Strange starter issue.

[Kern Dog]

Hey guys,
My '70 has developed a strange problem related to the starter.
In 2009 or so, I installed this Denso mini starter I bought from Mancini racing. I have a 440 based 493 with 2 " TTI headers so the starter is pretty much trapped by those headers.
In 2013, I relocated the battery to the trunk. To make it all work, I changed up a few things. The stock starter relay is still underhood.
The positive cable from the battery goes to a post on a FORD ST81 starter solenoid. On the other side, a 1/0 size cable runs across the axle hump and along the left side and directly to the starter. The Ford solenoid acts as a switch so that the starter cable is only live when cranking the engine. The large and small terminals on the starter are bridged together. A trigger wire runs from the factory relay to the Ford solenoid. This closes the switch and allows the battery power to energize the starter.
I have a ground cable from the left cylinder head to the core support. There is another from the right head to the battery and a third one from the right rear frame rail to the battery.
This has worked fine for many years. Spring 2019, the Optima Red Top battery seemed to strain when starting the car. Cold and hot starts were met with slow cranking.
I blamed the battery and switched to a new NAPA AGM unit. It seemed okay but now the car has returned to the former habits.
It cranks slow when cold. The battery can have voltage in the 12.8 range and still spin slowly. It spins over fast once the engine has warmed up a bit and that confuses me.

[Kern Dog]

I have tried different batteries and the same condition persists. Slow cranking when cold and fast cranking when moderately warm.
Today I went out for a drive. I stopped for gas after about 10 minutes. It was high 90s today. The car strained a bit but started within 6-8 seconds. I drove another 10 minutes or so and it would barely turn over. After a 5 minute cool down, it still spun slow but it was enough to start the car. Back at home, I checked the battery voltage.

[Kern Dog]

Looking at this battery chart, it seems that I should be fine:

[Kern Dog]

I have another starter that I am going to try. Changing starters is a pisser though. The spark plugs and wires have to come out, the header has to be unbolted and wiggled around to make room too.
What I find strange about this is that the starter spins slow when cold and at full temperature but spins fast when the engine is between 100 and 160 degrees. I could understand slow cold cranking  if I was running 60 weight oil in sub zero weather. I am not though. I run 15w40 diesel oil.

[70 sublime]

Maybe try putting a battery charger on the battery and make sure it is fully charged to see if there is any difference
It would suck to change the starter and still do the same thing then find out the alternator was the problem

[XH29N0G]

Running while charging or with another battery could be an interesting test.

I'm not an expert in electrical so this could be wrong.  I wonder whether measuring the voltage at the battery, or closer to the starter, while the starter was cranking cold and hot might give information?  My thinking is:

• the voltage is the potential that drives the starter, but the draw of amps runs it.  
  
• If the voltage dropped more when cold (maybe because the battery was freshly charged after the car had warmed up but not when the car was cold) that might point to something in circuit that changed, possibly the battery.  
  
• What is different with the battery in the trunk is the temperature it is in doesn't change, but the time since its most recent charge might.  
  
• I am assuming you have put it on a charger, but maybe the alternator charge and the external charge is also different. I am also assuming that a change in the voltage while cranking is related to the source (battery) rather than something else in the circuit (starter or connections)

If the battery can be taken out of the equation then either it is something with the starter (which you can change with some work) or the connections.  It seems unlikely to me that a connection would flake out when cold and then be better when hot, but I am just thinking if it creates sufficient resistance in the circuit that it could change the voltage the starter sees.

Again.  I'm not electrical.

[c00nhunterjoe]

Bypass your relay before changing starters. Seen burnt spots in the old ford relays do that. May not be your problem, but less headache then a starter.

[john108]

I don't understand all your mods but I would suggest disconnecting the battery in your trunk.  Get a freshly charged battery alongside your engine and jump start it.
With your mods, I don't know how to do it but I am confident you can figure it out.
Just my thoughts.  If if works, the problem is in the mods, not the parts.

[Kern Dog]

Bypass your relay before changing starters. Seen burnt spots in the old ford relays do that. May not be your problem, but less headache then a starter.

I have bypassed the Ford solenoid and had the same reaction. I changed to a new solenoid and again, same reaction.
The battery is in the trunk for several reasons including better handling due to less front weight bias, better traction due to weight over the rear, cooler battery since it isn't near the engine heat and a less cluttered engine bay.
The wiring is in good condition. No melted or softened insulation anywhere.

[John_Kunkel]

Not trying to pick a fight but I have never understood the fascination with the Ford solenoid. I have always run the positive cable directly from the trunk to the starter terminal and the ground cable directly to the block. I don't trust the unibody to be a satisfactory ground even though the modern LX cars do it that way.

[Kern Dog]

Thank you.
I trusted the advice from a guy more knowledgeable that I am. 383Man from Moparts, Ron. Very nice and helpful guy.
Keeping the long starter cable inactive except when starting makes sense to me. Am I being too cautious?
A buddy of mine ran his cable directly to the starter from the trunk battery and his starter turned over slow no matter what he did. Other factors were involved but 383 man seemed to make more sense.

[Kern Dog]

The new starter is in. At first the starter wouldn't engage so I put the car back up on the lift and noticed that the big terminal on the starter was making contact with the engine block. I was able to unbolt it and rotate it enough to cut the excess length off with a cheap Harbor Freight body saw. The header stayed in place.
It still starts a little slow when cold but seems better with the engine up to temperature.
Not entirely a win-win but at least it starts when warm. Maybe the 15w40 diesel oil is just too thick for the engine when cold. I wouldn't have chosen that weight except for it being the higher quality diesel type of oil.

[XH29N0G]

I would still look for a voltage drop.  Either with the battery when you first start it (cold wouldn't be the cause, it would be that the battery wasn't delivering consistent voltage when a load is put on it unless it had recently been charged with the alternator)  or I would look for some connection in the circuit from the battery to the starter that changes resistance when warm and cold (some sort of connection issue).  I am sure you have considered both, but I do not think that thick oil will make that much of a difference in cranking rate.  I could be wrong, so I'll wait.   

[b5blue]

Check all crimped connections, pull/push/wiggle while them cranking and as always redo ground connections to freshen contact. 

[Kern Dog]

Thanks guys. This one is testing my already limited patience!
I did change the oil to some Valvoline 5w30 and ran it long enough to warm up to around 190, then shut it down. Oil pressure was a bit lower but not by much. An hour later, I tried to start it and it cranked real slow again. The battery voltage was over 12.5 before I tried to start it and 11.7 after. I was able to jump start it though.

My local NAPA store has no equipment to do a load test.
I am tempted to just admit defeat and put the battery back under the hood. The entire reason for the trunk mount was for better handling and traction but in all reality. I am not racing this car. Whatever tiny advantage the weight bias (Front to rear) may have seems to come at a steep price.

[c00nhunterjoe]

I run 1 optima red top in the trunk. Positive cablefrom battery to front of car at factory locations. 1 ground from battery to trunk support. 1 ground from engine block to k frame. 20w50 oil. Spins fast, fires right up hot or cold. You have more grounds then i do. I dont care for the ford solonoid either but you already bypassed it for testing with no change. You replaced the starter and the battery. To rule out the car wiring, you could rig your current battery to the fender for a trial run. You said when replacing the battery it was cured and now is back. That leans me towards a battery.

[Kern Dog]

I would still look for a voltage drop. 

The location of the starter cable at the terminal is very difficult to reach. Testing cranking voltage would be really tough to do.

[XH29N0G]

I would still look for a voltage drop.

The location of the starter cable at the terminal is very difficult to reach. Testing cranking voltage would be really tough to do.

I suspect my suggested test is a poor person's variant of a load test.  I still do not know if it would work.  It might not matter whether you checked the voltage at the starter or at the battery while cranking. You might be able to snake two long wires from a digital volt meter in the car to some other part of the circuit by the battery.  I think a load test will be the best bet to rule out (or determine) the battery is your culprit because we probably won't know how to interpret a voltage drop (large or small) and I am sure a load test will be calibrated to good/bad. 

If it is in the connection from the trunk to the engine compartment and changes, then I would look at connections closer to the engine, remove, clean, and remake them.  You had this working before, right? 

It could be that the longer circuit to the starter makes the car less forgiving to a drop in potential, so it might still be something related to the battery, but where the battery would work closer to the starter. It probably does require a strong battery and good connections because (I believe) any resistance between the battery and the starter will reduce the voltage at the starter. 

I also think that you made it work before (RIGHT?) and it worked for a while.  So you might just have to figure out how to fix it this time and keep an eye on it for future fixes. 

[alfaitalia]

When I had a similar issue (on my Jeep) it turned out moisture had got into the main big battery wires (both) turning the copper wires green and vastly increasing resistance when under heavy load (like starting) but acting fine the rest of the time.. Someone over on Jeep forum suggested cutting back a little of the insulation....I did to find the dark green mess. Another clue I should have picked upon the was slight discolouring of the insulation near the terminals due to the extra heat when cranking. New wires and was good as new. Might not help of course but just thinking out load.

[Challenger340]

Hey guys,
My '70 has developed a strange problem related to the starter.

So this is a 'new' problem that has developed recently....... or has it always cranked slower when cold ?

[b5blue]

Just move it up front! 

[Kern Dog]

Hey guys,
My '70 has developed a strange problem related to the starter.

So this is a 'new' problem that has developed recently....... or has it always cranked slower when cold ?

THe car isn't driven as much as I'd like so the problem started about 18 months ago. At first I blamed the problem on inactivity because the car sat so much. The battery would be discharged and it would crank slow. I'd charge the battery and get it to start then it would happen again a few weeks or months later. I bought a 2 amp trickle charger last October along with the new battery.
It used to be that the car could sit awhile and still crank over fine. I have a 67 Dart and a 75 Power Wagon that can sit for a month or more and still crank over fine.
This is the only one with the trunk mounted battery. This one has 10.12 compression. I have noticed that it cranks faster with the throttle cracked open a bit.

[Kern Dog]

Moments ago:
Cold start, first of the day, fast cranking and an easy start up. Battery read 12.62. Last night, approx 12 hours ago it read 12.66.
150 degree restart, the point where it has traditionally performed best, easy restart. Less than 1 revolution to restart engine.
190 degree restart, same as above. Fast crank, engine fired right up.
I'm letting it sit now to see how it starts after a heat soak.

[XH29N0G]

Was there something you did to change things?  Good to hear it is working.   

[Kern Dog]

Was there something you did to change things?  Good to hear it is working.   

Yesterday I changed the starter and the oil. I had 15w40 oil, I changed to 5w30.