Running issues/Ecomony

[Lost_Cause]

Hey lads,
after getting my G40 back on the road after being off for 6 years, I want to get her running that bit better now.
I'll start with the problem. Ecomomy seems to be pretty bad. I've had it on the road now for around a month & have nailed it at times to clear out any old deposits/crud that may have been in it from sitting around.
Earlier in the week I stuck in €20 of petrol @ €1.48.9per litre & the car returned 100miles. (I'm in Ireland by the way, hence the euros)
Working out the mpg, is this right. 20 / 1.489 = 13.43.  So 13.43 litres.  Converted to UK gallon= 2.954
100 / 2.954 = 33.85. So, approx. 34 mpg is the result?!

This result is from pretty calm driving, nothing serious.
First, are my calculations right??

Modifications I've done are as follows:
Ashly manifold, decat, jetex centre, twin scorpion motorbike rear cans. Slight leak between decat & centre box.
R1 charger rebuild, but now with standard, de-restricted airbox & new, standard filter.
Timed by ear (need a timing light) but idles approx at 1050-1100rpm, any lower & she gets very sluggish.
Lambda is out of a 1.3 skoda felicia (due to cost restrictions, I realise it's not right.)

I've taken off the blue temp sender plug (as is often suggested) to check for a change in revs/running but there doesn't seem to be any. I replaced the C0 pot with a new one a while back & it's set to approx. 550 ohms.

Do the results above seem ok considering & how much of an adverse effect will having the wrong lambda in place have?

Cheers lads,

Donie.

[Lost_Cause]

I realise nobodys given their 2 cents yet, but the more I think about it, the more I feel the current lambda won't be doing it any good. Doing a bit of digging as to which lambda to get. Found Bosch ones available on ebay,seem genuine to me.
Now I just need to decide which one. Found 3 that fit the bill:
1: year '87-90   no cat,                 3 wires,            length 950mm               Bosch P/N: 0258003114
2: year '90-94   + cat,                  3 wires             length 1020mm              Bosch P/N: 0258003171
3: year '90-94   cat not mentioned, 3 wires,            length 950mm               Bosch P/N: 0258003171

Because mine originally had a cat, now doesn't, which is the best one to bank on?
Obviously, the only difference between 2 & 3 is the length. Does that mean that 90-94 G40s all had the same Lambda regardless of whether they had a cat of not?

Would I be better off getting the pre-90 item that's designed to run without a cat?

[Jezza-7]

Hi there,

This is the one i got, from ebay.

http://www.ebay.co.uk/itm/LS3973-Bosch-Lambda-Sensor-VW-Polo-Coupe-1-3-G40-86-87-PY-01-87-08-90-/180731925468?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2a147653dc#ht_3473wt_956

Also in reply to your mpg, i get around 39 mpg but i got a 1341 cc bottom end so i guess your calculations are about right.

[scotsjohn]

Why take the pre-90 one if your car's a 90-94? Either no2 or no3 will be OK just a bit of extra length on the cat model which won't  do any harm.

[Lost_Cause]

@Jezza- that lambda you linked to has a different connector to the one I have, but yeah, it's the same supplier.

@scotsjohn- thought because the pre-90 one definitely wouldn't have a cat, then that would be the one that would work best. But slighlty different ECUs would probably cause more ball ache in the long run.

Will go for for the newer one when funds allow.
Cheers lads.

[G40supercharged]

I would just use the correct one for a cat equipped car. The idea of the lambda sensor is to set the mixture to the critical point where the various chemical reactions in the cat will work. The ECU doesn't know (or care) if the cat is there or not. 34mpg doesn't sound too bad to me unless you are doing long motorway runs at a steady speed.

[Lost_Cause]

Yeah, that's kinda what I was thinking, due to the lambda being before the cat. Unlike newer cars where it's metered again after the cat. 34mpg is a 'best case scenario' result of keeping it below 3.5k rpm and basically combined driving,not motorway stuff.
Million and one other things to check,clean,remove anyway, but no point a while til the lambda is got. At least I'll have a zero point to work off with everything else.