I just bought a used 1991 F-350 with a 351ci (5.8L), C-6 auto trany and 105,000 miles. I took the Oregon DEQ emissions test and failed. The hydrocarbon max is 220 ppm. Mine had 505 ppm. The carbon monoxide max is 1%. Mine was 6.5308%. This vehicle has California emisions, if that helps any. After the test fail, I gave the engine a tune up. The plugs came out ok but did have fuel residue on them. The cap & rotor needed replacing, which I did. Ford recommends replacing the O2 sensor every 30,000 miles so I put a Bosch one in. The old one was very black. I checked the thermostat to find it came out in parts (about 4). Not sure how long it was running without one. Once I replaced it, the temp guage started working again. After doing all this, I noticed that the engine was running a lot better (no more jumpy idle and more power at higher speeds). Assuming everything was ok, I went to DEQ again. So much for ok. The hydrocarbon went down (from 505 to 415, but 220 is the max) but the carbon monoxide went up (from 6.5308 to 7.3266, Max is 1%). Also, the CO2, which did pass, has to be at least 6%. On the first test, it was 10.4%. On the second test, it was 9.8%. I bought a code reader since the "Check Engine" light came on at highway speeds. It gave me an all clear on relays with the Key On Engine Off. It then gave me a stored code of 173 (Chilton says "HEGO shows system always rich" & the code reader book says "HEGO (HO2S) sensor fault/rich". I followed the directions and ran the code reader with the engine on. The timing check was ok and the only code returned was 173 again. I checked all the vacuum lines and replaced a few but still get the same code. I just put some "CRC Guaranteed to Pass" fuel treatment in it and will run the tank dry to see if this helps but I would rather find the problem as it would probably save me some fuel. I also found a post about the Mass Air Flpow sensor being bad but according to my local parts store (CarQuest), I don't have one. Any help on this would be greatly appreciated. Thank you, gr

 

Check the fuel pressure regulator. Take the vacuum line off and check for fuel. If you have fuel then the diaphram inside is screwed and leaking fuel into the vacuum lines. It is about $70 and is quite simpre to change, 3 bolts and a vacuum line. Also check the ground on the 02 sensor as the 02 sensor switches between lean and rich as the computer requests it input and is not a running meter producing constant data. The ground could possibly be on the rear passenger side intake manifold bolt, as it was on my 88. To get to it requires removing the upper intake manifold, so i recommend sourcing that fuel pressure regulator first. Other than that, i couldnt tell ya. Good luck.

 

The fuel pressure regulator is another thing I found to check in other posts but I did not think it applied to this problem. The Chilton book is not very clear on this part but I will give it a go tomorrow. thank you for the reply, gr

 

I recently went through the same thing trying to get my 89 F-150 to pass Ontario emissions. Had to do a full tuneup, o2 sensor, throttle position sensor, egr position sensor and ran methol hydrate (alcohol) in the fuel and it barely passed. These are not easy trucks to make emissions legal once they get old, I'll tell you that. Try the methol hydrate, and retard the timing a little. Also, if you put smaller tires on the rear wheels, that can help. Just little tricks.

 

Remove the spout connector to retard the timing. It sounds like the vehicle is running real rich, or the ignition sytem is not performing properly. The numbers you are getting and fuel residue on the spark plugs support this. I think you are going to have to solve this problem first as the tricks will work , but my experience has been the engine has to be in a excellent running condition. neevav is right that it is not easy to get a pass on these older trucks. Standards in Ontario for the hcs on my 1988 - 5.0 are 90 ppm for hc's. Check your fuel pressure for a start. If it is real high it can cause the problems you are experiencing.

 

From My Understanding Here In Missouri F-350's Are Exempt From Emissions.sorry To Hear U Gotta Do It With Your 350

 

Thank you, Tdvjenson for the advice on the regulator. I checked the line and there was no fuel in it. As far as easy to replace, you must be joking. I have California emissions on this thing (if that is any different from a regular truck) but there are about 4 different dashpots and lines above the regulator that need to come off first. I am not sure I could put them back where they belong as my Chiltons does not have a picture of the engine compartment. I have a low pressure fuel gauge (10 PSI). The Chiltons recommends a 150 PSI gauge for this truck. The best price I could find for that gauge is $125.00. The Ford dealer will put it on their machine and gauges to diagnose it for $89.00. I see no other choice since my wife runs the checkbook. By the way, here are the readings from DEQ after running the fuel additive. The hydrocarbon max is 220 ppm. Mine had 379 ppm (down from 415). The carbon monoxide max is 1%. Mine was 8.6348 (up from 7.3266). I am not sure if I am going the right way or not so I hope the dealer can do a better job of finding out what is wrong then I can. I am scheduled to go into the dealer Friday morning so I will let you know what they find. Thank you all for your help, gr

 

This emission stuff can get frustrating. Hopefully the diagnostics will pick up the problem.Keep us posted.

 

Here is an update: My mechanic put a fuel pressure tester on the injector rail and said I have 95 PSI. Since Chiltons says it should be about 40 PSI, I think we found the reason it will not pass DEQ. My mechanic seems to think it is either the regulator or a check valve between the tanks but will not be able to check those for a few days as I need the truck. I will keep you posted. Thank you for all your help, gr

 

I bought a fuel pressure gauge at Sears for $30. Probably a little late for you, but at least you know where to get one now.

 

How long ago? I checked Sears here in Portland Oregon and they wanted $110.00 for a high pressure guage. The low pressure (10 PSI) guages run about $20.00 to $30.00 and I have one of those but I don't want to hook it up to this truck. I could just see myself on the evening news as I blow up the truck and house! Anyway, since the diag was cheaper than a new house and truck, I guess I did ok. gr

 

Maybe a year ago - and it's the high pressure gauge. I've used it several times on EFI trucks. It goes up to 150 psi I think.

 

150 PSI is what the one Sears has here so I guess the price went up lately. Oh well, a year late and a few dollard short---The story of my life, gr

 

Definately the fuel pressure is to high. That pressure will lead to problems with the 02 sensor and if left long enough can plug up the cat converter. I think a fuel pressure gauge can be purchased for around 30-40 dollars at some of the chain type auto parts stores. Could you buy the low pressure gauge and replace it with a high pressure gage. The gauges are about $12.00 or so. I use a gauge for testing pumbing systems without any issues. Make sure the return line fuel to the fuel tank is not pinched or collapsed. I had bought a used truck and the person who installed the new fuel tank pinched the fuel return line when installing it and created 100 psi problem for me.

 

Got me one of these so I can do it myself. Works fine. You have to purchase the tool to remove the fuel filter if you want to measure the pump pressure. I only check the fuel rail pressure.

Fuel pressure gauge