i just went to have my emissions done. I didn't expect to pass as it's been running rich for a while. I have an exhaust leak at the pass side manifold somewhere. But would that make my hydro carbon and carbon monoxide be really high? The engine was replaced last summer. The senors seem to be all good. Not throwing any codes.

 

I don't see how an exhaust leak could cause an engine to run too rich. That is almost always a fuel / air delivery problem. If your engine has a carb on it, it is either sending more fuel or less air to the engine than it needs. More fuel is the likely culprit.

I don't know about fuel injection but it could be doing the same thing. With FI, that could be a computer problem.

With a carb, it is likely to be either an adjustment or a mechanical problem. Check and see if the choke is working. It may be that the choke does not turn off when the engine is warm and it should do that. The butterfly valve at the top of the carb should be shut when choking the engine and it should open as the engine warms. Does it? Choking a warm engine will always make it run rich. The plugs will be fouled with carbon and you may see some black smoke come out the tail pipe when you rev the engine.

I've seen vacuum leaks in the area of the carb or intake manifold cause an engine to run rich. Is it possible that your engine has a cracked or missing vacuum hose?

If your engine has a carb, is it tightly bolted to the intake manifold? If so, then it either needs a new gasket, an adjustment, or perhaps rebuilding. If a rebuild does not fix this problem, then you may need a remanufactured
or even a new carb.

A leaking carb gasket can usually be heard if you start the engine, put the end of a piece of rubber tubing very close to your ear, and hunt for vacuum leaks with the other end.

One other thought on the emissions. Does this vehicle have a catalytic converter? If so, it may need replacing.

Ed

 

it's a fuel injected engine. i do have som cracked/missing vacum hoses. how do i go about getting new ones? just go to Pep boys and get some Vacum hose and just plug it in. the hose i have on the truck now is old and incredibly brittle. i'd have to run complete new hose. anyone know what size vacum hose that is?

 

The only way I know is to measure the hoses you have, write down the internal and external diameters and then go to an auto parts store for replacements. Depending on how much you need, it should be possible to buy several feet of each of 2-3 sizes and then cut them to whatever lengths you need. Most auto parts stores should have hose of this type in bulk reels, so you can peel off what you need and buy it by the foot. Replacing old vacuum hoses is easy but a little time consuming.

It's the missing hoses that are a royal pain in the rear. I'm sure that there are diagrams that show the vacuum system but I don't know off-hand where they would be found. My 1st guess would be in a manual, such as a Chilton's, Haynes, or a factory shop manual.

When replacing the hoses, make sure that the hose barbs are thoroughly cleaned before putting the new hoses on. I use a rag, some mineral spirits, and maybe a little fine steel wool to remove any junk from the barb. That way, you will get a good seal between the barb and the new hose. A real thin film of petroleum jelly can be useful in getting the hose onto the barb if it is extra tight. Use your thumb and forefinger to apply a super-thin film. Be careful not to get any of the scrapings into the barb or the new hose.

Ed

 

if you exhaust leak is before the O2 sensor it will cause you to run rich cause it throws off the reading at the O2 sensor because it's not getting the full exhaust gasses. then the ECU tries to compensate for this by throwing more fuel at it. I learned this when I had my truck datalogged and we could watch the ECU throwing more fuel at the side that had the exhaust leak




Jim

 

So the O2 sensor somehow measures the volume of exhaust gas? It would have to since a leak should only affect the amount of exhaust gas present and not the concentrations of unburned fuel or O2. Interesting stuff. I had not considered the O2 sensor, thinking that it only measured the concentration of O2 present. Thanks for the info.

Ed

 

the O2 sensor is brand new, like 3000 miles. taisa said makes sense. i guess i'm ordering some headers. any suggestions on brand. what type of gasket? Thanks

Keith