'88 F150 5.8L 4x4


Entire exhaust from the manifolds back replaced 2 years ago. The last two years it has passed with flying colors.

It failed today.

HC standard is 220. It read 1879 at high speed and 543 at low speed.
CO standard is 1.20. It read 2.69 at high speed.

Passed all other readings.

Any suggestions?

 

First thing to do is pull the codes. It *may* point you in the right direction.

It sounds like it's burning too much fuel. How's the gas mileage? Is it down from the last time it was tested? Is it running cold maybe? Stuck thermostat? What temp is the t-stat in it rated to open at? 195 is stock, if it's anything else I'd change it.

 

If you have passed the previous years and your hc are at 1879 something has failed. Is the air pump ok,check to make sure the connection to the cat converter hasnt come off. Its usually noisy if that happens but worth looking at. Check your fuel pressure, is the air filter plugged up, spark plugs are ok. For some reason there is a lot of unburned fuel going out the tailpipe.Was the cat converter damaged at some point. With the high co check your O2 sensor.These are some things you can have a look at.

 

Gonna tune it up next weekend and see where that gets me.

 

After a tune up I failed again. Here are the readings.

High RPM
HC standard 220 current 1692
CO standard 1.2 current 2.65

Low RMP
HC standard 220 current 746
CO standard 1.2 currnet 1.8

High RPM numbers slightly lower, but Low RPM numbers considerably WORSE.

????????????

 

Check your codes. You may have a bad EVP or EGR. I had very high HC readings this year, pulled a bad EVP code, replaced the EVP and tested fine. I think the computer tried to compensate for a bad EVP/EGR causing it to run rich. Also, replace your PCV for a few bucks.

 

What does EVP stand for?

 

when you say tune up what did you do?

 

I was going to ask the same thing. Did you have a look at the O2 sensor. I had a look at my previous 4 emission tests. The highest hc that I had was 226 ppm. Our standard now to pass on the dyno is is 90 ppm(hc) and at idle 200 ppm(hc). My latest test results on the dyno were 51 ppm(hc) and at idle 55(hc). When I checked the other tests the idle and dyno test (which is about 35 miles per hour ) the results were close regardless of a pass or fail.In your case your high rpm test is way up there along with your low rpm and the spread is fairly high . Something is not allowing for complete combustion or there is much more fuel entering the system than it can handle for these high numbers. I would check fuel pressure, O2 sensor,air pump and controls,fuel injectors, is the intake all caked up with carbon, for a start. If you are not getting any codes it is a matter of checking out the components. Dont replace parts for nothing .You can waste a lot of money and still not get to the root of the problem. Another thing to consider is does the testing agency that you are going recalibrate there equipment on a regular basis.Is it worth it to try a different place. There has been cases here where people have failed at one shop and driven to another the same day and get a pass. Keep us posted.

 

I tried to edit but couldnt . I forgot to add check for vacuum leaks also.

 

Tune up consisted of plugs, wires, cap, rotor.

I think I'm just gonna take it in and get it diagnosed instead of throwing parts at it.

I'm gonna check the o2 sensor before I do that, but it might be a while. Football has just started and coaching is 7 days a week for the next 3 - 4 months.

 

EVP is EGR Valve Position sensor, mounted on top of the EGR. Before you buy parts, check your codes. Go to Autozone and get them checked for free, or you can buy a code reader for $35.

 

I am in Texas, and have never had any emesions checks. When did they start checking emesions????

 

Depends on the county you live in. Not all counties in Texas check emissions.

 

replace air cleaner, clean throttle body, check timing.

what brand cap/rotor/wires/plugs?

if not motorcraft they should be a brand name.

you did not put in bosch platinum anything i hope.

change oil and filter also, dirty oil does not help smog test.

what kind of cats do you have?

is exhaust clogged?