///// How long will a mark iv jetta run without the alternator working? ////

Hi All,

I drive a lot at night and was wondering how long the jetta can run If the alternator stops working (charging)

Assume everything is stock and driving at night.

Also, I know on older Cummins 6bt engines the fuel solenoid can be removed and the engine can be turned off using a pull cable .... thus eliminating a forced shutdown when battery power gets too low because the fuel solenoid snaps shut ....

Is there a similar modification that it can be done on the Jetta injection pump?

On the flip side I suppose if power gets so low the computer shuts off the engine will shut off because of that also..

So how long time wise can the car run without a charging alternator?

Thanks in advance for any and all help.

Andrew

One could disable the alternator and measure the draw on the battery. Lights pull more than the computer.

Eliminating the c/o solenoid by removing the plunger and disconnecting the wire would save a tiny bit. No manual control required, the ECU would kill the engine.

well your low beam are 55 watt. so just the low beam draw 9-10 amps. tail lights about 3. I presume the computer would work to around 9 volts. If you dont use high beam, radio, blower motor, or any other non essential. theoretically, an hour maybe. if it failed with the car running. City or highway would have an impact also. So many variables to consider. I may be close or way the heck off.
As suggested . bring a jump pack (or battery) disconnect wires from alt and drive. post your findings.
I had a gasser run an hour with a failed alt. luckilly a shop charged me up for free so i could get home. figured out what i needed to change it and brought it to the parts store. Did it in the lot. Had 3 water pumps from them start leaking within a week. got really good at changing them in the lot. You get some strange looks. And some knowing ones.

bad idea to try it, the EGU controls things like boost and fuel map. you WILL be driving with out even a limp mode to keep you safe.
but ti answer your question, i would have to assume its like 15 minutes, maybe 20 if its a new battery. they are fairly beefy.

It will go for several hours if you can disable the headlights (can't do that at night, obviously). A slight pull on the handbrake will turn them off w/o applying any rear brake. Turn off radio, cabin blower fan, etc. The battery is large and if in good condition will run the ECU a long time. Headlights would be the big draw and in an emergency night drive in remote areas you could run with just the DRL on (no marker or tail lights).
I've had to do similar on a trip with my old suburban pulling a trailer back from Canada. Complete alternator failure on a remote stretch 65 miles from nearest "town" and most cell signal. And it was cold, but had been up ice fishing so had cold weather gear available on board. Turned off heater fan, unplugged trailer lights, no radio, just ran with the DRL low beams. As long as the battery had enough power to run the electric fuel pump and ECU we were fine. Lights got pretty dim but kept running for over an hour and a half on a lot less battery than the TDI.
W/o the electric fuel pump in the ALH I think three or four hours might be possible depending on how you can manage power use. Maybe changing out to LED headlights could extend that range?

a tow home would be better than risking a night drive with a unsafe and illegal setup.
did you know that in some states you can get a reckless driving violation of driving like that with no lights on!

point is, a tow home is usually in the $100 range, big deal, much cheaper than the damage done by hitting a dog, deer, pothole you could not see, etc............

and several hours? probably more like several days. If you were to theoretically run a TDI with just enough amps to run the ECU and some how disable everything else!

Long in time or in distance?

If you need to make a short run and can do it at or above the speed limit, I'd say go for it. However, if there is some sort of incident along the way that causes a traffic hold-up, well, you'll probably be screwed.

As for time, test it. Start the engine and let idle with the headlights on as if you were out on the road............. get back to us with the test results!

Side note: About five years ago (in my Vanagon with ALH engine, no DRLs), I was a bit southeast of Ashville, NC, about 4 hours from home and noticed the Battery light flicker a few times. Then about 15 minutes later, it began to flicker more and more often. I noticed my one digital volt meter would indicate a voltage drop.......... So, rather than be stranded and in a location that no help from a guru could be summoned on a short notice. I purchased an extra battery and headed home. When I hit I-40 toward Knoxville, TN, it was about an hour before one would normally turn on the headlights. So, I drove without headlights until I was afraid it was too dangerous. The ALT did do some charging occasionally the entire distance home. Anyway, I was about 45 minutes from home when the engine began to act strange. I stopped and installed the new battery and went on home.

Hi

Thanks for all the information and input... it's good for me to have a rough idea on what can be done in the jetta to make home or to safety ....

An alternator issue did happen to me whilr using my girlfriend's Corolla and that made me wonder how a similar issue would work in my diesel car..

Thanks

I have driven without the serpentine belt a couple of times, both instances where the idler pulley failed me going on a long stretch of highway, coincidentally the same Dallas to Houston highway. With DRLs on, you can get at least 1.5 hours. I have the standard battery for TDIs that comes from the dealer.

You can easily disable the DRLs on a Mk4 by temporarily disconnecting the headlight switch or for a permanent disabling you can bend one of the pins on the switch. That will get you even longer time which I did not do because I didn't think of it.

The symptoms of a battery that is too low to keep the car running will show up on the dash with certain lights appearing as the ECU starts to disable systems. ABS is usallly first followed by the EPC light... and you might as well plan your exit to a safe spot. It will soon just start to lose power and then die.

Back in 2014 I think it was I drove from Refrew, Ontario to Maxwell, Ontario (about 390 km or about 4.5 hrs) on battery power after the alternator pulley decided to separate. I drove with the e-brake pulled one click to disable the daytime running lights for most of the way (the annoying chime goes away after a few minutes of driving but comes back when you stop for a stop sign or red light). I drove a few hours in the dark and used only the DRL's and tried to use the driver in front of me as much as possible. Everything stopped working, the speedo stopped, odometer, even the battery light on the dash. I eventually gave up when the PCM had no power and the engine sounded like it was pinging on hills.

On the return trip home with a fully charged battery it made it the entire 6 hour drive home and still had enough juice to start the car when I got home. Lights are definitely the limiting factor.

If its the belt that goes dead, you can rig up some shoe laces, it actually works, not well, but enough

If you’re really worried about it you could carry a spare alternator, a spare belt, and some tools.

Or, put a new alternator in and keep your current one as the spare.

Folks,

Several years ago I bought a 2002 Golf TDI that had a bad alternator. I knew this when I bought the car. When I picked the car up, I brought two batteries with me (out of a couple of my other TDIs) and my tools. I was driving in the daytime but the daytime running lights were on. I didn't use the radio and turned the blower switch off. The first battery lasted about an hour before the cluster started going crazy: warning lights coming on, speedometer/tachometer jumping around/stopping. I pulled over, put the other battery in and made it home just fine (I only had about 30 minutes until I would be home).

Eric

When I made the drive home with the suburban when I was finally able to meet up with some assistance they brought me another battery which sat on the passenger floor and jumper cables out the window hooked up to the dying battery. Made it the rest of the way home to the garage. When it's remote area, dark, below -0F and in the middle of nowhere you have to do what you can.

Next time don't connect the good battery to the bad. Disconnect the neg cable from the deader battery. You made it but the good one was dumping power into the bad one along with running the car.

Mike_04GolfTDI said:

If you’re really worried about it you could carry a spare alternator, a spare belt, and some tools.

Or, put a new alternator in and keep your current one as the spare.

Click to expand...

Where is the fun in that? Livin on the edge is a lot more fun.

KLXD said:

Next time don't connect the good battery to the bad. Disconnect the neg cable from the deader battery. You made it but the good one was dumping power into the bad one along with running the car.

Click to expand...

The last leg of the trip with the "extra" battery connected was only about 15 miles and was a hurried fix to get home. But, yes, aware that it would have been advisable to take the "dead" battery out of the system.

Hi

Thanks for the great stories and advice on how to make it or try to make it home with a failing electrical system.

Here are some things I thought of as a result of some of the postings ...

1) before even thinking about being dead in the water as a result of a failed alternator I did have most of my lights changed out to LEDs ....

I think the headlights are only 35 watts each as far as energy consumption and they are really bright so that's good .

I don't know the power consumption of the other smaller LED bulbs but I do know they are much brighter than stock and I just being led and nature that's good so i guess they use less electricity to boot...

For what it's worth, I did not put resistors in line to slow down the hyper flashing because resisters would simply use more power in and of themselves ...

Speaking of resistors ... I guess it doesn't matter how dimming down the inside gauge lights does it since the dimmer switch is simply a variable resistor and if you burn up power in resistance vs light output you sre still using electricity or are you overall saving electricity by using the dimmer switch and dimming the lights?

2) since I was running LED headlights and worried about the reduced voltage of the daytime running lights being compatible with them , i took my switch and bent the tab to disable the daytime running lights ....

After reading about using the daytime running lights as actual headlights in the event of a real problem electrically I did look up the specs on my LED headlights and apparently they will run down to 9 volts ...

Armed with that new knowledge I did go out and get another headlight switch assembly from a junk yard so if something happens bad at night I can at least I can at least use daytime running lights to run my LEDs so I can see to drive home while saving on electrical consumption by not having all my other lights running also...

Just a thought I thought of now .... how many volts go to our headlights when in daylight running mode is that at least 9 volts? If not I guess my LEDs would be useless as daytime running lights for headlights in an emergency...

3) I like the idea of carrying a booster pack for extra energy in case you need to really make it just a little bit further. ... theoretically I know a full size battery as a backup would be better but that's an awful lot of weight to carry around ... sadly I'm trying for maximum fuel economy also and even thought about ditching the spare tire but I have not been able to bring myself to that just yet ....

4) I guess it goes without saying to minimize other electrical usage in the event of an alternator outage. .. no ac ... no radio ... off for blower fan ... unplug anything from the cigarette lighter etc . .

5) carrying around an extra belt might not be such a bad idea but I really wouldn't look forward to trying to do that in the middle of the night out in the middle of nowhere although I suppose I could drive to somewhere safe and do it there....

Andrew

Andy, you're not alone in misunderstanding how resistors affect power consumption.
A resistor in series with the load will reduce the amperage or draw of the circuit.
A resistor in parallel with the load will increase the amperage or draw of the circuit.

flee said:

Andy, you're not alone in misunderstanding how resistors affect power consumption.
A resistor in series with the load will reduce the amperage or draw of the circuit.
A resistor in parallel with the load will increase the amperage or draw of the circuit.

Click to expand...

Hi

So does using the dimmer for the interior gauges effectively cause power usage to decrease overall ..... i dont know how its wired up to the lights since it just plugs into the wire harness.

Thanks

Yes, probably.
A dumb dimmer will reduce the current going through the lamps by increasing the
resistance and a 'smart' dimmer will reduce the duty cycle and thus the current, too.