VT fuel consumption and reverse stalling...

[sasquire]

Hi,
Over the last year our 98 VT wagon has become a crime in regards to fuel economy. We're now calculating at $35 of fuel gets us about 100-130km of about town driving. Highway driving isn't too bad. As we're going to sell the car in a few weeks (new people mover arriving), we want to get this fixed for the new owner (and maybe make a few dollars more on it).

Another problem (which I believe is related) is that when reversing on cold mornings only, the car will stall when we stop to switch from reverse to drive - only does this coming out of our driveway.

About 6 months ago we had a total tune/service. All filters replaced (fuel filter, air filter, oil filters... spark plugs etc etc). And it made no difference.
Reading some threads, we recently had our oxygen sensors replaced. We were thrilled at first as our gauge went from saying 310 left to 480. But it turned out to be just lies Our fuel gauge always lies XD ... once it gets to 50km until empty, it'll drop a km every second you drive. Very scary sometimes.
Happy to change them anyway as the old ones looked like hell. And I think it has helped slightly.

My guess is the fuel pump. But I don't want to spend money on a car we don't want anymore to only find it's something else. Putting the car into diagnostic mode using a paper clip, and it shows no errors.

Any thoughts?

[mangzilla]

is it a V8? Ive got a 5L vt, and i get around 300-350km to a tank of town driving, costs me about $80 to fill, maybe a touch more. On the highway its brilliant but town driving gets very thirsty. My distance to empty is also similar, sometimes it drops from 75km to empty down to 55km to empty in the short distance of my street. I just never let it get low if i can because its so unreliable.

[sasquire]

Nah, a standard V6 3.8l. So we're guessing over 20litres per 100km.

[Full Spectrum]

If i do plenty of stop start all local driving over the week mine will return 15.5l/100 easy.

But if you don't want it no use in giving suggestions to try and fix it then lol.

[sasquire]

Just hope it won't be hard to sell if it's hitting 20l/100. And often people can get a bit nervous about any car that stalls, even if its only reversing on cold mornings.
Don't want to end of like some houses with rotting holdens strewn all over their frontlawns XD.

[wrx884]

does the fuel light come on? i assume it does wen it starts counting down the KMs lol mayb uve just got a faulty sender and uve got more fuel in the tank than u think? have u ever run out of fuel?

mayb check ur cats? they can use a bit of fuel if they r stuffed.

[sasquire]

Yeah, fuel light comes on. Never run out of fuel before. It might have more fuel then reporting, but it's still burning through it like crazy.
Is there anything I should look for to identify a stuffed cat?
Thanks for you help as well. Even if I don't get it fixed, at least I can give a good idea to the buyer what it could be. But I'd prefer to get it fixed before hand.

[sasquire]

An update and possibly a small emergency:
The problem has esculated. The car now threatens to cut out when idle at any time (eg at the lights etc). It appears the revs are going too low. And now when you accelerate, there's this "whoosh" sound everytime, like a bike pump.
Was worried I hadn't put on the O2 sensor right. I opened up the bonnet and the sound 'appears' to be coming from the top of the engine where the accelerater (throttle) cable joins up (sorry for the bad explanation but I don't know cars that well). When you put your foot down and the cable pulls.... whoosh! Not sure how'd it cause that sound, but that's my best guess where it's coming from.

So begging anyone if they have an idea to let me know It'd be very much appreciate.

[Joshcovl]

hey mate are all the hoses connected to throttle body i know the small one on the bottom doesnt seem to stay on to solid maybe sound you described could be coming from there im not sure as mines never done it and i am no mech but worth a 5 sec check and mine was idling real low and rough untill i cleaned the plenum and tb and goes great now have you done that

[sasquire]

Thanks Josh. Will have a check first thing tomorrow

[NV-MY-VT]

Mate, not sure if you get a chance to read this, I have a VT V6 3.8L, and was having a very similar issue. I removed the throttle body, IAF sensor and the MAF sensor (Basically, follow the air line up from your airbox and remove the metal sandwich box and the... well you know what the throttle body is...) and clean those.

Unscrew the black sesor thingo at the top of the throttle body. Careful, it has a washer on it which you need. Clean this sensor within an inch of its life. You can actually with a little bit of play, take it apart more, but just be calm, slow and careful as you clean it. There IS white plastic underneath the black crap, I promise. You CAN use Carby cleaner on this, I used switch and terminal cleaner for electronics.

The Throttle body can be cleaned with carby cleaner. Get a can... or two, and really get rid of all the crap it in. Be careful to avoid the TPS if you can. People say clean it, I say leave it alone or replace it. It's too... touchy.
I would also recommend doing the IAF first and leaving it out so avoid washing any crap back onto it.

If you've got a fair bit of carby cleaner and rags laying around, do the plenum while you're there. Because... why the #### not.

Once thats all done, refit the (plenum?) and throttle body, and then clean the MAF sensor. The MAF sensor has three little resistors that work as heating elements, measuring how much energy it takes to keep them at a constant temperature allows the engine to gauge how much air is flowing into the engine. I wouldn't use carby cleaner on it, and I wouldn't even TOUCH them. They are very small and fragile. Use switch and terminal cleaner, or if you're feeling rich, buy a special can of "MAF cleaner" It's the same shit as switch cleaner, but costs 10 dollars more. Your choice. If you're really picky, get a cotton bud, and GENTLY rub the little buds in the middle of the wires. When you're looking at it, you'll know what I mean....

I did this and an oil change and it solved my problem. No joke. Also increased performance by a noticeable amount (I'm not talking fully sick 40kw at the rear wheels increase mind you...).


Good luck, PM me if you got any concerns, I can send you some links or some pictures or something.

[sasquire]

Just a heads up that indeed the hose had popped off as Josh had mentioned. It doesn't connect bakc very well (as if the hose isn't long enough). However, I put some glue around the edge and got it on as best I could. I can imagine that it was never on properly and may have been causing the reverse stall. Time will tell and I'll report back later.

NV-MY-VT, I've actually become very tempted to go through with all that. I was recently reading the help thread here HOWTO - Replacing fuel injectors and cleaning plenum chamber on VT commodore which while probably a bit beyond my courage, I'd still be interested in cleaning as much as I can. I've got a haynes book which I intend to go over so I can identity what is what to increase my courage.

These forums are not only a stress relief, but entice a person to get very personal with their cars

[Longman]

Hi Mate,

If that hose doesn't fix your fuel consumption problem -

when was the last time you had your brakes checked/changed? Old faulty calipers could cause brake binding. The pads would only have to be rubbing on the rotors slightly to cause your car to use more fuel. Aside from that is there any fuel odour at all, either in the cabin or in the engine bay?

[kangavxss]

Is your car parked outside? Sure someones not stealing ur fuel or check if u got fuel tank leak.

[sasquire]

No smell of petrol. We'll see how we go with the hose and check the fuel economy over the next few days. A brake issue is possible. Our car shakes in its usual way coming off the freeway when breaking (gathering some of the rotors are out). Maybe there's still some binding even at slower speeds?

[sasquire]

Just an update.
Obviously the new Bosch O2 sensors are in. There was no immediate change to petrol consumption unfortunately.

However, as the weeks have passed, the economy is ever so slowly improving. Before we were getting roughly 20l to every 100k. Now it's more like 20l for every 130k. Still not great, but better. Is this normal at all? I thought the improvement would be instant.

Also, we now got a CEL error now and then which turned out to be the O2 sensors. But they're brand new! I checked them and they're in right and no issue. There was no error light with the old ones. Confused about it all together.