1988 v12, turn key and nothing at all except buzzing from main relay next to fuel pump relay. Nothing at starter, nothing at fuel pump. Lights and everything else works fine. Any ideas were to look?
Sounds like either a dead battery or possibly a faulty starter relay. Turn your lights on and see if they dim when you try to crank the starter. If they dim it is likely that your starter has failed. I have had similar problems before due to bad batteries, failed starter relays, and failed starters. You should also check the battery cable connectors on the battery and chassis/terminal post and make sure that they are clean, corrosion free and tight.
Paul
No dimming and no fuel pump running. Battery strong cables tight
How about the inertia switch on door post?
Would disconnecting wire eliminate it. Tried it and no change
inertia switch kills ignition, not starter.
Inertia switch kills the fuel pump.
Paul
right you are, Paul. I suppose I was thinking in terms of running vs starting.
Should have said something like kills ability to run, not ability to turn over (crank)
Found that I do not have power to the coils in both the main and fuel pump relays
FWIW, I just walked outside to the garage, got in my car, and tripped the inertia switch. Turned the ignition on, and a silent fuel pump was the result. Turned the key to the start position and , again, silence from the starter. I then pushed the button down on the inertia switch, and the car started as it always does. Go figure! Maybe it’s really an anti-theft device!
Indeed! Good info. There is nothing shown on the WSM wiring diagram that stops engine cranking except the transmission lock which stops the starter relay from responding to the key.
I am more discouraged by the day with the stupid WSM content which seems to be wrong more often than not.
I looked up "Inertia switch’ in the archives, and found that this confusion started around 1998!
Much discussion, and apparently inaccurate wiring diagrams as well. Some of the threads on the switch helped explain to me exactly what is “enabled” through the inertia switch. Interesting reading!
The big deal I just found is the EMS main relay loses voltage when the inertia switch is off and it in turn kills the fuel pump relay which is daisy-chained. No juice to the EMS means all sorts of stuff will not work.
Oh, and the transmission neutral switch is a player, too. AND the security system. Good heavens.
With my two Series III XJ6s (1984 and 1987) and my wife’s 1990 XJ-S convertible if I trip the inertia switch by pulling up on the pin this will kill power to the fuel pump but not the starter or ignition system. I have found this helpful when troubleshooting or doing things like compression tests where I want the fuel pump disabled. However if I pull up on the inertia switch pin on my 1990 V12 Vanden Plas (an XJ12) not only does the fuel pump not work but the starter will also not engage ( I am not sure about ignition). I have never tried to figure out why that car is different than the others but perhaps it is a clue to Vans issue. Perhaps a relay or wire involved with this feature has failed. If someone has the S57 Electrical Guide for Van’s 1988 model year perhaps something could be discovered there in the EFI wiring diagrams.
Paul
BRGXJS,
What is a WSM wiring diagram?
Paul
Work shop manual …
This is from back in '03.
Quote- The inertia switch is in the operating path for the main relay.
Also- The solenoid of the start relay is controlled through the feedback inhibit relay, the solenoid of which is grounded through the neutral switch and which obtains +v through the EFI main relay, which obtains +v from the ignition switch and grounding via- the inertia switch.
I think I’d be looking at the inertia sw. and the ignition sw.
Just want to verify location of the Inhibit relay. My wiring diagram calls it by a different name and the manual is not to clear as to location . Is it the middle silver metal relay on drivers side above fuses? If I jumpered the 2 wires to the inertia switch would it allow the system to run?
Not true. In some cars, it kills the starter. I’ve never figured out why it apparently acted in different ways in different cars.
Methinks that’s a bad relay. They’re not supposed to buzz. Either that or the power to it is flaky for some reason.
I haven’t yet seen mention of the most common cause of this malady: ignition switch. When it won’t start, try turning the key back and forth from OFF to START about fifty times. Sometimes this will wipe the crud off the poorly-designed contacts within the ignition switch and suddenly it’ll start working.