The troubleshooting game.

[S204STi]

Yeah the cold air probably saved you.  The motor oil in the sump would have been cooled somewhat which would have helped cool the engine internally.

I was starting to lean towards an external leak but I had this mental image of sudden loss of hot air, etc.  I would have figured water pump leaking since I do so many of those on GMs, not sure how reliable they are on Mopars.

Good one.

[S204STi]

Alright, this one is going to make you all curse my name before the gods.


The car: last generation Pontiac Grand Am (I believe it was a 2004 to be exact).

Engine: is irrelevant.

Symptom:  Heater (again we return to HVAC as a common source of complaint) blower operates on only M3 and High.

To help you:  Blower has five speeds: Lo, M1, M2, M3 and Hi.  Temperature and distribution of air not an issue.

[GoCougs]

Alright, this one is going to make you all curse my name before the gods.


The car: last generation Pontiac Grand Am (I believe it was a 2004 to be exact).

Engine: is irrelevant.

Symptom:? Heater (again we return to HVAC as a common source of complaint) blower operates on only M3 and High.

To help you:? Blower has five speeds: Lo, M1, M2, M3 and Hi.? Temperature and distribution of air not an issue.

Did the blower on M3 and Hi correct at the correct, respective speeds?

If yes, I say broken rheostat on Lo - M2.

If no, I say worn brushes on the DC motor.

[AutobahnSHO]

Perhaps I cheated a bit. There wasn't actually anything broken per se. I actually I ran it almost competely empty of coolant.


All told, I figured that with what I had to add to get it filled, I'd run it about 90% dry. The thermostat housing must of leaked far more than I had figured. After that, I started it up, and had plenty of heat in short order. IMO, I didn't suffer catastrophic damage due to the cold weather and howling wind. I didn't have those inner fender splash guards, so wind was entering the engine compartment with ease. I'm sure the engine (and especially the water pump) took somewhat of a beating, but I never had any problems with it after that.

As long as it's wintertime and cold, you really can run most cars without coolant, at highway speeds.
I blew the upper rad hose (without knowing it) on a 79 Subaru about 25 miles into a 100mile trip (back to college, forgot to upshift after I had downshifted to get up a Wyoming "hill".)   The heater didn't work for a few weeks, that engine bay had lots of room for air to circulate.

The heater core went out on a 94 Crapalier (free from family, I promise!) in NY at about midnight when we were headed to NH for Christmas 2000.  It was EXTREMELY cold that night, we had to keep scraping ice from the inside of the windows and put about 5 blankets on the baby..   We were so tired we stopped to sleep but couldnt because we were too cold. We were so silly when we got there that my wife missed the turn to her parents' house...

[S204STi]

Did the blower on M3 and Hi correct at the correct, respective speeds?

If yes, I say broken rheostat on Lo - M2.

If no, I say worn brushes on the DC motor.

Let me describe the circuit for you:

Source voltage comes from the battery through a fuse to the blower switch (what you called the rheostat, though that is a misnomer).  The blower switch directs the current through 5 possible circuits .  the first four, Lo through M3, pass through the blower resistor.  The Hi circuit bypasses the resistor.  From the resistor ( or switch in case of Hi) voltage passes through the motor and on to ground.

To answer your question: the blower works fine on M3 and Hi.

[Pancor]

Let me describe the circuit for you:

Source voltage comes from the battery through a fuse to the blower switch (what you called the rheostat, though that is a misnomer).  The blower switch directs the current through 5 possible circuits .  the first four, Lo through M3, pass through the blower resistor.  The Hi circuit bypasses the resistor.  From the resistor ( or switch in case of Hi) voltage passes through the motor and on to ground.

To answer your question: the blower works fine on M3 and Hi.

Resistor toast?

[S204STi]

Resistor toast?

Yeah.  I had never seen a resistor blow on only a few of its circuits; they usually drop all three or four.  In this case only the first three speeds were lost.   I figured it out by checking for source voltage at the resistor on each individual terminal, and found I got the same thing every time on each setting on each circuit, so it was obviously the resistor.  Popped a new one in and voila! all five speeds.

[GoCougs]

Did the blower on M3 and Hi correct at the correct, respective speeds?

If yes, I say broken rheostat on Lo - M2.

If no, I say worn brushes on the DC motor.

I think I was kinda close. In "rheostat" I meant that a portion of the variable resistance circuit of the blower motor control (variable resistence = variable voltage = variable speed for a DC motor) switch was was bad for Lo - M2. From your description of the resistor, the variable resistance nature was contained inside one single component.

[GoCougs]

I've got lots of these...

Vehicle: 2nd gen Camaro
Engine: 305 V8 w/ 2bbl carb
Tranmission: TH250 AT
Miles: ~ 130,000

Problem: Car runs fine under partial throttle, but when under heavy throttle, backfires through the carb. Further, upon returning to part-throttle driving, the car runs rough, and is prone to stalling. Waiting a bit of time either with the engine off or via part throttle driving, car returns to normal.

Hint: Not fuel system related, and not a broken valve spring.

[AutobahnSHO]

Yeah.? I had never seen a resistor blow on only a few of its circuits; they usually drop all three or four.? In this case only the first three speeds were lost.? ?I figured it out by checking for source voltage at the resistor on each individual terminal, and found I got the same thing every time on each setting on each circuit, so it was obviously the resistor.? Popped a new one in and voila! all five speeds.

Resistors are funny-
There's an Army satellite comms system that uses a really big slow-blow resistor in it: it's about 3 inches long.  When we test the system on the bench we'll sometimes defeat the "interlock" (switch that knows if the cover's off) by holding the switch down.  If you accidentally let go of the switch it will burn through the resistor in a few seconds, but if you push the switch back down you can sometimes save it, but it will go faster the next time..

If it weren't such a pain in the butt to dissemble/solder that resistor back in, we'd blow them for fun- they start to smoke, then almost catch on fire, then finally POP!! and some sparks.. 

[S204STi]

I think I was kinda close. In "rheostat" I meant that a portion of the variable resistance circuit of the blower motor control (variable resistence = variable voltage = variable speed for a DC motor) switch was was bad for Lo - M2. From your description of the resistor, the variable resistance nature was contained inside one single component.

Well...a rheostat is by definition a variable resistor, not a circuit that accomplishes the same, so by nature I could not accept that answer.? A rheostat is the dimmer for your dash lights, or your fuel guage sensor in the fuel tank.? You were on the right track.

[S204STi]

I've got lots of these...

Vehicle: 2nd gen Camaro
Engine: 305 V8 w/ 2bbl carb
Tranmission: TH250 AT
Miles: ~ 130,000

Problem: Car runs fine under partial throttle, but when under heavy throttle, backfires through the carb. Further, upon returning to part-throttle driving, the car runs rough, and is prone to stalling. Waiting a bit of time either with the engine off or via part throttle driving, car returns to normal.

Hint: Not fuel system related, and not a broken valve spring.

Vacuum advance distributor?

[Eye of the Tiger]

I've got lots of these...

Vehicle: 2nd gen Camaro
Engine: 305 V8 w/ 2bbl carb
Tranmission: TH250 AT
Miles: ~ 130,000

Problem: Car runs fine under partial throttle, but when under heavy throttle, backfires through the carb. Further, upon returning to part-throttle driving, the car runs rough, and is prone to stalling. Waiting a bit of time either with the engine off or via part throttle driving, car returns to normal.

Hint: Not fuel system related, and not a broken valve spring.

Spark plugs might be fouling due to improper gap, heat range too cold, or just plain weak ignition, possibly a bad ignition coil. Timing might be off due to a stretched out timing chain, which would explain the backfiring more.

[GoCougs]

Everthing to do with vacuum, timing and ignition proved to be in working order.

Hint: think a bit about the hint regarding the valve spring. It behaved similar to a busted valve spring, but that wasn't it.

[Eye of the Tiger]

Everthing to do with vacuum, timing and ignition proved to be in working order.

Hint: think a bit about the hint regarding the valve spring. It behaved similar to a busted valve spring, but that wasn't it.

With a hint like that, the obvious answer would be a weak valvespring, but I don't suppose you'd make it that easy. Are the valves just burned up? I don't think that would explain how it would gradually smooth out under light throttle though... maybe the hydraulic lifters are leaking?

[S204STi]

Everthing to do with vacuum, timing and ignition proved to be in working order.

Hint: think a bit about the hint regarding the valve spring. It behaved similar to a busted valve spring, but that wasn't it.

I'm not so good with driveability.  Got me here.

[GoCougs]

With a hint like that, the obvious answer would be a weak valvespring, but I don't suppose you'd make it that easy. Are the valves just burned up? I don't think that would explain how it would gradually smooth out under light throttle though... maybe the hydraulic lifters are leaking?

Close. It was a completely dead (i.e., completely flat) cam lobe.

I didn't diagnose it myself. Someone I knew who had infinitely more automotive knowledge knew exactly what it was without turning a wrench or even popping the hood.

Of course I replaced it with a cam befitting a high compression, 4bbl, 350+ V8, which promptly ruined any and all driveability, and damaged pistons in the process (didn't replace the springs).

[Eye of the Tiger]

Close. It was a completely dead (i.e., completely flat) cam lobe.

I didn't diagnose it myself. Someone I knew who had infinitely more automotive knowledge knew exactly what it was without turning a wrench or even popping the hood.

Of course I replaced it with a cam befitting a high compression, 4bbl, 350+ V8, which promptly ruined any and all driveability, and damaged pistons in the process (didn't replace the springs).

I see... 

[AutobahnSHO]

Of course I replaced it with a cam befitting a high compression, 4bbl, 350+ V8, which promptly ruined any and all driveability, and damaged pistons in the process (didn't replace the springs).

Doh!

How did the cam get damaged???

[GoCougs]

Doh!

How did the cam get damaged???

Just wear. Back in those days they used flat-tappet lifter cams. The lifter-to-cam interface was simply flat steel. Nowadays, they use roller cams; the lifter-to-cam interface is literally a roller.

I've replaced a number of high-mileage flat-tappet cams and they all wear substantially. I'd never seen one that had a completely flat lobe. Could've been a bad heat treat or something.

[S204STi]

Just wear. Back in those days they used flat-tappet lifter cams. The lifter-to-cam interface was simply flat steel. Nowadays, they use roller cams; the lifter-to-cam interface is literally a roller.

I've replaced a number of high-mileage flat-tappet cams and they all wear substantially. I'd never seen one that had a completely flat lobe. Could've been a bad heat treat or something.

Flat tappets are still very common, but I think maybe they have a bit more of a convex shape to them...will have to look that up. 

[GoCougs]

Flat tappets are still very common, but I think maybe they have a bit more of a convex shape to them...will have to look that up.?

That's a good point. I meant for today's pushrod V8 engines; especially owing to their much stiffer valve springs relative to OHC engines.

[S204STi]

That's a good point. I meant for today's pushrod V8 engines; especially owing to their much stiffer valve springs relative to OHC engines.

I guess that's true.  I think the OHV v-6 engines I have seen lately use a hydraulic flat-tapped lifter, which is much easier on the cam. 

[Eye of the Tiger]

Vehicle: 94 Sundance Duster
Engine: 3.0 V-6 (6G72)
Tranmission: 5spd manual
Miles: ~ 145k

The problem: It started with an intermittent no crank condition, primarily when the engine was warm (all the other accessories and electronics worked though).
Now when the key is turned to "ON", the idiot lights come on very dim, the seatbelt chime sounds like it's about to die, the fuel pump does not come on, and the radio only comes on after a few seconds. Headlights still work like normal. When turned to "START", the dash lights dim, but starter does not crank.

[VTEC_Inside]

Vehicle: 94 Sundance Duster
Engine: 3.0 V-6 (6G72)
Tranmission: 5spd manual
Miles: ~ 145k

The problem: It started with an intermittent no crank condition, primarily when the engine was warm (all the other accessories and electronics worked though).
Now when the key is turned to "ON", the idiot lights come on very dim, the seatbelt chime sounds like it's about to die, the fuel pump does not come on, and the radio only comes on after a few seconds. Headlights still work like normal. When turned to "START", the dash lights dim, but starter does not crank.

I'd start by chasing grounds.

[S204STi]

Vehicle: 94 Sundance Duster
Engine: 3.0 V-6 (6G72)
Tranmission: 5spd manual
Miles: ~ 145k

The problem: It started with an intermittent no crank condition, primarily when the engine was warm (all the other accessories and electronics worked though).
Now when the key is turned to "ON", the idiot lights come on very dim, the seatbelt chime sounds like it's about to die, the fuel pump does not come on, and the radio only comes on after a few seconds. Headlights still work like normal. When turned to "START", the dash lights dim, but starter does not crank.

Is this one you have already solved, or one you want us to solve for you?

Sounds like an odd condition, the fact that it doesn't like to start after warming up.   I would start with the basics: battery, starting, and charging system tests.  Where those sound?

[S204STi]

I'd start by chasing grounds.

Good point, something Nissan always had me do first was to loosen and retighten the ground for whatever circuit I was diagnosing.

[GoCougs]

Vehicle: 94 Sundance Duster
Engine: 3.0 V-6 (6G72)
Tranmission: 5spd manual
Miles: ~ 145k

The problem: It started with an intermittent no crank condition, primarily when the engine was warm (all the other accessories and electronics worked though).
Now when the key is turned to "ON", the idiot lights come on very dim, the seatbelt chime sounds like it's about to die, the fuel pump does not come on, and the radio only comes on after a few seconds. Headlights still work like normal. When turned to "START", the dash lights dim, but starter does not crank.

To me it sounds as if there's a high impedence connection somewhere. I don't know if those cars have a remote starter selonoid, or if it's on the starter. I'd check this device where ever it may exist. Contacts or connections could be worn causing this condition.

[Eye of the Tiger]

Is this one you have already solved, or one you want us to solve for you?

Sounds like an odd condition, the fact that it doesn't like to start after warming up.? ?I would start with the basics: battery, starting, and charging system tests.? Where those sound?

This is something that I'm not sure about, but I think I know what it is.

Battery is charged, altenator works fine, headlights are bright and accessories that are not run through the ignition switch work normally. Which I guess gives away the answer I was thinking of... I think it's a bad ignition switch.

Anyway, it will be easier to pay $30 and replace the ignition switch than to start chasing grounds.

[AutobahnSHO]

Vehicle: 94 Sundance Duster
Engine: 3.0 V-6 (6G72)
Tranmission: 5spd manual
Miles: ~ 145k

The problem: It started with an intermittent no crank condition, primarily when the engine was warm (all the other accessories and electronics worked though).
Now when the key is turned to "ON", the idiot lights come on very dim, the seatbelt chime sounds like it's about to die, the fuel pump does not come on, and the radio only comes on after a few seconds. Headlights still work like normal. When turned to "START", the dash lights dim, but starter does not crank.

I had a Taurus (not the SHO) that sounded about the same but intermittent ANYTHING working- turned out to be the battery-starter cable was corroded inside. (couldnt see it from outside.)