Hey guys, appreciate some help to nail down the problem. Here're the symptoms

1. Car was starting absolutely fine just a week ago. Over the past week however, cold starts (first thing in the morning) has been getting harder and harder. Took about 5s for the engine to fire today.

2. Once the engine has started, i can turn it off and restart and it'll fire up straight away

3. I checked the resistance of the coolant temperature sensor, seems to be ok (i.e. the resistance broadly follows the curve i found online)

4. The car drives absolutely perfectly on the road, regardless of speed or rev range. On idle, i can feel a slight misfire *sometimes*. Like it judders maybe once every 10s but this has always been there for the past 4-5 years that i've been driving it.

5. When i try to start the car, the tachometer does jump to around 200 rpm and then fire to life 5s after. I read that this kinda rules out the crankshaft sensor.

Any ideas? The only thing i'm suspecting now are
(A) faulty injectors ... do i have to replace all of them or is there a way i can easily test those?
(B) faulty camshaft position sensor : given that it was perfectly fine a week ago, i don't think the camshaft position sensor can gradually go out of sync/time?

Please help!! Thank you!

Best,
Kopi

 

The camshaft sensor is different then the crankshaft in that it's a hall effect sensor and not a inductance , the CEL code is PO340 . Mine went away after cleaning the connector .

There is a check valve in the fuel pump that will trap fuel pressure for days . This eliminates the need for a longer priming of the fuel rail if it is lacking this trapped fuel pressure . One way to test it is to let the car sit for a while ( a day , a couple of hours ? ) and crack the fuel line and see if you have any fuel pressure remaining .

 

 

If the fuel pump check valve is not retaining the pressure on the fuel rail you can place a check valve of a certain size just outside the tank others have used negating the need to replace the pump .

Another possibility is the fuel pressure regulator other then regulating the pressure on the rail at 43 psi , when not in use ( engine not running ) could be leaking the trapped pressure off .The FPRs don't last forever as a whole appears in the rubber diaphragm and they are around $ 65 US . If it is regulating at too low a pressure it would be underfueling the cylinders with the same injector pulse width in the critical start phase .

To test this by removing the hose that goes back to the tank and place a catch jar and see what happens overnight . The hose to remove on the FPR is the one pointing aft .

Fuel filter blocking flow ?

Injectors binding / dirty causing underfueling ?

Just a bad tank of gas where the gas is under performing ?

 

Try this simple test to see if you have fuel pressure loss overnight.

On next cold start, BEFORE cranking the engine go through 3 or 4 cycles of Key on - Wait 5 seconds (hear the fuel pump run) - Key Off.

Then start the engine.

This process will build up any lost pressure. If it starts normally then you will need to trace the source of the loss (likely the pressure check valve as referenced by Lady P above.)

If it still takes a long time to start then fuel pressure is probably not the issue.

 

As B1mcp mentioned ,

With the key turned only to the on position before the start position the fuel pump will turn on for about 4 seconds and then turn off by itself . a couple of these cycles will surely prime the fuel rail to proper fuel pressure assuming there is nothing wrong with the FPR not regulating too low or the check valve not wide open.

Still suspect the Camshaft position sensor in that it takes time to revert to the Crankshaft sensor , normally it does this anyway but the Camshaft sensor will have fired the cylinders off already and not the missing 5 seconds .

 

 

Sounds like it (though I'm perplexed why either failure would limit the effects to cold-start - One of mine had a failed fuel-check-valve and long-cranking was EVERY start. Same car later had a failed cam position sensor and the long-crank starts were seemingly random...sometimes long, sometimes immediate light-off....didn't notice any trend in cold vs. hot start)

No: Unfortunately, there is no Schroeder valve in the X300 fuel system through which one might monitor what is going on with pressure.

Likely not: You don't say how many miles are on the car, but while it is over 20 yrs old....I have three, with mileages from 130k to 240k and nary a one of the 18 fuel injectors are causing any problems....AFAIK, likely all originals having not been removed and serviced.

It sounds like either the check valve in your fuel pump has gone wonky, or your FPR. I'd probably change the FPR first, because that is easiest. OR....you could put a check valve in the fuel supply hose between the bulkhead hard-line and the fuel-rail. Lots written here on the check valve approaches, along with pictures. Search the X300 forum for key words "Fuel Check valve" and you'll have lots of fun reading ahead.

 

Thank you guys! Looks like i got my work cut out for me this weekend. Will report back!

 

Turns out its the pressure control valve ... CBC7714

 

The Rochester valve CBC7714 pic below ( not on all X300 production #s ) only involve fuel gasses

A Delco brand # X is a common av ailable substitution .

The fuel pressure regulator is also commonly available as a non jaguar source /

 

Take care with the installation. Isn't this the valve that causes the tank to swell up like a dead pig in the sunshine if installed backwards?
Or collapsed via vacuum....