injectors not firing
Discussion
well it started off as a bad day and got worse! flat battery on the tin top this morning, so dragged the wedge <350> out of its slumber and set off, got 2 miles down the road and it stopped dead! checked all the usual suspects and finally called the breakdown guys, after much head scratching they called for back up....a flaming recovery wagon!! arrived back home 3 hours after I left and spent another 3 hours with multi meter in hand freezing my ass off, result??? injectors not firing and I'm buggered if i can find why, so if this is an easy one to resolve can anybody help?
thanks for all the info and help, but still no luck, replaced the coil with a new one just to be certain that the plugs are firing under compression, plugs only have 1k miles on them and are clean as a whistle, squirted some easy start directly into the plenum to see if it would at least try to fire up....result= 0 nothing, zilch! checked to see if the valve gear was lifting, thats seems ok too, I'm completely stumped now and considering calling a "professional" anyone got any more ideas???
thanks for all the info and help, but still no luck, replaced the coil with a new one just to be certain that the plugs are firing under compression, plugs only have 1k miles on them and are clean as a whistle, squirted some easy start directly into the plenum to see if it would at least try to fire up....result= 0 nothing, zilch! checked to see if the valve gear was lifting, thats seems ok too, I'm completely stumped now and considering calling a "professional" anyone got any more ideas???
Edited by chedder on Monday 29th January 20:12
Dead easy 
First, does the fuel pump run if you lift the airflow meter flap (with ignition on) and is there plenty of fuel in the tank? Do you get nice fat sparks at the plugs?
The injection system only needs one input to fail and it won't fire. That's the trigger signal from the ignition amplifier (usually, but not always, mounted on the distributor).
There's usually a wire from the dissie that passes round the left side of the engine bay and joins the injection loom somewhere around the airflow meter. In that wire there is a bullet connector. If it corrodes or pulls apart the injection will just sit there and look at you.
Apart from that, there are two relays and a red 'steering module' that power the injection system. The steering module rarely fails but the relays could.
The ECU main connector has a poor latching arrangement; it's worth unplugging the connector, bending the latch spring in a bit and replugging, making sure the latch is secure.
The injection system is earthed to a stud on the rear of the l/h cylinder head. If it corrodes or the engine to chassis/ engine to battery earth is poor, the injection may not be earthing. Usually this coincides with a sluggish starter motor.
Similarly, the Power Resistor module (left-hand inner wing, usually) has two brown/orange feed wires going into it. If these have no 12v supply (from one of the relays meantioned earlier) or the plug is corroded then the injectors get no power. It's unusual for both of those feeds to corrode at the same time; if one corrodes then you lose 4 cylinders but not all 8.
Assuming none of the above has fixed it, switch the ignition on and rapidly flick the throttle open a few times. If you hear a 'tick' from the injectors then the injection is probably OK and either you have no fuel or the trigger signal is missing as in Chapter 1
As a quick check, work out a way to get 12v to the cold start injector and crank the engine. If it tries to fire then the ignition is OK and you DO have an injection fault.
First, does the fuel pump run if you lift the airflow meter flap (with ignition on) and is there plenty of fuel in the tank? Do you get nice fat sparks at the plugs?
The injection system only needs one input to fail and it won't fire. That's the trigger signal from the ignition amplifier (usually, but not always, mounted on the distributor).
There's usually a wire from the dissie that passes round the left side of the engine bay and joins the injection loom somewhere around the airflow meter. In that wire there is a bullet connector. If it corrodes or pulls apart the injection will just sit there and look at you.
Apart from that, there are two relays and a red 'steering module' that power the injection system. The steering module rarely fails but the relays could.
The ECU main connector has a poor latching arrangement; it's worth unplugging the connector, bending the latch spring in a bit and replugging, making sure the latch is secure.
The injection system is earthed to a stud on the rear of the l/h cylinder head. If it corrodes or the engine to chassis/ engine to battery earth is poor, the injection may not be earthing. Usually this coincides with a sluggish starter motor.
Similarly, the Power Resistor module (left-hand inner wing, usually) has two brown/orange feed wires going into it. If these have no 12v supply (from one of the relays meantioned earlier) or the plug is corroded then the injectors get no power. It's unusual for both of those feeds to corrode at the same time; if one corrodes then you lose 4 cylinders but not all 8.
Assuming none of the above has fixed it, switch the ignition on and rapidly flick the throttle open a few times. If you hear a 'tick' from the injectors then the injection is probably OK and either you have no fuel or the trigger signal is missing as in Chapter 1
As a quick check, work out a way to get 12v to the cold start injector and crank the engine. If it tries to fire then the ignition is OK and you DO have an injection fault.
thanks for that Wedg1e, have checked for those problems but still no V8 rumble, cant get any voltage to the injectors, steering module checks out ok, main relay is clicking but the other one doesn't seem to do anything swapped the relays around and still no luck.
tried 12v to the cold start valve but to no avail, any more help would be appreciated!!!
Feul pump is definately running and supplying feul to the rail, big fat spark at the plugs, voltage to the resistor pack and the dizzy module seems to check out too, am beginning to wonder if the ecu is at fault????
tried 12v to the cold start valve but to no avail, any more help would be appreciated!!!
Feul pump is definately running and supplying feul to the rail, big fat spark at the plugs, voltage to the resistor pack and the dizzy module seems to check out too, am beginning to wonder if the ecu is at fault????
The second of those two relays feeds the fuel pump. If the pump runs the relay must be OK... or maybe your relays are installed in the wrong order (wouldn't be the first time the chart didn't match the car).
The brown/orange wires at the resistor pack are tied to the same colour wire at the airflow meter and are fed by the main relay. You could try pulling the relkay and inserting a wire link between terminals 30/51 and 87... that takes the relay and steering module out of the equation. You also need to put 12v onto the Blue/Yellow wire from that relay (feeds the ECU!).
That should get power to the injectors.
I would say it's unlikely to be the ECU as you're not getting any injector supply.
The brown/orange wires at the resistor pack are tied to the same colour wire at the airflow meter and are fed by the main relay. You could try pulling the relkay and inserting a wire link between terminals 30/51 and 87... that takes the relay and steering module out of the equation. You also need to put 12v onto the Blue/Yellow wire from that relay (feeds the ECU!).
That should get power to the injectors.
I would say it's unlikely to be the ECU as you're not getting any injector supply.
Go to page 34 of the EFI system PDF here..........www.pixeltechnology.co.uk/wedge/maintenance.html check for Ohms (not voltage) 6 ohms on each etc. etc.
Edited by dickymint on Sunday 28th January 18:53
chedder said:
Should be 3v not six! brain gone numb with cold! looks like it may be the resistor pack that is as fault, can anyone confirm this? before I run out and spend some more of my hard earned????
Exceedingly unlikely that the res pack is duff, they normally fail open-circuit and then only if shorted to earth for any length of time. And it would take all 8 outputs to be shorted to lose all 8 injectors.
Yeah sorry, looking at the wiring diagram the common on the resistor pack is battery +, the erath braid that goes to the block must just be for RFI suppression.
So the question becomes - is the common lead properly supplied with battery +? This seems to come from the main relay and/or from the AFM (though that might be to the AFM and thence to the ECU).
So the question becomes - is the common lead properly supplied with battery +? This seems to come from the main relay and/or from the AFM (though that might be to the AFM and thence to the ECU).
ANother easy check is the throttle thing. Turn on the ignition, then get your head under the bonnet and rotate the throttle spindle quickly. There should be a click from all the injectors half to 3/4 of the way round. (He He)
This test is independent of the ignition-derived injector firing.
Another useful tool to diagnose this is an oscilloscope, which can pick up too-short pulses that won't fire the injectors.
This test is independent of the ignition-derived injector firing.
Another useful tool to diagnose this is an oscilloscope, which can pick up too-short pulses that won't fire the injectors.
Edited by adam quantrill on Monday 29th January 11:27
1/2 to 2/4 eh? not much of an angle that!! he he.
The injectors should fire based on the speed at which you open the throttle pot. [with the ignition on and the the engine not running] . At least it did on my 350 and my 390 both flapper injection. Of course if the plugs are fouled due to too rich a running it can stop the car - had a similar problem when the plasic bleed down valve broke on the distributor feed line - the missing caused the plugs to go sooty.
-jim
The injectors should fire based on the speed at which you open the throttle pot. [with the ignition on and the the engine not running] . At least it did on my 350 and my 390 both flapper injection. Of course if the plugs are fouled due to too rich a running it can stop the car - had a similar problem when the plasic bleed down valve broke on the distributor feed line - the missing caused the plugs to go sooty.
-jim
right then time for an update!! resistor pack values check out ok, but the resistance values for the maf unit dont! 3 sets of values are shown on the relevant docs but all of mine are approx 35% down on them? so if thats the case can I assume that the maf unit is knackered? have also discovered that the plugs are getting a deposit of fuel on them but it still doesn't fire up even though the plugs are sparking.
Have connected a timing light into the plug lead and this is flashing when the engine is cranking so i assume it's safe to say that the plugs are firing under compression?
Any more help or ideas would be greatly appreciated as this has me baffled!
Have connected a timing light into the plug lead and this is flashing when the engine is cranking so i assume it's safe to say that the plugs are firing under compression?
Any more help or ideas would be greatly appreciated as this has me baffled!
If you have wet plugs and the plugs are black, you probably ran rich, and the plugs are fouled. You need to either remove the plugs and get them cleaned with a grit blaster, or put new plugs in - I would advise a set one heat range hotter while you are diagnosing the problem. I think standard are heat range 7 (NGK) . So you want to stick in a set of 6 or even 5 to make sure the ceramic gets hot enough to self clean. That should get you going enough to diagnose the overfueling / ignition cause. There is a risk with leaving 5s in for too many miles, as the ceramic gets very hot and can fracture (looks pretty and white though!)
Let us know how you get on.
-Jim
Let us know how you get on.
-Jim
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