For the last week engine starting has been intermittent, but now won't fire. After reading several posts on this subject and noticing no movement on the Rev counter, indicating CPS fail. Having just put a new one in, the car still wont fire.

Any Ideas please.

 

Hi Philip,

With the new CPS installed, does the rev counter/tachometer now show about 200 rpm while cranking the engine? If not, check the electrical connector for the CPS to confirm that none of the terminal pins has backed out of the connector housing and that the connector is not contaminated with oily sludge.

The second most likely cause of cranks-but-won't-start is low battery voltage while cranking. If the voltage while cranking sags much below 11 volts, the engine control module (ECM) will not trigger the ignition to fire.

Another common issue is water in the fuel. If the small drain tube in the rubber gaiter around the fuel filler neck becomes clogged with seeds and leaves, water can pool around the fuel filler cap and seep down into the tank. Over time, enough water accumulates in the bottom of the tank to prevent the engine from starting.

When you turn the key to position II (ignition ON), before cranking the engine, do you hear the fuel pump run for a couple of seconds to prime the fuel system?

Please keep us informed.

Cheers,

Don

 

I must sound like a broken record, but try a new rotor

Larry

 

Thanks for the suggestions/tests

With regard to Don B's post:

1. New CPS connector is good did a continuity test across connector, still cranks at 0 revs.
2. Good battery fully charged before todays tests (now flat and charging tonight)
3. Rubber gaiter is clean (had rained last night no standing water so assumed drained properly)
4. I don't hear the fuel pump run on key turn (this happened once before last christmas & revved 200 on crank, after was all ok till this weeks troubles)

With Lawrences post:

A new rotor arm was put in last October along with new plugs, cleaned breather hoses/dis cap before MOT.

Thanks
Phil

 

Hi Phil,

A few ideas:

1. Is the reluctor ring/sensor pulse wheel on the crankshaft clean, or are the spaces between the teeth filled with gunk? If it's dirty, it is possible the CPS signal pulses could be weakened. Are any teeth broken? I have had at least one new aftermarket CPS that was dead, so that is also a possibility.

2. The CPS connects directly to the ECM via Red and Blue wires. The Blue wire should be shielded. If the shield is not grounded properly, the CPS signal may be corrupted by EMI from the distributor, ignition amplfier, coil, etc.

3. Water ingress into the ECM electrical connector or its circuit board is know unknown. This can interrupt critical sensor signals.

4. Here is a fuel pump diagnostic procedure by Bryan N at the Jag-Lovers forum that has worked for me every time I have needed it:XJ40 - ‘93 / ‘94 Fuel Pump Circuit Test Procedure - Issue 2
[Assuming that you have dash lights with the ignition 'ON']

1) With ignition OFF
2) Remove fuel pump relay (black base, right rear corner
trunk above BFM)
3) Do you get 12 volts at pin 30 (Brown/yellow) of the fuel
pump relay base from fuse C6 in right fuse box?
4) If yes, jump pin 30 (Brown/yellow) and pin 87 (Blue/red)
in fuel pump relay base - does the pump run continuously?
5) If pump does not run, fault is in the wiring / connector
between fuel pump relay and pump
6) If pump runs, suspect fuel pump relay is defective.
7) Replace / re-fit fuel pump relay
8) Remove oxy sensor heater relay (yellow base on firewall)
9) Do you get 12 volts at pin 30 (Brown/pink) of the oxy
sensor heater relay base from fuse C4 in right fuse box?
10) If yes, jump pin 30 (Brown/pink) and pin 87
(Blue/purple) in oxy sensor heater relay base - does the
pump run continuously?
11) If pump runs, suspect oxy sensor heater relay is defective
12) Replace / refit oxy sensor heater relay
13) Remove EMS main relay (black base on firewall)
14) Do you get 12 volts at pin 30 (Brown/yellow) of the EMS
main relay base from fuse C1 in the left fuse box?
15) If yes, jump pin 30 (Brown/yellow) and pin 87
(White/brown) in EMS main relay base
16) Try this both with the ignition ON and the ignition OFF
17) Do you hear the fuel pump give its half-second priming
burst? [You can repeat this many times and you (or an
assistant listening at the open filler neck) should hear the
half-second 'whirr' of the pump every time you jump pins
30 and 87 of the EMS Main relay base]
18) If yes, suspect the EMS main relay OR the EMS ECU is
defective (the latter, very unlikely but possible)
19) Turn ignition OFF
20) Replace / re-fit EMS main relay
21) Remove Ignition 'ON' relay (on a '94 it should be in a
white base on the firewall but on a '93 it may be buried
under the dash behind the radio)
22) Do you have battery voltage at pin 30 (Brown) of the
Ignition 'ON' relay base?
23) If yes, temporarily jump pin 30 (Brown) and pin 87
(White/pink) in the Ignition 'ON' relay base
24) Do you hear the half-second priming burst from the pump
each time you jump those pins in the Ignition 'ON' relay base?
25) If yes, suspect the Ignition 'ON' relay is defective or
fuse A5 (fuse A3 on ‘94 models) in the left side fuse box -
but if either is defective, you will get NO dash lights when
you turn on the ignition.
26) If when you jump pins 30 and 87 of the Ignition ‘ON’
relay base you do get dash lights but you do not hear the
half-second priming burst from the fuel pump suspect the EMS
Main relay.

Cheers,

Don

 

Thanks for the suggestions, will get testing once the weather clears, have found an old cps dad had, i assume is ok as he kept it, going to drop it in just in case the new one is defective, had experiance with a defective new o2 sensor before.

your 2nd surgestion regarding the shielding how do i go about testing.

Thanks
Phil

 

On some of the aftermarket CPSs, the wires in the pigtail harness are exposed, and you can see either the shield, or a wire that is supposed to connect to the shield. On some aftermarket CPSs I have received, the shield wire was cut! You can test for continuity/low resistance to ground between the shield and the ground stud at the right inner fender/wing.

You can also test the shield via the connector - test for low resistance continuity from the harness connector shield pin to the ground stud.

 

Don B

Cool Thanks

Will report back

Phil

 

Finally got through the bad weather, with the aid of the diagnosis list problem solved.

The issue was with both Oxy Sensor Heater & EMS Relays suffering from furred up pins, once cleaned and reinserted car fired up, revs waivered a bit and close to stalling but after a few minutes was steady.

I assume the EMS relay is what basically switches on the Engine Management Computer as after cleaning the relay both the fuel pump and CPS came back to life and engine started, so probably didn't need to buy a new CPS after all.

The other thing worth mentioning, it might be peculiar to my car (other things have been in the past) at step 14 the wiring is back to front, pin 30 = White/Brown & 87 = Brown/Yellow with 12 volts, plus relay diagrams from several manuals show EMS relay is Light Blue 4 pin but mine has Pink 5 pin with 4 in total on the left side of the bulkhead, not 6 on the right side as on the diagram..

Thanks to Don B for all the help.
Phil

 

When I need to crank the engine without it firing up, I remove the oxygen sensor heater relay. Stops the fuel pump.

Larry

 

Phil,

Congratulations! And thank you for reporting your successful diagnosis! It will help other owners for years to come.

Regarding your CPS, yes, you did need to buy a new one, because the old one was going to fail, and probably by some failure mode that would be intermittent and difficult to diagnose. But keep your old one in the boot as an emergency spare. That's what many of the rest of us have done.

Great job!

Cheers,

Don

 

A further update - Some time later it happened again and after re-checking the EMS relay i discovered the wires leading into the relay socket were severely corroded and broken, having soldered a replacement socket from a donor loom all is good