Lpg pressure cutout issues

[Lpg08]

Hi guys

I have a toyota landcruiser running a lpg injection system for a while with a king ecu, kehin injectors and amr cm7 converter (1 year old)

Just recently i have had issues with the gas switching to petrol due to low pressure , it forst started when accelerating hard but now car will hardly drive.

If i leave it to idle the pressure will start to drop from 1.6bar to 0.7 eventualy and cut out to petrol

The problem seems to go away some days and then somedays will start after idling in traffic for a while then suddenly start to loose pressure and die.

To test i have replaced the gas map sensor (no change)

Removed lpg converter solenoid and internal plunger to make sure free gas flow.

Checked gas flow at main line (had heaps of gas)

Checked tank solenoids (ok)

Conmected vac hose to converter as amr suggested (no change) besides lower pressure at idle before hose was 2 bar after 1.6

Checked gas filter

Removed gas filter low pressure line which had gas but unsure if enough pressure or gas supply.

Car has two tanks connected via a hydrostatic T so i turned of one tank to isolate and vice versa to no difference in pressure.

Could this be a fault converter? What usualy can cause this in them


Il give amr a call tomorrow and see what they think.

Thanks

[Brian_H]

A few things to suggest, firstly check the reducer is getting hot as it should do. If it does, then checking the pressure your actually getting might be an idea, get it to the state where its showing the lower end of what you'd expect, and squeeze the hose near the pressure sensor, if its as low as 0.7 bar you should be able to squash it fairly easily compared to the 1.6/2 bar you were seeing. If the reducer seems to be getting hot but the pressure seems to drop, the final thing I'd suggest is its got full of heavy ends, in which case your best bet is work out a way of draining them. Not sure with your specific reducer, but the general way to tackle it is to run the car to get it hot, move the reducer to get the outlet (or drain plug if you have one) to the lowest point, then let it run out (leaving it to run for a few minutes on petrol may help there).

The other possible cause is that the pickup tube in the tank has come off the valve, so your not reliably picking up liquid. But if that is the case, depending on the tank and where its fitted, you might be able to hear it rattling around. This will also depend on the type of tank fitted, less of a problem with a tank that has the valve at the bottom than at the top.

[LPGC]

Agreed with Bri, would also ask and say...

What ECU is fitted? Edit Scrub this question you've already given the info
Does the system have a vacuum sensor and a gas pressure sensor or does it only have a gas pressure sensor? Edit Scrub this question you've already implied the info.

You have been changing vacuum connections - Depending on how vacuum was connected to the reducer and vacuum sensor before, by changing vacuum connections you could have inadvertently caused these problems. There's gas pressure, manifold pressure and delta pressure (delta pressure is the difference between gas pressure and manifold pressure). Most LPG ECUs (including your King) want to see delta pressure and most injectors are more likely to work properly with delta pressure but by changing vacuum pipe arrangements it is possible to make the system read pressures incorrectly (so delta pressure reading will be incorrect) or read pressures correctly (so delta pressure reads correct) but for delta pressure to respond incorrectly. As long as the pressure sensor is connected to both vacuum and gas pressure the ECU will correctly read delta pressure... But if the reducer isn't connected to manifold vacuum the reducer will output gas at pressure relative to atmospheric pressure instead of relative to manifold pressure (delta pressure higher at low engine loads and lower at high engine loads). Or if the reducer is connected to vacuum but the pressure sensor isn't connected to vacuum then delta pressure will respond correctly but the ECU will read it incorrectly (it will read lower than actual at low loads and read correct at high loads).

I've seen a few AMR reducers that seem to have a problem of allowing a bit of liquid gas to be vaporised even when the reducer is under no load (when the jet that allows liquid gas into the reducer should be closed). In this situation any gas between the reducer solenoid and the reducer itself will be turned into vapour even if the reducer pressure is set very low, so you can have a situation where when the system has first switched to gas the injectors are fed with the vapour present in the system because of the problem with the reducer inlet jet but then when this excess has been used the reducer is set at too low a working pressure and the system switches back to petrol due to low pressure.

Remember you can only set reducer pressure when the engine is actually running on gas, you can't set reducer pressure with the engine not running or running on petrol. You might want to try experimentally disconnecting the vacuum pipe from the reducer again and/or adjusting the reducer to a higher pressure.

If you changed vacuum piping you will have at least changed delta pressure reading, it is possible that your engine stalls because the ECU compensates for the new delta pressure reading so now provides incorrect fuelling. The answer in this case would be to re-calibrate, but first make sure there isn't another problem such as your suspected failing reducer.

I've tried a couple of AMR reducers myself, they're supposedly rated for very high power levels... but I found them to be less capable than the hype, very unstable in pressure and have the problem (mentioned above) of seemingly faulty inlet jet that causes over-pressure under no load.

What spec Keihin injectors are fitted? Some Keihin are very low resistance (1 Ohm), some are higher. There can be problems using very low Ohm injectors with some ECUs, I wouldn't fit them with a King ECU.

[Lpg08]

Hi thanks for the suggestions.

It was previously running with no vac line for over 6 months perfectly fine onpy reason i added it was becuase amr suggested i do but the issue started before the fact and disconnecting it does not help.

Also i wouldnt thibk it would be tank pick up becuase i have turned of each tank at a time and they run the same on either and i wouldnt think you wpuld have pick up issues with both.

I have not made any pressure adjustments as it was working fine and i see no reason to without forst understanding whats happening.

The kehin injectors are yellow dots from memory. And the king ecu supports low impedance hana injectors so it runs them fine and has been for a over a year.

[Brian_H]

I'd missed the bit about having 2 tanks, that would seem you've ruled out the tanks being the source of the problem. That said, the usual point of problems can be the T pieces if any debris has managed to get caught in them. A loose piece of debris could explain your problem only being there some of the time, and may not be easy to tell without taking the t piece out to inspect it. Given the age of your vapouriser failure of that seems unlikely to me.

[LPGC]

Yes if an anti back-fill T is fitted they can certainly get the internal ball bearing stuck thus blocking off flow of gas to the exit, they can get gummed up.

Probably a moot point regards low impedance injectors but there can be a difference between ECU's and software/firmware claiming to support them and how the ECU performs with them fitted, I and another pro found this many years ago.

If the problem isn't the one way T I would be looking at the reducer again.

[Lpg08]

So i went to amr and got the converter tested all tests came back good but they still gave me a new converter judt incase which was very kind of them.

So i install the new converter and the issue still remains. I even cranked up the pressure via the converter and it still cuts out.

I took out the hydrostatic T and it was clean inside nothing looks odd, i tried blowing through the t and i couldnt so tried compressed air and it blows past fine.

Im not to sure what else to do know. When i undo the main gas line at the converter while the engine is running theres heaps of liquid gas coming out but i have no way to leasure how coneistant this flow is while accelerating

Any way to measure tank pressure?

Both tanks are full so i cant even remove the multivalves.

Any ideas? I have run out of them at this stage.

[Lpg08]

So the idle pressure drop issue is still there.

Il let it idle for a while and it seems to be back.

Pressure gradually dropping till switch over

[Lpg08]

I have also checked all lines and theres no kinks.

Also is it possible for the excess flow valves to activate and stop flow?

[LPGC]

The only excess flow valves will be in the tank valves but you've got 2 tanks, would expect efv's to be more likely to close under high engine load conditions only on more powerful engines, you've found plenty gas in the lines feeding the reducer anyway.

Talking mostly about the issue under idle conditions now, does it still cut back to petrol due to low pressure under load?

Besides pressure are other readings OK (reducer water temp)?

[Brian_H]

The excess flow valves should only activate if there is a (severe) leak on the outlet.

You have 2 tanks - have you tried running with just one of them connected to the ecu for its solenoid (just unplug one of them). Just thinking if the ecu is starting to struggle to keep all 3 valves fully open that it may be restricting flow. This could also get worse as the ecu warms up.

If that does help, it can be worked around by using a relay to operate the tank solenoids operated by the gas ecu output (thereby reducing load on the ecu).

Alternative if you haven't already tried it, is to use the manual shutoff on the valve to allow you to remove the insides of the solenoid post to remove the possibility of it either being gummed up, or not opening properly. You just undo the post that sits under the solenoid coil, remove the bits inside noting how they go currently (as you will want to put them back later) and put the empty post back in its place.

I was in the middle of typing this as Simon replied above - can you see the actual ecu temp when it starts doing this as well?

[Lpg08]

Yes as soon as i start to drive underload it switches back.

Its odd because it was fine for a while and only cutout initialy at high rpm but after idling a while the idle and acceleration issue started.


Also thinking back this problem seems to have started after i filled the gas up ingot home and it died. I left it and next day it drive to work fine but started to act up on way back and has been having this issue ever since.

I cant tell if its a temp issue or just a coincidence


All other readings look fine

Gas temo about 34degrees at idle

Converter 80degrees (hot to touch)

Gas pressire 1.5bar until it starts to drop

New map sensor

Map reading 0.3 ish bar at idle from memory

[Lpg08]

I can hear the lpg solenoids opening with alot of force nice click so dont think its struggling.

But i will remove them and gut the interbal plunger and try

When it starts to act up isnt hot just slightly warm

[Lpg08]

I meant temp of ecu

[Lpg08]

I meant temp of ecu

[Lpg08]

So i have found the issue.

Took the filter out to inspect again (using a brc filter with replacable internal cartridges) before puling it apart i blew into it and i couldnt blow through it.

Taking it apart i realised the fikter had walked back abit in the housing fully blocking of gas flow that comes in via the end cap.

Pushing it back in and the car runs great on gas again

I am going to have to make a new end plug in the filter that stops it from walking back.