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> ‘74 1.8L L-Jetronic Cold Start Low Idle, Next challenge!
Van B
post Nov 7 2021, 04:01 PM
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Ok fellas, here’s the run down Aux Air Regulator (AAR) and Cold Start Valve (CSV)/injector both work fine. Many of you have also been keeping up with my high idle issue that we figured out.

But yet, when the car is cold, i.e. room temp, I don’t get the high idle I should on start-up. Instead she cranks a bit and then lumbers to life. Idle lopes around 700-800rpm and then smooths out as it warms.

In all other aspects of operation, the engine seems to be pretty happy.

Thoughts? Experience? (IMG:style_emoticons/default/confused24.gif)

-Van
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emerygt350
post Nov 7 2021, 04:13 PM
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Hmmm.... Are you sure about the aar? Just unplug it from the plenum while you cold start. See if that changes anything.

Low idle tends to be a rich condition or retarded timing.
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Van B
post Nov 7 2021, 04:23 PM
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I took off the AAR and put 12v to it and watched it close. It definitely works.
I don’t own a timing light since my other Porsche just needs a laptop lol… but even if I got one I wouldn’t know the difference between right and wrong numbers (IMG:style_emoticons/default/unsure.gif)
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emerygt350
post Nov 7 2021, 04:47 PM
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The aar may work but I would still just pull it and see if it changes anything. And by pull it, I mean create the equivalent vacuum leak. When I bought mine some fool had both ends of the aar plugged into the plenum.

I wouldn't worry about timing yet. Just two of the things that tend to cause low idle.
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wonkipop
post Nov 7 2021, 04:50 PM
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mine does the same.

have done all the checks back a couple of years ago.
all perfectly timed, valves adjusted etc.
aar working and checked.

mine starts promptly and strongly. the cold start injector works and its thermoswitch as well.

once the cold star injector cuts out it goes down to a weaker idle below or at about 800,
then it comes up nice and steady after about 5 minutes.

i just let it warm up for 5 minutes before i drive it.

i'll be interested to see others answers to this one.

one thing you can check is the cold start injector and its associated thermoswitch.
i can dig that data up for you later.

there is a bit of myth around that the cold start injector only comes on below a certain termp. like an on off switch. i don't believe this is so. i believe the cold start injector operates fully below a certain temp for its full timing and above that temp the thermo switch progressively times it on for less and less duration - right up to a cut out temp which is relatively high. i will dig out all those various temp ranges for thermo switch later and post them up. others can chime in on the cold start injector/switch.

i think mr. perrine will have the facts on that.

(IMG:style_emoticons/default/beerchug.gif)
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Van B
post Nov 7 2021, 05:05 PM
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So, I pulled the CSV/injector today and put some tape over the manifold. Kept the CSV connected and cranked the engine. It gave a nice cooling gasoline spritz all over the engine while I was cranking the engine, but once the car started, it was content with the work accomplished and went to sleep.
So, if that’s all it’s meant to do, it’s doing a great job. But if it was supposed to do more, something is telling it not to.

Van
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emerygt350
post Nov 7 2021, 07:21 PM
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According to the manuals that is all it is supposed to do. Hardly seems worth it but I guess it must be important on very cold days. As mentioned above, there is a variety of opinions on how much and when with that csv.
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emerygt350
post Nov 7 2021, 07:24 PM
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I would add that mine starts right up and it does take a minute or so before I notice the aar making a difference. I put a valve on mine and often I just leave it closed (taking the aar out) since the car runs just fine without it in the summer. I am starting to see some more benefit now that it is getting colder. I would suggest the valve addition to anyone. It really is nice to have when troubleshooting and for setting the max idle when aar is on.
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wonkipop
post Nov 8 2021, 03:28 AM
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QUOTE(Van B @ Nov 7 2021, 05:05 PM) *

So, I pulled the CSV/injector today and put some tape over the manifold. Kept the CSV connected and cranked the engine. It gave a nice cooling gasoline spritz all over the engine while I was cranking the engine, but once the car started, it was content with the work accomplished and went to sleep.
So, if that’s all it’s meant to do, it’s doing a great job. But if it was supposed to do more, something is telling it not to.

Van


sounds about right.

a couple of years ago when i was recommissioning mine the engine would run for around 5-10 seconds or so on the cold start valve alone. did not have a stop watch on it. the injectors despite reconditioning were kaput, but she would start and run off the cold start valve for a short time.

that was around the end of autumn (you call it fall). temps in workshop would have been about 15C or 60F in USA temp. the cold start definitely kicks in above 50F as others state is some kind of on/off cut off.

i was down at the workshop today working on the falcon ute so i asked mike, who is the mechanic looking after all our cars. i went over the cold idle thing with him.
my car is all set up properly tuned off the analyzer when the engine was fully warm with the correct fuel/air mix. his view is that the AAV is probably inhibiting fast cold idle.
basically they get old. they just have a sprung steel coil in them that heats with electrical current. after 50 years of cycling the thermo coil spring degrades etc. they just don't work like they did when new. the coil weakens. which means that they close a bit quicker than they are supposed to, or close enevenly or even stick and then suddenly close.

we tested mine a couple of years ago and it appeared to open and it appeared to close.
did the fridge test and then hooked it up to a battery. but its not like i timed it against any data. my memory was that it closed reasonably fast, maybe in 2 minutes or so.
which might be too fast?

anyway, i don't worry about it too much. i know the engine is set up nice with air fuel mix when its warmed up to operating temp.

i really can't shed any light on the problem other than to suspect the AAV might be not behaving as it would have 50 years ago, which is how i look at mine.

i've got a feeling it idled more strongly from cold start when i first recommissioned 2 years ago and lately its been a little weaker for the first minute or 2 of operation.
could be my imagination. if i get time i might take another look at the AAV and electrical connection. probably at christmas.
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wonkipop
post Nov 8 2021, 04:39 AM
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ps @Van B

part of my conversation with mike today involved him saying he had never seen absolute first version L jet until he helped me recommission. you don't see that stuff in australia.
he reminded me its half a century old and it still goes. then swept his hand in the general direction of the door and said everything fresh on the road at the mo won't be even vaguely operational in 20 years time.

i was reminded of him pointing at the AFM housing on the air cleaner a couple of years back with a sh$t eating grin on his face saying its a 001 part #. you don't see that often, the first version of something.

i got told some more stories about his apprentiship tech classes when he was shown by an an older experience FI tech how to adjust a fuel pressure regulator that had gone weak. but it in the vice and squeeze it. he said this instructor could actually do it - fix up a screwed up non adjustable fuel pressure regulator. bush mechanic stuff.
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Van B
post Nov 8 2021, 09:17 AM
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The temp switch is an interesting point. If in fact it's set for what humans would call cold weather and not what an engine would consider cold, then I may not have ever had it cold enough to truly activate the cold start. I found some document that covers some decent detail on the 912E L-Jetronic system and it mentioned exactly what you said.

Cold Start Thermo-switch:

912E = 30C/95F
914 = 15C/55F

That temp for the 914 makes zero damn sense!

I also found some wires on my dual relay that were loose. I don't understand how one side has the plastic plug and the other side looks like a hack job of different clips and pig tails?
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wonkipop
post Nov 8 2021, 04:16 PM
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QUOTE(Van B @ Nov 8 2021, 09:17 AM) *

The temp switch is an interesting point. If in fact it's set for what humans would call cold weather and not what an engine would consider cold, then I may not have ever had it cold enough to truly activate the cold start. I found some document that covers some decent detail on the 912E L-Jetronic system and it mentioned exactly what you said.

Cold Start Thermo-switch:

912E = 30C/95F
914 = 15C/55F

That temp for the 914 makes zero damn sense!

I also found some wires on my dual relay that were loose. I don't understand how one side has the plastic plug and the other side looks like a hack job of different clips and pig tails?


here is what i have Van.
From a L - Jet fuel injection manual for VWs generally.
see attached illustration.

3 different thermoswitches for the cold start valve are covered and listed with different bosch part #s.

would seem to imply fitting thermoswitches to suit different climate zones?
all three have different temp ranges but all having same spread of 18F between coldest and hottest.

but just to throw that off, I have another L jet guide that says the thermoswitch opens fully at 50F and closes above 104F. ?????? to me the 50 to 104 makes the most sense, as i would define an engine sitting at 104F as "cold" and needing a tiny squirt of start up fuel? or am i wrong.

anyway - all that means is thermoswitch opens cold start injector for full max timing at lowest temp, does not open it at all above the highest temp and in between its a diminishing amount of time the switch opens and the injector delivers.

in the 914 factory manual the test mentions the switch when tested below 50F should not open for more than 20 seconds. so 20 seconds is max amount of cold start injector delivery?

the truth is its really just got to work and more importantly switch the cold injector off.
to me its just a machine doing a synthetic couple of pumps on the gas pedal as you do for a carby car?

however -- thats not the fast idle warm up enrichment that takes over after the cold start injector does its job.

i know my cold start injector works, yours does too, but the enrichment cold idle phase is not quite right.


Attached Image


warm up enrichment is really controlled by 3 things as far as i can tell.

temp sensor 1 - in the intake air sensor of the Air Flow Meter. (intake air temp)

temp sensor 2 - the cylinder head temp sensor. (engine temp)

AAV - supplying the additional air for warm up.

and its kind of analogue like a clock, especially the AAV.

so one of those things is probably playing up and giving me the no fast idle warm up like you have on yours as well.

we tested all three of mine back 2 years ago and they all appeared to be working but i think this christmas i might re test and go over them maybe more closely.

i don't really worry about it at this stage as i know its running fine when its warm and i can put up with the little hitch starting the car cold every weekend and letting it get up to speed - and i never have to touch the gas pedal to start the car or keep it going during the warm up, so i figure its almost still all working after half a century and thats not too bad a situation for now.
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emerygt350
post Nov 8 2021, 05:30 PM
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QUOTE(wonkipop @ Nov 8 2021, 05:16 PM) *

QUOTE(Van B @ Nov 8 2021, 09:17 AM) *

The temp switch is an interesting point. If in fact it's set for what humans would call cold weather and not what an engine would consider cold, then I may not have ever had it cold enough to truly activate the cold start. I found some document that covers some decent detail on the 912E L-Jetronic system and it mentioned exactly what you said.

Cold Start Thermo-switch:

912E = 30C/95F
914 = 15C/55F

That temp for the 914 makes zero damn sense!

I also found some wires on my dual relay that were loose. I don't understand how one side has the plastic plug and the other side looks like a hack job of different clips and pig tails?


here is what i have Van.
From a L - Jet fuel injection manual for VWs generally.
see attached illustration.

3 different thermoswitches for the cold start valve are covered and listed with different bosch part #s.

would seem to imply fitting thermoswitches to suit different climate zones?
all three have different temp ranges but all having same spread of 18F between coldest and hottest.

but just to throw that off, I have another L jet guide that says the thermoswitch opens fully at 50F and closes above 104F. ?????? to me the 50 to 104 makes the most sense, as i would define an engine sitting at 104F as "cold" and needing a tiny squirt of start up fuel? or am i wrong.

anyway - all that means is thermoswitch opens cold start injector for full max timing at lowest temp, does not open it at all above the highest temp and in between its a diminishing amount of time the switch opens and the injector delivers.

in the 914 factory manual the test mentions the switch when tested below 50F should not open for more than 20 seconds. so 20 seconds is max amount of cold start injector delivery?

the truth is its really just got to work and more importantly switch the cold injector off.
to me its just a machine doing a synthetic couple of pumps on the gas pedal as you do for a carby car?

however -- thats not the fast idle warm up enrichment that takes over after the cold start injector does its job.

i know my cold start injector works, yours does too, but the enrichment cold idle phase is not quite right.


Attached Image


warm up enrichment is really controlled by 3 things as far as i can tell.

temp sensor 1 - in the intake air sensor of the Air Flow Meter. (intake air temp)

temp sensor 2 - the cylinder head temp sensor. (engine temp)

AAV - supplying the additional air for warm up.

and its kind of analogue like a clock, especially the AAV.

so one of those things is probably playing up and giving me the no fast idle warm up like you have on yours as well.

we tested all three of mine back 2 years ago and they all appeared to be working but i think this christmas i might re test and go over them maybe more closely.

i don't really worry about it at this stage as i know its running fine when its warm and i can put up with the little hitch starting the car cold every weekend and letting it get up to speed - and i never have to touch the gas pedal to start the car or keep it going during the warm up, so i figure its almost still all working after half a century and thats not too bad a situation for now.


Great stuff. I would add that as you find all the gremlins, stuff that used to behave badly often starts behaving well. Don't necessarily assume something is broken. I have found many of the simpler things (cht, aar) were working perfectly, just not when the hoses are messed up or there is a vacuum leak.
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Van B
post Nov 8 2021, 05:44 PM
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We need an online database for all these manuals. I would love to have a pdf of the complete Porsche service manual… you know because the 914 IS A PORSCHE lol! (IMG:style_emoticons/default/oilleak914.jpg)
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Van B
post Nov 8 2021, 07:16 PM
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Is the cylinder head temp sensor the one on top of the right bank next to the distributor? Aka single wire connector?

I did my one obligatory cold start this evening to see if fixing the connectors on the dual relay changed anything… it didn’t.

That said, when it’s warm it hums a long real nice and the decel valve is working like a champ.
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wonkipop
post Nov 8 2021, 07:28 PM
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QUOTE(Van B @ Nov 8 2021, 07:16 PM) *

Is the cylinder head temp sensor the one on top of the right bank next to the distributor? Aka single wire connector?

I did my one obligatory cold start this evening to see if fixing the connectors on the dual relay changed anything… it didn’t.

That said, when it’s warm it hums a long real nice and the decel valve is working like a champ.



the CHT is further back on the right bank, hidden under the rear most intake manifold pipe.

the circular one in the engine tin nextto the distributor is the oil pressure switch.
it goes straight into the engine block just near where the oil cooler is.

i'm sure you have spotted the thermo switch connection to the cold start valve.
the thermoswitch is tucked under the plenum near the front right hand intake runner.

the CHT is a tricky thing to get out.
i'll try and find the page in the manual and post it up for you.

and i'm trying to remember where i got my factory manuals from as a download.
it was 10 years ago but i have a vague memory it might have been from the wonderful 914/6 GT website a guy folks in the USA must know. i think it was there. i could try and go have a look again. it was some kind of 914 resources site i found.
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Van B
post Nov 8 2021, 07:49 PM
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I was hoping you wouldn’t tell me that was the CHT sensor lol. I traced that wire while I was warming up the engine… manifold definitely has to come off.

My thermo switch was missing the wire clip for the Bosch connector. So I robbed the one off the CSV and used safety wire for the CSV since I can reach it. I would love to know where I could buy those wire clips. My AFM is missing it’s large clip too. The safety wire works better than Ziptyes but it’s not quite snug enough.
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wonkipop
post Nov 8 2021, 08:07 PM
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there is a technique for getting it out.

and the check values as well.


good luck (it is a bugger to get it out but it can be done),
it might have been in there for a long time - go easy with it.
you can test it without getting it out.

some other members here might want to offer some advice before you go hammer and tongs at it.

Attached Image Attached Image


as far as i know there is not much you can do about temp sensor ! in the AFM unit.
its part of the unit.
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Van B
post Nov 8 2021, 08:25 PM
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Wonki, I will pay you money for that manual! Give me that manual lol!

Also, thanks by the way. I’ll chop up a socket and see if I can make that tool.

IMO all these basic sensor are eligible for the modern day remove/replace strategy. They’ve served their time and have earned a retirement. I’ll test it after I take it out and if it’s still good, it earns a place in the spares box!
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wonkipop
post Nov 8 2021, 08:47 PM
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here you are Van,
found it for you.

http://p914-6info.net/Manuals.htm

big downloads.
but you can pull it down section by section.


fabulous website.
thanks very much to the person who runs it.
you don't have to pay me, buy the bloke with the website a beer for me (IMG:style_emoticons/default/beerchug.gif)
i assume he lives in the USA somewhere. (IMG:style_emoticons/default/smilie_pokal.gif)


i'm looking forward to your discoveries re the warm up phase.
you will get to them before me.
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