Engine runs louder once its warmed up

[krbballer]

My 88L, 4speed, carb'd runs very well when you first start it. The engine is very quiet, and the idle seems perfect. However, after driving it for 3-4 mins or until the temp guage gets to normal temperature, the idle seems to increase and the car is a lot louder.

The engine doesn't sputter/hesitate or misfire, its just louder with a higher idle. I don't know the numbers because my car doesnt have a tach. Any ideas?

[25Horseplay]

Is it a louder ticking noise? This year Festiva has solid lifters and as the engine warms up the oil thins out and the lifter noise seems to be a little louder.

[krbballer]

Its not really a ticking noise, the engine is just louder and the rpms seem higher. The difference in noise between the car running cold and the car running hot is the car sounds quiet and new when cold, and loud and old once warmed up. When its louder, the idle doesnt vary, it doesnt sputter, its just louder.

[ejp2fast]

does it have a tach? by how much is the rpm's increasing?

[krbballer]

No tach. I'm not even sure if louder is the right word. It just doesnt run the same. Cold its nice, hot it seems like im driving a crappy car. Louder like a small hole in the muffler louder.

[jglutz]

1st) check the coolant level.....maybe after the t'stat opens the water pump is creating havoc.

2nd) not so good....rod bearing slipped....this will be a loud 'knocking sound. I'm surprised that it would not show up at idle.

[JPT]

Is the car using water? I had a Buick that acted like that. Ran nice when cool, but after a long run down the highway it just didn't run the same. It was louder and sluggish. It was always low on coolant too. I checked for leaks, found and fixed a few, but it still did it. A couple of months after it started doing this it died of a massive head gasket failure.

[FestYboy]

guys, listen to what the symptoms are and when they occur...
idle increases after warmup, and ONLY after warmup. this indicates a gasket issue where when the head is cold, the seals are tight, but once warm, there is either an intake gasket/vac leak, or an exhaust gasket leak (or a little of both).

once warmed up, spray intake gasket area with ether, and also look for carbon traces at the exhaust manifold gasket.

[WmWatt]

Some other things which kick in after the engine warms up are the O2 sensor and the computer. While the engine is warming up the timing is controlled mechanically by the vacuum and centrafuge(?) inside the distributor. The ignition control module inside the distributor has separate circuits for idle, load, cold, and warm. If it's an ignition timing symptom I think any of the above would be suspect.

[FB71]

Some other things which kick in after the engine warms up are the O2 sensor and the computer. While the engine is warming up the timing is controlled mechanically by the vacuum and centrafuge(?) inside the distributor. The ignition control module inside the distributor has separate circuits for idle, load, cold, and warm. If it's an ignition timing symptom I think any of the above would be suspect.

huh? no... not really. The PCM controls all aspects of timing in an EFI car. Carbed (and '89 auto EFI) car timing is controlled bymechanical and vacuum advance, with 2 deg of retard triggered by the PCM at higher elevations (triggered by BP or barometric pressure sensor). In an EFI car, the module in the dizzy only detects cylinder position and broadcasts that info to the PCM. The PM determines the advance curve, and triggers the coil thru a large driver transistor mounted externally, next to the coil. The O2 sensor just provides feedback about fuel/air ratio, and has no influence on timing at all.

[WmWatt]

FB71 is right about the air/fuel mixture but the computer also advances the timing which makes the engine run faster. That might be what krbballer is hearing. Before the O2 sensor warms up the timing advance is controlled by the vacuum hose and centrifical weights in the distributor. After the O2 sensor warms up it is controlled by the computer. The computer gets it's timing input from the ignition control module, in the distributor in carburetted models.

The Haynes manual has a wiring diagram for the computer. Along the bottom are the inputs (sensors). Along the top are the outputs (actuators, aka servo-mechanisms). I found most of them and pencilled in their names and locations on the diagram, which just goes to show retired guys have 'way too much time on their hands.

[FB71]

FB71 is right about the air/fuel mixture but the computer also advances the timing which makes the engine run faster. That might be what krbballer is hearing. Before the O2 sensor warms up the timing advance is controlled by the vacuum hose and centrifical weights in the distributor. After the O2 sensor warms up it is controlled by the computer. The computer gets it's timing input from the ignition control module, in the distributor in carburetted models.

The Haynes manual has a wiring diagram for the computer. Along the bottom are the inputs (sensors). Along the top are the outputs (actuators, aka servo-mechanisms). I found most of them and pencilled in their names and locations on the diagram, which just goes to show retired guys have 'way too much time on their hands.

closer, but still wrong.

The carbed cars use vacuum and mechanical advance all the time. There is a separate input to the distrubutor (single wire) that commands a few degrees of retard only during certain conditions (high altitude). The computer has NO OTHER CONTROL over timing. It's primary function is to manage the air bleeds, vent and fuel cut solenoids, to manage fuel/air ratio.

[FestYboy]

^yup