Cold start issues / runs very lean

I've been having an issue that appears to be getting worse where on cold starts the engine idles at around 500-650 and seems like it's going to stall for about 15-20 seconds. it returns to normal and has a slightly high idle ~1000 rpm.

The exhaust smokes for a few minutes and there is a strong gas smell. It's hard to tell if the gas smell is coming from the exhaust but it doesn't seem to be white or sweet enough to be a head gasket issue (also fluids all look clean).

interestingly short term trim is very normal (0 to 2) until it changes to closed loop and suddenly it jumps to ~13%. The long term fuel trim is almost 20% so I imagine this has been a persistent issue during closed loop / higher rpm driving.

Things to know:
I've cleaned the MAF sensor
the fuel injectors were professionally cleaned by MW
The EGR is new (Amazon non OEM)
previous owner deleted Cat

I have a new cat and upstream o2 sensor i'm ready to install but I want to make sure that either the o2 sensor/cat will resolve the problem or that I can resolve the lean issue so it doesn't destroy my brand new fancy carb cert cat

any ideas?

 

tossed codes?

 

Oh sorry I forgot to mention that.

It's throwing a P0420 code. I just pulled the upstream o2 sensor and it looks noticeably black in certain areas even since I replaced the studs a week or two ago. The smell of gas and wispy smoke point to a rich condition i'd think.

Tonight I noticed one of the exhaust manifold studs is totally missing. My current theory is that the car is actually running very rich but it thinks its running lean because of the unmetered air entering the system right before the upstream sensor.

Is this sound logic?

I think I may have promoted this project car to daily driver a little preemptively fellas...

 

NO. NO. NO. 1000 times NO.

You do not have a rich condition. I can follow your thinking, but your logic is technically incorrect. YOU HAVE A LEAN CONDITION. Too much air, not enough fuel.

You have a massive vacuum leak. Somewhere. A vacuum leak means your engine is no longer 100% sealed with respect to "sucking in" air where it is not supposed to. And that air is not metered by the MAF sensor. This vacuum leak could be anywhere. Intake manifold leak. Throttle body gasket leak. Exhaust manifold leak.

What happens is your O2 sensor(s) will detect too much oxygen in the exhaust stream because of the vacuum leak. Again, this is a lean condition.

When this happens, the engine computer (PCM) will starting adding fuel. As you have correctly determined by observing your fuel trims.

Reminder:
Fuel trims in "open loop" engine mgmt mode --> when the engine is cold and the O2 sensors are not hot yet (like 900F) ---> are usually zero. The engine computer is using a look-up table for the 1-2 minutes until the engine and O2 sensors get hot.

As soon as your O2 sensors get hot, the PCM switches into "closed loop" fuel mgmt strategy where the O2 sensor readings are used by the computer to adjust fuel aka "fuel trimming".

Again, and not to be repetitive, but if your O2 sensors detect too much oxygen in the exhaust stream, this is a lean condition. And the computer will start adding fuel - thus your crazy high postive fuel trim values (both short term and long term). The computer is ADDING fuel because of your lean condition.

{{If you had a "rich condition" it would be subtracting fuel}}
{{Lean conditions are usually something like 100 -1000 times more common than rich conditions}}

--------------------
That you have a fouled, black, contaminated O2 sensor proves my point. TOO MUCH FUEL due to a lean condition will cause that. And then you have symptoms like poor idle quality, hard starting, and raw gasoline spitting out your exhaust. Too much fuel will also plug your cat converter and reduce throttle response and power. This explains your P0420 code. Plus that it is missing in the first place.

---------

FIND AND RESOLVE YOUR VACUUM LEAK. THEN INSTALL YOUR NEW CAT(S) AND O2 SENSOR(S).

Congrats on your new used truck. Welcome to the forum.

Hope that helps

 

One cause here supports BigCarbon as well as your discovery of missing exhaust stud


https://www.engine-codes.com/p0420_toyota.html

 

Thank you for the detailed response. I appreciate it

Update: I changed the o2 sensor and noticed on top of everything it might not have been on tight enough. The truck didn't even start the first time and then ran incredibly rich according to my scanner (around -20%) tons of gas smelling smoke.

I drove it around the neighborhood and immediately noticed the engine seemed to be running smoother after the first few minutes. during the drive the short term fuel trim hovered in normal range and the long term drop significantly to about 5%

what would you guys recommend as far as detecting vacuum leaks?

 

The missing E stud….that is a Known
Can you feel gas escaping?

piece of paper or tissue will show if stud not too close to cooling fan

 

You can spray water or carb cleaner, one will retard idle and other will increase it, for vac leaks. You can tape a shop vac to the tailpipe so that it blows in it and spray soapy water to check that exhaust leak. A good inspection of your vac hoses will prob show any issues well enough. Just check one at a time and put back to port you found it in, reference under hood placard.

 

Yep
I took Thatt’s advice way back
Just replaced all my 28yr old vacuum hoses


Red color was used bc Ace hardware had all correct sizes…..in red
I embraced it
Since then Amazon sells a complete vacuum hose kit(still lil cheaper at Ace)

 

In the past I've used the vacuum method in the past with decent success.

Thanks for the tips THatt I'll try that out for vac leaks.

side note... how do I remove this stupid broken off exhaust stud?

 

The funny this is I just replaced all the vacuum lines that looked suspicious. I'll have to check again

The red lines look pretty cool carcontrol, I also see that fuel pressure gauge...I bought all the parts to DIY on at the fuel rail but I've had bigger fish to fry

 

Get us a pix of this exhaust stud

The answer will be dependent on how much (if any) of the stud remains
And location

 

Ok so good news and bad news.

the stud thats not there looks like it fell out or was never installed. So far the manifold doesn’t look cracked.

The beginning of the exhaust looks like a total hack job but it doesn’t actually appear to be leaking

The major leak looks like it around the upstream o2 sensor itself and the manifold where there is no stud and the one next to it.

 

That dog ain’t gonna hunt

Need to take tht manifold off and investigate further

Might be able to re-use
But I would start looking for replacement options
IIRC can upgrade with new tubular header from 2nd gen 4cyl’s

 

This is what we’re dealing with. It looks like you can see the soot from where exhaust is escaping where the gasket is.

right now I’m planning on hitting the manifold and o2 bung with a wire wheel and getting some new gaskets / studs.

it does seem like a good time to look into headers…

 

Yep that’s your E leak.

funny
I just started researching headers
Browsing….haven’t written notes done
(That happens when I have researched everything)
So far 3 choices
-the $800 LCE headers(lil pricey for me but worth it)
-newer gen OEM header not cast but tubes and very reasonable
-the wide world of the $150-$200 AM headers….in my limited research, found some perfect fit….some not so much

 

I’m thinking in the short term I need to just put the old one back on with a new gasket and hope for the best. The studs seemed a litttttle too easy to take off but I’ve never had to do this before.

I appreciate the research. This car is becoming more of a money pit than I wanted but that being said I do adhere to the “buy once cry once” mentality

 

OK! You are making good progress. Good call on replacing your O2 sensor. And that exhaust manifold was certainly leaking something.

You may have a fighting chance of reusing that exhaust manifold, but I would consider replacing it. Also so you can use the cat you have waiting in the wings. An OEM equivalent from RockAuto will be fine IMHO. Get new studs while you are at it.

If you do decide the re-use that exhaust manifold, I would recommend you use a 3M type scotch bright "whizzy wheel" over anything anything with wire bristles to clean it up first. Check the mating edge for flatness on the flatest surface you can find. Or with a precise straight edge. You're not so much worried about any warpage that is like the thickness of a piece of construction paper. A new crushable type gasket will compensate for that.

If it is warped however and rocks noticeably, then just get a hew header.

The sum total of these action should get your fuel trims back in line and your truck running much better. +/-5% on fuel trims is A-OK.

Good luck!

 

Excellent Job 2R-Steez

impressed with your attentiveness!

 

Thanks for the detailed response BigCarbonFootprint, this is the exact advice I need right now. I have a little extra cash lying around since I sold my 5-lug so I think I’m going to bite the bullet on some need headers.

in the short term I need something working by Tuesday morning to get to work

I’ll keep you guys updated on how this helps with my fuel trims / hard starts