haraldpost

My driver side rear cam seal is leaking oil on the O2 sensor wiring. I have a few receits for the car going 15 years back, but can't see the O2 sensors has ever been renewed. I haven't tested them but I almost hope they're lazy so I can swap them and instantly improve mileage......

There are cheap O2 sensors to be had on ebay...are they any good or do I have to spend big money on Bosch replacements? They are 3 times the price.

My car is a C4 2.6 ABC automatic. Before conversion to LPG I once did 25 MPG on petrol long distance driving. For three years I've driven on LPG, and mileage has been varying. Mileage did improve from 18 to 19 MPG after changing a faulty F76 temp. sensor (the 25 MPG on petrol was with a faulty sensor.) I then had the LPG adjusted/remapped(?) and improved to 19.3 MPG. I saw no further improvement when installing new Magnecor KV85 ignition cables, although I thought a cold start misfire went away.

The last 1000 miles my mileage has been 18.7 MPG, mostly driving long distance. Not great.. I've measured 18 in/Hg at warm idle. I've measured G62 sensor (CTS) to 233 ohms on a hot engine. Reference value is 200 ohms @ 80 celsius and 2k ohm at room temp. So at least I know that my sensor is not fooling the ECU to believe that the engine is cold when indeed it is hot.

My engine threatens to stall when I slow down to a stop, and some times does. I can see on my receits that the dealer tried to fix this issue back in 2002, and state they did a "throttle body butterfly adjustment".

What's next? O2 sensor testing? Get new cheap type O2 sensors anyway? Get Ross-Tech...?

Rusty Spokes

Harald,

Not many people here in the USA have done a LPG conversion so the problem is not familiar.

That said..air leaks are not unusual and cause problems similar to yours.

I personally like Denso O2 sensors..they seem better built than the Bosch. I would be careful buying off the Bay.

CRAZY_RUSSIAN

i have no experience with denso, so i cant say anything on their behalf. but most people would recomend to get a Bosch sensor as they seam to be OEM replacement for the cars and last a reasonable amount. usually O2s are replaced every 80-100k miles, so keep that in mind.
the problem that you are describing sounds like a vacuum leak
if purchasing from ebay, check that it is actually a Bosch part and not advertised as bosch oem replacement, usually they will state the manufacturer in the add.
always liked the LPG fuel economy, i wish it was more common and more affordable here in the states

haraldpost

Hi Rusty,

Are you referring to increased mileage and/or engine stall? When I measured the 18 in/Hg idle vacuum I did try to provoke an rpm increase by spraying start gas around the inlet, but engine kept running steady.

CRAZY_RUSSIAN

IIRC, the euro 2.6 has a plastic intake manifold, ive heard of them developing cracks. trace all you lines, including the ones on the back of your valve covers, check for cracks
does your car stall when its on LPG or on benzine?

haraldpost

I did a quick A/B test, switching to petrol and braking to a stop. The engine revs drops to well under 600 rpm - almost stalls - then revs up and stabilizes at 800 rpm. Same thing happens when running LPG. I remember the car stalled on me when pulling off the high way three years ago, when I was on my way to have it LPG converted. And I found a receit tracing this problem back to 2002.

haraldpost

I actually have bought a spare 2.6 intake manifold. It is alloy but both the top and bottom part are as you say plastic, and held on by a number of tiny screws. Maybe I should make it a project of mine to bore and taper the fittings for LPG on it and swap IM. I'll smoke test the new IM before I do anything with it.

CRAZY_RUSSIAN

you may want to look into swapping a 2.8 manifold. i don't recall the details on this but i think it's possible. With a 2.8 intake there is some room for improvement on overall flow and you don't have to worry about it breaking on you. the only other thing i can think of is the idle stabilizer valve being slow to respond and causing your engine to stall.

haraldpost

I do have a 2.8 manifold from an Audi 100, but "upgrading" from the 2.6 manifold seem a bit complicated..

2.6 IM does not have dual long/short tracts and hence no switch-over mechanism. Hooking up this mechanism might be difficult if my engine management is not "ready" for this. (I could leave it alone and always run the long intake tract. The short tract is designed for >4100 rpm, and I very seldom rev my engine that high anyway.)

Then there's the idle control valve, which I haven't been able to locate on my 2.6 IM...

And if I take the 2.8 manifold I guess I'd have to port polish it, as from what I've seen online it looks very rough inside compared to my 2.6 IM.

Anyway I should port match the IM/head I swap it!

haraldpost

2.8 IM





2.6 IM