Hot Start and Bucking Problem

[SlowLane]

Be focused.

Be focused.

Be focused.

Be focused.

Some things just can't be over-stated, apparently.

[Amskeptic]

Be focused.

Be focused.

Be focused.

Be focused.

Some things just can't be over-stated, apparently.

Stupid slow US internet with public wifi in the slow lane, SlowLane.
Stupid slow US internet with public wifi in the slow lane, SlowLane.
Colin

[drober23]

Ok, there was more evil lurking in the wiring of the double relay than originally met the eye. Colin spotted that in addition to the original flaw in the wire that I had patched, there was a place where the wire had been worn and the insulation gone to the point that the wire had been exposed and even damaged a bit. If this had been shorting out from time to time, it could easily cause a cutting out problem.

There was also another bad fix I had done (wire nuts were involved) that was repaired properly. See the 2012 Itinerary - Colin Visits the Dome in Carleton, MI thread for all the nauseating details.

Anyway, holding my breath in hope that we got it this time.

[drober23]

Finally got to put some serious miles on the bus! 330 mile trip to Columbus, IN for work last night (and a return trip Thrusday ngiht).

I have put a total of 600 miles on since Colin's visit, and there has been no hint of a hesitation. I think this problem is fixed! (Woo!)

When Colin visited, my bus had been parked for a few days. When we went to start it, the battery was horribly low. After the visit, I checked for residual draw and found NONE! New battery time. Since the new battery, I have not experienced the Hot Start problem again. I would have expected the bus not to start after the halfway stop (3 hours of driving into the trip), and again at the end of the trip (6.5 hours). Bus started confidently each time.

I'm trying to wrap my brain about how a bad battery could cause the solenoid not to trip when hot, but still have enough juice to turn the starter motor over. Plus, the alternator is working (14.5 v when running under some load), so the battery should not be the least depleted when I get the hot start problems.

Maybe this is fixed, or maybe it is just in remission. Hmmmm....

[Amskeptic]

I'm trying to wrap my brain about how a bad battery could cause the
solenoid not to trip when hot,
but still have enough juice to
turn the starter motor over.

26 feet of 18 gauge wire from battery to ignition switch back to solenoid windings


2 feet of 10 gauge battery cable to solenoid across a contact to motor.

[grandfatherjim]

An interesting measurement is to check the voltage at the battery, and then the positive terminal of the coil, with the engine running. The lower voltage at the coil terminal is after current has run from back to front, through ignition contacts, and back to the back again.
On my 72 I was dropping almost 2 volts.

[drober23]

Point taken Colin!

Jim, I will do that. I use the coil as a "known positive voltage" point when poking around, but the actual reading has not sunk itself into my brain.

Thanks!

DJ

[grandfatherjim]

The relay at the left end of the coil has been connected thusly:
a) I used to have a gas heater, which was supplied by a heavy-duty red wire connected to the always-live terminal on the solenoid. This is now incoming power to the switched terminal of the relay (red)
b) the wire from the ignition switch, that used to go to straight to the coil, now turns on the relay (white).
c) the other side of the relay's coil is grounded (black).
d) the other switched terminal on the relay now goes to the coil positive terminal (yellow).

This way, all the poor old worn out contacts on the ignition switch have to do is turn on the relay. Once it goes click, power is run from the solenoid straight to the coil - 3 feet instead of 23 feet (or whatever it is to the front and back).

My many wires on the coil terminal are for:
-reverse lights (not there in the picture but black)
-fuel pump and fuel shutoff valve (yellow with black stripe)
-chokes (2) and carb shutoff solenoids (yellow with blue, and orange)
-electronic ignition (red with black stripe)

Voltage at the coil now is very close to battery voltage. Chokes get full voltage and can open fully (unknown whether this was an issue), coil gets about 16% higher voltage, and hence spark is likewise about 16% higher voltage, I guess reverse lights are a bit brighter, and perhaps the electronic ignition benefits slightly - though I would hope not.

Altogether I think this is a worthwhile upgrade i.e high benefit/cost ratio.

Jim

[Amskeptic]

power is run from the solenoid straight to the coil - 3 feet instead of 23 feet
Voltage at the coil now is very close to battery voltage.

Jim, coils do not want full battery voltage at all times. The history of the gasoline engined automobile, particularly in America, has been one of figuring out how to cool the voltage to the coil and only have it subjected to full strength at starting. The American solution was to install ballast resistors (Chrysler) or ballast wires between the ignition switch and the coil, with an additional wire that energized the coil directly from the starter solenoid only during start.
Volkswagen's solution was to merely move the engine away from the ignition switch several feet.

[grandfatherjim]

I knew about this, but forgot.
Typically in my experience the coil's primary voltage is cut roughly in half once the engine is running....but in this case there are all those other items running form the same terminal which will experience the same drop, leaving me wondering what's up.
Could it be that we have here one of the "internal ballast" types of coil? (Not that I can imagine how they can work without another terminal dedicated to starting...)

[Amskeptic]

I knew about this, but forgot.
Typically in my experience the coil's primary voltage is cut roughly in half once the engine is running....but in this case there are all those other items running form the same terminal which will experience the same drop, leaving me wondering what's up.
Could it be that we have here one of the "internal ballast" types of coil? (Not that I can imagine how they can work without another terminal dedicated to starting...)

Do the voltage/resistance math 12.? volts divided by 3 ohms however the formula goes . . .

[drober23]

Well, however the formula goes my solenoid did not want to engage this morning.

I drove 350 miles to Columbus, Indiana, then drove around for three days, and 350 miles back with no problem. Then got in the bus this morning and nothing. Battery voltage was 12.9, so the juice is waiting to flow. Tapping the solenoid didn't work either. No helper to turn the key, or I would note the voltage at the solenoid while cranking.

Sooo... looks like I'm gonna have to do something. I have a replacement starter switch, but it doesn't fill me with confidence. I could try a relay.

Grumbling aside, the bus performed tremendously on the trip! Not one hint of hesitation or bucking. I really enjoyed driving it. Once I get a fix on this solenoid problem, and look at the back brakes not holding an adjustment I think the bus is ready to roll for a while. But it is time to start taming the rust monster (oooohhh!)

[grandfatherjim]

The "hot start relay" fixed it for me. I have not had a single failure to start since installing it, and I had symptoms just like yours.

[dingo]

The only way youll ever know for sure is to do a simple Volt drop test.

what about the copper contacts inside the solenoid housing ? someone once suggested drilling a small hole, and filling it up with WD-40, then JB Weld

[Amskeptic]

what about the copper contacts inside the solenoid housing ? someone once suggested drilling a small hole, and filling it up with WD-40, then JB Weld

That is a long road to utterly questionable results.
You can disassemble a solenoid and merely flip the contact washer over. Like-New Performance!
But the problem with VW's hot-start is not a balky contact washer, but rather resistance in the coil windings.
Colin