Starting problem M40

Post Mon Apr 14, 2014 1:17 pm

Forgot about "if it is not broken..." as received a new compression gauge which had to try on something.

All cyl. same 150psi in specs. (265K km.)

Plugs looked nice, runs on LPG.

Back together, started but missing on one. Decided I must have disturbed and damaged a plug lead, so swapped in a new set, along with new plugs. Because cyl 4 plug lead has a sensor the connector of which seems to be rather hard to get at, left it there - it tests OK.

On start, rougher and occasional backfire. Plug leads are correct - I checked on the diz cap.

There is fuel at the fuel rail (must start on gasoline til warm) but now it is just firing one cycle and stopping each time.

Anyone point me in right direction please ?

Post Mon Apr 14, 2014 1:36 pm

Start by posting this in the main technical section, not the wiki section.

Ben

Post Mon Apr 14, 2014 2:12 pm

Moved to Technical

Post Mon Apr 14, 2014 2:17 pm

Moved for you.
First of all, disable the LPG system by pulling its fuses, or the plugs off of the gas solenoids. You can get some confusing running problems when a car tries to run on both fuels at the same time. Golden rule is to get it running right on petrol first.
What type of LPG system do you have? Mixer type or vapour injection? Is there a (totally unnecessary on an E30) emulator fitted
IF this problem is nothing to do with the LPG system, then it sounds like a duff fuel pump that is stopping under the reduced cranking voltage.

Post Wed Apr 16, 2014 2:17 am

Brianmoooore wrote:Moved for you.
First of all, disable the LPG system by pulling its fuses, or the plugs off of the gas solenoids. You can get some confusing running problems when a car tries to run on both fuels at the same time. Golden rule is to get it running right on petrol first.
What type of LPG system do you have? Mixer type or vapour injection? Is there a (totally unnecessary on an E30) emulator fitted
IF this problem is nothing to do with the LPG system, then it sounds like a duff fuel pump that is stopping under the reduced cranking voltage.

Thanks for moving this. Vapour injection. Removed fuel line from fuel rail and it pumps fuel under cranking. Will try what you suggest, thanks

Post Thu Apr 17, 2014 11:35 am

There appears normal spark at all plugs, and fuel pump seems OK (removed fuel line and let it pump into container while cranking - heaps), but only fires about 1 cycle each time, then stops.

While fuel line was off ,didn't fire at all.

Seems like the injectors are not getting the signals to open.

Have I dislodged a wire somewhere ?

Post Thu Apr 17, 2014 1:53 pm

LPG system probably disables the petrol injectors by interrupting the common 12 volts feed to the injectors, so I suggest you connect a 12 volt bulb between the red/white wire at one of the injectors and an earthing point on the body, and check that this bulb stays lit.

Post Fri Apr 18, 2014 1:05 pm

Running again OK, many thanks

I had the connection between the filter box and throttle body out, and this meant no connecting hose to the ICV. Seems without this feedback from the intake manifold, no fuel is dispensed.

The wiki is very handy too.

Post Fri Apr 18, 2014 9:16 pm

PLTE3001 wrote:Running again OK, many thanks

I had the connection between the filter box and throttle body out, and this meant no connecting hose to the ICV. Seems without this feedback from the intake manifold, no fuel is dispensed.

If the hose between the filter box and the throttle body is off, then little air will pass through the AFM, so the ECU will inject very little fuel to go with that air. Air that gets in any other way won't be detected by the ECU.