Declining MPG
11-10-2008, 09:12 AM
#1
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Declining MPG
Hello- Before I put on a pair of heavy duty rubber gloves to work on a toilet (while gagging) I thought I'd post this question in hope of a response or two. The mpg on my truck (89 ext. cab 4x4 w/22 re, AT and 358 k miles) has dropped from 21+ to 15-16 range. Gasoline prices have dropped but I know they're going to go back up. I've recently replaced the fuel filter, tank and pump (the 2nd replacement pump). I repacked the wheel bearings, topped off tranny/transfer case and axles, and replaced the thermostat. I,m thinkin' maybe the o2 sensor ($$$) but I'm not pulling any code/s. Does anyone have any other suggestions to check out before I spring for a new sensor? This is a great site and my late fifties body gets excited when I see some of the rigs pictured on here. nec aspera terrent
11-10-2008, 11:01 AM
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...my truck runs like (purrrrrs) a charm. Wouldn't a clogged cat cause it to run poorly? I also just had a new exhaust (2") from the cat back to a new muffler and a 2.25 tail pipe put on by a "muffler shop" I've trusted for years. The truck has been running on generic 31-1050s since I replaced the original 225s it came with years ago. Thanks for your input. I guess I'll try the o2 sensor. The Latin is from one of the old units I had the priviledge of serving with when it wasn't fashionable and is all the Latin I know except for 'etcum spirit tu tu o o ramus' (sp?) from mass when I was a young un. Again, thanks!
11-10-2008, 11:04 AM
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My cat was clogged and ran perfectly fine at idle. But when you tried to accelerate under load, it was gutless. It practically fell on its face.
This kept getting worse and worse until i replaced it.
Just an fyi
This kept getting worse and worse until i replaced it.
Just an fyi
11-11-2008, 06:33 AM
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I'd replace the plugs, wires, cap and rotor. If you're getting a weak spark, you're not getting a complete burn and can lose mileage (though 5MPG is huge). May also want to pull the intake and clean. Pull and clean the injectors while you're at it. I'd replace the O2 sensor...it's a $40 part and can cause problems even while not throwing a code. Also check the air filter and AFM.
If you're driving habits have remained the same, then a drop that big in MPG indicates a mixture or burn problem. If it were me, I'd start with the spark and make sure all cylinders were firing with good fire. I'd also do a compression test. Then, I'd clean the fuel intake system and replace the O2.
If you're driving habits have remained the same, then a drop that big in MPG indicates a mixture or burn problem. If it were me, I'd start with the spark and make sure all cylinders were firing with good fire. I'd also do a compression test. Then, I'd clean the fuel intake system and replace the O2.
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11-11-2008, 07:03 AM
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Check your TPS. If it is not working right your ECU will run on a "rich" map because it does not know throttle angle only air flow and O2 readings. Do a search for TPS check or read a manual to tell you haw to check it. You will need a multi meter.
11-11-2008, 07:27 AM
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with 358k on it, if it's never been replaced, the O2 is a strong candidate. typically (and people's results do vary) they last 75-100k.
as well, a partially clogged converter can cause the same effect. what opening there is will allow exhaust at idle to pass through fine, thus not affect idle quality, but will restrict exhaust flow at higher engine speed.
matt16 also has a valid point- "winter gas" is required this time of year in a lot of places and it is basically 'reformulated' to bring some molecules in with it that give up oxygen easily to more completely burn the rest of the fuel. that extra oxygen usually comes from adding ethanol to the gasoline, and will adversely affect mileage.
as well, a partially clogged converter can cause the same effect. what opening there is will allow exhaust at idle to pass through fine, thus not affect idle quality, but will restrict exhaust flow at higher engine speed.
matt16 also has a valid point- "winter gas" is required this time of year in a lot of places and it is basically 'reformulated' to bring some molecules in with it that give up oxygen easily to more completely burn the rest of the fuel. that extra oxygen usually comes from adding ethanol to the gasoline, and will adversely affect mileage.
02-03-2009, 12:52 AM
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How would I go about checking this out myself?
02-03-2009, 01:59 AM
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with 358k on it, if it's never been replaced, the O2 is a strong candidate. typically (and people's results do vary) they last 75-100k.
as well, a partially clogged converter can cause the same effect. what opening there is will allow exhaust at idle to pass through fine, thus not affect idle quality, but will restrict exhaust flow at higher engine speed.
matt16 also has a valid point- "winter gas" is required this time of year in a lot of places and it is basically 'reformulated' to bring some molecules in with it that give up oxygen easily to more completely burn the rest of the fuel. that extra oxygen usually comes from adding ethanol to the gasoline, and will adversely affect mileage.
as well, a partially clogged converter can cause the same effect. what opening there is will allow exhaust at idle to pass through fine, thus not affect idle quality, but will restrict exhaust flow at higher engine speed.
matt16 also has a valid point- "winter gas" is required this time of year in a lot of places and it is basically 'reformulated' to bring some molecules in with it that give up oxygen easily to more completely burn the rest of the fuel. that extra oxygen usually comes from adding ethanol to the gasoline, and will adversely affect mileage.
I agree with abecedarian completely; especially the cat. If you haven't changed it int he last 300k+ miles, that's almost certainly your main problem.
02-03-2009, 08:28 AM
#15
During winter driving, my milage drops from 18 city down to about 9 mpg. Winter gas, cold air (molecular density), having the hubs locked, carrying extra junk around (ie: chains, shovels, sand) driving through snow and towing people out of ditches really do a number on the figures.
02-03-2009, 09:40 AM
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02-03-2009, 09:43 AM
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Don't chintz on the O2 sensor; go to www.sparkplugs.com and get a good NGK or Denso O2 sensor or you'll be sorry later...
02-04-2009, 05:35 AM
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A Denso O2 Sensor will run you $48.99 plus tax at Auto Zone. A Bosch O2 Sensor, which is just as reliable (in my opinion), will run you $34.99 plus tax. While Bosch makes crap for spark plugs, their O2 Sensors have been found to be very reliable.
02-04-2009, 05:40 AM
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On second read, I withdraw my statement. For some reason I thought he had a 1989 4Runner. I now see it's a pickup...yep, a bit more than $40. Either will run you about $140 plus tax for OEM and $100 plus tax for universal.
Sorry about that.
Sorry about that.
