Slow to start when warm. She's a mystery to me, Roy Orbison 1988
2005 XF Coupe, 50 000 km (30 000miles)
New battery
No check engine light
BlueDriver v2,6 (love it) no codes, no primary codes
Starts on the first turn of the key when cold
Starter turning the engine over plenty fast
New, RCM yesterday, RockAuto
No stumbles, runs like a thoroughbred on the highway

Need the collective wisdom ot this forum. All past experiences and ideas appreciated.

TY Rupert

 

Mine did that when it was just short of 3 years old. Ended up being the fuel pump - got it replaced under warranty and it has never happened again.

 

Sounds like a failing CPS.

 

I’m currently dealing with the exact same issue on our 2004 Limited coupe. I had the RCM refurbished and have replaced both the crankshaft position sensor and camshaft position sensor with bosch units. Starts right up when cold and runs great once started but is slow to start when warm. Plea update this thread if you get it figured out. I intend to have our fuel pressure checked but haven’t gotten to it yet. A new fuel pump could be and expensive fix but if I know it works well worth the investment for peace of mind. be

 

Just a thought. The problem for slow starting after warm up could be a fuel related issue. If the fuel near the point of entering the engine is getting hot enough before startup it could be partially vaporizing creating a mild case of vapor lock. I use 93 octane and haven't experienced this problem but I also haven't parked my roadster in 100 degree + temps either. If the slow startup problem goes away once the air temperatures begin to lower then I would conclude your problem is fuel related as in ethanol additive in the fuel. As a test, you can try adding some Marvel Mystery oil to a tank of fuel to help reduce the possibilities of your problem being vaporization related.

 

Now I am ready to start resolving this slow/hesitation to start when warm..
New camshaft position sensor, Bosch 0232 1030 50 eBay
New crankshaft position sensor, Bosch 0261 2101 70 RockAuto
New fuel gauge pressure tester, RockAuto

I will start with the new camshaft position sensor. This idea came from ZERACER plus I found the following on a Mercedes forum.

Intermittent starting – This is a very common problem if the Camshaft Sensor starts to fail. You may notice the car starts fine one day and then hesitates to start the next. It could also be that the car starts fine when cold, but if it warms up, it’s hard to restart it.

Hopefully, I can eventually report the solution to a slow/hesitation to start when warm.

 

Great your tackling this! Just a question, for your benefit? When you get your BOSCH sensors, check if they are original BOSCH. I have heard of, and seen (in ads) many BOSCH sensors sold on both (and supplied by various sellers) that advertise BOSCH, but somewhere in the extra fine print says something like it is a substitute. The devil is in the details, for sure! Just an FYI that if a knockoff or substitute, may save you a lot of headaches. Good luck!


.

 

The camshaft position sensor needs to know the camshaft position to set the fuel mixture and the proper timing.

 

If the camshaft and crankshaft sensors are hall effect-type sensors they, in general will not work intermittently if they are damaged. I feel your problem is thermally related or as someone has mentioned fuel delivery related.

 

If memory serves me correctly both of them are not Hall effect sensors.

 

Camshaft sensor IS Hall Effect, crankshaft sensor is reluctance ( magnet and wire )

 

.


And, if I remember correctly, the use of non-Bosch sensors have satisfactorily been agreed (proved) to be mostly related to the pins within the connectors not fitting properly at the sensor. If this is correct (what I remember), then there are a bunch of posts relating to this, for your research/edification. Good luck!


.

 

I found the source of my problem. When the engine is running the fuel pressure is 58 PSI. When I turn the engine off the pressure drops to 0 PSI. The check valve is not holding. Is the check valve in the fuel pump or fuel filter?

TY

 

fuel filter

 

I am awaiting the final resolution to this issue. I had already replaced my camshaft and crankshaft position sensor‘s and had the RCM rebuilt soul expected it to be a fuel delivery issue. My fuel filter was replaced with either BOSCH or MANN brand. I ordered a fuel pump but was waiting for Rupert to solve his issue before having mine installed. The car runs fine once started and usually starts well when cold Is it possible to install the fuel filter incorrectly and would it still allow the engine to run?

 

I have a new fuel filter ACDelco ACD#GF893 GM#89034698. This is the correct one as confirmed by previous posters.
I am attaching two pictures. The fuel filter has - 4 ports 4 stampings . I get TANK and PUMP but what is MOT and CAN. Please enlighten.
My garage situation is town house/row house. No matter how careful I am,


there will be a gas spill. So I have found a local independent garage that specializes in European cars. The local Independent European garage is super busy. My booking is five weeks from now.

 

Page 14-9 through 12 in the service manual has a decent description of the functions of the connections and the filter itself.

 

It looks like post number two was correct. I had the same symptoms as Rupert but had already installed a BOScH fuel filter as well as sensors and repaired RCM. I just had a new fuel pump installed and now it is holding pressure When the key is turned off. The check valve must be in the fuel pump itself rather than in the filter as suggested in a previous reply.

 

I pulled this from the service manual. Pages 4-10/11. Looks like both filter and pump have a part to play.
The combination Fuel Filter/Fuel Pressure Regulator
is located along side of the fuel pump as part of
the fuel filter assembly. It is transversely mounted to a
chassis crossmember (left-to-right).
FUEL PRESSURE REGULATOR
The Fuel Pressure Regulator is a mechanical device that is calibrated to maintain fuel system operating pressure of
between 3.7 - 4.1 bar (54 - 60 psi) at the fuel injectors.
Fuel is supplied to the Fuel Filter/Fuel Pressure Regulator by the Electric Fuel Pump directly.
The fuel pump assembly contains a check valve to maintain some fuel pressure in the system when the engine is
not operating.
If fuel pressure at the pressure regulator exceeds a set amount, an internal diaphragm closes and excess fuel pressure
is routed back into the tank through the pressure regulator.
The Diaphragm Pressure Regulator regulates the fuel pressure by means of the return flow (10) quantity to the
fuel tank.
If the pressure rises above the set pressure, the diaphragm is pressed further against the compression spring.
The valve attached to the diaphragm opens the passage for the return flow further. If the pressure drops below
the set pressure, the valve is closed again by the compression spring .

 

You have explained the system well but it's not a simple matter to test all the functions pressure and flow functions identified in your garage. If I had to guess what part I would flip it would be the pressure regulator. It is probably working but not properly over its complete operating range. Usually if a pump is beginning to have seal
or electrical related issues you would experience problems consistently cold or hot.