GOING BACK TO PETROL ON DECELERATION

[hitman]

Hi GuYS

Been looking in from time to time and glad to see the forum is still breathing

Had no problems whatsover with the car the past year or so but now after rapid acceleration or more accurately when throttle butterfly goes shut on the overrun the car is defaulting back to petrol , once accelerate again through the point of changeover its back onto gas.

any ideas how to resolve?

I have checked , reducer temp gas temp and appear to be ok map ok , nothing obvious to my eyes

king ecu
magic jet inj
range rover 4.2s/c

any help will be great , one thing I did note when looking at the laptop when encouraging the fault the battery light at the bottom of the four little dots on the bottom left of the king sofware page flicked amber? could this be my issue and how do I solve?

over to the gurus

Eta car battery shows 12.41v will give it a charge anyway but alternator is less than a year old.

[LPGC]

Switching back to petrol during over-run situations may be intentional. On a 4.2sc Rangerover running on petrol, during over-run the petrol injectors wouldn't be pulsed and to prevent a rise in fuel pressure (from pump running with no fuel return while petrol injectors are not being pulsed) the fuel pump is turned off too. This arrangement means that if you suddenly lift off the throttle on a standard (none LPG converted so no fuel return) model the fuel pressure stays the same as it was at the time you lifted off the throttle. But if a physical fuel return is fitted because the vehicle has been converted to LPG, when you lift off the throttle and petrol injectors are not being pulsed the fuel fuel pump still stops but if the fuel return remains active fuel pressure falls to zero if over-run continues long enough. Then when you get back on the throttle at first there's little fuel pressure, the petrol ECU compensates for the low pressure by increasing pinj, the LPG ECU bases ginj on pinj so the mixture is too rich on LPG until fuel pressure is restored back to normal for the driving condition. Usually on a King install the fuel return solenoid will be wired in parallel with gas solenoids, so one way of closing the petrol return solenoid during over-run on a King install is to have the King ECU close all (gas + fuel return) solenoids which means 'hard' switching back to petrol. Usually employing a setting such as 'return to pertrol' or 'petrol' (in gas/petrol screen) won't cause a 'hard' switchback where solenoids are closed, will only cause a 'soft' switchback to petrol duing which solenoid valves remain open. If the idea is to close the petrol return solenoid during over-run we'd want a hard switchback but a hard switchback means meeting the 'switchover to gas' settings criteria again in the 'changeover' screen before it will switch back to gas again.

Or it may be unintentional - Is the rpm wire connected? what are settings for rpm detection?

Another reason the system will switch back to petrol is if there's no rpm or pinj detected and the manifold pressure reading is close to 1 bar, because to the LPG ECU these readings in combination are consistent with the engine having stalled. Would expect the LPG map sensor to be correctly connected to manifold pressure if you've got anything like decent results from the system.

Another reason is if the ECU momentarily loses the 'ignition on' signal (12v on red wire usually to petrol injector positive). If this happens the LPG ECU believes the ignition was turned off. If the ignition signal resumes but there's no pinj reading it won't open solenoid coils until there's a reading for pinj again. Where does your setup connect to ignition on 12v?

The very bottom light in software denotes 'petrol contribution', it can light if petrol contribution is enabled in software (gas/petrol screen) and conditions for petrol contribution are met, can light if certain 'extra injection' settings (in modify carb screen) conditions are met, iIrc it can light for certain conditions such as not detecting rpm (as in above short paragraph). It can momentarily light (a quick flash) for spurious other reasons too lol.

[hitman]

HI Simon

thanks for the quick reply

car has just started to do this so something has changed

rpm is not connected and gets signal from injection

re connection to 12v I haven't a clue tbh

I have attached some screen shots to show how things are set up , it does have petrol addition selected , selecting return to petrol or petrol made no difference

[hitman]

n

[hitman]

Fixed

Compared code reader map to king ecu reading and realised straight away something wasn't quite right and looked like pulling in air.

Sure enough cracked pipe from the reducer to the map sensor, all the rest looked OK, so changed the bad section and all is back to normal.... I suppose that length suffers the most heat degradation due to location.



And this comment from Simon made me have another look at things.

Another reason the system will switch back to petrol is if there's no rpm or pinj detected and the manifold pressure reading is close to 1 bar, because to the LPG ECU these readings in combination are consistent with the engine having stalled. Would expect the LPG map sensor to be correctly connected to manifold pressure if you've got anything like decent results from the system.

[LPGC]

Just read your last 2 posts.

Even if I hadn't read your last post I would have known what the problem was from seeing the readings in your first post (0.81 bar map at idle) - The reason for the switching back to petrol was because you had a vacuum pipe leak between the manifold and pressure sensor, so (like I said in my last post) when there was no pinj the LPG ECU assumed the engine had stalled (because of manifold pressure reading being near atmospheric pressure).

Glad you've found and fixed the problem - It wouldn't have run properly if you'd put your foot down either with the vac/boost pipe leak.

=====================

Off on a bit of a tangent but all this has just made another thought occur - On installs like this another way of preventing petrol pressure to fall to zero during over-run conditions would be to wire in pulse detection electronics (rpm detector) to pinj so that with 0 pinj LPG map sensor voltage is pulled to reflect 1 bar. The usual way would be to wire in said detection to disable the 12v feed to the fuel return solenoid. Some ECU's have a separate 12v out that can be programmed to switch in conjunction with pinj / ginj pulses.