3FE stalling issues (1 Viewer)

[wildsidelife]

Calling all 3fe-heads!

I'm currently fighting an engine gremlin that I can't seem to get to the bottom of and I'm hoping someone on here has learned from past experience and can pass this wisdom on to me.

I'll start by saying I have a 91 80 series with a 3fe. Just over 200k on the odo and love the thing. She's a tank! Attached are a couple pics if you're interested

After running my engine hard (prolonged mountain driving [live in Colorado], hard offroading, mostly prolonged high revs/flooring it) and I come to a stop, the engine comes close to stalling and frequently stalls out if I don't get on the gas again. It putters out, all of the dash lights pop on and bam, dead. I can start the car normally right after it stalls out, but I'd rather figure out the problem than to just deal with it. I'm by no means a mechanic, but I try to do most of the work on my 80 that I can.

To me, I think this problem looks air/fuel ratio related, and that it would be something going on post MAF. I checked the all of the intake for any cracking or old worn out parts where air could maybe get in/out, replaced them, still having the issue. I checked all of the EGR lines in case it was related to that. They're old but none are cracked or leaking at all. I have no dash lights or other leads besides what I've listed. I chucked some BG44K through in to maybe clear up the injectors if that was causing the issue but no dice. A longshot but thought I may as well give it a try. I really don't want to have to pay for a mechanic to fix this and would love to tackle whatever this project entails myself.

Please feel free to ask for more info or clarity if you need, and please help me fellow cruiser-nuts!

 

[jonheld]

This sounds like a torn intake plenum after the AFM.
The flap in the AFM runs the logic for the fuel pump. At low RPM, if there's unmetered air getting in downstream of the AFM, the spring loaded flap will start to close cutting off the fuel pump.
If a slight increase in RPM gets it running right, then that's your issue.
Alternatively, the top half of this motor wants to be air tight. Any unmetered air getting in the system will cause havoc. Oil fill cap, oil dipstick, valve cover gasket and grommets, side cover gasket, etc. all want to be air tight.
This is a 1986 tractor motor. Always look at the easy things first. Proper idle speed is 650 RPM at normal operating temperature.

 

[wildsidelife]

This sounds like a torn intake plenum after the AFM.
The flap in the AFM runs the logic for the fuel pump. At low RPM, if there's unmetered air getting in downstream of the AFM, the spring loaded flap will start to close cutting off the fuel pump.
If a slight increase in RPM gets it running right, then that's your issue.
Alternatively, the top half of this motor wants to be air tight. Any unmetered air getting in the system will cause havoc. Oil fill cap, oil dipstick, valve cover gasket and grommets, side cover gasket, etc. all want to be air tight.
This is a 1986 tractor motor. Always look at the easy things first. Proper idle speed is 650 RPM at normal operating temperature.

Hey Jon,

I appreciate the insight, and glad my assumption is probably correct. A slight increase in RPM does in fact save it from stalling out. Could you explain a bit further what you mean by "torn plenum"? If by plenum you're referring to the intake manifold that's aluminum so I'm not sure how that can be torn. Or are you referring to what's in between the manifold and the AFM? If so, I did check that region for leaks and didn't see any but will double check. Again I'm no mechanic so maybe my terminology is just different than yours. No offense meant, just need clarification.

I'll also check all of the items you noted where air could be slipping through. I'm sure it wouldn't hurt to replace some of those gaskets anyways.

Thanks

 

[jonheld]

Could you explain a bit further what you mean by "torn plenum"?

The (what is now sure to be incredibly brittle) rubber plenum between the AFM and the intake. These love to crack/tear on the underside of the bellows section when you lift the air filter cover. After 30+ years of service it really doesn't owe you anything more.

http://www.sdsysdesign.com/TLC/images01/plenum2_full.jpg

I would remove the plenum (both rubber sections) and carefully inspect for cracks/tears or simply replace. Remember to tighten the clamps, and I always run a thin coating of grease around the mating surfaces.

80 Series 3FE Intake Air Hose Kit

80 Series 3FE Intake Air Hose Kit (AIH-3KIT)

absolute-wits-end.com

 

[wildsidelife]

The (what is now sure to be incredibly brittle) rubber plenum between the AFM and the intake. These love to crack/tear on the underside of the bellows section when you lift the air filter cover. After 30+ years of service it really doesn't owe you anything more.
I would remove the plenum (both rubber sections) and carefully inspect for cracks/tears or simply replace.

80 Series 3FE Intake Air Hose Kit

80 Series 3FE Intake Air Hose Kit (AIH-3KIT)

absolute-wits-end.com

Jon,

Thanks for clarifying. I have in fact replaced the part with the metal barbed fitting connected to it as I accidently ripped it apart when doing spark plugs a while back. The other piece I did take off and have a look at but didn't seem to find any cracks or holes where air could seep in. Again, I'll double check it again and update if I just missed it the first time, but I don't think those are the problem. I didn't check the new part because I thought with it being new it would be fine, however the problem did begin after that new part was installed, so I'll double check that one as well.

I do in fact have a minor oil leak towards the rear of the engine and it begins to leak only on steep inclines. Air could be getting in through the gasket where oil might be escaping.

 

[jonheld]

I didn't check the new part because I thought with it being new it would be fine, however the problem did begin after that new part was installed,

LOL. That should have been the very first thing you said, not the last.

 

[wildsidelife]

That should have been the very first thing you said, not the last.

It was a while after, but in fact after that was installed. So not a direct correlation but makes sense now that I'm thinking about it.

I still don't understand why the stalling only occurs after prolonged high RPMs though. Why isn't it stalling all of the time? Does that fact help narrow down where the leak could be at?

 

[jonheld]

It was a while after, but in fact after that was installed. So not a direct correlation but makes sense now that I'm thinking about it.

I still don't understand why the stalling only occurs after prolonged high RPMs though. Why isn't it stalling all of the time? Does that fact help narrow down where the leak could be at?

Hard to say over the internet, but keep in mind that nothing is static under the hood. Things are moving around in there. Perhaps so excess heat is making things a bit soft and allowing it to gap somewhere.

 

[Marco Lau]

Do you have an idling issue before the drive? What is your rpm at idle ?

 

[wildsidelife]

Hard to say over the internet, but keep in mind that nothing is static under the hood. Things are moving around in there. Perhaps so excess heat is making things a bit soft and allowing it to gap somewhere.

My thoughts exactly. I'm glad your insight lines up with my thoughts on what's wrong. That's one step closer. I'll do some digging and post my results.

 

[wildsidelife]

Do you have an idling issue before the drive? What is your rpm at idle ?

No idling issues at all. Sits at 650 rpm.

 

[Marco Lau]

No idling issues at all. Sits at 650 rpm.

interesting... My idle is a bit lower after a long /hard drive as well. Usually about 630-640 vs 650 on start up...no idea why tho...

 

[wildsidelife]

interesting... My idle is a bit lower after a long /hard drive as well. Usually about 630-640 vs 650 on start up...no idea why tho...

I haven't paid much attention to my idle after those hard drives because usually I'm too concerned about the actual stalling out haha. But the weird thing is that it starts right back up and seems to idle fine afterwards.

 

[91FJ80FD]

Have you tried keeping the A/C on? To help it not stall out at low RPM's? Might be a vacuum line issues? I'm chasing a low RPM's when coming up to a stop light at normal street driving speeds, it likes to dip down low below 400 RPM's. just my $.002

 

[wildsidelife]

Have you tried keeping the A/C on? To help it not stall out at low RPM's? Might be a vacuum line issues? I'm chasing a low RPM's when coming up to a stop light at normal street driving speeds, it likes to dip down low below 400 RPM's. just my $.002

I have not tried that AC trick, but even if it does work it's only putting off the issue. I'd like to fix it completely, as I burn through enough gas with the AC off I'm pretty confident it's a vacuum leak of some kind, just can't seem to find it.

Also, an update: I've replaced a bunch of old hoses that I may or may not have cracked while taking everything apart looking for a leak. Took apart the idler valve, cleaned it up nice. Idle improved slightly, but still stalling out. Maybe that could fix your idle issue? LND CRUZIN on youtube has a good video on how to do it. It's pretty easy.

I did realize that the issue is not just after running the engine hard, but now will try to stall out after every high rev, even while parked in the driveway. As soon as it shifts back into first when approaching a stop, the revs drop very low and it tries to stall. Going to have some cruiser heads I met take a look at it and see if they can help diagnose the issue. I did also notice a wobble hose barb when changing out hoses. Should this be wobbly? If not, maybe that's our leak?

 

[jonheld]

That is you PCV valve/grommet. If it's 30 years old, it's past time for replacement. The grommet should be supple/flexible rubber to seal properly on the valve cover.
PCV Valve 12204-35040
PCV Valve Grommet 90480-18001

 

[wildsidelife]

That is you PCV valve/grommet. If it's 30 years old, it's past time for replacement. The grommet should be supple/flexible rubber to seal properly on the valve cover.
PCV Valve 12204-35040
PCV Valve Grommet 90480-18001

Not sure if that's oem as I'm the 3rd owner, but good to know it should be flexible. It was still flexible and not hard crunchy like some of the hoses I've come across. The PCV hose attached to it was replaced before me.

 

[ppc]

That throttle cable is also in dire need of replacement and could be part of your problem.

 

[wildsidelife]

That throttle cable is also in dire need of replacement and could be part of your problem.

View attachment 3295819

Agreed, that cable has seen better days and should be replaced. I can give that a try as well. Thanks for pointing that out. Didn't cross my mind that it could be contributing to the issue. Although I do think it's still seal related, new parts never hurt.

 

[wildsidelife]

UPDATE: I had some cruiser heads take a look at it and after some searching, they stumbled upon the issue. We now know where the issue is, but not yet why:

When taking out a few vacuum lines to check for leaks, they unplugged a connector powering the pump that pushes more air in the exhaust to dilute it in order to pass emissions. After that connector was disconnected, the stalling went away, meaning there is probably leak is somewhere within that air pump system.

Very glad I took it in as I would have never found that myself. I will post pictures of which connector I'm talking about if people are interested. I am now driving around with that connector unplugged, which solves the stalling issue, but I may not pass emissions. I will fix it eventually but it's a bandaid fix for now.

Now that I know the problem, I will investigate further when I have time and diagnose what exactly the issue was coming from. Just thought I'd update in case you all are having a similar issue!