emission failure-NOX-'93 eldo

[hyarnell1]

I'm at my wits end. I cannot find the reason for my '93 eldo (4.9) flunking the States emission test for NOx.
HC and CO are fine; real fine, but the NOx is just out of spec. I've run it thru 5 times now (with repairs each time), and it comes out the same. Here's what I've done:
new cat
cleaned floor ports under throttle body (carboned up)
new vacuum hoses to egr valve and solinoid
new EGR solinoid (open coil)
EGR valve seems free (diaphram moves freely)
engine stumbles when egr diaphram is activated by hand, but does not stall.

Any ideas what I should look at next?

[caddydaddy]

Is the ignition timing correct? Are the plugs, wires, etc in good shape?

[hyarnell1]

Havn't checked timing, and since HC and CO were low, didn't suspect plugs or wires.

[maxwedge]

Originally Posted by hyarnell1

I'm at my wits end. I cannot find the reason for my '93 eldo (4.9) flunking the States emission test for NOx.
HC and CO are fine; real fine, but the NOx is just out of spec. I've run it thru 5 times now (with repairs each time), and it comes out the same. Here's what I've done:
new cat
cleaned floor ports under throttle body (carboned up)
new vacuum hoses to egr valve and solinoid
new EGR solinoid (open coil)
EGR valve seems free (diaphram moves freely)
engine stumbles when egr diaphram is activated by hand, but does not stall.

Any ideas what I should look at next?

I would really clean up the egr passges to assure full flow here, NOX is typically reduced by egr and or/cat efficiency also, yes timing and engine temps are critical too.

[DFBonnett]

[quote=hyarnell1]
EGR valve seems free (diaphragm moves freely)
QUOTE]

At this point the valve itself seems suspect. I'd do all the inspections and adjustments that Maxwedge suggests, particularly the timing. I'd then pull the EGR valve itself and inspect the pintle. While it's off, inspect the passages at that end for carbon deposits. In your place, and if the passages at the EGR end aren't too bad, I'd just replace the EGR at that time because it is such a PITA to remove and reinstall. Don't forget a new gasket. The old one is likely to come apart.
FWIW
YMMV

[hyarnell1]

Timing! Why didn't I think of that. In this day of distributorless ignition, you forget about timing. It'll be the first thing I'll look at if I can find my timing light.
Someone mentioned possible clogged exhaust ports to the EGR valve. The 4.9 doesn't have pass-thru exhaust passage thru the manifold (intake) like other cars; it just has one exhaust inlet for the EGR. The passage from the EGR valve to the floor ports under the throttle body are clear. My question is, what's at the head-intake junction gasket? Is it a square hole the shape of the port, or a small hole that's easily clogged?

[hyarnell1]

Well, I checked the timing. Spot on 10°. But that wasn't with pins A&B on the ALDL shorted, like you're supposed to, to check timing. Shorting A&B, and the timing jumped to 24°. Adjusted the distributor back to 10°. Getting to the holdown nut is a PITA.
Not sure this will do the trick, but I'll run it thru again and see what readings I'll get.

[caddydaddy]

Originally Posted by hyarnell1

Well, I checked the timing. Spot on 10°. But that wasn't with pins A&B on the ALDL shorted, like you're supposed to, to check timing. Shorting A&B, and the timing jumped to 24°.

The timing was at 24 degrees? Did it knock when it was at that setting?
Just an FYI, I run my 4.9 at 12 degrees, since the factory settings are on the low side to compensate for the occasional use of low octane gas. You can get a little more power at 12 degrees. If you do set it to 12 degrees, be sure to always use 93 octane.

[hyarnell1]

No, it did not knock. Good point. I would have thought it shoulda knocked. Premium fuel is always used. Retarding it didn't seem to affect performance, but with the ECM controlling timing, who knows what the 'real' timing is. Shorting terms A&B together, to set base timing, takes the ECM out of the picture, at least that's what I think.

[DFBonnett]

Something is wrong. Are you certain you were shorting A to B and that diagnostic mode was off?

[hyarnell1]

Pretty sure. The pins arn't easy to identify, so I went to the shop manual and determined which was A&B. The message center said SET TIMING, or something like that. Why do you think something's wrong?

[DFBonnett]

Hard to imagine that it would start, much less run reasonably well, with base timing advanced 14 deg above spec. It certainly seems that you set up the ALDL correctly in that the message came up on the DIC. It just seems backwards that the timing would show 10 deg unshorted and 24 deg shorted. This is a puzzler.

[hyarnell1]

Yea, that's what I thought. If by shorting A&B, you eliminate the ECM control and go to base timing (this case 24°), and then 10° with ECM control; does this mean the ECM can retard spark BELOW base timing? Ya know, I didn't check timing AFTER I removed the jumper.
I think I'm going to look into this a little further; when it quits raining...

[maxwedge]

See what the timing does by going into obd using the ac control panel, I believe that will set it to base, also reading the timing off the obd is only what the pcm is doing to the timing not an actual reading including the base.

[hyarnell1]

Now I'm confused. Engine running, idle,no diagnostics; timing seems to be 24°. Go into diagnostics, no change, 24°. Go into ECM DATA,PD08, and it shows 38°. Short A&B, and it's 10-12°. So what's my timing?