Engine Dying Out When Going Downhill

[Knucklehead97]

Earlier today i was driving down a hill and popped it in neutral to coast, then when i got to the bottom i noticed that the engine had died out. I didnt think much of it untill it happened 2 more times! What would this be? Old or clogged fuel injectors?

[Geonovast]

Does it only do it when you pop it into neutral?  Fire right back up?

 

Sounds like the IAC to me.

[Knucklehead97]

It fires up immediately. It didnt when going down hill in gear if i remember correctly. Whats a iac?

[Geonovast]

Idle Air Controller.  It's a small motor in the throttle body, it's what gives the motor air when you're not giving it any gas.  They can stick and choke out the motor if nothing's keeping it going.  Can be fixed(usually) by pulling the TB off, pulling the motor out, and cleaning everything up with 02 safe TB cleaner and a toothbrush.

[64 Cheyenne]

I'm wondering why your puttin it in neutral to coast?

I know it isnt as bad as if in a commercial vehicle, but it is bad form to "not be in gear."

As far as professional driving goes :no:  Just sayin...

[Knucklehead97]

I only coast in neutral when going down a steep hill, saves gas lol. And ill try that when i get the chance. Is there any way to check if thats whats broken? It seems to idle fine when just sitting in neutral on level ground

[ComancheJon]

If this happened while driving stick, I had literally the EXACT same thing happen today whilst driving my brother's 85 4 speed 2.5l. I popped it into neutral because a turn was coming up and I would be downshifting anyway, but as I neared the turn I realized I had no power brakes or power steering. Good sphincter workout considering it was under a 90 degree turn.

[Geonovast]

I don't understand a taboo about coasting in neutral downhill.  There's nothing wrong with that.  What there is a problem with, however, is the idiots I've talked to who've shut their motors off intentionally while coasting to "save gas."

 

Usually incline related issues have to do with fuel delivery, but I'm still thinking you should tackle the hell out of your IAC before going any further.

 

You say it idles fine, what about driving around on flat surfaces, traffic lights and such?  Some IAC issues can be that it sticks for just a moment, so when you take your foot off the gas to start slowing down for a stop, it may try to die, but the trans keeps it going long enough for the engine to catch and keep itself going.  Wouldn't be the case if you were popping it in neutral.  If you go for a drive before you can take out the IAC, try popping it in neutral with no throttle on a level surface(and an empty road) to see what it does.

[HOrnbrod]

Saabs have an selectable freewheel system that controls sliding counterweights on the clutch plate. When you take your foot off the gas going down a hill, the weights slide in and disengage the clutch automatically. To engage the clutch while in freewheel on level ground, you give it more throttle and the weights slide out and you have the driven clutch again. It was nice to use on the interstates and saved gas, but terrible on mountainous roads because it ate up the brakes faster. But it's selectable to use when you want.

[Knucklehead97]

It seems good while driving on normal level surfaces, i mean i drove a good bit today and it only died on the hill. The idle seems a little low but nothing rough. And yes it is a stick. I think it is the iac from what youve said.

[Geonovast]

If this happened while driving stick, I had literally the EXACT same thing happen today whilst driving my brother's 85 4 speed 2.5l. I popped it into neutral because a turn was coming up and I would be downshifting anyway, but as I neared the turn I realized I had no power brakes or power steering. Good sphincter workout considering it was under a 90 degree turn.

 

Probably a completely different issue, since the 2.5 was carburated in 85.

[ComancheJon]

 

If this happened while driving stick, I had literally the EXACT same thing happen today whilst driving my brother's 85 4 speed 2.5l. I popped it into neutral because a turn was coming up and I would be downshifting anyway, but as I neared the turn I realized I had no power brakes or power steering. Good sphincter workout considering it was under a 90 degree turn.

 

Probably a completely different issue, since the 2.5 was carburated in 85.

What could my problem have possibly been then?

[AeroNautical]

I think I may have the solution. This exact thing happened to me awhile back, and it turned out that my battery connection was loose, and when my battery disconnected it shut off my motor. This meant that the alternator was bad as well. So I tightened my battery terminals and changed my alt and it hasn't done it since. 

[cruiser54]

I don't understand a taboo about coasting in neutral downhill.  There's nothing wrong with that.  What there is a problem with, however, is the idiots I've talked to who've shut their motors off intentionally while coasting to "save gas."

 

Usually incline related issues have to do with fuel delivery, but I'm still thinking you should tackle the hell out of your IAC before going any further.

 

You say it idles fine, what about driving around on flat surfaces, traffic lights and such?  Some IAC issues can be that it sticks for just a moment, so when you take your foot off the gas to start slowing down for a stop, it may try to die, but the trans keeps it going long enough for the engine to catch and keep itself going.  Wouldn't be the case if you were popping it in neutral.  If you go for a drive before you can take out the IAC, try popping it in neutral with no throttle on a level surface(and an empty road) to see what it does.

Medium duty trucks have a synchro system using conical aluminim clutches which get torn up freewheeling. Most automotive applications have brass synchros. Guess what a BA-10 has? The aluminum ones. Don't freewheel it.

[cruiser54]

OP. Make sure your intake bolts aren't loose.

Clean your throttle body and IAC

Ever refresh your grounds?

[Geonovast]

Medium duty trucks have a synchro system using conical aluminim clutches which get torn up freewheeling. Most automotive applications have brass synchros. Guess what a BA-10 has? The aluminum ones. Don't freewheel it.

 

That's quite possibly one of the stupidest things I've ever heard.  I bet that's a large factor of why those transmissions are so crappy.   I have always put my manual vehicles into neutral when coming to a stop unless I needed the motor to help slow me down.  Why would anyone design a transmission with a system that damaged itself when moving in neutral?  Which still doesn't make sense... when you're in one gear, as far as the synchros for the other gears are concerned, you're in neutral.

 

I've been on this board for 6 years, and this is the first I have ever seen this come up.  :hmm:

[cruiser54]

Well, if you had owned a towing business for 13 years, you would be more aware of it. Even some of the NV gearboxes used the aluminum synchro deal as did some 1/2 and 3/4 ton trucks. It's ok to throw it into neutral at a light, but coasting for any distances does noth throw lube up on to the synchros as the counter gear is not moving, only the output shaft.

[Geonovast]

But they would be moving if the clutch was engaged.  The only way the gears wouldn't be moving is if the trans was in neutral and the clutch pedal was down.

[cruiser54]

No. Only the output shaft is turning coasting in neutral.

 

Let's not blow this out of proportion.

 

It's okay to pop it into neutral and coast to a light. At speed, like going down long grades, does the damage. Greater speed and greater distance multiply the damage.

[HOrnbrod]

Unless you're driving a Saab.  :yes:

[Geonovast]

I'm not blowing it out of proportion.  I've been inside our transmissions.  If the clutch is engaged and the motor running, the input shaft and counter shaft are both spinning, which causes all gears except the reverse idler to spin.  If the motor is running, the only way to stop the counter shaft from spinning is to push in the clutch, which wouldn't make any sense to leave that in if you've popped the transmission into neutral.

[Knucklehead97]

Ive actually been meaning to make new battery cables considering mine are corroded. It cranks every time though. So i should clean my TB, check the IAC, refresh my grounds and tighten battery cables, and stop coasting downhill. Anything else guys?

[64 Cheyenne]

Coming to a stop at low speed, neutral coast OK.

Long downhill coasting in neutral, not OK.

Long downhill coasting with the clutch in causes undue wear on the TO bearing.

My dad said you want to stay in gear to be in better control of your vehicle.

When I drove a semi, try finding the right gear in a hurry if you have 18 of them after you were coasting at highway speed.
Offroad in 4wd, steep downhills definitely stay in gear, all the running gear stays tied together

all brake action tied together, makes sense all around.

Coasting is a bad habit like riding the clutch, or taking somebody home from the bar

that you don't want to be seen with the next day. Whats the point?

Nuthin, just sayin. :rotf:

[Knucklehead97]

Well i deffinetely won't be coasting down hill right now, considering if it dies out i don't have power steering nor brakes >.> hopefully this week i can get everything checked out. Oh and to all the guys who helped with my fender flare problem, broke one bolt earlier by tightening to far. Luckily i was practicing with the broken flare

[gogmorgo]

I've heard fairly often that you actually use less [read no] gas going down a hill in gear with an injected engine because the injectors get shut off and the vehicle's momentum is enough to keep everything spinning, vs in neutral where you need fuel to keep the engine running.

 

http://www.popularmechanics.com/cars/alternative-fuel/news/coasting-in-neutral-fuel-economy

Can't confirm this applies to our MJ's, though, as most often I see it written as "modern" fuel injection. But it's a principle I stick to. It feels a lot safer than freewheeling, too.