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I've been chasing poor mileage problems on the wife's V70 GLT for ages now. To date I've worked through CEL for front 02 sensor, replaced. Spent months working on vacuum lines including the entire oil separator/flame trap system. Virtually every soft line and elbow has been changed. Highway mileage is about 22, but city is only "up" to about 15. Recently changed the ECT as it was slightly out of spec, but no code. I have a known good MAF coming too, just in case.
Recently someone suggested the IAT (intake air temp sensor), but the info I'm digging up here and on the web is anything but clear, including one thread that seems to think the IAT is the airbox thermostat (which I don't have). The IAT seems to be present or not depending on manufacture date. There are so many posts about where it is located, intercooler plumbing, intake snorkel, under the airbox, in the airbox, on the core support; I have not been able to find it regardless. The cabin temp sensor in the air guide seems to be fine. There are posts saying this is the only one, and that the injection does or does not use it, and others saying there is a second sensor on the passenger side with a blue connector. This car is "late", in that it has the later style belt tensioner, but I don't know about late as far as injection, or if that truly matters.
Can anyone clarify? I can see that an intake temp sensor thinking the charge is very cold would make the car run rich. My reading has always indicated that the MAF in this car is more of a temp sensor than anything else. Isn't that the case? One post says no, the MAF does not have an IAT. Others say it IS the IAT.
Thanks,
DS
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Here's an update on a year old+ post:
After replacing many lines and connections, fiddling with MAF and ECU as extremes, managed to coax average mileage to the 20 range. Still not what we were used to, even with boost levels down. City mileage is sometimes as low as 18, highway as high as 24 best.
About three months ago I stopped fiddling for the most part and just decided to wait. I figured eventually, if this was a vacuum leak I'd not found, the car would throw a code of some sort. The car passed smog meanwhile.
Three weeks ago I used the car and noticed that my wife had the heater temp cranked to the max on both sides...and it had been just under sixty the previous afternoon when she had used it. I took it out the next morning in 26 degree temp and sure 'nuf, the engine temp did not reach normal for nearly half an hour. Replaced the thermostat, knowing that the cold temp will cause the ECT to run the engine rich. Heater problem and warm-up time fixed, but the mileage has not improved.
Finally, about four days ago, wife reported a check engine light. It went out before I got a chance to check it, but the computer stored P0172 for rich condition. I started looking for vacuum leaks again, found nothing. CEL returned yesterday. I used nearly an entire can of carb cleaner before switching to starting fluid. Finally found that the base of the vacuum tree is sucking air. Removing it exposed a flat o-ring seal that was not as thick as the depth of it's slot for about 50 degrees of circumference.
An old trick is to see if parts houses stock the items you suspect as being bad. Smart places won't stock anything that never sells. I see that FCPG and several other places stock the tree and seal, either together or separately.
For the moment I'm going to repair this with some sealant and see what happens.
DS
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Don't think I've ever posted back on such an old topic! After twiddling with various fixes on this car for nearly a year, including sensors and such, I recently had the good fortune to stumble across a couple of ECU's in my favorite yard, both in heavily rear-ended vehicles. A 98 S70 GLT and a 98 V70 T-5. I took both. Our ECU was the OEM unit, tuned by SpeedTuning USA.
First thing we noticed with the GLT ECU in place was better idle. A month of driving has shown us mileage around the 22mpg range with almost no highway driving. One tank with a 100 mile trip on the freeways gave us 24. Thus, not exactly where we'd like, but a huge improvement. There have still been a few skip 'n dip episodes though. Rrrr!
I put the T-5 ECU in today. Some posts I've found on the web indicate this would throw a CEL, but fifteen minutes of driving showed nothing but a grin on my face. Decking the pedal at about 2000 rpm is just a trip.
Roadtrip to the Bay Area end of this week. We'll check the mileage. Clearly though, something is wrong with the old ECU and that was the biggest issue.
DS
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I always wanted to find a spare ECU for my 1998 R. I could have it 'tuned' and still have a fall back. Not that I don't trust tuners... but, you never know.
The T5 ECU in your low pressure turbo unit must be a little strange. It is expecting more rpm and much higher boost. I would be surprised if it doesn't throw a code, perhaps at 5500 rpm? Be careful, your rpms are not as free as the 2.3L engine.
Klaus
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Volvos should be saved from the junk yards, not donated.
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It is a little unusual Klaus. I find that the low and midrange boost is much stronger, VERY snappy. However dropping it a gear further up the rev range doesn't feel much different from the stock ECU. I can't help wondering how much the injectors have to do with that too. Haven't checked, but I don't think the GLT has the same injectors as the T-5.
DS
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The injectors might be the same, it is the length of time the injectors are open that makes the difference.
My problem with the additional power would relate to the wrist pins and crank bearings on the 2.4L engine. The 2.3L is much stiffer in that regard. Of course, the 2.3L can get turbo pressure over 20lbs which would kill the 2.4L.
I am glad you found these ECUs and can make the test.
Klaus
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Volvos should be saved from the junk yards, not donated.
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The time and the maximum flow of course. Either way, I don't think this is an ECU I would leave in the car. Interesting to test though.
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For those following:
The ECT seems to have made a major improvement. Vacuum lines and such got us an MPG or two. This last tank, all city driving and short runs has netted out 18mpg. First major improvement so far. Not what I believe the car is capable of, but we are now certainly in the acceptable range--at least. I'm almost certain we were doing 20 in the city prior to things going South.
DS
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Dave, one more thing. If the temp gauge is slow to get warm, could your thermostat be stuck open?
You really should be getting 20-22 around town.
Klaus
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There is no present time, just the past and future
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Agreed Klaus. Those are the numbers I recall, about 25-26 highway, and the ones we are shooting to recover. The thermo seems to be fine. The car warms up very quickly, even now with the morning temps near 20.
DS
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The 1998 has 2 temp sensors. One that is 'supposed' to be stuck into a hole in the passenger side airguide. I always assocated that one with outside air temp display.
There is another stuck in the small grill on the driver's side bumper. That should be the IAT. Others will disagree with that logic.
Regardless, if the IAT fails, there will be an error code.
Usually, the failing sensor is the ECT causing the engine to run rich. Check the resistance of the ECT at various engine temps.
Klaus
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My advice is free, so you got what you paid for...
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Hi Klaus, thanks for your continued help.
Air guide temp sensor on the left is for the cabin readout and yes, they seem to always have fallen out. This one is fine and the readout is good.
On the other sensor--a grill in the bumper itself? Or in the plastic grill where the fog lights mount, below the bumper?
The ECT was slightly out of spec from about 120 degrees on up up--can't remember what I read, but I had a new one on the shelf so I installed it yesterday. One of the problems I have is that I drive the car so infrequently, I really don't have a feel for it. However my wife just returned from errands and asked if I did something to the car because it feels different. She says it idles more smoothly and that low end acceleration feels "more like it used to". That's encouraging.
Lack of codes has been no help at all!!!
Dave
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If you have a computer, take the car to a highway and 'reset' the average mpg. Put the car on cruise and wait 5 minutes to get a true average. You should get 26-28mpg, depending on the wind and velocity. Easy check and you don't have to burn a tank of gasoline.
A low reading ECT sensor is not a 'failure' to be picked up by the ECM.
Yes, there is a temp sensor in the little grill on the driver's side. It snaps into a small round hole in the grill.
The temp sensor on the passenger side is 'supposed' to be sticking through a small hole in the airguide. Mechanics never bother to put it back when the airguide is R&R'ed. I zip tied mine to the small grill on that side so that it is exposed to fresh air.
Klaus
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My advice is free, so you got what you paid for...
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posted by
someone claiming to be bob
on
Sat Dec 31 12:29 CST 2011 [ RELATED]
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The sensor you are looking for lives in the plastic air guide that deflects air from the spoiler to the radiator. One mounting screw on each side, a tab that slides into a slot on the bottom of the radiator. It basicly covers the area between the spoiler and the radiator. the sensor plugs in to the passenger side of the air guide
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Okay, unseasonably warm temps have allowed me to refresh my memory. One sensor in the passenger side of the air guide, facing right. The other sensor is in the left side auxiliary grill, where the fog lights mount when you have them. Intake sensor is in the air guide and the one in the small grill is the cabin temp, or vice versa?
Thanks all,
Dave
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