Slow cranking, good battery & alternator

[hakukamana]

This just started about a week ago on the Eliminator. Usually when I go to start the truck the starter whirls for about 2 seconds and then pow the engine fires right up. So initially I checked the battery (size34 AGM) $200 + at Autozone. Battery tested good, put the load tester on it, tested good, just for the heck of it, put it on the charger over night, 13+ volts. Checked while running alternator is kicking out 14.3. But it is slow to crank, but catches and then starts. This is not normal for the truck. Grounds are all done, I am wondering if its the starter relay or the starter solenoid itself. Usually a slow cranking of the starter would indicate a low charged battery or the battery not taking a charge. This one has me puzzled.

[Ωhm]

Check battery terminals. Clean terminals, contact at starter solenoid  and contact at engine block.

Take voltage drop test across each battery cable. Use the battery post for each test.
Connect DVOM between battery positive post and contact at the starter solenoid. Looking for 0vdc.
Connect DVOM between battery negative post and contact at the engine block ground. Looking for 0vdc.
 

[Ωhm]

I left an untested gap (starter motor case to engine block ground).
Connect DVOM between battery negative post and starter motor case. Looking for 0vdc.

[hakukamana]

Ohm,  Battery 13.2v static. Terminals and posts clean. Battery B+ to starter solenoid 0vdc, Battery Neg-  to engine block ground 0vdc, Battery Neg- to starter case 0vdc. I kinda figured these were good I'm kind of anal regarding my connections and their condition. Everything is clean and tight.

Edited April 16, 2020 by hakukamana
spelling

[Minuit]

My bet is the starter itself. That was the case on my 91. Very slow cranking with near-0 voltage drop through the cables was my symptom.

[Ωhm]

Next would be a starter draw test (Amps), but that may show good even with a bad starter. IDK the spec.

[jdog]

What about a voltage drop across the starter, pos. To terminal, neg to case.

[Ωhm]

9 minutes ago, jdog said:

What about a voltage drop across the starter, pos. To terminal, neg to case.

If I understand this right, wouldn't that just show battery voltage during CRANK since all voltage is being drop across the starter circuit.

[hakukamana]

Ohm, it looks like approximate cranking amps is 160 based upon the 88 electrical manual. They are using a S-VAT-40 meter its the old style carbon pile load tester and a CCA tester. I have a load tester but not like the S-VAT-40 tester, I also have a Fluke 88 meter so I have some good electronic instruments,  I have a clamp on amp tester but I don't know what that would show. Amp draw during cranking from the battery or the starter relay ????? Shouldn't the voltage draw and the amperage draw be the same during cranking from the B+ battery post and the starter relay feed ?

[Ωhm]

11 minutes ago, hakukamana said:

I have a clamp on amp tester but I don't know what that would show. Amp draw during cranking from the battery or the starter relay ?????

If your clamp on amp tester is on the battery cable (RED 4 gauge) to the starter you will read starter motor current during CRANK. If clamp on amp tester is at the starter relay (RED 8 gauge) you will read current through the fusible links, including starter hold in windings during KEY ON, CRANK, ENGINE RUNNING.

[silvertwinkiehobo]

If the starter is a permanent magnet motor, the magnets losing their gauss strength will cause slower cranking without a resulting rise in amperage, as opposed to winding-built motors (the big, heavy buggers), which cause a rise in amperage with a commensurate loss in torque due to partial loss of total field strength.

[omega_rugal]

7 hours ago, hakukamana said:

it is slow to crank, but catches and then starts.

 

the starter, worn brushes, happened to me...

[hakukamana]

Worn brushes was the culprit. I took it to my local alternator/starter rebuilder in town, we tore the case down and there was little to nothing left of the brushes. New Mitsubishi starter, works like it did before the issue. I wonder how long the brushes last? Thanks for the help guys, never had this issue happen before so was not clued in to the brush issue with the starter.

[omega_rugal]

37 minutes ago, hakukamana said:

Worn brushes was the culprit.

 

told ya

[Comanche1]

Help! Starter motor done in. Trying to replace. 2.5 87 Bosch type.  What size is torque type socket and why are they unbelievably tight? I’ve done hundreds of starters and can’t get these bolts to budge. Quick response would be appreciated. 

[hakukamana]

Try PB Blaster, a little tapping on the bolts, and either a 14mm or 15 mm for the bolt heads. Never had the starter bolts seize. If all else fails use a MAP gas torch on the heads after a good soaking of the PB Blaster, between the heat and the rust eater they should come out. Be patient the last thing you want is a snapped bolt head. Good luck