Bench test problem.

[DaveH]

Bought a (used) replacement engine for my 05 ranger 2.3 two wheel drive. I can hand crank the engine, leak down shows good on all 4 cylinders. I just wanted to test compression as a final check before installation. Here is where the trouble began. Bench tested the starter, spins like a champ and pops forward as should. Load tested my battery and it is showing 12.4 volts and holds a load. Now for the head scratcher. When jumping the starter to crank the engine it cannot spin the engine fast enough to get the compression test. Womp........womp........womp nothing. I know the engine isn't seized, I know the battery is good and I know the starter functions. Voltage drop????? Jumper cables causing the issue?

 

[franklin2]

Dinky jumper cables can cause a problem. Most of the smaller jumper cables are designed to "help" a low battery, not supply all the power needed to turn the engine over.

Another clue of the problem is heat. If the jumper cables or cable ends get hot or start smoking, that is a problem. Heat and smoke are a sign of power being lost.

 

[Josh B]

I also believe the battery voltage is a bit low. I saw somewhere yesterday it required 12.8 to be good

 

[DaveH]

Dinky jumper cables can cause a problem. Most of the smaller jumper cables are designed to "help" a low battery, not supply all the power needed to turn the engine over.

Another clue of the problem is heat. If the jumper cables or cable ends get hot or start smoking, that is a problem. Heat and smoke are a sign of power being lost.

You are spot on with this one. I cannibalized the main wiring loom from the spare engine and used those battery cables. Voila' the engine spins just fine. I had a massive voltage drop with the jumper cables.

 

[DaveH]

I also believe the battery voltage is a bit low. I saw somewhere yesterday it required 12.8 to be good

Yes Josh, the battery was a large 6 year old one. Fully charged I get 12.4 volts. When I changed the cables to feed power to the starter it did provide enough juice to spin that motor.