VEMS AAN cut out - engine goes dead..?

[Thuppu]

Some may have seen in my project thread that I had some trouble with the fuel pumps stopping and the engine stalling. It usually happens when there is some load on the engine, boost is rising, between 3000-6000rpm.

I have now changed all wirings, releays and fuses for my fuel pumps, but it seems that it's something elese that causes the fail. When the engine goes dead and the fuelpumps stop and car is running, I just can cut off and on the ignition and the engine/pumps fires up, or I could press the clutch and let the engine die and release the clutch and engine fires up.

Have been testing that when it happens I can start the pumps with a separate wire directly from the battery, but the engine doesn't start, so there is something else that goes dead(and propably also causes the fuel pumps to stop running). I have tried to change the orginal fuel pump relay, as I have it to trigger my setup, but no luck. My rpm gauge is working when this happens.

So what can cause this? What goes dead and needs the engine to stall completly or a fast ignition turn off before the engine can restart? Could it be a problem in the ECU?

[mike74]

One of my chums had a similar sounding issue to this with an Emerald ECU he ran in his Golf track car. It would randomly cut out and misfire when driving...turned out there was a dodgy connection at the ECU. Fixed that one wire and it ran perfectly

[V6quattro]

At what pin did you connect the fuel pump relay? Some people say its not good to use pin 15 for the relay.

http://www.vemssupport.com/forum/ind...2nq53#msg22376

[Thuppu]

This is a VEMS board build in a Motronic box with Motronic connector. Did buy it used and PnP for AAN. I don't know what pin is used, can I see it the Vemstune settings?

[V6quattro]

I think you can yes. Maybe you can look in the outputs and then assign output chanels

[diesel des]

Vems also will test it for you at a price. Might take a little while.

[Thuppu]

Ok, seems to be the low current(0.3A) pin 15 in use... So the stock fuel pump relay also feeds power to the injectors, right? That could be the reason why the engine doesn't fires up if I bypass the fuel pump feed. Will try to bypass the relay under the dash, then we know if the injectors cut the engine off. And then the fault will propably be in VEMS. What output pin would be better to use, than the 15?

[blackS2]

We usually use an unused Injector Channel f.e. PIN 18 Injector output 5...

[RS246]

Looks up RFS Performance on Facebook he is a vems guru!

[quattro-nick]

it's strange that the problem came afther the rebuild
probably vems cut off relais j17 during the problem
maybe you can check the powersuply for vems during the problem
this is what it needs(on AAN ecu) + bat on pin 18 (white/black) coming from fuse s 102
+ ign on pin 27 (black/green) coming from fuse s 115
- ground on pin 24 (brown/white)
- ground on pin 19 (brown/red)

there is origional a ground on the intake manifold and you swapped the intake so maybe there is a loose connection somewhere?

[Thuppu]

It did it ones before the build, close to the rev limiter. I just ignored it back then. Now it seems to come every time I drive a little harder. Could low battery voltage cause this? Log from today shows 11.53V just before cutting. Feels also that it happens easier with a cold car, when I have been driving for a while it's a lot harder to get the cutting.

I have the intake groundings fitted on the head, so they havn't been un-plugged lately.

[quattro84]

I'd say use the advice of running it through another injector port, hoping this is a separate IGBT driver? I guess it will be a piece of fried HW on the board and a flipping transistor or mosfet does match your symptoms

[diesel des]

Measure the battery voltage with the engine running and compare to vems. It can be calibrated to read the same if off. But 11.5 seems low. Test supply and ground wires.

[quattro84]

Use different output: http://www.vemssupport.com/forum/index.php?topic=2006.0

InjGroup - 7A - injector output
I259 - 7A - ignition output
S259 - 1A - stepper
P259 - 350mA - low current output

Ignition outputs have best protection, P259 weakest.

Low voltage protection sounds like an option, though possible to calibrate? Low voltage can make your Vref signals flip is the onboard Vref chip is not capable of maintaining the desired level, could be anything from coil packs undercharging and, increased current frying your pump fuse & relais

[Thuppu]

Measure the battery voltage with the engine running and compare to vems. It can be calibrated to read the same if off. But 11.5 seems low. Test supply and ground wires.

Can't rise the calibration value any higher as it's maxed 200.