[Narfadan]

After my wagon (218,000 miles) gets up to operating temperature it becomes hard to start. When initially starting the fuel pump runs normally until the system is pressurized but after warmup I do not hear the pump run on restart, even after sitting for 15 or 20 minutes. Most often the car will restart after a couple of seconds of cranking but occasionally it goes through what I presume is a cranking time-out cycle. The second try seems to always start instantly. My first thought is fuel pump failure but I wonder if there may be any known heat-related issues with the fuel pump's control system?

I do not experience any performance issues once the car is running...no hesitation, stalling or any other symptoms that might indicate a fuel-flow problem. The fuel filter has been replaced within the past 60 days.

Any thoughts?

 

[mrboca]

Hello

The way I understand the start process is when the key is turned to start a start timer is started, and the key can be returned to "run" position as the start relay is held "ON" by the ECU till the timeout occurs or when the engine rpm exceeds 100, whichever is earlier.

The ECU gets the rpm information from the crankshaft position sensor. If the CPS (also called CKP) is flaky, under hot engine conditions, the rpm information is not properly signaled to the ECU and the timeout occurs. If the CPS is flaky, it will get worse over time.

The fuel supply is also an issue but one cannot explain why the car does not start, and after an immediate try it does..

Have you ever replaced the CPS ?

Next time you try cranking under the hot engine conditions, check the rpm on tachometer.

 

[Narfadan]

The timeout does not happen every time...only very occasionally. I have noted the tachometer and it does not indicate engine rpms until the engine actually fires. There is no discernible movement of the tach needle while cranking.

Aside from routine items I have replaced only a water pump in the 3+ years I have owned the E320. Save for the starting issue when warmed up the car runs beautifully.

Thanks for your reply.

 

[mrboca]

Could it be a flaky fuel pump relay ?

 

[Narfadan]

I had considered the relay but why would an electro-mechanical device act in such a manner only after the engine is at operating temperature? I would expect poor relay contact closure to happen at any temperature.

I'll have to look into that further and, if swapping the relay is relatively simple and inexpensive, just replace it.

Thanks

 

[mrboca]

Have you tried measuring the fuel pressure immediately after the ignition off and after 30 minutes ? Possibly you have a check valve issue in the fuel pump.

If you do not have the fuel pressure gauge, I believe you can get a loaner from one of those parts shops.

Check the attached out.

Just multiply the bar unit with 14.5 to convert to psi.

 

[Narfadan]

I will check on this.

A search of the Internet found a couple of good sources of information so I at least now know where the Schrader valve is located so I can perform the test.

Thanks!