2001 Buick Century limited

Billy8362

New member
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Buick Ownership
2001 Buick century
Ok, this car is driving me crazy. I have a 2001 Century with the 3.1 V6 that I just bought for my daughter. When it is cold out, the thing does not want to start very easy. Sometimes it will start, but at a low idle and sometimes it won’t start without feathering the throttle. I have changed the IAC, temp sensor (it was for sure bad), plugs, wires, air filter, fpr, fuel filter and the MAF. I also changed the alternator because the bearings sounded bad. I checked the fuel pressure and it was good at start and idle, around 43-45 psi. It did not seems to bleed off after sitting. Could really use some help.
 

chem_man

Buick Newbie
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Fallston, MD
Buick Ownership
1999 Century
Check the fuel pressure regulator (FPR) to make sure the internal diaphragm has not ruptured. Easiest way to check it is to take a 6 foot section of 3/16" vacuum line and connect it to the fuel pressure regulator. Put the other end of the vacuum line into your mouth and carefully suck being careful not to get a mouthful of gasoline! If you can create a vacuum, the diaphragm is OK. If you cannot or if liquid gas wants to full the vacuum line, then the diaphragm is ruptured and the FPR needs to be replaced.
 

Billy8362

New member
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Buick Ownership
2001 Buick century
I have done that. I also replaced it with a new one just for safe measures. I have also checked the new one after putting a few miles on the car. By a miracle it started this morning, with the temp being 9 degrees. However the idle was really low. I know if I would have put it in gear and tried to take off it would have died.
 

chem_man

Buick Newbie
177
53
28
Fallston, MD
Buick Ownership
1999 Century
Have you hooked up a code reader/scanner to see if there are any pending or current codes?

Another thought - how fast is your engine warming up? Normal operating temperature is in the range of 195 - 215 Deg F. If the engine is not warming up as it should, that can cause problems and the thermostat could be sticking open. If the engine is warming up as it should but the temperature gauge on the instrument panel shows a low temperature, the engine coolant temperature (ECT) sensor could be flaky.

If the ECT sensor is flaky, it could be sending the wrong information to the Powertrain/Engine Control Module (PCM/ECM) and the throttle body is then not being sent the correct information from the ECM, and the engine does not want to easily start when it's cold outside.

If you have a fairly decent code reader/live data scanner, you should be able to see what temperature is being sent to the ECM from the ECT sensor.
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Billy8362

New member
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Buick Ownership
2001 Buick century
Good call, I drove the car yesterday and noticed the car is not getting up to temp. My code reader does not show any codes. I did watch the temp on my code reader and it only got to around 150 to 160. If the car is parked and is idling it will get up to 195 and when I look in the radiator I can see the thermostat open. When it is cold, I do not see the coolant moving in the radiator. I am wondering if it is not closing all the way. Does the ECT also control if the AC will come on? I have also noticed that it will not cycle anymore when the defrost is on. It was working when I first got the car about a month ago.

Another thing I was wondering, what voltage should the tps show at idle? I was thinking it .5 volts. Mine seems to only want to idle at .7 volts.
 

chem_man

Buick Newbie
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53
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Fallston, MD
Buick Ownership
1999 Century
I think the engine would benefit from a new 195 Deg F thermostat and a new ECT sensor.

The ECT indirectly controls whether or not the AC compressor is allowed to engage. The PCM reads the temperature the ECT sensor sends to it, and if it meets or exceeds the preprogrammed temperature programmed into the PCM, then the PCM will command the AC compressor to engage.

I do not know what theTPS voltage should be at idle. I'm sure it's contained in a professional level service manual. (here is a link to one - McDowell County Public Library - Chilton Auto Repair).

Good Luck!
 

Billy8362

New member
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3
Buick Ownership
2001 Buick century
Ok, replaced the thermostat and that fixed the temp issue. Replaced the temp sensor also. Still having an issue with low idle at cold start.
 

chem_man

Buick Newbie
177
53
28
Fallston, MD
Buick Ownership
1999 Century
OK. Probably the best way to begin troubleshooting that is to monitor fuel trim values to see if the engine is running rich. Do you have a fairly decent code reader/live data scanner? If not, let me know and I can recommend something for you that is inexpensive and fairly powerful as code reader/live data scanners go for. Only requirement is that you have an Android device.
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Billy8362

New member
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Buick Ownership
2001 Buick century
I do have a code reader that shows live data. I have watched the fuel trim. The short term jumps around from .78-1.56.
 
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chem_man

Buick Newbie
177
53
28
Fallston, MD
Buick Ownership
1999 Century
OK on the having a code reader that let's you look at fuel trim values. However, you might need to go into the settings and change the units.

Normally, while Fuel Trims can be read for both short term and long term, they are expressed as a Percentage in the range of -10% to +10%. What you indicated for short term fuel trim looks more like the O2 sensor's voltage output that is a response to the amount of oxygen in the exhaust stream. The voltage readings for an upstream O2 sensor will bounce around allover the place.

Here is a link to a quick lesson on what fuel trims are and how to use and interpret them. It's short and to the point.


aa1car.com has a lot of good reading material.
 
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