system throws low gas pressure fault and wont manually switch untill high reducer temp (fixed: post #43)

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LPGC
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Re: system throws low gas pressure fault and wont manually switch untill high reducer temp

#41 Post by LPGC » Tue Feb 12, 2019 1:40 pm

It's a very quick and relatively uninvolved job to take apart the reducer solenoid, it is external of the reducer and quite separate from it, you don't even have to remove it from the reducer to work on it.

Putting a repair kit in a reducer isn't too difficult but takes more time and is relatively involved. A repair kit won't solve all types of reducer problem, you only really get soft parts such as seals and diaphragms in a repair kit. If a (the) diaphragm is broke gas will come out of the reducer's vacuum pipe, if a water seal is broke gas may get into engine coolant or leak externally out of the reducer, if certain gas seals are broke gas may leak externally of the reducer. Such problems amount to just about the only types of reducer problems a repair kit would fix but as yet nothing you've said points to such a problem (though I don't think you've yet checked for gas coming out of the vacuum pipe?).

Someone already explained that there are 2 solenoids one on the tank one on the reducer. Since the problem only seems to occur when the engine is cold and goes away when the engine is warm it would seem that the part causing the problems (if any) will be one that sees different conditions when the engine is cold/warm and the only solenoid out of the 2 to see different conditions (cold/warm) when the engine is cold/warm is the reducer solenoid. There's also more potential for the reducer solenoid to see a wider difference in inlet/outlet pressures than the tank solenoid (assuming both solenoids close)... because as engine bay temperatures cool gas vapour in rubber engine bay pipes will cool, pressure will fall with lowering temperature, when pressure falls below a certain level the reducer will convert liquid gas (from the small bit of liquid gas between the reducer solenoid and the reducer itself) into vapour, if/when all that liquid gas is used the pressure on the outlet side of the reducer solenoid will fall sharply. Due to solenoid design it takes more mechanical/magnetic effort to open a solenoid as the pressure difference across it (inlet pressure greater than outlet pressure) increases. Could still be the tank solenoid but (if it's a solenoid problem at all) the symptoms point more to the reducer solenoid.
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Darren
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Re: system throws low gas pressure fault and wont manually switch untill high reducer temp

#42 Post by Darren » Tue Feb 12, 2019 2:41 pm

Ok i will avoid taking the reducer apart as i can not smell or see and gas leaks around the reducer, i have tried unplugging the vacuum hose and again there was no smell of gas and no noticable draft coming from the reducer vacuum hose while the engine was running. Yes i believe brian pointed that out to me and we were focus solely on it being a mechanical problem but ive learned quite a bit more than i did before about the software from your help so this has been very educational. Are there any settings that i should change back or are they good where they are? (I still have Hemi ticked which im unsure if that was only meant for the one test or not)

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Re: system throws low gas pressure fault and wont manually switch untill high reducer temp

#43 Post by Darren » Sat Feb 16, 2019 5:43 pm

Ok so i just got back from the shed which is in the middle on nowhere with 0 reception. Did some few maintenance bits on the car while i let the reducer/valve cool down enough to work with. And oh boy was it dirty!! Pulled the solenoid off and then unscrewed the valve. Had strange inner workings and i couldn't figure out how to remove the spring inside the valve so i left it as shown in the picture. First i cleaned the cylinder which had quite a decent amount of gunk in it. Then i proceeded to push the spring in and out and cleaning the metal that was visible from the inner workings each time it got gunked up until i could no longer get gunk out, had a little help with some brake cleaner. Cleaned it up as much as i could and put the whole assembly back together and waited for the engine to cool down, waited until it was at 20c and fired it up letting it idle. Temp got to 27c and long and behold a smooth switch over to lpg. Now i must wait until i can try a proper cold start but from all the build up it does indeed look like the problem was a gunky solenoid valve! Thank you both so much for your help!!

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(image folder https://imgur.com/a/U8afUZE )

Brian_H
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Re: system throws low gas pressure fault and wont manually switch untill high reducer temp

#44 Post by Brian_H » Sat Feb 16, 2019 9:04 pm

Good stuff - it doesn't take a lot to block it as its quite small as you now know. No need to remove the spring either.

Thanks for posting back when you have, least it lets people know what the fix was so might be useful for others with the same sort of problems.

If you do still find the odd problem theres another one on the tank of the same sort of design, but make sure you either shut the valve off if it has one, or empty the tank as far as possible first.

You should be able to post images directly to the board btw - shouldn't be a need to use imgur anymore (not a problem if you do unless they go the way photobucket did, but also should be easier to do that and link it as well as it will all be on the same site).

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Re: system throws low gas pressure fault and wont manually switch untill high reducer temp

#45 Post by LPGC » Sat Feb 16, 2019 11:06 pm

I had a customer the other day, a Stag system I didn't fit on a Merc E class V6 but was asked to sort. When switched to gas it would constantly misfire on one cylinder, turned out that one of the injectors was really gunged with thick black sticky stuff that severely raised the closing speed of that injector and led to the cylinder that injector fed with gas running very rich, though the injector would seal when not worked. I identified stripped and cleaned the suspect injector but even then it still flowed too much gas due to lateral play in the injector shaft and disintegrated rubber pad (at the top of the plunger that prevents plunger from metal to metal contact at the top of it's stroke) and still flowed much more gas than other injectors. I managed to sort it all so it runs great on LPG but only by cleaning out the injector and then setting a -25% fuelling adjustment for the affected cylinder, +10% adjustment for all other cylinders and a large adjustment to the map. Still a workaround because with lateral movement of the plunger(s) at that extent and a fuel trim of that extent the real (and soon to be only possible) fix will be to fit new injectors. It is very unlikely that any sort of injector cleaner would have cleared the gunj I did, the gunj causing most of the problem that created the misfire was at injector spring level (high in the injector) where cleaner would not get to. To me an injector or bank trim more than just a few% indicates an underlying problem, but on this install I had to set an effective single injector trim of 35%... it will definitely need new injectors soon and I would recommend a different brand of injectors. The owner was advised accordingly but I reckon he might just wait until it won't run anything like properly again on LPG before coming back for the proper fix. At least for the price of a (proper) diagnostic I got it running properly again, no parts fitted, most would not have managed that... but I did have better new injectors in stock and could have got perfect long term results. Up to him and you never know if the customer might be thinking ahhh all sorted now, by saying he could fit new bits mightv'e been just hoping I'd bite... But really I'd have made maybe only another £20 from fitting new injectors and recalibrating and then his problems would have been truly sorted.
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Darren
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Re: system throws low gas pressure fault and wont manually switch untill high reducer temp

#46 Post by Darren » Sun Feb 17, 2019 2:30 pm

Started it up this morning with reducer at around 8c and switched over perfectly again so i think its safe to say that its all fixed, with such little effort too which is a surprise to me but i sure as hell am not complaining about that!

@Brian_H
Do you have any more details about that valve? When i was Googling about Solenoid mechanisms i didn't happen to come across one that looked like that at all so I'm a bit curious about it now. And no worries I've been through enough forums where the thread creator never responded and its infuriating, or they simply say its fixed and don't show what they did! I'll keep that in mind too and next time the 2 solenoid will be the very first thing i check. After looking a bit closer to the full editor i discovered the attachments tab... oops, guess I'll know for next time though and might edit my posts later on to add them to the forum incase imgur does go down that path. Thanks for the tip.

@LPGC
So if i start getting misfires it would most likely be the injectors? If i was to end up replacing them all in the future and i replaced them with the exact same ones currently would i have to mess with the ECU/calibration at all? Or would they more or less be plug and play? I noticed in the KME program that there was a automated injector tester/calibrator, is that a reliable way of calibration?

Brian_H
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Re: system throws low gas pressure fault and wont manually switch untill high reducer temp (fixed: post #43)

#47 Post by Brian_H » Sun Feb 17, 2019 6:17 pm

You need to identify the type of tank - this may be easy or not, depends where the valve actually is on the tank, which depends on the type of tank and also how its been mounted into the vehicle.

Generally speaking tanks come in two basic shapes - Torriodal, which are designed to fit into a spare wheel space and are shaped like a tyre, or a cylinder type. Both of those can be either single or 4 hole tanks.

If its a 4 hole tank its unlikely to have a shutoff valve (a 4 hole tank has a hole for each valve under the cover)
If its a single hole tank it probably will do (these have a larger single hole which a multivalve goes into, which contains all the valvework the 4 separate ones would have).

With the torroidal type tank if its a single hole type, the valve can be on the outside edge of the tank, or in the middle. I don't know if the spare wheel well is underneath the car or accessed via the boot, but some combinations of tank and vehicle can make access a pain to get into the valve (wheel stored under the car and a central valve meaning you need to drop the tank to access the valve for example as one of my previous vehicles had).

Really easiest bet is when you get chance, find the tank and see if you can locate the valves on the tank, then if your not sure post a photo here of the valves and someone should be able to answer what you have and what to do. Or just run it down as low as you can before you undo anything!.

Only other thought - The same vehicle i mentioned above had a thumbscrew valve on it, so might not be a yellow lever your looking for!

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