Car jerks on LPG only. Advice please.

[Autogas1985]

Hello.

I was wondering if anyone can give me advice, or might have have similar issue.

The car (Honda Jazz, 1.3, Auto, 2006) recently started to jerk on LPG, on petrol drives absolutely fine. I have BRC system installed about a year ago and covered 9k miles so far. Had no issues previously.

The car jerks on lower speeds, most prominently between 2-2500 rpms.

I would like to sort the problem myself but not quite sure where I should start. Any thoughts on the matter would be appreciated.

Many thanks.

[Brian_H]

The usual thing to cause that to start happening suddenly would be ignition related. Either worn or poor spark plugs, or a coil pack thats started to fail. The usual recommendation on plugs is to stick with the manufacturer standard ones, LPG specific ones are at best a waste of money, and at worst a possible failure with certain brands.

Do you have any access to obd data to see if any particular cylinder is flagging misfires?

Does it have a lube system fitted? BRC commonly uses a method of injecting valve saver fluid upstream of the injectors and letting it get to the engine that way. Simon (LPGC) has posted a few times about this causing issues with injectors.

[LPGC]

Agreed with Brian_H

[Autogas1985]

The usual thing to cause that to start happening suddenly would be ignition related. Either worn or poor spark plugs, or a coil pack thats started to fail. The usual recommendation on plugs is to stick with the manufacturer standard ones, LPG specific ones are at best a waste of money, and at worst a possible failure with certain brands.

Do you have any access to obd data to see if any particular cylinder is flagging misfires?

Does it have a lube system fitted? BRC commonly uses a method of injecting valve saver fluid upstream of the injectors and letting it get to the engine that way. Simon (LPGC) has posted a few times about this causing issues with injectors.

Hello. Many thanks for your reply. I have plaid with the ignition coils as have few spare but no improvement there. Will try to change the plugs. I have lube system fitted, and will look for the info from Simon. I have no access to obd, but if needed will have to source one. Might be anyone know one that is not to precept but would be enough for diy car owner?

Thank you.

[Gilbertd]

This is what I use https://www.ebay.co.uk/itm/cReader-6-ge ... 4551411886

[Brian_H]

For fault codes on a vehicle of that age pretty much any odb tool should do it, provided it supports whatever protocal is required. I generally use a bluetooth dongle and the torque app on a phone. The c Reader posted above offers quite a bit for the money it is (around the price a lot of places would charge for a code scan if you took it to them).

Example of my usual goto dongle > https://www.ebay.co.uk/itm/UK-New-HHOBD ... 3927073969 Cheap, and small enough to keep in the car out of the way if needed.

The lube system put as simply as possible, follow the pipes and see how they join the inlet manifold. Take photos if you aren't sure of the injectors and pipework and post them here. The BRC lube system will join the injector pipes somewhere, most if not all others join the manifold elsewhere.

Changing plugs, particually if they haven't been changed in a long time, is not a bad idea in itself.

[Gilbertd]

As Brian says, the CReader will do everything, including JOBD, the proprietary standard used on Japanese imports (which is what made me buy it in the first place). As well as reading and clearing fault codes, it can display live data, can show up to 4 parameters as a graph and can save them so you can look at them on a computer later. I've used it on numerous different cars and it's never failed.

[Autogas1985]

Thank you for all your help, I will look into the reader.

I have replaced lpg filter as I had one from the old car, which didn’t seem to do much, however few days later I refuelled lpg and the car started to run fine again. I have no idea why though.

[Brian_H]

Sticky solenoid post may be a possibility that you could rule out (strip the solenoid down and clean it, reassemble). A wiring issue to the solenoid also possible and may come and go as the car moves around/warms up etc. If it is that sort of thing its liable to show fairly random errors, whereas if it was ignition or injector related, its likely to show specific cylinders on the car side being a problem. Did you manage to have a look at the valve saver pipework to see how it joins to the manifold pipework yet? If its the way described above, sticky injectors could be a possible issue, again this might come and go at first.

[LPGC]

As Brian says, the CReader will do everything, including JOBD, the proprietary standard used on Japanese imports (which is what made me buy it in the first place). As well as reading and clearing fault codes, it can display live data, can show up to 4 parameters as a graph and can save them so you can look at them on a computer later. I've used it on numerous different cars and it's never failed.

Just bought one, more than happy to go on your recommendation. I have loads of diagnostics gear including JOBD stuff but for the cost I'm happy having another backup.

Probably test it on various vehicles and keep it to one side, like the Toughbook (also a good call on your recommendation).

[Autogas1985]

Many thanks. I have ignition coil broken. I haven’t picked it up as it was replaces not long ago. OBD reader was very helpful in identifying the issue. It is running fine now

[Brian_H]

Sometimes obd can save a lot of time when it points you towards which cylinder has an issue, Good to know you located the issue. Worth noting as you now are aware, that ignition problems can be more noticable on gas than petrol as well.