engine dies

[subzali]

I have this problem that's only been happening maybe since last fall; I don't really remember it happening last summer at all. If I'm going along and come up to a stoplight (happens most of the time coming off the highway, but will happen between stoplights in town too) and push in the clutch, the engine will idle down all the way until it dies. This will also happen if I'm going down a long hill and put the tranny in neutral and coast. It does not appear to be dependent on whether I have the brakes engaged or not, though sometimes it seems as if having the brakes engaged makes it worse. Once the engine quits I can tap the gas a couple times and it will start right back up and idle fine. Except once the other day when it quit again while I was sitting at the stoplight. That time it was sputtering and would not idle at all, I had to keep it revved up to keep the engine running.

I can't think of anything that I changed before I started noticing this, but any suggestions at this point would be welcome. I tried 87 octane instead of 85 just for grins and that didn't change anything.

 

[DaveInDenver]

Which truck is this?

 

[subzali]

the Cruiser, sorry.

 

[treerootCO]

not enough vacuum at idle, idle jet screwed all the way in, miss adjusted fast idle/slow idle, choke getting sucked shut/miss adjusted...

If I had to guess, your idle circuit is plugged. Swing by tonight and we can fix it.

 

[subzali]

Sorry Mike truck is at my parent's house, but thanks for the tip I'll see if I can fix it. I was kinda thinking the same thing about the idle circuit, is it fairly easy to fix? I just have a Haynes at the moment and don't know how detailed it is.

 

[treerootCO]

stuck PCV or EGR will also cause this. FSM has detailed instructions on how to check both. If you know what hose to suck on you can rule both out pretty quick. The carb adjustment is less likely an issue but it is also in the FSM

 

[MDH33]

Everything Mike said...

Also, is this mainly happening when the engine is warmed up? Could be vapor lock due to the high temps. Does your 40 have the carb cooling fan in place?

 

[subzali]

I thought about vapor lock, and no I don't have a carb cooling fan (when did it start on 40s?), but it starts right back up with no problems after it quits once. However it does seem to happen usually only when the engine is warm, but not necessarily...

 

[treerootCO]

There are a few carb cooling fans laying in the yard if you want to put one in. Why is your truck in Sedalia?

 

[subzali]

cause it's not running right

besides I got the red truck running again, so since gas is so expensive I'm driving that

I might have to take you up on your offer for the carb cooling fan...

 

[subzali]

Well I'm starting to think it's the brake booster (again - that's the 3rd one, I'm getting sick of this ) unless it is carb related. The only way I can figure it to be carb related is if something got jammed in a passage somewhere - which is possible since I had the carb off for a few weeks while I was doing the head work this spring.

I've checked the PCV before but I should just get a new one anyway...

don't know how to check the EGR, guess I could look at that at some point.

 

[60wag]

Just cap off the booster vac hose to see if the idle is fixed. I bet its a clogged idle circuit or a vac leak. Plug a vac gauage into the manifold to rule that out. A stuck egr valve would do it too.

 

[nakman]

Carb fan is really for only after you shut the truck off. Intentionally.

wouldn't help you in this case, afaik.

 

[MDH33]

Carb fan is really for only after you shut the truck off. Intentionally.

wouldn't help you in this case, afaik.

Right.

My 40 is doing the same thing as Matt's except it will stay running if i give it a tiny bit of choke. I'm going to pull my carb today and see what's up.

 

[treerootCO]

Check for vacuum leaks first. PVC or stuck ERG first. Call me if you want me to walk you through that. To baseline it, do what Bruce mentioned above about the brake booster but also block off the EGR and PVC hose completely. None of them are needed and can be capped for testing purposes. The idle circuit is only engaged when the throttle plate is completely closed. There is an extremely small hole just below the throttle plate if you look. The needle that adjusts your air fuel at idle points directly at it and in fact pokes through it when the needle is fully seated.

 

[MDH33]

I just checked my PCV and it is stuck. Good call.

 

[treerootCO]

stuck open or closed? Open you run lean and burn up the valves, stuck closed you'll build pressure in the crankcase and might start causing leaks.

 

[MDH33]

stuck open or closed? Open you run lean and burn up the valves, stuck closed you'll build pressure in the crankcase and might start causing leaks.

The ball bearing inside wasn't moving, I soaked it, and it seems to be free again. My guess is that it was stuck open because it would only run with choke.

 

[treerootCO]

good catch, want to come see my dad's burnt valve because if that? Today we are putting a new head on.

 

[subzali]

I plugged the brake booster, EGR and got a new PCV and I still got it to die. If I'm on the throttle in 4th gear at about 50 mph for a little while and push the clutch in so the engine drops to idle pretty fast that's pretty much a guaranteed way to do it. I've only really been able to get the engine to do it when it's warm. There seems to be a smell associated with it, my guess would be unburnt fuel/rich smelling, but it doesn't smell like straight gasoline. I checked my carb and the gas is real high on the sight glass right after it dies FWIW.