AJsArmor

86 4runner 4wd, stock 4.10 gears and 31's, 22re motor with a new head, cam and the intake to throttle body cleaned. New temp sensors (both), new o2 sensor, adjusted TPS, timing good, rerouted intake to battery side, Thorley header...

So here's the scoop, did the majority of that work and it was getting 19-21mpg fairly consistently. Sometime this winter the mileage dropped off quite a bit and I started getting a CEL, code it brought up was O2 sensor detects lean/rich condition. Now with the CEL it only comes on while I'm driving down the highway, never in town. Get on the highway, engine gets up to about 150 degrees and poof it comes on and stays on, come to a stop or coast down a long hill and it goes off until I'm back up to speed. Same code all the time.

I've tried 2 different O2 sensors, Denso and currently one from the dealership, made no difference at all in the code or mileage. I've done a valve adjustment, checked the TPS and timing, retorqued the head and header as well. It runs great, idles smooth and starts up quick. My mileage at best now is 12-14 mpg.

Unplugged the cold start injector with no change. Starting to wonder if it's the AFM?

874runnersr5

Could be the afm, if that doesnt work. You could always lean it out with tuning the afm. But thats just covering up the problem.

sb5walker

After bad O2 sensor, clogged injectors are 2nd most likely cause of alternating lean/rich codes. Best chemical for cleaning them is polyether amine (PEA), which was invented by Chevron. About the only product that still contains a lot of PEA is Red Line's SI-1 Complete Fuel System Cleaner - even Chevron no longer lists PEA in their own Techron MSDS. I'd add a bottle of the Red Line SI-1 to 2/3 to 3/4 tank gas and run until 1/8 tank, then add a second bottle and fill tank again to 2/3 to 3/4 full, and run down to 1/8 again. An alternative is to have a shop feed concentrated cleaner directly into the fuel rail - that will work even better than the Red Line cleaner.

VAFM also a good suggestion. Grab an ohmmeter and check it per the factory manual. Pay particular attention to VS-E2 - not only that the resistance is in spec with vane closed and full open, but also make sure the resistance between those terminals changes smoothly "in a wave pattern", without any spikes or dropouts.

Less likely - but still worth checking - is the TPS. You mentioned adjusting it: did you verify that VTA-E2 resistance is in spec w/throttle both closed and full open, and again verify that resistance between them changes smoothly with no spikes or dropouts?

By the way, there appears to be a typo in the VTA-E2 at idle specs in the 1993 fsm that people often reference:
http://personal.utulsa.edu/~nathan-b...34throttle.pdf
The upper limit of the range is listed at 8.1k ohms. Both the 85 & 89 fsms show the upper limit as 0.8k ohms.
85 & 89 fsm: 0.2k - 0.8k
93 fsm: 0.47k - 8.1k
I think the 85/89 values are correct, since it makes no sense that the idle position resistance could be permitted to exceed the full open resistance. Also, there are some other pretty egregious typos in the 93 specs, with the idle position throttle clearance listed as 0 mm or 10 in. !! And .57 mm is supposedly equal to 10.0224 in.

The range for VTA-E2 at the throttle full open position are comparable, with the 85/89 specs a bit tighter:
85 & 89 fsm: 3.3k - 10k
93 fsm: 3.1k - 12.1k

AJsArmor

A friend of mine who does injector service, cleaned and balanced the injectors and at the same time I put in a new fuel filter as well.

TPS was within spec last I checked but it's not going to hurt to doublecheck.

The problem initially started when the weather got colder which I attributed to winter gas, longer warm up times, which is usual for mileage to drop a bit. But getting into the 50's and 60's with no change.

Cold start injector stuck open? Wouldn't that cause idle issues when it's warmed up?

Check the AFM tomorrow and see what I find.

BTW- plugs, cap, rotor, wires all new too.

jimep

check for intake leaks also since you said you moved that. or vacuum leaks

sb5walker

If not the vaf meter, and since injectors are clean and fuel filter new, I'd next think about a fuel pressure & volume test. Could be pump, pressure regulator or damper.

I'm assuming the relocated intake is free of leaks, but if air were sneaking past the meter, that could cause some mischief...

Edit: Oops, there's an echo in here!

myyota

You said your engine gets up to 150 degrees on the highway, what temperature thermostat are you running ?, because that not hot enough, you should have 195 degree thermostat in the engine, otherwise your truck might not go into closed loop and that could cause a code to come up.

AJsArmor

The CEL comes on about 150 that's what I meant. With an aftermarket gauge it normally runs 185-ish pretty rock solid all the time. I have a gut feeling it's going to be one of those simple overlooked things that will make me slap my forhead.

annoyingrob

I have a similar problem in my truck lately. I'm thinking it's my fuel pump.

AJsArmor

Ok, how exactly would that cause poor fuel mileage?

ozziesironmanoffroad

very easily, aj. if the fuel pump isnt working correctly, it will either send too much fuel, or not enough.

yodercrawler55

I had the same exact problems and it turned out to be the injectors were clogged and one was broke.

sb5walker

Bad fuel pump couldn't cause high pressure - regulator dumps extra pressure down the return line. But a bad regulator or pinched return line could do it.

Assuming vafm, tps & fuel pressure regulation are okay, another thing to check would be bad crankshaft position signals. Since these are used by the ecu to time pulses to the igniter, and the igniter in turn sends pulses back to the ecu which it uses to time injector pulses, there might be something there. Check the signal rotor clearances and signal coil resistance in the distrib. Specs in the fsm in the IGNITION - ON VEHICLE INSPECTION section.

And one more - clogged cat? If it's been running rich, that's a possibility. Not sure what type of cat (if any) you've fit in with your header system, or how old it is, but direct fit magnaflows are available on ebay for $99 shipped.

I'm assuming compression is good.

When you run out of ideas, you can always spend a few hours with a voltmeter and the MFI SYSTEM - TROUBLESHOOTING pages of the fsm, back-probing wires on the ecu...

abecedarian

Is the O2 a single wire or 4 wire and where is it mounted?
Is the header a recent addition? Since you're getting the code only at speed the exhaust may be cooling down too much due to the airflow around the header and exhaust pipe causing the O2 to go out of operational temperature.

AJsArmor

Injectors were rebuilt/balanced last summer as well as the fuel filter, plug color is the same on all cylinders and darker than it should be which makes sense running rich.

Cat is Magnaflow, replaced last year. Haven't checked the rotor clearance, will definitely check it out. Thanks!

O2 is a single wire and located on one of the header tubes. The header is a Doug Thorley ceramic coated which I installed last summer. Retorqued it and nothing had loosened up, no leaks that I could hear or detect. Your idea about the airflow cooling the header down makes sense but I can also get the CEL light to go off by simply coasting at highway speeds for like 5-10 seconds.

Today I tried unplugging the cold start injector thinking maybe it was stuck open, nope it started a little harder. Left it unplugged and CEL still came on just like clockwork. As soon as it gets around 170-180 and traveling down the highway, it pops on and stays on until I am off the gas (coasting or coming to a stop). Right now I'm baffled. I can drive through town, lugging the motor with the gas pedal heavy into it for awhile and it never, not ONCE has come on. Just highway speed. BUT I did notice it didn't come on as quick the other day when it was really nice out, 60 degrees. The warmer the weather, the less it's coming on. So...???

nimaxpro

Old thread, BUT.....

I'm having the exact same issue described by the OP...
Bad mileage (12-14mpg, tops).

Any guidance/ideas from anyone?
What was the resolution to this issue? I so wish it was posted, been trying to figure this out...
Any help is appreciated.

Kean

Perhaps I'm stating the obvious but I hope folks with tires larger than the OEM diameter are taking that into account when calculating their fuel economy. Actual vs. indicated mileage can be different depending on the scenario.

nimaxpro

I have stock sized tires, so not applicable to my problem


Here's my problem....
1986 22RE
110k miles

Engine runs rich - based on poor fuel economy of around 13mpg, unburnt fuel smell in the exhaust, and all spark plugs being black.
Throws the "05" code for O2 sensor. (I am guessing for being too rich, obviously)


I've tested:
- O2 sensor (alternating voltages properly, and registers really rich at times when the engine chokes --- sometimes when idling it will sputter)
- vacuum hoses
- AFM
- TPS (it was bad with a slow/sticky return spring - replaced with another used unit that tests out and adjusted properly)
- starting injector temperature sensor
- coolant temperature sensor (for ecu)

The truck has been getting no more than 15-16mpg since I got it last fall, and that's the highest mpg it got. Lowest was about 10mpg when driving highway at about 75mph. Obviously not the most optimal speed with the 4sp transmission.

Here's the interesting part - I had the truck on a trip to Big Bend park in SW Texas and one day there had awesome results. It only lasted one day. I kept the speed at no higher than 50mph and got 190 miles on a half tank of fuel (roughly 7-8 gallons). That's about 25mpg.
It took about 90 miles just to get the gas gauge to come down to "full" mark (from above full). My worst run on the same trip got 100 miles from topped out tank to 1/4 --- about 10mpg, however, that when I averaged 75mph for those 100 miles.
Now, this is not fully speed dependent - my other drives at 50mph haven't yielded anything close to 20mpg.
It is something intermittent, more on the side of running rich all the time, but clearly with the occasional good run when it's not wasting fuel.

My next step is to pull the learned fuel trims from the ecu just to see how it's handling them....but I have to wait until I can drive the truck for a bit - I reset the ecu last time I worked on it and need for it to relearn.
After that, I'm ready to take the injectors out and send for cleaning/testing.

Any other ideas for what to look at or think about?

Thank you,
Nick.