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Volkswagen Jetta, Golf, GTI: 1985-1992 (A2) 1991 vw jetta won't start!!


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Last Post: Apr 10, 2009 11:11 PM Last Post By: FKH161
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Mar 23, 2009 7:44 AM   in response to: FKH161 in response to: FKH161
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hey just a quick question your hall sensor on the harnss plug side, are these wires suppose to get power and how much? cause im not getting any?
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Mar 23, 2009 8:47 AM   in response to: stevo442 in response to: stevo442
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another silly question i get power with the key ON to all 4 wires to the coil is this normal?? there 2 black and 2 red black
FKH161

Posts: 7,634
Registered: 12/29/05
Re: 1991 vw jetta won't start!!
Posted: Mar 23, 2009 10:23 AM   in response to: stevo442 in response to: stevo442
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The hall sensor plug has 3 wires:

- the outer 2, one is power (bat volts) and the other is
ground
- the middle is the spark trigger for the ICM

Yes, key ON, all those wires on the coil will have power. Not
until the engine is running will the "-" side of the coil
blink (testlight will flicker).
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Mar 23, 2009 11:00 AM   in response to: FKH161 in response to: FKH161
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k thx, im gonna check and see if im getting power from the icm and if it stops somewhere from there to the sensors/grounds cause if i remember i had power there, ill have to check again ill inform you when i get it running thx

stevo
FKH161

Posts: 7,634
Registered: 12/29/05
Re: 1991 vw jetta won't start!!
Posted: Mar 23, 2009 11:24 AM   in response to: stevo442 in response to: stevo442
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Hall sensor gets power from ECM (pin 8 according to wiring diagram).

The center wire (spark trigger as I call it) first goes to
ECM and then the ECM "triggers" the ICM... sorry about the
ill worded last reply.
tcovenant2000

Posts: 1,778
Registered: 12/09/03
Re: 1991 vw jetta won't start!!
Posted: Mar 23, 2009 2:29 PM   in response to: FKH161 in response to: FKH161
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Just to help clarify:

The coil + gets 12V from wire #15 (switched power through ignition). The coil is simply that. A long piece of wire coiled up. The - side of the coil will read 12V because the voltage is coming through the wire from the + side. The only time you get anything other than 12V on the - side is when the - side is grounded by the ECU. The ECU knows to ground the - of the coil because it receives a signal from the hall sensor telling it that the rotor is turning and it's time to apply ground to the coil.
The hall sensor is just a device that senses a magnet in the rotor assy. When the magnet gets close, the hall sensor conducts and sends voltage to the ECU. The ECU looks at a couple of things and decides how the timing should be and then grounds the - of the coil.

Hope that helps a bit.

Thomas
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Mar 24, 2009 12:02 PM   in response to: tcovenant2000 in response to: tcovenant2000
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k thx alot im just waiting for some time in the shop with it, im gussing it must be a bad ground soemwhere i know my knock sensor sheild is busted but i don't think that would cause it drom not starting? im hoping its just a ground it's a braided wire from pin #7 from the ecu (computer). ill let you know hopefully soon lol
FKH161

Posts: 7,634
Registered: 12/29/05
Re: 1991 vw jetta won't start!!
Posted: Mar 24, 2009 1:17 PM   in response to: stevo442 in response to: stevo442
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Make sure that the main ground for the ECM (Pin #19) is
attached to either the side of the intake manifold or on
the top stud of the side coolant flange... should be a brown
and black wire.

The ignition module main ground (pin #2) is at the battery
negative clamp... brown/white wire.
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Mar 25, 2009 1:17 PM   in response to: FKH161 in response to: FKH161
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hi i now have power at the red/white wire in the ignition harness and now get spark but my injectors/fuel pump cant here. i have no power going to the injectors from the computer pin 12 any idea's thx
FKH161

Posts: 7,634
Registered: 12/29/05
Re: 1991 vw jetta won't start!!
Posted: Mar 25, 2009 1:29 PM   in response to: stevo442 in response to: stevo442
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Pin 12 is the GROUND for the injectors.

The injectors get power all the time from the fuel pump
relay... have a look at the wiring diagrams I posted.

Bridge the fuel pump relay (30 & 87) and see if you get
power to the pumps & injectors... might want to check
your fuel pump fuse as well.

The fuse only protects the fuel pumps... the injectors get
non-fused power from the fuel pump relay.
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Mar 27, 2009 8:28 AM   in response to: FKH161 in response to: FKH161
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im getting power at the red and yellow wire i believe is the injector power on the back of the fuse box, but none for the red wire (fuel pump i think) , is this not supposed to have power if its got enough fuel pressure? . tryed to bridge pins 30 and 87 witch neither have power but there is one pin in the circuit that does have power with key ON position. Also if the hall sensor is not sending a "trigger spark" to the computer would this cause no fuel pump/injector movement??
tcovenant2000

Posts: 1,778
Registered: 12/09/03
Re: 1991 vw jetta won't start!!
Posted: Mar 27, 2009 10:26 AM   in response to: stevo442 in response to: stevo442
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One at a time:
One terminal will receive power when key is on. This is #15, switched ignition power. It tells the relay the key is on.
Terminal 30 should have power at all times. This is voltage direct from the battery. I believe there is no fuse in this line, but you can verify with wiring diagrams.
Terminal 87 is connected to terminal 30 when the relay operates. This causes battery power from term 30 to go to term 87 which is connected to the fuel pumps.
If you have no signal from the hall sensor then the relay will not close and will not apply power to term 87 and the fuel pumps will not run.
Putting a jumper from 30 to 87 bypasses the relay and makes the car act as though the relay is always on, and the pumps should run.
If you have no power on 30, then you've got to start there.
I may be mistaken, but I think that the hall sensor doesn't go to the relay on your car. Instead it goes to the ECM which then sends a signal to the fuel pump relay. FKH will correct me if I goofed, thankfully! :)

Thomas
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Mar 31, 2009 8:53 AM   in response to: tcovenant2000 in response to: tcovenant2000
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k i was gonna send it to a local canadian tire store instead i took it to a mechanic iv'e heard about knowing vw's, Anyways it's been a couple days and i called and he say's he's gonna try a fuel Pre Pump (91 jetta 1.8l 8v), is this a possible cause? ill let you know in a couple thx.
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Mar 31, 2009 8:54 AM   in response to: stevo442 in response to: stevo442
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theres lots of spark he says, just no fuel.
tcovenant2000

Posts: 1,778
Registered: 12/09/03
Re: 1991 vw jetta won't start!!
Posted: Mar 31, 2009 5:35 PM   in response to: stevo442 in response to: stevo442
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Yes. Since it's now sparking, but no fuel, the "lift pump" or "in-tank pump" is the place to start...though I'm leery about "he's going to try" it...a good mech should be able to test the flow of the lift pump without having to "try" another one.
Thomas
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Apr 1, 2009 8:22 AM   in response to: tcovenant2000 in response to: tcovenant2000
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good point thats what i was thinking i hope he tryed it even just with a battery, ill let you know this friday he said a couple days call him back thx for the reply.

stevo
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Apr 3, 2009 11:38 AM   in response to: stevo442 in response to: stevo442
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hey me again 91 8v, silly question is there a way i could run a on/off toggle switch from the battery to both pumps? and also do the pumps get full 12volts?? im gussing theres just no power going there what so ever.

thx
steven
tcovenant2000

Posts: 1,778
Registered: 12/09/03
Re: 1991 vw jetta won't start!!
Posted: Apr 4, 2009 9:46 AM   in response to: stevo442 in response to: stevo442
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The pumps should receive voltage direct from the battery via a relay.
The relay has two large terminals. #30 is tied direct to battery. #87 (or 89? never can remember) goes to the pumps. It also as #15 which is switched power from the ignition to tell it that the key is on. #31 is ground. The last terminal comes from the ECM to tell it the engine is turning. If you have no power to the pumps, try putting a jumper across the large terminals and see if the pumps turn on.
You can put a toggle switch, but you endanger yourself. If the car is in an accident where fuel is leaking under the hood, the relay will shut off with the engine and prevent the gas from leaking out under pressure. With a toggle switch this won't happen.
If the fuel pump works when the relay is jumped, you should look at the relay as suspect, but also check for the switched power.

Thomas
stevo442

Posts: 30
Registered: 03/18/09
Re: 1991 vw jetta won't start!!
Posted: Apr 4, 2009 11:25 AM   in response to: tcovenant2000 in response to: tcovenant2000
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I definitly have power from 1 smaller pin ignition i think ill have to double check tues. Theres no power at all coming from #30 and on, is there a way i could just (test) jump it with a battery and a piece of jumper wire or would this just melt the wires?? i tried to jump it from 30 to 87 but nothing at all.
tcovenant2000

Posts: 1,778
Registered: 12/09/03
Re: 1991 vw jetta won't start!!
Posted: Apr 4, 2009 7:13 PM   in response to: stevo442 in response to: stevo442
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If you have no power on 30, then you have a connection problem or a blown fusible link. Check wiring diagrams for the location of this. It should be a dedicated wire. Check, also, all the wires at the + battery terminal. Sometimes corrosion causes a wire to not make connection or to pull out. I'd start at the + battery terminal and follow the wires, looking for connection problems and/or fusible links or fuses. Don't know specifically about your '91 Jetta, but my volvo has an actual fuse in a funky holder under the hood. The car died. The fuse was fine, but the fuse holder had fallen apart. Mid '80's plastic and 20+ years don't work well together.

Thomas

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