even less when stumbling.

As far as verifying the eng and body are grounded, check the voltage drop between the eng and the body with the the blower, headlights, etc turned on. It should be very close to zero.
If it's more then abt .2 volts, that would point to bad eng/body connection(s).

The batt is grounded to the eng, so it usually does have a good ground. Body is connected to the eng, not the batt.
If the body/eng ground is bad, anything needing a ground from the body will suffer.
Make up a temporary ground wire to connect the eng to the body.
If interior voltage conditions improve, start checking the ground straps. I know there are some ground straps on the back of the pass head. They're a little tough to get at.

If you want to monitor ECM voltage, just put the voltmeter on the ECM fuse at the fuse block.

For the starter problem:
The starter solenoid has a metal disc inside that connects power to the starter after the bendix (starter gear) has engaged the flywheel. This disc will degrade over time due to the large amount of current that burns it a little every time it is used. At some point, the connection at the disc deteriorates to the point it will no longed make contact. You'll still hear the bendix kick out and engage the flywheel, but no current flows to the starter.
Low voltage will only make matters worse.

You need to check the voltage at the big wire on the solenoid when starter is engaged.
If it reads abt 12v and it dosen't change much when starter is engaged, and you hear the solenoid click, you need to replace the solenoid.
If the voltage drops to near 0, check your battery, ground, and solenoid connections.

breathment

im pretty sure that its the low votlage causing the engine to stumble.. cause it can be running fine. and say i turn on the rear defrost and the voltage inside the car will drop.. (batt volts stays about same) and ther engine will run rough until i turn it off,


but thanks for all the suggestions. ill check the ground straps tomorrow.. how many is there usualy on a a tpi car?

Vader

Check the power connections at the battery, fusible links near the battery, connections and links at the starter, ground on the left frame rail near teh battery, and large braided ground strap on the RR of the engine/head. If none of those proves to be a problem, start looking closely at teh bussing on the back side of the fuse panel. I've had those start to get resistive on me, too.

IROCmonkey

another possibility...have you had your altenator checked? A blown diode in the alt will still leave the alt putting out voltage but with no amps behind it, making any load on the system that much more draining