rockin ronnie

Hi all, I am new to teh forum and from what I have seen there are a lot of very knowledgable folks on this forum. I have read many of the threads that may relate to my problem but it somehow appears a little different.

Last week I bought a 91 Stanza with 297,000 K on it. When I looked at it, and bought it, it ran like a TOP.

I am hoping that I can explain this with all the info needed that someone can help me make a diagnosis.

While on the highway with Cruise and Air on I noticed that, at random times, the engine would almost seem to stall ever so briefly before coming to life again. When this happens the speed and the Tach don't fluctate in the least bit and no warning lights appear. During the trip, one of the kids had to "GO" so when I pulled over and the wife took the kids in, the idle suddenly increased dropped back down and now it doesn't want to idle it wants to stall when not on load.

Today while it started fine and ran good for a while the warmer it got the rougher it ran. Shifting to neutral and revving it and letting it drop, it is now blowing black smoke.

At first I thought it might be a fuel pump but now I am not convinced that that is my problem at all and it may be something more serious.

I am going to read through the rest of the forums but if anyone has some suggestions to start looking I would appreciate any ideas or thoughts.

 

rockin ronnie

Good day all, could the sputtering have been caused by low fluid levels? I checked the Distributor Cap, doesn't appear to be any problems with it, but when I looked at the radiator reservoir it was just below the low markings?

I topped up the reservoir and it appearsto have remedied the situation.

Can anyone tell me if these engines run really bad in hot temperatures or when they get hot?

Lastly, I get better gas mileage in my pathfinder than I do in the much smaller Stanza? The car does run really smooth so teh mileage reallu surprises me?

Stumped in Saskatoon

Thanks for all the anticipated HELP!!!!

de2r

Smoke color: Blue = oil, White = coolant, Black = gas

I would pull your plugs and check for signs of unburned fuel. They should be a nice tan color - and dry. If they're black and wet ... you got issues. Report your findings and we can go from there.

__________________
de2r

rockin ronnie

Smoke color was black.

I will pull the plugs and have a peak and let you know.

Thanks

rockin ronnie

OK, finally had a chance to check the plugs, they look like they are brand new, nice and clean.

Since I filled teh reservoire the car has been running just like the day I bought it. I really think that it was running hot which caused itto run so rough.

What confuses me is teh poor gas mileage, especially now.

Thanks for your help,

Ron

 

Multimillion

What kind of mileage are you getting? My multi gets ~10L/100km in the city and I don't really know on the highway since I don't drive too far.

rockin ronnie

That sounds like approximatley 600K to a full tank of fuel in the city?

I couldn't tell you exactly what I am getting, I've only had teh car a short time but it seems to be getting roughly 400K city and highway driving. I would have thought it would give me a lot better mileage than that.

Maybe I'm expecting a little much???

Thanks

ron

bradw

Try putting a new oxygen sensor in. When that goes bad the computer dumps in to much fuel.

Macc

Since you think adding coolant solved the problem here is what might have happend. If the car runs good when it is cool, and gets worse as it warms up then it could be a problem with the coolant temperature sensor. When you first start your car its in "open loop" and the ECU monitors the coolant temperature (during this time the car runs at a higher idle). When the temperature reaches a certain point the computer goes into "closed loop" and the idle decreases. If there is a problem with the coolant temperature sensor it will cause the engine to hunt for the correct rpm. One example of this is if the sensor develops an air pocket around it. If this happens the sensor gives an inaccurate reading. This could explain why your problem stopped when you added coolant.
Furthermore, as the coolant temperature increases, the sensor's resistance decreases and results in a corresponding voltage decrease. If the resistance of the sensor is higher than expected (say for example due to corroded contacts on the sensor) this will make the ECU think the engine is colder than it actually is and the ECU will supply more fuel than is really needed (this could explain the black smoke and running rough and poor gas mileage). The same effect will be seen if there is a poor conductivity anywhere along the sensor's electrical path. This will result in higher resistance and cause the sensor to give the ECU an inaccurate reading. Therefore, if you continue to experience the problem trace out the circuit and make sure it is clean and sound. In addition, it is possible the sensor itself is starting to go out. Often when they start to go bad it (like many other sensors) will act up here and there.

Like someone else posted the bad mileage could be due to a problem with the O2 sensor. A faulty O2 sensor will cause some hunting, but generally the ECU reverts to a limp mode that over fuels just to make sure. The O2 sensor is more for idle and low rpm monitoring and doesn't have as much to do at cruising speed. Some of the symptoms are: (1) excess fuel consumption (2) car chokes and/or stalls (3) rpms fluctuate (4) exhaust smells like rotten eggs/gas. But, don't just assume the sensor is bad. It could be the wiring, corroded contacts, or a faulty relay causing it to give an inaccurate reading.

Two other thoughts that could cause poor mileage and poor performance are a faulty fuel pressure regulator or possibly a leaking fuel injector. Either one can damage an o2 sensor and the catalytic converter. Good Luck!

Kurt

I'm with Macc on this one. He's been reading his FSM I see...