I have a '97 Lesabre that surges slightly when it is warm outside and under load or slight load. It doesn't do it when it is cold outside. When it is under heavier load, going up a hill, it is at times extreme. It did not do it all winter, but now that it has warmed up outside, it is back. It feels like fishbite. It is not a miss and it feels like an overall slight powerloss. The tach needle fluctuates down in even intervals as it does it. As it does it, you can feel the intermittant power loss. I broke down and took it to the dealer for diagnosis as this has been going on for a long time. The mechanic said nothing could be found. There were no codes in it at all. The tranny checks out fine. The computer is fine, etc. He drove it and did not get it to do it. He did note that the fuel pressure was borderline low, but within specs. So, it is probably around 40 pounds. He said if it were the ignition module, it should register a code. He seemed to lean towards the fuel system, but said that nothing seemed really wrong with it. I replaced the fuel filter last fall and the problem persist. Plugs and wires have been replaced. O2 sensor is fairly new. I noticed in the book that for '98 on, the low end of the specs for the fuel pressure is 48 lbs, however, for 97 it was 40 lbs. Since he said the pressure is on the low end (for a '97), maybe I will go ahead and replace the fuel pump. Possibly, when it gets really warm, the fuel pressure drops even further and causes the surge. Does any one have any thoughts on this problem? Could slightly low fuel pressure result in such a problem? The problem usually occurs at cruising speed right after it shifts into high gear. When in high gear, it will start the surge. It is more noticable between about 45 to 60 mph, although it will still do it at 80 to 85 mph. It is just less noticable at higher speeds when it is cruising at higher RPMs. Thanks for any help.

have them check to see if the overdrive is going on and off. it might be slightly slipping in overdrive. not fully shutting it off but just slipping, like a weak spring or valve.

Okay. First, I am going to go ahead and replace the fuel pump since the pressure is somewhat low. If that doesn't fix it, I will take it to this guy I heard about yesterday. He is supposed to be very good at diagnosis work. Supposably, the dealer refers cases to him that they can't figure out. I think he charges about the same as the dealer for diagnosis work. I'll tell him about the overdrive. Thanks.

I decided not to replace the fuel pump after all. I took it to a transmission shop. They think it is hydraulic "fade out". They may do one more test on it to see for sure if the hydraulic pressure in the transmission is changing when it acts up. This would confirm that the problem is in the transmission. They checked the torque converter lock-up circut and said that it is fine. They ran it with the computer on it. Basically, they eliminated the electical system with the tests they ran on Friday. They think that once it gets good and hot, that there is a rubber piece in the transmission that probably expands resulting in the problem. I am considering putting on a transmission cooler. If the transmission temp could be maintained about 20 degrees lower, it probably wouldn't do it at all. This might put off a rebuild for 20 or 30 thousand miles. The transmission shop said that after the pressure test, they really can't tell to much more about it until they pull it out and tear into it. He said at that point, they recommend a rebuild because the part with the problem may not be obvious. The other alternative is to keep on driving it with the problem. The lurching gets pretty extreme sometimes though.

I installed a transmission cooler on the Buick and it has greatly reduced the surging behavior, although not completely. I also installed a switch on the torque converter solenoid. If it surges, I can flip the switch and voltage is applied to the torque converter solenoid in the transmission. This disengages the locked-up torque converter. It runs beautifully this way, very smooth and no surging whatsoever. The tach reads about 300 RPMs higher though than when it is locked up, but it is hardly noticeable. I suspect fuel economy will be impacted to some degree. Does anyone know if there any reason why I can't run it this way indefinitely? I don't think it could hurt anything. When cruising down the highway, I can leave the converter switch on because it normally doesn't surge then. Climbing hills is where it really gets annoying. From what I have read, the valve body in the transmission has a regulator valve that is spooled. It has an aluminum cylinder and a piston. When these wear, the valve won't maintain the hydraulic pressure necessary to maintain the lock-up. Consequently, it surges. The only way to fix it is to pull the transmission and install a kit that has a new sleeve and piston or, replace the valve body. Thanks for the input.