Duncan Posted November 10, 2012 Share Posted November 10, 2012 Hi all, Iv bought a Disco 1 3.5 v8 Efi that won't start, the previous owner said all was fine then one day-nothing. It's sparking and turning over right, fuel is getting to the fuel rail and you can hear the fuel pump ok, but the injectors don't let the fuel out! The ECU won't let the injectors pulse or even the starter solenoid wire to work. I have checked the resistance on the fuel temp sensor and block they both read a bit of resistance then lower to zero as get heated by a lighter. there is a 3 wire sensor on the downpipe I think is an oxygen sensor-If this is broke could it cause the engine not to start or would it just run rich/lean etc. I can't see any immobiliser and I just have the key. So can any broken/dodgy sensors not let it start? Thanks! Duncan Quote Link to comment Share on other sites More sharing options...
teabag Posted November 10, 2012 Share Posted November 10, 2012 Have you check for iffy comnnections on top of the coil as that is also where the ecu gets a signal from. With your sensor I would have thought you would have had two, each one before each cat. This link may help u http://www.britishv8.org/Articles/Rover-14CUX-EFI.htm Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 11, 2012 Share Posted November 11, 2012 The ECU needs a signal from the coil -ve to tell it the engine's turning, if that's dodgy it won't fire anything. No other sensors would stop it from firing, coolant/air temp/afm would just make it run rich/lean. Flapper AFM has a contact in it for the fuel pump I think, all the diagrams are on the forum and there's a full diagnostics guide in the technical archive. Quote Link to comment Share on other sites More sharing options...
Duncan Posted November 11, 2012 Author Share Posted November 11, 2012 Hi thanks for replies, I previously checked and just rechecked the connector to coil -ve is fine, also the +ve. Ok so sensors will not stop her starting that's good! Iv read that link before and checked a few resistances but couldn't trace the problem. I would be thinking Alram Spider box thing but this is a 1993 Disco. No alarm goes off or flashing light on dash so don't think its the immobilser but I only have 1 key so can't check isnt the Immobiliser. When trying to start theres no signal to the solenoid, When bypassing this the starter works fine but no fuel comes out of the injectors If an Injector was not dodgy but broken could the lack of signal etc cause this? break in a circuit sort of thing. Not sure where to look next :/ Quote Link to comment Share on other sites More sharing options...
teabag Posted November 11, 2012 Share Posted November 11, 2012 That's what the immobiliser does cut the starter and fuel pump if your disco is UK spec, you don't have passive immobilision so no 'spider' it's manual so the key in the drivers door lock will immobilise or remobilise the vehicle, but as u say you can still crank (turning over) the engine then I doubt u have a problem with that. Looks like you may soon be needing to be checking the ECU and the outputs from it. Quote Link to comment Share on other sites More sharing options...
Ally V8 Posted November 12, 2012 Share Posted November 12, 2012 I think the immobiliser part of the alarm ecu has failed,all it does is to provide and earth path to pin 34 (Black / Orange wire) of the engine ecu.So if you unplug the loom from the engine ecu see if there is continuity to earth on that wire - if not,it isnt going to go.Seen it before on a RRC 200TDI,(Same Alarm ecu,just inhibits the starter and disables the stop solenoid.) I guess there is a wiring diagram in the archives on this site - please check I have the pin # and wire colour right as I only have RR diagrams at home,but the 14CUX part should be all the same. Quote Link to comment Share on other sites More sharing options...
Duncan Posted November 12, 2012 Author Share Posted November 12, 2012 Old hand - The engine does not crank I was just bypassing it to check starter,sparks etc. Could well be the Immobiliser failed I have been out checking the pins tonight But I can't find any listed as the immobilser to ECU wire!? The ECU has its 12v supply, ignition supply and 2 earths ok. It also has the transmission gear switch(34) working ok so when in Parked it earths-so thats ok. Sends current to fuel rail when ign on like it should But I'm not too sure which outputs to check now from the www.britishv8.org link Ally V8 - that wire sounds perfect, but on mine pin 34 is the trans gear switch so provides an earth when in park so will start, I wonder if the immobilser is in line with this function? If so would appear is alright? Where next folks? Quote Link to comment Share on other sites More sharing options...
Ally V8 Posted November 12, 2012 Share Posted November 12, 2012 Old hand - The engine does not crank I was just bypassing it to check starter,sparks etc. Could well be the Immobiliser failed I have been out checking the pins tonight But I can't find any listed as the immobilser to ECU wire!? The ECU has its 12v supply, ignition supply and 2 earths ok. It also has the transmission gear switch(34) working ok so when in Parked it earths-so thats ok. Sends current to fuel rail when ign on like it should But I'm not too sure which outputs to check now from the www.britishv8.org link Ally V8 - that wire sounds perfect, but on mine pin 34 is the trans gear switch so provides an earth when in park so will start, I wonder if the immobilser is in line with this function? If so would appear is alright? Where next folks? Yes,that is the wire and its inline with the alarm ecu.Just remembered early Disco fusible links along the inner wing,more than once I have seen them where there is power there but the fusible links are so corroded they wont pass enough current to do anything.Pull the sheathing back and see if they are going green. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 13, 2012 Share Posted November 13, 2012 Hi thanks for replies, I previously checked and just rechecked the connector to coil -ve is fine, also the +ve. The ECU connecction *may* be separate, it should be a white/black or white/blue wire. One some models it went from the ignition amplifier. One some cars it goes via a relay mounted on the shock turret near the airflow meter, which is switched by a vacuum switch on the back of the plenum. You can bridge out the relay contacts (not the coil pins!) to bypass it. It's entirely possible for the coil to be getting power & ground & making sparks but the signal not getting down the wire to the ECU. Quote Link to comment Share on other sites More sharing options...
teabag Posted November 13, 2012 Share Posted November 13, 2012 Old hand - The engine does not crank I was just bypassing it to check starter,sparks etc. Could well be the Immobiliser failed I have been out checking the pins tonight But I can't find any listed as the immobilser to ECU wire!? The ECU has its 12v supply, ignition supply and 2 earths ok. It also has the transmission gear switch(34) working ok so when in Parked it earths-so thats ok. Sends current to fuel rail when ign on like it should But I'm not too sure which outputs to check now from the www.britishv8.org link Ally V8 - that wire sounds perfect, but on mine pin 34 is the trans gear switch so provides an earth when in park so will start, I wonder if the immobilser is in line with this function? If so would appear is alright? Where next folks? The only time u need to look at the ecu circuits is because your injectors are not opening, the engine ecu has no connection with the immobiliser either on your system or the later Thatcham 'spider' system The immobiliser just interfaces with the ignition circuit so if you believe that is a problem there then the only option u have is to replace the alarm ecu but of course u could rig up a new direct ignition feed as u have already done. Once you can remobilise the engine and the engine cranks and still find it's not running because as you have already stated the injectors don't open then look at the engine ecu to check that i'ts giving the negitive 0 volts switching signal required. There's more info on the www on fault finding testing of V8 ECUs and the various sensors. As an example http://www.rv8r.co.u...andardecu1.html Quote Link to comment Share on other sites More sharing options...
Duncan Posted November 19, 2012 Author Share Posted November 19, 2012 Ok I really think this is a dud ECU problem now, I have checked lots of wiring out on the weekend, Power is getting to the starter relay and fuel pump relay they all click on and off as mean't to. the negative to the ECU that is comes from the starter relay through a crazy earth based resistance thing and the automatic inhibitor switch seems fine and no change if you direct earth it. there are just soo many wires disappearing behind the dash it's a nightmare and the haynes wiring diagram is heavily simplified from whats really there. Any decent way to get the engine running without the ECU just so I can check engine is ok and gearbox works before breaking? by 'decent' I mean better than spraying easy start into the air intake! Quote Link to comment Share on other sites More sharing options...
Duncan Posted November 19, 2012 Author Share Posted November 19, 2012 I also found the inertia switch square black box with pull up red bit on the top, I figure up is the reset position it was down when I found it, simply lift up or do you have to do something else as well? Quote Link to comment Share on other sites More sharing options...
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