my '93 5.0 F-150 w/146,000 miles recently failed Ca. smog check. Since I had to go to a "test only" station the tech could only give me advise, but couldn't check out anything. Here's the information I have.

ASM Emisission Test Results

15 mph
HC (ppm) max 116, avg 35, meas 243 Failed
NO (ppm) max 992, avg 267, meas 738 high result, but passed.

25 mph
HC (ppm) max 93, avg 24, meas 93 result at max limit

Tech advise;
clean EGR port
check EGR selenoid

the EGR valve was operating, but was functioning properly according to the tech.

Replace the Oxygen Sensor.

Are these repairs that should be made based on the results given? Would the check engine light come on if either one were out or malfunctioning? The check engine light has not come on at all. Is there a way to test either one? Overall the truck runs very good. Any help would be greatly appreciated before I go dump $300 for unessesary replacement parts.

 

The HC indicates that the engine is running too rich, the catalytic converter is old and inefficient, or both.

The NO indicates an EGR system not completely up to snuff, excessively advanced ignition timing, or the engine is running too lean, or all three.

A tired, slow oxygen sensor could cause the engine to deviate too far in both directions from stoichiometric, which would result in a mix of high HC and high NO. The catalytic converter should be able to clean up the HC (a modern 3-way catalyst could clean the NO as well). But perhaps the catalyst is tired as well.

Cleaning and checking the EGR valve and port doesn't cost anything. Oxygen sensors don't cost very much, and yours should be replaced if it has more than 60000 miles on it -- you may see enough improvement in gas mileage to pay for the thing in a few weeks.

The technician gave you good advice. These are the cheap repair steps. You may need a new catalytic converter which is going to run to more money.

I'd suggest you also check your ignition timing and fuel pressure. Pull the vacuum hose off the fuel pressure regulator, cycle the key from off to on a few times, and check for any fuel appearing at the fuel pressure regulator vacuum port (indicates a failed regulator, which will cause rich running). Run a KOEO test and KOER test and see if the computer is flagging any codes. The "check engine" light is rarely lit on these trucks except in cases of overt and fairly severe failure, but the computer will flag codes in many cases of marginal operation.

 

Sounds like good advice!

 

fefarms thanks for the detailed reply.

I purchased both the egr valve (current is original from '93) and the o2 sensor (old one has 50k miles on it) from Ford. I'll replace the 02 sensor, but should I just go ahead and replace the egr valve with the new one since I have it or clean the old one & see how it does?

Went the muffler shop down the steet that installed my 3" exhaust 2-3 yrs ago (including new cat) and they said the cat was bad. They were going to do a back presure test & temperature, but before they did that the tech hit the cat with his hand and it rattled. Based on that he said the cat was bad.

I haven't done the KOEO or KOER test yet. I wanted to check the timing but could not find the "single wire SPOUT" to unplug. I have a 5.0 EEC TFI, any ideas where it is?

My fuel regulator and fuel pressure were checked out in Nov. '04 due to some intermintent stalling and both were good.

 

If the cat rattles when you bang on it, make sure it isn't the external heat shields that are rattling. If the rattles are definitely coming from inside the cat, the "bed" inside it has failed and the cat is junk. This would cause your HC levels to be close to the test limit with a perfectly running engine, and over the limit with a typical high-miles older truck. This may be the bulk of your problem right here.

You will have to remove the old EGR valve to put in a new one. Be careful not to damage the old one -- the down-pipe connecting the exhaust manifold to the valve is often rusted pretty tight. If you can get it off, I would stop there with a quick clean and inspection. Look particularly at the pathway from the down-pipe to the plenum. See if the diaphragm holds vaccuum, the pintle moves, etc. Your old valve/EVP are probably good if the computer is not setting codes. The passages can get blocked with carbon, and the computer cannot detect this, which is why you want to do the clean and inspect bit. A restriction on EGR flow may be causing your high NOx readings.

Keep the replacement EGR valve "new in box", and return it if you can't see anything wrong with the old one. The oxygen sensor is your choice, 50K miles is within its expected useable lifetime and you could keep using the old one. But now that you have it, it may be less hassle to install than to return.

 

About your SPOUT question.Located your TFI/ICM harness.Now there should be a single wire connector going into this wire bundle.The figure I have shows it near the oil filter.But on mine(95 F-150 351W)its near the coil pack.This is usually a yellow wire coming off of the distributor connector.
If you still can't find it find the TFI module.It should have a six pin connector on the end and 3 blade terminals on the top.Looking at it with the blades up and connector to the right.The SPOUT wire is the terminal 2(second down from the top ). I looked at the wiring diagram in Haynes manual and it says its a pink wire going from you ignition control module to the PCM.Good luck with your problem.

 

see my original post for the specifics, but those of you who replied are up to speed.

Between rain storms here in southern ca. I managed to get the following done.

Checked the timing (SPOUT removed) It was at about 14 BTC and is now set at 10 BTC, idle speed between 710-730 rpm. Could this cause it to run rich? Don't know if it was actually running rich.

"The NO indicates an EGR system not completely up to snuff, excessively advanced ignition timing, or the engine is running too lean, or all three." from fefarms


Ran KOEO & KOER test and both had codes of 111, no problems.

So, back to the EGR valve and O2 sensor. Would I have gotten codes if there were problems with them?

Still need to replace cat. Haven't checked the EGR valve yet.

Should I replace the cat and O2 sensor and retest for smog at this point? Only $15 for the retest.

 

The KOER test will exercise the system enough to do some basic tests of the EGR valve and the O2 sensor. Since the test passes, you know they are not completely dead. On this design, the computer cannot tell whether exhaust actually enters the plenum or not; just that the EGR vavle appears to be opening. If the passage is blocked or partially blocked with carbon, no (or less) exhaust gas will enter. That's why it can be worthwhile to remove the valve and clean the passages behind it, even with no codes set.

The advanced timing may have contributed to the NOx levels. It would not have affected the mixture ratio (and HC) one way or the other.

If the catalytic converter rattles internally when you bang on it, it needs to be replaced. If you do replace it, the smog test will almost certainly pass.