Injector sticking open - symptoms?
Discussion
Sorry to ask this in major mods, but I figure it's the greatest concentration of relevant expertise...
I have a strange occasional misfire symptom on my 4.3 Griffith. No pattern to its occurence that I can discern. I have a 12v LED wired across each bank of injectors and originally I observed that during misfire one bank glowed brighter than the other. Legend has it that if the Lucas 14CUX suffers a very short interruption to it's power supply the software can corrupt and cause one injector bank to saturate. Well suffice it to say I've pretty much ruled that out, and on close observation I'm wondering if actually it's the other bank that's dimming.
Given this is a 12LED ACROSS the injector banks it must represent a drop in injector drive voltage? Or at least injector pulse length (maybe due to the bottom of the injector drive signal being clipped?).
The misfire is most evident up to 3500-4000 rpm. It's accompanied by a smell of fuel (not overpowering, but detectable). The car will idle rough - doesn't stall at tickover. If I accelerate through the misfire, suddenly all 8 come on song (@ about 3500rpm - with a bit of coughing) again and the car picks up and flies.
So here's the question:
If one injector was sticking OPEN - flooding that cylinder as the excess fuel was unburnt - would the electrical characteristics of the injector somehow change (as presumably no solenoid - or whatever the injector has inside it is being driven) and lead to a lower impedance for that injector? Could that effect a voltage drop across the whole bank and cause the other injectors to underfuel?
This might explain the smell of fuel (from the overfuelling cylinder), and the fact that the misfire is much more noticable than if I just disconnect one injector connector (which I can hardly notice the effect of, and which does not change the brightness of the injector bank LEDs). My theory goes that at about 3500 rpm the injector pulse duration is enough for the healthy three injectors to get enough fuel for a burnable mix, and maybe even the charge of the stuck injector's cylinder is combustible.
Your thoughts would be much appreciated. Needless to say I have checked/replaced all the usual suspects. This is all with open loop fuelling btw.
I have a strange occasional misfire symptom on my 4.3 Griffith. No pattern to its occurence that I can discern. I have a 12v LED wired across each bank of injectors and originally I observed that during misfire one bank glowed brighter than the other. Legend has it that if the Lucas 14CUX suffers a very short interruption to it's power supply the software can corrupt and cause one injector bank to saturate. Well suffice it to say I've pretty much ruled that out, and on close observation I'm wondering if actually it's the other bank that's dimming.
Given this is a 12LED ACROSS the injector banks it must represent a drop in injector drive voltage? Or at least injector pulse length (maybe due to the bottom of the injector drive signal being clipped?).
The misfire is most evident up to 3500-4000 rpm. It's accompanied by a smell of fuel (not overpowering, but detectable). The car will idle rough - doesn't stall at tickover. If I accelerate through the misfire, suddenly all 8 come on song (@ about 3500rpm - with a bit of coughing) again and the car picks up and flies.
So here's the question:
If one injector was sticking OPEN - flooding that cylinder as the excess fuel was unburnt - would the electrical characteristics of the injector somehow change (as presumably no solenoid - or whatever the injector has inside it is being driven) and lead to a lower impedance for that injector? Could that effect a voltage drop across the whole bank and cause the other injectors to underfuel?
This might explain the smell of fuel (from the overfuelling cylinder), and the fact that the misfire is much more noticable than if I just disconnect one injector connector (which I can hardly notice the effect of, and which does not change the brightness of the injector bank LEDs). My theory goes that at about 3500 rpm the injector pulse duration is enough for the healthy three injectors to get enough fuel for a burnable mix, and maybe even the charge of the stuck injector's cylinder is combustible.
Your thoughts would be much appreciated. Needless to say I have checked/replaced all the usual suspects. This is all with open loop fuelling btw.
If you're running the original hotwire setup with lambda sensors then a blocked injector on one bank could cause that cylinder to run lean, causing the ECU to richen up the entire bank to compensate? Alternatively it could be sticking open I guess, which might have the reverse effect? The ECU dropps out of closed loop mode at around 3000 rpm which might explain why it suddenly clears?
GreenV8S thanks.
The symptoms I described were for a open loop -everywhere- (non-cat) map. I have run a closed loop ECU with lambdas and the injector banks do not differ significantly on the LEDS - the ECU does seem to compensate.
However, the engine seems much more prone to stalling or cutting out with the closed loop map. Frankly with the closed loop ECU the engine feels throttled as well as misfiring. It's almost as though (and I could kid myself I can see this on the LEDs) the mixture on both banks cycles rich and lean - before the ECU gives up and cuts out.
I have tried a new ECU by the way.
Frankly I'd hoped running closed loop might resolve (if not truly solve) the problem, but it just makes the car less driveable in the misfire condition and clearly does not solve the problem so I've gone back to open loop for the time being.
Boosted, again thanks. Unfortunately I cannot reproduce the symptoms. It's been 18 months between misfires before! But at the moment it's more like 1 hour or 50 miles. Hence I've not pulled the plugs hot. When cold (inevitably having returned home with the engine purring like a litter of kittens) the plugs are all a good colour. One or two have been damp in the past but I'm not sure it was consistently the same ones (I'll have to check my records).
I'm going to disconnect an injector and wire 14-16 ohms of resistors across the terminals, switchable in the car. Although it won't simulate an open injector it might at least support my theory about a voltage drop across the other three in the bank.
The symptoms I described were for a open loop -everywhere- (non-cat) map. I have run a closed loop ECU with lambdas and the injector banks do not differ significantly on the LEDS - the ECU does seem to compensate.
However, the engine seems much more prone to stalling or cutting out with the closed loop map. Frankly with the closed loop ECU the engine feels throttled as well as misfiring. It's almost as though (and I could kid myself I can see this on the LEDs) the mixture on both banks cycles rich and lean - before the ECU gives up and cuts out.
I have tried a new ECU by the way.
Frankly I'd hoped running closed loop might resolve (if not truly solve) the problem, but it just makes the car less driveable in the misfire condition and clearly does not solve the problem so I've gone back to open loop for the time being.
Boosted, again thanks. Unfortunately I cannot reproduce the symptoms. It's been 18 months between misfires before! But at the moment it's more like 1 hour or 50 miles. Hence I've not pulled the plugs hot. When cold (inevitably having returned home with the engine purring like a litter of kittens) the plugs are all a good colour. One or two have been damp in the past but I'm not sure it was consistently the same ones (I'll have to check my records).
I'm going to disconnect an injector and wire 14-16 ohms of resistors across the terminals, switchable in the car. Although it won't simulate an open injector it might at least support my theory about a voltage drop across the other three in the bank.
Ben
I've have said you've got one intermittently firing injector, either the injector itself or the wiring to it.
It sound like to me the injector stops every now and then but as the revs come up there's enough fuel kicking around in the plenum to partially mask the problem.
I would try disconnecting the injectors one at a time and then drive the car and see how it feels compared to the misfire situation.
Matt
I've have said you've got one intermittently firing injector, either the injector itself or the wiring to it.
It sound like to me the injector stops every now and then but as the revs come up there's enough fuel kicking around in the plenum to partially mask the problem.
I would try disconnecting the injectors one at a time and then drive the car and see how it feels compared to the misfire situation.
Matt
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