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Hi guys, how are you?
I posted in the newbie section a little while ago. Thanks for your (and Eric’s help)… I ordered the ETCG baseball cap so I can look cool when doing my auto repair from now on B)
I’m sure it’s said a lot here but how awesome are Eric’s vids? Love watching them every week.
Just as an introduction to myself I’m 30 and I’ve just switched (thanks to my company) from full time in a UK Building Society (bank) to part time while I study to become a technician. I’m 3 months in and absolutely love it. Another 2 years and I’ll be qualified! :ohmy: 😉
Anyway as per the subject title I have a car… it’s a Vauxhall Omega 2.5 V6. I believe there is a Cadillac equivalent for you guys in the US.
Well I’ve recently (over the last few months) a drastic decrease in the MPG I’m getting from the old girl.
I’ve recently watched ETCG’s performace issue vids and was kind of thinking I could apply the same logic here. I’ve checked the fuel pump. no probs. i’ve replaced the fuel fuel filter. i’ve replaced the air filter. I’ve cleared the breather pipes of carbon build up and i regularly (3k miles) change my oil. i also had a code reader put on it where we discovered all the vital statistics are fine i.e. coolant temp sensor, MAF etc…
Things i havent done…. search for vacuum leaks with carb cleaner (although a good visual inspection done when inlet manifold removed to clean breathers), cleaned the MAF sensor.
after i do the above what else can I do?
Thank you.
Steve.
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How confident are you that the fuel is up to speck? If you are on to E85 or something similar, the economy per Liter will significantly decrease. Otherwise, if you are not having performance issues, start with the tires and work your way up.
Tire Pressure
Engine Temperature
Fuel Leak
Intake Manifold leak
Vaccum Leak – You can use low pressure water to check for intake leaks.[quote=”Jotmon1″ post=39839]How confident are you that the fuel is up to speck? If you are on to E85 or something similar, the economy per Liter will significantly decrease. Otherwise, if you are not having performance issues, start with the tires and work your way up.
Tire Pressure
Engine Temperature
Fuel Leak
Intake Manifold leak
Vaccum Leak – You can use low pressure water to check for intake leaks.[/quote]Thanks for your reply.
Fuel is standard unleaded, nothing special. And you’re correct i have no performance issues (sorry should have perhaps pointed that out)tyre pressures are correct as per manufacturers rec. for the usual load.
engine temp…. bang on the half way point on the gauge all the time.
no visible fuel leaks and no smell of petrol in the engine bay.
intake/vacuum leak… next on my check list.thanks for that.. i feel im going in the right direction 🙂
If you have a good scan tool, look at fuel trim data. It will show you if the PCM is trying to compensate for a lean running condition.
How many miles are on the engine?
Hi Dreamer, thanks for the reply.
Yes I’ve had the scanner put on it. All readings looked normal except my mate who did it mentioned that I have some lazy O2 readings. However, I thought that would simply mean a replacement set of O2 sensors. But he said that they were more than likely being lazy due to something else e.g. vacuum leak, bad MAF sensor etc.
I’ve today done a vacuum leak check (following that guide…thanks for that) and idle never changed.
Apart from cleaning the MAF I’m wondering where to go now.
It is worth mentioning that it is a big car that only really ever does short runs so I’m aware that it’ll pretty much always be running on the choke due to it taking time to get to temp. I’ve also tried to change my driving style.
With all this taken in to consideration it still seems pretty low.
I’m now wondering if perhaps there is nothing wrong as such and perhaps the above factors are solely causing the MPG drop.
Oh and the car has 96000 miles on it 🙂
Thanks for your help 🙂
when was the last time you had a front end alignment?
with the car being driven short trips and the given mileage.
have you ever professionally had the injectors cleaned? your
intake valves and combustion chambers could be full of carbon
acting as a sponge when fuel is sprayed.here is a video to show
a professional injector service.the video is how to move a vehicle
without fuel pressure. its the canister and solvent procedure we are
interested in.+1 on the short driving contributing the low MPG.
I would recommend taking the vehicle on a spirited drive often. That will burn off any contaminants of the oil (moisture as an example from short trips).
Also make sure your tires are inflated to the correct PSI.
If you can see the pre-cat o2 voltage readings, you could create your own vacuum leak and see how the o2 sensor responds. Just remember what you see on your scan tool is what the PCM is seeing.
One more thing to add is when looking at the live data on the fuel trim numbers you want them to be as close to 0 as possible. If they are positive (by a significant amount) then the computer is adding fuel because it sees a rich condition. If the numbers are negative it’s removing fuel because it detects a rich condition. Also be sure it goes into closed loop. If not then the O2 will not be monitoring the mixture for optimum fuel mileage. If it’s not going into closed loop look to the coolant temp sensor. If it’s faulty the computer will not put the engine into closed loop and mileage will suffer. You can consult your service manual for the proceeders for checking your coolant temp sensor. One last thing to add is that it may not be the sensor at all. If say your thermostat is sticking open then the engine will not come up to temperature properly and the result will be the same, no closed loop. So if you don’t see the engine getting up to temperature look to the thermostat first.
Thanks for the replies folks; really sorry I haven’t replied earlier but for some reason the e-mails saying I’d had replies had been auto placed in to one of my folders. Weird!
Anyhow, yeah I have had an alignment done. I’ve never had my injectors serviced. If I did that would also driving it hard sort out the ”sponge” syndrome in the combustion chamber you mentioned?
I’ve got the correct pressures in my tyres and I plan to drive more spirited more often 😉
Regarding the fuel trim: got to be honest I’m only still in school so I don’t fully understand the results of the reading session. I may have to get it done again (as he kindly does it for free) and report the findings here.
Other than that I’m really believing it’s the short journeys and that there’s actually not a problem.
Oh and the car gets to temp in good time and doesn’t overheat or overcool.
Cheers.
I’m still waiting to learn about how to do a professional fuel injection service. One mechanic told me that the job should be done with each injector individually, not as a group while on the car. I guess I was under the presumption that a bad injector would usually give a lean condition for a single cylinder. But, on thinking about it, if the computer detects a lean condition downstream then it would boost fuel to all, resulting in bad mileage and maybe misfires. Eric, where’s that video you did but never posted, on fuel injection cleaning?
[quote=”spelunkerd” post=41285]I’m still waiting to learn about how to do a professional fuel injection service. One mechanic told me that the job should be done with each injector individually, not as a group while on the car. I guess I was under the presumption that a bad injector would usually give a lean condition for a single cylinder. But, on thinking about it, if the computer detects a lean condition downstream then it would boost fuel to all, resulting in bad mileage and maybe misfires. Eric, where’s that video you did but never posted, on fuel injection cleaning?[/quote]
Would be very handy to see. I’ve got a spare fuel rail that I’ve pulled the injectors out of so if this is something that can be DIY’d I could practise on them first.
Having said that I don’t think it’s that expensive over here (UK) to get the injectors cleaned. Just really wonderig if this should be done as a service type thing.
I suppose there are different methods of cleaning the fuel system but all I’ve ever done is used my fuel injection cleaning set up and I’ve been fine with that. As for the video I don’t have one on that operation specifically at this time but I do have one that I’ve shot doing a fuel injection cleaning as part of a diagnosis. That should be out early next year.
Thanks Eric, I’ll look out for that.
Does it make any difference that I’ve narrowed down the problem to cold starts? I think what’s happening is it is very poor acceleration at start up and then it gets better as it warms up. What could this be?
That is an important observation and it’s a good idea to focus your search during those times to best nail down the issue. The more you can ‘learn’ about the problem the better. Based on your description I’d be looking to a mixture problem so be sure to check fuel delivery and for vacuum leaks.
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