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maf prob?

February 20, 2010
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City, State
Michigan City IN
Year, Model & Trim Level
1994 exploerexlt
my 1994 explorer has had a miss for awhile. when i run a cylinder balance test it says #2 is dead. well last night i disconnected the maf sensor and ran the balance test again. with the maf unplugged the test passes, but with the maf plugged in cylinder #2 always fails. any ideas im lost. also no cel light is on, and it runs rougher with maf unplugged.

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Disconnect the fuel injector harness from the #2 cylinder and see if the idle of the engine changes (lower idle or becomes rougher). If nothing changes when you disconnect the injector then most likely you have a bad injector that's not opening. If the idle changes then the injector is probably OK.

Next, pull the plug from the #2 cylinder and look at it. If it looks good, pull a plug from another cylinder and if possible, switch plug wires also. Rerun the cylinder balance test and see if the dead cylinder follows the plug / wire. If so, then replace the plug and at a minimum check the resistance of the wire against another wire.

thanks for the reply. i have unplugged the injector before with no change in idle. also i have switched plugs and plug wires and it shows cyl #2 dead till i pull the maf sensor off then it passes? also that injector was ticking really loud for awhile and now it is quiet. i guess it could had went bad? but does it make sense that the cyl passes with maf unplugged? when im running cyl bal test with maf unplugged ther is black smoke coming out of exhaust like there is raw fuel getting poured in the exhaust. but it still passes? thank you

If unplugging the injector doesn't make the engine run any differently and it's quiet now, then the #2 injector probably needs to be replaced.

As to why it passes the cylinder balance test with the MAF sensor unplugged - I have no idea. The MAF measures the volume of incoming air and the PCM determines the pulse width of the injectors based on the reading from the MAF. It's possible that with the MAF unplugged the PCM goes into a "fail safe" mode and dumps a preset amount of fuel into all the cylinders.

my next question is, can i take that injector out without pulling the lower manifold off? the reason is i just changed it not to long ago. but if i have too then i will. thanks

The upper intake manifold and the fuel supply manifold both have to come off, but the lower intake manifold stays put.

SWEET..........Thank You VERY VERY MUCH Buddy

I am going to go way out on a limb here, but my guess is that if the MAF is unplugged and thus indicates a MAF fault to the PCM, the actual cyl balance test is not run when requested and you automatically get a result that will not indicate a fault. Just a theory.

i pulled the injecters today and found the cyl #2 injector completley plugged. cleaned them all off and it is running like a new truck. also passing the balance test....Thank You iron weasel

Welcome. Glad to hear you got it fixed. :)

one more question if i may, since i fixed the injector when it has sat overnight when i start her up she smokes for a bit then stops. but it does not smell like oil and i dont see water like it is burning off crankcase moisture. it does not smell like antifreeze either. smokes maybe 5 mins, not bad but i can see it when i am outside of the truck. no smoke i can see driving. never did it before so i was wondering since the cyl never worked till 2 or 3 days ago when i fixed it do you think that has something to do with it? it runs fine i am just curious. also it has royal purple 10w40 oil and a motorcraft filter. it never burnt oil and it is still full as of this morning with 1200 miles on the oil. i have a 300 mile trip tomorrow so i will check it before i leave and get back to see if it is using any now. also not losing coolant. your help appreciated. Thank You

What color is the smoke?

One possibility considering the previous injector issue is that the #2 injector is leaking fuel into the cylinder overnight and what you're seeing is the excess fuel being burned off.

If you have (or can get) a fuel pressure gauge with the appropriate adapter, you can check the fuel pressure after it's been sitting for a while. Key on, engine off should give you between 35psi - 45psi. Of course, this is all based on the injector being the issue.

It's also possible that the smoke could just be condensation (water) that's being passed out the exhaust and once the engine reaches operating temperature the condensation evaporates before coming out the tail pipe.

My wife is the first one in it in the morning, so i have only seen it when it was getting dark.(because i stay up all night lol) but after it sits for like 8 to 12 hrs it looks like it is white smoke to me. no real smell to it that i can tell. if it is cold out it will burn moisture off and drip water out of the exhaust. the weird thing now is it is about 80 degrees here at night and it does it, without the water as far as i can tell? Thank You

White is usually water and / or coolant. Water out of the exhaust is completely normal and shouldn't be a cause for concern. Since it only does it on startup and doesn't last more than a few minutes, I wouldn't worry too much about the white vapor as it's most likely just condensation / water.

If it becomes continuous, then you might want to start worrying about it since that's generally a sign of a leaking / blown head gasket or other internal engine problem that allows coolant into the cylinders.

Quick science lesson if you're interested in why water is normal: :D

Gasoline is made up of carbon chains of different lengths ranging from C7H16 through C11H24. Although gasoline contains many different chemical compounds, it is made up mostly of hydrocarbons, and all hydrocarbons form the same products when they are burned (just in different amounts). When a hydrocarbon is burned (that is, reacted with oxygen), it forms carbon dioxide (CO2) and water (H2O).

For our "average" gasoline of C8H18, the reaction is 2 molecules of octane reacting with 25 molecules of oxygen (O2) to form 18 molecules of water and 16 molecules of carbon dioxide. Of course, this reaction only occurs completely in an ideal world. In the real world, there is usually not quite enough oxygen available fast enough inside your car's engine to allow the reaction to occur completely, so there is also some carbon monoxide (CO) formed as well. In addition, since the oxygen is provided by bringing air into the engine, and since air consists mostly of nitrogen, some oxides of nitrogen (NOX) are formed as well. Finally, some of the trace elements in the gasoline (such as sulfur) can react to form small amounts of other pollutants, such as SO2.

So, to sum up, gasoline is a complicated mixture of hydrocarbons boiling between 120 and 400 degrees F, with chemical formulas between C6H14 and C12H26, but a good "average" compound is C8H18. These react in an ideal situation to produce carbon dioxide and water, but in an actual automobile engine they also produce some amount of undesirable compounds including carbon monoxide, oxides of nitrogen, and sulfur-containing compounds.

I just got back from a 700 mile trip. it ran great and the gas mileage is considderly better. also it is not smoking on start-up anymore? and the oil is full. just thought i would let you know and thanks again Weasel