20 Mpg!!!!!

[unkleG'sif]

Happy new year guys and gals

Just a quick question before i dash off with work..... something that has been troubling me for a little while

Ever since I had a new engine fitted (blew exhaust valve and a good head came with complete engine) to my LPT, and had it FPT converted with the system from the car the engine came from..... ive never had an average MPG over 20.... which is quite bad when I drive 20 miles to work everyday (and back) ..... and work for a charity - so the old payslip is a tad thinner than my actual worth
Other people seem to have reported 25-30mpg here

Im just trying to bounce some ideas around here, but for some reason I think that the problem could be with the Lambda Sensor. I base this crude assumption purely on previous posts regarding AMM adjustment, and this being irrelevant on cars with Cats and O2 sensors.

Basically the car is in good order, well serviced, and have checked the usual things (tire pressures, brakes rubbing etc)

Does anyone have any more advanced tips that I would not otherwise have thought of?

Gotta go now, but ANY advice would be HUGELY welcomed as I cannot afford my petrol bill at the moment
Adios
G

[trackside]

Firstly my car with the same EFI alway returns quite substantialy worse mpg in the winter - about 20% worse. However 20mpg is very low even for a short journey of 20miles in the winter. Here are my suggestions;
Adjust the timing to 20deg BTDC and bend or grind back the stop tab on the retard lever to get back to 10 deg on boost. Check thay the resistance on the AMM is around 350Ohms between 1 and 6- even on a Lambda car this does seem to make a difference - then experiment with higher or lower settings. Check that the resistance from the NTC sender is correct when the car is warm. Are you getting any check engine lights? and is the engine check light functioning? Check and double check for any air leaks. Other possibilities dirty fuel injectors, missaligned cam timing -easy to do when reassembling the head, low compression, leaking or worn FPR, worn out and slow lambda sensor, faulty ecu, faulty amm. Lastly - driving style - a heavy right foot will drink petrol faster than all of these things.

[Alex]

Originally Posted by trackside

Firstly my car with the same EFI alway returns quite substantialy worse mpg in the winter - about 20% worse. However 20mpg is very low even for a short journey of 20miles in the winter. Here are my suggestions;

20 miles isn't really that short, the average journey distance in the UK is 5 miles .

20mpg is rather low, both my c900 and my 9K 2.3auto give around 30mpg on my 20 mile each way commute.

As suggested check the timing, make sure it is atleast on stock settings. Compression as well if gauge is available. Fuel leaks would be another one to look at, especially when the engine is running and the system is under pressure. Get a voltmeter on the lambda and check how quickly the voltage is swinging around the 0.5level, it should cycle fairly quickly. If it goes slowly or not at all then look at replacing it.

[trackside]

I assume that is 10 miles each way? - in winter even when the water temperature is up to normal oil temperatures, especialy in the gearbox, and lubricants in the rest of the drive train are still quite cold and viscous - this will kill your mpg.

[ShadowWorks]

Welcome to my world! 20Mpg is about the best i get right now and has been for a while.

have you changed your IC by any chance?

Is it possible that a bigger IC would allow more air into the engine and so mess the fuel mixture up?

[trackside]

"Is it possible that a bigger IC would allow more air into the engine and so mess the fuel mixture up?" - no. I get the feeling form your previous posts that your AMM may be bad - try adjusting it the other way and see what happens.

[Alex]

My intercooler made no difference to the mileage. OTOH the failed AMM did.

[unkleG'sif]

well, in response to your replies (cheers btw dudes).......

Trackside:
Head was not removed from the new engine... prefered a complete swap rather than get stuck halfway thru a head swap, so as far as i know, the advance timing and valve timing should be stock (but not gaurenteed of course). Thats one i'll have to sort later, as i dont have a timing gun etc

Ive got a spare AMM (original from the car I think - engine came with EVERYTHING, inc entire wiring loom, front to back ). Ive tried testing the resistance between 1-5 on the spare.... was down a bit..... but couldnt get the little blue cover off to get at the adjuster screw. I even have a spare ECU that came from the doner car ('88 Carlsson getting scrapped - missed out on the kit tho )

Remind me once again what the NTC sensor is?
Due to my 20MPG, I dont have a heavy right foot

Alex
Ive never had the O2 sensor off... How do I test it (ie, where/which plugs etc)?

Shad
IC is stock, due to my 20mpg eating into my limited budget that would otherwise be spent on IC hoses and piping (had a Volvo 740 Turbo IC to go on for a year now)!!!

Cheers for this guys
G

[trackside]

Try the other AMM but the one from the 88 won't be compatible as it's Bosch. The NTC is between the intakes on the head - if this is faulty it will give a check engine light.

[unkleG'sif]

Trackside
Its definately a Lucas AMM, but i' sure that the car was not fitted with an O2 sensor.... could this be a potential cullprit? (spelling?)

I'll check with the source of the engine re' its age (88 was a bit of a stab in the dark )
G

[trackside]

If it's a Carly it will be Lucas. The AMM is the same for Lambda and no Lambda cars - drill out the plug and set it to 335 Ohms between 1 and 6. While you are at it check the resistance between the pins on the NTC is below 400Ohms at running temp. Have you checked your timing as well ? Actualy I'm looking at my Saab workshop manual for the Lucas system right now - the check engine light will only illuminate under 3 situations; Faulty NTC signal, no AMM signal and Lambda signal fault - everything else can be read by the codes but you won't have a check engine light. In the tech help there is a fault pulling guide for the Lucas - Shadow Works and Drg23 would be advised to do this first.

[unkleG'sif]

Cheers Trackside

I'll have another crack at the AMM (metaphrical) tonite, and go thru the ECL guide also.....

FWIW, i have no ECL showing at the moment, but thats not to say that the bulb is a dudd

G

[kemosaabey]

if your getting 20mpg in stop start cold weather conditions it's not much worse than expected....I can maximise my economy just by keeping the boost gauge in the white.

[unkleG'sif]

sorry, forgot to say in last post.......
..... 20 mile there, 20 back - so 200 miles a week, just for work!
..... 20mpg is an average of all driving, mostly A roads @40mph then 7 mile motorway each way - i wouldnt be so concerned if it was a daily grind thru the city

just 'avin brew and a giant tea cake (mmmmmm ) then out to swap AMM, may even swap to the ECU that came with the carlsson engine

G

[trackside]

Don't swap the ECU - it won't take the lambda signal.

[ShadowWorks]

I will also try the AMM again, whats the lowest resistance you can get on it?

Does cleaning the AMM with brake cleaner hurt it in anyway? I will have to source a second hand Lucas one now, there pretty rare, will the Bosch ones work?

[unkleG'sif]

Originally Posted by trackside

Don't swap the ECU - it won't take the lambda signal.

righto
g

[trackside]

I wouldn't use brake fluid as it's quite corrosive of plastics - I've used carb cleaner though without problems. You can't use bosch AMM on the Lucas ECU. The Lucas AMM is also found on some Rover cars and Landrover/Rangerover's if you cant find a unit off a Saab. No idea what the lowest setting is - mine's at 255 which is below nominal - if it's rich at this it' s likely to be faulty or there is some other problem.

[unkleG'sif]

what a rubbish time for my voltmeter to give up the goose

[Alex]

Originally Posted by drg23

sorry, forgot to say in last post.......
..... 20 mile there, 20 back - so 200 miles a week, just for work!
..... 20mpg is an average of all driving, mostly A roads @40mph then 7 mile motorway each way - i wouldnt be so concerned if it was a daily grind thru the city

just 'avin brew and a giant tea cake (mmmmmm ) then out to swap AMM, may even swap to the ECU that came with the carlsson engine

G

Similar in many ways to mine, though I have 5miles of A road and 15 of motorway. If anything the long 40mph bit should help the economy so your 20mpg really does look a bit low.