The car is a 1996 XJS, 4.0, 100K miles. It's been very reliable until about 2 months ago, virtually refused to start one morning. May in Baltimore, no severe weather. I could get it started with ether, and then it would drive pretty well. It would start after being warmed up, but once cool wouldn't start. I've replaced the fuel pump and fuel filter (inside the wheel well). No difference.

After turning the key to on I can get a squirt of fuel from the fittings near the back of the engine.

The tachometer indicated about 200 RPM cranking.

Based upon forum feedback I checked the CPS (front of engine). It read as an open circuit, so I ordered a replacement. The new sensor checked in at 1345 ohms.

I put in the new sensor and it started but runs really poorly. Smell of fuel so I assume rich or not burning fuel well. If it were an older engine I'd say the timing was way off. Won't accelerate, runs between about 600 and 1000 RPM, engine shake. The tach is moving a lot, more so than the engine speed changes.

I pulled the plugs, very sooty. Put in new ones, same behavior.

I believe the failure is consistent with the sensor, just stopped working. The new sensor obviously made a big difference, just didn't quite do the trick. Thinking about getting another sensor.

 

Hi Len

Have you checked the Vacuum to the FPR (Fuel Pressure Regulator) loss of Vacuum can make the Car run 'Rich' as can also an FPR with a failing diaphragm

 

Orangeblossom,

I did try a check of the FPR. I disconnected the vacuum line and started the car. Acts just like it did before, very poor surging idle. I re-installed it and got the same response. So connecting/disconnecting the vacuum line has no effect. I could hear air sucking through the line when it was removed and it stopped when I put my thumb over it. The car ran the same through all of this.

Sound to me like it may be bad, what are your thoughts?

Len

 

Hi Len

Ask a favor from a 'Shop' and get them to Test the FPR with a Vacuum Pump or buy one for a few bucks

If the FPR does not hold the Vacuum, then the diaphragm in the FPR is shot, which is easy to replace and would cost around £45 (UK) If that's the problem it's an easy fix

 

Orange Blossom:

So I took your advice and checked the FPR. No signs of diaphragm leaking. This got me looking back at the CPS. I took out the new one and the old one. Repeated the resistance testing and sure enough the old one was open circuit, the new one was about 1350 ohms - which from what I can see is considered in spec. Never the less, of all of the things that I've tried the CPS is the only one that had a true cause and effect, and I had a known bad part. So I bought a second CPS from a different source (the first was UltraPower, the second was Intermotor, both aftermarket made in China...)

Put the new sensor in, car runs perfectly. So now it's got a new fuel pump, new fuel filter, and a new CPS. I'm certain that if I had changed the CPS first then it would have fixed it.

Thanks again for the help,

Len