Rough cold idle and really really rich... Help?

[Yuk]

My '92 Sentra has a really rough cold idle and blows enough rich black smoke to impersonate a coal fired locomotive. I've changed the thermostat, radiator temp. switch, PCV valve, O2 sensor, distributor, rotor and cap, spark plugs, ignition wires, air filter and checked the timing. The air/fuel mixture can not be adjusted and I'm stumped.

Can anyone help?

 

[brianl703]

If I had to take a wild guess, I'd guess that the coolant temperature sensor is telling the computer that the engine is much colder than it really is, causing it to richen the mixture too much.

I have no idea what the radiator temp switch is. Perhaps it's to turn the electric cooling fans on? I certainly wouldn't expect a switch--a binary device with two states--to convey enough information to the computer about the engine temperature coolant for accurate mixture control. So I'd look for another sensor, one that changes resistance according to the coolant temperature.

 

[55Test]

Did you unhook the battery for 15 minutes or so after you replaced the sensors so the ECU can relearn the functions on the new sensors?

 

[mechtech]

Carbureted? Stuck power valve, floats bad.
Catalytic converter may be toast.

 

[Gary Allan]

Injectors do degrade. What I'm looking for is for you to say that, once warm, it runs totally fine and delivers stellar long trip mileage. If that is the case, then I'd say that your PCM cannot narrow/shorten the pulse width enough for cold start/low speed conditions due to leakage perhaps

. Your MAP could have something to do with this as well ..since it's about the only thing you haven't changed and it is the primary input for fuel curve in open loop.

 

[jorton]

Wifes 92 Sentra was hard to start until finally it wouldn't start period. Had it towed to an independant shop.

The mechanic said he traced the problem to a bad (coolant?)temp sensor wire and he repaired that. He also replaced the fuel fouled spark plugs with NGK.

If you are using Champion plugs, NGK may solve your problem.

Joe

 

[Yuk]

quote:

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I have no idea what the radiator temp switch is. Perhaps it's to turn the electric cooling fans on?

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Sorry... I should have said coolant temperature switch. And yes, it does control the electric cooling fans.

quote:

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What I'm looking for is for you to say that, once warm, it runs totally fine and delivers stellar long trip mileage.

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Well it hiccups and coughs until warm, and then the idle smoothes out a lot. The idle isn't perfect when warm, but it sure is a lot better. She still smokes when warm though. As far as mileage goes, she hasn't been on the highway since I changed the distributor, rotor and cap last week, so I can't give an opinion on " stellar long trip mileage".

BTW, This engine is a fuel injected E16i.

I’m sure the valve lash needs to be adjusted, could this be causing the problems?

 

[Yuk]

Ok, now I'm going nuts

. I reset the timing tonight to around 7 degrees BTDC and rechecked it again after about half an hour of idling. It was all over the map, fluctuating from about 5 degrees past to 10 degrees BTDC! What would cause the timing not to stay put? I have no reason to believe that this replacement distributor is bad, so what is?

Also, am I correct in assuming that when attached to a properly firing engine, the timing light would be emitting a steady strobe effect? If so, than all four cylinders are missing. What do I do now, change the coil or ecu? Or do I just concede defeat and pay a mechanic?

 

[mechtech]

Is there mechanical or vacuum advance, or is it controlled by the computer?

 

[Gary Allan]

quote:

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What would cause the timing not to stay put?

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Well, you can easily check for shaft play in the distributor ..but with a trigger type distributor you probably can't have the timing (dwell) side effects that you could with point type distributors.

Do you have a timing chain?? This would wreak havoc with your computer controlled timing.

 

[Yuk]

quote:

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Is there mechanical or vacuum advance, or is it controlled by the computer?

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The manuals I have do not speak of mechanical or vacuum advance, so I'm assuming it's computer controlled.

Gary,

I have felt no play in this distributor, and it functioned very well on the other Sentra I scavenged it from.

This Sentra engine uses a belt, not a chain. Can driving with the ignition timing out for a couple of days cause the valve timing to slip?

 

[brianl703]

If the timing is computer controlled there is usually a jumper or connection that must be broken in order to correctly set the timing.

This jumper breaks the communication between the computer and the ignition module so that the timing reverts to base timing.

Otherwise, what you'll read is base + computer commanded advance. Not real useful for setting the timing since the computer commanded advance changes according to current engine operating conditions!

 

[mechtech]

Having the ignition timig off will have no effect on the cam timing.
A loose, floppy timing belt will affect your ignition timing however, as the dist. is run off the cam.
Electronically controlled ignitions can't be checked without the proper procedure - some variance is normal at idle. Like said above^^ there is usually a jumper to connect or disconnect.