Unbelievable Gas mileage

[Outrider]

If you can take the downtime, remove all the injectors to have the cleaned and checked...

-Charlie

And if you do that, make sure you replace o-rings, especially the middle (large) o-ring. Don't ask me how I know that is an absolute requirement.

 

[JayRolla]

Cleaned the MAF again, new plugs all around, and new coil on number one, still getting a P0301, am starting to think it's the injector. OK, just did the old long screwdriver on it trick, and NUmber 1 injector is quiet. I think I am starting to get somewhere here finally.

Get a mechanics stethoscope, super cheap at harbor frieght.

 

[JimG]

OK, if I knew I could trust it I'd not bother fixing . . .
Anyway I have a 1999 3.4 standard with around 310,000 km, currently it is getting 33 mpg imperial, which I think is 28ish US.
When warm if I take it above 3000 rpm it starts to stutter. I finaly got it to throw a P0301 code yesterday (miss-fire on #1) cold it starts and runs smooth and perfect till it warms up, and the colder it is the higher I can rev it till it powers out. Feels exactly like the high rev limiter is kicking in. Anyway new plugs are ordered, and I will change out the #1 coil pack when I change plugs because I have a spare.
My heart tells me it's the crank position sensor, but I'm going to follow basics and change the simplest and cheapest for now.

I know it's a shot in the dark and just speculative, but any thoughts on what else?
I have dumped 2 cans of seafoam, and one can of rislone 2 part cleaner in over the last 6 tank fills.
The coolant level remains constant, oil stays clean between changes, and when cold runs perfect. Thanks in advance

Well the new injector helped . . . but it still seems to limit out somewhere between 3500-4000, no code, pending or otherwise, am going to change the fuel filter, but would be suprized. I guess drive it till it throws another code.

 

[JimG]

And as expected, new fuel filter didn't help. I guess drive it till it throws a code . . .

 

[spmarfatia]

Ignition cables? when did you last change yours? they were disintegrating on mine when I recently changed them on my 98, at 195K miles.

 

[19963.4lsr5]

Well the new injector helped . . . but it still seems to limit out somewhere between 3500-4000, no code, pending or otherwise, am going to change the fuel filter, but would be suprized. I guess drive it till it throws another code.

Your cat could be clogged, MAF sensor dirty, bad or going bad preCat O2 sensor....

In my experience a bad crank sensor totally shuts off engine. Not act like a rev limiter.


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[JimG]

And I give up, two mechanics I trust both figured it might be fuel pump given what I've done so far. replaced the fuelpump, and still bucks when the revs are up. I guess drive it till it quits, or throws a code.

 

[tvpierce]

And I give up, two mechanics I trust both figured it might be fuel pump given what I've done so far. replaced the fuelpump, and still bucks when the revs are up. I guess drive it till it quits, or throws a code.

Did you clean the MAF sensor?

 

[Nate_GB]

Did the problem just start out of the blue one day or did you slowly develop a problem? I don't particularly believe a dirty MAF is to blame here. I would test the spark plug wires. If you had a misfire code and are getting drive ability issues the way you describe, the wires could be arcing all over the place and not getting the spark where it needs to go. A quick Google search yields multiple tutorials and videos on testing spark plug wires.

 

[JimG]

Did you clean the MAF sensor?

Yes, twice.

 

[JimG]

Did the problem just start out of the blue one day or did you slowly develop a problem? I don't particularly believe a dirty MAF is to blame here. I would test the spark plug wires. If you had a misfire code and are getting drive ability issues the way you describe, the wires could be arcing all over the place and not getting the spark where it needs to go. A quick Google search yields multiple tutorials and videos on testing spark plug wires.

I don't know, I noticed it out of the blue one day because I normally don't drive hard. The misfire code was taken care of with a new injector, the wires are relatively new, and don't seem to be the problem. It runs like a dream up until 3200 when it starts to stutter. Next step will be to try it cold and see if it only stutters once warmed up, and to pull a new plug and see if it's actually running lean.

 

[CDNsldr]

I do it the old fashioned way, 467.4 km divided by 55.052 litres gives me 8.49 L/100km. Aaaaaaaaaand the problem was with me, I either entered something in wrong but on a conversion chart that now gives me 24 mpg Imperial. Which is normal for me. (I drive like an old man because . . . well I am one) Thanks for getting me to double check my figures. Just goes to show when something is unbelievable it usually is. (still doesn't help my intital problem)

Yes, the problem was you. lol Your math is backwards. Divide the L by KM (i.e. 55L divided by 467km = 0.117783 then move the decimal two places to the right for L/100km)

 

[Ricktuk]

try going old school. go out at night with no lights around. open hood and throw a blanket over you to make sure there is no light. have someone crank the vehicle. look for sparks. Might not help but doesnt cost anything but time.

 

[djr01974]

you may have a spark plug boot arching threw into the tube. Or You may have cracked a plug putting new ones in. Pull them all out and look for any carbon trails on the side of the plugs.