How is the pigtail ground strap from engine block to body? Have you had engine diagnostic test done? Voltage rVOLTAGE DROP TEST
A voltage drop test is the
only effective way to find excessive resistance in high amperage
circuits. It's a quick and easy test that doesn't require any
disassembly and will quickly show you whether or not you've got a good
connection or a bad one.
To do a voltage drop test, you create a
load in the circuit that's being tested. Then you use a digital volt
meter (DVM) to measure the voltage drop across the live connection
while it is under the load. Voltage always follows the path of least
resistance, so if the circuit or connection being tested has too much
resistance some of the voltage will flow through the DVM and create a
If a connection is good, you
should find little or no voltage drop and see less than 0.4 volts for
most connections, and ideally less than 0.1 volts. But if you find more
than a few tenths of a voltage drop across a connection, it indicates
excessive resistance and a need for cleaning or repair.
CHECKING THE STARTER CIRCUIT
To check the starter circuit
for excessive resistance, you need to measure the voltage drop at the
battery, battery cable connections and starter while the engine is
The first check is "available battery
voltage." For the starter to crank at normal speed, the battery must be
at least 75% charged (12.4 volts or higher). Low battery voltage can
not only affect the starter but every other electrical system in the
A. Set your DVM to the 20 volt scale,
then connect meter positive (+) lead to battery positive (+) post (not
the clamp or cable), and the meter negative (-) lead to battery
negative (-) post.
B. Disable the engine so it will not
start when it is cranked. (Ground the ignition coil wire, or disable
the ignition circuit or fuel pump relay.) Limit cranking time to 15
seconds or less.
C. While cranking the engine, record
the volt reading on the DVM. D. Next, connect your meter positive (+)
lead to the battery terminal stud on the starter, and the meter
negative (-) lead to the starter housing.
E. While cranking the engine, record the volt reading.
F. Compare the two voltage readings. If both are the same, there are no excessive voltage drops on the positive feed side.
G. If available voltage at the starter
is not within one (1) volt of battery voltage, there is excessive
voltage drop in the circuit.
The next test is for voltage drop on the positive side of the starter circuit.
A. Make sure the battery is fully charged.
B. Disable ignition.
C. Set DVM on 2 volt scale.
D. Connect meter positive (+) lead to
positive (+) battery post, and the meter negative (-) lead to the
battery terminal stud on the starter. While cranking the engine, record
the voltage reading.
The maximum allowable voltage drop
including the solenoid or external relay in the starter circuit should
be 0.6 volts or less.
If you find more than a 0.6 volt drop
in the starter circuit, you can isolate the bad connection by using the
following voltage drop tests.
* Check the positive battery post and
cable connection by measuring the voltage drop between the two while
cranking the engine. Connect the meter positive lead to the battery
post and the meter negative lead to the cable clamp. A good post/cable
connection should have zero voltage drop.
* Check the positive battery cable by
measuring the voltage drop end to end while cranking the engine.
Connect the meter positive lead to the clamp on the positive battery
cable, and the meter negative lead to the end of the cable at the
starter. Crank the engine and note the voltage reading. A good cable
should have a voltage drop of 0.2 volts or less.
* To check the starter solenoid or
relay connections, connect the meter positive lead to positive battery
terminal on the solenoid or relay, and the meter negative lead to the
starter motor terminal. Crank the engine and note the reading. A good
connection should have a voltage drop of 0.2 volts or less.
Next, you need to check the negative
side of the starter circuit. To check the entire circuit, connect the
meter positive lead to a clean spot on the starter motor case and the
meter negative lead to the negative battery post. Crank the engine and
note the reading. The voltage drop on the negative side should be 0.3
volts or less.
If the voltage drop is too high, set
your DVM to the 2 volt scale and start checking each connection on the
negative side to find the bad connection or cable. Use the DVM leads to
check across each connection while cranking the engine as before.
Check the negative battery post/ground cable connection (should be zero voltage drop).
Check the negative ground cable from the battery to the engine (should be 0.2 volts or less).
Check between the negative battery post and starter housing (should be 0.3 volts or less).
Check between the engine block and starter housing (should be 0.10 volts or less).
CHECKING THE CHARGING CIRCUIT
To check the alternator connections on the positive side for excessive resistance:
A. Set DVM on 2 volt DC scale.
B. Connect the meter positive lead to the alternator output stud (B+ terminal).
C. Connect the meter negative lead to the positive (+) battery post.
D. With the engine running at 1,800 to
2,000 rpm with all lights and accessories on (except the rear electric
defroster), check the voltage drop reading. It should be 0.5 volts or
less. If higher, the connections between the alternator output stud and
battery need to be cleaned. Also, look for loose connections or
To check the alternator connections on the negative side for excessive resistance:
A. Set DVM on 2 volt DC scale.
B. Connect meter negative lead to alternator case.
C. Connect meter positive lead to battery negative (-) post.
D. With engine running at 1,800 to
2,000 rpm with all lights and accessories on (except rear defogger),
check the voltage drop reading. On the negative side, it should be 0.2
volts or less. If excessive, the connections need cleaning or the
negative cable needs to be replaced. Some alternators are mounted in
rubber bushings and have a separate ground strap. If so equipped, be
sure to check the voltage drop across this strap, too.
egulator checked with voltmeter?