Mp9 cold start issues

[Reedo]

Hi guys

Hoping someone has some info for me on the cold start on the mp9 system

I know some of you probably feel this topic has been discussed more then a few times but I've checked and don't find a problem just like mine

So it's been a long 3 year project building my mk1..
Converting to injection.. Spraying the body etc etc..

I finally got the car done..
Only to find the ECU I bought had a messed up coil driver..
Anyways long story short..
Bought another ECU.. Another tank.. Coz mine had plenty rust etc etc..

Now I finally got it running smoothly no problems good power etc..

Problem I'm having is first start of the day.. In the morning when cold..
My golf does not want to start easy at all..
Takes about 7 times of swinging to actually get it to fire.. When it eventually does.. It's very sensitive.. If I apply throttle it will die.. Have to give it few minutes before I can drive..
My cold start does not come in as it idling at about 800-900 Rpm..
Once warm car starts on the. First kick.. And runs perfectly fine..

I've had the ignition timing set..
Tested fuel pressure at the pump is 4.0bar..
Did clean my injectors.. Rail.. Fuel lines.. New fuel filter as previous tank messed everything up..

Replaced 4pin temp sensor.. But still no help..

Looked at the wiring done.. On the 4pin sensor..
Pin 1 brown.. Main earth Ecu..
Pin 2 brown/red.. Goes to ECU..
Pin 3 grey/ green.. Goes to Ecu.
Pin 4 yellow/ red.. Goes to temp gauge as it's a old spec dash..

Looked at the ECU mp9 diagram.. Only yellow/ red wire is dizzy phase sensor input..
No wire for yellow/ red temp from 4 pin sensor..

Now I'm confused.. Does the ECU not need to know what temperature the car is at??
There is no wire for this unless it is the grey/ green..
I checked each wire going to the box.. All is fine..
I tried another ecu and same problem.. No cold start and hard starting in the morning..

So is there anything I'm missing here..
Please if anyone has experienced some problem like mine or has information thanks any help will be appreciated

[Ashveer03]

here's my opinion on it..
Instead of fiddling around with the wiring, it's simple just to plug in a scantool and see what temp the ecu is seeing. If it's seeing a ridiculous temp then there's a problem with the sensor/wiring/ecu, if its seeing a more reasonable temp then u are most likely heading in the wrong direction.

Fuel pressure tests are generally done at the rail so that u can test the pump along with the regulator at the same time.
*T piece* the fuel line at the rail and test fuel pressure there, mp9s generally have a 3bar regulator. So if u still getting 4bar in that configuration then change out that regulator.

Higher rail pressure = flooding (on a stock tune), especially when the engine is cold because the ecu already altered fueling for the cold start. If the engine has wear, the struggle is worse.

Off topic:
Iv seen engines with bad compression fail to even start with a measly 1 bar higher fuel pressure. It makes a difference in my opinion..

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[Rudi46]

Where are you based? Maybe somebody close to you can do a Vcds scan and check if the ecu is getting all the correct readings.
Where did you buy the temp sensor. Sometimes you get a Dud as well

[Reedo]

Hi thanks alot for the reply..
I'll try over the weekend to get it plugged in and scanned
As well as test for fuel pressure at the rail.

Yes think I'll do a compression test as well and post all my findings here

The 4pin sensor I bought at GW

[Ashveer03]

Compression test not really needed in your situation but it wouldn't hurt to get it done anyways..

And yes, brand new sensors can be faulty right out the box no matter where u buy it from.

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