1.2spi drinking fuel, weak mixture, save my wallet!!

[jeremy fisher]

Hi all, my 1.2 spi crappy Corsa B daily is costing me waaaayyy too much in fuel. Last tank I used I got 29mpg with pretty carefull driving, and it gets a good run including motorway to work and back regularly. When up to temperature the engine light comes on and the paperclip test revealed code 44, weak mixture. The way it drives (very slow and surges a fair bit) seems like weak mixture also, but its drinking fuel? I have been trying to sort this for a few weeks now and have changed the lambda sensor, coolant temp sensor and thermostat. Before changing the thermostat it never really got up to temperature but now it does but no real change in fuel consumption. Also the flap in the airbox that diverts air from the exhaust manifold into the engine was always doing just that and not allowing any cool air in even when at temperature so I removed the vacuum line to it and blocked it off. I've gone down all the fuel system and can't see any leaks. I have sprayed WD-40 around the inlet with it running to try and check for airleaks and nothing obvious. The cam belt is timed up right and I serviced it a couple of months ago. I bought this car and the problem was already there so it hasn't developed while I've been driving it so no idea how long its been there or how it used to drive. I will be filling it up again in a few days and will check my figures but if anything it seems to be getting worse.
So anyone have any ideas please?
Or someone want to sell me a Nova cheap?! I used to get 44mpg from my 1.2 carb Nova!!

Thanks

Nick

[MK999]

30mpg is about what I'm getting out of a corsa B sp-****e on the motorway too, basically they just don't like it. My 1.2i nova was the same, sipped gently at fuel under 50 but anything over that and you're really pushing a piss poor engine along and it's splashing lots of fuel vaguely in the direction of the cylinders.

You seem to have checked all the obvious, the weak mixture code might suggest it's registering something badly but tbh you've already spent 4 times what most people will on a 1.2i lol

[mowgli]

surely its got to be the lambda sensor.. its saying its weak, & turning the fuel mixture up....

[MK999]

surely its got to be the lambda sensor.. its saying its weak, & turning the fuel mixture up....

Already been replaced.

[meritlover]

get back to basics.

the only way the ecu knows theres a lean mixture is by what the lambda sensor tells it. its seeing either a genuine weak mixture or its being fooled by air entering the exhaust somewhere.

check for air leaks around the exhaust/manifold, check the fuel pressure and ECT. thats about all you can do.

check the base timing too. remember that a missfire will give a lean mixture due to the unburned O2 and fuel being pumped down the zorst.

[mowgli]

Already been replaced.

doesn't mean the replacement is any better.... or it could be a wire at fault

[jeremy fisher]

Thanks for the replies. I have checked for a blowing exhaust and nothing around the manifold. The centre section to backbox join is blowing but that surely won't have an impact? From the way it drives I think it is running weak though obviously not 100% sure. Might see if a friendly MOT place will stick the gas analyser down the exhaust for me. Was wondering if the injector might be shot but surely that wouldn't cause high fuel consumption?
Thinking about using what fuel I have left to torch it!! Doesn't help me get to work though!

[meritlover]

you wont know what the mixture is by driving it. check the timing (both ign and cam) the gas analyser is the best option to be sure of what's going on. although this wont tell you whats going on under load.

[jeremy fisher]

checked the cam timing whilst doing thermostat and its spot on. I'll check ign timing later. Is there any way of adjusting it or is it just ecu controlled? Think I'm going to take the summer Nova to work tomorrow, prob get better mpg from it, and make me smile instead of cry!

[meritlover]

its ECU controlled, but it takes a reference or 'base timing' from the cam pick up in the distributer (assuming SPI) which is variable by twisting it around. MPI uses a 60-2 on the crank.

ive never been able to find the correct procedure for setting it up, but most of them sit with the notch on the head aligning with the dimples on the flange of the distributer.

[jeremy fisher]

Gas analyser says its very very very very rich... off load anyway. Asked the guy at the test station if he had any ideas and I've already done everything he suggested. How do you go about diagnosing a wire fault with the lambda? Looks ok from what I can see, but thats not a lot before it dissappears into the loom. Does it go directly to a pin on the ecu or anything?

[meritlover]

how rich? what were the results?

there is very little to go wrong on an SPI, theres MAP sensor, CTS, a cam trigger, a TPS and lambda for closed loop. measure the CTS values. all the injector does is pulse depending on what the above tell it. unless the FPR is knackered and fuel pressure too high then its not likely that.

i would check the MAP and vac hose to it. If the MAP is reading low pressure by either being knackered or the VAC line being choked or disconnected/punctured then it would be measuring atmospheric pressure and the ECU would take this as high-load and give an aweful lot more fuel. Im sure the TPS is just for transient load sensing.

MAPs are cheap, and easy to get to and to replace. check all wiring to it as well. should be about 5V (across the pins) with the plug disconnected from it. same goes with the CTS.

the lambda is a single wire. i think it will be volt-free as the voltage is generated from the lambda sensor. You will have to bell it out on resistance, from the manifold back to the ECU pin.

that's pretty much all there is to check

[jeremy fisher]

I don't have the results printed off, he was going to do it for me but he was busy and his paper had run out in the printer so I said not to bother. The CO was 10.something though, I'm sure he said it should be about a hundredth of that. What would diconnecting the lambda sensor do? Will it just not like it?
Thanks

[meritlover]

normally on the SPI an OC lambda doesnt do anything until 70mph cruise, at which point it tries to look for it to run closed loop and fails. it wont prove much.

have you checked all of the other suggested points to check?

if its running as rich as that, expect your cat to be melted.

[jeremy fisher]

Filled up again and did 24mpg from last tank so getting worse! It seems to drive a lot better without the lambda connected. Replaced vac hose to MAP as it was pretty perished and no real change. Measured voltage at MAP pins 12v, at CLT 5v. Haven't had chance to get another MAP to try. Voltage between manifold and lambda pin on ecu is around 10mv and resistance around 30KOhms. Checked fault codes again and had 44(weak mixture again), 13 (lambda disconnected) and 93 (quad drive module in ecu). don't know if the last one is there because I disconnected the lambda or if it is more relevant? It seems to me that if the car thinks its lean and its actually rich then it must be a lambda or ecu fault???
Thanks
Nick

[meritlover]

interesting...
was the lambda voltage with the engine running or the sensor out in fresh air? or were you measuring back to the ecu on the loom side to earth?

have you checked the engine earths? i say this because the single wire o2 sensors are very susceptible to induced voltages and poor earths. i would seriously doubt if it was an ECU issue, but you do seem to have changed everything else.

are you certain its code 93? it doesnt tie in with what i have here or what i can find online:

http://smogcarsuck.tripod.com/obd-i-generic-codes.html

i have seen QDM codes up with non related faults. once they are cleared it goes away. one time it was inferred by the crank sensor being out of sync with the cam trigger due to the crank pulley slipping (not relevant in this case) but shows how codes can lead you off on the wrong track.

can you get access to a code reader which can read the live values of the engine running, rather than just the codes?

[mowgli]

i really am not that familiar with spi engines. but try this for an idea... if the lambda was broken, and someone tried setting the injection up, so that it ran right ish... then the lambda got swapped, surely it would have all its settings all over the place..?

[meritlover]

mowgli, theres nothing to setup at all really. I dont even think theres a CO adjustment screw anywhere. even if there was it would be purely for the idle and wouldnt play much part at cruise.

its getting to the long shots now, but the only things left really is a stuck injector, FPR failed high, or blocked fuel return line.

[marc69]

This might be a really stupid suggestion and might not even apply to your engine but, years ago my mini cooper used to give really low mpg (it's still lowish!), it wasn't until a failed mot on emmisions that it was investigated. Hundreds of pounds to garages for sensors etc, still wouldn't pass.

By chance I was at a mini show and spoke to a chap who told me there is a seperate temperature sender for the ecu, they were known for failing. Bought it for £5, end of story. The gauge sender is on the head but the ecu temp sensor is in the inlet manifold.

If the vauxhall spi engine also has seperate sensors, might be worth a look.

[meritlover]

thats a fair point marc, but if he is measuring 5v then im assuming it must be the ECU CTS.

is the engine actually getting up to a steady temp when driving? it could be the inj system is all fine and its just genuinely running cold, ie. thermostat jammed wide open.

[jeremy fisher]

I have changed the thermostat and it gets to temp fine now, wasn't before.
I was being retarded and I didn't check the MAP sensor, it was something else! I have now changed vac hose to the actual MAP sensor and had 6.4v across two pins and 6.7v across another two pins and zero with the other combination. The CLT has been changed. I will check fault codes again and I think a mate has a cheapo code reader, not sure if you can read live data on it though, I'll try and get hold of it.
Checked the lambda values with engine running and sensor in situ, one probe on the back of the pin at the ecu, one probe on the exhaust manifold.
I will try and get to the scrappers on friday and get a couple of MAP sensors and lambdas if I can get them out!
I'll check out my earths too, might just stick a jump lead from block to battery and take it for a drive.
Thanks
Nick

[meritlover]

try that, then the only thing left is the throttle body with integral FPR.

[jeremy fisher]

I tried a MAP sensor from scrappers and no real difference, loads of fault codes cropping up again. Then tried a lambda from the scrappers yesterday and it seems better. Took it for a drive and no eml, drives much better, with the lambda connected too. Bit early to say for sure but I'm hoping its sorted it. Wish I'd have gone to the scrappers in the first place, how silly of me to think a brand new sensor would be right!! Hopefully I'll not be posting in this thread again.
Thanks.

[oVerboost]

Fingers crossed it's all sorted for you now bud :)

[mowgli]

i hope you kept the receipt for the new sensor.

[jeremy fisher]

They don't accept returns on electrical related items! Just part of the list of things I've spent money on for this cheap run around. Wish I'd kept my Nova daily.
Haven't done that many miles yet but fuel certainly seems to be lasting longer.
My fingers are very crossed!!
Thanks
Nick

[mowgli]

name & shame them please.

there is something called the sale of goods act. and if something is not capable of doing its job, it should be returned & either a refund given or a replacement supplied

[meritlover]

lambda sensors often say on the box that returns can only be accepted if the bag the sensor is in is unopened.

i suppose its a bit like returning pants.

[jeremy fisher]

It was from Sutton Auto Factors in Long Eaton (think they've got a few branches around the Nottingham area). The more I think about it the more I agree with you Mowgli, especially considering I spent even more money with them trying to sort it after they sold me a duff sensor. Might pop in and see if they can offer me anything. I'm just happy to be getting a few more miles out of my fuel atm. Don't know exactly what it's doing but I've been watching the gauge carefully and I'm certainly getting considerably more.

[meritlover]

dont go by the gauge, you have to neck it calculate volume against miles since last necking,
The pump is fiscally calibrated, the fuel gauge is not..

[jeremy fisher]

Thats exactly what I do, but I have to fill up again before I can work it out. I've been watching the gauge a LOT though recently and I've kinda got used to how many miles to how much has been used and I'm getting more for sure.