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

[Van B]

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

They are NLA as well. I’ve been looking at the later model Nissans that have a similar body but a different plug… but ultimately decided to do some more investigation on the root cause first.

[wonkipop]

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

They are NLA as well. I’ve been looking at the later model Nissans that have a similar body but a different plug… but ultimately decided to do some more investigation on the root cause first.

im guessing what clay is saying is there is info on a modern sub or alternative for the Nissan (Datsun) that is still floating around. unlike trying to find info on a sub for a 914/924/944?

i know down here the smart 911 mechanics have figured out the coolant temp sensor for a certain model holden (GM) commodore is the same as the head temp sensor on certain 911s. .....and can be screwed straight in to do the job. and you guessed it, its cheaper (of course).


EDIT

here is an ebay ad of interest maybe?


its a rebuild kit for AAV. not strictly right one, for VW Golf 1 etc. german by the looks of it. but i'm betting its so close its not funny when it comes to these things. ie 924.
how far is that from a golf passat engine of same era. or a 914.


https://www.ebay.com/itm/185166067358?_trkp...7Cclp%3A2047675

[ClayPerrine]

Just an FYI.... the CHT for a 914 is NLA. The aftermarket ones are problematic and fail randomly.

But you can use a CHT from a 911 Carrera. It will screw in the head, and has the correct curve when warming up. But you have to change the harness to get it to plug in. Just use an L-Jet injector connector. Hook one side to the existing CHT wire, and hook the other side to ground. The Carrera sensor does not ground through the head.

Clay

[wonkipop]

Just an FYI.... the CHT for a 914 is NLA. The aftermarket ones are problematic and fail randomly.

But you can use a CHT from a 911 Carrera. It will screw in the head, and has the correct curve when warming up. But you have to change the harness to get it to plug in. Just use an L-Jet injector connector. Hook one side to the existing CHT wire, and hook the other side to ground. The Carrera sensor does not ground through the head.

Clay

thanks again. might need that at christmas time.

[StarBear]

Just an FYI.... the CHT for a 914 is NLA. The aftermarket ones are problematic and fail randomly.

But you can use a CHT from a 911 Carrera. It will screw in the head, and has the correct curve when warming up. But you have to change the harness to get it to plug in. Just use an L-Jet injector connector. Hook one side to the existing CHT wire, and hook the other side to ground. The Carrera sensor does not ground through the head.

Clay

Good thing I have a spare or two. Almost everything electronic aftermarket is problematic it seems. (IMG:style_emoticons/default/chair.gif)

[djway]

My 2.3 build won't idle until head temp gets to 250 then all is good.
An AFM spring compromise to use the L Jet

[Porschef]

Hmmmmm

This is interesting, an adjustment on the AAR? Never knew that. The 2056 probably would like more air to keep the AFM flap open to feed more fuel during cold start conditions…

(IMG:style_emoticons/default/idea.gif)

Kinda what my foot does at that time

Gives me some hope… (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/beerchug.gif)

[Van B]

That's right wonki. Bypassing the AFM will throw off the whole fueling equation. It opens more variables than it eliminates. Popping the line to the AAR to check for air draw is feasible once the car is running. But I'm opting for pinching the short line in order to keep everything else accounted for. If pinching that line during cold start makes the condition worse, then to me it makes a strong case that the AAR is not meeting air flow requirements. Conversely, you could say that the engine is being over fueled, but given the objective of higher RPM than normal for engine warm up, such a statement doesn't make sense.

So, I start the car and then pinch the line:
1. RPM increases
2. RPM decreases
3. RPM remains the same

If #1 happens, then it's a lean condition I'm suffering from during warm up. If #2 happens, then it's a rich condition. If #3 happens, then the AAR is already closed.

What am I missing?

Alright, I’m back home today and this morning it was a chilly 4C. So, I was able to give it a proper cold start and do my little test.

First, I started the car as normal and then jumped out and pinched the short line from the AAR to the manifold. To my surprise I only got a subtle 100-ish RPM drop. I unclamped and reclaimed just to be sure, but yeah, that’s all I got.
Also, the car started no different today at 4C than it does at 15C. I thought that was interesting too.

Second, just for S’s and G’s I pulled the line from the boot to the AAR and the car died instantly. And I mean the instant I disconnected that hose. I had no time to even put my thumb over the ends. So, as predicted that is a lost cause.

Lastly, I moved the adjustment pin on the AAR all the way to the outside but got no change. I didn’t expect much really given how cold it is. I’m pretty sure the AAR is as open as it can be.

My thoughts so far:
I’m confident that everything is in fact functioning, but if I want to get the idle higher, I’m going to need more air flowing through the AAR channel during warm up.
Which means, I’m at a dead end for now.

Van

[emerygt350]

Very interesting! I am glad it dropped. That means you are rich and that is easier to deal with (I think). I would get one of those aars the guys were talking about. I doubt they are expensive. I suspect yours isn't opening enough.

[emerygt350]

On my 2.0, when I cut the aar off at cold start the idle drops 300 rpm, as the car warms the differential gets more and more. So after a few minutes of warm up it will be at 1400 rpm, and will drop to 800 when I close the valve.

[Van B]

Very interesting! I am glad it dropped. That means you are rich and that is easier to deal with (I think). I would get one of those aars the guys were talking about. I doubt they are expensive. I suspect yours isn't opening enough.

Yeah, I don’t know what they are talking about. The 280SX AARs are NLA as well and the ones you can get as NOS are just as much as the VW part. I’m not quite to the point that I’d be willing to spend money on a rebuild.

Now what would be cool is if I can devise a way to get a secondary air injection pump in the loop so that the AFM can still determine proper fueling… but that’s just me dreaming right now…

[wonkipop]

Very interesting! I am glad it dropped. That means you are rich and that is easier to deal with (I think). I would get one of those aars the guys were talking about. I doubt they are expensive. I suspect yours isn't opening enough.

Yeah, I don’t know what they are talking about. The 280SX AARs are NLA as well and the ones you can get as NOS are just as much as the VW part. I’m not quite to the point that I’d be willing to spend money on a rebuild.

Now what would be cool is if I can devise a way to get a secondary air injection pump in the loop so that the AFM can still determine proper fueling… but that’s just me dreaming right now…

@Van B
yes to the datsun stuff being just as expensive.
i think i know of a datsun bloke i can ask about this though and maybe there is a substitute that is around that some folks know about. otherwise, mine is just going to get another clean! (IMG:style_emoticons/default/smile.gif)

can i ask a favour. we are researching some stuff on the history of all the vac tube set ups between dist and throttle body for 1.8s.

can you take a photo of your emission sticker thats in the engine bay?
give us a Vin date. month and year.

and take a photo of your throttle body and distributor showing the vacuum line hook ups for advance and retard. post them up here. if you got time.

(IMG:style_emoticons/default/beerchug.gif)

[emerygt350]

Maybe that's an idea too. I think you said you checked to see if it was functioning on the bench but did you check to see if it was opening all the way when cold and holding it? Perhaps just more cleaning? The crap I pulled out of my idle bleed passage today was totally f'd up. I mean how could that much crap end up in an idle bleed?

[wonkipop]

That's right wonki. Bypassing the AFM will throw off the whole fueling equation. It opens more variables than it eliminates. Popping the line to the AAR to check for air draw is feasible once the car is running. But I'm opting for pinching the short line in order to keep everything else accounted for. If pinching that line during cold start makes the condition worse, then to me it makes a strong case that the AAR is not meeting air flow requirements. Conversely, you could say that the engine is being over fueled, but given the objective of higher RPM than normal for engine warm up, such a statement doesn't make sense.

So, I start the car and then pinch the line:
1. RPM increases
2. RPM decreases
3. RPM remains the same

If #1 happens, then it's a lean condition I'm suffering from during warm up. If #2 happens, then it's a rich condition. If #3 happens, then the AAR is already closed.

What am I missing?

Alright, I’m back home today and this morning it was a chilly 4C. So, I was able to give it a proper cold start and do my little test.

First, I started the car as normal and then jumped out and pinched the short line from the AAR to the manifold. To my surprise I only got a subtle 100-ish RPM drop. I unclamped and reclaimed just to be sure, but yeah, that’s all I got.
Also, the car started no different today at 4C than it does at 15C. I thought that was interesting too.

Second, just for S’s and G’s I pulled the line from the boot to the AAR and the car died instantly. And I mean the instant I disconnected that hose. I had no time to even put my thumb over the ends. So, as predicted that is a lost cause.

Lastly, I moved the adjustment pin on the AAR all the way to the outside but got no change. I didn’t expect much really given how cold it is. I’m pretty sure the AAR is as open as it can be.

My thoughts so far:
I’m confident that everything is in fact functioning, but if I want to get the idle higher, I’m going to need more air flowing through the AAR channel during warm up.
Which means, I’m at a dead end for now.

Van

i've got some thoughts on this now.
and its to do with the retarded ignition on idle that some cars have.
for emissions.
your car may or may not have it.
see photo request above.
its the vac line off the back of the distributor that runs to the vac port on the TB.
thats the port on the TB that faces towards the front of the car.

been doing some reading about problems of cars back in the day.
weak idle at cold start up caused by above.
?????
but who knows.

[emerygt350]

Vacuum retard makes a nice idle possible...

[Van B]

Never seen an emissions sticker in the engine bay. But the car is dual vacuum and was manufactured 12/73

[Van B]

Maybe that's an idea too. I think you said you checked to see if it was functioning on the bench but did you check to see if it was opening all the way when cold and holding it? Perhaps just more cleaning? The crap I pulled out of my idle bleed passage today was totally f'd up. I mean how could that much crap end up in an idle bleed?

I never put it in the freezer to see how open it would go. But it seemed to open and close with ease. I spent my day winterizing my boat… which I was a bit late on lol. But maybe I can have some time tomorrow to mess with that a bit.

[wonkipop]

@Van B

thanks for photos and vin info.

if the emissions sticker is still there its on the lhs side wall of the engine bay,
just above where the relay board and the air cleaner are.

be handy to know what engine code it has written there.
be something like EC-B or EC-A.

any idea where the car might have been originally sold new.
did you get a glovebox manual? would have a dealer stamp maybe.

-

re the retard at idle.
i think you already know about this?

but for emerygt350's interest.

some, but maybe not all 1.8s hook up both sides of the double can vac on the distributor.
the small side is known as a retard can. the larger side is advance.

the small side if it is connected to the throttle body port that is downstream of the throttle plate (engine side) uses engine vacuum at idle to retard the ignition a further 3 degrees or so than 7.5 btdc (or ideal idle). what that does is make the engine reduce NOx emissions at idle. lowers combustion temp. though it also has the effect of raising exhaust temp (Still got to get my head around that bit). at that retard (about 4 deg btdc) you won't get a smooth take off at that level of retard except the minute you snap the throttle open the engine instantly comes off vacuum and the distributor snaps to 7.5 - and you do get smooth take off.
also the engine cranks and fires at 7.5 for ideal starting before it goes into its full emissions retard idle.

emery350gt -its why you time the 1.8 at 7.5 btdc at idle with the hoses off.
you get it to 850+ or -. then you put the hoses back on and do a fine tune on the idle speed after they are back on. some say to block both the hoses, but my logic tells me you only need to block the retard hose. it doesn't hurt to block both. the manual mentions nothing about blocking the hoses at all. so (IMG:style_emoticons/default/confused24.gif)

i've come across some material that says this - while it was good for meeting the idle emissions standards it did cause the engine to run hotter while stuck in traffic. and it was mentioned could cause weak and stumbling warm up idle.

i'm wondering if that is a feature of our cars with both vacuum ports connected to both throttle ports. an easy test would be to pop the vacuum retard hose off the back of the distributor can at start up and see what it does. (you need to pop it off and block it just so you are not pulling any air in the port near the throttle.) basically disable the retard at idle and see if its a steadier faster warm up?

i think vw and porsche might have been doing this themselves right through 74 trying out variations as there seem to be a number of distinct versions with and without both hoses hooked up.

[wonkipop]

@Van B

yours is the splitting image of the setup on mine. (IMG:style_emoticons/default/beerchug.gif)

[Van B]

@wonkipop retarding further is just sparking later and sending the exhaust out while it’s still burning.
Also, there’s no mechanical difference between blocking both the advance and retard distributor port or leaving them open to atmosphere. Either way neutralizes them. But blocking does ensure nothing gets in the port. However, I think you would want to block the port on the TB to avoid air leak.

Testing your cold start theory wouldn’t be hard. But it would be time consuming given the need for a cold engine. You would have to start the car, get it warm, pull the retard port, set air screw for correct warm idle, pinch/block line from TB, and confirm timing is correct. Then, stare at the car outside in the cold for several hours while you wait for it to cool down completely*, and start it again to see what happens.

I’ll try it tomorrow and report back.

*or go do something else