aram987

Hey all. Sorry to make my first post here one where I'm asking for help right off the bat. I've been meaning to write an intro and say thanks to all you great people for the amazing amount of help and knowledge I've already gleaned in my brief 4runner ownership. SO...thanks all, I've already solved a number of problems I never would have been able to without this great resource and everyone here being so willing to share what they know and take the time to do some amazing writeups.

I got a 1990 runner with the 3vze about a month ago, and I love it. I've had 2 3rd gens in the past, and though the 2nd I now have is a little slower and uglier (not the styling, I like that better, but mine is old and shows it), I still think this truck is awesome. I have many mods and swaps in mind for the future, but right now it's the DD and I am on a budget (or so my girlfriend tells me ).

Here's my issue at the moment: as I said, I bought it about a month ago, and just took it in to get my emissions test. It failed for NOx.

I have a test report from the PO dated AUG 11 2012 and it passed with flying colors. Not even close to the numbers I just got today. Here are the numbers side by side:

AUG 11
HC GPM: 0.4701 Limit: 3.0
CO GPM: 5.3151 Limit: 25.0
CO2 GPM: 434.4136 No limit listed
NOx: 1.5010 Limit: 5.0

NOV 23 (Same limits as above)
HC GPM: 0.7662
CO GPM: 18.9709
CO2 GPM: 636.7331
NOx: 5.3346

So, obviously there has been something that changed in a big way in a few months. I don't have a CE light, or any other light. I can't imagine that carbon buildup is to blame, as it's only been 3 months. The only thing I know has been done is PO did plugs and wires. I know he used cheapies to replace, so I'm going to do them with quality parts now. The truck seems to run well, it's slow, but it is a 3.0. MPG seems within normal range for these things.

Does anyone have any idea on a part that won't throw a CE and could go bad causing that big a shift in readings? I do my own work, and would like to throw as few parts at this as possible (duh). Any input appreciated a great deal. If there are any relevant test procedures associated with any ideas that come this way, those would be appreciated as well.

Thanks all!

scope103

The EGR system is there to reduce NOx. That's its job. That's its only job. So that's where I would start. http://personal.utulsa.edu/~nathan-b...77exhaustg.pdf Work through the diagnostics there, with particular attention to the vacuum routing.

The EGR gas goes through the valve into a tube that projects into the plenum. The plenum will, over time, accumulate a lot of "gunk." If you get enough gunk in there, not enough of the EGR gas (exhaust) will input into the plenum, and your NOx will rise. If you get to disassembling the system you can ease the tube out; if you have to pull on the tube, you've got a problem. This isn't listed in the manual (probably because they didn't have old trucks when they wrote the manual). If the tube is completely blocked, the EGR gas temp sensor should pick that up and throw a code, but you may not be "completely" blocked.

The cat has a limited effect on NOx, but you're only over by a limited amount. Since your HC and CO have also increased (a lot), you may be at end-of-life for the cat.

High HC/CO suggests running rich (not enough O2 to burn up all the gas and the CO). An exhaust leak can cause that (O2 leaks INTO the exhaust, fooling the sensor into going rich when it should be going lean). Lots of things can cause running rich.

A good resource of understanding how the various gases interact is www.autoshop101.com.

By the way, do you have any idea what GPM means? grams per cubic meter?

Good luck! (And let us know how it turns out.)

jerry507

Good analysis

Should be grams per mile, for all parameters listed.

aram987

Thanks for the replies! I'll definitely check the egr and see how that's looking. Cat, egr, or O2 sensor were my first thoughts, but the lack of a dummy light threw me off the trail on those. I'm a relative newbie on 4runners so I may be totally off on this, but isn't the whole job of the downstream o2 sensor to trip a CE light if the cat isn't functioning properly? I'll certainly explore that possibility, and I'm sure there is a grey area in the system where the cat isn't working right, but isn't working badly enough to trigger a code. Hmmmm...lots of work to do tomorrow. My next move in the morning was pulling and cleaning the MAF. Could that cause this, or am I barking up the wrong tree there? Thanks for the thoughts, and I'll update as progress is made. Any new thoughts are more than welcome as well. In Denver e-test is $25, if you fail you get one free retest. Fail that and you have to pay for the next, so I want to get this as sorted as possible before using my freebie.


Oh, and I've got no idea what gpm stands for. I would wager meter, as output per mile could change substantially based on all sorts of variables.

scope103

So far as I know, only California trucks had the second (downstream) o2 sensor. But who knows where your truck has been! That is the purpose of the second sensor; to detect when the cat is not working.

VAF is probably the wrong tree; if the VAF was reading incorrectly the initial mixture would be wrong, but the feedback from the o2 sensor is designed to correct that (within limitations, but you don't have a "rich" code indicating that the adjustment has hit the limit).

aram987

I see. So looks like I'll be checking out the egr today. I'll try to do a cat inlet and outlet temp test as well.

On the passenger side of the egr valve there's a threaded port with nothing in it, any ideas what that is? I've just been wondering. It doesn't look like mine has ever had anything in it, so I'm not worried about it, just curious.

scope103

Uh, oh. Could it be this?


That's the EGR gas temp sensor. Why would someone remove it? Because they were getting a Code 71, and got the code to "go away" by bypassing it. Why were they getting a code 71? Because they were getting just barely enough EGR gas flow to pass smog check, but not enough to do it correctly.

You don't NEED the gas temp sensor, but lacking it makes diagnosing your problem that much harder.

aram987

Hmmm...that is what I was looking at. The port there has definitely been empty a while. It rusted equally with the body of the egr valve (surface rust). So I'm sure it wasn't in there when e-test was done in Aug.
I have to go junkyard scavenging tomorrow anyway, so I'll see if I can find the parts for that.

I pulled the egr valve today, and the tube into the plenum had some gunk on it. It slid out easily, so it wasn't too bad. Before I cleaned it I did some blowing through it and it seemed unobstructed. Also tested the vsv and it seemed good. I'll check the cat tomorrow after the junkyard.

aram987

Whoops, didn't test the vsv, it was the vacuum modulator

aram987

Well, after a busy weekend and early week, I took the runner in today and it passed. The numbers were not as low as I would have liked to have seen them, but it passed and I'm happy for the next 2 years (next test date). Hopefully this truck will be sporting a new engine and loads of new parts by then.

NOx ended up testing at 3.23. Still a substantial increase over PO's last test a few months ago, but legal. Still don't care for the idea that the truck isn't running as it should be, but I'll take baby steps.

In the end, I seafoamed the engine, ran a can of 44k (both of which seem to have got this thing running WAY better, more power, better MPG, and a smoother idle), pulled and cleaned the EGR valve, tested and cleaned the vacuum modulator, did plugs and wires (post seafoam), and I think that's about it.

I had one REALLY stupid adventure in the process as well. I pulled the VAFM cause I thought I'd clean it. Me, being an idiot who always wants to know how everything works, unscrewed the plug and tried to pull it out, breaking the connections to the board in the process. I tried to solder it back together, but no joy, tabs were too far gone. Went to the junk yard to look for one, but all I could find was a 91 camry. The VAFM looks really similar, and as my 4r wasn't with me so I thought for $10 I'd give it a shot. The camry VAFM is a bigger unit than its runner counterpart, so no love there. I ended up pulling both apart (desoldering on the camry board instead of ripping it apart like an idiot), and making a frankenstein VAFM out of both parts in the runner VAFM body. It works after some adjusting of the tensioner and the truck seems to be running happily. I've read about doing a mod using the camry VAFM, but it involved redoing most of the air intake from the plenum to the airbox, and I didn't know how it would impact emissions to have a bigger VAFM (or if it's worth the effort at all), so I didn't do it. If I can find another for that cheap, I may just put something together and fit it up to see how it runs.

At any rate, thanks so much for the assistance, scope. It was a big help, and that troubleshooting guide was great.

A little off topic, but there is a guy on my local CL who's got a FSM (vol 1 and 2) for cheap. It's for a 91 (mine is a 90), there wouldn't be any substantial differences that would give me headaches, would there?

scope103

If there are any differences at all 91 to 90 you'll probably never find them.

While it's hard to beat free http://personal.utulsa.edu/~nathan-buchanan/93fsm/, $60 is a really good price for both paper manuals.

If he has the ELECTRICAL volume, well, you could get your scanner out and we'd all love ya!