Crank speed sensors - go/no go?
Discussion
When the crank position sensor on my wife's 307 failed the car wouldn't start - or even try to fire. No fuel injected either. No prior warning, drove onto the drive the previous evening without issue, refused to start in the morning.
What diagnostics have you had done? And have these been done with Jaguar specific diagnostic equipment? Changing parts at random in the hope it will cure a fault is often unsuccessful but usually expensive
What diagnostics have you had done? And have these been done with Jaguar specific diagnostic equipment? Changing parts at random in the hope it will cure a fault is often unsuccessful but usually expensive
Edited by paintman on Friday 21st December 18:02
paintman said:
When the crank position sensor on my wife's 307 failed the car wouldn't start - or even try to fire. No fuel injected either. No prior warning, drove onto the drive the previous evening without issue, refused to start in the morning.
What diagnostics have you had done? And have these been done with Jaguar specific diagnostic equipment? Changing parts at random in the hope it will cure a fault is often unsuccessful but usually expensive
Good Post. We have reached the point with all modern high tech cars where the first point of call for any apparent fault must be computer diagnosis. That would be my suggestion, Crank sensors are on/off but you may have an oddity.What diagnostics have you had done? And have these been done with Jaguar specific diagnostic equipment? Changing parts at random in the hope it will cure a fault is often unsuccessful but usually expensive
Edited by paintman on Friday 21st December 18:02
Thanks. The days of replacing the condenser & setting the points gap with a bit of Rizla packet are long over
Unfortunately some garages also adopt the 'lets replace this & see what happens'approach but still include the bits that didn't make a difference on your bill.
With the dizzy I wonder whether wear could be a factor?
This may be of interest - note that it refers to points distributors & I'm unsure whether the same would apply to an electronic dizzy:
http://books.google.co.uk/books?id=gmSavy1RPxEC&am...
Unfortunately some garages also adopt the 'lets replace this & see what happens'approach but still include the bits that didn't make a difference on your bill.
With the dizzy I wonder whether wear could be a factor?
This may be of interest - note that it refers to points distributors & I'm unsure whether the same would apply to an electronic dizzy:
http://books.google.co.uk/books?id=gmSavy1RPxEC&am...
Edited by paintman on Friday 21st December 20:51
The only time I've seen a crank sensor be intermittent was on a rebuilt engine, no-one realised it but the crank disc had been bent, not by much but just enough that the car would fire and then die instantly. Caused some scratching of heads for a while. In the end the crank came out again, a good disc put in and all was fine.
Won't apply in this case though? unless there is a lot of end float?
I'm thinking the first thing is cover the basics, which you've started. Compression test both hot and cold, fuel pressure. Have a really good look around for an air leak on the inlet side - vac hoses, gaskets, pipes - absolutely everywhere.
Next thing would be to find someone that can live data read off it to check load - if its getting the fuelling wrong it could cause the misfire, this could point at a dodgy MAF/MAP sensor.
Won't apply in this case though? unless there is a lot of end float?
I'm thinking the first thing is cover the basics, which you've started. Compression test both hot and cold, fuel pressure. Have a really good look around for an air leak on the inlet side - vac hoses, gaskets, pipes - absolutely everywhere.
Next thing would be to find someone that can live data read off it to check load - if its getting the fuelling wrong it could cause the misfire, this could point at a dodgy MAF/MAP sensor.
I believe they can give intermittent issues, but this will only be shorted lived before total failure. Certainly that's how it worked on the only car I've had a crank sensor fail on, it started to to misfire, stall, etc, but a couple of days after issues started it was totally nada...
I agree with Eveluzion
I fitted Megajolt 3D mappable ignition to an old Pinto in a kit car
Took me a long time to get to the bottom of intermittent ignition issues turned out to be wires breaking in the plug, they would mostly contact untill giving it the beans then intermittent.
Took 2 complete rewires until I supported the cable to the plug.
Everything ok since then
I fitted Megajolt 3D mappable ignition to an old Pinto in a kit car
Took me a long time to get to the bottom of intermittent ignition issues turned out to be wires breaking in the plug, they would mostly contact untill giving it the beans then intermittent.
Took 2 complete rewires until I supported the cable to the plug.
Everything ok since then
Thanks for all the input on this. The miss or stuttering is really bugging me. One thing I have noticed is on the plug leads. I fitted a set of Magnecor leads to replace the tired Jaguar originals. If a little dust has built up on them you can sometimes see star shaped witness marks on the leads, like they are arcing. Its not very obvious, but its there. What could this point to? I have since heard mixed reports on Magnecor plug leads. I have thought about going back to Jaguar OEM leads.
The car is a 1994 Jaguar XJS AJ6 engined model and does have a distributor and does have a crank sensor, just to clarify some earlier questions.
Another suggestion was take it to a Jaguar dealer for a diagnosis. My local dealer does not have any equipment anymore for this age of Jaguar, but I did take it into them to look at. They couldn't even detect the misfire. I also fear they would just go down the route of replacing parts in the hope of finding the problem. I don't think there is a garage in my area I would entrust to work on the car regarding electronic diagnosis. (I live in a small city in the southern USA......if it ain't a Ford or Chevy......go figure). With this age of car I don't think there is much plug and play capability correct?
I am going to remove the crank sensor and take a look at it, maybe there is some dirt or grease on it? (Clutching at a straw or two here). I will clean the connector plug too.
What about a faulty oxygen sensor?
I will also check the fuel supply, filter etc. Could be an intermittent blockage.
Faulty ECU?
More suggestions welcome.
The car is a 1994 Jaguar XJS AJ6 engined model and does have a distributor and does have a crank sensor, just to clarify some earlier questions.
Another suggestion was take it to a Jaguar dealer for a diagnosis. My local dealer does not have any equipment anymore for this age of Jaguar, but I did take it into them to look at. They couldn't even detect the misfire. I also fear they would just go down the route of replacing parts in the hope of finding the problem. I don't think there is a garage in my area I would entrust to work on the car regarding electronic diagnosis. (I live in a small city in the southern USA......if it ain't a Ford or Chevy......go figure). With this age of car I don't think there is much plug and play capability correct?
I am going to remove the crank sensor and take a look at it, maybe there is some dirt or grease on it? (Clutching at a straw or two here). I will clean the connector plug too.
What about a faulty oxygen sensor?
I will also check the fuel supply, filter etc. Could be an intermittent blockage.
Faulty ECU?
More suggestions welcome.
I doubt anyone would suggest the main dealer for diagnosing problems. Most get confused if they have to do any more than an oil change.
There's bound to be a mechanic with a brain somewhere near to where you live ?
As for the leads arcing. Unless they were damaged during fitting, it is unlikely. Simple test, run the engine in pitch darkness, and any arcing will be very apparent.
There's bound to be a mechanic with a brain somewhere near to where you live ?
As for the leads arcing. Unless they were damaged during fitting, it is unlikely. Simple test, run the engine in pitch darkness, and any arcing will be very apparent.
Im with this man- People put on "race" leads thinking they will gain something. Even though Magnecores do have some DC resistance, a lot of the resistance is made up by the fact the leads are inductive, so present an effectively resistive path when a rapid AC pulse is applied to them in the form of an HT pulse. The idea is you don't loose as much HT energy like you do in a conventional lead as the effective resistance drops as the HT voltage reduces. The problem is the lower "resistance" makes the coil discharge more quickly which causes larger voltage spikes on the coil primary. More importantly the HT system has been designed with enough excess energy to maintain a perfectly good spark with resistive leads in the first place, so you dont actually gain anything, except bigger spikes that can affect the surrounding electronics. There is a place for low resistance leads when firing LPG, using Nitro, or very high boost pressures where you need all the power you can get to ignite the spark in the first place, but not your normal engine. If you really want to spend your money want Magnecores go and read their web site, and make sure you choose the right ones. Id stick with quality OEM ones any day myself, at a quarter of the cost and work just as well.
As for the crank sensor- the magnetic ones that count the fly wheel teeth, have a magnetic core that cause a magnetic loop to be formed as the teeth pass, which induces a small voltage into the coil around the magnet that the ECU picks up. The sensor will become intermittent as the magnet ages, so the signal level drops to a point they become intermittent as the voltages become too small to be detected, so its not quite go / no go.
As for the crank sensor- the magnetic ones that count the fly wheel teeth, have a magnetic core that cause a magnetic loop to be formed as the teeth pass, which induces a small voltage into the coil around the magnet that the ECU picks up. The sensor will become intermittent as the magnet ages, so the signal level drops to a point they become intermittent as the voltages become too small to be detected, so its not quite go / no go.
I will look some more into the leads. I have had my suspicions about them. Maybe also check out a new cranks speed sensor. They are too much. I know its going down the road of replacing partst until we (hopefully) find it, but by narrowing down the possible causes through a process of elimination it might not coat me an arm and a leg, just an arm......
Just as a comparison with no intelligence behind it, I started my Triumph Herald Christmas Eve. First time its run in nearly 2 years. The carb was a bit gummed up, so took it off stripped and cleaned it in 20 mins, fresh petrol supply and she fires rights up sweet as a nut.
Just as a comparison with no intelligence behind it, I started my Triumph Herald Christmas Eve. First time its run in nearly 2 years. The carb was a bit gummed up, so took it off stripped and cleaned it in 20 mins, fresh petrol supply and she fires rights up sweet as a nut.
geeman237 said:
I will look some more into the leads. I have had my suspicions about them. Maybe also check out a new cranks speed sensor. They are too much. I know its going down the road of replacing partst until we (hopefully) find it, but by narrowing down the possible causes through a process of elimination it might not coat me an arm and a leg, just an arm......
Just as a comparison with no intelligence behind it, I started my Triumph Herald Christmas Eve. First time its run in nearly 2 years. The carb was a bit gummed up, so took it off stripped and cleaned it in 20 mins, fresh petrol supply and she fires rights up sweet as a nut.
Swapping parts without testing will cost an arm and a leg unless you are incredibly lucky.Just as a comparison with no intelligence behind it, I started my Triumph Herald Christmas Eve. First time its run in nearly 2 years. The carb was a bit gummed up, so took it off stripped and cleaned it in 20 mins, fresh petrol supply and she fires rights up sweet as a nut.
I would highly doubt the leads are the problem, but it isnt impossible.
Any dummy with a scanner should be able to see if the rpm signal is erratic though which would give you an indication if the problem does lie with the crank signal. Better still, stick a scope on it and check the signal.
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