Hesitation Issue 1990 Buick 3.8

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Thread: Hesitation Issue 1990 Buick 3.8

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    Hesitation Issue 1990 Buick 3.8

    I recently purchased a 1990 Buick Electra Park Avenue from this little old lady. It has 76,000 original miles on it. It's in essentially mint condition. You could eat off the engine. The only thing is a few scuffs on the bumper. It's white with a soft top and red leather interior. I'm in love.

    Anyway, the only issue I have with it is a hesitation that's most noticeable upon takeoff when it's first started. The only other time it's noticeable is when you rev it while in park at any time. While in park and you rev it, it's like it stumbles while the gas pedal is depressed to a certain position and then continues with no issue as you give it slightly more throttle. It's most noticeable under acceleration when it's first started. If I push the throttle to the floor it accelerates with no problem. It's only when giving it partial throttle that it hesitates.

    Here's what I've done so far. I've replaced the plugs and wires (original wires and plugs were still on it), replaced top and bottom of coil pack with a spare new unit I had from my last 90 park ave. Also cleaned all battery and coil pack connections. I also had the crank shaft position sensor replaced.

    As far as diagnostics go I've disconnected the TPS with no change in symptoms, disconnected the MAF sensor from throttle body and it actually ran much worse. I've also cleaned the MAF and throttle body with cleaner.

    I'm at a loss as to what to do next. I know it almost has to be something electrical. One of my mechanics said it may be the computer, but it seems like it would cause more issues than just a hesitation.

    Anyway, any suggestions are welcome. Thanks. Kyle

    Dream Vehicles: 88-91 Reatta, an early 80s Buick Wagon, or any 79+ Riviera
    Current Vehicles:
    2005 Buick Park Avenue Ultra Special NYC two tone Edition (1 of 300 made) 70K miles
    1990 Buick Electra Park Avenue White w/ soft top and red leather interior. 76K miles
    Dead/Retired Vehicles:
    1998 Buick Riviera ~105,000, and totaled after being rear ended
    1990 Buick Park Avenue ~300,000 loyal miles before death from oil starvation. May you R.I.P. Christine.

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    Re: Hesitation Issue 1990 Buick 3.8

    With the low miles and driver type it could be a carbon build up. Back side of valves, throttle plate etc. This would require taking to a shop and have a quality fuel injection cleaning done where they run high strengh chemicals through the fuel rail, not a pour in the tank style cleaner.

    Have you checked fuel pressure while the hesitation is occuring?

    I would like to have a scanner hooked up while running the tps through its range and make sure the voltage smoothly increases.

    The computer is behind the glove box. Look to see if it is p/n 1228253 as those failed often back then. Open the glove box and flip it down so you can see the ECM. With the car running rap your knuckles, or screw driver handle, on the case of the ECM. If the car stumbles then replace the ECM. Do the same too the MAF sensor. It should not stumble at all with a tap on the sensor.

    Also for preventitive maintenance I'd consider pulling the egr valve off and clean it and the passages of carbon. For the price of a gasket and some labor it is a cheap investment.

    Congrates on the "new" old ride, I'm kinda partial too those old boxy Buicks. If the a/c is getting weak remove the blower resistor and look down at the evaporator core and see if there is any oily/dirty residue on the core. If there is the core is leaking, we replaced many of these under warranty.

    Hope this helps.

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    Re: Hesitation Issue 1990 Buick 3.8

    Quote Originally Posted by Lowboy View Post
    With the low miles and driver type it could be a carbon build up. Back side of valves, throttle plate etc. This would require taking to a shop and have a quality fuel injection cleaning done where they run high strengh chemicals through the fuel rail, not a pour in the tank style cleaner.

    Have you checked fuel pressure while the hesitation is occuring?

    I would like to have a scanner hooked up while running the tps through its range and make sure the voltage smoothly increases.

    The computer is behind the glove box. Look to see if it is p/n 1228253 as those failed often back then. Open the glove box and flip it down so you can see the ECM. With the car running rap your knuckles, or screw driver handle, on the case of the ECM. If the car stumbles then replace the ECM. Do the same too the MAF sensor. It should not stumble at all with a tap on the sensor.

    Also for preventitive maintenance I'd consider pulling the egr valve off and clean it and the passages of carbon. For the price of a gasket and some labor it is a cheap investment.

    Congrates on the "new" old ride, I'm kinda partial too those old boxy Buicks. If the a/c is getting weak remove the blower resistor and look down at the evaporator core and see if there is any oily/dirty residue on the core. If there is the core is leaking, we replaced many of these under warranty.

    Hope this helps.
    I did run some sea foam through the gas. I noticed no difference. Of course that was the pour in kind. Would just driving it harder than a little old granny eventually clean it out? I haven't checked the fuel pressure. I'm not exactly sure how to do that. Is there a gauge I can rent from Autozone or something?

    I read about testing the TPS. Just any old voltmeter connected to the leads on the TPS will work? Why would it continue to do it even after I disconnected the TPS though?

    The guy I talked to about the computer said the same thing about tapping on the ECM. I did try doing that and it didn't do anything different to the car while running.


    As far as the AC goes I actually converted it to r134. The compressor when I got it wouldn't turn on for more than a few seconds. So I bought a "conversion" kit and did it that way. So far so good. Although the compressor does make a sound like that of an actual air compressor. It works fine though. Blows cold and doesn't seem to be losing anything. My last Park Ave of the same year had over 300K on it and the AC worked until the day it died.

    I absolutely love these cars. I get incredible gas mileage. I get about 25MPG according to fuelly, which is better than my 05 Park Ave and only 2MPG off what I got with my rental HHR when my Riviera was totalled. So much for fuel economy improvements...

    Anyway if you could give me a few more information tidbits about testing farther that would be appreciated. Thanks.

    Dream Vehicles: 88-91 Reatta, an early 80s Buick Wagon, or any 79+ Riviera
    Current Vehicles:
    2005 Buick Park Avenue Ultra Special NYC two tone Edition (1 of 300 made) 70K miles
    1990 Buick Electra Park Avenue White w/ soft top and red leather interior. 76K miles
    Dead/Retired Vehicles:
    1998 Buick Riviera ~105,000, and totaled after being rear ended
    1990 Buick Park Avenue ~300,000 loyal miles before death from oil starvation. May you R.I.P. Christine.

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    Re: Hesitation Issue 1990 Buick 3.8

    Quote Originally Posted by GMFreak8 View Post
    I did run some sea foam through the gas. I noticed no difference. Of course that was the pour in kind. Would just driving it harder than a little old granny eventually clean it out?
    No, if it has carbon build up on the back of the valves hard driving will not help. The carbon throws the fuel/air mix off when it absorbs the fuel and then releases it. Years back they had a system the used ground up walnut shells to clean the backs of the valves in severe cases. If your lower intake gasket is leaking and you replace it you can inspect the valves at that point.

    I haven't checked the fuel pressure. I'm not exactly sure how to do that. Is there a gauge I can rent from Autozone or something?
    There is a schrader valve on the fuel rail, looks like a large valve stem that the gauge hooks too.

    I read about testing the TPS. Just any old voltmeter connected to the leads on the TPS will work? Why would it continue to do it even after I disconnected the TPS though?
    Back probing the sensors needs to be done carefully to not damage the seals. However the scanner will show you what the ECM is seeing, or thinks it sees, and not just what the sensor is sending.

    The guy I talked to about the computer said the same thing about tapping on the ECM. I did try doing that and it didn't do anything different to the car while running.
    That is one good sign on the ECM, doesn't give it a clean bill of health yet.
    Can you swap it with the one from your other '90 parts car?

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    Re: Hesitation Issue 1990 Buick 3.8

    Quote Originally Posted by Lowboy View Post
    No, if it has carbon build up on the back of the valves hard driving will not help. The carbon throws the fuel/air mix off when it absorbs the fuel and then releases it. Years back they had a system the used ground up walnut shells to clean the backs of the valves in severe cases. If your lower intake gasket is leaking and you replace it you can inspect the valves at that point.
    I'd really like to do the work myself if possible. I just like learning about everything. Is there a way to clean the system at home?

    The lower intake gasket actually looks good. No leaks, and the coolant level stays put. Oil stays up too. Although I did notice that the rear valve cover has some oil sitting by the bolts. Doesn't seem to be a noticeable loss though.

    If the carbon was the issue would it stop hesitating upon acceleration after you drive it for awhile? Like I said it's most noticeable when you first start it up and take off. Afterwards the only time you can get the hesitation is if you're in park and step on the throttle. Then it tends to stumble when the pedal is down a 1/4 of the way and you give it slightly more and it stops stumbling. I hate revving it like that so I don't do it often.

    I should mention that driving it home from a trip it bucked, the coolant light came on quick, followed by the check engine light and the car continued. Then it bucked again and completely quit. I pulled to the side of the road, and tried restarting it and it failed to start. I waited about ten minutes, and tried again and it started back up. The coolant light only flashed whenever the car bucked, so I know it's just a false reading. I babied it and got it home and did the old paper clip trick. It pulled a code 42 EST Electronic spark timing circuit. That's when I brought it to the mechanic and they replaced the crank shaft position sensor. That issue has not cropped back up since.

    What exactly would cause that code? The mechanic didn't think it was the crank shaft position sensor, but I had him put it in anyway, because I know those tend to go bad.

    The only other thing I can think of in addition is the fact that I was playing around with the harness on the coil pack. If I wiggled the wires it would cause the engine to hesitate a little. Are these known to cause issues like that? If I leave it alone of course it works fine.

    There is a schrader valve on the fuel rail, looks like a large valve stem that the gauge hooks too.
    I know exactly what you're talking about. What's the normal readings?


    Back probing the sensors needs to be done carefully to not damage the seals. However the scanner will show you what the ECM is seeing, or thinks it sees, and not just what the sensor is sending.
    Can I rent one of these scanners? I didn't even realize you could scan the older OBD systems.

    That is one good sign on the ECM, doesn't give it a clean bill of health yet.
    Can you swap it with the one from your other '90 parts car?
    Unfortunately no. I had to get rid of the old car due to environmental regulations. The ECM was not one of the parts I bothered pulling unfortunately. If I had known I was going to acquire one exactly like it I probably would have. I could kick my self for getting rid of it now.

    I don't believe it's the part number that you referenced above either, but I can't be sure. i"ll get back to you on that.

    Anyway appreciate all the help.

    Dream Vehicles: 88-91 Reatta, an early 80s Buick Wagon, or any 79+ Riviera
    Current Vehicles:
    2005 Buick Park Avenue Ultra Special NYC two tone Edition (1 of 300 made) 70K miles
    1990 Buick Electra Park Avenue White w/ soft top and red leather interior. 76K miles
    Dead/Retired Vehicles:
    1998 Buick Riviera ~105,000, and totaled after being rear ended
    1990 Buick Park Avenue ~300,000 loyal miles before death from oil starvation. May you R.I.P. Christine.

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    Re: Hesitation Issue 1990 Buick 3.8

    Quote Originally Posted by GMFreak8 View Post
    I'd really like to do the work myself if possible. I just like learning about everything. Is there a way to clean the system at home?

    If the carbon was the issue would it stop hesitating upon acceleration after you drive it for awhile? Like I said it's most noticeable when you first start it up and take off. Afterwards the only time you can get the hesitation is if you're in park and step on the throttle.
    Carbon build up usually affects the engine when cold.
    The only way I can think of too clean it at home is too pull the intake and physically scrap the valves clean and vacuum out the carbon. An old trick to remove carbon from the pistons/combustion chamber is to get the engine hot and ingest a water mist. The cold water will hit the carbon and hopefully the temperature change will fracture the carbon deposits and dislodge them. I have my doubts that will work on the valves. On carbureted engines we would spray the mist into the carb but on yours you want too pull the water in behind the MAF sensor.

    When you cleaned the MAF sensor did you use cleaner rated for that use?
    IIRC, regular carb cleaner is too harsh for the MAF sensor element and can damage it. We had good luck using the GM top engine cleaner on the carbureted/TBI engines back in the day. Never tried it on a port fuel car, might be hard too stall out and "flood" the intake with the cleaner to allow it too soak properly.

    I should mention that driving it home from a trip it bucked, the coolant light came on quick, followed by the check engine light and the car continued. Then it bucked again and completely quit. I pulled to the side of the road, and tried restarting it and it failed to start. I waited about ten minutes, and tried again and it started back up. The coolant light only flashed whenever the car bucked, so I know it's just a false reading. I babied it and got it home and did the old paper clip trick. It pulled a code 42 EST Electronic spark timing circuit. That's when I brought it to the mechanic and they replaced the crank shaft position sensor. That issue has not cropped back up since.

    What exactly would cause that code? The mechanic didn't think it was the crank shaft position sensor, but I had him put it in anyway, because I know those tend to go bad.
    Crank sensor is not something that would show up on my radar for a code 42 on that car. 3 main items that I can think of are ignition module, ECM and wiring.

    The only other thing I can think of in addition is the fact that I was playing around with the harness on the coil pack. If I wiggled the wires it would cause the engine to hesitate a little. Are these known to cause issues like that? If I leave it alone of course it works fine.
    This bit of info could be huge.
    There were/are issues with the wiring harness running down by the water pump rubbing through. Also the electrical pins at the module could be loose, they are supposed to have spring tension on the female end of the connector which is in the harness plug. With a small pick tool you can tweak the terminals to tighten them up sometimes, other wise you can solder in a whole new pig tail if need be.

    Now if you go back up one paragraph you might have a harness issue that was moved while replacing the crank sensor. IF that is the case it will come back at some point in the future. It will either short too ground again or will suffer from corrsion since the wire is exposed now.



    I know exactly what you're talking about. What's the normal readings?
    IIRC, 32-36 psi




    Can I rent one of these scanners? I didn't even realize you could scan the older OBD systems.
    Not sure. I have an older Snap-on MT2500 scanner that does both OBDI & II systems up too model year 2000ish and as far back as 1982.
    I would much rather work on your 3800 than say a CCC (Computer Controled Carburetor) with M/C solenoid or '82 era 2.5L TBI with hall effect switch......



    Unfortunately no. I had to get rid of the old car due to environmental regulations.
    explain "evironmental regs" please.

    A scanner is still usefull as you can watch the block learn #s to determine if it is running rich/lean and watch the MAF reading to see if the air flow readings jump around and more. With the age/miles it wouldn't hurt to install a new O2 sensor either. They are of the single wire design and fairly inexpensive compared too the newer heated 4 wire designs.

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    Re: Hesitation Issue 1990 Buick 3.8

    Quote Originally Posted by Lowboy View Post
    Carbon build up usually affects the engine when cold.
    The only way I can think of too clean it at home is too pull the intake and physically scrap the valves clean and vacuum out the carbon. An old trick to remove carbon from the pistons/combustion chamber is to get the engine hot and ingest a water mist. The cold water will hit the carbon and hopefully the temperature change will fracture the carbon deposits and dislodge them. I have my doubts that will work on the valves. On carbureted engines we would spray the mist into the carb but on yours you want too pull the water in behind the MAF sensor.

    When you cleaned the MAF sensor did you use cleaner rated for that use?
    IIRC, regular carb cleaner is too harsh for the MAF sensor element and can damage it. We had good luck using the GM top engine cleaner on the carbureted/TBI engines back in the day. Never tried it on a port fuel car, might be hard too stall out and "flood" the intake with the cleaner to allow it too soak properly.
    What about seafoam? I looked online and there are a few guides to do a complete cleaning. I'm wondering if this is something I should look into anyway considering the age and driving history of the vehicle.

    I used a cleaner specifically designed for a MAF sensor. I didn't physically touch any of the MAF sensor wires either.

    Like I said, the car will drive fine after it warms up. If I take off right after starting the car, it takes my foot to the floor to get it to move. After that it hesitates just like I'm running extremely low on gas and it's starving for it. When it's warm the only time I can notice even the slightest hesitation is if I'm parked and revving it.



    Crank sensor is not something that would show up on my radar for a code 42 on that car. 3 main items that I can think of are ignition module, ECM and wiring.
    I changed the ignition module, the coil packs, and the plugs and wires. Only thing I didn't check is the ECM. I haven't had time to open the dash and look at the model number.

    This bit of info could be huge.
    There were/are issues with the wiring harness running down by the water pump rubbing through. Also the electrical pins at the module could be loose, they are supposed to have spring tension on the female end of the connector which is in the harness plug. With a small pick tool you can tweak the terminals to tighten them up sometimes, other wise you can solder in a whole new pig tail if need be.

    Now if you go back up one paragraph you might have a harness issue that was moved while replacing the crank sensor. IF that is the case it will come back at some point in the future. It will either short too ground again or will suffer from corrsion since the wire is exposed now.
    The harness looks in great shape by the water pump area. The only time I noticed any difference in engine performance is when wiggling the pigtail slightly. I'll have to see if I can get it any better fitting. This wouldn't explain why it runs good once warmed up though when in gear.




    IIRC, 32-36 psi
    I'll test and report back when I get a chance. I'm switching jobs right now. The next few weeks are going to be hectic. I've gotta go to florida for training.





    Not sure. I have an older Snap-on MT2500 scanner that does both OBDI & II systems up too model year 2000ish and as far back as 1982.
    I would much rather work on your 3800 than say a CCC (Computer Controled Carburetor) with M/C solenoid or '82 era 2.5L TBI with hall effect switch......
    I love working on this engine. It's the perfect combination of manual control and computers. Not too advanced for it's time and relatively easy to fix.


    explain "evironmental regs" please.
    The local government doesn't allow any unregistered car or salvaged vehicle to be on your property, unless you apply for a recyclers license. It's one of the reasons I couldn't keep my totaled Riviera either.

    A scanner is still usefull as you can watch the block learn #s to determine if it is running rich/lean and watch the MAF reading to see if the air flow readings jump around and more. With the age/miles it wouldn't hurt to install a new O2 sensor either. They are of the single wire design and fairly inexpensive compared too the newer heated 4 wire designs.
    I was thinking of changing the O2 sensor as well. There's only the one before the cat on this car right? I wish I could find an old OBD1 scanner so I could see this info. OBDII is awesome for that. I have a module that plugs right in and allows me to use a program on my phone via bluetooth to read a lot of information.

    Dream Vehicles: 88-91 Reatta, an early 80s Buick Wagon, or any 79+ Riviera
    Current Vehicles:
    2005 Buick Park Avenue Ultra Special NYC two tone Edition (1 of 300 made) 70K miles
    1990 Buick Electra Park Avenue White w/ soft top and red leather interior. 76K miles
    Dead/Retired Vehicles:
    1998 Buick Riviera ~105,000, and totaled after being rear ended
    1990 Buick Park Avenue ~300,000 loyal miles before death from oil starvation. May you R.I.P. Christine.

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