High Nox on my 93' altima---Nistech, any suggestion?

[510SX]

Took my car to smog twice, both time failed with high Nox.

First time:15MPH---CO2 (15.0%), O2(0.3%), HC(7PPM), CO(0.00%), NO (1363PPM)25MPH---CO2 (14.9%), O2(0.3%), HC(4PPM), CO(0.00%), NO (1637PPM)

Second time (Changed the cat coverter, was suggested by Smog man)15MPH---CO2 (14.5%), O2(0.2%), HC(16PPM), CO(0.04%), NO (1404PPM)25MPH---CO2 (14.4%), O2(0.3%), HC(12PPM), CO(0.02%), NO (1489PPM)

I knew it wasn't the cat converter, o well. This clearly the EGR circuit, am I correct?

Here is what I found so far; the EGR valve is not opening at any RPM. EGR, BPT and EGR solenoid checked out ok. EGR Air Temperature sensor is good. Vaccum hoses were replaced about a month ago, the stainless steel tube was cleaned.

I checked my neighbour's 94 altima, his EGR is oscilating at 2000 rpm. I ran out the idea.

You think the distributor causing the problem? any suggestions?

TIA

[NISTECH]

You are correct your EGR is not functioning. Funny thing to about your readings, they were better before you replaced the cat. Hope it was the same smog guy. He clearly doesnt do much smog repair , those readings scream EGR problem. Your EGR wont open at a static point but it may or may not flutter like your neighbors. Take a 1 1/8 socket and clamp it in your exhuast pipe tip with a pair of vise grips. Then hold your throttle a 2000 rpms for a few seconds then goose it, at the same time feel if your egr at least flutters when you do that.

The socket provides a slight restriction in your exhaust creating some back pressure so the BPT wil close the vaccum line to feed vaccum to your egr. It would also be best to t in a vaccum gauge between the BPT and EGR to see if it gets vaccum or not. If it does note how much and post back if it doesnt get vaccum something is wrong with the BPT or the EGR solonoid. In this case you would need to check for available vaccum to the BPT off idle.

[510SX]

Take a 1 1/8 socket and clamp it in your exhuast pipe tip with a pair of vise grips. Then hold your throttle a 2000 rpms for a few seconds then goose it, at the same time feel if your egr at least flutters when you do that.

Excuse my poor English. I don't quite understand what you mean by goose it. I just assume goose=snap the throttle.

I did what you told me to do; I placed a 30MM socket at the end of the exhaust. Hold the RPM for a few sec, then snap the throttle (~3500RPM), I get about 12in of vacuum. Without the tailpipe restriction, I got about 9in of vacuum.

Note: The vacuum only held for fraction of the sec; it doesn't remain at steady 12in.

Another note: After I connect all the vauum lines back, and left the vacuum gauage connect. I noticed I got about 9in of vaccum for 1/3 of a sec ONLY when I snap the throttle. If I press the throttle steady increase the RPM, the gauge's needle wouldn't move.

[NISTECH]

Thats exactly right. So your saying you got vaccum to the egr valve after the BPT correct??

If so that is good, It wont stay because the ECM also needs to see road speed sp the quick flash of vaccum is a good sign it says your controls are working. The vaccum difference with the socket in the pipe is ok too as you have a slightly restricted exhuast with the socket in. What you were after was the back pressure to close the BPT.

Now what you need to do is see if the EGR will hold vaccum. You need a vaccum pump to do this. When you pump it up it should hold the vaccum. You only nbeed to bring it up to about 5 Hg of vaccum as that is all it really operates on.

[510SX]

Thanks for the follow up, Nistech.

Thats exactly right. So your saying you got vaccum to the egr valve after the BPT correct??

Yes, I unpluged the EGR vacuum hose and connect to a vac gauge.

I've just re-checked the EGR valve again, it holds vacuum fine.

Let me ask you, is my EGR circuit working normal?

Note: I also have done another test this moring. I "T" off the intake vacuum from the fuel regular(18in) to one port of the BPT valve and the other port connects to the EGR valve as usual. The engine runs real rough at idle. Is it normal? I am not positive on this one. isn't all the vacuum should be bled to the side? or only some of the vacuum?


Modified by 510SX at 5:38 AM 8/29/2005

[NISTECH]

The vaccum going to the BPT should be coming from the egr solonoid, not the fuel pressure regulator.

[510SX]

Nistech, I think I've done everything in the FSM and what you said. The EGR still won't operate (it works only I snap the throttle).

I even took out my neigbour's BPT and solenoid and put on my car. It's still the same.

Do you have any other suggestion?

[NISTECH]

The EGR will not open at a stand still. It is designed not to. If the ecm does not see a speed signal it will shut the solonoid off. If it does see a speed signal it also needs exhuast back pressure at the bottom of the BPT. The only way you will get back pressure is under load or with the exhuast restricted as I mentioned.

[510SX]

Do you think my EGR circuit is actually functioning?

[InsanityInc]

Do you have an aftermarket exhaust system?

[510SX]

Do you have an aftermarket exhaust system?

no, everything is stock. except the cat I recently installed. It's OEM weld on cat, I had it installed before I took my car to smog for the second time. Compared to the first time smog readings, they are about the same.

[NISTECH]

It sounds as if it might be. Set your vaccum gauge up t'ed into the line between the BPT and egr valve . position it so you can see it while driving. Take it for a spin and watch the vaccum gauge see if it has vaccum during cruise condition while on steady throttle. best results will be seen on a slight incline.

[510SX]

Here is the latest, Nistech, I took my car to the smog repair shop (all they do is smog repair). The guy told me the EGR circuit is not working (I knew that). He said the common problem causing the EGR valve not working on atimas and hondas are the passages inside the intake were plugged up.

He mentioned I have to remove the intake manifold, and there are four plugs on the bottom of the intake. I need to remove the plugs and clean inside.Do you think what he says making sense?
Modified by 510SX at 6:01 PM 8/31/2005

[NISTECH]

Not if your car stalls when you apply vaccum to the egr valve at idle. That means you have flow. With the readings you have it suggests egr is flat out not working. So your car would not stall when you applied vaccum if that was the problem.

[510SX]

Set your vaccum gauge up t'ed into the line between the BPT and egr valve . position it so you can see it while driving. Take it for a spin and watch the vaccum gauge see if it has vaccum during cruise condition while on steady throttle. best results will be seen on a slight incline.

This morning, I teed the vacuum gauge between the ported vacuum line and the EGR solenoid, and took my car to a spin. I get aout 5 in of vacuum when crusing, and more than 7-8 in during accelerating or shifting.

Then I teed the gauge between the EGR solenoid (Port A) and the BPT valve, same driving condition, I get 3 in of vacuum max (most of the time I get 2- 2.5 in)

Also, I teed the gauge between the EGR valve and the BPT valve. I get 2-2.5 in of vacuum. (same driving condition).

I used a vacuum pump to test my EGR, it would take 3 in of vaccum just to feel the diaphram to move. It would take at least 5 in of vacuum to feel the diaghram to lift.

Questions in my mindwhat is the good ported vaccum reading for Nissans (9 in)?

Why I lose 2 in of vaccum going thru the EGR solenoid, even I plugged the charcoal canister line? BTW, I tested the EGR solenoid several times. It's known good, also tried my spare onces, no different.

Any inputs?

[NISTECH]

The vaccum line running between your egr solonid port (a) and BPT valve there may be a restrictor in that hose. Replace the hose with a non restircted hose and recheck it. It may be that restrictor is plugging up. Also try cleaning your throttle body as that line comes from the vaccum hose off of it , the port for that vaccum sorce is in the throttle chamber.

[510SX]

Just an update. after I checked this and that, everything in the EGR circuit seemed working. I was running out of suggestion, so I finally took the intake manifold apart (did what the smog repair shop told me to do), I found 3 out of 4 holes were plugged up solid. I cleaned up all the plugged up holes and installed the manifold back. I took the car to smog this morning. It passed!!! After 6 hours of removing, cleaning and installing the manifold back, it paid off.

Thanks for your help NISTECH

[ricebike]

[threadjack] would using seafoam be just as beneficial? just attach to a vaccuum source & hopefully it'll clean those passeges out w/out dissasembly? [/threadjack]

hmm, sux that you had to spend $ on a new cat that u didn't need...

[NISTECH]

Sea foam will help prevent it but it will not clean out a completely plugged passage. The way he cleaned it is the only way to get it out. The stuff is like rocks when you dig it out.

I am truly suprised your car would die with 3 of the 4 passages clogged. I have never personally witnessed it. I have seen the car still stumble with them plugged but never die. Interesting.