Unbelievable Gas mileage

J

JimG

New member
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
 
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It sounds like when the ECM is in open loop (at least when it's cold) it's running okay but as soon as it goes to closed loop it gets crappy. Does it shutter under WOT? Maybe it's a MAP sensor or a Throttle position sensor like you said. Do you have access to live stream data at all?
 
Yeah it is rather unbelievable it gets 33 mpg imperial while throwing runability codes but hey they're about as tough as 60s vdubs and old briggs/straton engines that will run well even when Way out of tune. Luck and enjoy. :cowboy:
 
4Rosey said:
It sounds like when the ECM is in open loop (at least when it's cold) it's running okay but as soon as it goes to closed loop it gets crappy. Does it shutter under WOT? Maybe it's a MAP sensor or a Throttle position sensor like you said. Do you have access to live stream data at all?
Click to expand...

WOT = Wide Open Throttle? Yes, it does shudder then once it reaches 3000, when cold it doesn't shutter till 4000 on the road. I couldn't get it over 4000 this morning while relatively cold.
I do have the bluetooth reader and torque on my phone, so think I have live stream data, but not sure what I'm looking at.

I know this is all guess work for now and won't know anything till I pull the plugs, but my heart is telling me if it was plugs the gas mileage would go down not up . . .
 
Coils brake down........when they get warm they fail.
Or you may have a failing injector.
Or a failing spark plug.
Or a valve in that cylinder getting tight and it's time for a valve adjustment.

It's something to think about. Does your coil say Denso or Toyota or is is not labeled?


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19963.4lsr5 said:
Coils brake down........when they get warm they fail.
Or you may have a failing injector.
Or a failing spark plug.
Or a valve in that cylinder getting tight and it's time for a valve adjustment.

It's something to think about. Does your coil say Denso or Toyota or is is not labeled?


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Click to expand...
The one coil I can see easy says Toyota in red, and Denso in blue. I am assuming they are original.
I had the sparkplugs replaced shortly after I got it, but not sure how many klicks on them since then, would need to look up, rough guess 50,000 km. I don't know what sort of plugs went in, but I trust the mechanic who did the work, so am assuming he put in the right ones. I have NGK's with the dual electrodes ordered. Since I have one I will put a new coil on number 1 while I have things apart.

Still it all comes down in my mind that if these things are failing shouldn't gas mileage drop? (but yes, anything is possible) When it first started acting up, if this was in the old days I would have said the centrifugal weights in the distributor were seised.
 
jgue467 said:
Yeah it is rather unbelievable it gets 33 mpg imperial while throwing runability codes but hey they're about as tough as 60s vdubs and old briggs/straton engines that will run well even when Way out of tune. Luck and enjoy. :cowboy:
Click to expand...

yes, only I would complain about that sort of gas mileage. The gas gauge didn't work when I got the 'Runner, so keep an eye on the trip meter usually fill at around 300k, and was in puckermode if I was going to get home when I had 460k on the trip, and the gauge showed just under half a tank. And you are right these things are tough, main reason I don't mind putting money/effort into it once I know what's wrong.
 
T4R2014 said:
Maybe it's running way too lean? I wouldn't drive it like that.
Click to expand...



If he doesn't have a DTC for running lean based on the Long Term Fuel Trims I don't think it's a lean condition it also be popping out the intake........


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JimG said:
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
Click to expand...

OK, changed plugs and number one coil, no missfire code, but sure stutters bad at around 3500, Wide open throttle doesn't help, it just reachs 4000 ish and bucks. idles smooth, but runs rough on the highway, not enough to notice, but I can feel it.
 
JimG said:
OK, changed plugs and number one coil, no missfire code, but sure stutters bad at around 3500, Wide open throttle doesn't help, it just reachs 4000 ish and bucks. idles smooth, but runs rough on the highway, not enough to notice, but I can feel it.
Click to expand...

Your fuel economy seems out of whack. Are you getting 28mpg (US) over several tanks?

As far as drive-ability, have you cleaned your MAF sensor?
 
tvpierce said:
Your fuel economy seems out of whack. Are you getting 28mpg (US) over several tanks?

As far as drive-ability, have you cleaned your MAF sensor?
Click to expand...

I'd have to do the calculations to be sure, but yes, it has seemed to be going further on less fuel over the last few tanks.

Yes, I cleaned the MAF as well when I did the plugs and coil right now. The plugs all looked ok, no noticeable difference in colour between them.

I starts and drives well up until 3000-3500 ish (it varies) and then starts loosing power, bucking, stuttering etc.

No I have not changed the fuel filter.
 
AuSeeker said:
Have you checked all of your vacuum hoses for leaks?
Click to expand...

Yes, and gave them another real good looking over while I was under the hood. Replaced the line that runs from the side of the airfilter over to the intake manifold, it was cracked where it goes on didn't make a difference. All the others looked good, (doesn't mean I missed a leak though)

Fuel filter is on order, if that doesn't make a difference I'll just stick close to home until it throws a code I guess, or get fed up enough to take it to the garage.
 
BrianSD_42 said:
Well your title is correct, I don't believe it. You are not getting 28MPG or anywhere close in a 3rd Gen 4Runner, not if you are properly measuring it on a full trip tank 200+ miles. Your scangauge is not accurate.

See how to measure gas mileage. Use this:
https://www.fueleconomy.gov/mpg/MPG.do?action=calcMPG

How to calaculate gas mileage


:)
Click to expand...
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)
 
I have a 4th Gen so I don't now as much about 3rd Gens, is the fuel pump in the tank?

That being said/asked, I would do a fuel pressure check if possible, it could be (if the pump is in the tank) a partially clogged screen which would make the engine starve for fuel at higher RPMs, also the fuel pump could be on it's way out, I know electric fuel pumps usually go bad almost instantly but I have seen some that did go bad a little slower and had similar symptoms.
 
AuSeeker said:
I have a 4th Gen so I don't now as much about 3rd Gens, is the fuel pump in the tank?

That being said/asked, I would do a fuel pressure check if possible, it could be (if the pump is in the tank) a partially clogged screen which would make the engine starve for fuel at higher RPMs, also the fuel pump could be on it's way out, I know electric fuel pumps usually go bad almost instantly but I have seen some that did go bad a little slower and had similar symptoms.
Click to expand...

Yes, fuel pump is in the tank. Good plan on a pressure test, it doesn't have a sensor (that I can see anyway) to give a fuel pressure reading on torque. Something I think I need to get a shop to do for me.
 
JimG said:
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)
Click to expand...

That is definitely quite unbelievable, lol.

I'm lucky to get anywhere under 15L/100kms on mine. I don't think I've ever seen much more than 300kms on the trip meter before the needle hits the E in mine.

My personal best was 313kms on 47 Litres of fuel.
 
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