L-Jet going full Rich on Deceleration Options

[emerygt350]

The fowling is something to think about though. I have had many carbed cats over the years and decel fowling wasn't an issue. I think I have seen hints of it in my car but nothing terrible. When it warms up I might experiment with that. I can't imagine that was ignored by the manufacturer. Perhaps that is something we can tune away to some extent.

know what you are saying.

i am curious about mine.

i don't have a probe in the exhaust to drive around and find out.
probably just as well.
but i guess when i get it in the workshop i can get an analyser on it and do some stationary tests watching what it does on the way down from closing the throttle from higher revs?

Man, trying to imagine my engine packed up with chickens. Don't post pre-coffee.

Anyway, fixed that.

I am going to try two things, one of which you could do if you have some hills around. I am getting a new probe (I think my 50 year old engine burns enough oil to do terrible things to o2 probes), and will look at both the numbers on the gauge but also plug condition. I have a hill that I know results in some fouling (not fowling, man that is something to imagine), and there is a parking lot at the bottom. I am going to let the engine drag down the hill (10% grade, maybe 500 feet decent, 1/2 mile) and then check the plug condition.

I found a 36 dollar wide band that should work with my autometer gauge, it will be interesting to see how it stands up to the original.
Dan

whats the conversion rate from horsepower to chookpower?

Chookpower you say?

Perhaps it's a southern hemisphere thing...

[wonkipop]

chookyard = chickenyard.

think the limeys call them chooks too.
a ye olde english thing more so than original aus slang.

limeys = usa slang. = poms in aus. translates as prisoners of his/her majesty i believe.
ie prisoners trapped in the motherland. ignoring as australians do that they were the original prisoners of another prison island. aus slang is endless circles of b s.

------

getting back to topic.
does this sound like your afr readings brian.

[wonkipop]

Let's just blame autocorrect on all of that....

Really an interesting topic. I wonder if the afm shut off wasn't taking advantage of residual pressure. Sure the pump will stop when the afm closes but residual pressure will give another second of gas. If the engine is still running the afm will open again.

Just went for a little test run. Did the downhill drag (not intense, just normal kind of hill driving) and when I got to the bottom my idle was about 200 low. Engine was quite cool though. 186 head temps. It was hard to tell if I was fighting a computer induced rich condition rather than fouled plugs. The car ran fine beyond the low idle. By the time I got to the next stop sign and the temp came back up to 260ish, idle was back at 900.


I did notice that my vacuum on decel was 23. And that was not rpm dependent. If I was dragging down the hill at 4k rpms, the vacuum was the same as 1800 rpm.

In a 2.0 we have the mps measuring plenum vacuum for normal operating conditions (and at high vacuum fuel duration is cut) but we also have a more active tps, and one of its jobs is to tell the ecu to ignore the mps at closed throttle.

Need to get my new o2 sensor to play more with this... I just have to imagine that the engineers would have cut fuel almost completely during decel.

yeah emery

what interested me was it does it cold but not when warm.
during warm up i believe the engine must be getting 2-3 times amount of enrichment.
and with vac working on fuel pressure regulator, fp goes down to 28.

and injectors won't squirt below 26. thats the bit i have to check. someone must know.
its not something i found in manual. it was just something someone wrote somewhere.

so maybe it can dip down enough when its cold to truly cut the injectors briefly.

because it don't happen warm.

as always. i dunno.

and i have read and read and read on the fuel cut off thing.
its not in this early version of L jet.
but i'm guessing that in a situation where the decel is disconnected and there is no action on the flapper that the throttle switch controls the fuel amount. so it delivers idle fuel portioning all the way down. ??? but not a cut off.

some slightly later bmws have the fuel cut off on decel. fuel is cut off at higher revs then as it drops to around 3000 revs fuel is resumed. but not it seems in these babies.

the decel does a couple of things.
it sort of simulates the way a carb can come down smoothly and resume idle.
ie it keeps combustion going and lets it subside gently to idle level.
but it also cleans up emissions because its letting in fuel on the way down via the flapper (i think?) and its burning it with air from the decel valve. and on top of that with an original distributor it retards timing back a little from centrifigal position and burns it slightly later - even past the exhaust valve and into upper stubs of exhaust manifold.
i think that is how they did it with these early L jets in relation to emissions.
all of which would lead you to a leaner condition measured with a probe. because its also burned up excess hydrocarbons in upper exhaust. these don't pop or detonate later in exhaust causing that usual burble - rather they get burned as they leave.
i think i have all that correct for a stock set up.

brians is a little harder to understand.

like how long is this rich thing persisting.
is it all the way down the hill/mountain coasting. or is it just initially on backing off to coast.

[wonkipop]

here is another note on that decel thing.

the idea that the L jets can do a lean condition on deacceleration may not be entirely attributed to its primitive lunar module brain and pre program routines.
it might also be a kind of frankenstein sledgehammer/cuckoo clock attached to the side of it all with vac hoses.

ie it just burns the excess hydrocarbons on back off with a good old vac retard trick.

reason i say this is @Van B brought up the different decel valve on the 75 1.8s on another thread.
and it is different. its a big monster flat can thing. which i know little about.

but i do know that the exhaust manifold stubs on the 75 1.8s were different as well.
they were thicker and held more heat in them. vw and porsche referred to these thicker stubs with real fancy words. "thermal reactors". not the thermal reactors we later came to know and love.

i'm putting 2 and 2 together here and coming up with 15 i know.

but a bigger decel can (more O2?), get those exhaust stubs nice and hot, change the distributor slightly (think its a different distributor too) and........do you burn even more hydrocarbons coming off the gas pedal and pass the emission test without an air pump.
and all the time you think the dumbo brain controlling it all is doing something smart with the air/fuel mix.

i dunno.

in 76 the 912E had to get an air pump. i don't know when and how the air pump kicks in. don't have a 912E. never seen one. none here. but they had L jet and had to get that air pump to pass the ever increasing emission test. 914 1.8s didn't need the air pump. so is the whole lean off thing about these gadgets and requirements of emissions.

i would have thought a temporary spike in richness on back off is not a terrible thing.
but if is persistent then that is something different i'm guessing.

[emerygt350]

I bet Mr. Injector could tell us exactly how they perform at sub 28 psi.

My gt350 has this crazy soft fall mechanism on the throttle body to stop the same kind of dip issue on throttle close. 14 years later, well 10 years after l-jet, with O2 sensors, and space shuttle computers, and they still couldn't keep a fuel injected motor running with a rapid throttle close. It was so bad, and fudged, that they wouldn't even give you fuel injection with a manual transmission. That took several years for cfi and a complete change to multiport injection (86) for the 302 ho.

[wonkipop]

I bet Mr. Injector could tell us exactly how they perform at sub 28 psi.

My gt350 has this crazy soft fall mechanism on the throttle body to stop the same kind of dip issue on throttle close. 14 years later, well 10 years after l-jet, with O2 sensors, and space shuttle computers, and they still couldn't keep a fuel injected motor running with a rapid throttle close. It was so bad, and fudged, that they wouldn't even give you fuel injection with a manual transmission. That took several years for cfi and a complete change to multiport injection (86) for the 302 ho.

interesting what you say about no manual with fuel injection.

the EC-A, EC-B research i did turned up that VW pushed the L jet into production with primary focus on the VW 412 with auto trans. they could not make D jet work with auto trans and pass emissions test and be driveable. but they could achieve it with L jet.

3 months after the 412 comes the 914 with L jet. and a manual trans. and quite a different set up in terms of distributor, decel valve operation etc. all tweaked differently.

hard to find out info on 412 with the 74 L jet setup. and do i really want to know.
not really. but it is different the way it all works. think it even copped an EGR when the 914s didn't.

[Van B]

chookyard = chickenyard.

think the limeys call them chooks too.
a ye olde english thing more so than original aus slang.

limeys = usa slang. = poms in aus. translates as prisoners of his/her majesty i believe.
ie prisoners trapped in the motherland. ignoring as australians do that they were the original prisoners of another prison island. aus slang is endless circles of b s.

------

getting back to topic.
does this sound like your afr readings brian.

That’s opposite. That example is going super lean.

[Brian Fuerbach]

I checked the fuel press reg and all is golden. (IMG:style_emoticons/default/biggrin.gif)

I get the same low idle at the bottom of hills as you do GT350. Runs great as I get going again. I dont think it is fouling but maybe with the temporarily reduced head temps the computer is doing something to cause this. I will note my vacuum on the hill and see if it compares with yours.

Wonkipop, where in Oz do you live? I worked for a Brisbane company called EGR Automotive for a couple of years here in the US office. I currently have been employed for the last 13 years by an Aussie owned company.

[wonkipop]

I checked the fuel press reg and all is golden. (IMG:style_emoticons/default/biggrin.gif)

I get the same low idle at the bottom of hills as you do GT350. Runs great as I get going again. I dont think it is fouling but maybe with the temporarily reduced head temps the computer is doing something to cause this. I will note my vacuum on the hill and see if it compares with yours.

Wonkipop, where in Oz do you live? I worked for a Brisbane company called EGR Automotive for a couple of years here in the US office. I currently have been employed for the last 13 years by an Aussie owned company.

melbourne.

nihil44 who is on this site lives in brisbane. the weather there is nice (except in high summer when its horribly humid). i was originally born in far north queensland and my grandmother lived in brisbane where i spent teenage summers. lots of fun.
skateboarding, sailing, even some surfing if we could get out to stradbroke island.
its getting to be a big go ahead city these days. a giant urban agglomeration from brisbane to the gold coast.

good news about fuel pressure reg. (IMG:style_emoticons/default/beerchug.gif)

how long does the rich condition last on your probing spectrometer when it comes up.
is it all the way through deacceleration and on coasting all the way down hills?

[wonkipop]

chookyard = chickenyard.

think the limeys call them chooks too.
a ye olde english thing more so than original aus slang.

limeys = usa slang. = poms in aus. translates as prisoners of his/her majesty i believe.
ie prisoners trapped in the motherland. ignoring as australians do that they were the original prisoners of another prison island. aus slang is endless circles of b s.

------

getting back to topic.
does this sound like your afr readings brian.

That’s opposite. That example is going super lean.

thats good,
its interesting for me then.
it seems to say with those 911s its not shutting off fuel, but the fuel is going to a lower level not influenced by air mass sensor (or equiv to afm, not sure what they have).
and since its not getting air its a pretty small amount of fuel?

must be what mine does when i back off gas without decel. just goes down to idle metering of fuel. i sure don't get what that pelican poster called popping. i might get some what i would call burble. so i doubt i get the rich thing fuel dump. probably get the opposite. not enough for anything much to happen except engine braking and a bit of fuel being expelled into exhaust and doing a little snap and crackle without the pop.
but there is no real combustion going on. its just spitting out a bit of fuel that is coming in. which is detonating in the exhaust. but its not a "real" rich condition thats occuring under true power combustion.

brian's thing is interesting.

is it possible that the oil filler cap might be coming into play.
given we discovered the horror of it being a pcv valve.

the mechanism seems to want to close off the crankcase if exposed to engine vacuum.

it can't get exposed to that when the throttle is closed. not via the throttle plate - crankcase vent port is above the throttle plate.
but could it be drawing as a result of the decel valve wanting to draw air in during decel. be exposed to fairly high manifold vacuum (draw) that way during over-run. is the pcv valve then meant to close in those instances. could it be drawing in excess of crankcase vapors, blow by fumes, oil mist etc.
could that increase the afr reading? "fowl plugs" as emery would say. you guys would know more than me about what can send one of those probes down the scale to say there was more "fuel" in it - besides perhaps real fuel so to speak.

[Brian Fuerbach]

I checked the fuel press reg and all is golden. (IMG:style_emoticons/default/biggrin.gif)

I get the same low idle at the bottom of hills as you do GT350. Runs great as I get going again. I dont think it is fouling but maybe with the temporarily reduced head temps the computer is doing something to cause this. I will note my vacuum on the hill and see if it compares with yours.

Wonkipop, where in Oz do you live? I worked for a Brisbane company called EGR Automotive for a couple of years here in the US office. I currently have been employed for the last 13 years by an Aussie owned company.

melbourne.

nihil44 who is on this site lives in brisbane. the weather there is nice (except in high summer when its horribly humid). i was originally born in far north queensland and my grandmother lived in brisbane where i spent teenage summers. lots of fun.
skateboarding, sailing, even some surfing if we could get out to stradbroke island.
its getting to be a big go ahead city these days. a giant urban agglomeration from brisbane to the gold coast.

good news about fuel pressure reg. (IMG:style_emoticons/default/beerchug.gif)

how long does the rich condition last on your probing spectrometer when it comes up.
is it all the way through deacceleration and on coasting all the way down hills?

I was supposed to go the the EGR factory in Oz but missed out on the trip because my wife was 8 months pregnant at the time. I left the company shortly after.

Went to check vacuum on the hills and realized I couldn't. Thought it would be as simple as using the 123 dist app as it displays vacuum. Well, the app displays port vacuum not manifold vacuum. Going to look for my vac guage and try again.

I will also note the downhill afr's and rpms to see if they change at all.

The oil cap drawing fumes is an interesting hypothesis.

[wonkipop]

I checked the fuel press reg and all is golden. (IMG:style_emoticons/default/biggrin.gif)

I get the same low idle at the bottom of hills as you do GT350. Runs great as I get going again. I dont think it is fouling but maybe with the temporarily reduced head temps the computer is doing something to cause this. I will note my vacuum on the hill and see if it compares with yours.

Wonkipop, where in Oz do you live? I worked for a Brisbane company called EGR Automotive for a couple of years here in the US office. I currently have been employed for the last 13 years by an Aussie owned company.

melbourne.

nihil44 who is on this site lives in brisbane. the weather there is nice (except in high summer when its horribly humid). i was originally born in far north queensland and my grandmother lived in brisbane where i spent teenage summers. lots of fun.
skateboarding, sailing, even some surfing if we could get out to stradbroke island.
its getting to be a big go ahead city these days. a giant urban agglomeration from brisbane to the gold coast.

good news about fuel pressure reg. (IMG:style_emoticons/default/beerchug.gif)

how long does the rich condition last on your probing spectrometer when it comes up.
is it all the way through deacceleration and on coasting all the way down hills?

I was supposed to go the the EGR factory in Oz but missed out on the trip because my wife was 8 months pregnant at the time. I left the company shortly after.

Went to check vacuum on the hills and realized I couldn't. Thought it would be as simple as using the 123 dist app as it displays vacuum. Well, the app displays port vacuum not manifold vacuum. Going to look for my vac guage and try again.

I will also note the downhill afr's and rpms to see if they change at all.

The oil cap drawing fumes is an interesting hypothesis.

a very long flight. still maybe one of the longest in the world. (IMG:style_emoticons/default/sad.gif)

going to aus is something you would probably do once and never again. too far?

but when you finally get there......

pluses
- language translates easily into amerilish without the use of a phrase book.
- friendly natives.
- better coffee
- beer
- good wine if thats your thing or the beer runs out.
- mount panorama

minuses
- smaller food servings.
- no rib joints.
- expensive fuel.
- bad drivers.
- dangerous wildlife.
- sharks.
- low ozone in atmosphere/uv levels that will age you 10 years in 2 minutes.
- too close to new zealand
- great ocean road ruined as drivers paradise.


had a look at EGR website.
realise i have used their building products.
namely waterproof internal boards.
i am not a fan of tiling. the boards are good stuff.
color range is better than the alternative manufacturers.
glad EGR survived the destruction of the domestic auto manufactures here.
one of the worst moves one of our former governments did.
decimated the component industry grouped around GM and Ford.

A visit to the factory would have put you in what i would call the inner ring of brisbane. would have been the edge of the city in the 50s. nicely positioned for further recreational after work activities. its a bit of a trip to get to the coast when you are in brisbane. it sits on moreton bay which is kind a tropical mangrove area. mud.
stradbroke island is the place to get to if you go there. car ferry ride. nice spot.
i rate brisbane as a serious city these days. rivals melbourne when it comes to food and coffee. melbourne is over-rated and has gone into decline. i've had some mighty fine meals in brisbane. used to do a bit of work up there and spend a bit of time in the town about 10 years ago.

[wonkipop]

@Brian Fuerbach

there was a discussion recently around the oil filler cap.
you might have already read it brian.

http://www.914world.com/bbs2/index.php?sho...l44++smoke+test

i attempted a cross section sketch of the cap and posted in that thread.

but this is probably a bit closer to what its really like.

[emerygt350]

Does that line head into the plenum or the air box?

[Brian Fuerbach]

Wonkipop,
I did read the thread on on the cap. I came to the conclusion that the cap must function as a crankcase valve of some sort years ago while changing the seal and o-rings. I had tested my cap to see if the membrane was operational and it checked out.

emerygt350,
The crankcase vents into the rubber intake tube in between the Air box/AFM and throttle body. The AAR valve and Decel valves also enter in that area.

[wonkipop]

Wonkipop,
I did read the thread on on the cap. I came to the conclusion that the cap must function as a crankcase valve of some sort years ago while changing the seal and o-rings. I had tested my cap to see if the membrane was operational and it checked out.

emerygt350,
The crankcase vents into the rubber intake tube in between the Air box/AFM and throttle body. The AAR valve and Decel valves also enter in that area.

emery, here is a photo of mine.
brian's will be the same.

i was having the thought because of the location where the decel hose connects.
its between the crankcase vent hose and the afm. it could sort of want to draw air from either direction.

but brian's report of the condition of his pcv valve/cap kind of puts paid to my theory.
so unless his cap is misbehaving since he tested it, its not a valid thought.



i did come across descriptions of momentary full rich as an afr reading.
happening immediately after closing the throttle.
if fuel has condensed on the inlet manifold and port areas.
closing the throttle and high vac moment causes condensed fuel to suddenly boil off the surfaces and be drawn into the combustion chamber and expelled. it doesn't last for long and is transitory.
depends a bit on the the design of the inlet system.

then there is always the question of the gauge and probe behaving correctly.
came across people describing some gauges actually measuring full lean, but having maxed out indicating this as full rich. ???? ie unreliable indications!

[emerygt350]

interesting. I assume that PCV system is like the 73 where it is vacuum sensitive. At high vacuum it actually closes up (well, it has a little metered breathing available), opening under low vacuum when you actually need it.


That initial rich is definitely a thing, but the going full lean on full rich is obvious on my autometer at least. The gauge actually kind of says "well, if we are going to be like that, screw you" and pegs itself to full lean and stays there for maybe a couple minutes. Mine is analog so there is normally movement in the arm at all times. When the computer gives you the finger, you can tell because it stops moving at full lean. It only does that when it gets too rich of a signal. Stupid. My digital AEM in the mustang doesn't do any sort of stupid thing like that.

[Brian Fuerbach]

interesting. I assume that PCV system is like the 73 where it is vacuum sensitive. At high vacuum it actually closes up (well, it has a little metered breathing available), opening under low vacuum when you actually need it.


That initial rich is definitely a thing, but the going full lean on full rich is obvious on my autometer at least. The gauge actually kind of says "well, if we are going to be like that, screw you" and pegs itself to full lean and stays there for maybe a couple minutes. Mine is analog so there is normally movement in the arm at all times. When the computer gives you the finger, you can tell because it stops moving at full lean. It only does that when it gets too rich of a signal. Stupid. My digital AEM in the mustang doesn't do any sort of stupid thing like that.

I have the wideband AEM Also.

[wonkipop]

interesting. I assume that PCV system is like the 73 where it is vacuum sensitive. At high vacuum it actually closes up (well, it has a little metered breathing available), opening under low vacuum when you actually need it.


That initial rich is definitely a thing, but the going full lean on full rich is obvious on my autometer at least. The gauge actually kind of says "well, if we are going to be like that, screw you" and pegs itself to full lean and stays there for maybe a couple minutes. Mine is analog so there is normally movement in the arm at all times. When the computer gives you the finger, you can tell because it stops moving at full lean. It only does that when it gets too rich of a signal. Stupid. My digital AEM in the mustang doesn't do any sort of stupid thing like that.

yes emery - am sure thats how it works on the 74 L jet too.
might also do a little balancing act between crankcase and inlet pressure differences at other times.

guess i was trying to think of the next thing to look at to be sure the info telling brian this was happening was 100% reliable.

is this a new thing brian? never done it before with the probe hooked up?

[Brian Fuerbach]

interesting. I assume that PCV system is like the 73 where it is vacuum sensitive. At high vacuum it actually closes up (well, it has a little metered breathing available), opening under low vacuum when you actually need it.


That initial rich is definitely a thing, but the going full lean on full rich is obvious on my autometer at least. The gauge actually kind of says "well, if we are going to be like that, screw you" and pegs itself to full lean and stays there for maybe a couple minutes. Mine is analog so there is normally movement in the arm at all times. When the computer gives you the finger, you can tell because it stops moving at full lean. It only does that when it gets too rich of a signal. Stupid. My digital AEM in the mustang doesn't do any sort of stupid thing like that.

yes emery - am sure thats how it works on the 74 L jet too.
might also do a little balancing act between crankcase and inlet pressure differences at other times.

guess i was trying to think of the next thing to look at to be sure the info telling brian this was happening was 100% reliable.

is this a new thing brian? never done it before with the probe hooked up?

The lower idle has always happened after a hill. Only noticed the correlation between afr and this after the probe was installed. Not sure where I read it but I was under the impression that fuel was to be cut off with the throttle closed. When this was proved wrong by the probe I wanted to find the issue. May not even be an issue. Maybe what I read about fuel cutoff was pertaining to D-jet?