Tachometer not working and car "cuts off", have i fried the ECU ? (3b)

[rally_johan]

I'll start to apologize from the beginning for my poor english.

Car: audi s2-91 3b ECU

The car has not been driven(just started and driven around the block) since summer 2006 due to finacial situation, and when it was put away it worked just fine.

Then last spring (2007) i was going to start it up but i only had a poorly charged battery(almost dead), well i tried anyway but when i turned the key nothing happened except there was a strange sound from the ecu, it sounded almost like a machine gun and i heard it very well cause the starter engine wasn't even turning.

So after a couple of tries i gave up and about 1-2 months later i bought a new battery and then it started at the first try. Well, i drove the car out of the garage and had it ideling for 5-10 minutes, then when i was going to rev it a bit i noticed the rpm meter was dead, it doesn't move at all, the needle is stuck at 0 rpm constantly.

And when i drive the car at full trottle for more than approx 2 seconds i get the "forehead through the windsheild" effect and then i have to restart the car to be able to get another 2 seconds of action before it cuts off again.


So what's happened ? i've heard that the ECU is pretty sensitive to voltage peaks so maybe i've broken/fried it ? Does anyone else have any experience of this problem ?

The car and everything in it works just fine as it has done before except from the dead rpm-meter and the cut-offs, and it works fine to drive around if your easy on the gaspedal, but thats just booring


Hoping for a solution.

Best Regards // Johan

[Keith]

I'll start to apologize from the beginning for my poor english.

Car: audi s2-91 3b ECU

The car has not been driven(just started and driven around the block) since summer 2006 due to finacial situation, and when it was put away it worked just fine.

Then last spring (2007) i was going to start it up but i only had a poorly charged battery(almost dead), well i tried anyway but when i turned the key nothing happened except there was a strange sound from the ecu, it sounded almost like a machine gun and i heard it very well cause the starter engine wasn't even turning.

So after a couple of tries i gave up and about 1-2 months later i bought a new battery and then it started at the first try. Well, i drove the car out of the garage and had it ideling for 5-10 minutes, then when i was going to rev it a bit i noticed the rpm meter was dead, it doesn't move at all, the needle is stuck at 0 rpm constantly.

And when i drive the car at full trottle for more than approx 2 seconds i get the "forehead through the windsheild" effect and then i have to restart the car to be able to get another 2 seconds of action before it cuts off again.


So what's happened ? i've heard that the ECU is pretty sensitive to voltage peaks so maybe i've broken/fried it ? Does anyone else have any experience of this problem ?

The car and everything in it works just fine as it has done before except from the dead rpm-meter and the cut-offs, and it works fine to drive around if your easy on the gaspedal, but thats just booring


Hoping for a solution.

Best Regards // Johan

Hi,

well it seems that you have two problems :

1) rpm meter :
It could be simply a fuse problem, or the rpm sensor could be dead.

2) boost :
Your ECU gets on secure mode it can happen when :
a) Boost value higher than max authorized (should be around 1 bar for 3B)
b) the ECU gets no boost signal for more than a few seconds (leakage on hose between engine and ECU boost sensor / boost sensor dead

check if all small hoses are between intake manifold and ECU are OK.
You should not hear any leakage inside the car.

see ya.

Keith

[Keith]

I forgot one thing.

Take your MAF sensor out and clean the wire with Brake cleaner (spray).
Only use a evanescent product without residues.
Don't physically touch the wire !

[rally_johan]

Hi,

well it seems that you have two problems :

1) rpm meter :
It could be simply a fuse problem, or the rpm sensor could be dead.

2) boost :
Your ECU gets on secure mode it can happen when :
a) Boost value higher than max authorized (should be around 1 bar for 3B)
b) the ECU gets no boost signal for more than a few seconds (leakage on hose between engine and ECU boost sensor / boost sensor dead

check if all small hoses are between intake manifold and ECU are OK.
You should not hear any leakage inside the car.

see ya.

Keith

I've checked all fuses and measured both g4 & g28 sensors and they are both ok.

i normally run the car without the boostvalve installed, it's just connected in the socket but not plugged into the system, i manage the boost through a manual boost-valve instead and i usually runs about 1,65bars of boost, but now i run the car at the boost that my wastegatespring provides (about 1,3bar) and it still cuts of, i have other programs in my ecu that are made for 1,5 bars of boost and it has worked just fine earlier.

i'm almost 100% sure that these two problems are connected as they appeared at the exact same time.

maybe i should get a hold of another 3b ECU and try with that one.

[kwlw]

i'm almost 100% sure that these two problems are connected as they appeared at the exact same time.

I won't be so sure (never say 100% ). It happens sometimes, that tachometer (usually dashboard metal on plastic "wires") fail. Your car was standing for a long time as far I understand. Cars not used sometimes develop strange electrical "gremlins", which are real PITA to find and fix.

I would say, that you have boost leak, and failed tachometer (for some reason).

maybe i should get a hold of another 3b ECU and try with that one.

That would be quite a solution to check if the problems are related.

Sau