Lost my gas mileage after timing belt, coil and tire replacement

I went from about 24 with my 99 2.5 to about 20. I put a Bosch Coil in which I am going to put my old one back in and see if it is the difference. It’s hot as heck and running the AC constantly. The timing belt was the OEM.

Anyone else lose gas mileage to this extreme. Also replaced both front axils.

Thanks for any thoughts. I will also keep you posted on what I track down.

Does your mileage history extend back more than a year so we can rule out the A/C use?

Other items that might change mileage a bunch would be O2 sensors perhaps messed up during service. Exhaust leak upstream of the sensors possibly caused by service? Timing belt installed not quite lined up. Last belt I did was off on one cam on one bank before the change. Correctly installed it picked up about 25% more power, but it had other issues before that point that prevented checking mileage.

What sort of scanner can you get access to for drive testing? Lack of codes doesn't mean everything is fine, it just means it isn't totally failed. With a live data scanner we can look at what is going on inside the engine to help find faults.

Does your mileage history extend back more than a year so we can rule out the A/C use?

 

Other items that might change mileage a bunch would be O2 sensors perhaps messed up during service. Exhaust leak upstream of the sensors possibly caused by service? Timing belt installed not quite lined up. Last belt I did was off on one cam on one bank before the change. Correctly installed it picked up about 25% more power, but it had other issues before that point that prevented checking mileage.

 

What sort of scanner can you get access to for drive testing? Lack of codes doesn't mean everything is fine, it just means it isn't totally failed. With a live data scanner we can look at what is going on inside the engine to help find faults.

It’s my first summer with this one. I put the original coil back in. The after market was the NGK not a Bosch. I’m leaving the batter disconnected till morning to make sure the computer resets. When I put the NGK in I disconnected the battery for only the few minutes it took to install.

It’s going to cool down a bit but I’m going to keep using the AC to see what this tank gets me. I can see if AutoZone as a drive scanner I can use. It hasn’t felt quite right since all the work done on it.

You remember me talking about the leak in the passenger side dash. I’ve tried to get it to leak with a hose to no avail. Also, when I use the fresh air setting it rattles with leafs or something in it. I get the feeling the rain takes a few days to fill up whatever eventually overflows into the cab.

Who know, when I get in tomorrow maybe it will run like a top. Crossing my fingers. If not I will visit my friendly AutoZone for a scanner.

New tires are Mazama Reputation Luxury Touring 205/70R15 95T M+S. They were on sale and 80K tires. Haven’t owned 80K tires in a long time.

Thanks for the input. Will keep you posted.

I would start with checking that the timing belt is absolutely correctly timed. It can be a real pain in the butt to get right as there are some markings that are ambiguous. Just one or two teeth off could be enough. Running a compression test could give some clues too.

As for the AC - make sure that it disengages when you turn it off. It shouldn't be that hard to check.

Ignition coil isn't that likely if the engine is behaving well and not misfiring.

And check that the brakes aren't dragging - run the car for some distance, slow down without braking, stop and go out and check the temperature on each wheel, they shall all be alike.

Both NGK and Bosch are making good parts, even though I think the OEM parts are usually Denso (but it can vary by model year and market), but since it's a Japanese car it's usually either Denso or NGK.

I would start with checking that the timing belt is absolutely correctly timed. It can be a real pain in the butt to get right as there are some markings that are ambiguous. Just one or two teeth off could be enough. Running a compression test could give some clues too.

 

 

 

As for the AC - make sure that it disengages when you turn it off. It shouldn't be that hard to check.

 

 

 

Ignition coil isn't that likely if the engine is behaving well and not misfiring.

 

 

And check that the brakes aren't dragging - run the car for some distance, slow down without braking, stop and go out and check the temperature on each wheel, they shall all be alike.

 

 

Both NGK and Bosch are making good parts, even though I think the OEM parts are usually Denso (but it can vary by model year and market), but since it's a Japanese car it's usually either Denso or NGK.

It runs it's poorest from 25 to 35 mph. It's not hideous, it's just not right. I would like to take it to the local dealer but they charge $115 to diagnose and without check engine lights have little faith as I have had issues with dealer diagnoses in the past where it cost me thousands of dollars fixing all the wrong things.

I put the factory coil back in and I don't notice any real difference. I haven't shut my AC off yet. I'm just about down to a half a tank where I might decide to check my fuel mileage and then run it without the AC for a time.

I did put brand new brake pads on about the same time I got the new tires and I better check to make sure they aren't making constant contact. They sure seem fine but will check the temperatures and take your advice on checking them further.

It idles very nice when I first start it up in the mornings when it is still cool. Idles just a little funky on and off when it gets hot outside. It's not a consistent thing though.

The change in gas mileage is the main sign/symptom tipping off to something wrong, well and the consistent rougher running from 25-35 mph. That is very consistent.

When I first changed the plugs right after buying the car, the driver side plug closest to the cab had little to no point left on it. I attributed that to the people who replaced the plugs before not replacing that one because it is the hardest to get to. I'm wondering if I should take the 45 minutes to pull it and check it again.

If you can - pull all plugs and make sure that they look identical. That's a decent sign of a healthy engine. Not entirely conclusive, but at least on track.

If the plugs are different, then it's time to figure out why.

Some people have had problems with the idle due to valve clearance issues, so that's one thing that you might want to check, but it's a bit of a pain in the ass on these engines.

And make sure that all hoses are properly on and not leaking. The EGR valve might also be slightly open causing some side effects. There have been some issues with dirty throttle body as well, and that's where the MAP sensor is located, and if that's not giving a correct measurement it can be a bit quirky too.

Not all problems that arises will give a fault code.

My jumped timing on my 2nd gen mostly didn't CEL (sometimes long idling would be a random misfire). It ran better at cold start than after warmed up.

I think it would be pretty easy to pull off just the outer timing covers and see if the four cams agree with each other. It's not usually the crank being out with the cams all being ok relative to each other.

Be gentle putting the timing covers back on, you're not building a bridge, it's just plastic covers.

+1 on many dealerships not being able to figure things out without a code until they've blown more money than a chimp in a banana bar.

My jumped timing on my 2nd gen mostly didn't CEL (sometimes long idling would be a random misfire). It ran better at cold start than after warmed up.

 

I think it would be pretty easy to pull off just the outer timing covers and see if the four cams agree with each other. It's not usually the crank being out with the cams all being ok relative to each other.

 

Be gentle putting the timing covers back on, you're not building a bridge, it's just plastic covers.

 

+1 on many dealerships not being able to figure things out without a code until they've blown more money than a chimp in a banana bar.

I've been that chimp in a banana bar with my Chevy truck. I knew it was the fuel injectors but didn't want to pay $400 for all new injectors and after spending $2500 on everything but injectors, replacing the fuel pump 4 times I finally put to used injectors in after 2 months of replacing parts more than once and having it in the shop for two weeks without getting fixed and bam, fixed.

One thing I have to wonder about, the tires were bald and now I have 80,000 miles with what looks to be like 1/2" of tread and on top of the extreme heat and constant AC I suspect I might have a difference in my speedometer reading from going from bald to high tread and a loss of mpg for the AC.

I'm gonna pull some plugs ehsnils to give them a look just in case. I might start changing some sensors too. I have cleaned the throttle body shortly before the increase. We shall see.

OK, spoke to the shop who I bought the car from who put in the timing belt. They say there is no way they could have it off a tooth.

I'm thinking the rough feel from 25 to 35 miles might be something in the cv joints they replaced. They put the wrong ones in first and then had to take them out and put another set in. That makes me think, maybe the engine isn't rough but just a very noticeable wiggle at that speed. It is most noticeable on a gently slow acceleration. If I accelerate more rapidly I don't notice the wiggle/vibration.

The shop says if it was a tooth off there would be all kinds of check engine lights on. Does anyone know if this is the case?

It's cooling down and will soon run it without the AC and see what the millage difference is.

My new tires are 25 1/2 inches tall. I'm wondering if this brand might be over sized? Anyone else have any relatively new tires they can measure to see if these tires are part of the difference?

First, they put in the wrong CV joints, but there is no way they could mis-align the belt? Bah! I've seen skilled people get one tooth off three or four tries in a row until they got it right. It is very fiddly to do. A shop where they are always in a rush might not even check for one tooth off after pulling the pin on the tensionner.

Second, it is absolutely not true that it would have all kinds of check engine lights. I've seen many cars off a tooth with zero codes. Mine was off three teeth and it would only once in a while give a random misfire code that would self clear after a few seconds. No codes that would indicate to most people that there was a cam timing problem.

First, they put in the wrong CV joints, but there is no way they could mis-align the belt? Bah! I've seen skilled people get one tooth off three or four tries in a row until they got it right. It is very fiddly to do. A shop where they are always in a rush might not even check for one tooth off after pulling the pin on the tensionner.

 

Second, it is absolutely not true that it would have all kinds of check engine lights. I've seen many cars off a tooth with zero codes. Mine was off three teeth and it would only once in a while give a random misfire code that would self clear after a few seconds. No codes that would indicate to most people that there was a cam timing problem.

Yep, I didn't buy the line about lights and junk but figured I should bring it up.

I've always had bad luck with timing belts and shops. Our German shop screwed up our Passat and refused to fix it on his dime. It would have been another $2500. My Suby before this one, the guy blew the valves and had to replace them but he did get it right.

Because they also replaced the CV joints, it's more difficult to diagnose the feel when 25-35 miles. I feel it in the steering wheel and the gas pedal, and it is just a mild vibration. I can't tell if it is the engine vibrating or the front end.

It hasn't misfired any. If it were not for that funny feeling from 25-35 mph and the poor gas mileage I would think all is great.

I will set an appointment with them and let them figure it out.

Thanks guys.

Check your fuel trims. That will indicate if you're running rich.

Well this will be a new experience for me. I'm driving with my AC only only going home from work to see if it makes a noticeable difference. The engine lugs pretty noticeable when I kick it on. I wonder if they might have the belts too tight or something as they replaced all belts with the timing belts.

Belt tension wouldn't increase the load on the engine. It would increase the stress on the bearings for that belt driven item and wear it out sooner if too tight, or make the belt slip if it were too loose.

If your engine power is down compared to normal that would be a fuel or spark problem such as cam timing or a sensor out of calibration. I say compared to normal because these guys aren't race cars and the A/C does hurt acceleration a very noticeable amount when everything is working right.

I wish you were close enough for a visit because pulling the outer timing covers would take just a few minutes and then we could see for sure if everything is lined up. Then from there concrete steps could be taken.

I'm thinking I might investigate my 02 sensors, even though I'm not getting a code thrown. My car did almost lug out when I tried pulling out into traffic today and it seems sluggish at start of acceleration.

It's my understanding that the upstream and downstream are the same sensor. Am I correct? If so, which one is most likely to be the issue with poor gas mileage or are they equally responsible? They don't give these things away. I would like to see if I can see a difference before buying a new one or two.

Thanks fellas.

Belt tension wouldn't increase the load on the engine. It would increase the stress on the bearings for that belt driven item and wear it out sooner if too tight, or make the belt slip if it were too loose.

 

If your engine power is down compared to normal that would be a fuel or spark problem such as cam timing or a sensor out of calibration. I say compared to normal because these guys aren't race cars and the A/C does hurt acceleration a very noticeable amount when everything is working right.

 

I wish you were close enough for a visit because pulling the outer timing covers would take just a few minutes and then we could see for sure if everything is lined up. Then from there concrete steps could be taken.

 

The front sensor is more responsible for AFR and therefore mileage. The rear sensor is more for monitoring the health of the CAT. Not absolutely one and the other, but more like 80% / 20%. So if you are going to swap an O2 sensor, do the front one.

It was much cooler last night. When driving to work, I didn't have the shimmy I feel in the steering wheel and gas peddle until the car had been at operating temperature for about 5 miles then it was very slight. I didn't have the AC on either.

It kills me how it's a 2+ hour job to check the timing position at $105 an hour at my local Subaru dealer. It's $55 an hour at the used car dealer I bought it at but because they replaced it and are adamant they did it right I hesitate to take it back to them. I tell myself they would check it and probably fix it and just tell me it was fine and no harm done except a hour's labor and some other reported fix to say solved it.

It sure runs better when the temps are cooler and the engine is still warming up. Other than it almost lugging out on me yesterday pulling into traffic, it's just a nuisance knowing I plan on putting 150,000 miles more on this car and I want it running like new.

When my O2 sensor comes in, I will drop it in and see what happens. It's getting to that time of the year where I want to be driving the car up into the mountains and filling it with wild game.

Hey fellas, I added some sea foam for like a third time a few days ago and this morning I changed the upstream o2 sensor. But I am getting the feeling the much cooler temperatures outside have already eliminated my problem with the hesitation from accelerating from a stop. I tried to get it to produce the issue yesterday and couldn't get it to hesitate.

I will keep vigilant to see if it happens on one of the 90 degree days coming up, two of them in the forecast.

As of now, the slight shimmy from 25mph to 35/40mph seems to be my only issue.

If cool weather solves the hesitation issue does that narrow anything down. Mass air flow? Throttle Position? Or is that something that might be solved by the upstream O2 sensor I just replaced?

Thanks fellas.

Fellas, I'm wondering if me tinkering with the throttle cable when I thought it might have been affecting my cruise control might be causing the occasional hesitation from a stop?

Still have no check engine lights on, gas mileage has gone up some with out the AC on. It still seems to idle pretty smooth.

Someone mentioned TRIM and asked if I do smell exhaust/fumes when starting from a stop and if I have my windows down I do smell enough to make you lower the windows even further. I'm wondering if maybe I have the throttle cable off enough to monkey with starts and mixtures? Thoughts? Thanks.

The throttle cable itself shouldn't impact any mixtures and unless it's sticking it shouldn't give any hesitation, but that would more be that it's not reacting well when you release the throttle.

Hesitation might be the MAP sensor. But how does the hesitation manifest itself? Is it sluggish up to a certain rpm and then it starts to get into power or how does it behave?

The throttle cable itself shouldn't impact any mixtures and unless it's sticking it shouldn't give any hesitation, but that would more be that it's not reacting well when you release the throttle.

 

 

Hesitation might be the MAP sensor. But how does the hesitation manifest itself? Is it sluggish up to a certain rpm and then it starts to get into power or how does it behave?

When it is an extreme reaction like pulling into traffic it sputters out almost as I hit the gas and jerks a little bit then takes off like normal. Doesn't do it all the time. Sometimes it happens when I start up and try to back out of a parking spot and sometimes it happens when I idle at a stop and then take off. It never dies. It doesn't back fire. I've tried cleaning the map sensor to no avail. Would like to replace that and the TPS but they aren't cheap and not sure I want to buy a cheap ebay part yet.

sounds like a vacuum leak or plugged PCV. hvae you checked the the vacuum hoses?

It was a bad vacuum line that was causing the cruise to not work when I got the car so it could be other cracks here and there I could start to check. I can sure check the PCV.

Thanks for the help.