Engine felt odd this past tank....

It may seem weird but i swear my 1st gen 3.4L engine goes through like... mood swings or something. Sometimes it feel super powerful, other times not so much. I noticed that a bit of power drain occurs with the A/C on. After talking to some people i found thats normal. I started driving with the windows down and found that the power was always good. But this last tank of fuel was odd. My last few fill ups i got around 18 almost 19 mpg mixed driving and the engine felt great. power to spare. Then all of a sudden my engine performance dropped off. felt like i had the A/C on but i didn't. Just felt anemic in a way. to top it off i only got 16.4 mpg.

I filled up at a local Mobil 1 that I use regularly but not exclusively. It's starting to get pretty hot down here in florida. I was thinking maybe the knock sensor has had to retard the timing further?? I saw the sticky here that says my truck should be fine on 87 octane. But i did notice that the PDF service manual i use online says 91 is recommended. I found a place with cheap 93 octane and put that in today. Im going to see how it goes. I did the math and i only paid $2 more overall. Does anyone make a product that will tell you when your knock sensor is retarding your timing, and by how much?

Other than that, maybe it's my filter. I pulled it out and banged out a bit of dust. I went off-roading a few weeks ago and forgot to check it. But the truck has felt fine since, until lately.

Any thoughts?? This isn't the first time my truck has seemed to lose and regain power. But it's the first time since I found out that the A/C robs power. So i dismissed all the earlier times because i couldn't remember if I had the A/C on or not. This time i know i didn't have the A/C on and i know it felt odd.

BTW truck has 131k miles

 

Have you done a proper tune up lately? I'd replace the air filter instead of knocking the dust off unless it's a washable filter.

 

i noticed that my '07 4.0 auto i can tell a power difference with ac on vs off. i hear that is normal on like all cars and trucks. i have windows down allot.

 

same. but this time i noticed it even with the windows down. which was odd. I mean it's starting to get into the upper 90s down here with high humidity. so thats why i thought maybe the knock sensor was killing some power.

Ya im going to change the air-filter asap. Idk if i should go with aftermarket re-usable, aftermarket paper, or OEM. i saw a debate about it brewing elsewhere on the forum

 

fuel filter, fuel injectors, spark plugs, 91 octane. Have you done/replaced these recently?

 

A/C systems actually take an average of 30-40HP to run, (My buddy told me this from his mechanics trade school). so it's a pretty sizable difference between having them on or off.

 

I might've misread what your trying to say, but I'd dispute you on that, lemme try to find a good source. Cause even on my 07' I notice a difference between having it on or off.

 

yeah i see it with window down too. and this past week it was over 90 everyday! sunday was 94 monday was like 93 i know Wednesday was 96. one day it was 90 and that was the low for 7 day. and the 90 was low as far as the high for the day.

 

Running 93 octane right now. Found a place that had it for 3.99. regular around here was 3.77 at the time and i only put in 10 gallons at a time so at the end thats only like $2.20 higher. Seems to be running better. But more at lower speeds. feels snappier from take off to 40. Feels a little better than regular on the highway but not as pronounced. I can report MPG in a couple of days.

I need to look into the deckplate mod. I wonder what else can be done short of a Supercharger that can add some umph to this thing. No offense to any 4 cyl guys, but im pretty glad I held out for a 6 cyl.

I also want to grab a compression tester and test my pistons. A little nervous though.... Hate to find bad news.

 

5-6 is a good amount when u're only making 190hp like I am. The thing about the 1st gen is that peak hp is at 4800rpm. I've never looked at a 1st gen tacos dyno curve, so i don't know how flat it it is. But in any case. to have peak HP that high up in the rev range is a little crazy. I'd never rev my taco out to 4800. So i doubt i'll ever see all 190 horses the engine can make.

 

That reminds me i want to check my MAF sensor.