hard start, battery shows 13.4v

87 MJ 4.0 2wd ba-10

this just started yesterday, and is getting progressivley worse. it cranks extremely slow, like the battery is dead. i put a volt meter on the battery and it shows 13.4 volts. im thinking maybe a bad ground?

another oddity... when i put the directional signals on, the voltage gauge dips when the signals flash. maybe alternator going bad? once it starts it runs fine, and i can pull the ground cable off the battery and it stays running. if the alternator was going out it would die, wouldnt it?

Check for corrosion on the positive cable - these are symptoms of that, but it isn't guaranteed. Cut the sheathing off of it a bit and peek inside - mine was corroded ALL The way through. Eight bucks and no more start probs hehehehe.

Take your battery an alt in to AUTO ZONE, they can TEST it for you....:jester:

scottmcneal said:

Take your battery an alt in to AUTO ZONE, they can TEST it for you....:jester:

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:twak: you should know better.

battery is good, i just would like to get some ideas before i pull the alt.


there is no corrosion ON the cables, but tomorrow i will check resistance on them.

OUCH, ok ... Did or have you check your starter? Mine was draging real bad

Things to check (going off of the "slow crank" statement, and not a "long crank"):

1) Corrosion at the battery clamps. Remove, clean, and reinstall.
2) Corrosion or contamination at the main engine ground, behind the dipstick bracket.
3) Check that the starter is firmly attached to the engine block, and that that attachment is clean. The starter motor grounds through the case and the engine block - contamination at this connection can cause trouble.
4) Check that the connection between the primary battery cable and solenoid screwpost is clean.

There are also contacts in the starter solenoid that can be eroded by high-current sparking, but they can't be readily checked. If everything turns out fine, you can remove the starter motor and "bench-test" it yourself easily with a pair of jumper cables. Here's how:

1) Remove the starter motor, secure it to something solid (it will jump about.)
2) Get out your jumper cables. Connect them to the battery, connect the negative cable to the starter case (usually to a mounting ear,) and the positive cable to the large screwpost on the solenoid that is not connected to the starter motor.
3) Using a lead, screwdriver, or a "bump switch" (the last is preferred,) energise the small screwpost on the starter motor solenoid. Expect the unit to jump when you do so. Do not hold engaged for more than ten seconds!

If the starter motor turns slowly, then either the contacts in the starter motor solenoid are eroded, or the starter motor shaft bushings are worn, or the brushes are hanging up on the comm ring (it's a DC motor, so it's a segmented commutator.) Replace.

If the starter motor turns quickly (as normal,) then turn your attention to the reciprocating assembly in the engine. Remove the spark plugs and turn the crankshaft by hand - if it binds up, find out why (it should turn relatively easily with the spark plugs out, since there will be no compression.)

The battery can show good voltage than drop under a load when you try to crank it. Min was showing 12.5 volts, and woudln't even power the headlights. I thought I had some wierd electrical problem, it was just the battery. They can "load" test it at a parts store.. or.. try turning on the headlights, and check the voltage.. or have someone else try to start it and check the voltage. Don't spend too much time trying to chase down an electrical problem.. start simple..

FYI i work at a parts store, a NAPA in fact. the first thing i did was test my battery. its an optima yellowtop, its putting out 13.4 volts, and under load its registering 850 CCA. its not my battery. i really dont want to pull the alternator if that might not be the problem as this is my DD and that is a pain in the ass. i'll check the resistance on the cables tomorrow.. i hope its just a bad ground.

Years ago I had a similar problem on my Jeep CJ-5. I ended up replacing the starter. Fixed the problem.

Electrically, there is no reason your alternator should be at fault in slow cranking if you have a fully charged battery in good condition.

Resistance measurements will not necessarily tell you whether the cables and grounds are capable of supplying adequate current for starting. Better are voltage measurements as suggested by stephenspann27.

i say clean the posts really well and make sure the cables are good. sounds like the started isnt getting enough. mine was doing it a few days ago and cleaning the posts did the trick.

GrimmJeeper said:

FYI i work at a parts store, a NAPA in fact. the first thing i did was test my battery. its an optima yellowtop, its putting out 13.4 volts, and under load its registering 850 CCA. its not my battery. i really dont want to pull the alternator if that might not be the problem as this is my DD and that is a pain in the ass. i'll check the resistance on the cables tomorrow.. i hope its just a bad ground.

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Then why are you screwing around with it in your jeep? :repair: :laugh3:
Some poor bastard's probably stranded, pissed, and wondering who the hell stole his Optima!:gonnablow

OK mike, i gave you time to CHECK your grounds.. Did that help?

scottmcneal said:

OK mike, i gave you time to CHECK your grounds.. Did that help?

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just coming in to update and YES.


ohm tested the negative cable and it was well within spec. cleaned the oil off the cable on the block connection side, cleaned and wire brushed the mounting stud, and she fired right up. problem solved.

thanks for the advice folks.

:twak: Way to go mike.. :conceited

You should have let him change the Alternator :laugh3:

:smsoap:

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I know...Sorry