hi. i recently bought a 90 xjs in running condition, next day no start. have spark and fuel. tested coolant, air sensor etc anyone know the correct resistance for crank sensor's?

 

See the very first post at the top of the forum.

 

Being a Marelli car, and my knowledge of them is very low on any scale,

BUT,

I would first go to the ignitors on the radiator panel, unplug and replug them, carefully. Then do the same with the coils.

Since to have spark, this may do nothing, but it will also do no harm.

Next.

Look down the front of the engine, just below the oil filler cap. There is a loom connector, 2 wires from memory, unplug it and clean it reaaly clean, replug, and try starting the engine. That little plug has stopped 2 in our little group.

After that, Warren will get here when he wakes up, and has a beer or 2, he is the Marelli man.

 

thank you for the reply, i was certainly unaware of the little plug below filler cap and will do as instructed first thing in morn. dark where i am at now and would prefer to be cautious and thorough.

 

Welcome to XJS ownership, it is wonderful and frustrating all at the same time.

Anyway.

There are a numerous reasons for no start.

1 The inertia switch which is down by your knee as you get out of the drivers seat on the bottom of the A pillar.

2 Front and rear crank sensors, Front is the TDC sensor (which Grant said to clean the connector) and the engine speed sensor is on the flywheel cover, ECU needs BOTH of these to start. Check sensor gap 0.018-0.042”. Too wide a gap will prevent starting.

3 Poor spark, the spark needs to be able to jump at least 1/4” gap, remove each HT lead from the distributor and hold it 1/4” from the engine block or suitable unpainted metal part.

4 Dreaded white wire (engine speed signal ESS). There is a wire from Pin 24 of the Marelli ECU to pin18 of the EFI ECU, without this signal no start. On early cars this wire goes from the Marelli to the engine bay (in the V) then back to the EFI ECU. Check for the connection under the fuel rail usually on the LHS.

The EFI ECU will provide an injection pulse when the ignition is turned on (priming pulse independent of ESS) then as the car starts to crank the EFI ECU will use the ESS to pulse the injectors once for each engine cycle, if you have no injection pulse when cranking then the ESS (dreaded white wire) is almost certainly the cause.

Check all of these first, and report back.

 

thank you as well, hopefully i ll have knowledge to contribute myself at some point and help somebody along. i will tackle the spark jump test in the morning, ess is ok, used a stethoscope earlier to establish an audible pulse relating to injectors, crank sensors are good, at least to pins 5 and 19 for front, dont know wich pins for flywheel but resistance at terminal was roughly equal to front so im guessing its ok too. 9 also previosly removed and cleaned front earlier the plug was close to center of the motor up top so i thought there was another loom connector under filler cap as described that i missed. inertia switch is in proper position as well ( passenger side ) on this car. i ll be hoping its weak spark and go from there since im getting suspiscious of the ecu at this point