Engine missing/hesitating....

[muleskinner]

A friend of mine has a 92' festiva and it keeps missing or hesitating like it wants to die on him. He will shut off the engine and start it up, then it will be fine for a while. He has replaced all the seals and gaskets on the engine & the Vane meter has been replaced with another used one. Has new points and condenser, spark plugs, fuel filter, & replaced the hose that is known to choke off gas ..... & it still has that problem.

He doesn't get on the computer, so I am asking this question for him.

I have searched for this question and nothing comes up! I thought this would be a popular question.

[bravekozak]

Check computer codes first.

[nonamekid]

...Has new points and condenser...

If it is a '92, and he replaced the points and condenser, that might be the problem. There are no points or condenser: maybe it was the cap and rotor? All joking aside, when it is running fine does it drive fine also? When it is missing and hesitating, is it driveable? Does it only happen at idle, or through the complete RPM range? How old are the plug wires? Does it happen on dry days and on humid/rainy days? Does the engine leak or burn oil?

[Movin]

The hesitation miss can have a lot of causes but if you use the shut off and restart phenomenon
that gives a good place to start.

One thing restarting does is to restart the computer in open loop. One sensor that is ignored during this time is the O2 sensor and learned data that the computer compiles from the O2 sensor is ignored as well. When the computer goes back to closed loop the problems are back.

The second thing that happens is any silt clogging the fuel filter or pump screen falls away on the bottom side. This will give good fuel pressure for a short time after restart.

There electronic and ignition possibilities, dirty injector possibilities etc. but you mentioned the restart thing...

You also mentioned the hose that is a carburetor problem so that leaves us wondering how accurate the info is?

[TominMO]

I had a similar problem coming back from the recent Indy meet. Turned out to be corrosion inside the coil, where the coil-to-disty wire is inserted. One more thing to check.

[muleskinner]

If it is a '92, and he replaced the points and condenser, that might be the problem. There are no points or condenser: maybe it was the cap and rotor? All joking aside, when it is running fine does it drive fine also? When it is missing and hesitating, is it driveable? Does it only happen at idle, or through the complete RPM range? How old are the plug wires? Does it happen on dry days and on humid/rainy days? Does the engine leak or burn oil?

He would just be driving along and it would start missing, hesitating, lose power all of a sudden. He would shut the engine down and start it right back up while still rolling and it would be fine for a while.
Plug wires are new.
It happens during any weather conditions.

[muleskinner]

The hesitation miss can have a lot of causes but if you use the shut off and restart phenomenon
that gives a good place to start.

One thing restarting does is to restart the computer in open loop. One sensor that is ignored during this time is the O2 sensor and learned data that the computer compiles from the O2 sensor is ignored as well. When the computer goes back to closed loop the problems are back.

The second thing that happens is any silt clogging the fuel filter or pump screen falls away on the bottom side. This will give good fuel pressure for a short time after restart.

There electronic and ignition possibilities, dirty injector possibilities etc. but you mentioned the restart thing...

You also mentioned the hose that is a carburetor problem so that leaves us wondering how accurate the info is?

My mistake on the hose thing. I told him awhile ago that could be the problem & he said he replaced a hose, but obviously that wasn't it. lol!

[scitzz]

Another vote on fuel. You may recall,last madness, Geneva Dirt had the almost exact same problem, and it turned out to be the fuel filter. If it has the original fuel filter, replace that on general principles anyway.

Running around outside the asylum again with my tappy talky appy

[muleskinner]

I will have him look into the 02 sensor & the fuel filter....

[bhearts]

The hesitation miss can have a lot of causes but if you use the shut off and restart phenomenon
that gives a good place to start.

One thing restarting does is to restart the computer in open loop. One sensor that is ignored during this time is the O2 sensor and learned data that the computer compiles from the O2 sensor is ignored as well. When the computer goes back to closed loop the problems are back.

The second thing that happens is any silt clogging the fuel filter or pump screen falls away on the bottom side. This will give good fuel pressure for a short time after restart.

There electronic and ignition possibilities, dirty injector possibilities etc. but you mentioned the restart thing...

You also mentioned the hose that is a carburetor problem so that leaves us wondering how accurate the info is?

Brilliant problem solving

[bhearts]

If it could have to deal with open loop, you could always just unplug the o2 sensor. Then it can never get into closed loop

[jayber]

O2 sensor wont cause it to shut off. Is suspect the fuel supply or spark.

[Movin]

it only hesitates, he turns it off.

[WmWatt]

If O2 sensor is not sending valid voltages the computer should sense that, set a code, turn on the check engine light, and go into loop back mode. At least that's what I've read for OBD II standard. If it's missing and hesitating it wouldn't hurt to wipe down the ignition wires and check the ends where they go to the plugs and into the cap and coil (as mentioned above re coil). I think you said new distributor cap? If not give it a good wipe. Also would not hurt to check spark plug gap, even if they are new. I set mine to 40. No cost to do any of the above and might clear up the problem.

[Movin]

Apparently it is still running good enough that the computer is happy with the info from the sensor. No mention was made of the check engine light . Even brand new sensors can be off enough to affect fuel mileage. Some brands come to mind. As long as the sensor is putting out data with in a certain window the computer will use the data and go into closed loop. Unplugging the sensor and the battery for a bit will put the computer in open loop with factory base line data. It should run better if the sensor is the problem.

Engine wear, bad weather, altitude all are things that cause the computer to make learned corrections to run good. The O2 is the best part of learned corrections when it is working right. It should run better, not great, but better. If there is no change really then there is a whole bunch of stuff to check and look at. Restricted fuel etc. By now you have already checked the tune up stuff with no change? Second hand communications can really send one on a goose chase.