I have gotten some great input from Jagboi64 and others regarding my '94 XJSV12 6.0L Convert. not starting once warmed up.

Has anyone else had a problem with BWD Aftermarket parts such as the Crank Case Position Sensor??? I am getting stories of after market parts not working and searching for OE solving the problem. MY car was fine starting hot or cold when Code FF77 came up requesting a new CPS......Ordered the BWD Part CSS961 from my local Advance Auto Parts and had it installed. The check engine light went out but now she only starts when cold. We have since replaced the fuel pumps, regulator, filters, and strainer to the tune of nearly a thousand dollars having to pull the fuel tank is a big deal. It is feeling stupid just throwing parts at this problem. Looks like I may have no choice but to find an OE sensor and throw more money and parts to my Jag

Have other folks had a problem with these aftermarket CPS's

 

Did you replace both crank sensors? As I understand Marelli ignition, the front sensor relates to timing, and the rear is fuel delivery. This is one of those things that I strongly advise folks to replace on the Marelli ignition cars, as these are now 20+ years old.
My first attack on this would be to test for spark when hot. If you have spark, I would think that then it would be fuel related. It could be something as simple as the coolant temp sensor. Maybe check resistance on the coolant temp sensor when cold, then again when hot.

 

Marelli Front sensor is TDC for A bank and rear is engine speed.

The sensors are VR and generate an AC voltage with Voltage and frequency directly proportional to how fast the relutctor teeth passes the sensor. Voltage is usually in the order of a few volts not millivolts so I would be surprised if the replacement sensor was the issue, although not impossible. Have you checked the gap if this is too large then the voltage generated could be lower than the Marelli ECU trigger setting.

Marelli engine primary sensors for starting are
the 2 crank sensors front and rear
MAP sensor

 

I am 73 and partially handicapped and unable to wrench the car myself. So, I am coaching a local mechanic ….who is not a Jag expert ….nor am I ...He only replaced the front sensor and tells me he does not know of a gap adjustment on it....can someone explain this gap??

The check engine light went off when new front sensor was installed …...do you think we still need to replace rear sensor and coolant temp sensor.....Are there gap adjustments on them also?
You guys are tremendous ….thanks for the input

 

If the gap is too large the sensor will not generate a voltage high enough to trigger in the ECU. The gap should be 0.018"

 

To "adjust" the gap, the only way I found to do it was to file the mounting boss down a little at a time, then keep checking it with a feeler gauge. The front one is very tricky, as there are three metal "fingers" bolted to the damper. On my cars, those fingers aren't consistent, so I just filed the mounting boss until I got the sensor to .020 on the closest one. On my 89 Marelli car, a shop ran through several thousand dollars, replacing just about everything including the wiring harness. The owner forfeited the car in lieu of payment. I bought it on eBay. Took me 40 hours to diagnose, but the rear crank sensor gap was around .047. I fixed that, and the car started right up.

 

With a genuine Jaguar sensor the gap is set, as these are NLA aftermarket units may not be exactly the same causing the larger gaps. My car still has its original sensors and gaps are about 0.020"

Basically you want the sensor as close as possible to the teeth without fear of the sensor tip being knocked off.

 

If you vehicle crankshaft position sensor get faulty during journey there are some temporary fixes which help you reach a mechanic for replacement. Read Here really helpful

 

The first time I replaced the CPS on my 4.0 was with an aftermarket CPS that proved to be defective from the factory. The car went from running poorly to no start at all. I bought another replacement and that fixed both problems. Unfortunately, I do not remember where I bought the defective CPS as I had carried it as a spare for quite a while.