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Looks like this could be the end of the road for my F800

Bruce from Can.

Bruce from Can.

Well-known Member
Location
Woodville, Ontario, Canada
Can't get it to pass the emissions test, passes the high rpm test fine it is the low rpm test that is killing it. We have rebuilt the carb, and fooled with the timing, but it still kicks out to many Hydrocarbons . I am wondering if the in take manifold gasket could be the fault. Anyone have ideas ? Let's hear them. Bruce
 
Only really two causes, misfires or rich mixture. Intake leaks can make it lean so it misfires at light load, worth checking.
 
If it won't pass don't junk it plenty of places in the US with no emission tests to sell it.Here in Virginia emissions are only tested in a small area of the state and non tagged farm use vehicles are not tested anywhere and can run 75 miles from the farm with no state tags just has to have Farm Use on a tag or painted on the doors.
 
When you say low RPMs, do you mean at idle or just in the lower RPM range of operation?
Having high HCs at idle is usually a problem with the idle circuit. A leaking ecomiser valve can cause that problem. Intake manifold leaks will usually result in rough running - mainly at idle.
If you can get access to an exhaust analyzer, you can fine tune the idle circuit to reduce the HC emissions. It would also help to know what the CO level looks like.
 
Wouldn't an intake manifold leak cause a lean fuel mixture at idle? Your engine should have high vacuum at idle, that could suck oil past worn valve guides and worn rings at idle. There is probably a good reason for the high hydrocarbons, try to do some deeper diagnosis then decide if it's worth fixing.

I bought a used '86 Ford pickup with a 351 4V HO engine that I could not get to pass the emissions test in St Paul, MN. It also had high blow by for only 100,000 miles. I had a Ford dealer look at it and they could not fix it either. I assumed it had worn rings and worn cylinders. I should have done a vacuum test, compression test and a leak down test, but soon after that I moved out of the Metro area no longer needed to pass any emission tests. A year later the top of one of the pistons separated. When we pulled it apart, more of the pistons were cracked. I was told that was a symptom of over speeding.
 

Here in Spokane county WA if you can prove you spent xx amount of dollars trying to fix the problem they will give you a pass....anything like that where you are at?
 
what year?

Maybe put in a real hot thermostat, and lean mixture out as much.

I did not think you could get a carb to pass anything.
 
Ideas? Get rid of the tree huggers in your state and all will be fine. Or better yet, move away from them.
 
When did the rule change for farm trucks? I ran farm plates on the pickup until last year and never had to do a drive clean test.
 
Pick up trucks are exempt , all heavy trucks in Ontario must pass E-test and a safety inspection every year. Regardless if you have a Farm or commercial plate. Flat bed and livestock trailers also must pass annual inspectors as well. Real pain in the butt , and sure doesn't help to compete with farmers in other locations that don't have such draconian government rules to follow. I am sure fellas in NY or CA face the same over regulation. These trucks don't go many miles each year , and not far from home.
 
I would ask them for the report. The CO ( carbon monoxide) is the best indicator of what's going on. If CO and HC are both high it is a rich mixture. If HC is sky high with normal or low CO then its a lean misfire, which could be the intake manifold leak you mentioned , among other things.
 
It does depend on what they are looking for.

Advanced timing will lower CO, but raise NOx and vice versa.

Depends on what you value truck at, can put EFI on for less than $2K.
 
Did you try taking it put and running it hard for a hour or two? Sometimes they just need to be cleaned out.
 
Throttle plate sloppy, EGR valve restricted, vac hose leak. I would plug all the vac ports on the carb and manifold, check the throttle plate, and just replace the EGR valve. Test again, and if it's still bad, start sprizting carb cleaner around the top of the engine intake, and if the idle goes up, you've found your vac leak.
 
Along that same line of thinking, a leaky float can also cause a rich mixture. A leaky float can be easy to test when the carburetor is apart, but tough to diagnose on a running engine.
 
dunno if it would work for you or not, but i have a 72 corvette. it would not pass emmission. ended up re-jetting the carb to lean it out, hotter t-stat, and ran the fuel down to below 1/4 tank and refilled with e-85 fuel. went right through. after the test, filled the car with normal gas and drove the tank to near empty and then put regular fuel in it. the car is now exempt diue to age and no longer gets tested. may be worth a shot.
 
As stated it would help if we knew the CO and HC level.

A high CO is a rich mixture and will always lead back to problems in the carb.

A normal CO with a high HC is fuel that is not being burnt for some reason and is very seldom a carb problem.
Ignition system malfunction such as bad plugs or wires. Anything that will cause a miss.
A very lean fuel mixture that causes a misfire caused by vacuum leak in hose; intake or stuck open egr valve.
Low compression or timing to far advanced.

From what little info we have to go on it sounds like you have a miss at idle.
First thing I would do is replace all the vacuum hoses and spray starting fluid all around the intake looking for air leaking into the system causing a lean mixture. Also if the plugs and wires are old replace them.
 
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