2000 "chugs" when gas let off

My wife says her car "'chugs" when she lets the gas off at highway speeds. For example, if she is following a car and is getting too close, she lets off the gas and the car "chugs" as she says. It is fine if she gives it gas again. Of course it will not do it for me. :banghead: It accelerates fine, has lots of power, but she has this problem. The way she explains it, I can only think the engine is about the stall out, or runs real rough when the gas is let off. It just idled fine in the driveway. Maybe a fuel problem? Had a look for the fuel filter, but no clue where it is in a 2000. I would start there if someone would let me know where the filter is. Then maybe the fuel pump? Or maybe someone has a better idea. There are no engine codes and the car has 120,000 miles with the 3.8 engine. Thanks for your time.

Definition of "Chug"

make repeated thudding sound: to make a repetitive thudding sound like that of a small engine

Ask your wife if the sound she hears is a “repetitive thudding sound like that of a small engine”. If so, that may be backlash in the transaxle which is not that uncommon for a car with 120K. Have you been able to duplicate the "chug"?

She tells me there is no sound associated with the problem. Now this morning she tells me there is a small thump, thump, thump in the truck when she is stopped at a light, (fuel pump?) but no sound with the 'chugging' at highway speeds. To me, it sounds like she is describing an engine about to stall or runs rough when she takes her foot off the gas at highways speed, but it is fine when she resumes. I haven't been able to duplicate anything in my limited time with the vehicle. Today, when she gets home, I will spend some time with it, and her, out on the highway and see if I can better explain the problem. Thanks for your help.

Ok, what seems to happen is this....driving along at about 60 mph and take foot off gas and everything fine. Driving at about 50 mph, take foot off gas, and car shudders. Give it gas, and all goes back to normal. Not noises. With my limited auto experience, it feels like the lock up torque converter in disengaging and engaging rapidly, giving the 'chugging' shuddering feeling.
I know the converter locks at about 50 mph, but under normal circumstances will disengage at about 30 mph. Could this the problem? Thanks.

OK, now you are talking the talk! :icon16: I would not discount converter shudder as being a contributing factor; however, this problem is more common with secondary ignition misfire. I.E. coils, wires & plugs. You could have "spark scatter" from the wires or terminals.

Keep in mind, the DIS ignition is a very high voltage ignition system and all components must be in very good condition to handle the load. I recently found a dead wire on a 94-PA at the #1 cylinder. The coil was still firing, however, not through the wire, but throwing an arc from the wire boot on the coil, down to the ICM. When diagnosing the problem, we noticed the 50-60 mph "shudder" you described.

This problem is not uncommon on cars with DIS ignition, high final drive ratios and low speed lock-up converters. I would invest in a good set of wires, (ACDelco or MSD) and plugs. If you have a weak coil, you may have to replace one, or all three. I recommend changing all three, to keep an even balance. :iceslolan

Thanks for the reply, HotZ28. I had a problem with an 88 lock up, which would not disengage and caused stalling at a stop light. I solved the problem by disconnecting the electric plug. MPG probably suffered, but no more stalling. To rule out my current problem, possibly the lock up TC on the LeSabre, can you tell me where the electric plug is on a 3.8. For the life of me, I can't find it. I will test drive and see if the problem is gone.

Regarding the possibility of bad wires, would running the car in a dark garage,
show "spark scatter" from the wires or other components? If so, I will replace them. I would hate to start replacing good items, if not necessary.
Thanks very much for your help.

I performed a full rebuild on my 2000 LeSabre transmission at 120k miles for this very same reason. If you follow my other post on here, I was able to narrow the problem down to the 4th gear clutch hub splines inside the transaxle. To make a long story short, I decided to perform the rebuild job myself. By the time I finally tore down the transmission, it had completely stripped out the clutch hub splines inside the input sun gear. The problem is extremely common on this car and the splines are simply very weak. Every transmission shop you speak to will tell you to replace the 4th clutch hub with an aftermarket hardened part, which costs about 30 bucks online. If your problem is related to 4th gear, you will probably lose 4th all together if you havn't already. The computer will probably set a TCC code since the failure of the splines tends to shock load the TCC clutch and cause it to slip during the shift to 4th. At times, the 3-4 shift may occur at speeds as low as 45 mph. Once the shaft splines are completely stripped you won't feel much of anything but you won't have any 4th gear. My recomendation is to get the car up to a nice smooth 70 mph late in the evening on a highway and downshift from overdrive to 3rd and back to overdrive a number of times and see how the shift feels. You can safely manually shift this car as low as 2nd gear at speeds as high as 70mph. Something like 30% throttle at 65mph will invoke a downshift to 3rd and then 60% or so will give you a downshift to 2nd for quick passing. You should focus on how the shift feels when you manually upshift from 3rd to overdrive at high speeds. The transmission design results in a natural down shift to 3rd in the event of a loss of the 4th clutch hub splines. That explains why you only feel problems when the transmission is attempting an upshift to 4th, downshift feels normal.

If you don't seem to notice any trouble in the 3-4 upshift then you should purchase a transmission/engine oil pressure gauge kit to monitor the line pressure on the external service port at the top of the transmission. Shop manuals and the ATSG manual for the 4t65e will list out appropriate line pressures for each of the 4 gears and lockup. You want to make sure the TCC isn't slipping as a result of poor line pressure rise from the TCC apply valve in the valve body. Sonnax makes a valve kit that is designed to correct line rise problems in the TCC apply circuit. I installed the kit during my rebuild and found that my TCC apply feel is significantly more firm now.

pcmos...thank you for your reply. You may have misread my problem, but there is no issue when the transmission is attempting to upshift to 4th. I don't have a 4th gear. My vehicle has a three speed, but some may think the lock up torque converter is a fourth gear when it kicks in.

My problem happens when the lock up engages at about 50 mph. If you immediately you let off the gas, particularly when going up a hill, it seems the lock up disengages and engages in rapid succession, causing a jerking sensation. If you apply the gas, it goes away. If I am doing 60, and let off the gas, there is no problem. Everything disengages fine and auto downshift is normal.

I have shifted the transmission manually through all ranges and all speeds, and both the upshifts and downshifts were very smooth. I am no tranny expert, but I do not believe I have stripped gears; I think my problem is with the lock up converter.

The only way I can prove/disprove my conclusion is to disconnect the electrical plug controlling the lock up. Would someone please tell me where the electrical control plug is. My old 1988 had a single two wire plug, easily found. This vehicle has a large plug, with several wires, going into the transmission housing. Because it has so many wires, I don't believe this is what I am looking for. There is a small plastic plug, locate just about the large plug, which has three wires going into it, but nothing going out into the transmission. Is this the control for the converter?

Could I simply disconnect fuse number 13...Transaxel Control?

I have rebuilt my hobby car's five speed twice over the years, but I have no interest in rebuilding this automatic. Before I bring it into the dealer, I would just like to know if it is the converter, so I don't get the BS and have my wallet extracted through my nose. Thanks to you all.

pcmos...thank you for your reply. You may have misread my problem, but there is no issue when the transmission is attempting to upshift to 4th. I don't have a 4th gear. My vehicle has a three speed, but some may think the lock up torque converter is a fourth gear when it kicks in.

Could I simply disconnect fuse number 13...Transaxel Control?



Are you sure about that? How did you get just a 3 speed? Since this is a 2000 LeSabre you should have a 4T65E autotransaxle. This is a four speed transmission with OD being 4th gear. There is a 4th gear clutch pack and spline, etc. And the shift solenoid matrix will give a 4th. The TCC lock/unlock only occurs in 4th and just an extra feature for fuel economy.

Do not pull the fuse!!!!! You will lose most tranny functions and the car will start in what will feel like 2nd and over-rev significantly to get going. You will lose the 12 volts that goes to all solenoids.

Are you sure about that? How did you get just a 3 speed? Since this is a 2000 LeSabre you should have a 4T65E autotransaxle. This is a four speed transmission with OD being 4th gear. There is a 4th gear clutch pack and spline, etc. And the shift solenoid matrix will give a 4th. The TCC lock/unlock only occurs in 4th and just an extra feature for fuel economy.

Do not pull the fuse!!!!! You will lose most tranny functions and the car will start in what will feel like 2nd and over-rev significantly to get going. You will lose the 12 volts that goes to all solenoids.

Thanks, I will not pull the fuse.
The shift mechanism on the column only indicates 1,2,3 and when I drive the car I can only feel it shift from 1 to 2 to 3, and then the lock up, or maybe it is fourth. It has been like this from new. From what I have read, if the fourth gear was a problem, I would get a Service Engine Light. No lights. Maybe it is a four speed, I don't know or care at this point. I just want to know from anyone, can I disconnect the lock up torque converter, and if so, where is the connection? Please and thanks.

The D should have the O around it for OD. Nonetheless, it is technically a 4 speed.

Anyways, GM has a TSB out stating that "chuggle" aka "fishbite" can be cause by a flaky throttle position sensor (TPS). You can check it with a multimeter at the electrical connector output to the PCM module.

Also, this tip has known to work to illiminate chuggle providing it is not a real malfunction such as a torque convertor or other internal tranny problem or engine problem such as secondary ignition components. It should clear the adaptive shift information contained in the PCM module.

Remove the battery negative for a few hours or better yet overnight and reconnect. Then run it and let it relearn the adaptive shift information and your driving habits. Note: Before disconnecting battery have your climate control turned off and have radio Theftlock codes, if active. Good luck!

BNaylor, thanks for the reply and additional tests. Good to know and I will try it. I have asked this question in four separate posts now, and still no reply addressing it.
Is there a way to disconnect the lockup torque converter, and if so where is the plug?
Thank you!!

You're welcome.

Not without disconnecting all electrical tranny commands to and from the PCM module. The 20 way connector is the one you see at the top left (driver's) side of the transmission. Should be gray colored. You would need to find the right wire by pin and color coding to disable the TCC. We have a pin out and diagram posted someplace on AF. I'd have to find it and post the link.

Thank you!! I hope you didn't mind the RED print. You have confirmed what I was thinking. I will try to find the info also, and plan to disconnect the battery overnight as you suggested. I am beginning to think I may as well "bite the bullet" and take it in to the dealer.
Thanks again. I will post whatever I find out, to help anyone else who may get this problem in the future.

PS Found this post. Seems same as my problem but without any Engine Codes.
http://www.automotiveforums.com/vbulletin/showthread.php?t=737050&highlight=20+way+transmission+connector

That is the right post. :thumbsup: Direct link is below:

Click here (http://www.tripleedgeperformance.com/4T65E_Transmission_Info.php)

I don't know about the dealer but I would consider a reasonable and reputable independent tranny repair shop. You may save some money since GM dealers typically charge more. Good luck!

I agree, a transmission shop may be a cheaper alternative to the dealer for transmission problems, however, before you proceed, keep this in mind; If you do take your car to a transmission shop for diagnosis, they may test the transmission, but that is all! These shops are in the business of rebuilding transmissions and that is their bread & butter. Most, but not all of them, will tell you that you need a rebuild, regardless of the findings.

It is sort of like going to a surgeon with back pain. Of course, they will tell you they can cure the pain if you will agree to have surgery! Surgery is there specialty & livelihood!

Now, I do not usually recommend taking a car to a dealer for simple diagnostics, however, in this case, without the proper equipment to test it yourself, I think it would be to your benefit. At least, a dealer has the right equipment to check both the engine and transmission under load. If you are lucky, they may be able to duplicate your “chugging” problem, while the scanner is in data record mode. Remember, secondary ignition breakdown will not necessarily set DTC’s. Scanners can detect random or single cylinder misfire, before it develops into a P0300 code.

BTW, I could tell you, which wire from the PCM would disable the TCC solenoid, however, for your protection, I choose not to participate in that. This is not a recommended testing procedure. That is the reason we have scanners! TCC solenoid function and TCC engage/disengage, are easy to read on a scanner. If you did disable the TCC, it could cause accelerated overheating of the transmission and might lead to fatal damage.:uhoh:

Actually before taking it to the GM dealer or any tranny shop he should try the test I suggested. We have annecdotal info right here on AF that the solution has worked to illiminate the chuggle/fishbite and other TCC lock/unlock anamolies. :grinyes:


Remove the battery negative for a few hours or better yet overnight and reconnect. Then run it and let it relearn the adaptive shift information and your driving habits. Note: Before disconnecting battery have your climate control turned off and have radio Theftlock codes, if active.

Actually before taking it to the GM dealer or any tranny shop he should try the test I suggested. We have annecdotal info right here on AF that the solution has worked to illiminate the chuggle/fishbite and other TCC lock/unlock anamolies Yes, I absolutely agree with the above, and assumed from reading post #14 (below) that was done, or will be done, before putting the scanner on it. :)
Thank you!! I hope you didn't mind the RED print. You have confirmed what I was thinking. I will try to find the info also, and plan to disconnect the battery overnight as you suggested. I am beginning to think I may as well "bite the bullet" and take it in to the dealer.
Thanks again. I will post whatever I find out, to help anyone else who may get this problem in the future.

PS Found this post. Seems same as my problem but without any Engine Codes.
http://www.automotiveforums.com/vbulletin/showthread.php?t=737050&highlight=20+way+transmission+connector

Well. I disconnected the battery for about 15 hours. My wife had to run a short errand and says the problem is gone. I am going to reserve my joy until she drives it to work tomorrow. If she comes home and doesn't complain, problem solved. Seems a little too simple a remedy, but if it worked, I 'ain't' complaining. Thanks again to you all for your ideas and help.

Thanks for the feedback polarzak and you're welcome. Yeah, I wouldn't be popping any corks just yet and celebrating until you get several drive cycles where the driving habits are re-learned and the adaptive shift points are re-establised which does have interaction on TCC operation.

I know of only one case where the fix did not work but evidently that member had other tranny problems. Hopefully it works out for you and good luck.

Well it is good I did not pop any corks. The problem is baaaaaaaak. The car has an appointment at the shop on Wednesday. Will let you know the bad news then. Thanks.

Well I went to a transmission shop and one of the techs drove the vehicle and it happened a couple of time for him. He put the scanner on and there were no transmission codes. It was his opinion that the 4th gear was fine, as there was no noise, and once in 4th, the car ran very smooth. He didn't think there was a problem with the lockup torque converter as it would send a code to his scanner. Soooo, he suggested a transmission flush and refill, thinking that something might be sticking and the transmission is "searching". Anyway, the flush and refill did nothing and the problem is still there. I feel the guy did his best and didn't try to sell me on an expensive tranny repair. Just going to let my wife drive it as it is, and tell her to keep her cell phone handy.
Thanks again to all. Time will tell if it is major or not.

Update. Last week the LeSabre was getting code 300 and 306. I checked in my "book of words" and found that to be multiple misses and a number 6 miss. Since there are a lot of miles on the car, I replaced all the wires and plugs. (Damm those back plugs are a dog to remove.) Anyway, no more codes and best of all, no more transmission problem!!!!

All I can guess is that there must have been a miss which was giving the transmission problem? Why it did not give any codes before last week is beyond me. Anyway, it appears that new plugs and wires solved my tranny problem. Thanks for all of the help.

Anyway, it appears that new plugs and wires solved my tranny problem. Thanks for all of the help.
Thanks for the feedback! If the wires & plugs solved your problem, you never had a "tranny problem" in the first place. Secondary ignition breakdown on these cars will feel very much like a tranny problem! :screwy:

BTW, sorry I never addressed your earlier question, concerning what is the best way to test ignition wires. This is very simple if you remember Ohm’s Law: The law of physics that states that electric current is directly proportional to the voltage applied to a conductor and inversely proportional to that conductor’s resistance. :wink:

All you need is a good digital VOM. Just connect one lead of the meter to one side of the wire and the other lead to the opposite side. I recently checked some NEW ACDELCO wires and they tested about 800 ohms per ft of wire. That is considered very good for "carbon core" wires. I also tested the set of MSD 8.5mm wires before installing them on my PA and as expected, they tested exactly 50 ohms per ft. Some of the cheaper wires will read anywhere from 1500-1800 (1.5K - 1.8K) per ft. anything more than 2K per foot, would serve a better purpose in the garbage can! :grinyes:

Let's hope that your wife can now enjoy many more miles of chugless motoring!
:cheers:

Thanks for the feedback! If the wires & plugs solved your problem, you never had a "tranny problem" in the first place. Secondary ignition breakdown on these cars will feel very much like a tranny problem! :screwy:

BTW, sorry I never addressed your earlier question, concerning what is the best way to test ignition wires. T
Let's hope that your wife can now enjoy many more miles of chugless motoring!
:cheers:

Yes, I know now it never was a tranny problem. Poor wording in my post.
Also no 'sorry' necessary about testing wires. With all of the help you provided me and the help given to others, no problem at all. You actually diagnosed the problem in your #5 post, and if I had 'listened' to you, I would have checked the wires for spark scatter back then. Strange there were no stored codes then.

Once I did get the 300 and 306 codes, I did check the wires in my dark garage and could see some spark scatter. I do have a good VOM, but seeing a spark jump from the wire to metal on the engine, I figured that was a good enough test.

Again I thank you. My wife will thank me later. :grinyes: :grinyes:

i was paying attention to mine over the weekend. its designed to shift into overdrive at 45mph. so instead of ripping your tranny out at 70mph and jerking it into 2nd to see if you have a "4th" and resulting in a trip to the shop; accelerate to about 40 and count your gear shifts to that point and ride in 40 a little bit, youll be in 3rd. then accelerate slowly and when you hit 45, youll drop into over drive. ease up to 50 and hold it there, and watch your tach. the way the lock-up is designed on this model, you wont feel lock up. watch your tach as you hold it at 50 and your tach will slowly drop about 500rpm. thats lock up.

probably what you were feeling as lock up, was actually the shift into overdrive.

:2cents:

jase2386, Thanks for the post, but it was not a transmission issue at all. It was a bad wire. Replaced all wires and plugs and the problem is gone. Mentioned all this in my number 23 post.