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Back To That 96 Buick Century, Another problem.


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It just does not seem to end..... After fixing the bad wire, and leaking brake lines, and leaky power steering line, and now I finally get to try it out on the road, I find it has no power on the hills. And now, a check engine light is on all the time. The engine starts easy, but surges a little on start up, and if I give it a little throttle and release it, it will idle smoothly. The throttle works though about 1/4th the range and revs fairly high. From 1/4 to 1/2 the engine will start to run ruff. From 1/2 to full it will die out and almost stall and then will rev again and then almost die and continues to cycle the same way as long as it is help in full position. If I unplug the throttle positioning sensor I notice that the engine goes into a high idle and seems to run smooth. Plug it back in and the engine returns to low idle. The car only has 47,000 miles on it. It seems to have good fuel pressure.

Things I have done.

1. Changed the fuel filter.

2. Checked every vacumm line and module that I could for a vacumm leak.

3. Tried a Throttle Positioning sensor from another car.

4. Changed the Air filter.

6. Unpluged the sensors one at at time to see if there was a change. No change, it continues to run the same.

Any Ideas??? Dandy Dave!

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Dave, I would suggest getting a can of Idle Air Control Sensor cleaner and then have at the throttle body. The IAC sensor is supposed to be a very fine fillament wire exposed in the cranny in the throttle body. The cleaner is like carb cleaner but supposedly developed just for cleaning that fillament wire. Carb cleaner is supposedly too strong for the fillament.

As for no power on the open road is it possible the fuel has gone bad? The car has been down all winter, right? Possibly water in the tank?

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What's the code from the check engine light?

That might give a clue or help narrow it down.

I don't have a code reader. Maybe I should get a nice 1970's Buick Apollo, or Mid 70's Chevy Nova. They were very reliable and the best part is that I could fix them with out a lot of computer controled BS. Dandy Dave!

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Dave, I would suggest getting a can of Idle Air Control Sensor cleaner and then have at the throttle body. The IAC sensor is supposed to be a very fine fillament wire exposed in the cranny in the throttle body. The cleaner is like carb cleaner but supposedly developed just for cleaning that fillament wire. Carb cleaner is supposedly too strong for the fillament.

As for no power on the open road is it possible the fuel has gone bad? The car has been down all winter, right? Possibly water in the tank?

JD, That is the sensor on top of the air intake just before the butterfly? I noticed another sensor that is in the rubber hose from the air cleaner to the engine intake that is smaller but has a similar filliment wire. The gas smells good and the car does start easy and idles well. Would not bad gas make it hard starting?

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Dave, on the 3800 throttle body that IAC is in a cubby hole at the top of the throttle body. I assume it's the same on the 3100, but don't know for a fact.

The sensor in the bottom of the air tube is either the Mass air flow or the MAP sensor. I don't know about the starting charistics of bad gas, but if the gas and ethanol separated you may be drawing water particles into the fuel stream, and of course we all know about condensation in the tank, especially with this odd ball winter we've had.

Here's one more thing I can tell for a fact. When Doug had his third 89 Lesabre T type, there came a time we changed the engine to one we heard run before acquiring. The new engine sat for a while ( maybe 6 months or more) and then once it was installed there was a surging problem. Doug went through just about every single sensor in the car and it kept surging. Finally I told him to just drive it and it got a little use and got a little better. Then he drove the car down to Long Island for the meet there and it ran beautifully. It appears it was just a situation where with use the problem self corrected.

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Without a ALDL connector to read the codes that are tripping the check engine light you will not get to the bottom of your problem. The CEL could be a host of reasons for poor performance. Unplugging sensors is not the prescribed way to find the problem. Chilton manuals for driveability issues have flow charts for each specific code. You also need a volt/ohm meter. As you keep pulling sensor wires you add more codes to the computer. Clear the codes by disconnecting the battery. Reconnect and drive to Advance Auto. I think they will read your codes for free. Narrow down what is throwing your CEL.

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Not a fan of the computer stuff either, my service engine soon light came on, all over the fact that the thermostat is not opening or closing when the computer says so... anyway, lack of power on hills sounds like a bad cat to me, been there done that. I'd disconnect the cat and try a hill, noisy ride but try it.

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How is the converter/oxcy sensor and gas cap, they can cause service Eng.????

The car only has 47,000 miles on it so I doubt it is the converter or oxy sensor. It has plenty of power backing up a hill and below 15 MPH, and going forward the same. Starts to break up above 15 MPH. I can get it to 55 MPH on a flat road, but it takes a half of a mile to get it there. The car ran good with no lights on before the fuel pump wire failed. Will check the gas cap and filler hose connections as we had to dissconnect these to drop the tank. Dandy Dave!

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A clogged cat will give you trouble at just about every speed. I would diconnect the battery for no less than 10 seconds to clear the codes. Start the car and allow to warm unit "closed loop" is achieved. Closed loop is when the computer really takes control of fuel delivery via reading from, MAP, MAF, coolant temp, TPS and speed of the vehicle. Allow the CEL to illuminate on blinding you and go to Autozone for free scan for codes. Once obtained find the appropriate flow chart in the Chiltons manual and follow the instructions. Have a volt/ohm meter handy. Your drivability problem will not be remedied any other way.

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Without a ALDL connector to read the codes that are tripping the check engine light you will not get to the bottom of your problem. The CEL could be a host of reasons for poor performance. Unplugging sensors is not the prescribed way to find the problem. Chilton manuals for driveability issues have flow charts for each specific code. You also need a volt/ohm meter. As you keep pulling sensor wires you add more codes to the computer. Clear the codes by disconnecting the battery. Reconnect and drive to Advance Auto. I think they will read your codes for free. Narrow down what is throwing your CEL.

I have a volt Olm meter. I figgured that unplugging them was maybe not the best thing to do, but thought I might just see a noticable change somewhere. No way I'm driving it there as there is to big hills to climb to get home. If the SOB dies then I have bigger problems. Better if I just put it on the trailor to go that route. I have a buddy I can call, or I could even trailor it to him. Also, another friend that has a scanner and has offered but he is a long ways away and it will be a while before he will be out this way. I do have some manuals on the way. Dandy Dave!

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A clogged cat will give you trouble at just about every speed. I would diconnect the battery for no less than 10 seconds to clear the codes. Start the car and allow to warm unit "closed loop" is achieved. Closed loop is when the computer really takes control of fuel delivery via reading from, MAP, MAF, coolant temp, TPS and speed of the vehicle. Allow the CEL to illuminate on blinding you and go to Autozone for free scan for codes. Once obtained find the appropriate flow chart in the Chiltons manual and follow the instructions. Have a volt/ohm meter handy. Your drivability problem will not be remedied any other way.

Note taken. Thanks. And also, thanks to anyone I missed. Dandy Dave!

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ALDL readng tools are fairly cheap these days. Always good to have on hand. Maybe price one. Probably less expensive and time saving than trailering the car to the parts store.

I worked on these cars for years. Drivability problems were always a chore to diagnose and repair. Easier than Ford with a breakout box though.

Take a quick look to see that all vacuum lines are attached or not sucked closed when the engine is running. Vacuum leaks or sucked closed vacuum lines can ruin a whole day...

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Sounds like a clogged cat. An easy way to check it is to pull the Oxygen sensor ahead of the catalytic convertor and then go for a quick drive it it seems better you will notice a change as the exhaust has a way to get away...don't do it for long as the exhaust gases will melt stuff.....

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Say, What do you fellows think of this???

ALDL OBD1 OBD cable OBDI OBD2 engine codes

Or...

Check Engine Light OBD2 OBDII scan tool OBD

Something like this may just get me out of the caveman approach of the old 5 senses. Dandy Dave!

Both are good and handy. I'm not sure if you have the OBD1 or OBD2. The repair manual should offer the answer to which Onboard Diagnostic connection you have. The pictures offered at the site are clear and should give you which one you have.

As far as the 5 senses for repairing, these are much needed as well. This tool will tell you what sensor is throwing a code. It will not directed you to the actual cause of the code. From there on its up to your five senses to follow the flow chart in the manual for the code thrown. GM was never my favorite in the computer department. Chrysler was ok. Just cycle the key and the CEL would flash codes. No data connection required. Ford was a nightmare of it's own.

Edited by avgwarhawk (see edit history)
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1996 is a little bit of a freak and is kind of a OBD 1.5 (I had a 96 Regal). It has some of the functionality of both and depending on how the reader is set up may or may not get all your codes. Go to Autozone/O'Reilly's/Advanced/NAPA and see what they are using and ask them to check for you and they should give you the right stuff.

For the cost of those units you can get a simple scanner at Harbor Frieght and your neighbor hood autppoarts place for less.....all you typically need is a little hand held unit.

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After doing a little internet research, there is a sticker under the hood that conferms it is OBD II. Makes me feel like one of them Star Trek shows with the Borg running around saying, You will be assimilated. You will be part of the collective. What, a Rebbel like me??? :P Bawaaaaawwwwwaaahawhawhawhaw.

How about this... Buy Actron Auto Scanner OBD II Code Reader CP9575 at Advance Auto Parts

Welcome to the dark side of the force..... Dandy Dave!

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I was talking to Larry Schramm yesterday who is very knowlegable on the GM systems. He said that the hand held scanners do not check everything, only the goverment mandated parts which, as an example, may only read 40 codes out of 200 or more for whatever X brand of car. To really do a thorough check you really need a GM based program like one of these.

2011 GM Tech II Scanner Tool Kit V31.007 GM Tech 2+Candi+TIS+32MB card scanner | eBay

Kind of pricey and it only does GM cars. And to think, these cars will be 25 years old not all that far into the future. My hat goes off to those future collectors that are savvy enough to keep these car going as they become antiques. Dandy Dave!

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OK, So I picked up a Code Reader and a fuel pressure gage. Now I'm on to something just like I've been saying. The code that I got was a lean fuel code. If this thing was carburated, I would say that it is starving for fuel. The gage reads only 10 to 12 PSI. From what I can find on the web it should be 35 LBS or better. Taking a stab at it, it must be the fuel pressure regulator that has failed? It seems like the only logical thing to me at this point. What do you Buick buddies think??? Dandy Dave!

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I would check and replace the fuel filter first. Be careful when loosening the filter as the system is under pressure. Gas will squirt out for a second or two. The pick up in the tank has a screen as well. Not knowing how long she sat it is uncertain if anything is caught in the pick up screen. Probably unlikely but one never knows. Anyway, the fuel filter is inexpensive and probably needs replacing. Check your pressure after new filter installed.

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Looking at the age and milage the car must have sat a lot. What was the fuel pump pressure reading and what is the pump suppose to have???? If you still have the filter cut it open to see if it had a lot of crud in it. Were you able to clear the code and did it come back

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Yes, I cleared the codes, and the the code for system bank too lean (bank one) came back. The code was P0171. This car only has one O2 sensor. With a mechanical pressure gage I am only getting 10 to 12 PSI. From what I have found on the web it shoud be 41 to 47 PSI for my year vehicle. The diaphram on the regulator does not leak, but who knows if the regulator spring has not collapsed and it is just dumping the fuel back into the tank before it reaches proper operating pressure. Yes, the car did sit for a lot of years, but I have put 10,000 miles on it since I purchased it. I see on the web that sometimes this is cleared by cleaning the MAS, but mine is clean and dry. No oil in the intake at all. What else could it be? A defective fuel pump not building enough pressure? Even just turning the key on and off for two, or three times without starting the car gives the same pressure reading as when it is running. When I pick up the scanner, my gut feeling was to also pick up a fuel pressure gage. What I have been saying all along is that the car sounds like it is starving for fuel. Dandy Dave!

Edited by Dandy Dave (see edit history)
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Pinch the fuel return line, energize the fuel pump and observe fuel pressure. If the pressure increases the regulator is bad. We had a shut off valve that was installed in the return line. The pressure should hold until the return line is released. If it does not hold there is a leak. It could be the check valve in the pump, a leaking injector or the regulator. The fuel pump check valve will occasionally seat itself when the return line is pinched. Also inspect the vacuum port of the regulator. There should not be evidence of fuel. If there is fuel the regulator must be replaced. Good luck.

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Leaky injector would create a hard rough start problem if the pressure in the rail is in fact being released at that injector when the engine is off. Rick60 has a good plan of attack. Let us know what you find.

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I've Arrived. :D The problem was a defective fuel pump. Pump ran but did not build enough pressure. Second time pulling the tank down and replacing it. Lemon parts. :mad: The car runs smooth now and will take the hills around here quite easy at 60 MPH. :cool: Thanks All, :) Dandy Dave!

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I've Arrived. :D The problem was a defective fuel pump. Pump ran but did not build enough pressure. Second time pulling the tank down and replacing it. Lemon parts. :mad: The car runs smooth now and will take the hills around here quite easy at 60 MPH. :cool: Thanks All, :) Dandy Dave!

Hopefully, you kept your earlier receipt?

Minimum 55psi to pop the injectors. Anything less is "cranking time". We sold MANY more fuel pumps/pump modules than we did fuel pressure regulators for port-injected engines. Just our experiences . . .

Glad you finally got things going again!

NTX5467

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