V8 Flapper system - stopped starting!!
Discussion
Here you go, a sketch showing the supply and control for one injector 
From the left:-
1. Ignition is off so main relay open; no supply reaches the injector. ECU is not powered.
2. Ignition on, main relay closes and sends 12v down to the resistor module via the Brn/Ora wires. Each Brn/Ora feeds 4 resistors in the module. If you conside the injector unplugged, the 12v passes through the resistor and can be measured at the injector plug (Yel/xxx wire, the xxx depends on which injector) as virtually unaltered by the resistance; this is because a multimeter presents hardly any load (i.e. draws microscopic amounts of current) to the 12v present so it isn't 'dropped' by the resistor. OK, technically it will be by a small amount, but to see 11.95 V and think the resistor is faulty would be incorrect.
3. With the injector connected, the 12v flows through the injector winding (a coil of very fine wire wound in a cylindrical shape) and all the way to the ECU (via the Gry/xxx wire). So it would be possible, if you removed the ECU multiplug, to measure about 12V at each of the injector return wires.
Once you plug it in, each bank of 4 injectors is linked together by circuit board tracks and taken to a power transistor (there are two, one for each bank). With the engine not running, the transistor is in its 'off' state , does not conduct and the injector just sits there doing nothing.
4. Once you crank the engine and the ECU starts seeing the trigger signal from the coil (-) rail (i.e. the ignition amplifier output) the electronics begins to generate a 'pulse train' that is fed into the base of the transistor. In much the same way as energising the coil of a relay forces its contacts to change state, energising the base of a transistor makes it change into a conducting state, so current flows through it, in this case taking the injector winding down to earth, making current flow through the winding and making the pintle lift to spray fuel.
So...
If any of the four resistors had somehow burned out - they're not actual resistors in the sense of discrete components soldered to a circuit board, they're formed by having the copper tracks meander around the board thus increasing the resistance of the path the 12v has to take, like this:
- then you could have 12V going in on the Brn/Ora wire but nothing leaving on the Yel/xxx wire. However, it would need a dead short on the Yel/xxx to cause enough current to flow for that to happen, and the other four Yel/xxx wires in that 'half' of the matrix should still show 12V. If all 4 had a dead short, say by chafing on a steel bulkhead, then certainly you could lose them all and have a dead bank, but for ALL 8 to burn out would be some spectacular bit of fireworks! As the wiring from the resistor pack to the injectors doesn't pass through any steelwork this seems extremely unlikely.
As an aside, if the ECU had failed it would do one of two things: either not fire at all, which can happen, or as is more usually the case, one of the power transistors goes short-circuit (conducts all the time irrespective of any base current) which permanently earths all four of the injectors connected to it and the car over-fuels like crazy as soon as the fuel rail pressure comes up.
Phew, must be time for a rum...
From the left:-
1. Ignition is off so main relay open; no supply reaches the injector. ECU is not powered.
2. Ignition on, main relay closes and sends 12v down to the resistor module via the Brn/Ora wires. Each Brn/Ora feeds 4 resistors in the module. If you conside the injector unplugged, the 12v passes through the resistor and can be measured at the injector plug (Yel/xxx wire, the xxx depends on which injector) as virtually unaltered by the resistance; this is because a multimeter presents hardly any load (i.e. draws microscopic amounts of current) to the 12v present so it isn't 'dropped' by the resistor. OK, technically it will be by a small amount, but to see 11.95 V and think the resistor is faulty would be incorrect.
3. With the injector connected, the 12v flows through the injector winding (a coil of very fine wire wound in a cylindrical shape) and all the way to the ECU (via the Gry/xxx wire). So it would be possible, if you removed the ECU multiplug, to measure about 12V at each of the injector return wires.
Once you plug it in, each bank of 4 injectors is linked together by circuit board tracks and taken to a power transistor (there are two, one for each bank). With the engine not running, the transistor is in its 'off' state , does not conduct and the injector just sits there doing nothing.
4. Once you crank the engine and the ECU starts seeing the trigger signal from the coil (-) rail (i.e. the ignition amplifier output) the electronics begins to generate a 'pulse train' that is fed into the base of the transistor. In much the same way as energising the coil of a relay forces its contacts to change state, energising the base of a transistor makes it change into a conducting state, so current flows through it, in this case taking the injector winding down to earth, making current flow through the winding and making the pintle lift to spray fuel.
So...
If any of the four resistors had somehow burned out - they're not actual resistors in the sense of discrete components soldered to a circuit board, they're formed by having the copper tracks meander around the board thus increasing the resistance of the path the 12v has to take, like this:
- then you could have 12V going in on the Brn/Ora wire but nothing leaving on the Yel/xxx wire. However, it would need a dead short on the Yel/xxx to cause enough current to flow for that to happen, and the other four Yel/xxx wires in that 'half' of the matrix should still show 12V. If all 4 had a dead short, say by chafing on a steel bulkhead, then certainly you could lose them all and have a dead bank, but for ALL 8 to burn out would be some spectacular bit of fireworks! As the wiring from the resistor pack to the injectors doesn't pass through any steelwork this seems extremely unlikely.
As an aside, if the ECU had failed it would do one of two things: either not fire at all, which can happen, or as is more usually the case, one of the power transistors goes short-circuit (conducts all the time irrespective of any base current) which permanently earths all four of the injectors connected to it and the car over-fuels like crazy as soon as the fuel rail pressure comes up.
Phew, must be time for a rum...
Do you have a ballast resistor in the ignition circuit? I haven't seen any mention of these in this thread because they are not normally fitted to V8 TVRs.
The ballast resistor sits between the ignition connector and the coil in normal running. It drops the voltage available to the coil to around 7 volts. When the starter is cranking the ballast resistor is bypassed and the full 12 volts (minus what the starter is dragging) goes to the coil.
If the ballast resistor is shot or if the ignition to it is disconnected then the car will start when cranking but stop quickly when the key is released.
You can check this quickly by bridging a permanent 12 volts to the coil (it won't do any harm for a couple of minutes).
Russ
The ballast resistor sits between the ignition connector and the coil in normal running. It drops the voltage available to the coil to around 7 volts. When the starter is cranking the ballast resistor is bypassed and the full 12 volts (minus what the starter is dragging) goes to the coil.
If the ballast resistor is shot or if the ignition to it is disconnected then the car will start when cranking but stop quickly when the key is released.
You can check this quickly by bridging a permanent 12 volts to the coil (it won't do any harm for a couple of minutes).
Russ
Heavy, do you have a constant 12v on the brown/orange wire supplying the power resistors? You mentioned earlier ">The lack of voltage at the power resistor<" . Switched by the main relay or the AFM.
I would be tempted to break into the wiring to one injector to monitor voltage, although this would then involve a joint.
TPS is a useful way to trigger injectors for fault finding, it can be disconnected and the car should still run (so unlikely to be the cause of the no-start fault). It can cause erratic running if it's faulty.
I would be tempted to break into the wiring to one injector to monitor voltage, although this would then involve a joint.
TPS is a useful way to trigger injectors for fault finding, it can be disconnected and the car should still run (so unlikely to be the cause of the no-start fault). It can cause erratic running if it's faulty.
MrPicky said:
Do you have a ballast resistor in the ignition circuit? I haven't seen any mention of these in this thread because they are not normally fitted to V8 TVRs.
The ballast resistor sits between the ignition connector and the coil in normal running. It drops the voltage available to the coil to around 7 volts. When the starter is cranking the ballast resistor is bypassed and the full 12 volts (minus what the starter is dragging) goes to the coil.
If the ballast resistor is shot or if the ignition to it is disconnected then the car will start when cranking but stop quickly when the key is released.
You can check this quickly by bridging a permanent 12 volts to the coil (it won't do any harm for a couple of minutes).
Russ
Non-standard car so it's a possibility, and easy to test! The ballast resistor sits between the ignition connector and the coil in normal running. It drops the voltage available to the coil to around 7 volts. When the starter is cranking the ballast resistor is bypassed and the full 12 volts (minus what the starter is dragging) goes to the coil.
If the ballast resistor is shot or if the ignition to it is disconnected then the car will start when cranking but stop quickly when the key is released.
You can check this quickly by bridging a permanent 12 volts to the coil (it won't do any harm for a couple of minutes).
Russ
No clicking from the injectors is the thing to pursue at the moment (IMHO), but important not be set on one path. As pointed out by others, it is possible that the injectors are fully open (so no click), but then the engine would have hydrauliced when the pump was permanently running (another reason not to bridge the switched terminals to the pump relay).
Looking at the wiring diagram, flicking the white/black trace wire from ECU terminal 1 to earth should have the same effect as rotating the dizzy for triggering the injectors (assuming voltages from AFM are correct). I can't see what other inputs to the ECU are required to trigger the injectors, provided 12v supply to the power resistors is up and earths are good (anyone?).
Always a bit dubious about grounding (or applying voltages to) terminals to ECUs though
Cheers for all the info everyone and good to know there's a fellow rum drinker on board Wedg1e!
Am down south in the Bournemouth/Ringwood area.
Yep, still have 12v on the 2 orange/brown wires at the power resistor but next to nothing on the other 8 although when unplugged the engine won't even fire briefly.
Haven't accidentally swapped the relays, problem started after being parked for 2 weeks and didn't touch anything in the meantime.
Will check voltage at the injectors when I can get over to the workshop this evening. Will also remove the bridging wire on the fuel pump relay and check voltages at both relays and steering module when cranking to see if the pump is shutting down when the engine fires and coming back on as soon as it dies.
With regards to Wedg1e's pre-rum post, I do have 12v at the ECU multiplug yet at the same time nothing at the power resistor which seems impossible if I'm understanding it right? And am getting a reading of 5.6ohms through all 8 pins of the power resistor which implies the 'resistors' haven't broken down?
Am going to try running another wire from the coil -ve to ECU pin 1 just to see as although the continuity test seems ok a fault here would explain the symptoms...but not the lack of voltage at the power resistor.
Haven't seen a ballast resistor yet but will carry on looking, think the original Essex V6 did use one but in the guise of a high resistance wire...but the wiring to the coil is now all part of the Rover loom....I think!
V8 Fettler - What do you mean by 'flicking' the coil -ve wire exactly? Putting 12v to it?
Just had a thought...should I be looking for voltage at the power resistor with the plug connected? I've been measuring with it disconnected? Am I being stupid?
Cheers!
Am down south in the Bournemouth/Ringwood area.
Yep, still have 12v on the 2 orange/brown wires at the power resistor but next to nothing on the other 8 although when unplugged the engine won't even fire briefly.
Haven't accidentally swapped the relays, problem started after being parked for 2 weeks and didn't touch anything in the meantime.
Will check voltage at the injectors when I can get over to the workshop this evening. Will also remove the bridging wire on the fuel pump relay and check voltages at both relays and steering module when cranking to see if the pump is shutting down when the engine fires and coming back on as soon as it dies.
With regards to Wedg1e's pre-rum post, I do have 12v at the ECU multiplug yet at the same time nothing at the power resistor which seems impossible if I'm understanding it right? And am getting a reading of 5.6ohms through all 8 pins of the power resistor which implies the 'resistors' haven't broken down?
Am going to try running another wire from the coil -ve to ECU pin 1 just to see as although the continuity test seems ok a fault here would explain the symptoms...but not the lack of voltage at the power resistor.
Haven't seen a ballast resistor yet but will carry on looking, think the original Essex V6 did use one but in the guise of a high resistance wire...but the wiring to the coil is now all part of the Rover loom....I think!
V8 Fettler - What do you mean by 'flicking' the coil -ve wire exactly? Putting 12v to it?
Just had a thought...should I be looking for voltage at the power resistor with the plug connected? I've been measuring with it disconnected? Am I being stupid?
Cheers!
">Just had a thought...should I be looking for voltage at the power resistor with the plug connected? I've been measuring with it disconnected? Am I being stupid?<"
Brown/orange trace wire as marked:
My understanding is that this should be live at 12v when the multi-plug to the power resistors is disconnected (ignition on, main relay in and steering module working.Alternative 12v supply via AFM when flap is moved). I'll check mine later. Voltage might drop when injectors are fired.
Original drawing by Honestjohntoo
I'll post another marked drawing for the flicking of the ignition amp wire
Edit: not certain about connection to AFM, could be an input to the AFM
Edit again. As I see the wiring diagram, if the ignition is on and the steering module is working OK, then the main relay should always be in and therefore there should always be 12v to the power resistors (brown/orange trace), therefore shouldn't need an alternative supply via the AFM. Therefore, the connection to the AFM is probably a signal to the ECU (signals that the main relay is in and that the flap is operated), this would be consistent with the notation used for the switching within the main relay and the fuel pump relay ("hinged" bit of switch is live)
Brown/orange trace wire as marked:
My understanding is that this should be live at 12v when the multi-plug to the power resistors is disconnected (ignition on, main relay in and steering module working.
Original drawing by Honestjohntoo
I'll post another marked drawing for the flicking of the ignition amp wire
Edit: not certain about connection to AFM, could be an input to the AFM
Edit again. As I see the wiring diagram, if the ignition is on and the steering module is working OK, then the main relay should always be in and therefore there should always be 12v to the power resistors (brown/orange trace), therefore shouldn't need an alternative supply via the AFM. Therefore, the connection to the AFM is probably a signal to the ECU (signals that the main relay is in and that the flap is operated), this would be consistent with the notation used for the switching within the main relay and the fuel pump relay ("hinged" bit of switch is live)
Edited by V8 Fettler on Tuesday 19th November 11:12
Edited by V8 Fettler on Tuesday 19th November 11:32
heavy squad said:
Know what you're saying GV!!
Have just called in to a friendly Land Rover place in the New Forest and one of the guys there with an interest in old Fords is going to dig me an ECU out of his shed at home and donate it to the cause for free! Hopefully it's a functioning one!!
That's a spot of luck, let us know how you get on.Have just called in to a friendly Land Rover place in the New Forest and one of the guys there with an interest in old Fords is going to dig me an ECU out of his shed at home and donate it to the cause for free! Hopefully it's a functioning one!!
Slight update - turns out I am a complete dimwit and there is in fact battery voltage at the power resistor when it's plugged in...schoolboy error!! Suppose the lack of injector click must be down to either iffy TPS or because of having listened to too much Black Sabbath and Motorhead over the years!!
Tried running in another wire from coil -ve to ECU pin 1 but no difference.
Just waiting for the battery to charge back up a bit and will take some readings around the relay/steering module area whilst cranking. Failing that then hopefully my new best mate will come up trumps with another ECU tomorrow.
Tried running in another wire from coil -ve to ECU pin 1 but no difference.
Just waiting for the battery to charge back up a bit and will take some readings around the relay/steering module area whilst cranking. Failing that then hopefully my new best mate will come up trumps with another ECU tomorrow.
adam quantrill said:
Granted, but the injector click test is one hell of a useful (and simple) diagnostic tool. If it's not clicking it could be a symptom of a knackered ECU, is all I'm saying...
Errr... I know 
I felt that the OP was getting sidetracked by looking at things that aren't relevant to the problem. If the pot. had a broken wire, for example, yes it would be a fault, no the injectors wouldn't click but it wouldn't stop the car starting either... is all I was saying As he's now proved the resistor pack OK it may well prove to be an ECU issue.
Has anyone suggested clouting the ECU yet? 
Wedg1e said:
adam quantrill said:
Granted, but the injector click test is one hell of a useful (and simple) diagnostic tool. If it's not clicking it could be a symptom of a knackered ECU, is all I'm saying...
Errr... I know I felt that the OP was getting sidetracked by looking at things that aren't relevant to the problem. If the pot. had a broken wire, for example, yes it would be a fault, no the injectors wouldn't click but it wouldn't stop the car starting either... is all I was saying As he's now proved the resistor pack OK it may well prove to be an ECU issue.
Has anyone suggested clouting the ECU yet? V8 Fettler said:
For a correctly installed flapper EFi system, the TPS test offers an easy, no cost, quick method of testing injector function. How can that be a sidetrack?
Scroll back and in my very first post you'll see I suggested checking it. Once Heavy repeatedly said he couldn't hear the injectors clicking (mentioned it in his first post, in fact) but wasn't measuring anything from the resistor pack he went off in search of voltages at the throttle pot.As I said later on, until he resolved the resistor pack issue there was no point in looking further.
Aside from that, whilst the ECU may correctly respond to the throttle flick, it may also fail to respond to the ignition trigger input, so the fact that the injectors fire when you flick the throttle doesn't necessarily mean the ECU is hunky-dory and the car will start. And the converse applies: an ECU that will let you start and drive the car can fail to respond to the 'foot-down' input when you floor it.
I'm an electronics techie, I've spent thirty-odd years diagnosing faults on everything from CB radios to washing machines to industrial x-ray systems - and cars. I know how easy it is to get drawn into a long hunt for an irrelevant voltage, signal or resistance. I'm just trying to 'inject'
some of that into fixing a car that's 330 miles from where I live.Gassing Station | Wedges | Top of Page | What's New | My Stuff