Thanks I'm in wigan. Car is new to me had it in local 4x4 specialist to fit lp fuel pump and pipes also new fuel filter but he said couldn't get it to start no compression. I said what about crank sensor he said live data showing a pulse .I said cambelt but mechanic never checked. I have checked cambelt and oil cover all ok.
4x4 specialist said fuel pressure good I've checked cambelt all looks good even though mechanic never checked I had to do it .said crank sensor getting pulse on diagnostics.also said not getting compression but he didn't say weather he tested it or just assumed. So I'm going to get the codes read again and get compression tested correctly.
How do you get a compression reading with an oscilloscope?fingers crossed isn’t anything too serious , indeed always best to get it double checked
if the garage has a oscilloscope, which assume they have , can test the engines compression without having to remove anything, saving a lot of time and Ur pocket
As a side note , crank sensor sits down by the turbo
if there’s no compression , I’m fearful the crank has snapped as indeed the crank sensor would still get a signal, really hope I’m wrong
Plse let us know how things go
How do you get a compression reading with an oscilloscope?
From the starter motor I presume if that is the case, sounds a pretty unreliable method to me.I have no idea, but would hazard a guess its to do with power draw.
I know you can do compression test on modern trucks using just the diag computer, again I am assuming along the same lines as oscilloscope.
It is probably along the lines of it is seeing if they all have the same power draw.
I agree, too many possible variables to rely on load variation to compute compression pressures, I guess it would show no compression though.Only way forward is a compression check IMO..
With a proper tester!
I agree, too many possible variables to rely on load variation to compute compression pressures, I guess it would show no compression though.
I've never heard of it either, as I say, it might be OK as an all or nothing test for a broken crank, but I don't see it being possible to compute actual pressures from current variation, too many things could affect the readings from a weak battery to dodgy connections.I've never used a computer to do a compression test, never really heard of it tbf..
Probably "easier"?
Worth the effort doing it properly, even on a big rig, Scania V8's are an arse to do!!
Clever stuff, the signal from the starter motor is as noisy as hell, must have some good filters to remove the garbage. MOT centres over here have a box that plugs into the cigarette lighter socket, it produces n RPM reading from the alternator generation frequency which it transmits to the test computer via bluetooth.I think it is more of a comparitive test between cylinders, ie they are all pretty much the same so the problem is elsewhere.
With the diag laptop you can shut down individual cylinders whilst the truck is running, again I would assume for comparison purposes, ie shut down one cylinder and the others have to up their game to keep the thing running, the computer works out how much extra effort they are taking.
You can do some proper clever stuff these days, and we only really scratch the surface.
It’s used on td5 to check compression on 5th cylinder as no glow plug on 5. Saves having to remove injectorsI've never heard of it either, as I say, it might be OK as an all or nothing test for a broken crank, but I don't see it being possible to compute actual pressures from current variation, too many things could affect the readings from a weak battery to dodgy connections.
Clever stuff, the signal from the starter motor is as noisy as hell, must have some good filters to remove the garbage. MOT centres over here have a box that plugs into the cigarette lighter socket, it produces n RPM reading from the alternator generation frequency which it transmits to the test computer via bluetooth.