‘74 1.8L L-Jetronic Cold Start Low Idle, Mystery solved! Options

[emerygt350]

Wow, so basically a pot on the throttle and a TPS on the flap, and the aar cheats the TPS on the throttle by sneaking air without moving the throttle plate. Interesting, and explains the extreme sensitivity to vacuum leaks in ljets. If it is all based on ratios of signals between those two pots...

Yeah, squeeze away or get yourself a good hydroponic valve like mine....

[wonkipop]

@emery350gt (IMG:style_emoticons/default/smile.gif)

thats the point of L jet.
its actually way simpler than D jet in most ways.
its measuring air flow into the engine, what your throttle wants, before it gets to the throttle. its all downstream of the air flow meter.
which is why it plain doesn't like air leaks.

its pretty much what EFI became from then on for a long time.
just got more sophisticated with more sensors and more real time feedback.

L jet on a 914 is the proto system. its the adam or the eve, take your pick, of EFI that followed.

thats why i bought my 1.8 30 years ago.
i'm a geek. or i was one.
too old to be a geek now, just a geezer. (IMG:style_emoticons/default/beerchug.gif)

[wonkipop]

Wow, so basically a pot on the throttle and a TPS on the flap, and the aar cheats the TPS on the throttle by sneaking air without moving the throttle plate. Interesting, and explains the extreme sensitivity to vacuum leaks in ljets. If it is all based on ratios of signals between those two pots...

Yeah, squeeze away or get yourself a good hydroponic valve like mine....

or another way to see the aav is a temporary throttle plate for warm up only
but its still moving the air flap because its got to.

[Van B]

Wow, so basically a pot on the throttle and a TPS on the flap, and the aar cheats the TPS on the throttle by sneaking air without moving the throttle plate. Interesting, and explains the extreme sensitivity to vacuum leaks in ljets. If it is all based on ratios of signals between those two pots...

Yeah, squeeze away or get yourself a good hydroponic valve like mine....

or another way to see the aav is a temporary throttle plate for warm up only
but its still moving the air flap because its got to.

More of a kitchen timer really lol…

[emerygt350]

Not sure if I would say simpler than djet, possibly more adaptive. As far as moving parts we are about equal. Us djets just have that crazy mps going on instead of your flapper.

And we both have the egg timer... And the decel valve. Talk about cruft.

[wonkipop]

Wow, so basically a pot on the throttle and a TPS on the flap, and the aar cheats the TPS on the throttle by sneaking air without moving the throttle plate. Interesting, and explains the extreme sensitivity to vacuum leaks in ljets. If it is all based on ratios of signals between those two pots...

Yeah, squeeze away or get yourself a good hydroponic valve like mine....

or another way to see the aav is a temporary throttle plate for warm up only
but its still moving the air flap because its got to.

More of a kitchen timer really lol…

(IMG:style_emoticons/default/beer.gif)

hooked up to a cuckoo clock and a windmill!

[ClayPerrine]

Wow, so basically a pot on the throttle and a TPS on the flap, and the aar cheats the TPS on the throttle by sneaking air without moving the throttle plate. Interesting, and explains the extreme sensitivity to vacuum leaks in ljets. If it is all based on ratios of signals between those two pots...

Yeah, squeeze away or get yourself a good hydroponic valve like mine....

Actually, there is no "TPS" on an L-Jet system. There is only a idle switch and a wide open throttle switch, so the ECU only knows those two states of throttle movement. And the 912-E didn't even have the WOT switch.

It was that way on the evolution of L-Jet called DME until 1995. The 964 has a switch like the 1.8L L-jet that only shows WOT or idle. The first DME to get a real TPS that actually measured throttle position was the 993.

Clay

[emerygt350]

Crazy. I am surprised just the flapper can tell the engine everything it needs, very cool. Just thinking of all the potential combinations like part throttle decel (high volume moving past a small throttle opening) vs very open throttle chugging at low RPM.

[ClayPerrine]

Crazy. I am surprised just the flapper can tell the engine everything it needs, very cool.

With the L-Jet system, there is more than just the flapper. There is the cylinder temp sender, the air temp sender (located in the air flow meter), and the engine RPM. The throttle position is extrapolated from the RPM and the air flow meter information.


Clay

[wonkipop]

the master has arrived ( @ClayPerrine ). good.


@Van B .
re AAV.
porsche used the AAV on 1.8s all the way through to the first series 944.
in the 914 PET it has a 944 PN (944 606 103 00). i guess its a supersede part.

i did a bit of searching - 944 AAV problems.

this thread is good.
someone figured out how to really clean them out.
seafoam? got more gunk out of it than carb cleaner.
he further shows how it might be possible to adjust it?

https://rennlist.com/forums/924-931-944-951...tibility-2.html

[ClayPerrine]

I don't see why you have to fix them....

You can get a direct, bolt in replacement from FLAPS. Just get one for a 79-83 Datsun/Nissan 280ZX. It fits with no mods at all.

Nippondenso built L-Jet under license from Bosch, so it is an exact copy of the Bosch part. And it is not as expensive.

http://www.2040-parts.com/280zx-280-zx-oem...datsun-i421153/

Clay

[StarBear]

I don't see why you have to fix them....

You can get a direct, bolt in replacement from FLAPS. Just get one for a 79-83 Datsun/Nissan 280ZX. It fits with no mods at all.

Nippondenso built L-Jet under license from Bosch, so it is an exact copy of the Bosch part. And it is not as expensive.

http://www.2040-parts.com/280zx-280-zx-oem...datsun-i421153/

Clay

Awesome! Thanks, Clay!
(IMG:style_emoticons/default/first.gif)

[Big Len]

Thanks Clay !!!

[Van B]

the master has arrived ( @ClayPerrine ). good.


@Van B .
re AAV.
porsche used the AAV on 1.8s all the way through to the first series 944.
in the 914 PET it has a 944 PN (944 606 103 00). i guess its a supersede part.

i did a bit of searching - 944 AAV problems.

this thread is good.
someone figured out how to really clean them out.
seafoam? got more gunk out of it than carb cleaner.
he further shows how it might be possible to adjust it?

https://rennlist.com/forums/924-931-944-951...tibility-2.html

Yeah, I’ve seen that thread. Can’t wait to be home so I can get back to sleuthing!
My little experiment should confirm a direction to focus regardless of outcome.

Oh, and none of these AARs are cheap anymore…

[Van B]

I don't see why you have to fix them....

You can get a direct, bolt in replacement from FLAPS. Just get one for a 79-83 Datsun/Nissan 280ZX. It fits with no mods at all.

Nippondenso built L-Jet under license from Bosch, so it is an exact copy of the Bosch part. And it is not as expensive.

http://www.2040-parts.com/280zx-280-zx-oem...datsun-i421153/

Clay

What the hell is “FLAPS”? I’m not into alternative lifestyles just to let everyone know lol!

[ClayPerrine]

I don't see why you have to fix them....

You can get a direct, bolt in replacement from FLAPS. Just get one for a 79-83 Datsun/Nissan 280ZX. It fits with no mods at all.

Nippondenso built L-Jet under license from Bosch, so it is an exact copy of the Bosch part. And it is not as expensive.

http://www.2040-parts.com/280zx-280-zx-oem...datsun-i421153/

Clay

What the hell is “FLAPS”? I’m not into alternative lifestyles just to let everyone know lol!

FLAPS - Abbreviation for Friendly Local Auto Parts Store. The place you go to buy motor oil and wheel bearing grease.

[Van B]

Ah ok hahaha. Yeah, I’m into FLAPS!

[StarBear]

the master has arrived ( @ClayPerrine ). good.


@Van B .
re AAV.
porsche used the AAV on 1.8s all the way through to the first series 944.
in the 914 PET it has a 944 PN (944 606 103 00). i guess its a supersede part.

i did a bit of searching - 944 AAV problems.

this thread is good.
someone figured out how to really clean them out.
seafoam? got more gunk out of it than carb cleaner.
he further shows how it might be possible to adjust it?

https://rennlist.com/forums/924-931-944-951...tibility-2.html

Tried it; reminded me of how much I dislike that site - WAY too many pop up ads and crap that only freezes up my computer. Never was able to check out the cleaning comment. (IMG:style_emoticons/default/confused24.gif)

[wonkipop]

Thanks for the datsun tip @ClayPerrine .
think i can rustle one of those up down here.
(IMG:style_emoticons/default/beerchug.gif)

[wonkipop]

the master has arrived ( @ClayPerrine ). good.


@Van B .
re AAV.
porsche used the AAV on 1.8s all the way through to the first series 944.
in the 914 PET it has a 944 PN (944 606 103 00). i guess its a supersede part.

i did a bit of searching - 944 AAV problems.

this thread is good.
someone figured out how to really clean them out.
seafoam? got more gunk out of it than carb cleaner.
he further shows how it might be possible to adjust it?

https://rennlist.com/forums/924-931-944-951...tibility-2.html

Tried it; reminded me of how much I dislike that site - WAY too many pop up ads and crap that only freezes up my computer. Never was able to check out the cleaning comment. (IMG:style_emoticons/default/confused24.gif)

i have the same problem with that site,but can work it if i shut some ad pop ups.

here are the screen grabs, its only one guy and two comments that are relevant.