Like Mace I don't see much noise on your scope trace though Davew?

davew wrote:

The Crank Sensor is just a basic coil, and there is precious little attempt to clean up the output

I was talking another make/model vehicle

The signal still looks very square even with the scope set on a faster time base but I didn't take any pics on faster time bases.

The engine symptoms (sudden multiple cylinder misfires) and rev counter reading fluctuation (also rpm reading in OBD live data) occurred simultaneously with the double width pulse, no double width pulse no symptoms, no symptoms no double width pulse. Tried with several different crank sensors fitted the results always the same. The fault and symptoms mostly occurred with pinj>9ms (> around 0.8bar map) and rpm > around 2K but it also sometimes displayed symptoms of poor starting.

mace wrote:

Interestingly enough, I hooked my scope up to my crank sensor a week or two ago, trying to find a reason for slightly lumpy running. Noticed that most of the signal spikes were the same amplitude, but three or four of them were higher. Took the cover off and very subtly tweaked a couple of teeth which weren't bang on parallel, and it made a big difference to the running. Bizarre, but hey.

My best guess is that the ECU looks for a voltage increase above a threshold, and the faster ramp time on the big pulses was causing it to fire ever so slightly early.

I should have mentioned that I tried a couple of replacement crank sensors before reaching the conclusion.
The output from these crank sensors always give pulses of the same amplitude and the connecting wire to the ECU isn't a shielded wire, I expect the crank sensor on this vehicle contains electronics that clean up / filter the signal and always output the same amplitude pulse. There are 30 grooves on the flex plate for the crank sensor to pick up on (the crank sensor doesn't use ring gear teeth) set in 3 groups of 10, each group separated by a long uncut section. I expect that if the crank sensor misses a groove (due to seeing a double width pulse) it will count 9 pulses (instead of 10) in quick succession and then interpret the longer pause (due to the uncut section) before seeing a 10th pulse as a sudden drop in engine rpm, the rev counter and OBD readings certainly seemed to agree with this. Looking through the crank sensor hole I rotated the engine looking for any scars / debris / dirt, I did find some seemingly magnetic particles stuck to the flex plate and removed them, don't know if these came from a failed previous crank sensor or from the starter motor, same problem remained after I'd cleaned the flex plate best I could anyway. I got someone to crank the engine while I watched the flex plate, there was a little bit of run-out as it turned but I didn't think it excessive or enough to cause the problems. I considered trying to use a de-gauzing wand on the flex plate but working through the small hole the crank sensor uses I doubt I could have got in with a de-gauzing wand even if I could find one (probably last saw one my dad owned for tape recorder heads around 40 years ago lol) and if I'd have got it wrong with the de-gauzing wand could have created even more problems. Using my scope (and it's limited capabilities including it's low resolution small screen) I could only accurately see around 180 degrees of engine rotation at around 2000rpm but I ran the same tests many times and the double width pulse and engine symptoms only ever occurred simultaneously.

While I've been typing this the owner has txted me to say he's been to the specialist vehicle dismantler who has spent 6 hours changing crank and cam sensor looms and 'running various other diagnostics'. I asked if he'd used a scope to check the crank sensor pulses...No he didn't. He doubts the flex plate or crank float is the problem (even though he hasn't checked the long pulse) and suggests changing the main loom for £400. The owner asked me if I wanted to buy the car, er no thanks! I reckon I could fix it by changing the engine (and making sure the replacement engine comes with a flex plate) but I don't want to change another engine. On this model car it's almost just as easy to change the engine if the gearbox has to come off so I wouldn't just change the flex plate while I had it in bits I'd change the engine to rule out crank float and bearings at the same time as flex plate.

Morat wrote:

Well, it's about time I came over for an LPG service on the P38 if you want to hook up diagnostics to it while I'm there - no worries.
How are you fixed?

Hi Miles!

A busy week next week but may be able to do Friday 19th if we could play that one by ear... Could do Fri 26th for sure, may be able to do an earlier day that week too. Any problems with it? Yes we can try the Launch on it if you don't mind.

Hope this isn't too far off-subject...

I recently bought an Launch X431 Diagun 5, it will do OBD2 and OBD1 stuff on a wide range of vehicles and communicate not just with the engine ECU but also with other ECU modules. I had a P38 here for LPG diagnostics repair only yesterday but didn't really have an excuse to connect the Launch because I diagnosed and fixed the LPG problem in no time but I'd have liked to have tried the Launch on the P38 to find it's capabilities on the P38, I doubt it will feature as much on a P38 as a Nanocam but it would be nice to know if it could do suspension level sensor learns etc. The 'fix' to get the LPG working again on this P38 turned out to be to open the manual shut-off valve on the old Ikom 30 degree tank (old enough to have a 12mm copper fill pipe) lol. But as soon as it pulled up I told the owner he probably had a knacked lambda sensor, I could smell the exhaust running rich. Turned out these 2 young lads run a P38 dismantlers/scrapyard and were already aware their P38 needed a lambda probe. I told them it was needed on bank2 and advised them to join this forum - could be good news for some of you too if they do join up (since they run a scrapyard for P38's).

On another make/model vehicle I recently attempted diagnosis of an intermittent misfire accompanied with error codes pointing to the crank sensor and sometimes cam sensors, the same codes occurred even with the cam sensors ruled out (running the engine in group injection mode with cam sensors unplugged a fault still occurred pointing to the crank sensor and the revcounter reading that is crank sensor driven fluctuated when the fault was occurring). Using my cheap digital oscilloscope I diagnosed this problem as one of a knacked flex plate, something related to massive crank thrust bearing problem or knacked rear main crank bearing... because when the fault occurred the crank sensor signal connected directly to the scope showed an occasional double width pulse (the flex plate teeth seemed in good order and the same results were repeatable with several different crank sensors). This conclusion seems a little far fetched even to me (I made the conclusion) but when you've ruled out everything else the remaining possibility(s) must be true and I can think of nothing else that could be true in this situation. The car has since been to another 'specialist' (vehicle dismantler rather than diagnostics master in reality) whom, like me, at first suspected a dodgy engine ECU. He swapped and recoded a replacement ECU but the problem remained. The same car will be going back to the scrapman in a few weeks and I'm quite certain that this specialist won't be connecting an oscilloscope... But I do expect he could fix the problem by fitting a replacement engine along with it's flex plate and he has easy opportunity to do that because he has plenty engines lying around. If he ends up fitting a replacement engine I reckon that either the flex plate will be the fix or the engine without mega excessive crank end float would be the fix... and I expect my unusual diagnosis conclusion to be correct.

I remember watching 'tomorrows world' on TV as a kid when the toilet roll oil filter would supposedly mean very clean engine oil for very high mileages between changes... but didn't mention the breakdown or use-up of additives in the oil during that time. Which is why I expect it never became popular and people still needed to do regular oil changes (additives and detergents). Still I don't worry about cleanliness of oil, running on LPG sees to it that oil remains much cleaner than running on petrol and especially cleaner than running on diesel. ;-)

Can do maybe 3 times the mileage for same oil colour change on LPG versus petrol, probably less important regards detergents etc. But not much will protect against ground off metal bits found in a filter except perhaps good engine design.

I'm surprised modern engines don't have a supplemental electric oil pump fitted to build oil pressure before the mechanical pump kicks in with the engine running... The electric pump could run from turning on the ignition through cranking the engine until rpm is well above cranking speed.

On vehicles where the oil filter isn't orientated with the fitting at the top I've often wondered if changing the filter if not needed does more harm than good... The old filter might have still been doing it's job properly, a new filter will take a short time to bleed up during which time the engine runs without oil pressure.

Still like most other people I change the oil filter with every oil change.

Can understand that a used oil filter might be more effective at filtering than a new filter... but maybe not if the same total amount of oil flow is squeezed through parts of filter that are less blocked than the more effective (at filtering) parts - maybe in this case some parts of the filter are effectively blocked to flow and there will be more pressure difference between none blocked parts and open parts so more crap can get through.

I don't do much general servicing (oil changes etc) on customer cars but when I have done them I've found that the most common types to have collapsed screens are the standalone (none cartridge) type as fitted on BMW's, Mercs and (particularly) Vauxhalls. These are normally very easy to access but probably because they can get very tight to remove and because the housing is plastic (an owner can't just knock a screwdriver through the side to use as a lever without breaking the housing) they often go unchanged for years.

In my post #625 above I should have written 'stops until cranking but obviously pumps during cranking'.

You can't force start most BRC gas systems on gas.

I don't think the potential for a leaking LPG injector or reducer has been mentioned? Run on gas and the gas system gets pressurised, turn the engine off and gas leaks into the manifold, try to start the engine and the engine gets petrol and gas instead of petrol and air until there's been enough cranking to pump the gas out of the manifold but by which point the plugs might then be wet with petrol.

At least worth ruling this out by driving on petrol for an hour before turning the engine off so if there is such leak gas will have been used with the engine running rather than displace air in the plenum?

Others will know better than me but iIrc the pump doesn't work on these until cranking, either that or it runs for a couple of seconds in pos2 then stops until cranking. 17 Seconds after stalling is probably about right?

A lot of engines give a really long 1 or 2 petrol injector pulses immediately on turning to the cranking position before reverting to normal pulse lengths for cranking which may be temperature dependent.

Great write-up!

That's what I would have presumed thanks Bri.

Gilbertd wrote:

They'd need a good excuse because you don't fall under the distance selling regs.

Thanks for that. What about 'cool-off period' ?

My mate in Liverpool deals in used motorhomes now, in the past he's been a used car dealer. In both cases he's had people buy one but come back just before a couple of weeks are up saying they want their money back having put over a 1000 miles on the clock. He told them he'd charge them a rental and cleaning fee, in some cases this has led to solicitors exchanging letters but as far as I know he came out on top.

I've never had it but I wonder how I would fare if I converted a vehicle to LPG for someone and a couple of weeks later they returned and asked for the system to be removed and their money back - I imagine I could charge them for the labour but have to refund the cost of components?

75 Litres is 16.48 gallons.

185 miles from 16.48 gallons is 11.23 mpg. Which could be right if driving is around the doors, or would be low for a 60mph constant steady cruise on the motorway.

Mpg much depends on the driving conditions. If you're stuck in a long traffic jam and leave the engine running the whole time you could achieve 0 mpg, if you drive at 120mph you might get 4mpg.

My first thoughts were along the lines of flaps like Brian said in post #2. I'm not familiar with heater box design on P38's but if flaps move sideways and have become free to swing (actuator broke or something) it would be easy to imagine turning causing them to swing sideways.

I have known heaters get hotter/colder when turning, going uphill/downhill or with changing engine rpm due to water flow aspects but usually when there's a problem with water flow or just not enough water in the system.

It runs on LPG so will have an LPG pressure reducer plumbed into the heater system. I've known cases where reducers have been plumbed in parallel and most water has gone through the reducer at the expense of flow through the matrix in some conditions but centrifugal force during turning can change the dynamics and pushed more hot water through the matrix. Or plumbed in series and overall flow has been restricted but centrifugal force has caused more overall water flow perhaps by seeing the reducer (if fitted at a high point) is more fully bled up.

Although the problem is described as occurring when the heater is being used, if AC is on it could be due to something that causes the AC clutch to disengage when turning right.

Cornering might imply body roll and/or a change in engine rpm.

Wouldn't want to go far and it completely break. If you're not going out much due to lockdown it could be the ideal time to arrange a date with insurance windscreen fitters, they might not be as busy as usual due to people not using their cars so much, or if they're busy (maybe they get busier with cracked screens this weather) and mess you about changing the date of an appointment you won't mind so much if you don't have any plans anyway due to lockdown. Any down sides to fitting a windscreen in cold damp conditions? If it's not an inconvenience it's a bonus... new completely pit free screen with fully working electric heating.

Would it help to take the plugs out? Thinking it will crank faster so oil light will go out quicker while there won't be as much weight on bearings in case there is no oil pressure.

A mate used to have a race spec engine from a 70's 3L Capri in a mk2 Escort, it had a manual oil pump he'd pump a few times before starting the engine. Could anything like that be plumbed to the oil pressure sensor port to get oil around the engine and speed up the time it takes for the oil light to go out next time you time cranking?

I used to rebuild my own alternators, there was a local firm called Start & Charge in Grimethorpe. He kept all the brushes and bearings in stock, if you turned up with your alternator would identify which bits you needed, sell you the bits for a couple of quid and tell you how to do the job. Don't know if they're still there.

Some will have heard my story about having an alternator fail on a bank holiday weekend when me and my son decided to go and explore Scotland? No chance I could get the alternator fixed or a replacement on the bank holiday and I knew I could fix it for a couple of quid back home... so I bought a generator, wired it's 12v output to a cig lighter socket and drove all the way home with the genny powering the car electrics, no heater or radio and only sidelights on.

Gilbertd wrote:

It's looking more like the figure given by OBD2 standard and displayed by the Nano, is calculated differently to how Land Rover calculate it.

I wouldn't be surprised at that. What diagnostic gear do Landrover use?

You'll have to remind me if this is Bosch or Gems, I probably don't fully remember intake ducting arrangement for Gems but all air including IAV passes through the MAF on Bosch(?) and I seem to remember (though now expect to be corrected) it does on Gems? Gas entering downstream from the MAF is still gas, doesn't detract from the air the engine needs.

On quite a few P38 LPG conversions, and in fact on quite a lot of other vehicles too, I have seen engine load decrease at idle running on LPG compared to petrol. Some of this can I'm sure often be attributed to new LPG injectors supplying more equal cylinder to cylinder mixture than old/worn petrol injectors but I think there's a bit more in it than that because the same happens on some engines even with petrol injectors known to flow exactly the same - I believe it's related to the difference in stochiometric ratio. Another advantage (in some cases) of a mixer over injection is that if there's any difference in airflow cylinder to cylinder (which can effect cylinder to cylinder mixture in the same way as worn injector flow rates) a mixer will see that each cylinder gets the same/correct mixture anyway.