hey guys when i had my car on the rolling road the car was running rich on low revs then lean on high revs running on 3 cylinders.

now i got the car sorted and running on all 4 i thought great the car will be fueling properly.

but just fitted a air/fuel gauge and its not looking good.

on idle the gauge sits badly rich then it will flip to lean and sweep back to rich and will stay there for about 5 secs then do another sweep so on so fourth.

when driving the car it sweeps the whole gauge but sits into lean quite alot.

its deffo wired up right as its the same as my other scooby, which when on idle will sweep between lean and optimal mainly staying in optimal and when i drive it, it would do the same sort of movement but would stedy itself on the optimal/rich mark as it should do.

so can anyone tell me if there is infact something up with my engine?
i know the previous owner changed the fuel pump, so if the car was mapped for a uprated pump and he then fitted a standard pump would that cause problems?

 

bttt

 

car wont need to be mapped for a fuel pump.

if it is fluctuating wildly at idle then there is a possibilty that your lambada sensor is fubbared. If it is doing it all off the time ie even when driving then I would double check all the connections (especially the earth)

 

its a new lambda fitted. but now i think about it when i fitted the lambda to my other scoob it was doing the same thing if i remember right. but was the right lambda for the car?????

 

oh and when it was on the rolling road he had a sensor up the rear pipe and told me the car was running lean/rich so could the lambda cause this?

 

the sensor up the rear pipe is probably an emmisions sensor the same as what they use at mot time. Obviously from the emmisions the operator would be able to say that it is running rich/lean

A faulty lambada will cause fluctuations at idle as it tries to maintain stoich.

If you have a new sensor fitted then I would check the wiring on that as well. (did you use the type where you have to splice it into the existing loom?)

 

it was subaru specific but needed to add length to the wires

 

it would help if you gave more information.
for starters what year car?
what model?
what ecu?
heavily modded or stock?

The sensor up the pipe would have been a wideband o2 sensor (£150-300), it measures the o2 content and calculates the afr value under all conditions.
You more than likely have a lambdalink or simple afr gauge (about £60-100) which will only give a good reading under load.

You would expect the afr to "dance" all over the shop at idle and cruise, this is normal behaviour as its trying to acheive a stoichmetric mixture (ie L=1), the car isnt able to hold it at L=1 so it bounces about trying to continually compensate to get a best fit.

you dont mention what o2 sensor you fitted.
but it doesnt really matter as long as it had the same amount of wires, either 3 or 4. Many of us used hotwires sensors from halfords at £30 a pop without issue. currently I run open loop so dont have any o2 sensor

my guess is that you have a standard ecu, the sensor was failing or had failed, the ecu was compensating as best it could.
You changed the sensor, but did you recalibrate the ecu to it?
did you reset the ecu to perform a sensor sweep?

You can test o2 (and MAF) by disconnecting the sensors, certainly on a classic not sure on newage.
if a disconnected maf makes the car stall then its ok, if the car runs still then its fubar. Not sure on the expected results of an o2 disconnect, but then you could have easily searched for "failed lambda or failed o2" and called up the thread in question anyway

 

Hi mate, you need to be specific, is it lean or is it rich??? there is a huge difference! the guage you have will not work 100% without a wideband lambda sensor, i have one too and its all oer the shop unless i accelerate, when its on the slightly rich side of things. Rich isnt so bad, not ideal, but not so bad, if its runnin lean then you WILL melt a piston or 2. Your best bet is to take it to a rolling road and ask them to run it under laod and test the mixture, its the only way you can be 100% sure, plus its peace of mind for you, it might cost you 40quid or so, but i can assure you its cheaper than a re build!
Going back to the fuel pump, if the duty cycle has been upped for more power and the supply of fuel has been removed then (unless i am wrong) the engine will run lean -feel free to correct me here!-
So if i was you, do 2 things, check the pump, whip it out and see what it says on it, if its not a walbro, fit one. Take it to a garage and get them to check it over, might be worth having a chat with a mapper to see if it can be sorted easily. Main thing, drive sensibly, dont boot it, it doesnt take long to destroy a piston.

Mike

 

Also, very simply, dont put too much faith in the guage unless you get a wideband. Get it checked mate, peace of mind is worth the cash.

 

i recon it could be the lambda sensor

 

but you said you replaced it??

 

a like for like fuel pump will pump the same amount of fuel so you dont need a remap. The regulator however can control it so if there was an aftermarket one fitted and set at say 3.5 bar and was mapped accordingly, then it was swapped back to a standard at 3 bar then it would run lean as the engine would be mapped for more fuel

 

thats true enough assuming that the regulator and pump both went.
if the reg is still on, and set to the same fpr, as long as the pump can handle the demand then its all good.

seeing as how we know ****all about the car though its all a guess