COLD START PROBLEM, Fuel Injection? Options

[Steve H]

Help Needed and Appreciated:
I have a 1974 1.8L completely stock 914 with L-JET fuel injection. Once started and warmed, it runs like the day it came off the showroom floor. It idles at about 800 rpms and then pulls all the way up to the top without ever a hesitation. It will run all day at 75-80 mph. The problem: The Cold Start. If attempting to start properly, fuel pump is allowed to engage in but when the key is turned to start, the starter will instantly turn over but the engine will not start up. It usually takes 8 or 9 tries like this until I goose the throttle and it finally starts. Once it is allowed to warm up, it will restart instantly until the next time when it has been allowed to sit for a day or two. I even gave up and installed a NOS, cold start valve this week but no luck. Any help would be appreciated. Thanks

[barefoot]

Could you verify if the cold start valve is actually spraying fuel in cold start conditions ?
pull it out and insert into a jar & try the start.

[930cabman]

Could you verify if the cold start valve is actually spraying fuel in cold start conditions ?
pull it out and insert into a jar & try the start.

I cannot recall, but what triggers the Cold Start Valve?

[Freezin 914]

Had a very similar issue check the cylinder head temp sensor.

[Rand]

What are your ambient air temps? The cold start valve is activated by a thermostatic switch, only below very cold temperatures. Your profile says you are in LA, so don't waste time pulling the CSV - it's not going to be spraying anyway.

[wonkipop]

Could you verify if the cold start valve is actually spraying fuel in cold start conditions ?
pull it out and insert into a jar & try the start.

I cannot recall, but what triggers the Cold Start Valve?

in part it is controlled i think by a thermo time switch - but that might be more what closes it off.
this is located near the cold start valve under the intake runner closest.
i'm not 100% on this as i have not had a problem with my cold start valve.
but i think this switch controls at least the duration of time the cold start valve stays open for. There is a cold start relay somewhere in the system as well, when you crank the engine the cold start valve is activatedL I guess the thermo switch shuts the valve after a certain amount of time. L Jet gurus can correct me, they will know how it all really works together as a sequence.

the cylinder head temp sensor also has a part to play.

from what you are describing it sounds like the cold start valve is maybe not activating.

i have an old VW L jet manual that gives me detailed trouble shooting guides.
and i use the factory manual to give me the proceedures for how to remove some of these parts without breaking them. The trouble shooting sequence is to first test the valve is spraying when you crank the engine cold (with the valve out). you move to the other items one at a time. the thermo switch, the cylinder heat temp sensor and the final mention is the cold start relay. along the way you are checking the wires.

I'm not even sure where the cold start relay is located.
i have never had to do it. someone who has will have their heads around it.

[wonkipop]

What are your ambient air temps? The cold start valve is activated by a thermostatic switch, only below very cold temperatures. Your profile says you are in LA, so don't waste time pulling the CSV - it's not going to be spraying anyway.

i've read lots of slightly confusing information on this.
regarding when and when it does not switch in and for how long.

i could be wrong but from some manuals and sources it seems that temps lower than 50 deg F the cold start valve will open for the full time - around/approx 20 seconds.
at temps above 104 deg F it should not open at all. it could be that in between those two temp limits it opens but for shorter amounts of time related to temp.

If that was so, even in LA it could be kicking in on a cold start.

i know mine does and i live in aus. down south in melbourne where its coldish in winter and very warm in summer. not too far different to LA.
when i first recommissioned the car, i could get the engine to run off the cold start valve for 10-20 seconds before it died. the injectors themselves were stuffed. but at least i knew the cold start valve (injector) worked.

[Rand]

Yes, you could be wrong (me too), but no way would it be 104. I never even run a CSV and had no trouble in Seattle winters. I was thinking it was under 40, but I've also read freezing. I guess we'll have to wait for someone to quote from a manual.

[Rand]

As many will tell you around here, this is the DJet bible:
https://members.rennlist.com/pbanders/djetfund.htm

Brad says 32 degrees. I know the OP is running Ljet, but don't see why the cold start temp would be so different.

The CSV should never activate in LA, certainly not right now. A bad CHT is way more likely to cause trouble than a CSV.

[wonkipop]

Yes, you could be wrong (me too), but no way would it be 104. I never even run a CSV and had no trouble in Seattle winters. I was thinking it was under 40, but I've also read freezing. I guess we'll have to wait for someone to quote from a manual.

i'm digging into my manuals a bit now.
like i say i haven't had to go into it in my car.
was something i glanced across a while back doing recommission.

I found this much in my VW L Jetronic manual.
it points to 3 different thermoswitches that could be installed in VWS running L jet.
with three different ranges of operation each with different part #s/

Test chart values.
Thermo-Time Switch

0 280 130 219 (bosch part #s)
0 ohm at 50F infinite ohm at 68F

0 280 130 221
0 ohm at 56F infinite ohm at 74F

0 280 130 214
0 ohm at 86F infinite ohm at 104F

and the parts number for the thermoswitch in 914 parts manual
is
MY 74 before ECO 037 521 = 022 906 163 (vw part numbers)
MY 75 from ECO 037 522 = 043 906 163

and i found in factory manual test check for thermoswitch.
Disconnect plug from cold start valve.
connect text buzzer or ohmmeter between both
both contacts must make connection when temp is below 59 F
when eng temp is above 59 F, buzzer or ohmmeter must indicate an interruption in circuit.

the L jet manual seems to imply the cold start valve operates over a 18 deg range?
in three different types of ranges corresponding to different thermoswitches fitted?
someone who knows a lot more can interpret that test chart data above. and say what it means.
i had some how remembered that 50F lower temp and 104 F upper temp from a couple of years ago but had forgotten it was a total range over three different types of thermoswitch.


would have to do a vw part # to bosch part # search to figure out if the part number listed for 914s corresponds to any/which of bosch part #s from VW L jet workshop manual.

but i think i am right in saying the thermoswitch maybe controls the duration of time the cold start valve opens for and at what temp range?

i reckon mine was working for about 10-20 seconds running the engine on its own when the amb temp here was somewhere between 10 deg C and 15 deg C (50 -59 deg F).

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[Rand]

Dude. The CSV is not his problem.

[wonkipop]

Dude. The CSV is not his problem.

talking about the thermo switch.

not saying your wrong with the cht.

just remarking i don't think the thermoswitch is a kind of black and white on and off thing at a set temp. think it works across a range. so its got something to do with cold start on cooler colder days. if you look at the mid range ts its cutting out at 74F which is warmish.

[Rand]

I wish I knew which wonkipop was trying to twist my oober wundr\

Ugh, can we please help now.

[wonkipop]

I wish I knew which wonkipop was trying to twist my oober wundr\

Ugh, can we please help now.

am trying to help.

i got a diag chart.

and the cht is on it just like you say.

but there are a couple of other things too.

basically your saying the csv is irrelevant in california and does not come into play.
i don't disagree with you.

i got a trouble shoot chart says to check the csv, and to fully check thats working, you check the thermoswitch too. thats all.


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if steve is goosing the throttle to start the car.
and thats an americanism.
but i take that to mean holding the throttle open not just stabbing the pedal.
its not getting enough air at start up from the aux air valve maybe?
and your bypassing that with the partly opened throttle.

if it were me i might add that to the checklist and just see if its working.
a stuck closed a a v won't affect a hot/warm start.

[Steve H]

Thank you all so very much for your time and willingness to pass along appropriate strategies to check for the source of the problem. I'll start back on it this next weekend and see if I can get dialed in. Thanks again all for your help. Regards,