Down on MPG. The diagnostic procedure…

[Steve Webb]

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.

Topic

[Jimmy]

Tire Pressure
Alignment
Dirty Filters (Fuel Filter)
Try using a fuel system clean
When was your last tune up

[Michele Pensotti]

In the past I had lots of problems of high mileage on my mk1 punto because of its O2 sensor, which after 15 years showed its age, increasing fuel consumption and a lot.

BUT also I’ve seen in the past some very tricky high fuel consumption due to one or more rear stuck caliper (on my MG ZR for example).
I did all my homework as you’re doing and one day in my garage I noticed I could not move the car by hand, as I’m used to do since it’s so small.

It was like the handbrake was on, but it wasn’t!
And in the end it turned out both rear calipers were stuck!

Hope this helps 🙂

Live long and prosper (and stay dirty!)

10nico

[Steve Webb]

Thanks for that info Nico. That’s actually something I hadn’t even considered.

I actually have to replace my rear pads this month so I’ll check their moveability and when I replace the pads I’ll polish up the surfaces that make contact and then I can cross that off the list 😉

Thanks for that 😉

[Steve Webb]

Hi guys, hope you’re well.

Ok, I am narrowing this problem down bit by bit and I’ve got a horrible feeling that it’s an exhaust manifold leak I have. As the car is a V6 and everything is very tight in there I got to get underneath and search for this potential leak.

A mechanic friend mentioned using a stethascope on the exhaust down pipe and manifold to ”track” the leak. Any idea how to do this i.e. what should I be hearing? Presumably I’ll be looking for the noise to get louder through the sthascope?

The only thing I am concerned about is actually locating a hole, I’ve heard pin hole leaks I won’t see anything and hardly hear anything.

Any help you could give me would be great! 🙂

Cheers.

[EricTheCarGuy]

This makes things much easier.

[Steve Webb]

Thanks for the vid.

I actually took it to a shop who offer exhaust checks for free so they have done some tests and no leaks apart from one small one near the back box which they’ve kindly filled for free… I presume being just behind the back box this couldn’t affect the fuel economy being that far past the O2 sensors??

Anyways I’ve also tried to re-do a vacuum leak test using the carb cleaner method and also using a length of hose to listen for ”squeals” from vacuum leaks. The trouble is my intake manifold is the plenum style and there’s simply no room to get the carb cleaner where you want it or indeed get the hose to where you want it either. There is also (due to the positioning of the plenum) nowhere to hook a vac gauge up to.
The only method I’ve seen done is the ”smoking out” method using a cigar. Does this work? I’ve seen Scotty Kilmer’s vid on it…

…but I would have thought you’d have to feed the smoke in under pressure? Any ideas/experiences of this?

If not I’ll have to be satisfied thus far and move on to the other things on my list to check.

Cheers guys.

[EricTheCarGuy]

The above method will work. However hooking up a vacuum gauge will not tell you if you have a vacuum leak.

Looking back on this post you did mention a key thing and that’s how you drive. If you’re only driving short distances especially in winter, your gas mileage will suffer. Winter gas is different than summer gas and the longer your engine stays out of closed loop the more fuel it will burn without setting a check engine light. We may be making mountains out of mole hills here. Let’s not ignore the obvious.

[Steve Webb]

Well, as per my previous posts I was having a high fuel consumption issue. Just town driving was giving a return of 19MPG.

These are the things I’ve done so far which to be honest didn’t have any impact…

Exhaust leak test – Visually and aurally by me including a ”marigold” test (marigold on exhaust pipe to check for pressure. Also for a fiver I got an emissions test inc. them looking for exhaust (specifically manifold area) leaks. All good.

Vacuum leak test – This was a bit hit and miss because you can’t really get in to all the places you need to with the carb cleaner. BUT there was no leaks in the places I could get to.

Voltage leak test – Done in the dark to see if there were any sparks or ”arcing” between the HT leads. Again, I couldn’t find anything.

Stuck caliper checked for. Put car in neutral and rolled. No resistance at all.

Cleaned EGR – Performance seemed to increase slightly but nothing really noticeable.

SO…..

I was constantly checking fuel consumption with no improvements at all. THEN….

I decided that as I had a spare MAF sensor (from a previous car of the same make/model) and as my reading from my last scanner data was low (9 kg/hr) I took my electric contact cleaner and virtually emptied half a can spraying the sensor and it’s connector… left it to dry for about a week in the garage, stuck it in and immediately noticed what I believed to be an increase in power.
Checked consumption today using the brim to first click method and what do you know, with no change in type of driving …… 25.6MPG

I’m still going to do the other things that have been suggested like swap out the Disspac as I have a spare one.

BUT at least I now have hard evidence of very good improvement. I’ll keep checking consumption but I’m going to call this done

Cheers to everyone for ALL your help

[college man]

keep us posted if things change.

[spelunkerd]

Thank you for the update. With the price of gas these days most of us are looking for ways to improve mileage, and a dirty MAF will now be on my (already long) list of things to look for. It is vaguely disconcerting that many of these problems can be silent for a long time, during which the unsuspecting victim is bleeding cash.

[EricTheCarGuy]

Cleaning MAF sensors could almost be considered a maintenance item. In fact I think it was covered in some of the videos I posted for you. I’m glad you’re seeing improvements. Keep us posted of any new developments.

[Steve Webb]

Hi guys, hope you’re well.

Another development in this case…. for the good! 🙂

Following the MAF swap out I reported seeing an immediate improvement in MPG and performance. Well I left it at that thinking the issue was solved. I did an MPG check (using the brim to brim method) and found I was getting 14mpg….. WTF! lol

Anyhow, I was disappointed to say the least but I simply continued on the diagnostic path i’d been on. luckily for me the real fault manifested itself very quickly….
[URL=http://s1226.photobucket.com/user/webbybear1/media/egrfekked_zpsd71dbadd.jpg.html][IMG]http://i1226.photobucket.com/albums/ee402/webbybear1/egrfekked_zpsd71dbadd.jpg[/IMG][/URL]
The EGR pipe from exhaust manifold to inlet manifold had a crack… I found it following a tip i’d picked up where you put a bit of tissue on the end of a pen or something and slowly move it around the exhaust area… as soon as the leak was found it started blowing and flapping my piece of tissue :):):)

Swapped out the pipe (£10 from a UK breaker) and since then everything has REALLY picked up. the fuel tank stays filled for a lot longer and the performance is fantastic.

So in conclusion it’s all about perseverance. I liken this fuel economy issue to Eric’s performance issue series… going through the basics and searching and searching but in a logical way.

I have hardly spent any money fixing this… but a lot of time. I have to say though that the journey has been really interesting. and I’ve learned so much. and as i’m in college learning mechanics it’s really helped.

Anyway thanks for all input from everyone. :):)

[college man]

Thats a happy ending. great job! 🙂

[Steve Webb]

Cheers CM.

Big learning curve. in addition to ETCG vids of course :):):)

[Author]

Replies