Getting LPG sorted

zoidberg · Nov 8th, 2014, 00:52

Called in to see Simon (Yorkshire lpg ) Thursday and arranged to have it looked at on Tuesday, so hopefully the cutting out problem can be solved. Typical though, it drove the 25 mile back and ran rest of the day without cutting out !!!

Lpgc · Nov 12th, 2014, 11:51

Had a look yesterday...

Petrol ECU is generating post cat lambda (well post cat fuel trim) code when running on petrol or on LPG, yet the post cat figures seem OK on the scanner.

The dashboard sometimes shows 'change up gear' messages while running on LPG but the OBD scanner shows correct rpm (no spikes / glitches), and this can occur at any engine rpm.

Difficult to see actual lambda figures when running on LPG due to the wideband lambda and the LPG system feeding the petrol ECU with an emulated lambda (running on gas, OBD live data just shows the emulated lambda figure).

Increasing gas pressure slightly made a very small improvement to idle on gas and brought idle manifold pressure down a little.

The reducer isn't leaking gas through the vac port and it's pressure output does seem relative to vacuum reference, reducer seems OK.

The engine runs poorly on gas, manifold pressure on petrol at idle is about .3 bar as expected, rising to over .4 bar on gas... to be expected with the apparent misfire problems but if running properly should show the same .3 bar.

Clamping off any of the continuous injection feeds to the manifold injectors makes very little difference, but clamping off cyl 4 feed makes maybe slightly more of a difference. Cylinder 4's pipe at the distributor unit is the only one that has had it's clip replaced with a jubilee clip. Difficult to say if one cylinder in particular is misfiring, code reader reports random / multiple cylinder misfires P0300, in the past the owner has seen misfires reported on 3 specific cylinders at a time but can't remember cyl 4 ever being one of them.

The clip on the electrical connection to the stepper has previously been broken off - given the J clip on cyl4's pipe at the distributor and the missing clip on the electrical connection, someone's probably been at the distributor before.

While running on gas, pulling off petrol injector connectors makes no difference to the running.. It isn't a case of cylinders getting both gas and petrol at the same time (unless petrol injectors are leaking - still unlikely to make this much difference).

The owner has fitted 4 prong plugs, not good, advised him to replace them with single pronged plugs, spec recommended on this forum by Classicswede. A good thing to do to rule plug problems out but would think this unlikely to correct the problem since the same problem is apparent at all rpms / loads including fast idle.

There was a point early during the visit where the engine refused to switch to gas, the switch flashed but there was no changeover.. Connecting a live feed directly from the battery to reducer (and hence tank solenoids since they're wired in parallel) got the engine to switch to gas and it switched to gas on every attempt after this even with the direct battery connection disconnected. The owner has seen it refuse to switch to gas on one occasion before / has had the vehicle cut out (not switch back to petrol) when running on gas on many occasions. I performed this check to test the solenoids and reducer (which worked OK), not expecting this to cure the problem of the vehicle not switching to gas - curious.

If it wasn't for the post cat OBD errors and 'change up' messages on the dash, things might seem more straightforward but these problems lend suspicion to other components - If this wasn't a Volvo (was a Vauxhall or Ford) I might be looking at rpm filters / black box lambda emulators. Even so, I still suspect there is a problem within the gas distributor (stepper motor) and with the manifold valve for cyl4 but the next step should be to change the plugs.

Simon

zoidberg · Nov 12th, 2014, 13:38

Hi Simon. Managed to drive the 25 miles back without cutting out and filled up with gas without cutting out. Went out in it earlier, did about 3 miles, and yep you guessed it.................it cut out lol.Parked up to buy some dinner, few minutes later got back in and it fired up whilst switched to gas !!
Will buy some more plugs later and see if it helps.

Nov 8th, 2014, 00:52	#1
zoidberg Master Member Last Online: Jul 28th, 2023 17:19 Join Date: Jan 2012 Location: batley	Getting LPG sorted Called in to see Simon (Yorkshire lpg ) Thursday and arranged to have it looked at on Tuesday, so hopefully the cutting out problem can be solved. Typical though, it drove the 25 mile back and ran rest of the day without cutting out !!!

Nov 12th, 2014, 11:51	#2
Lpgc LPG conversion pro Last Online: Mar 22nd, 2024 15:35 Join Date: Feb 2014 Location: Pontefract	Had a look yesterday... Petrol ECU is generating post cat lambda (well post cat fuel trim) code when running on petrol or on LPG, yet the post cat figures seem OK on the scanner. The dashboard sometimes shows 'change up gear' messages while running on LPG but the OBD scanner shows correct rpm (no spikes / glitches), and this can occur at any engine rpm. Difficult to see actual lambda figures when running on LPG due to the wideband lambda and the LPG system feeding the petrol ECU with an emulated lambda (running on gas, OBD live data just shows the emulated lambda figure). Increasing gas pressure slightly made a very small improvement to idle on gas and brought idle manifold pressure down a little. The reducer isn't leaking gas through the vac port and it's pressure output does seem relative to vacuum reference, reducer seems OK. The engine runs poorly on gas, manifold pressure on petrol at idle is about .3 bar as expected, rising to over .4 bar on gas... to be expected with the apparent misfire problems but if running properly should show the same .3 bar. Clamping off any of the continuous injection feeds to the manifold injectors makes very little difference, but clamping off cyl 4 feed makes maybe slightly more of a difference. Cylinder 4's pipe at the distributor unit is the only one that has had it's clip replaced with a jubilee clip. Difficult to say if one cylinder in particular is misfiring, code reader reports random / multiple cylinder misfires P0300, in the past the owner has seen misfires reported on 3 specific cylinders at a time but can't remember cyl 4 ever being one of them. The clip on the electrical connection to the stepper has previously been broken off - given the J clip on cyl4's pipe at the distributor and the missing clip on the electrical connection, someone's probably been at the distributor before. While running on gas, pulling off petrol injector connectors makes no difference to the running.. It isn't a case of cylinders getting both gas and petrol at the same time (unless petrol injectors are leaking - still unlikely to make this much difference). The owner has fitted 4 prong plugs, not good, advised him to replace them with single pronged plugs, spec recommended on this forum by Classicswede. A good thing to do to rule plug problems out but would think this unlikely to correct the problem since the same problem is apparent at all rpms / loads including fast idle. There was a point early during the visit where the engine refused to switch to gas, the switch flashed but there was no changeover.. Connecting a live feed directly from the battery to reducer (and hence tank solenoids since they're wired in parallel) got the engine to switch to gas and it switched to gas on every attempt after this even with the direct battery connection disconnected. The owner has seen it refuse to switch to gas on one occasion before / has had the vehicle cut out (not switch back to petrol) when running on gas on many occasions. I performed this check to test the solenoids and reducer (which worked OK), not expecting this to cure the problem of the vehicle not switching to gas - curious. If it wasn't for the post cat OBD errors and 'change up' messages on the dash, things might seem more straightforward but these problems lend suspicion to other components - If this wasn't a Volvo (was a Vauxhall or Ford) I might be looking at rpm filters / black box lambda emulators. Even so, I still suspect there is a problem within the gas distributor (stepper motor) and with the manifold valve for cyl4 but the next step should be to change the plugs. Simon Last edited by Lpgc; Nov 12th, 2014 at 12:02.

Nov 12th, 2014, 13:38	#3
zoidberg Master Member Last Online: Jul 28th, 2023 17:19 Join Date: Jan 2012 Location: batley	lpg Hi Simon. Managed to drive the 25 miles back without cutting out and filled up with gas without cutting out. Went out in it earlier, did about 3 miles, and yep you guessed it.................it cut out lol.Parked up to buy some dinner, few minutes later got back in and it fired up whilst switched to gas !! Will buy some more plugs later and see if it helps.

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