High NOx Smog Failure (Defeat or Bust) (Page 1/9)
Notorio FEB 11, 01:58 PM
Gents,

I'm ready to roll this baby off the nearest cliff. 88GT with 5 spd, partial engine rebuild. I've got all the particulars in the Table below. Haven't worked on this since September but have been reading old posts, searching the net, etc. Asking for your help to fill out my Table ... I'm sure there are Factors that I've missed that might account for High NOx, but there is also reasoning behind some factors and how to test that are missing (or just plain wrong.) Anyway, I thought it would be useful for future Fiero Owners to have all of this gathered up into one Table. Please review and let me know what you think.

My plan is to work on the possible vacuum leak trouble shooting this weekend. After my 2nd test failure I DID find a disconnected hose and that helped for the September test but there might still be a smaller leak, so I'm going after that with two test methods.

Thanks in advance for all your help and thoughts!!

John
IMSA GT FEB 11, 02:25 PM
I'll just go with timing or EGR. I believe those are the 2 main causes of high NOX. Are you able to time the engine without any problems? There have been times when the balancer slipped and the timing is WAY off.
Here is how the notches should line up:


Here's what happens when they slip:

[This message has been edited by IMSA GT (edited 02-11-2023).]

sanderson231 FEB 11, 04:22 PM
I would also put a scan tool on it and make sure that it is not running lean. The integrator can only adjust so much after that the engine runs lean for example if there is a vacuum leak.

Another thought would be dirty fuel injectors i.e. not all flowing equally. That could make a cylinder or two run lean even though overall the exhaust is on ratio. The lean cylinders could be making excess NOx.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

Notorio FEB 11, 07:35 PM
OK, first data on this adventure:

1 -- Cigar smoke test performed (after I stopped puking), hooking up to several different vacuum ports and also hoses, not even a hint of a leak. I'm a bit worried this might be a false negative due to not doing all possible ports/hoses.

2 -- Harmonic balancer checked (see picture below.) The HB has three slots, 2 thin, and 1 thick, and the thick one is indicated with the Red Arrow in the picture. It seems to be in approximately the right place although is not exactly like the diagram.

3 -- I don't have a scan tool. Is this an Autozone / O'Reilly's rental item perchance??

4 -- Now I'm just taking a moment to complain. When I went to jack the car up I was STUNNED to see brake fluid on the right, rear inside tire. This is one of my professionally rebuilt calipers, with <100 miles of use. There are two points where a drop form to drip down onto the rim, then the tire. I'm going to ignore this for now.

Next I think I'll try the shop-vac leak test.
Raydar FEB 11, 07:37 PM
Yeah. High NOx is caused by high cylinder temperatures.
Does it ping at all? It's almost guaranteed that if it pings, it's not going to pass.
Ethanol (lots of it) is a good suggestion. It will cool off combustion temps. (I would suggest backing off the timing, but I think they check that for "on spec".) If your balancer ring has slipped (as above) it'll be impossible to time correctly.

Mine was failing due to a vacuum leak in the EGR circuit. In my case, it was at the rubber elbow that connects to the bottom of the throttle body. Check all the rubber vacuum fittings. They're very old now and can deteriorate, stretch, and leak.
sanderson231 FEB 12, 02:52 PM

quote
Originally posted by Notorio:

3 -- I don't have a scan tool. Is this an Autozone / O'Reilly's rental item perchance??




I pretty sure that they don't lend out scan tools. They will read codes if you bring the car to them but you need to see what the short term fuel trim (integrator) is doing as the engine runs. Without a scan tool the other option is to datalog it with a lap top (or maybe Android phone) and a program such as WinALDL (free donwloads available). There may be cheaper options but here is one for $55 that gets you the necessary ALDL to USB cable, the software and I would think phone support if necessary:

https://reddevilriver.com/aldl.html

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

[This message has been edited by sanderson231 (edited 02-13-2023).]

Kitskaboodle FEB 13, 06:41 PM
Oh my, this is soooooo familiar!
This could easily be my thread as my car has virtually the same problem. Even fails at low rpm on the rollers like his.
Three fyi’s:
The FieroStore used to sell an OBD1 scan tool but no more.
Unless I missed it, I didn’t see any talk here about the computer. (I replaced mine but no change)
I regularly Sea-Foam my car regularly- didn’t see any comments on this either.

Ok, I’ll shut up now cause I’m anxiously waiting for a fix to Notorio’s issue because I’m in the same exact boat.
Kit
P.S. Recently changed caliper? I can’t begin to tell you how many times I had brake fluid leaks at the banjo fitting on the caliper. If that is where the leak is, I can almost guarantee you it’s the copper / aluminum crush washers. (copper is better in my opinion) Anyways, always use NEW ones and make sure they are the proper size and diameter. Ones that fit snugly around the banjo bolt are your best bet.

[This message has been edited by Kitskaboodle (edited 02-13-2023).]

sanderson231 FEB 13, 06:58 PM

quote
Originally posted by Notorio:

4 -- Now I'm just taking a moment to complain. When I went to jack the car up I was STUNNED to see brake fluid on the right, rear inside tire. This is one of my professionally rebuilt calipers, with <100 miles of use. There are two points where a drop form to drip down onto the rim, then the tire. I'm going to ignore this for now.




There's a rubber seal under the parking brake lever. I'd try replacing that and putting some silicone grease on it.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

Notorio FEB 13, 07:43 PM

quote
Originally posted by sanderson231:

There's a rubber seal under the parking brake lever. I'd try replacing that and putting some silicone grease on it.




I'll check that out! It gives me hope I won't have to remove and ship back to the rebuilder

Kit, I am bummed to hear you are STILL failing smog. My registration is in the strange, Twilight Zone where it is 'incomplete,' which means even though a year has come and gone the DMV didn't send me out a registration form for 2023. So when I eventually go to the DMV (by the way, none of the ones in my area are accepting appointments now ) I will have fines. The on-line status shows my car as 'non-Op' but I paid a sh--load of money last year to get it back into active status.

Trying to catch up with suggestions: I should have mentioned that the fuel injectors were professionally serviced, although one died and had to be replaced (to solve a regular, misfire issue.)

Haven't attempted the shop-vac trial yet or using the EGR trouble-shooting table from the FSM. An issue is that I have the New Style of EGR that makes it impossible to SEE if the valve is actuating or not.

And thanks for the suggestion on the scan tool. Looks very useful and not too expensive.

[This message has been edited by Notorio (edited 02-13-2023).]

armos MAR 06, 07:53 PM
First a very basic test of the EGR valve itself - if you reach underneath it you can push up on the diaphragm and force it open. If you do that, the engine should stumble.
That doesn't tell you if vacuum is actually pulling it open in operation though.

Since you cleared (visual) inspection I guess you don't have a code 32 showing? I'm surprised - that's the notorious EGR trouble code that people usually get.
The EGR solenoid is notoriously failure prone, and I'm not sure the ECM can detect all of the solenoid's failure modes. I wonder if there's a good way to test the solenoid for functionality.
Unfortunately they are unique to the Fiero and CA is very inflexible about non-original parts, so the factory solenoid is too "special" and expensive to replace without a really solid diagnosis that it's needed.
There is an old thread here from BuddyCraigg about how to rebuild that solenoid, and might have also had some testing methods.


Retarding the timing should reduce N2O - but they check that to be within an allowed tolerance of factory spec.
If you get desperate, and are able to mess with tuning your own chip - if you retard the timing at the chip then it won't show up in an inspection. They don't plug into the ECM on an OBD1 era car.
Otherwise, you have a small amount of wiggle room to change the distributor timing. On my tests the spec was always +/- 3 degrees, but I remember people on here insisting it was 2 or something. Maybe it depends where you live. Your test report should say what the allowed tolerance is and where they think it was when they checked it. Unfortunately reading the timing on these cars seems to be pretty fuzzy and subjective due to parallax and poor visibility in general. I also had a shaky timing mark (maybe yours is better).
You could probably take 1 degree out at least without much chance of getting failed for it.

This is an awfully dumb idea: but if EGR isn't opening properly, I wonder if a controlled leak of EGR would work at all. Maybe there's a sweet spot where it will still idle, be driveable but also pass the test. Who knows where that would be, though. Too much EGR and the misfiring would cause higher unburned fuel (HC).

I don't think your new catalyst is an issue, and I doubt the imperfections of your idle are much of a factor either.
My car has always had an unsteadiness and occasional miss at idle. I think it's just the way these cars run, the ECM isn't good enough to idle any better than that. My catalyst was brand new in 2012 and it's HC and CO readings were near zero even though I heard it stumble very badly during the 2500rpm test. (there was a tuning issue with my non-original injectors that I had not yet figured out)
I was never tested for N2O though. I lived in a rural area so I took the "two speed idle" test which doesn't measure N2O. It was still passing (but not as easily) in 2020, still a bit unsteady and prone to sporadic misfire as it's always been.

[This message has been edited by armos (edited 03-06-2023).]