wont start unless i disconnect sensor

dirk · Post by **dirk** » Fri Mar 23, 2007 8:31 pm

hello new to the forum
I recently fitted a 3.5 v8 flapper to my 130 , every thing ran fine for a short while ,
now it is very poor at starting just spins over . when it dose start it runs and goes fine .
If i disconnect the engine coolant temperature sensor the <one behind the easy one> it starts up first go but runs terrible .

Coil ,plugs fuel filter all new ,swapped coolant temp sensor no change . I have taken it to two garages with no luck as yet one said the fuel pump is running at 2 bar he said it should be higher he thinks that might be the problem . HELP

thanks for any advice given .

Post by **Coops** » Fri Mar 23, 2007 10:46 pm

i had a similar thing, turned out to be a buggered ecu

GreenV8S · Post by **GreenV8S** » Sat Mar 24, 2007 11:57 am

I think the standard maps are usually set up for 2.5 bar, but if your ECU has been remapped then it may require a different pressure. I don't know what the ECU will do with an open circuit on the coolant temp sender, but if it takes the resistance at face value then this corresponds to a very cold engine which might trigger some enrichment. Since it's a new installation I suggest you test all the sensor inputs at the ECU plug, make sure all the injectors are firing, make sure you have good sparks on each plug, make sure all the plugs are clean and if the cold start injector is still there, disconnect it.

jwriyadh · Post by **jwriyadh** » Sat Mar 24, 2007 4:03 pm

By disconnecting the coolant temperature sensor you are forcing the ECU to think that the ambient temp is way below zero, ie -20 degrees. The ECU will therefore open the injectors for longer to give richer mixture. However, the disconnected coolant sensor cannot signal increasing engine temperature so the rich starting mixture becomes too much and engine runs badly.

The fuel pressure should be 2.5 bar with engine static and 2 bar while idling, if these pressures are not correct then cold starting mixture will be weak.

I would re-check the fuel pressure and if not right then correct it. Fuel pump, fuel filter and fuel pressure regulator are favourites.

If fuel pressure is correct try making sure the cold start injector is working properly, that may help but is only normally necessary for below zero temperatures.

Failing all other proper ways of fixing it put a switch in the coolant sensor wire, switch the sensor off to start and then switch back on as engine warms up.

jw