99 gmc Yukon 5.7 shake.

[Big_easy]

Hello everyone, I have a 99 Yukon 5.7 vortec and my issue is that when driving once my truck shifts into overdrive and my rpm’s are low between 40mph and 60mph I got a shake not a crazy bad one but enough to notice the difference but once I give it a little throttle and it downshifts the shake goes away or if I find the sweet spot before it shifts to overdrive it won’t shake either. I’ve replaced spark plugs, wires, fuel filter a couple months ago, Dcap, camshaft position sensor, crankshaft position sensor, does anybody know what could be the issue? And if so I’m all ears. Any knowledge is very much appreciated. Thank you.

 

[exp500]

The easiest would be to put a scanner on it during a test drive. The live data should lead you to the proper repair. A cheap bluetooth will do the engine side. For trans you would require something like a TECH2 / MDI/ VCX nano. Here are a couple links-

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GM MDI 2 Diagnostic Tool with Wifi Card for GM 1996 to 2022

WIFI Version for all GM CHEVROLET BUICK CADILLAC GMC HUMMER PONTIAC SAAB Vauxhall/Opel 16 pin vehicles from 1996 to 2022. This GM MDI 2 scanner is without software,if you need software ,please choose item# SP163-S1.

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[Hoesgottaeat2]

Likely a misfire under load when in over drive. Find someone with a real time scanner that allows you to watch what's happening as it's happening. I have had (2) 5.7's that have had this identical symptom.

 

[OR VietVet]

Welcome to the forum.

@exp500 and @Hoesgottaeat2 have led you down the right path here. Want to diagnose to stop shooting the parts cannon at it. I believe you have a torque converter problem but I am not a transmission specialist by any means. Maybe @rockola1971 can share his opinion.

 

[Big_easy]

Thank you for the advice guys! I’ll have a scanner put on it today and see what the issue may be. Do y’all think it could be my ignition coil aswell? I was reading another forum with the similar issue and that’s what his problem ended up being but also I’m tired of just buying new parts for no reason for the ole gal. Lol

 

[Eman85]

Did you replace all of those parts because of this "shake" or did the shake start after the parts replacement? Are there any codes stored or is the CEL on? If you power brake it will it shake? You can make an ignition miss diagnostic tool for $1. Get a spray bottle, a little dish soap and fill the bottle with water. While someone lightly power brakes the vehicle mist the water at the ignition. Start at each spark plug and work your way towards the cap. When you hit it you'll know as the engine will miss and you might even see the spark arc.

 

[rockola1971]

I had a 99 GMC Sierra Z71 Vin R 5.7L (Buddy owns it now). Those engines are notorious for their distributor caps cracking in a year or so no matter what brand you use. But I would identify if it is the engine or the tranny causing the vibration or even the suspension. Could be torque converter shudder. First clue will be to look at engine RPM on a scanner while the thing is vibrating and take note how much the RPM's are jumping up and down and by how much either way.

 

[drakon543]

everyone has some great advice here but ill toss in something else thats an easy visual check. under specific speed or load your vibration comes or goes could also be drivetrain. its unusual as this has only happened to me once and it was only when i had my 97 tahoe. chased everything over myself and the only failing part i could find was the universals on my driveshaft. i replaced mine with some cheapies and the issue went away for 6 months before they were failing again. install error or bad part im not sure so i picked up some hd dana spicer universals and never had the issue again

 

[Big_easy]

Thanks for the advice guys! It’s my torch converter doing the shudder so I’ll do a trans flush and see if that fixes the issue

 

[Eman85]

Is it setting a ode P1870?