Well, I'm still fighting the same super high hydrocarbon problem with my 1990 Bronco 5.0FI with AOD transmission. I've changed practically everything I can think of and still fails our state's emission test. We are allowed 220 hydrocarbon limit. At an idle I pass with a low of about 27. At a high idle (2500rpm) I started with 1439 (timing 15 BTDC) and have gone as high as 2300 (timing 10 BTDC). After changing SO many parts I finally put on a new "Y" pipe with new catalytic converter. I went back for testing and it was 1800 (timing 20 BTDC) HC level with the new converter. The truck runs sluggish and I have long suspected a worn camshaft so it make it run better I had the timing bumped up to 20 BTDC. I moved the timing all the way back down to 5 BTDC and lowed the HC level to 777, still three times too high. My theory is either a bad computer itself, or a bad camshaft and the computer just throws fuel at the problem. It's odd as usually you would have higher HC level at an idle and it goes down with higher RPM not way up. Although I've changed it previously I may buy yet another O2 sensor and try that. What would be the result of a disconnected O2 sensor? Would the computer think it was getting too much or too little air? What about an O2 sensor hooked up but not installed, just hanging there? How would the computer read this? Any suggestions, please. I hate to buy a computer for nothing and the weather isn't too pleasant for a camshaft change.

 

In ky you have a $200 limit to spend on fixing the problem. You get a waiver after spending the 200 trying to fix the problem. Is this offered in your state?

 

Just for the record,here in Maryland it's $450 and you get a 2 yr. waiver.I would think all states would have a system like that to avoid putting too much time/money in a vehicle to get it to pass emmissions test only to find out the repairs cost more than the vehicle is actually worth.( this of course does'nt apply to Ford trucks,they're priceless).

 

We do have a waiver here in Delaware as well but I'm not sure how much the minimum is. I think though to get the waiver you have to either take it to a "certified" emission expert or have them "sign" off on it, either of which is money for nothing. I've been fighting this running sluggish and poor fuel milage for awhile, now so I've been buying sensors, tune up parts, etc for so long I'm not sure how far back you can even use the receipts for. I've tried everything except a new cam and a new computer.

 

Do you get any codes from your ECU?

 

No codes. The last time I got any code was for a bad ECT sensor. I replaced it, still had the code and found it was a grounded wire. Since then no codes and it still runs sluggish. So far, from the last few months to today, I've replaced spark plugs, plug wires, dist cap, rotor, throttle position sensor, ECT sensor, O2 sensor, fuel pressure regulator, fuel injectors, upper plenum gasket, Y pipe with catalytic converter, throttle body is spotless and all throttle body gaskets replaced. This is not the original engine but my older spare 302 with 351 heads. It does not have the emission ports in the heads. BUT, it has gone thru our state emission test twice before and passed both times. I've replace so many parts because it started running sluggish and using a lot of fuel months ago and I've been chasing the problem ever since. I've replaced so many parts I probably missed a few telling you. My guess is either the cam or the computer or both. Does anyone know what happens if you disconnect the O2 sensor, or hook one up outside of the exhaust and just let it "sense" the outside air instead of the exhaust? Would it make it run leaner or richer? What about the distributor or coil? Could it giving it a weaker spark that would allow it to run but get worse with higher RPM's. I'm going nuts trying to solve this one.

 

Change your oil lately?
Your numbers sound too high for that to cure it. But it will help if the oil is wearing out and dirty. Synthetic oil may also help by not producing HC when it does leak past the rings and burn in the combustion chamber.

Disconnected O2 will cause the engine to stay in open loop. It won't try to correct the fuel mixture because it won't be receiving info from the O2. Will probably also set a code.

O2 sensor hanging in free air will make the ECU think your running extremely lean. It will try to correct the situation by adding fuel. Which will make HC go up.

Are you using a stock thermostat? Ideal engine temp for emissions is close to 200 degrees. Stock t-stat is probably 192 to 195. A lot of people put in 180 and 160 stats because they think they'll help performance. Whether or not that's true, it will certainly hurt emissions.

Problems with ignition components can cause HC to go up. That would include coil.

Check for vacuum leaks. Check PCV valve. Bad PCV valve could lead to oil in the intake and high HC.

Other possibilities include cam/lifters/valves/springs, timing chain streatching, ring problems.

I could easily be missing possibilities here.

Good luck.

 

I would try a new smog place.

 

Kameronth, we have to take it to the state's emission testing at our DMV lane. We don't have private testers like some states do so we can't shop around.
Cloim, I've not changed the oil lately but I don't think it could drop the HC level 2000 points. The thermostat is probably a little low but the last trip I put a piece of cardboard in front of the radiator and brought the temp up over the half way point on the gauge. I don't think it's the rings. It doesn't smoke at all and the compression, while not exactly race car material, is about 140 lbs overall. As for a vacuum leak, I put in new injectors a couple of months ago so the plenum gaskets were replaced. I shot carb cleaner all around the intake while running and could not hear any RPM change. I was only speculating on the O2 sensor to see what the results would be unhooked etc. I also have a 93 Bronco that I may swap the distributor, coil, or both from to see if there is any performance gain. I know the timing chain is a little slack but I've long suspected the cam itself. I just wondered if the computer would dump more fuel if the cam was worn. I've fought the sluggish and poor fuel economy problem for months, long before I went to the emission test so that's why I've changed so many parts for so long. About the only parts I've not changed are the cam (and chain), the computer itself, and the coil and distributor.

 

If the O2 sensor isnt in the exhaust stream it will never get hot enough to activate, if its unplugged computer should be able to comp for it would turn check engine light on after a drive. If the cam is that worn that it is affecting air flow into a basicly stock engine i would be pulling the whole motor and rebuild, with the 351 heads on a 302 you lowered the compression ratio right? Are you sure you are not getting a high speed miss in it, one cyl drops out your count will go sky high. How old is the engine, Someone correct me if i am wrong but ford changed the firing order for the 302 when they went fuel injection didnt they? dont know just a possibility.

 

Really? That is interesting, I have never heard of that. Around here there is a smog check at every corner. My dad used to have problems getting his truck to smog but then he became friends with the smog guy and put an end to that!

 

CamoBronc, you are correct in that the 351 heads lower the compression but the power loss is offset a little by the larger valves. I have the original engine on the stand for a rebuild but have so much going on I never get to it. This engine has been in the Bronco for several years and always passed the emission test before. It started running bad months ago and has gotten worse, that's why I put on so many other new parts, tune up, etc. Compression is about 140 overall. Not race engine material but sufficient enough for a daily driver. No smoke, no high speed miss. Just sluggish and poor fuel milage and now horrific HC level. Ford didn't change the firing order on 302's to 351W pattern until about 1995.

 

You didn't mention your EGR valve, checked that? Also a cam generally does not wear down evenly and if you have one wiped lobe you will have a cylinder that's marginally dropping out, hence sluggish as well as high HC. I'm thinking your original cam, timing chain suspicion is close to the mark. 20° BTDC is just way too much and if you can get away with that it points to your cam, again.
Tex

 

Tex94F250, I've tried running it with the EGR blocked off (solid gasket behind it) and it made no difference whatsoever in the way it ran. It is very sluggish from right off the line to higher RPM's. I just wasn't sure of just why a worn cam or chain would cause the high HC level. Today I swapped the coil from the 93 to the 90 and again, no difference. There is so much of a difference in power that when I drive the 93 Bronco (when I get it away from the old lady) it seems like it's supercharged compared to the 90.

 

As much as I had to reiterate, I think you're correct with the cam, sorry. As any cylinder drops out, the fuel will redistribute and the mess of laminar and turbulent flow in the intake system will just about kill performance. One runner is backing up and interfering with the flow of another if the opening duration is not adequate. If the exhaust duration is not adequate as well you get very uneven engine performance.
Tex