Dave Barbieri
Full Access Member
Had some decent weather and some spare time, so I figured I'd try to sort out the 'slow spin' engine problem. Since I started work on this project, the engine has never spun over very fast. It sounded slow, and sure enuff, when I hooked up one of our MT2500 scanners a couple of months back, the cranking speed was around 115 - 120 rpm. It got worse. Last weekend, it was down to 80rpm. OK, time to find out once and for all whether it's an engine problem 
or a starter problem.
First, I tried the GM starter test called out in my '94 GM shop manual. The General sez that battery voltage at the terminal shouldn't fall below 9.0 volts during engine cranking. Great... My batteries are larger than stock, and I'm using #2 welding cable for battery/starter cables. To what degree does increased battery capacity/lowered conducter resistance effect the voltage reading? No one knew.
OK, on to Plan B - starter amp draw during cranking. GM does NOT publish specs for this, so I did a comparison last week end between my 1985 F250 6.9 and the 6.5. Ran directly off the starter solenoid, so there would be no glow plug or auxilliary system drain. Results: Ford - 235 amps, GM - 475 amps. OK, the reading is obviously higher, but I'm back to my original question - starter or motor??
On to Plan C - the bench test. GM's specs for the MT-series starter are 130amps max at 12volts and 2300rpm. We used the two 1000 CCA gel-bats from my Ford and a Snap-On amp probe. Results: initial start-up - 310 amps; continuous run - 140 amps. Time to bite the bullet and get a new starter.
New AC Delco ($162), back on the bench. We decide to test the new starter to set a baseline. Same setup. Results: initial startup - 170 amps; continuopus run - 105 amps.
Swung by the Chevy dealer on the way home and invested in new starter bolts (They are TIGHT!). Crawled under the truck and had that puppy installed in about 4 minutes. Also ran a second trigger/switch wire from the solenoid to allow for a switch under the hood. OK, the starter's installed, all wires reconnected, and both batteries back on line. We're ready to rock! I touch the trigger wire to BAT +, and...... NOTHING! Dead silence. Both batteries are stone cold dead!
Disconnect both batteries, connect the trickle charger to the Pax bat, and let it charge all night. Next morning, connect the charger to the other bat and let it charge all day while I'm at work. That night, after work, reconnect everything and try again. YOWZA!! Cranking rpm is 175, and that sucker is trying to light off! Couldn't get it to hit more than a couple of times, but I'm close!
or a starter problem. First, I tried the GM starter test called out in my '94 GM shop manual. The General sez that battery voltage at the terminal shouldn't fall below 9.0 volts during engine cranking. Great... My batteries are larger than stock, and I'm using #2 welding cable for battery/starter cables. To what degree does increased battery capacity/lowered conducter resistance effect the voltage reading? No one knew.
OK, on to Plan B - starter amp draw during cranking. GM does NOT publish specs for this, so I did a comparison last week end between my 1985 F250 6.9 and the 6.5. Ran directly off the starter solenoid, so there would be no glow plug or auxilliary system drain. Results: Ford - 235 amps, GM - 475 amps.
OK, the reading is obviously higher, but I'm back to my original question - starter or motor?? On to Plan C - the bench test. GM's specs for the MT-series starter are 130amps max at 12volts and 2300rpm. We used the two 1000 CCA gel-bats from my Ford and a Snap-On amp probe. Results: initial start-up - 310 amps; continuous run - 140 amps. Time to bite the bullet and get a new starter.
New AC Delco ($162), back on the bench. We decide to test the new starter to set a baseline. Same setup. Results: initial startup - 170 amps; continuopus run - 105 amps.
Swung by the Chevy dealer on the way home and invested in new starter bolts (They are TIGHT!). Crawled under the truck and had that puppy installed in about 4 minutes. Also ran a second trigger/switch wire from the solenoid to allow for a switch under the hood. OK, the starter's installed, all wires reconnected, and both batteries back on line. We're ready to rock! I touch the trigger wire to BAT +, and...... NOTHING! Dead silence. Both batteries are stone cold dead!
Disconnect both batteries, connect the trickle charger to the Pax bat, and let it charge all night. Next morning, connect the charger to the other bat and let it charge all day while I'm at work. That night, after work, reconnect everything and try again. YOWZA!! Cranking rpm is 175, and that sucker is trying to light off! Couldn't get it to hit more than a couple of times, but I'm close! 
