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Discussion Starter · #1 ·
I changed the cyl head on a 90 jetta (digifant) The car ran fine before I start working on it. After the new head was put on the car started ok but after 2 minutes it started to run very rich so rich that it is not drivable
O2: Replaced with new generic Bosch. No change at all
Ground: 2 brown wires are attached firmly to the head I can get 12 v when connect a volt meter to positive terminal of battery and the ground wire. Terminal 1 on ECU harness is also getting good ground.

ECU: replaced with another working unit. No change
Blue temp sensor: Values checked on blue temp sensor and ECU terminals.
If I unplug the O2 wire or disconnect the blue temp sensor the car runs fine with no problem. As soon as I plug them back it starts to run very rich so rich that I can not go faster than idle.
Any ideas?


Modified by kickster at 9:03 PM 6-20-2005
 

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Discussion Starter · #3 ·
Re: Digifant running rich. Out of ideas! (maximus_manx)

temp gets to 90C. no matter how cold it should never run this rich. It is so rich that it will stall if I try to drive it.
 

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Re: Digifant running rich. Out of ideas! (kickster)

Quote, originally posted by kickster »
temp gets to 90C. no matter how cold it should never run this rich.

The temp the car gets to wasn't the issue. I was simply asking because a buddy had similar problems with his digi-infected A2 a while ago; the previous owner couldn't get it to run consistently, and sold it to my buddy cheap....after buying all sorts of stuff used(ECU, MAF, harnesses, etc), it was discovered that the t-stat was a low-temp version.
The digi system relies pretty heavily on coolant temp for mixture adjustments - if the stat opens earlier than stock, the motor reads lower than normal coolant - it responds by keeping the mixture rich.
Never hurts to try and help.
 

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Discussion Starter · #6 ·
Re: Digifant running rich. Out of ideas! (Vdubsrdashizznit)

The car has stock thermostat. As soon as the computer gets info from o2 it starts to run mega rich. It has to be a ground problem but I cant find it.
 

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Re: (mk2jettarunner)

Yeah you can crack open the MAF (the black box) and click the dial back a couple clicks and try that.
Im no expert, but when i want the car to run richer i pop that open and advance it a couple clicks... makes me go through gas like a dirty pornstar would spooge.

This is NOT a permanent solution because something is clearly wrong... but if you do clock it back a bit... it might lean it out just enough for you to drive it till you figure out the problem.
 

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Re: (1.8Freaker)

another thing to check is the fuel pressure regulator. You said you changed the head, so how long did you have the FPR disconnected?? If they dry out they like to crack the diaphragm. I had that problem on my GTI when I rebuilt the motor.
 

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Discussion Starter · #10 ·
Re: (Black92EightValve)

Update:
I changed the MAF with no effect. removed the O2 sensor and there was a layer of carbon on it. Cleaned it and put it back in. o2 wires to ECU are ok.
the head was out for few hours and FPR was full of fuel.
So far
New O2
New spark plugs
New wires
New Cap and Rotor
New Timing belt
Replaced blue temp sensor
Replaced ECU
Replaced MAF
Water Temp is around 90c
Brown Ground wires are attached firmly to the intake.

When O2 is unpluged it drives ok. When it is attached it idle rough but doesnt even drive.
 

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Re: (kickster)

When you replaced the O2 sensor...Which Generic sensor did you use?
Plus Ive found my wiring to the O2 sensors to be cooked and cause a similar problem seeing as they pass over the ex. mani. Theres the two grounds to the side of the head (at the flange) and a random one to the valve cover. Also check the battery to the body to the block. And the ground to the O2 sensor. I ran a 3 wire sensor on my 4 wire system and I ground the ECU harness directly to the motor mount bracket.
 

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Discussion Starter · #14 ·
Re: (TwinScrew20v)

Quote, originally posted by TwinScrew20v »
When you replaced the O2 sensor...Which Generic sensor did you use?
.

I used a Ford mustang 3 wire Bosch plug. all O2 sensors with the exception of wide band O2 send the same signal.
 

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Discussion Starter · #15 ·
Re: (wannarado)

Quote, originally posted by wannarado »
why not just drive it with the o2 unplugged then

Digifant with no O2 doesnt drive ok. You will run rich low RPM and very lean on top. Your cat and fuel economy will go south and you may burn a exhaust valve if you run it too lean.
 

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Discussion Starter · #17 ·
Re: (TwinScrew20v)

Quote, originally posted by TwinScrew20v »
But the number of heater elements eff up the signal

why would they? How is the heating element effects the signal? All O2 sensors send similar signal. Are you saying this based on facts?
 
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