e34 535I Starting and misfire problems

[scrappyloz]

About 2 months ago i brought a 1990 535i se (M30) which has an LPG conversion. It had a head rebuild about 4000 miles previously but when i drove it i found it had no power in the top end. After taking the cam cover off i saw that it was timed wrong and after re timing it ran a lot better and quicker. I fully serviced the car at the same time with oil,filter,plugs Fuel filter etc. I also changed a lot of worn out gaskets whilst i was working on it.

You have to start it on petrol and rev to 2500 rpm for it to switch over to lpg (which is normal). It will then drive perfectly and idle fine on lpg.

But the car is very hard to start (petrol) and cuts out lots before you get to rev it to 2500 rpm to switch to lpg. also when driving if i switch it to petrol it runs very underpowered and wont rev fully and sometimes only runs on 5 cylinders.

Does any-one know where i should start cheers loz

[scrappyloz]

PS i just drove it 600 miles to france and back and it didnt miss a beat whilst driving on lpg at all

[Tiger]

Sounds like fuel injectors and fuel pump problem... test them both.

[scrappyloz]

how do i go about making sure i have the correct pressure from the fuel pump? i dont think it can be injectors as the lpg uses the injectors and runs perfectly. Also when i replaced the fuel filter i didnt depresurise the fuel system and i got sprayed by a lot of fuel so i know the pump is working a bit.

[Tiger]

Hook up fuel pressure gauge to the fuel line and you will know the exact pressure.

LPG uses the same fuel injectors? I heard about the LPG but doesn't know how they introduced LPG to the system... I assumed they used separate injectors.

Dirty fuel injectors will cause all sorts of problems. LPG probably can overcome this but petrol can't.

[scrappyloz]

what pressure should i be getting? There are two types of Lpg system. Single point injection and multi point injection. Mine is single point where the lpg is introduced before the MAF sensor and sucked through into the engine.

[scrappyloz]

Sorry i just read that the lpg system i have doesnt use the injectors. I will have a look at getting some other ones

[scrappyloz]

Are the injectors on a 3.5 m30 unique to that engine or will 3.0 or 2.5 ones work Same with a fuel pump

[Tiger]

Your Bosch injector is 0280150714... which is 19lb fuel injector... the 19lb fuel injector is used on probably all engines regardless of size... even the 318i use the same injector. You can use 0280150710 more modern Bosch 19lb fuel injector... instead of one hole, this is four hole and fit without modification at all.

You can also pull your injectors out and have it professionally cleaned... use those people who clean individual injectors... not on the car cleaning.

Fuel pump should be around 45 to 60 PSI depending on engine running condition.
...