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Fuel injection minimum voltage requirements - LJET air cooled
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rkoss
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PostPosted: Sun Dec 13, 2020 11:50 am    Post subject: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

Anyone know the minimum voltage reqs for the L-Jet FI system (air cooled)? Daily driver that starts strong in warm weather but still have summer thick 20W50 in engine and had a big cold snap kick in. Starter is cranking (slower than normal but as expected in -18*C). Dash voltmeter is showing my battery hitting 10.2V during cranking and I am not getting any ignition at all. Wondering if the voltage supply is dropping too low for FI system to function properly or if its just simply cranking too slowly. Too cold to stand behind her and start troubleshooting FI system today. Thought Id ask the Samba team first. Thanks
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sjbartnik
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PostPosted: Sun Dec 13, 2020 12:45 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

Below about 10.6v [EDIT: that was a brain fart/typo, I meant to say around 9.6v] is when the electronics of the L-Jet ECU won't work.

Change your oil; shouldn't be using 20W-50 in an air-cooled engine at all unless it's just super worn out.

Once thing that can help in the cold weather if it's cranking slowly is to push the clutch pedal in when cranking. That way you are only cranking the engine and not the transmission as well - the transmission oil when cold and thick can really drag down the engine cranking speed.

That said, I would guess that your battery is marginal, or you have a lot of time ahead to spend cleaning up your battery terminals, transaxle ground strap, etc.

Battery should read 12.6v with no load on it if it's fully charged.
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Last edited by sjbartnik on Sun Dec 13, 2020 1:15 pm; edited 1 time in total
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Vanagon Nut
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PostPosted: Sun Dec 13, 2020 1:01 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

I'd think a lack of spark or poor spark due to starter pulling majority of voltage is the issue. Existing inefficiencies like poor grounds, dirty plugs, poor wires etc. would be exacerbated by cold temps, slow turning engine, low voltage to ignition parts.

I don't see a voltage spec on 'check injectors' page in Bentley, just a test light procedure. I know it's cold out but with a trustworthy helper or remote starter switch.....

as a guess, if the light flickers, there's enough voltage getting to the injectors; they should be able to open with less than 12 volts.

If you smell fuel at tail pipe after attempting a start, that would likely suggest that the injectors are pulsing open.

Other items like the aux air valve could be affected by voltage being too low. This might cause a poor fuel mix.


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Wildthings
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PostPosted: Sun Dec 13, 2020 9:54 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

Could be your ignition coil getting old and weak.

Yes use something besides 20w50 oil, I am presently running Mobile 1 0w40 European Car Formula oil and at this point am quite happy with it.
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rkoss
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PostPosted: Mon Dec 14, 2020 12:14 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

Thanks all. Yes I run 10w40 for winter but we went from +15* to -18* in two days so I didn't get a chance to change it. Clutch always goes.in on cold mornings Smile

All electronics have been replaced over the years. Mostly last year as I did a major overhaul on the system. New grounds and a new engine wiring harness with lots of shiny new metals connections etc. Voltage gets to the appliances well, I've checked with the multi meter and everything is perfectly in spec Smile

Injectors are firing as I smell gas and hear them clicking. Coil is new and tests well. Spark plugs are under 20k kms and not fouled. Ignition is all.under 20k kms with pertronix electronic ignition (I've been running these for years).

I think it's coming down to just turning to slow with thick oil. I'm still surprised that I'm not getting any ignition sounds at all though. Not a pop or attempt or nothing. Starts up no problem when temps are back in the positives though... Battery stays stronger above 10.8V when cranking in warmth though. I'm dropping as low as 10.2V on extended cranks in the cold and thought that may be stopping the ECU or AFM from working right.

Editing after attempt just now - unplugs temp 2 sensor, flashes right up no problem! Runs rough and rich, plugs temp 2 back in while udling, smooths out to perfect idle again. Hmmm. Guess I'm testing my thermotime and aar next eh? Brand new temp 2 sensor 2 months ago, testing good on resistance today.
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MarkWard
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PostPosted: Mon Dec 14, 2020 12:46 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

Points or Electronic distributor?
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PostPosted: Mon Dec 14, 2020 7:00 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

I long ago went from having a coil with an internal ballast resister to one with an external resister and then using the spare male spade on the starter solenoid to bypass it during starting. This is how all of the cars and trucks I owned before I bought a classic VW were wired. Pretty much you would be running a 9 volt coil and hitting it with full battery voltage during startup (in your case 10.2V), while not over powering it at other times as the ballast resister knock the voltage down to the 9V+/- range.
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AndyBees
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PostPosted: Mon Dec 14, 2020 7:49 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

Grounding of the Temp II sensor was an issue I experienced several times with my 83 Air-cool. In '96, we were south of Anchorage, Alaska just driving along and the engine suddenly went to idle without any warning.... the Temp II sensor had backed out of the threads in the head.

Also, the Cold Start Injector is quite important on the Air-cool engine!
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PostPosted: Tue Dec 15, 2020 1:11 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

MarkWard wrote:
Points or Electronic distributor?


Electronic... Pertonix.
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rkoss
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PostPosted: Tue Dec 15, 2020 1:14 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

Wildthings wrote:
I long ago went from having a coil with an internal ballast resister to one with an external resister and then using the spare male spade on the starter solenoid to bypass it during starting. This is how all of the cars and trucks I owned before I bought a classic VW were wired. Pretty much you would be running a 9 volt coil and hitting it with full battery voltage during startup (in your case 10.2V), while not over powering it at other times as the ballast resister knock the voltage down to the 9V+/- range.


I dont think I understand how that could be the issue here? My battery is holding 12.4-12.6 when engines off (thats the residual voltage after sitting for hours, not the excited voltage from freshly turning off engine/charge). First position to ignition holds voltage, maybe drops .1-.2V. Its only during cranking that I am dropping to 10.6-10.4V. And again, daily driver for past 11 years. Literally every day. I dont see how all of a sudden the coil becomes an issue in a stock setup. Or why I would want to make this change...
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PostPosted: Tue Dec 15, 2020 1:21 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

AndyBees wrote:
Grounding of the Temp II sensor was an issue I experienced several times with my 83 Air-cool. In '96, we were south of Anchorage, Alaska just driving along and the engine suddenly went to idle without any warning.... the Temp II sensor had backed out of the threads in the head.

Also, the Cold Start Injector is quite important on the Air-cool engine!


Ya that T2 sensor... man oh man. Its given me headaches!! Same sort of issue earlier this summer but the wire snapped off of it at the top. The wire sheath was still in tact and holding it onto the sensor so I didnt immediately recognize it until the multi meter came out. Van just stalled while travelling down the road. Took a few hours to figure that out and I ended up just grounding out the circuit to get it started and limped home. I replaced that T2 a few months ago and its still all in good shape. Good contact in the head, wires all good. Multi meter tests all checking out fine.

So, whats not working in the FI system when everything else is up to snuff and it just wont start in cold weather unless T2 sensor is unplugged? When T2 is unplugged completely (not grounded out but disconnected and harness left hanging), what is the ECU doing... flooding or leaning the start? And when its connected and reading low level resitance (cold), it should be telling ECU to flood right? Even with the battery voltage low from heavy use trying to crank over, it fired right up the second I unplugged T2. Like, instant start! Idled fast, smelt righ. Plugged the T2 back in and idle dropped right back down to normal and everything runs as normal. Warm starts, no problem.
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MarkWard
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PostPosted: Tue Dec 15, 2020 1:21 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

We had an air cooled vanagon that we installed a pertronix in for the owner along with their coil. Coil died in less than a couple years. It actually died at the shop during an unrelated repair.

Its easy enough to try a different coil. In my experience, it is normal for the battery voltage to drop to your measured values. Thats likely not the problem.

You can remove the distributor connected key on and turn it by hand and it should fire the coil.
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PostPosted: Tue Dec 15, 2020 1:46 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

MarkWard wrote:
We had an air cooled vanagon that we installed a pertronix in for the owner along with their coil. Coil died in less than a couple years. It actually died at the shop during an unrelated repair.

Its easy enough to try a different coil. In my experience, it is normal for the battery voltage to drop to your measured values. Thats likely not the problem.

You can remove the distributor connected key on and turn it by hand and it should fire the coil.


Coils good. Starts and runs no problem when temps are warmer, engines warmed up, or T2 is unplugged when really cold.

Ya I found the voltages drop to be regular as well but was left scratching my head on how it went from starting perfectly fine to struggling with a little temperature drop. Now I know its not voltage related issues for the FI and just a single component acting up...
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Wildthings
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PostPosted: Tue Dec 15, 2020 3:49 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

rkoss wrote:
Wildthings wrote:
I long ago went from having a coil with an internal ballast resister to one with an external resister and then using the spare male spade on the starter solenoid to bypass it during starting. This is how all of the cars and trucks I owned before I bought a classic VW were wired. Pretty much you would be running a 9 volt coil and hitting it with full battery voltage during startup (in your case 10.2V), while not over powering it at other times as the ballast resister knock the voltage down to the 9V+/- range.


I dont think I understand how that could be the issue here? My battery is holding 12.4-12.6 when engines off (thats the residual voltage after sitting for hours, not the excited voltage from freshly turning off engine/charge). First position to ignition holds voltage, maybe drops .1-.2V. Its only during cranking that I am dropping to 10.6-10.4V. And again, daily driver for past 11 years. Literally every day. I dont see how all of a sudden the coil becomes an issue in a stock setup. Or why I would want to make this change...


Coils some times fail and often the first symptom is failing to provide a spark while the voltage is lowered while cranking. To have a coil suddenly get weak after 11 years of daily driving would not be unexpected. The reason to make the change was that it was an industry accepted way to help an engine start during colder weather, that VW saved a few pennies by not doing it this way doesn't say much for them in my opinion.
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rkoss
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PostPosted: Tue Dec 15, 2020 4:55 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

Wildthings wrote:
rkoss wrote:
Wildthings wrote:
I long ago went from having a coil with an internal ballast resister to one with an external resister and then using the spare male spade on the starter solenoid to bypass it during starting. This is how all of the cars and trucks I owned before I bought a classic VW were wired. Pretty much you would be running a 9 volt coil and hitting it with full battery voltage during startup (in your case 10.2V), while not over powering it at other times as the ballast resister knock the voltage down to the 9V+/- range.


I dont think I understand how that could be the issue here? My battery is holding 12.4-12.6 when engines off (thats the residual voltage after sitting for hours, not the excited voltage from freshly turning off engine/charge). First position to ignition holds voltage, maybe drops .1-.2V. Its only during cranking that I am dropping to 10.6-10.4V. And again, daily driver for past 11 years. Literally every day. I dont see how all of a sudden the coil becomes an issue in a stock setup. Or why I would want to make this change...


Coils some times fail and often the first symptom is failing to provide a spark while the voltage is lowered while cranking. To have a coil suddenly get weak after 11 years of daily driving would not be unexpected. The reason to make the change was that it was an industry accepted way to help an engine start during colder weather, that VW saved a few pennies by not doing it this way doesn't say much for them in my opinion.


Thanks for the explanation. The coil is less than a year old (Bosch german blue coil). I did not realize that the performance varied with temperature.

Regardless, it doesnt appear to be coil related as it starts great in cold temps with T2 disconnected. So the original problem has changed from low voltage not allowing ECU to function to only starting in extreme cold with T2 unplugged. New fun for me! haha
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PostPosted: Tue Dec 15, 2020 5:00 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

So you are adding fuel with the sensor disconnected. Have you visually verified the cold start valve is working?
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PostPosted: Fri Dec 03, 2021 6:43 pm    Post subject: Re: Fuel injection minimum voltage requirements - LJET air cooled Reply with quote

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