Hard start when the engine is cold

[Bimmerista]

In the past couple of days, my car has had a hard time starting up when the engine is cold or hasn't been started in a few hours. It takes approx 3-4 times of cranking before the motor fires up. The problem started a couple days ago when the temperature outside dropped to 40F at night.

From what I read when I did some searching, I have narrowed the problem down to a crank position sensor or possibly the main relay. I would like some additional input on this matter. When the engine is warm, the car starts just fine. Its only after sitting overnight or when I leave work after it sat for a few hours that it takes several tries before the engine fires up.

Once the car is on, there is no problem. Tune-up (plugs, wires, cap, & rotor) were replaced last Spring. There is no idle problem when the car is running and the car runs just fine.

Thanks in advance!

[jlevie]

The most likely cause of that, in order of probability, would be:

Intake leaks
Sticky ICV
Bad engine coolant temperature sensor
Fuel system problem (clogged filter, weak pump, or bad FPR)
Sticky AFM vane

A cold engine needs a richer mixture and in really cold weather it doesn't take much of a leak to cause problems. Have the intake smoke tested to find the leaks.

[Bimmerista]

Thanks for your input Jim! Glad you chimed in.

[Teaguer]

The gay!

[Bimmerista]

Installed a new VDO fuel pump & swapped relays. Still no go.

Teaguer did determine that the plug leading to the fuel pump has no power to it. Where do I go from here??

[matias88e30]

spray some carbulator cleaner in every single hose of the car to check for any vaccum leaks, also the bentley manual will tell u how to check afm, tps, icv etc.. good luck!

[Bimmerista]

There is no power going to Fuse #11...which supplies power to the fuel pump.

Any more thoughts? Perhaps the DME?

[funcrew]

The most likely cause of that, in order of probability, would be:

Intake leaks
Sticky ICV
Bad engine coolant temperature sensor
Fuel system problem (clogged filter, weak pump, or bad FPR)
Sticky AFM vane

A cold engine needs a richer mixture and in really cold weather it doesn't take much of a leak to cause problems. Have the intake smoke tested to find the leaks.

My car is acting identically to the OP's. Starts very hard, long cranking when cold. Once started, runs and idles beautifully. Smells like gas after a hard start.

Tune-up stuff is fresh, ICV moves freely, no vacuum leaks (fixed a few found with starting fluid), fresh temperature sensors, fresh stock injectors, stock chip, fresh fuel pump, fresh O2 sensor, no engine mods. Good compression on all cylinders. Did most of this work to pass smog which it just did.

A month ago, the car started right up, no problems. Driven daily.

Next, what order should I try AFM vane, FPR? Any other ideas?

[jlevie]

The next things to do would be to have a smoke test run and to run the fuel system tests in the Bentley manual. Actually those and the O2 sensor should have been the first things you did.

[Bimmerista]

Sorry, I forgot to update this thread. The problem turned out to be the crank position sensor.

[funcrew]

The next things to do would be to have a smoke test run and to run the fuel system tests in the Bentley manual. Actually those and the O2 sensor should have been the first things you did.

I actually never heard of the smoke testing prior to this thread. Just watched a Youtube of the smoke testing process, what a powerful tool. I'll bet there's a long list of nasty leaks on my 23 year old motor. O2 was already done to (successfully) pass smog, will do the other stuff next.

Thanks for your input!