Slow cranking - have checked all the common things

[ArtemisI6]

Got a '67 Mustang with an extremely worn out 200ci. In the past few weeks it's begun to really crank slowly. So slow the car can no longer turn on without my battery charger hooked up to it with it on the Jumpstart (200 amp) setting. Even with a portable jump-pak the cranking does not change.

Let me break it down here.

New battery
New starter
New solenoid
All three battery cables replaced

Tested the battery with my voltmeter (12.76v) and at the local CarQuest and it checked out perfectly fine. Also cleaned both battery posts, and both battery cable clamps. Cleaned the Negative battery cable's ground. Cleaned both sides of the solenoid connections. Nothing that I've done has had any effect on the slow cranking. I also bypassed the solenoid and connected the jump-pak to the starter cable to see what happened and it STILL had no effect. Does this car have an engine-chassis ground cable I may be missing, or something? I know there's a small supplementary ground cable runnning from a bolt on the starter to the firewall - while messing with it earlier today it didn't occur to me to check that, so I still have to do so.

Does anyone else know what in God's name could be causing this? I'm pretty thoroughly stumped.

 

[JackFish]

Not sure about your vintage, but my '78s have a ground strap from the back of the block to the firewall.
I don't know that it would affect your cranking though...I 'm stumped. :|

Except I just noticed you didn't mention your alternator?

 

[64falconsix]

my thought also . sounds like a bad ground. it is also possible to get a bad starterfrom the parts store. I would check the ground first and make sure you have a good connection to the engine. if no change go to the local auto parts and see if you can get them to do a current draw test on the starter while still in the car.

 

[mugsy]

I had a similar problem on my other project car. I had a helper crank the engine over while I checked the voltage drop along the current path. Try that to help zero in on where the most drop is occuring.

Also, what gauge wire did you use? That ended up being one of the issues in my case. The wire connected to the starter was too small (to small of a gauge).

 

[ArtemisI6]

I bought 4ga. Stock looked to be about 6ga, and when I buy battery cables I always like to up the ante a little. My Lincoln has 1/0ga cables all around if I remember correctly.

 

['68falconohio]

Is it like a too much spark advance, slow?

 

[Lazy JW]

..... Cleaned the Negative battery cable's ground.....

Exactly where is this ground connected?

As mentioned above, using an accurate voltmeter to check for voltage drop through the cables will tell if they are indeed good (regardless of how new they may be).

If the voltage drop checks ok and the grounds are good then you either have a bad starter or something binding inside the engine.

An "extremely worn out 200" should spin really fast due to the low compression.
Joe

 

[mannella]

My father had a 69 ford truck with a 300 six in it that had a similar problem. I had to run a ground cable direct from he battery to the starter housing to get a proper ground. I had removed the starter and cleaned everything but still couldn't get a good ground. Never had any trouble after installing the cable.

 

[ArtemisI6]

Is it like a too much spark advance, slow?

That was it! I hadn't noticed the distributor had come a little loose and edged to a little overly advanced. Car's been sitting for a week... I wish I had known it'd be that easy!

We're picking up a new motor next week... I'm happy that this wasn't an electrical issue that would follow the swap! Thanks!