M20 hot/cold starting problems

[gmannino]

Hi guys, I recently had the engine replaced in my car. Before, when I had the old engine,, I would be able to crank it just a couple of times and the car would fire up. But after the engine replacement, the car seems to have a hard time starting up when its cold. When the car is at normal operation temp, and I try to restart, it will crank right over. I usually wait a few seconds to prime to fuel but that still doesnt work. Most of the time, I have to pump the gas pedal to get it to start.

I want to get this fixed but I am unsure on where to look to find the solution. I was thinking about buying a check valve for the gas tank but that seems to only fix vapor lock and hot starting problems.

I need to figure out how to get my car started quickly when its cold? any tips?

[BillionPa]

fuel system cleaner
better spark plugs
clean distributor cap and rotor

[BillionPa]

oh, i live in minnesota, and im using an acetone/lubricant mix, and it starts up no problem at well below freezing after sitting in the cold outside for 24 hours.

im also using 0W40 oil, so it moves a lot nicer when cold, and it has lots of moly which lowers engine friction.

[DaveVoorhis]

Hi guys, I recently had the engine replaced in my car. Before, when I had the old engine,, I would be able to crank it just a couple of times and the car would fire up. But after the engine replacement, the car seems to have a hard time starting up when its cold. When the car is at normal operation temp, and I try to restart, it will crank right over. I usually wait a few seconds to prime to fuel but that still doesnt work. Most of the time, I have to pump the gas pedal to get it to start.

"Pumping" a fuel injection system doesn't actually pump anything, like it did with carburetors. Opening the throttle, however, will advise the ECU that you're off idle and want to deliver more fuel, which may help a cold start problem. It also can help with a hot start problem -- opening the throttle body delivers more air which can offset minor flooding, such as from leaky injectors.

I'd suggest checking the engine coolant temp sensor (see your Bentley for details) which is mounted to the thermostat housing. If the ECU thinks it's hot all the time, it won't enrichen the mixture at start. Make sure the blue plug is inserted into the lower sensor on the housing, and the brown one in the upper sensor. The blue one is the important one, here. A shorted sensor or sensor lead will advise the ECU that the coolant is hot.

[gmannino]

wounldnt the car's computer detect a bad sensor? and then throw a code or warning.

[gmannino]

Also the temp guage on the dash would not work. it would read hot all the time, mine does not. Isnt this correct.

[BillionPa]

i believe there are multiple sensors, one for the dash, one for the ECU, one for the AC.

[DaveVoorhis]

wounldnt the car's computer detect a bad sensor? and then throw a code or warning.
That depends on the failure mode of the sensor. If the ECU detects that the sensor value is out of range (e.g., dead short or open) then it should throw a code 1223. It won't detect that the sensor is in range but no longer responding to the environment, as could occur with a bad sensor or partial short. And, the sensor is easy to check and your symptoms seem temperature-related, so it's worth a shot.

Another possibility is a temperature-related problem with the fuel pump, or it's simply draining back over night.

The Air Flow Meter unit also contains an air temperature sensor. I do not know what effect its failure would cause.

I'm assuming, of course, that you've checked all the regular maintenance items whose failure could contribute to a poor start condition -- spark plugs, spark leads, distributor cap and rotor, vacuum hoses and intake boots for vacuum leaks, etc.

[DaveVoorhis]

Also the temp guage on the dash would not work. it would read hot all the time, mine does not. Isnt this correct.
The gauge sender and ECM coolant sensor are independent. The dash indicator sensor is the one with the brown plug.

[gmannino]

So if the dash indicator sensor is the brown plug, then the Coolant temp sensor is the blue plug correct? is there any other temp sensors I should check?

I installed a new check valve near the gas tank but it still has a hard time starting up.

[gmannino]

Any other suggestions? What about the fuel regulator near the intake manifold? Would that effect anything? Anywhere else to look?

[BlueM60]

There is also a black, round connecter just below the intake at the engine block. You may have to remove the airbox, intake pipe to get at it. These can become green and corroded internally and cause all kinds of problems. I had the same issue you describe on my 89 325i which is also M20. This connector is the splice for ecu temp sensor, cluster gauge, and basically the whole upper harness on the engine. If you know the NTC (blue) sensor to be good, check out this connector and I bet youl'll have found your problem. Hope this helps.

-Ben

[SnakeyesTx]

Did you put in that check valve from BMA already? I put mine in because it wouldn't start when it was cold due to fuel drain-back.

[gmannino]

Ya i installed it but it didnt help. I'm gonna try to swap my fuel pressure regulator from my old motor to see if that helps.

[gmannino]

UPDATE:

Swapped out the fuel pressure regulator on top of the engine and now my car starts up much easier!

[nizmainiac]

i had the same problem with my temp guage when i swapped engines, i found that one sender had one pin and would always read high , but when i swapped the other two pin sender it was fine and has been scince

[gmannino]

anyone know the part number for the coolant temp sensor for the ecu? not the sensor for the gauge but the one for the ecu which is the BLUE sensor. I didnt see it on bavauto.com. Is there another website that sells them?

[525inup]

was the motor rebuilt? or junkyard? maybe the rings arent sealing right until the frictions expands them.

[gmannino]

salvage yard, bavarian auto recycling. It starts up better now.