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  1. #1
    Join Date
    Nov 2007
    Posts
    8

    Default 4l80E lock up trouble

    I have a 4l80E and having trouble with the converter not staying locked up while at cruising speeds (70 to 80 mph). It slips in and out while on the highway. If I'm at 55mph it stays locked. I had it scanned at a trannie shop but shows no codes. They are wanting to rebuild it. All the shifting is fine, what would cause this? It's in a 2002 chevy silverado 2500hd.



  2. #2
    Join Date
    Aug 2004
    Location
    CHICAGO SUBURBS
    Posts
    761

    Default

    Throttle position is one thing that can cause this. If you are having to use too much pedal it'll kick it out of lockup. The converter itself can also get burned lockup clutches and can cause this. There are other things that can cause this, most could be fixed by a rebuild. If you can get someone with a better handheld scanner that can check realtime paramiters, you'll be able to see what's happening.

  3. #3
    Join Date
    Nov 2007
    Posts
    8

    Default

    I'll change out the throttle sensor this weekend and see if that helps. Any other things that would cause this?

  4. #4
    Join Date
    Nov 2007
    Posts
    8

    Default

    That didn't help changing the tps. The trans shop says everything is working right until it warms up, then the computer is telling it to unlock for some reason. Is there a sensor in the trans that tells the computer when to lock and unlock? Could it be shorting out when it warms up? The gauge for the trans temp works fine as far as reading consistant. It'll lock up when the trans is cool but when it gets above 140 degrees it doesn't stay locked. No codes showing slipping or anything.

  5. #5
    Join Date
    Oct 2007
    Location
    ridgefield ct
    Posts
    1,000

    Default

    gm knock sensors are very sensitive, enough that they can show knock when it's just drivetrain vibratio or shock from rough roads. to check which it is they will cycle the converter clutch. if there is vibration from something like a driveshaft it will keep cycling the clutch. a gm tech i used to work with said he's even seen it from the rear tires being out of balance. you couldn't feel it in the truck but the knock sensors picked it up!
    work in progress--for the next 10 years.
    1987 monte carlo ss 383ci, 9.7:1, xe274 cam, vortec heads, 200r4, 3.73 posi.

  6. #6
    Join Date
    Nov 2007
    Posts
    8

    Default

    Here's the latest, I took a ride on the highway kept it below 70mph and it stayed locked for about 30 miles. The return ride as soon as I got above 73 it would unlock and had a heck of a time trying to get it to lock back up under 65 mph. I shut it off and then would lock up again under 70 mph.

  7. #7
    Join Date
    Dec 2007
    Location
    michigan
    Posts
    371

    Default

    I know this wont help much, but there was an issue with certain gm trucks and what I think is a pressure switch (maybe a sensor) on the side of the transmission. It is also the switch that controls the harshness of the shift. You are supposed to beable to get to it just under a cover on the side, so no need to pull anything.

    Does your truck shift fine otherwise?

    sorry, I know not much help, ( I wish i could remember the exact name of the switch/sensor) my friend is a mechanic and has worked on several for this, I will try to get ahold of him so I can give you the actual name of the switch. but at least it may be an area to look into.
    2005 CBR 1000RR..."mostly stock".
    1968 camaro... "in the works".

  8. #8
    Join Date
    Nov 2007
    Posts
    8

    Default

    The truck shifts fine, never had any trouble with that. Only thing good that has came out of this so far is I don't speed no more so gas mileage has came up a bit.

  9. #9
    Join Date
    Jun 2005
    Posts
    467

    Default

    Also a loose connector on the brake switch or faulty brake switch (usually resides above the brake pedal and toggles when the brake pedal is moved) can cause this problem, because the converter also unlocks when the brakes are touched.

    You could also have a programming issue, though I don't know the stock setup very well. Like a mph-lockup setting or the TPS/WOT threshold.

    Lastly, it is worth checking temps because IIRC the 80E is smart enough to have the temp affect the lockup in certain situations.

    Jim
    Don't take a knife to a gunfight.

    Half-Assed = Half-Fast

  10. #10
    Join Date
    Nov 2006
    Posts
    200

    Default

    You need to see if you can get in on a scanner and watch the % of TCC slip. You should have under 200 RPM slip while locked up, in fact under no load you should see 0 slip. While under a load you can see some slipage occur. If you see the slip keep rising to about 220 - 250 RPM Slip it will kick the converter off. This is typically a converter problem. These converters are common about having a crack in the converter clutch piston. Another area to have some problems is in the TCC regulator valve. But with the mileage and the way that it has been described, I would say that you are in need of a converter. However, be cautions to just install a converter. I would recommend stator bushings, pump bushing, check the stator rings, update the TCC regulator vavle and spring and install a quality rebuilt converter. Let me know if I can help in any way. Good luck.

  11. #11
    Join Date
    Nov 2007
    Posts
    8

    Default

    The trans guy said there is no slipping on his scanner (snap-on). What I'm leaning to now is ....the truck feels like it is misfiring as I'm driving it. I've checked around and heard that a misfire will also disengage the convertor. Now I get to play around and find out why it's doing that. I've checked and there are alot of things that cause it. Just going to weed it out one at a time.

  12. #12
    Join Date
    Oct 2007
    Location
    ridgefield ct
    Posts
    1,000

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    a small misfire will definately cause the ECM to cycle the clutch. i'd check the tune up first. their 100k plugs really only last 55k. the ignition wires are notoriosly weak. you're almost guaranteed to break one when pulling them off to check the plugs.
    another common problem is the intake manifold gaskets will blow the "o-rings". this is worse when the engine is cold and can go away completely when the engine warms up. decent scanners can tell you which cylinder(s) is misfiring.
    work in progress--for the next 10 years.
    1987 monte carlo ss 383ci, 9.7:1, xe274 cam, vortec heads, 200r4, 3.73 posi.

  13. #13
    Join Date
    Nov 2007
    Posts
    8

    Default

    I sprayed the intake with carb cleaner looking for a vacuum leak nothing happened. I did do a tune up 2 months ago, maybe got some junk plugs or wires. I did by ac platnum plugs but the wires can't recall what brand. Maybe I have too much anti seize on the plugs. I never noticed if I had the miss before or after the tune up. I'd hate to take it in to the shop, I see too many rip offs. I think I may pick up a autoxray scanner , I think it would be cheaper than a shop.

  14. #14
    Join Date
    Nov 2006
    Posts
    200

    Default

    A miss fire will cause the converter to cycle off. One thing you want to be sure of is to replace the distributor cap, do not get an aftermarket one, use only GM cap. We have seen too many aftermarket ones cause issues. And ensure you use quality plug wires. If you put the vehicle in gear with your foot on the brake and give it some gas (brake torque the motor) do you get a miss? Should be able to see miss fire data on the snap-on scanner as well. Good luck. Keep us informed.

  15. #15
    Join Date
    Oct 2007
    Location
    ridgefield ct
    Posts
    1,000

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    that doesn't have a distributor cap i believe. it should be the coil packs and short straight wires. unless i'm thinking of a slightly newer design.
    work in progress--for the next 10 years.
    1987 monte carlo ss 383ci, 9.7:1, xe274 cam, vortec heads, 200r4, 3.73 posi.

  16. #16
    Join Date
    Nov 2006
    Posts
    200

    Default

    You are right, I overlooked the year. It shouldn't have a distributor cap. Sorry for the oversight.

  17. #17
    Join Date
    Nov 2007
    Posts
    8

    Default

    I have disconected the MAP sensor, it shifts great and stays locked no matter what speed I go. It acually locks up real nice. Could the MAP be bad or is something else that is related to the MAP? It doesn't feel like its missing going down the highway no more. (I have a manual shift for the 4X4 and hang on to that, I can feel any misefire that happens) I have also tried disconecting the EGR but that was worse before I did the MAP.

  18. #18
    Join Date
    Oct 2007
    Location
    ridgefield ct
    Posts
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    Default

    is the MAP mounted directly onto/in the manifold? if not check the vacuum line to it.
    if i remember correctly gm uses a MAP and a MAF sensor. if so reconnect the MAP and disconnect the MAF. if you get the same results then it's not the MAP. if it has the original symptoms then change the map.
    work in progress--for the next 10 years.
    1987 monte carlo ss 383ci, 9.7:1, xe274 cam, vortec heads, 200r4, 3.73 posi.



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