7.3 turns slow on the engine stand need some ideas

[Ranger0291]

Ok, this is driving me nuts.this has happened several Times. With different engines , starters and comp testers. When I put a 7.3 on the stand I pull all the glow plugs and it turns ok , but when I try to do a co press ion test they seem to turn too slow to get a good reading. This is my setup. I have an old ambulance with dual alternators and three batteries. I hook a set of 20 ft 4.gage cables between the ambulance and the starter on the test engine ,iuse my trigger to turn it over but damn it always seems to turn way too slow and I get abnormal readings . So what is the proper setup for testing on a stand. Need some ideas on different ways to do it.

[Justin@DP-Tuner]

Have you had the starter and batteries tested?

[Ranger0291]

i have, this seems to happen with any engine i test, or any starter i use, the ambulance has 500 amp charging system , it also has charge protection wich means it revs up like a generator when it get a load put on it, they are the biggest jumper cables i can find . and i used three different starters two used and one new. i guess im thinking my setup sucks. so im lookin for some ideas as to what other people use and how they run the compression test on an engine stand. its like its not getting enough juice , idk

[dieselcrawler]

Cables are too long. Get batteries closer. At that lenth even with good cables the voltage drop at the amprage you are pulling will be a major factor. Batteries need to be as close as stock with factory size cables.

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[ianstew]

Originally Posted by dieselcrawler

Cables are too long. Get batteries closer. At that lenth even with good cables the voltage drop at the amprage you are pulling will be a major factor. Batteries need to be as close as stock with factory size cables.

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What he said

4 gauge cable is not big enough, 00 or bigger for powering the starter.

[Matthews]

At that distance I am not even sure 00 would be big enough wire. That's a long way.

[ianstew]

Agreed. Definitely needs to move the batteries or power source closer to the engine. Seems as though he's trying to fire up the engine solely on jumper cables. He ought to just bring the batteries to the engine stand and use some good thick cables.

[JSchuricht]

Between the 4 ga cable and the alagator clips your voltage is droping way too low over that distance. Like the others said, move the batteries closer and use a short large cable.