Poor mpg's

leepop633 · Post by **leepop633** » Sun Jan 27, 2008 5:56 pm

I suffered a nasty backfire 6 months ago. Now its only getting 33 mile per £10 of lpg. Thats 7.9 mpg. Its a 1995 3.9efi disco with a single point leonardo closed lambda loop with a zavoli vapouriser. I have found the vaccum advance to be faulty so changed that, found a vaccum pipe off the back which goes from Stepper motor (petrol side) to the fuel regulator. Its got new NKG BPR6ES plugs gap set to 8mm, bosch ht leads and a brand spanker new Genuine Lucas cap and rotor. I have tried a manual flow valve in place of the leonardo stepper motor (LPG side) and this made no difference. Ive gone back to a standard air filter and its even been on a computer to check Leonardo system (although not sure how much the guy really checked). Its running very high CO% 10+ on petrol, 0.7 CO% on LPG although just found the pipe off the plenum last night so petrol maybe ok now. The plenum is sealed. Please please dont tell me the reason for backfire as im well aware of the reasons, lol. No offense meant but ive been round the houses for 6 months now. It was plugged into a testbook and seemed to be saying TPS is suspect. The guy cleared the faults and told me to go back tomorrow to check if they were old faults but the TPS wouldnt effect LPG would it as i took out the stepper (LPG side) and it made no difference. Any of you guys have any suggestions or does the mpg's sound normal? Also it isnt leaking ive been told. If it was wasting gas by not burning it would this show up in the CO%? Not sure how ritch LPG shows in CO%.

Post by **Rossco** » Tue Jan 29, 2008 7:37 am

As a quick thought your LPG CO is way too low. This will cause poor mpg.

It should be about 2.5 - 3.5%

leepop633 · Post by **leepop633** » Tue Jan 29, 2008 6:07 pm

Really? I assumed 0.7 was right. What can cause this then? Too much air e.g air leak somewhere? Is it possible for the vapouriser diaphram to be split but stil run ok?

Post by **Rossco** » Wed Jan 30, 2008 7:42 am

The backfire may have damaged the vaporizer diaphragm, or you could have an air leak.

leepop633 · Post by **leepop633** » Wed Jan 30, 2008 2:23 pm

Im now after many new parts suspecting an air leak but cant seem to find one on the plenum where i would expect it to be. I also cant find anyone to supply a service kit for my zavoli vapouriser. When i had it plugged into the computer surely it would show up if the diaphragm was gone? Also would not that use less gas as there wouldnt be the vaccum? I dont know much about the lpg system but slowly learning, lol.

ChrisJC · Post by **ChrisJC** » Wed Jan 30, 2008 3:47 pm

I could be wrong, but it sounds like it's running way too lean (which is not as efficient as running properly, so you use more fuel). A knackered diaphragm would completely break fuel metering. Why not take the vapouriser apart and check it out, they're normally quite straighforward.......

Chris.

leepop633 · Post by **leepop633** » Wed Jan 30, 2008 4:41 pm

Cheers chris. Does the CO% seem lean as i thought this was about right? If the diaphragm was split would it run tho? Im not wanting to touch it until i can find a supplier of my vapouriser spares. Im begining to think of changing the vapouriser for a one i can get service bits for. When it was on computer the guy said it was a little lean but he put it right but since talking to others in the LPG trade im not sure of him compatence.

Post by **Rossco** » Wed Jan 30, 2008 7:17 pm

Don't assume it is the plenum leaking.

Check out the vacuum system as well. A leak there can play havoc.

leepop633 · Post by **leepop633** » Fri Feb 01, 2008 7:37 pm

Had it plugged in today. Found something staright away. Computer said

Engine tune error
Throttle position sensor
Airflow Meter / TPS Correlation Fault.

So, he reset the ECU, i dorve it down the road and noticed a huge difference, came back, it ticked over evenly, without fluctuating too much, he plugged back in and no faults. Also before re set he said the engine tune error was due to Lambda B sensor not being right. It was showing 10 (i take it roughly 10%) where the other was 0.6. When it was re set and both showed 0.6 at tickover, on petrol. As the Leonardo ECU is jumped off Lamda B then this would tell the ecu something was up also. Guy said it any of the componants mentioned were unplugged while the engine was running then this would cause the correlation fault as the ECU wont know what to do. Didnt realise unless the faults are cleared without a new part being fitted, the ECU doesnt know what to do. When i backfired it was fairly hard revs so the AFM would of just lost all info when it spat the mixer ring off the plenum. cars running sweet now but still dont know what fuel is like quite yet. Got to take car back in a few days to recheck fault hasnt come back but fingers crossed. Next job is buy some Magnacore leads.

softdash3.9 · Post by **softdash3.9** » Sun Feb 24, 2008 5:13 pm

Hi,
Just seen your post's sound's as if your are beginning to get some where, what is your ignition advance set to?