GM 4l80e trans vibration in O/D when towing

rognelson777 · 02-02-2013, 01:55 PM

Towing with a 1998 motorhome, has 7.4l chevy towing a 28ft champion trailer. When cruising at 65 mph on flat ground all is well, as soon as we hit grade, vibration starts, feels like the converter cannot decide to unlock or trans wants to downshift. If I depress gas pedal to full throttle it will downshift and vibration stops, then it seams to upshift but not lock up converter, when back to level ground converter locks up and all is well. no other trans issues. Motorhome has 58,000 miles.

Been researching options, 1 is to upgrade converter to TCI/hughes/B&M
2 is to rebuild trans.
3 Fast has a tuner / transmission re calibration programmer that will change transmission settings.

also thinking off upgrading exhaust for a little more horsepower and torque.

If all of the above is necessary, then may be time to upgrade motorhome to newer model or diesel.
Any recommendations ?

Dave Noll · 02-04-2013, 12:01 AM

I saw a local shop sell a customer a trans rebuild for the same issue your having. When the customer got it back it, did the same thing. In his case the engine was missing under load. Common issue's would be carbon tracked plug, plug boot, weak injector if it has 8, coil output if it has 8, or plug wire etc.

Alan Roehrich · 02-05-2013, 08:19 PM

Make sure it does not have an engine miss.

In the event that it does not have an engine miss, have it rebuilt by a shop that has someone who has full knowledge of all of the fixes that Sonnax has for that transmission, and will install them correctly. Have the converter rebuilt by ACI in Old Hickory TN, just outside of Nashville.

Rob Petrie E395 · 02-05-2013, 11:34 PM

Put a fuel pressure gauge on it and make sure it holds pressure after its shut off. If it does not pull the upper intake so you can get to the vacuum line going to the fuel pressure regulator and the injectors. Disconnect the vacuum line from the fuel presure regulator and cycle the key so the pump runs and builds pressure in the sytem. If fuel comes out the vacuum port the regulator is bad. If no fuel comes out take the injectors loose and see which one leaks fuel with pressure on the system. My bet is Cyl #4 injector is leaking maybe others too. No idea why but of the several I have done #4 leaks everytime. The regulator and injectors are about 80 bucks a piece at napa. If the regulator is leaking after you replace it recheck and make sure it cured it and there is not one or more injectors leaking before you reinstall the upper intake. Also replace the small vacuum hose with a new piece of hose if the reglator was bad.

If all is well here and its holding pressure take a good look at your engine mounts. If it has a bad one and they are like the pickups let me know. And I will pray for you. They are a SOB to change.

Hope this helps

rognelson777 · 02-06-2013, 12:05 AM

Going to put new plugs wires and cap on. Injectors were checked last year by a fellow drag racer and they were okay. will check regulator.

Thanks for info. I will follow up when work is complete.

Dave Noll · 03-11-2013, 12:56 AM

Just curious if you got your Motorhome fixed yet ?

rognelson777 · 04-14-2013, 09:27 PM

Update, New plugs, wires,distributor cap, rotor and problem is gone. I OHM'd all the old wires and plugs and all matched the new wires and plugs.

I guess something was breaking down under full load.

Used over the weekend towing in virginia and all is well. Other crew members could not believe the difference.

side note, when checking fuel pressure at idle, it may be low, so give it a little rpm and it should come up to spec range of 54 to 57psi. Mine was 47 at idle but as soon as I touched gas pedal went to 54psi and stayed there, even under load.

thanks, class racer

Ed Wright · 05-09-2013, 08:48 PM

Next time somebody has an issue like this if you have somebody with a Tech2 scan tool ride with you and watch the mis-fire monitor. If missing it will show it and even which cylinder(s).

Keith 944 · 05-09-2013, 08:55 PM

good ideas, my 99 454 m/h does the same thing intermittent miss. changed plugs, wires, cap etc. ran great for year, think it is due again...

Ed Wright · 05-10-2013, 06:08 PM

Quote:

Originally Posted by Keith 944

good ideas, my 99 454 m/h does the same thing intermittent miss. changed plugs, wires, cap etc. ran great for year, think it is due again...

I have found a lot of that is dirty injectors. And no, pouring something in the tank won't fix it. LOL

02-02-2013, 01:55 PM	#1
rognelson777 Member Join Date: Dec 2010 Posts: 372 Likes: 20 Liked 132 Times in 72 Posts	GM 4l80e trans vibration in O/D when towing Towing with a 1998 motorhome, has 7.4l chevy towing a 28ft champion trailer. When cruising at 65 mph on flat ground all is well, as soon as we hit grade, vibration starts, feels like the converter cannot decide to unlock or trans wants to downshift. If I depress gas pedal to full throttle it will downshift and vibration stops, then it seams to upshift but not lock up converter, when back to level ground converter locks up and all is well. no other trans issues. Motorhome has 58,000 miles. Been researching options, 1 is to upgrade converter to TCI/hughes/B&M 2 is to rebuild trans. 3 Fast has a tuner / transmission re calibration programmer that will change transmission settings. also thinking off upgrading exhaust for a little more horsepower and torque. If all of the above is necessary, then may be time to upgrade motorhome to newer model or diesel. Any recommendations ?

02-04-2013, 12:01 AM	#2
Dave Noll Senior Member Join Date: Nov 2007 Location: Div. 6, Eastern, WA Posts: 694 Likes: 2,260 Liked 219 Times in 105 Posts	Re: GM 4l80e trans vibration in O/D when towing I saw a local shop sell a customer a trans rebuild for the same issue your having. When the customer got it back it, did the same thing. In his case the engine was missing under load. Common issue's would be carbon tracked plug, plug boot, weak injector if it has 8, coil output if it has 8, or plug wire etc. __________________ Dave Noll, E/FS ,L/SA 6526

02-05-2013, 08:19 PM	#3
Alan Roehrich VIP Member Join Date: May 2006 Location: Murfreesboro TN Posts: 4,915 Likes: 996 Liked 1,043 Times in 274 Posts	Re: GM 4l80e trans vibration in O/D when towing Make sure it does not have an engine miss. In the event that it does not have an engine miss, have it rebuilt by a shop that has someone who has full knowledge of all of the fixes that Sonnax has for that transmission, and will install them correctly. Have the converter rebuilt by ACI in Old Hickory TN, just outside of Nashville. __________________ Alan Roehrich 212A G/S

02-06-2013, 12:05 AM	#5
rognelson777 Member Join Date: Dec 2010 Posts: 372 Likes: 20 Liked 132 Times in 72 Posts	Re: GM 4l80e trans vibration in O/D when towing Going to put new plugs wires and cap on. Injectors were checked last year by a fellow drag racer and they were okay. will check regulator. Thanks for info. I will follow up when work is complete.

03-11-2013, 12:56 AM	#6
Dave Noll Senior Member Join Date: Nov 2007 Location: Div. 6, Eastern, WA Posts: 694 Likes: 2,260 Liked 219 Times in 105 Posts	Re: GM 4l80e trans vibration in O/D when towing Just curious if you got your Motorhome fixed yet ? __________________ Dave Noll, E/FS ,L/SA 6526

02-05-2013, 11:34 PM	#4
Rob Petrie E395 VIP Member Join Date: Dec 2007 Location: Woodlawn IL Posts: 1,093 Likes: 162 Liked 220 Times in 79 Posts	Re: GM 4l80e trans vibration in O/D when towing Put a fuel pressure gauge on it and make sure it holds pressure after its shut off. If it does not pull the upper intake so you can get to the vacuum line going to the fuel pressure regulator and the injectors. Disconnect the vacuum line from the fuel presure regulator and cycle the key so the pump runs and builds pressure in the sytem. If fuel comes out the vacuum port the regulator is bad. If no fuel comes out take the injectors loose and see which one leaks fuel with pressure on the system. My bet is Cyl #4 injector is leaking maybe others too. No idea why but of the several I have done #4 leaks everytime. The regulator and injectors are about 80 bucks a piece at napa. If the regulator is leaking after you replace it recheck and make sure it cured it and there is not one or more injectors leaking before you reinstall the upper intake. Also replace the small vacuum hose with a new piece of hose if the reglator was bad. If all is well here and its holding pressure take a good look at your engine mounts. If it has a bad one and they are like the pickups let me know. And I will pray for you. They are a SOB to change. Hope this helps

04-14-2013, 09:27 PM	#7
rognelson777 Member Join Date: Dec 2010 Posts: 372 Likes: 20 Liked 132 Times in 72 Posts	Re: GM 4l80e trans vibration in O/D when towing Update, New plugs, wires,distributor cap, rotor and problem is gone. I OHM'd all the old wires and plugs and all matched the new wires and plugs. I guess something was breaking down under full load. Used over the weekend towing in virginia and all is well. Other crew members could not believe the difference. side note, when checking fuel pressure at idle, it may be low, so give it a little rpm and it should come up to spec range of 54 to 57psi. Mine was 47 at idle but as soon as I touched gas pedal went to 54psi and stayed there, even under load. thanks, class racer Last edited by rognelson777; 04-14-2013 at 09:30 PM.

05-09-2013, 08:48 PM	#8
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 389 Times in 168 Posts	Re: GM 4l80e trans vibration in O/D when towing Next time somebody has an issue like this if you have somebody with a Tech2 scan tool ride with you and watch the mis-fire monitor. If missing it will show it and even which cylinder(s). __________________ Ed Wright 4156 SS/JA

05-09-2013, 08:55 PM	#9
Keith 944 VIP Member Join Date: Feb 2006 Location: Dela-where? Posts: 2,116 Likes: 1,004 Liked 1,649 Times in 521 Posts	Re: GM 4l80e trans vibration in O/D when towing good ideas, my 99 454 m/h does the same thing intermittent miss. changed plugs, wires, cap etc. ran great for year, think it is due again... __________________ KEITH MAYERS 2 X somebody many X nobody