Running rich

First post. i'll start by saying that this is my 3rd Toyota. 1st was a 1978 that got totaled by a drunk driver. replaced it with a 1987 4 speed 2wd that i bought new and had until it was stolen and found completely stripped, insurance totaled that one too.

got back into the Taco world with this 2001 2.7l 4wd. picked it up about 3 years ago with about 80,000 miles on it and it now has 120,xxx

i've been lurking and searching for awhile trying to find some answers as to why my truck is suffering the problems it now has. It ran great for first couple of years. then it threw some codes that indictaed bad O2 sensors so i replaced them both.

the codes popped back up and CEL came on but i wasn't having any drivabilty issues so i basically ignored it.

handed the truck over to my teenage son as his first vehicle and about 6 months ago he started complaining of poor mileage.

i knew it was previously getting 17-18 mpg in a combo of city/hiway driving and it is now getting about 8mpg.

the current symptoms are: poor mileage, black soot spitting out the tail pipe, rough idle when warm, and stumbling/hiccups when at cruising speeds

current codes are:
PO300 - random cylinder misfire
PO171 - bank 1 lean condition
P1130 - no definition

what i've done is: as mentioned earlier i previously changed O2 sensors, recently replaced MAF sensor, new air filter, and also changed the plugs (NGK iridium).

ive checked wire connections and vacuum hoses and all seem good. i put a vacuum gage on the hose to the brake booster and was getting -20ish

i picked up a

$80 bosch 1150 trilingual scan tool with autoid, live data, ABS and graphing

bosch 1150 scanner and have some real time data but not real sure how to interpret exactly what i'm seeing

here is some key numbers that may be of help: (after warmed up and in closed loop)
LT fuel trim - 39.8%
ST fuel trim - 19.5%
O2S12 - ~.910
O2S11 - 4.991 (this starts out around 3.3 and climbs to 4.991 and stays there as it warms up)

i have several ideas in my mind as to what else may be an issue but really don't know what to try first. i don't want to just keep throwing parts at it.

ANY help is appreciated, hopefully this is enough data for someone to help me on where to go from here.

thanx in advance

 

nobody has anything?

 

Possible the fuel pressure regulator is bad. Pull the line off and see if there is raw fuel in it.

 

pull the line off where?

 

there is "false air" entering the engine. False air is unmetered MAF (Mass Air Flow) air and the O2 sensors are forcing the ECU to try to compensate. I would start with taking the air intake tube off completly and look for cracks... bend it, twist it, ect to see if you can see any. Take the vacuum line off the brake booster and plug it and see if the fuel trims drop.

look on the rail that holds the fuel injectors and follow it until you see a round device with a vacuum line on it, that is the fuel pressure regulator. Like mentioned above, take the vacuum line off and see if there is raw fuel in that port and then check for presence of vacuum. See attached file.

I would get a can of Berrymans carb clean and start to spray around the upper/lower intake joints then where the lower intake seals on the head. Then spray around where the injectors seat on the head.

There are various vacuum lines that need to be inspected... pulled off and visually inspected.

if the leak is the upper/lower intake, use Toyota gaskets. I have had Fel-Pro's pull through on the thin spots between ports after a while.

If doing all of this and it still has an issue, professional help is needed.

 

I've seen a stuck open egr cause similiar issues. Does you motor have an EGR? Should be a picture on your vacuum diagram

 

Thanx Glamisman, that's the kind of response i was hoping for.

a couple questions for clarification:

when i pull the vacuum line off the booster and plug should i expect to see the fuel trims drop? (i mean are they typically supposed too or is that a symptom of an issue?) what does it mean if they do or do not?

i do have a vacuum gage, what kind of reading should get on the regulator line

also as a note, with the hood up and the engine idling i do hear somewhat of a hissing noise but have not been able to locate any kind of vaccuum leak (though i have not tried berrymans spray)

 

jeez, i don't know but i will check when i get home

 

another question....is there a good place to check for vacuum "overall". for example, does the reading i get on the booster line tell me anything like if i have enough vacuum or indicate there may be a leak somewhere?

 

checking at the booster line is fine but there are smaller lines that adapt to a "standard" size vacuum guage line easier, if that makes sense.
If the engine is in good shape mechanically 20- 21 steady inches at idle is fine. The vacuum gauge is more of a go-no go test. If the vacuum gauge drops then comes back up, then drops, then comes back up is telling you that there is a mechanical issue. If low and steady, suspect an intake system leak AFTER the throttle body. Low, high, just fine vacuum readings are relative to each motor and how it is built and its mechanical soundness. In the olden days a big Detroit V8 with a HP cam wouldnt generate enough vacuum to opperate the brakes where as the same motor but stock was just fine.

If I remember correctly... there should be manifold vacuum at the regulator at idle and it should drop as the throttle is opened. I have never checked fuel trims as I play with vacuum at the regulator.

 

On the v6 there's no vacuum. It just vents into the intake tube pre throttle body.

 

Your LTFT are out of control. The po1130 code should be a code for "slow switching bank 1 o2 sensor". Means it doesn't oscillate lean/rich fast enough. Could be a bad sensor that isn't sensitive anymore. Or in a rare case, like mine, you've got a 3" turbo downpipe and the exhaust velocity isn't high enough to switch it fast enough. Also if you're able to see your o2 sensor on a graph (like with Torque app), you should see it peak and valley. If it's holding steady voltage, you've got a bad sensor.

Be certain you got the right BANK 1 (front primary) o2 sensor. There were narrow band and wide band sensors available, so double check you have the right part.

Black soot indicate it is definitely getting enough fuel but your ECU doesn't know that, because of the black soot and the crazy high LTFT. You have an ECU feedback issue, and I suspect bank 1 o2 sensor.

Of course make sure you don't have a big ass vacuum leak first, but you would have found one that large.

 

ok, thanx for that vasinvictor. i'll be doing some extensive checks for vacuum leaks tonight.

as to the O2 sensors:
i just went back and looked at what i ordered and installed when i changed them. the downstream sensor appears to be the correct one for my application.

the upstream is a different story, it appears i ordered and installed a

$125 234-9002 Air Fuel Ratio Sensor

234-9002 (manual transmission) when i should have used a

$146 234-9001 Upstream Air Fuel Ratio Oxygen Sensor with 10.6” 4-Wire Harness, for Auto Trans Equipped Vehicles

234-9001 (4wd auto trans)

could this incorrect sensor be causing my problems?

 

Ok, you originally said 2001 2wd. In this last post said 4wd auto trans. Just clarifying which one you have.

Actually either way it doesn't matter, all the 234-900x sensors are widebands (AFR sensor). I was hoping perhaps you put a narrowband in there. Either one should work, the length of attached wire would be a bit different is all.

 

OH WAIT! Is your LTFT negative or positive? Your use of a dash has me confused.

 

that is a positive number. the dash was not intended to indicate negative.

also, yes it is 4wd, my original post was a typo

 

OK, still stands either 9001 or 9002 should work. And a fuel trim that positive indicates the ECU is trying to add 39.8% fuel to the engine (at that particular load and RPM) but still can't make the engine stoich, so it throws a lean code. You are looking for a MASSIVE air leak.

You indicated the vacuum was -20in/hg which is normal. If you have access to live LTFT and STFT, try to rev the engine to a steady 3,500 rpm which watching the LTFT and STFT. See if they get closer toward 0. Vacuum leaks become less obvious at higher RPM (less vacuum) so the LTFT should improve if this is the case. Other than that, a MASSIVE exhaust leak before the bank 1 sensor, but you'd definitely hear a leak that large.

With your reader, can you see TPS or MAF data? Still acts like a failed front bank o2 or MAF, but maybe something else can think of something else.

 

ok, so before i came in and read this, i sprayed all over the place with berrymans (trying to pinpoint a leak) and got no change to engine idle (better or worse).

i pulled the vacuum line off of the fuel pressure regulator and had no sign of "raw fuel", although i also noticed NO vacuum on that line. that line comes off of what is labeled as the "air connector" (basically a plenum/box attached to the air intake tube. i installed a vacuum guage and got a reading of '0' even when i revved the motor. if i applied a vacuum (with a hand pump) to the regulator i did get a slight increase in engine rpm's (20-30 rpms)

yes i can read TPS and MAF data

ABSLT TPS is 10.6 at idle and increses and i push the accelerator
MAF is .80 and also increases as i hit the accelerator

 

Fpr only references atmosphere. No vacuum on that hose.

 

yes i did check the diagram and there is an EGR. it is between the EGR vacuum modulator and the vacuum switching valve