brad11140

I wanted to get some input. I have some things to check still. Ok here's the skinny. I have a 1993 4runner that I just rebuilt the engine. It's been in and out of the shop that did the engine getting leaks repaired and such. I am only now really starting to drive it.

I took it straight to the smog station, where it barely failed on high hc. Nox was a bit high, but not out of spec. I replaced the cat and the oxygen sensor and am planning on returning to the test station soon. I have run a sea foam treatment through the gas tank. Power seems low, but I am also used to driving a 07 Tundra with 385 hp. I realize the 3.0 is a bit of a dog. The transmission started giving me a few problems shifting and only one time has it thrown a code 63. So I have new shift control solenoids on the way.

In addition to the cat and o2 sensor I have also replaced the plugs wires distributor rotor and cap.

Engine seems to idle fine. It does hunt a bit when I am holding the timing light on. It dosent sit rock solid on 10 btdc when the jumper is in, but when I pull the jumper out the timing advances like it should. Also when I remove the tps connector the idle speed jumps, like it should. So I think the the tps is fine.


Ok so with all the info out there here are the symptoms.

Power seems a bit lower than I would expect.

Gas mileage is horrible. I went 120 miles on a tank. What's that, about 7 gpm?

Can a bad egr valve cause those kind of problems? Gas mileage that bad? I was thinking of checking it because of the elevated nox readings.

What if my timing belt was off a tooth? Is it possible that is my root cause. Appreciate the input.

I am working now, but this weekend I plan to test the egr system and pull the timing belt cover back and see if I can see the marks without tearing the whole thing apart.

TNRabbit

Have you replaced the oxygen sensor?

Also, I'd us and UNLIT MAPP gas or Propane torch to check around ALL the vacuum hoses & intake tubes for any leaks; it will idle up if you find one. Be sure to check the miles of hose on the passenger side as well.

Also check the plastic valve behind/under the back of the plenum to see if it's been broken off (common). I recommend removing the hood to do all this; it's only 4 bolts & a piece of cake to remove/install versus a GIANT PITA to not be able to see or get at stuff with it on.

What size tires are you running? Oversize will KILL fuel mileage. Are we talking 4x4 or 2x4? That IS horrible mileage regardless~

brad11140

Oxygen sensor is new. I have heard some people allude to 2 sensors. The only o2 sensor I know of is directly upstream of the cat.

I'll try the mapp trick.

The plastic valve you are talking about. Are you talking about the valve that the fuel charcoal canister line goes to which redirects vapors to the tb. If so, this valve is fine.

TNRabbit

This is a dual-nipple thing that is screwed in on the passenger side & behind/under the plenum right by the firewall....I forget the name of it.

There are a couple of vacuum hoses that go all the way down to the front diff, too.

just call me smithy

it took me two times to pass my late 3vz, what i had to do was in-rich the air to fuel ratio, a lean mixture will have higher combustion temps or high Nox ratings, by in-riching the air to fuel ratio it drops the temps, granted it raised my carbon emissions but it was still within limits.

just call me smithy

the previous owner had played with the air flow meeter, see if yours has been opened or re sealed.

brad11140

Ok here is what I have done.

I pulled plug wires one at a time to see if I had a cylinder not firing. All 6 are working. I used gas to look for a vacuum leak. This was negative. I do not appear to have a vacuum leak.

It's funny you mention that smithy. I have two air flow meters. One of my buddies had cracked his open and played with it. I tried it with mine. I have since put in the other one which is sealed.

Tnrabbit, I am positive you are referring to the tvv valve which is a bimetallic valve in between the gas charcoal canister and the throttle body inlet. This valve is not broke. Both lines are attached appropriately

brad11140

Also, I do not have check eNgine light lit Nd there are no codes stored.

aa1911

iTrader: (1)

I rebuilt my first VAFM that was in my 93 runner, got it back within spec and worked fine but still wound up ordering a new rebuilt one, didn't notice any change in mileage. some people have messed with them to 'lean' them out a click or two to try to get more power, maybe you went the wrong way and made it too rich. still doesn't explain 7mpg though, ouch. the O2 sensor is the first thing I always recommend to replace as it has a service life of about 75k miles really but you've taken care of that... (pre-cat sensor was changed, correct?) that's the one that really matters for engine control.

brad11140

Well the vafm that is in there right now is a sealed one. I have not touched it. Yes the o2 sensor I replaced was right before the cat. Is there another one?

just call me smithy

if it were too rich he would have failed carbon emissions not Nox, i would in-rich your air to fuel to see if that helps.

brad11140

Smith I actually failed on BC. My nox was elevated but not failing. How do I adjutant the fuel to air ratio without opening the vafm.

just call me smithy

you have to open the vafm to adjust it... its the little black plastic lid on top of the vafm, its silicon in. but if yours has not been opened, in-riching ( if that is even a word )the air to fuel ratio might be just a bandade, i would first inspect and clean your EGR if all els fails then i can tell you how to tune your vafm

brad11140

Yeah this current vafm has not been opened. It shouldn't be going through that much gas. Me and a coworker went out and looked through the fuel system. I jumpered the fuel pump but we couldn't here it running. So we pulled the fuel line coming off the fuel regulator and tried again and sure enough fuel comes out although I imagined it would come shooting out there. If the regulator was bad could that possibly be forcing extra fuel through the injectors. Although I have to imagine that I would be seeing some visible exhaust if it were burning that much fuel. Can a dirty egr make you use that much more gas. Basically it's using twice as much fuel as normal.

aa1911

iTrader: (1)

yeah, that's about right, should be up at least around 13+ mpg's... I'm at a loss, sounds like you've checked and fixed most everything I know about. I don't think the 93 has a 'rear' O2 sensor, I'll have to check when I get home, even if it did, I don't think it would matter.

The EGR sucks, if you haven't checked that, pull it and clean it out good, make sure the valve is opening when it should, they get stuck after a while and cause issues.

Did your O2 sensor harness plug in exactly like the OEM harness? sometimes they will actually work (engine will run) with the wires switched around and that could certainly make your mpg's take a nose-dive, usually would throw a CEL though too. I had a short on my O2 sensor circuit when I installed my SC on the taco and it went from 20mpg to about 8mpg until I realized I hadn't insulated a wire. check the wiring of that O2 sensor, and your EGR/intake runners for clogs/excessive carbon, that's about all I'm good for at this point.

aa1911

iTrader: (1)

ECT sensor or similar? maybe bad enough to not throw a CEL but not allowing the ECU to go into closed loop operation? if for some reason your operating in open loop, that would certainly give you horrendous mpg's.... especially with no CEL's or major issues. just a thought.

just call me smithy

have you done a compression check?, one of my friends had two burnt valves witch caused him to have horid gas mileage. but the funny thing was you could hardly tell the motor was missing. he was in denial untill i convinced him, and what do you know? two valves later along with a shim job of the other valves he averages about 17mpg

brad11140

Hopefully it smogs next week and than back to the shop it goes. I checked the voltages on the vafm, they all check out good. I also checked my o2 sensor and it is ok as well. I will pull the egr this weekend and clean it real good.

How can you tell if the engine is in closed loop. Ect sensor should be easy enough to replace

When it goes back to the shop I will make sure they do a compression test.

cjolson140

The way I did that was connect a multimeter to a couple terminals in the diagnostic connector, I think it was VF and E1? Check the FSM becasue I can't remember if those are correct, but the multimeter should pulse back and forth between 5 volts and 0. You're supposed to count how many times it fluctuates in a certain period of time, and that tells you how well your oxygen sensor is working (if at all). Basically the fuel system enrichens or leans the mixture based on that voltage, and when working it goes back and forth rapidly; if you aren't in closed loop it won't do that at all, it will sit at 5 volts or 0.

brad11140

Yep that is the o2 sensor function test and it was successful. I don't know if it was those exact voltages but it was fluctuating healthy, over the required 8 times in 10 seconds.


On another site a Toyota tech suggested bad ignition coil as the culprit on a vehicle having a similar problem. So I used the Fsm procedure and checked the coil. 0.5 ohms in between the 2 tabs on the connector, which is in spec. However when I placed my negative lead inside the coil high tension connector location and the positive tab I have infinite resistance which is way out of spec. So it would appear that my secondary coil is bad. What is puzzling to me is how the car would run at all with a bad secondary coil. Will be interesting if this is what is causing my whole problem.

I also put the mfi system in test mode and drove around. It did not generate any codes and I am still cel free.