Low compression, bad fuel trims, but no oil loss

2001 Tacoma, 2.4l, w59 manual trans, reg cab short bed, 5-lug.

I’ve noticed my fuel trims being a little off. At idle it’s usually -1.6% but at highway speeds it at +7%. This may seem minor to some people but I’m SUPER particular. If I am worrying about something I shouldn’t please say so. What would cause it to change from correct at idle to being off while driving?
I’ve looks for any causes of this but came up empty handed. I saw several people say that the 2.4 & 2.7 liter engines were known for head damage farther in life but I’ve only got 133,000, not much for a Tacoma I’ve been told. I just did a compression test and found all cylinders to be right on 149-150psi. I thought it was strange for them to be so perfect. I saw it was supposed to be 175psi. So this seems a little low. I added a little amount of oil to one of the cylinders and it jumped to 165, a 10% increase. Is that a lot?. when I pulled the plugs to insert the tester the plugs looked pristine, no signs of oil burning. I looked into the cylinders and still could see some silver on the tops of the pistons, not carboned over like an oil burner would be.
From my research, I found that if all cylinders are low and wet compression didn't rise significantly it could be a timing issue. To my knowledge, the valve shims have never been adjusted. So could valves be out of spec causing this? It would seem that most commonly the valve lash decreases over time so if the intake valve did not close soon enough compression would be low. When should the valves be adjusted?
I don't think the piston rings are bad because of how little oil it burns. In a year and three month period, I only drove one thousand miles, but since it had been a year I changed the oil and emptied the previously installed catch can. The catch can only had a tablespoon of oil in it. I had taken a picture of the dipstick the last time I changed the oil so I could compare it and there was not a visible drop in oil level, it was right on the full line where I was over a year and one thousand miles ago.

 

Fuel trims between -10% and +10% Total (Long Term+Short Term) are considered normal.
If you have no misfires, oil burning, or noticeable loss of drive-ability or fuel millage I wouldn't worry about it, you can try cleaning the Mass Airflow sensor and see if that brings your fuel trims closer to 0 but otherwise I think your fine.

 

Too much worry about nothing. Dm93 is correct.

 

My MAF was cleaned not long ago and I replaced a faulty a/f sensor. I realize +7% isn’t horrible but increasing with rpm is consistent with a post I read about a 2.4l that was low on compression. It was perfect at idle but +10% at highway speeds and had 130psi. you guys didn’t address the low compression at 150psi when it supposed to be at 175 and when is it typical for the valve to need adjusting?

 

You could do a leakdown test and see where it's going.

 

Dude, Your compression is fine. You worry too much. The minimum is 127 PSI you are reading 149 to 150 psi. To repeat Dm93 "If you have no misfires, oil burning, or noticeable loss of drive-ability or fuel millage I wouldn't worry about it."

Compression pressure: 1,230 kPa (178 psi) or more.
Minimum pressure: 880 kPa (127 psi). Difference between each cylinder: 98 kPa (14 psi) or less.

(e) If the cylinder compression in one or more cylinders is low, pour a small amount of engine oil into the cylinder through the spark plug hole
and repeat steps (a) through (c) for cylinders with low compression.

- If adding oil helps the compression, chances are that the piston rings and/or cylinder bore are worn or damage.

-If pressure stays low, a valve may be sticking or seating is improper, or there may be leakage past the gasket.

 

OP you are fine. Cylinder compressions in a 5psi window are fantastic. Fuel trims will fluctuate all the time and +-10% is well within a normal range. (hell you can have fuel trims to fluctuate by simply filling up at a different gas station with more ethanol content or water in the fuel)

Needless to say you are way overthinking it. Make sure you have the proper amount of oil in your trucks motor and change it according to the manufacture specs and it will last a LONG time.

Also... you have a 1st gen tacoma... not a second gen.

 

OP, if your gas has any alcohol there was a special study field done on how LTFTs are affected by E10. The result was that the LTFTs are driven positive. Consider that the ethanol requirement is usually "up to 10%" (here the pump labels say "may contain up to 10% ethanol" and each batch can vary. Relax.

You are not "overthinking" anything, what ever that means.

 

Your compression gauge could also just read low. Have you validated your readings with a calibrated gauge? Are your results repeatable (across days, not across cylinders)?

 

Oops I could have sworn I hit 1st gen, but I guess not.

Thanks to all who have replied. Everyone agrees my fuel trims numbers seem normal which I kinda thought.

I’ve seen several people post their compression numbers that had twice the milage I do but still have perfect compression like a Toyota should. I'm kinda leaning towards getting what I paid for (not much) out of this cheap gauge.

I did a leak-down test just for fun because I bought one previously to diagnose an old minivan. I didn't expect to find anything; I just like messing with stuff. I had extremely little leak down.

My only question now is when the valves should be adjusted or what are the symptoms of them needing to be. Whether or not it's an issue now, I still want to know. My understanding is that that is just about the only issue these engines have and if left untreated cause cracked heads and burned valves.

 

@Timmah! has a video where he does this on a 2.7. AFAIK, it should be the same procedure for the 2.4.

 

I just hooked up my compression gauge directly to my air compressor at 110psi and the gauge read 110psi so my gauge seems accurate.

 

Your fuel trims will be effected by
1) MAF, dirty, or an aftermarket fake
2) fuel filter clogged
3) fuel pump not at 100 percent
4) fuel injectors needing serviced, each injector has a fuel filter that GETS plugged up slowly
5) any vacuum leak anywhere

I have had ALL these items fixed or replaced recently

My 3.4 numbers are

My fuel trims at idle are “0”
When full throttle maybe “5” max
When at highway speed “0+1”

 

Thanks for posting your fuel trims.
My MAF is clean.
My fuel filter is new.
I have never had the fuel pump or the injectors tested so maybe I'll check those for kicks and giggles some other time.
I am very confident I have no vacuum leaks.

I found some people would check their valves as early as 100,000 miles and as late as 400,000. I think, just to be safe, I will check the valve clearance sometime this summer.

I think I found everything I was looking for but if anyone knows their "Long Term Fuel Trim" and would like to post it; I would find that interesting.

 

My long term fuel trims are + or - 3

If you have never had the Fuel injectors cleaned, serviced and you have the original fuel pump,
99 percent chance those two items are NOT working at 100 percent.
Those plastic parts are now 20 years old!,,

If your not running a supercharger it doesn’t matter but if you are running a supercharger you need every last drop of fuel being delivered

 

Your trims are perfectly acceptable. I’m jealous. There’s a couple really good threads about trims if you search this forum

 

The 2TR-FE 2.7 Liter engine has Hydraulic lash adjusters and need no adjustments.

 

Thanks for your input. This is the 1st gen forum, so we’re talking about the 3rz.

https://en.wikipedia.org/wiki/Toyota_RZ_engine#3RZ

 

This thread was started in the Second Gen Forum see Post # 7 and Post # 10 above... Someone must have moved it to First Gen Forum.

So when you commented on a 2.7L I assumed you were talking about the 2TR-FE...

No harm no foul.

 

Sneaky mods…