1998 C70 T5 - Abhorrent fuel consumption/Could it be timing?

andreborges · Post by **andreborges** » 17 Jul 2014, 20:05

Thank you very, very much for the answers! I'll change the Coolant Temp sensor, as I have already bought one (because of the many reported failures). As soon as I have some reais, I'll spend in the O2 sensor, dear oragex!

Post by **E Showell** » 19 Jul 2014, 13:55

O2 sensors -- both -- are a maintenance item that should be replaced at 100,000 statute miles.

andreborges · Post by **andreborges** » 18 Jan 2015, 19:29

No perceivable improvement upon changing the front O2 sensor whatsoever. Any further ideas, guys?

Post by **misha** » 18 Jan 2015, 19:56

After replacing o2 sensors,maf sensor...you need to disconnect battery for at least 15 minutes in order to reset ecu & fuel trim adaptives.

After that,perform ecu re-learn procedure.You can find instructions on the forum,just search for "relearn procedure".

Post by **Ozark Lee** » 18 Jan 2015, 22:48

To your question on timing.

The timing on a whiteblock isn't really adjustable unless you alter the valve timing by rotating the camshaft sprocket in its slotted holes. Altering the camshaft timing really isn't recommended unless it is part of a custom ECU tune and the tuner will recommend the settings for you. From the factory the camshaft sprockets are set at the mid point on the slotted holes.

...Lee

andreborges · Post by **andreborges** » 19 Jan 2015, 08:48

Thanks, misha and Ozark. I performed the full relearning procedure upon replacing the sensor... No improvement.

Couldn't some mechanic in the past have messed the cam timing? Would there be any easy means of checking it?

Post by **misha** » 19 Jan 2015, 09:19

You can check it.Remove timing belt cover,front passenger's side wheel,bend plastic shield in the wheel arch,put transmission in neutral,rotate crankshaft and check for timing marks.

Use procedure which is used for timing belt replacement,up to the removing of the belt and after installation of the belt.Forget everything in the middle of it.
Check marks on the crankshaft and on cams.If the marks are alligned that's it,if not you will need to re-allign it.

Is your ac off?

andreborges · Post by **andreborges** » 19 Jan 2015, 20:58

Thanks, Ozark! I'll try that when I have a bit of time...

As for the A/C, it is blowing cold air. I believe it should, indeed, be a tad stronger, but nothing too discrepant.

villagepc · Post by **villagepc** » 20 Jan 2015, 00:15

Lemme tell ya a little about timing. My car's exhaust cam slipped 2 teeth and I experienced the same dramatic loss in MPG. I went from 25 / 26 mpg to about 18 /20 (i have a manual). I'd check the timing.

I'd also check for a blown out flex pipe on the exhaust system - its the braided steel hose deal that's on your downpipe from the manifold. Externally, it may appear okay - but could be collapsed internally (the liner). Now, i don't know a definitive test for this that doesn't require cutting it off - so my backwoods shade tree test may not help.
What I'm not going to tell you to do is: Go around to the back of your car while idling and see if the amount of exhaust "feels" like it should. I just place my hand over the tail pipe and feel the pressure... and if you're really a gear head, sniff your hand and check for antifreeze and for it running rich. Then wipe it behind your ears for the Eau De Volvo cologne. (kidding)

How about intake? How's the air filter? Check vacuum lines too, while you're at it. One nondescript vacuum leak can lose a few mpg's without throwing a CEL. How's the tranny fluid look ? Smelly / burnt?

andreborges · Post by **andreborges** » 27 Jun 2015, 15:25

Intake is fine, air filter is new and the vacuum lines have all been replaced... Seems like everything points me in the timing direction!