Regulator pressure decreases when engine gets hot

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mrtylmz
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Regulator pressure decreases when engine gets hot

#1 Post by mrtylmz » Sat Aug 01, 2020 2:18 am

Hi all,

I have a 98 Rover 416 si that has a semi sequential injection system, it has been converted to LPG fueled system but I'm having problems with the car.
The main problem is that, when I start the car in mornings regulator gas pressure is about 1 bar, however, when I drive the car 5-10 minutes, the pressure starts decreasing, so it is not stable, this results in the engine running lean and stalling when engine is really hot. Could the regulator be faulty?

There is no map connection on the regulator so the map sensor measures only the lpg injector rail/regulator output pressure

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Re: Regulator pressure decreases when engine gets hot

#2 Post by Brian_H » Sat Aug 01, 2020 7:53 am

If you haven't already checked it, I'd have a look at the filter on the front solenoid and the solenoid post itself, any restriction there could explain your symptoms. Best to disassemble front solenoid post and clean it if its sticky or gungy

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Re: Regulator pressure decreases when engine gets hot

#3 Post by mrtylmz » Sat Aug 01, 2020 12:29 pm

I haven't, I will try it, thanks

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Re: Regulator pressure decreases when engine gets hot

#4 Post by Brian_H » Sat Aug 01, 2020 12:39 pm

While your there, a crushed feed line might also cause it, if it's been caught by a jack or similar. More likely if you have a copper feed pipe than polypipe

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Re: Regulator pressure decreases when engine gets hot

#5 Post by mrtylmz » Sun Aug 02, 2020 8:42 pm

I've checked the post regulator filter and it seems all right, there is no pre regulator filter on the system. I have doubts about gas injectors, they may be faulty, and the other thing that confuses me is that LPG's density changes according to temperature so if the reducer temp increases, lpg density decreases so the amount of gas supply decreases which leads to engine running lean, am I right?

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Re: Regulator pressure decreases when engine gets hot

#6 Post by Brian_H » Sun Aug 02, 2020 9:32 pm

Well it should compensate for the drop in pressure by increasing injection times, by using the gas temp sensor. Providing its working of course.

Might help to know if this is a new conversion or an older one (what you've said above makes me think its more likely a "factory" type one, probabby a Landi or Landi Renzo if it is?

If its an older conversion, it may be that the regulator is clogged up with heavy ends, best way to try and do something about that is to get the system hot and move the vapouriser around so the gas outlet is at the bottom, and have the hose removed from it to allow the warmed up gunge to drain out. The model of vapouriser will help to see if thats an easy job or not so easy. While your there, check the vapouriser is actually getting hot as well/check you have sufficient coolant in the system (should be fairly hot to the touch once engine is warmed up). What model of vapouriser is fitted if theres no vacuum line going to it?

it may also be a sign that the vapouriser is in need of a rebuild or replacement if its getting old, you can find they struggle to maintain pressure as the rubbers age.

It may even be a gummed up injector if its been on there a while, could be sticking open when hot and messing it up that way.

Looks like you have access to the diagnostics software at any rate, theres a few other possible things you can do to narrow it down but some idea of what ecu it is will help there.

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Re: Regulator pressure decreases when engine gets hot

#7 Post by mrtylmz » Sun Aug 02, 2020 11:49 pm

The system is a domestic brand,Vikars here in Turkey(actually the brand is just a sticker, another factory which I think it is Bardolini-BSM, produces and distributes. ) , being an electrical engineer and a DIY guy I have installed the system myself, it is an old 2009 system.

This is the regulator, I disassembled it 6 months ago and the rubber diaphram and its inside seemed good.
https://productimages.hepsiburada.net/s ... 515954.jpg
Except the regulator the kit seems to be similar to this:
https://bsm-bg.com/images/B4Samo.jpg

I will check all you said, but the important point that you make is about lpg temperature sensor, the ecu has lpg rail temperature sensor and displays it on diagnostic software but there is no sensor on injector rail so I have fooled the ecu with a resistor so it displays always 66 degree celcius, but the reason I did this is that I have been told that the Ecu just displays it and it does no effect on injector time, but you may be right it could have effect on it, I will connect a variable resistor and check the injector time.

I appreciate your detailed answer.

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Re: Regulator pressure decreases when engine gets hot

#8 Post by Brian_H » Sun Aug 02, 2020 11:57 pm

Don't know your particular ECU, but some definitely have temp compensation, Simon would be better to advise on this but not all have the option to alter the temp compensation directly. It might be an idea to set it somewhere close to the vaporiser temp once its warmed up and see how that helps. Your variable resistor idea may be the best bet there.

Might be worth putting some screenshots of your settings up to get some idea of what other things can be altered to help too.

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Re: Regulator pressure decreases when engine gets hot

#9 Post by mrtylmz » Mon Aug 03, 2020 12:16 am

Here is the ss of the ECU software
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Re: Regulator pressure decreases when engine gets hot

#10 Post by Brian_H » Mon Aug 03, 2020 6:51 pm

Having had a brief look at the software it does seem to allow you to switch indivual cylinders between fuels. If your suspicious of injectors, that may allow you to see if it looks like one is sticking open once it gets hot. Or closed for that matter as well. one stuck open all the time might cause pressure to drop, though you should see it running rich if that was the case. If you suspect they may be leaking, switching the car to gas to get pressure there, then back to petrol and removing the injector hose to manifold should tell you if you have a leaky injector.

The photo of the regulator you posted seems to show a vacuum connection on the other side of the vapouriser to the rest of the connections, if that is there, is it connected to the inlet manifold? This would be used to increase flow when vacuum is low, your earlier reply makes me think it isn't currently connected or yours doesn't have that?

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Re: Regulator pressure decreases when engine gets hot

#11 Post by LPGC » Mon Aug 03, 2020 9:37 pm

Since the system meters rail temp and diff. pressure it is almost certain that it will compensate for both... But how well is a different matter.

Usually provided injectors aren't pushed to the lower limit at which they can accurately dose gas to cylinders (low ginj figures) default temp correction isn't far wrong, so would expect correction for both pressure and temperature to be near correct at least for off-idle conditions. However, would expect the reducer to have a map reference connection and unless reducer output pressure is referenced to manifold pressure it will probably be very difficult to achieve good calibration/fuelling anyway.

Almost all reducers output a bit higher pressure when cold - both the diaphragm and the spring are stiffer when cold. This shouldn't affect things much if correct injectors/nozzles are fitted and setup is correct, but since this system shows diff.pressure I'd expect correct setup to involve that reduce connection to manifold vacuum... otherwise slightly wondering reducer pressure will indeed cause different fuelling for different pressure readings.

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Re: Regulator pressure decreases when engine gets hot

#12 Post by mrtylmz » Mon Aug 03, 2020 10:57 pm

First of all, the vacuum hose to regulator is not connected, I have two reasons for this;

1-The map sensor measures only the differential pressure, not both, there are two hose connections on it, one for vacuum, one for gas pressure, however, as you can see from the software lpg to petrol switchover(when the tank is close to empty) realizes according to gas pressure and since ecu has no way of determining it, it uses dif. pressure which causes unwanted switchovers stemming from the engine's map effect.
2-Since the map is high when engine is cold, and my belief that ecu has no correction other than multiplying the petrol times, I thought that it is the reason for engine to run lean when hot, thinking that the actual regulator pressure drops. Although it did not seemed to help lean running problem, the engines response to gas pedal has been improved it has been smoother.
Since then it has been disconnected.

By the way the car runs perfect under load, I have a diagnostic software and knows how the car's ecu work, there is no long time fuel trim correction for all mapping(all load conditions), O2 sensor just regulates idle injection time, so the main problem is poor idle when engine is hot and under heavy traffic conditions.

But I will reconnect it and check whether it has effect on injection times, if it is, everything changes. I also checked injectors for leak but could not diagnose any, but I suppose the injectors have calibration problems(there are allen screws on it) since they are really old. Also, yes I can switch injectors one by one but it did not help to fix the problem, it just made it easy to calibrate injectors(I turned the screws on it till car runs well and smoothly)


I really appreciate your answers Simon and Brian.

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Re: Regulator pressure decreases when engine gets hot

#13 Post by LPGC » Mon Aug 03, 2020 11:45 pm

Plenty systems use only a diff pressure sensor but still the reducer output pressure should be relative to manifold pressure, so still the reducer needs to be connected to manifold pressure.

Don't have to read far between the lines in my points in my previous post to see why not connecting the reducer and sensor to vacuum reference will lead to all sorts of fuelling problems. This answers all your points including in part why it runs well under high loads.

You will need to recalibrate when you have changed the vacuum piping arrangement.
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Re: Regulator pressure decreases when engine gets hot

#14 Post by mrtylmz » Tue Aug 04, 2020 4:39 am

I have adjusted injectors one by one using their allen screws and observing the map sensor waveform using an ossilloscope and now I'm sure that injectors works well, all injects equal amount of fuel. Then I disconnected the rail temperature resistor that I have connected to fool ecu to switch lpg and after that I connected a variable resistor to see whether it has an effect on fueling, and I'm surprised that it has, it increases the fuel supply when it gets hot(I think this tolerates density change) and this also explains why the engine runs too rich when it's cold. I underestimated the ecu considering that it is old and the guy telling me that it had no effect on fueling it's just there for switchover.

I am going to get the rail temperature sensor and connect hoses as they are supposed to, hope it will fix all problems. Recalibration is easy part.

I'm so thankful to both of you that a problem that I have dealt with for 2 years will have been fixed hopefully, here the solution offered me has been changing the whole system, so I haven't it solved.

Not being a native speaker, sorry for my mistakes in English.

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Re: Regulator pressure decreases when engine gets hot

#15 Post by mrtylmz » Tue Aug 04, 2020 5:09 am

What should be the ideal lpg differential pressure when hoses connected, there is a manual which says it should be near 1.50 bar, the map of idling engine about 0.35 bar, so the actual lpg pressure on injector rail would be 1.15 bar in this case, right? I use 2.3 mm nozzles which the software recommends.

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Re: Regulator pressure decreases when engine gets hot

#16 Post by mrtylmz » Tue Aug 04, 2020 7:28 pm

I have tested that the only correction that ecu makes is dependent on th le lpg rail temperature sensor, dif pressure does not have any electronic correction effect. Also the reducer temperature sensor is only responsible for swtichover to lpg when cold. So I have fooled the reducer tempereture sensor with a resistor which results it to show constant 59 degree and I connected the reducer temperature sensor to lpg rail temperature sensor. Now it has effect on correction but my main problem still remains, after driving car 10 15 minutes, short time fuel trim starts to increase fuel, then I sprayed water on injectors and it immediately turns back to normal. Then I decided to change injector's location to somewhere cool but I haven't yet.

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Re: Regulator pressure decreases when engine gets hot

#17 Post by Brian_H » Tue Aug 04, 2020 7:40 pm

Pressure wise you need to set something which allows your injectors to work correctly. Gas injectors take a short time to open and close (longer than petrol injectors do), this time varies depending on the injectors you are using (not sure what these are, or if they are ones we would be familair with over here, but if you know what they are it would help to say). If you can find what this minimum time is, then you should be able to find a pressure based on that. Its a balance between having control over fuel at idle, and having enough pressure towards the top end to allow injectors to open and close in the available time.

Simon might be able to give you a guide to what pressure you want, 2.3mm nozzles are fairly large for the engine size you have, I would think your around right with the 1.15 pressure but he would know better than me.

Pressure should be stable under load though as well - if its all over the place and you have no leaks, that would suggest a vapouriser issue. You said you've had it apart previously, are the rubbers very flexible or do they seem stiff? The cooling of the injectors does suggest the issue is there, if it hasn't always been like that, it may be worth trying some cleaner through them, though relocating them may be better. Might help to see a photo of the current location to get some advice there?

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Re: Regulator pressure decreases when engine gets hot

#18 Post by mrtylmz » Tue Aug 04, 2020 8:34 pm

My injectors are Valtek's imitation, 3 ohm injectors, but after some research I found that they are notorious for not being stable, and requiring adjustment frequently. I will probably buy injectors but before I will change injectors' location since they are at top of the engine and trapped somewhere getting really hot. I have depicted the injectors location on the attachment.
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Re: Regulator pressure decreases when engine gets hot

#19 Post by Brian_H » Tue Aug 04, 2020 10:50 pm

The type 30 valteks are not very well regarded, so a copy of them isn't a good start. Location wise looks about as good as you could get to me, at least they are on the cooler side of the engine. Your English is fine by the way!, Its only the components your using that would make you think you weren't in the UK if you hadn't said otherwise.

You might have better luck with the single unit type injectors if the increased airflow round them helps, That said I've got OMVL injectors in a similar location on a Focus that have only needed a dosing with some IC12 to clean them up in 60k miles, but without the Turkish climate to deal with. These ones https://tinleytech.co.uk/shop/lpg-parts ... -ts-2-0mm/ are the ones I've used though there is now a newer version with the red coils rather than the blue, not sure how well they compare as not used the newer ones that are supposed to be identical. You will obviously need to check they are compatible with your ecu as well.

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Re: Regulator pressure decreases when engine gets hot

#20 Post by mrtylmz » Wed Aug 05, 2020 4:03 am

Today the engine started well and lpg rail temperature sensor corrects fuel trim when engine is cold, so one of my problems has been solved but the other one seems not to be solved even injector replacement because I realize that when the lean running problem occurs it also runs lean on petrol(not as much as lpg), so I suspect that another problem cause this, maybe there is an ignition related problem, vacuum leak or the worst scenario, head gasket.

By the way, I figured out that map sensor reading error increases when the sensor gets hot, I used a gauge and observed that when cold it is a little bit higher, which Simon said "normal", then it decreases a little bit and remains stable, not being influenced by higher temperatures, so reducer seems all right.

I checked the injectors you suggest but I can't get it here, and do not want to wait the shipping process. However, since their customer feedbacks are very good, and the ecu supports it will buy this injectors and give it a try,

https://n11scdn2.akamaized.net/a1/1024/ ... 061267.jpg

I could drive the car with this problem but not pinpointing the fault drives me crazy, I did not have lpg system when I bought it but the engine response was not that good on petrol too when it gets really hot(after cooling fans' working), the engine used to stall suddenly, but this is worse on LPG as it is expected so I started to think LPG system may not be my problem.

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