GM 4l80e trans vibration in O/D when towing

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

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02-05-2013, 11:34 PM	#4
Rob Petrie E395 VIP Member Join Date: Dec 2007 Location: Woodlawn IL Posts: 1,092 Likes: 162 Liked 216 Times in 77 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