Another way to think about heat affecting the fuel in the carb, or in this case, to NOT think about it for now:

Let's say your engine is in great tune and almost always starts up on the first or second rotation. Meanwhile, suppose you've still got a problem with the starter system so that you only get three lumpy rotations before the starter stalls out or the cranking speed drops way off.

If your super-tuned engine usually fires up within those three turns, your engine starts up and it gives the appearance of no problem. The engine started, right? How can that be a problem?

Here's the rub: The starter system should be able to reliably spin the engine for at least 15 seconds, whether the engine actually starts or not. That's what gives you a reserve to reliably start the engine even if there are other problems causing a hard start. Does that help 'splain why I keep harping on making sure the cranking speed is normal?

Hope this helps.

 

I will definitely do the voltage test tonight after work.

The only part I don't understand is the lack of consistency with the way the starter bogs. It can be on the first part of the crank, the second, or last. If the voltage drop affected the crank, it would almost seem to affect adversely as the voltage keeps dropping. For example, it would start fast and slowly degrade. But mine almost resembles a dead spot in the starter. Or mechanically in the engine, like the flywheel ring gear to tight on the starter in a spot. Almost immediately after I hit the bog in the starter, I let off the key and retry, normally it would then start just fine.

With all that being said, voltage drop test results will be posted tonight. Just giving ideas on what to test next.

 

If you're unable to duplicate the fault when you are actually testing, what's a poor guy to do? At some point, if testing is inconclusive, you have to swallow some pride and start throwing parts at the problem. However, you can still make educated guesses, and not just blindly act like a drunken sailor at a strip club with one of these:




From years of troubleshooting, if unable to isolate a faulty component, lean towards anything with moving parts or in a location subject to abuse. In my field of aviation, we even have an acronym, if you can imagine that: SWAMP, which means Severe Wind And Moisture Present.

For example, say my personal 747 has an intermittent problem with the indication for a hydraulic valve in the wheelwell. It's got a controller safely tucked away in the climate-controlled main electronics compartment, resting on a pillow with a mint on it. Meanwhile, the valve is hanging out in the extreme temperature and altitude variations of the wheelwell, subject to 200kt winds when the landing gear is extended. If I can't duplicate a fault when testing, the valve is what will be replaced.

 

Hold on a sec there hoss, drunken sailors are spending their own money.

 

I never have and refuse to throw money at a situation I can't isolate or find faulty, it's just a waste of money, however, replication seems to be my nemesis.

 

 

 

P.s. Engine seemed to crank over strong, never hiccuping. Distributor grounded to radiator frame. Absolutely cold. Radio blaring classic rock.

 

Update to the update, other than it being cold and wanting a few more cranks with fuel and being cold, she fired right up.

 

Wow, you don't fool around when it's time to buy a battery charger, do you? The Navy called and want to know if they can borrow it for their submarine fleet...

The 10.64 reading after 20 seconds of cranking is very good. The 12.71 initial is good, too, but that value isn't super critical. That just means the battery had a good state of charge before the test, which is what we want. The important value is the lowest voltage recorded during cranking.

I'm still puzzled by the über teeny .001v recorded on both legs of the starter circuit. It's normal to see .2 or .3v, and what you have recorded is WAY below that. I've never seen results that good. That seems almost too good to be true. This has me wondering if your cables and battery are in good shape, but the starter motor can't draw enough current to really load them up. Don't read too much into this, but maybe keep the starter in the back of your mind if you can't otherwise find a good fix.

One variable I can suggest is to repeat the test with the engine warm. A warm engine has higher compression and makes the starter work harder, aggravating any marginal faults. Maybe charge the battery again and then run the engine just long enough until it's fully warm. Keep the electrical load to a bare minimum to preserve the battery charge in case the charging system isn't up to snuff.

If you're satisfied with the cranking speed and repeatability when testing with a fully charged battery, the next step is to change the equation one thing at a time to reintroduce the fault. For example, don't use your charger and repeat the test after a normal day of driving. If the fault returns, that would point towards a supbar charging system not keeping the battery topped off. Or it could be caused by a driving routine of mostly short trips with high electrical loading, such as heater fan on max and high beams. Or if the fault is prevalent in the morning, that might point to a drain running down the battery.

You are to be commended for your patience tracking this down. Sounds like you're on the home stretch. Remember, resist the temptation to make multiple changes at once. Introduce one variable at a time so you can know what caused any change in behavior.

 

This is where I divulge my Marine Corp background, so insert random Navy joke here:

im also OCD and don't mess around with my attention to detail. I'm very happy with the results, and will now try to replicate the test after the engine is warm, hoping then to rule out whether or not the battery is sufficiently charging or have the coconuts to crank on its own power. Basically, I have ruled out the cables and connections, I will now try and rule out alternator, state of the battery, and warm compression results.

 

One more factor to consider:

Starter temperature. Didn't you say you have exhaust-powered underhood heaters, I mean headers? If so, do your best to get them good and hot and see if that radiant heat has any effect on the starter performance.

I also agree your cables are probably fine. There's no need to keep repeating the voltage drop portion of the test. You should be good just monitoring battery voltage under the load of the starter.

You might consider getting a digital voltmeter that plugs into the cigarette lighter. Due to the intermittent nature of the problem, you can keep an eye on the battery voltage at each start. Keep track of the voltage available during a good start so you can see the difference when the starter stalls. Just don't forget to unplug it so you don't run down the battery.

Also keep in mind the limitations of testing that way. Testing right at the battery is the most accurate method, but not always practical if chasing an intermittent fault. But your most recent testing was done immediately after putting the battery on a charger. Data gathered during normal driving? Your battery may not be fully charged at all times, so don't let that throw you.

 

Taking it to the next level for $11.42, the AcuRite 00888A3 Indoor/Outdoor Digital Thermometer:



Put the temp sensor on the side of your starter, closest to the exhaust, and see what kind of heat is present. I bet you will be surprised how hot it gets.

I was having some heat-related carb problems on my truck, so I installed this thermometer's sensor on the outside of the float chamber. The sensor has a 10 foot lead, and is easy to route through any small hole in the firewall. It has a min/max recording feature, so will even keep track of heat soak long after shutdown.

With your starter, be aware there are two failure modes to consider. One is if the starter has high internal resistance (arcing at the brushes, for example) and won't draw enough current to make the required output torque, so the starter stalls under load. In a case like that, battery voltage stays relatively high because amp draw is low.

The other scenario is an internal short (melted insulation, for example) causing an increase in current draw, but with no increase in torque output. Once again, the starter stalls under load. Excessive current draw causes the battery voltage to drop low.

I'd lean towards the high internal resistance based on your test results.

 

I like the idea of monitoring voltage from the cigarette plug. It's not been a debilitating problem yet, and it's darn near impossible to replicate. I may end up having to keep a log monitoring voltage, temperature, wind direction....

if if I could figure out a way to replicate it, I'm sure I'd have no problem with diagnosing.

 

My gut and a few mechanic friends say the starter has a bad spot. These are remanny duracrap units, we all know new can even fail. I have no way to test it, and the symptoms seem to link to it. The headers are wrapped and they are also fenderwell exit, so heat soak on the starter is probably not an issue.

i refuse to throw money away on it, however, this new starter is still under warranty and can probably get an exchange. Possibly for a motorcraft unit.its gotta be a starter issue at this point, there is no way an old style, non gear reduction unit can spin these engines all day long and not a gear reduction. The engine compression is not extraordinary, even when hot.

im obviously scratching the bottom of the barrel here.