Eurostang

New Member

• Sep 20, 2015

• #1

Hi all,

My 3.9 Discovery 1 has started to misfire/judder really bad below 2000 rpm and at light throttle. Seems to go away at higher rpms

It is particularly bad on a cold morning and results in a big drop in power / judder.

• The system is a Bigas Sequential (SIGN).
• I have replaced the plugs to NGK BPR6ES and gapped to 0.8
• New leads
• New distributor, rotor, cap and ignition module
• New coil

Could it be a sticking injector?

I have purchased a data cable to hook into the Bigas ECU, lambda is reading very high (over 4v)

Video of mis-fire here:

 

classic kev

Well-Known Member

• Sep 21, 2015

• #2

I have no idea about LPG but if it was petrol I would say check ignition timing, check vac advance is working properly. If all that checks out then possibly MAF or ECU. Be aware that sometimes on a cold morning you will have a misfire due to condensation in the distributor cap, once the engine is warm it goes away.

You say you replaced dizzy cap, rotor arm and ignition module ( I assume you mean the ignition amplifier). Are the arm and cap genuine Lucas? If not - fit genuine, more expensive I know, but oh so worth it.

 

Eurostang

New Member

• Sep 21, 2015

• #3

After replacing the distributor, amplifier etc. I had to retime the ignition, rehooked up vac advance and tested that it works.

I have started looking at the MAF and O2/Lambda sensors as a next port of call... With the engine at idle the MAF reads ~0.45 Which seems correct? HOWEVER As soon as the ignition is turned on, both O2 sensors read over 3 and 4 volts and continue to be that high while the engine is running? Does this indicate they are broken?

 

cooltide

sheep fancier

• Sep 21, 2015

• #4

Could be as simple as kev says. LPG can take 16 ish btdc but 95 petrol will start to pink around 12. Turn dizzy a degree anti clockwise first and see if it improves

 

Eurostang

New Member

• Sep 21, 2015

• #5

Sure, I'll advance and use premium petrol as far as possible. Will update with findings

 

cooltide

sheep fancier

• Sep 21, 2015

• #6

May also be an issue with using resistor plugs, though others do. Bp6es are non resistor.

 

Eurostang

New Member

• Sep 29, 2015

• #7

Update on this:

Advancing the timing to 14 degrees made a big difference but there was still a slight miss at low RPMs.

I took the car to Leeds LPG and it turned out the lambdas had not been hooked up to the LPG ECU (which explains the duff readings) and it was running a V8 base map. He hooked up the lambdas and did a full retune. £90 quid well spent!

Running beautifully now.

To summarize: LPG loves ignition advance and LPG specialists are totally worth the cash!