97 Lesabre with surging problem

[ramrodder]

Our 97 Buick Lesabre custom surges when your going down the road under load around the 50mph mark. Sometimes it does it and sometimes it doesn't. It does usually occur after it warms up and especially after it is warm when going up a hill. If you look down the rpms go up and down slightly. It does not "chatter". It is as if I were just moving the pedal up and down slightly as I drive along. sometimes it will just stop for a while and then start up later doing it. No service engine light and no codes. Runs great other than that. If anyone has any ideas please let me know.

Thanks

Pete

[avatar307]

#1 Change your fuel filter.

If the doesn't clear it up within about 25 miles, then you may try adding some fuel ingector cleaner in a futile attempt not to remove your gas tank.

#2 Replace fuel pump.

Which will involve dropping your gas tank out of the car, so clean and inspect the inside before you reinstall it. The tank may be corroded and need to be replaced (Whenever fuel pumps fail, it's usually due to corrosion in the gas tank getting sucked up and damaging them. IMHO)

Anyone with an alternate explination of what might be going on?

[gizmonic]

I've got a 97 LeSabre myself and noticed the exact same thing. I think it has more to do with the overdrive than any fuel problems. It feels like there is just enough load for the OD to kick in, and as soon as it does the car decides it no longer needs it and immediately shuts it off.

If you drop the car into 1 instead of Drive, the problem goes away, which is why I believe the fuel system is fine, and it is an OD issue. Gear 1 is just Drive, with no overdrive (from what I was told).

There may be a custom chip or something out there to correct it, but I haven't spent much time looking, myself.

Otherwise though, it is a very nice ride.

[ramrodder]

Originally Posted by gizmonic

I've got a 97 LeSabre myself and noticed the exact same thing. I think it has more to do with the overdrive than any fuel problems. It feels like there is just enough load for the OD to kick in, and as soon as it does the car decides it no longer needs it and immediately shuts it off.

If you drop the car into 1 instead of Drive, the problem goes away, which is why I believe the fuel system is fine, and it is an OD issue. Gear 1 is just Drive, with no overdrive (from what I was told).

There may be a custom chip or something out there to correct it, but I haven't spent much time looking, myself.

Otherwise though, it is a very nice ride.

Thanks for the replies guys, but I did try dropping into Drive instead of OD and it still was acting up. I think I will check into the fuel pump issue and see if that might be the cause.

[Mechanic_of_URL]

Dropping it into 3 will do not diagnose an overdrive problem. You have to put it down to (2). (3) still engages the Torque Converter Clutch (TCC), which is the overdrive.

P___R_N_D_(3)_(2)_(1)

D is gears 1-4, plus TCC. (3) is gears 1-3, plus TCC. (2) is gears 1-2, no TCC. (1) is gears 1, no TCC


I doubt that the fuel is the problem here.

[avatar307]

I think "overdrive" is just a fancy name for 4th gear. There are torque converters on 3-speed transmissions, and a 3-speed transmission doesn't have an overdrive selection. New cars just engage the torque converter via a electronically controlled solinoid in respond to half a dozen computer controlled variables.

As RamRodder stated, he isn't hearing any "chattering" which rules out him taking notice of the the classic 4T60-E "Torque Converter Chatter/Shudder" caused by the computer kicking open the solinoid at the wrong time.

If it was a transmission issue, I would expect the problem to be described in terms of "jerking." As when a transmission downshifts and upshifts incorrectly or hard, there is usually a noticable jerk. It it was related to the TCC Solinoid, I would expect a mention of "shudder" or "chatter" occuring.

RamRodder described the problem as "surging." Which feels similar to you driving through a 30 MPH zone alternating the accelerator between 10% and 50% throttle position with your foot. In my experience, surging is nearly always a fuel issue, and more specifically a fuel flow/pressure/availabilty issue.

42-47 MPH is approximately where the TCC engages and "TCC chatter" is often noticed when encountering a a slight grade. 50 MPH is near the top end of 3rd gear, provided throttle position is below 25%. (At 26-50%, 3-4 shift occurs around 55-60 MPH I do believe.)

Being at the top of 3rd gear means the engine in at the maximum RPMs before the 3-4 shift. This also means the engine is using the maximum amount of fuel for 3rd gear. (The engine RPMs probably won't hit that level in 4th gear until 70 MPH or so, just guessing.)

My point is, 50 MPH is approximately the point at which the engine would need the highest level of fuel (provided the transmission is in 3rd gear). That is most often when fuel availability issues are noticed, when the engines fuel demands reach the top end of the flow spectrum.

So... if the car has over 50,000 miles on it or you've been using really crappy fuel, I'd say just change the fuel filter and see what happens. A new one is like $10 at Wal-mart. (The service manual says there is no service interval for changing the fuel filter, it should last the life of the car, but I think they're nuts. All cars run better with new filters, no matter what filter it is.)

Troubleshooting the fuel pump is a good deal more complicated. You'll need to get a fuel pressure reading from the fuel rail. There is pressure test port on the fuel rail (located under the pretty engine cover).

However, I'm pretty sure you can't just use a tire pressure gage to get a pressure reading... there's a special tool for doing it. (If you can use a tire pressure gage... it will most likely be ruined afterwards... and it will likely leak gasoline on the engine. So do NOT try it when the engine is hot!)

Beyond that, there is a fuel pump relay located behind the glove box. Likely the biggest relay in that relay panel. If it is faulty, it could be clicking the fuel pump on and off at random causing low fuel pressure. (Note: When you first click the key to on, before starting the engine, if you have your door open and listen closely you can hear the relay engage the fuel pump and it pressurize the fuel system.)

You could also have a faulty fuel pressure sensor. False readings from this sensor would cause the relay to think there was enough pressure in the fuel system and click the fuel pump off prematurly.

Usually, at least in my experience with older cars, the problem lies with the fuel filter. I've often experienced surging in older model cars that required regular replacement of the fuel filter. IMHO, it's a flow issue not a pressure issue, the fuel filter would be the thing that restricts flow.

However, just to be clear, if the fuel pump is not generating enough pressure for whatever reason. Then the flow will be inhibited by even a new fuel filter, as the fuel filter is designed for a specific fuel system pressure.

Way, way, way, beyond that it could be a problem with your fuel ingectors. Loose connections, corroded connections, clogged injectors (hint: injector cleaner), or even another sensor on your engine causing the engine computer to send the wrong signals to the fuel injectors. However... there is usually noticable engine knock or misfiring with injector problems. For them to cause surging, they would really all have to malfunction in the same way at the same time in a regular pattern... kinda unlikely unless the computer is doing it in response to another faulty engine sensor.

Anyway, that's just my opinion on the whole thing. Maybe I'll pick up a engine manual and read some more about the fuel system. That's one of the chapters in the factory service manual I haven't read front to back yet. Maybe there's something I'm missing.

[sierrap615]

overdrive is any speed with a gear raito less then 1:1 (first is normally near 3:1 or 4:1, all others are normally between 2:1 to 0.7:1, higher the ratio - more torque. lower the ratio - higher speed) most 4 and 5 speed transmissions have one overdrive gear.

i would check fuel pressure, then replace filter and/or clean injectors

[avatar307]

See, Sierra agrees with me. *does the happy dance*

Alright... enough of that, it's 1:30 am and I OBVIOUSLY need to go to sleep. ROFL

[buickmastermind]

Not that I disagree with avatar, but my tranny shifts to overdrive at 35 mph. Oh, the joy of chassis service manuals, and some basic knowledge how an automatic works...too bad it can't accelerate at all without the tranny downshifting first (when in OD at that speed). I had even considered putting a manual override on the TCC when one of the pressure switches went bad, but decided to leave well enough alone, and replaced the switch.

If you are noticing a rough idle, I agree with the fuel pressure being low.

[avatar307]

*assuming rant position*

*raising finger*

Nevermind, I'm bored.

[beeaatch]

had a simular problem with my 96,pulled codes and had egr faults for pintle sticking,cleared at this time and hasent recured.still looking for time to remove electronic egr valve and attempt to clean and check for carbon build up.

[kevinnate]

My dad's '97 lesabre have the same problem about 3 years ago. There is a Gm service bulletin on it, the number is 87-71-75 ( vehicle surge, replace control valve bodyAssm). After many emails to Buicks consumer service about this TSB (techical service bulletin) they said the vehicle is too old , it was about 4 years old and only 40k miles,they decide not to paid the cost to fix it (about $1500). When it starts surging I would let the gas pedal off or tap the brakes with your left foot to disengage the lock-up converter (OD), my Dad decided to live with it until the tranny goes. The car now have 80k miles.

[creslevi]

Sorry guy's
I gotta weigh in with my opinion, As stated in previous posts, This condition is hard to describe I call it a Stumble/Miss while at cruising speed (no power just maintaining 45 to 55?MPH) Yet it would sit and idle very smooth all day so I suspected the tranny (TCC) but after 10 months of very conflicting opinion's the egr pintel circuit code showed up on a scan, And much to my delight It worked $45.00 wrecking yard off a Bonneville Pontiac, It hasn't missed or Stumbled now for 2 weeks.
I read somewhere ?? the fuel filter is expected to last the life of the car !! ??, I know mine is original and it has 216,000 miles on it, It's really easy to pressure/vo;ume test it.
I had my EGR off a couple months ago and it seemed fine to me very little carbon and free movement, But I have no idea how to test the electrical part of it, I think it was easier to change than the Serpintine belt about 3 minutes, i could be wrong but I think someone else just changed thier's and had the same results I did, Believe me I know where I will look the next time it stumbles.
Rick

[fredfast]

Originally Posted by ramrodder

Our 97 Buick Lesabre custom surges when your going down the road under load around the 50mph mark. Sometimes it does it and sometimes it doesn't. It does usually occur after it warms up and especially after it is warm when going up a hill. If you look down the rpms go up and down slightly. It does not "chatter". It is as if I were just moving the pedal up and down slightly as I drive along. sometimes it will just stop for a while and then start up later doing it. No service engine light and no codes. Runs great other than that. If anyone has any ideas please let me know.

Thanks

Pete

I spent a lot of money on this problem. Early on,50k miles,the dealer was no help. long story short. Transmission CCV any good trasmission shop can help you.

[auto trainy]

I know its a late post but have you checked for a bad plug or wire?