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> 1974 1.8L engine fast idle then stalls, Fuel injection issues
tshih914
post Feb 28 2023, 07:44 PM
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QUOTE(Van B @ Feb 28 2023, 04:51 AM) *

See the little hole near the front right off the AFM? That's your air bypass screw.


Thanks, now for my case is there any point in messing with that screw when it appears I already have some air bypassing the AFM?

Also since my decel valve appears to be farked up and there are no replacements has anyone opened one up to see if they can repair the damage?
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wonkipop
post Feb 28 2023, 07:51 PM
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QUOTE(tshih914 @ Feb 28 2023, 07:44 PM) *

QUOTE(Van B @ Feb 28 2023, 04:51 AM) *

See the little hole near the front right off the AFM? That's your air bypass screw.


Thanks, now for my case is there any point in messing with that screw when it appears I already have some air bypassing the AFM?

Also since my decel valve appears to be farked up and there are no replacements has anyone opened one up to see if they can repair the damage?


i probably wouldn't play with it at this stage.
its a new rebuilt AFM and theoretically should be about right.
but then again @Van B might have something to say.

i have never had to fool with mine.

i don't think you can open a decel.
its the sort of thing i would do of course.
attacking a fuel pump was a lot of fun.
but only with a spare to replace it.
i take the attitude destruction is likely.
i kind of looks like it would be pretty hard to get back together.
however there is a guy in australia who apparently rebuilds these things and other vac devices and has proper equipment to open up the crimping seams etc.
if it is farked up and won't respond to adjustment it will very likely be the diaphragm that is rat sh#t. so its pretty hard to fix unless you feel like becoming one of those kinds of experts.
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Van B
post Feb 28 2023, 08:07 PM
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Have you adjusted the decel valve or tested it to see what vacuum its opening at?

Also, they are still out there. You just gotta know what to look for:
https://www.ebay.com/itm/403375849459
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Van B
post Feb 28 2023, 08:09 PM
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@wonkipop quit being so scared to that mean AFM. All he needs to do is confirm how many turns out he is on the bypass screw… we’re just confirming baselines on the system.
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tshih914
post Feb 28 2023, 08:47 PM
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QUOTE(wonkipop @ Feb 28 2023, 05:51 PM) *

QUOTE(tshih914 @ Feb 28 2023, 07:44 PM) *

QUOTE(Van B @ Feb 28 2023, 04:51 AM) *

See the little hole near the front right off the AFM? That's your air bypass screw.


Thanks, now for my case is there any point in messing with that screw when it appears I already have some air bypassing the AFM?

Also since my decel valve appears to be farked up and there are no replacements has anyone opened one up to see if they can repair the damage?


i probably wouldn't play with it at this stage.
its a new rebuilt AFM and theoretically should be about right.
but then again @Van B might have something to say.

i have never had to fool with mine.

i don't think you can open a decel.
its the sort of thing i would do of course.
attacking a fuel pump was a lot of fun.
but only with a spare to replace it.
i take the attitude destruction is likely.
i kind of looks like it would be pretty hard to get back together.
however there is a guy in australia who apparently rebuilds these things and other vac devices and has proper equipment to open up the crimping seams etc.
if it is farked up and won't respond to adjustment it will very likely be the diaphragm that is rat sh#t. so its pretty hard to fix unless you feel like becoming one of those kinds of experts.

Just for the hell of it I google search " schematic of Bosch L-Jetronic decel valve" and came up with hit on last years' 914world post

http://www.914world.com/bbs2/index.php?showtopic=342479

Read all 3 pages and it appears that a 911 decel valve may be usable as a last resort. but the tests for proper function is given by GregAmy:

Testing the decel valve is fairly straightforward. With no vacuum on the port, the valve should be closed and you can't blow through it. Adding a vacuum via a Mity-Vac and the valve should open and you can blow through it. As I recall the desired setting for that cutover is 17mmHg?

If you can blow through it when it's off the car, and/or cannot blow through it with vacuum on it, then it's bad and/or out of adjustment. I wouln'dt be surprised if a prior owner danked around with the adjustment...

If it works fine but the cutover vacuum is either too high or too low, then it can be adjusted via that locknut and screw to ~17mmHg.

What are your current symptoms when testing in this manner?


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Van B
post Feb 28 2023, 08:53 PM
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Thats too low IMO. I posted the link to my thread on post #29 on your thread here.
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r_towle
post Feb 28 2023, 08:57 PM
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QUOTE(dr914@autoatlanta.com @ Feb 20 2023, 12:17 PM) *

for the hell of it check the throttle body boot for cracks

Ever check the boot after installing the afm?
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tshih914
post Feb 28 2023, 09:10 PM
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QUOTE(tshih914 @ Feb 28 2023, 06:47 PM) *

QUOTE(wonkipop @ Feb 28 2023, 05:51 PM) *

QUOTE(tshih914 @ Feb 28 2023, 07:44 PM) *

QUOTE(Van B @ Feb 28 2023, 04:51 AM) *

See the little hole near the front right off the AFM? That's your air bypass screw.


Thanks, now for my case is there any point in messing with that screw when it appears I already have some air bypassing the AFM?

Also since my decel valve appears to be farked up and there are no replacements has anyone opened one up to see if they can repair the damage?


i probably wouldn't play with it at this stage.
its a new rebuilt AFM and theoretically should be about right.
but then again @Van B might have something to say.

i have never had to fool with mine.

i don't think you can open a decel.
its the sort of thing i would do of course.
attacking a fuel pump was a lot of fun.
but only with a spare to replace it.
i take the attitude destruction is likely.
i kind of looks like it would be pretty hard to get back together.
however there is a guy in australia who apparently rebuilds these things and other vac devices and has proper equipment to open up the crimping seams etc.
if it is farked up and won't respond to adjustment it will very likely be the diaphragm that is rat sh#t. so its pretty hard to fix unless you feel like becoming one of those kinds of experts.

Just for the hell of it I google search " schematic of Bosch L-Jetronic decel valve" and came up with hit on last years' 914world post

http://www.914world.com/bbs2/index.php?showtopic=342479

Read all 3 pages and it appears that a 911 decel valve may be usable as a last resort. but the tests for proper function is given by GregAmy:

Testing the decel valve is fairly straightforward. With no vacuum on the port, the valve should be closed and you can't blow through it. Adding a vacuum via a Mity-Vac and the valve should open and you can blow through it. As I recall the desired setting for that cutover is 17mmHg?

If you can blow through it when it's off the car, and/or cannot blow through it with vacuum on it, then it's bad and/or out of adjustment. I wouln'dt be surprised if a prior owner danked around with the adjustment...

If it works fine but the cutover vacuum is either too high or too low, then it can be adjusted via that locknut and screw to ~17mmHg.

What are your current symptoms when testing in this manner?

I wonder what is the diaphram (redline in schematic) made of rubber or metal? If rubber then age will lead to hardening and cracking
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tshih914
post Feb 28 2023, 09:13 PM
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QUOTE(r_towle @ Feb 28 2023, 06:57 PM) *

QUOTE(dr914@autoatlanta.com @ Feb 20 2023, 12:17 PM) *

for the hell of it check the throttle body boot for cracks

Ever check the boot after installing the afm?


No I have a new one coming from AutoAtlanta that I will install along with new hoses and gaskets
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Van B
post Feb 28 2023, 09:58 PM
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Diaphragm is rubber. It gets hard and less flexible, but the spring is what wears out and what causes the required adjustment. Lots of movement and heat cycles over the years.

If you’ve read my thread, I was having high idle issues when running and idle hang when driving.

IMO, you have a whole collection of maintenance issues from deferred maintenance over the years. None major or you wouldn’t even get a high idle and smooth running.

I think your biggest issue is it not taking throttle input.
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wonkipop
post Feb 28 2023, 10:23 PM
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QUOTE(Van B @ Feb 28 2023, 08:09 PM) *

@wonkipop quit being so scared to that mean AFM. All he needs to do is confirm how many turns out he is on the bypass screw… we’re just confirming baselines on the system.


(IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)
its the only bit i am genuinely terrified of. (IMG:style_emoticons/default/smile.gif)

the rest of it i just tear into it.

agree with you, this poor baby has a ton of deferred maint. items that have all built up.
and its been tweaked along the way at various points to make it idle /whatever.
its finally accumulated to be "all too much" for it.
progress can be made when all hoses/seals are verified as non leaking and associated vac/electrical "gadgets"/ignition items tested and confirmed as spec operational.
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wonkipop
post Feb 28 2023, 10:40 PM
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QUOTE(tshih914 @ Feb 28 2023, 08:47 PM) *

QUOTE(wonkipop @ Feb 28 2023, 05:51 PM) *

QUOTE(tshih914 @ Feb 28 2023, 07:44 PM) *

QUOTE(Van B @ Feb 28 2023, 04:51 AM) *

See the little hole near the front right off the AFM? That's your air bypass screw.


Thanks, now for my case is there any point in messing with that screw when it appears I already have some air bypassing the AFM?

Also since my decel valve appears to be farked up and there are no replacements has anyone opened one up to see if they can repair the damage?


i probably wouldn't play with it at this stage.
its a new rebuilt AFM and theoretically should be about right.
but then again @Van B might have something to say.

i have never had to fool with mine.

i don't think you can open a decel.
its the sort of thing i would do of course.
attacking a fuel pump was a lot of fun.
but only with a spare to replace it.
i take the attitude destruction is likely.
i kind of looks like it would be pretty hard to get back together.
however there is a guy in australia who apparently rebuilds these things and other vac devices and has proper equipment to open up the crimping seams etc.
if it is farked up and won't respond to adjustment it will very likely be the diaphragm that is rat sh#t. so its pretty hard to fix unless you feel like becoming one of those kinds of experts.

Just for the hell of it I google search " schematic of Bosch L-Jetronic decel valve" and came up with hit on last years' 914world post

http://www.914world.com/bbs2/index.php?showtopic=342479

Read all 3 pages and it appears that a 911 decel valve may be usable as a last resort. but the tests for proper function is given by GregAmy:



yeah @tshih914 . i am the guy with the last post who has found himself a 911 decel valve. it is indeed perfectly useable. you just adjust it to the vac levels with Van B's research info as a base to set it to, and adjust if necessary after test driving.

the only difference in the decel valves is that the 911 ones may have been adjusted to a different vac level than 914 and they had the bracket brazed on a different angle.

i still have not done an install of my 911 decel, as i run it without the decel.
i actually have a fuel pressure valve subbed in and all the hoses run to it.
this is the same as blocking all the hoses off except it looks legit.
i think the first owner installed it back in the day as a state of maryland emissions cheat.

i enjoy the way the car snaps off throttle.
there is no danger of a backfire through the induction system with the car properly timed and tuned. the most it does is drop unburned fuel into the exhaust system and i hear soft bangs and burbles out the muffler. the unburned fuel goes off in the hot muffler.

very occasionally if i give it a bit of stick and fiddle the clutch as i am manouvring out of my "garage" down over my "non cross-over" 19 th century bluestone curb it will momentarily die for about 1 second and then burst back into life. the AFM flapper has bounced back beyond the fuel pump contacts and it cuts the fuel until it resumes position. decel valve in part is designed to stop that - slows and cushions the return of the AFM flapper back to near closed - as well as being a useful emission device to stop pathetic juvenile minds like mine being amused by exhaust pops and dumped hydrocarbons. (IMG:style_emoticons/default/beer.gif)

that only applies to L jets. i hear the decel is a little more essential to the long life of one highly desirable and difficult to procure part in the D jet set ups.
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wonkipop
post Mar 2 2023, 09:55 PM
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@tshih914

i knew i had this filed away but couldn't find it my L jetronic files.
eventually stumbled on it again.

could be helpful.

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combine this with the factory w/shop manual.
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wonkipop
post Mar 2 2023, 10:15 PM
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here is the rest of it.
its an idiots guide.
which i was 5 years ago and likely still am. (IMG:style_emoticons/default/beer.gif)

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tshih914
post Mar 3 2023, 10:11 PM
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QUOTE(wonkipop @ Mar 2 2023, 08:15 PM) *

here is the rest of it.
its an idiots guide.
which i was 5 years ago and likely still am. (IMG:style_emoticons/default/beer.gif)

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Well the new boot and throttle gasket was delivered yesterday so I replaced the old today. I also noticed that my air filter was badly mangled at one edge but after I replaced it with new one no difference in engine response to gassing it(stalls).


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tshih914
post Mar 3 2023, 10:12 PM
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QUOTE(tshih914 @ Mar 3 2023, 08:11 PM) *

QUOTE(wonkipop @ Mar 2 2023, 08:15 PM) *

here is the rest of it.
its an idiots guide.
which i was 5 years ago and likely still am. (IMG:style_emoticons/default/beer.gif)

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Well the new boot and throttle gasket was delivered yesterday so I replaced the old today. I also noticed that my air filter was badly mangled at one edge but after I replaced it with new one no difference in engine response to gassing it(stalls).



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tshih914
post Mar 3 2023, 10:13 PM
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QUOTE(tshih914 @ Mar 3 2023, 08:12 PM) *

QUOTE(tshih914 @ Mar 3 2023, 08:11 PM) *

QUOTE(wonkipop @ Mar 2 2023, 08:15 PM) *

here is the rest of it.
its an idiots guide.
which i was 5 years ago and likely still am. (IMG:style_emoticons/default/beer.gif)

Attached Image
Attached Image
Attached Image
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Well the new boot and throttle gasket was delivered yesterday so I replaced the old today. I also noticed that my air filter was badly mangled at one edge but after I replaced it with new one no difference in engine response to gassing it(stalls).




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tshih914
post Mar 3 2023, 10:18 PM
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QUOTE(tshih914 @ Mar 3 2023, 08:13 PM) *

QUOTE(tshih914 @ Mar 3 2023, 08:12 PM) *

QUOTE(tshih914 @ Mar 3 2023, 08:11 PM) *

QUOTE(wonkipop @ Mar 2 2023, 08:15 PM) *

here is the rest of it.
its an idiots guide.
which i was 5 years ago and likely still am. (IMG:style_emoticons/default/beer.gif)

Attached Image
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Attached Image
Attached Image


Well the new boot and throttle gasket was delivered yesterday so I replaced the old today. I also noticed that my air filter was badly mangled at one edge but after I replaced it with new one no difference in engine response to gassing it(stalls).



When after many attempts to fire up the engine starts to idle at 3000rpm. I pinched off the Aux air valve and the rpm dropped to 1200, when I release the clamp the idle goes back to 3000. When I put my hand over the snorkel I feel no air moving into the AFM (its adjustment screw is covered by a rubber plug to discourage tampering after it was rebuilt.
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Van B
post Mar 3 2023, 10:42 PM
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When you pinch the AAV hose, and the rpm drops to 1200, does the car take throttle? Or does it still stall?
Also, when you’re doing all this have you ever let the car warm up to operating temp?
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Van B
post Mar 3 2023, 10:43 PM
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One other thing, I’m not understanding how you just noticed the air filter, I thought we talked to you about pushing the afm flap with the key on to see if your fuel pump kicks on?
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