Bosch L-Jetronic cold start issue - Alfa Romeo Bulletin Board & Forums
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post #1 of 9 (permalink) Old 08-17-2019, 02:47 AM Thread Starter
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Bosch L-Jetronic cold start issue

1984 Spider with Bosch L-Jetronic injection. Basically anything from 1982 to 1987 is the same, I think.

Cold start: starts well but dies after a few seconds unless I keep revs. After a minute or two the engine is able to idle without my help. Hot start fine.
My suspect is oxygen sensor, because my car is fitted with 1-wire sensor (without heating).
However, it seems like the problem started to appear once I've removed catalyst. It was all rotten inside and local rules don't require catalyst on such old cars.

I'd like to hear a confirmation that non-heated oxygen sensor could cause this problem before I fork out 100$ for a new one.
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post #2 of 9 (permalink) Old 08-17-2019, 12:08 PM
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You can find a good write-up in the FAQ section on L-Jet issues. It could be cold start valve not spraying enough fuel, addition air valve stuck closed, not providing extra air, the thermotime switch, or it could be coolant sensors, one for ignition ECU and one for FI ECU.

Thats all I can think of off the top of my head...

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74 TR6
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post #3 of 9 (permalink) Old 08-17-2019, 03:43 PM
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Click the link in my signature to a page of info about the L-jet system in our cars.

I doubt the O2 sensor is the source of your car's problem. More likely is a non-functional AAV (Auxiliary Air Valve). The AAV is supposed to open to admit some extra air when cold. This increases the cold idle speed. A good work around is to install a manual AAV - basically a cable operated heater valve. You just have to remember that the manual AAV is self-closing (you have to close it yourself...). There is info about this in the Spider FAQ thread. BTW, it is best to not touch the throttle when starting an L-jet engine. Thus the importance of the AAV. At idle, the Throttle Position Switch tells the computer the throttle is at idle so it follows its programmed mixture settings. Once the throttle is open the computer tries to use the O2 sensor to adjust the mixture. But the non-heated (one wire) O2 sensor is usually not hot enough at idle for the O2 sensor to send a valid signal.

The Cold Start System consists of the Thermo Time Switch (TTS) and the Cold Start Injector (CSI). The CSI squirts a little extra fuel and is controlled by the TTS (not under computer control). The TTS sends power to the CSI for a few seconds (longer when cold, not at all when hot). A faulty TTS can either prevent the CSI from squirting when it should or allow to squirt when it should not. Info about this is in the Spider L-jet Diagnosis page.
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Last edited by ghnl; 08-17-2019 at 03:47 PM.
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post #4 of 9 (permalink) Old 08-18-2019, 07:09 AM Thread Starter
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Thanks, will check both AAV and TTS.
Only last night I came around a working link to your brochure. Been trying to open your file for the past 2 months. Most of the links on this website are outdated. This is the link that worked for me: https://www.hpsimotorsports.com/l-jetronic--spider-
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post #5 of 9 (permalink) Old 08-19-2019, 01:07 AM
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Quote:
Originally Posted by levp View Post
Thanks, will check both AAV and TTS.
Only last night I came around a working link to your brochure. Been trying to open your file for the past 2 months. Most of the links on this website are outdated. This is the link that worked for me: https://www.hpsimotorsports.com/l-jetronic--spider-
yep, that is exactly the link in Eric's signature.
I saved it as a pdf on my desktop.

Apart from AAV/TTS checks, I'd also check the CTS, not just the ohms, but maybe remove it and clean the probe that sits in the water flow.
The Coolant temp. sensor is a critical componant that has to work correctly.

Dom - Alfa Spider 1990 S4 - formerly: Alfa 101 Sprint, 2600 Sprint, Montreal - family classics: Jensen Interceptor II, '58 Hooper RR Silver Cloud I, Shadow II, '60 Corvette.
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post #6 of 9 (permalink) Old 08-20-2019, 02:21 AM Thread Starter
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Ok, after reading it seems like the correct term should be "warm up issues". Will investigate further but any ideas are welcome anyway.
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post #7 of 9 (permalink) Old 08-28-2019, 03:21 AM Thread Starter
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I've checked both CTS and TTS and they appear to be fine according to ohmeter readings.
I haven't checked the AAV but I don't think it has much importance with temperatures over +30C.
So it has to be either rich mixture or malfunctioning O2 sensor.
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post #8 of 9 (permalink) Old Yesterday, 02:16 PM Thread Starter
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Gents, another update and request for collective mind:
I've turned the revs up a little via the regulator by the throttle, so usually once you start the engine keeps on working and doesn't die. Well, maybe once, but then it starts right away and doesn't seem to die once again.

Now the engine revs at around 900 rpm when cold, but when it gets to working temperature, the revs go up to 1200 rpm. Totally opposite of how it is supposed to be.

What do I do to fix it?
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post #9 of 9 (permalink) Old Yesterday, 02:28 PM
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Most likely your AAV is not operating properly. Remove and test per the L-jet article.

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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