Suburban not shifting at WOT

Roger Tomfohrde · Jan 22, 2019

I bought a 1992 2500HD Suburban to pull a trailer for my tractor hobby. I am having trouble with the way the transmission is shifting. It will have normal shifts under moderate acceleration but if you stomp on it or go WOT it will stumble and not shift good, and then when you let off it will shift. Last week we ran down from WI to Nebraska with a small load of furniture and the head wind was causing it to down shift more than normal at almost 75MPH but all it did was lose speed and make noise as the engine sped up. I was reading it could be the TPS, do you guys think changing it out will fix it. There are/were no codes? Or is it the electronic shifting of the trans and I am going to have to repair the trans. Looking for opinions on it. After I bought it I wished I bought the 454 because it doesn't get many miles a year on it right now and this problem makes me to not want to use it. I wish you could buy a stick in something like this truck because I sure don't trust the autos.

ss55 · Jan 23, 2019

It might work better to tow up hills with the transmission in drive rather than overdrive. Pickup truck engines of that era were not as powerful as they are today. Check what HP your engine is rated at, an early 1990's 350 V-8 might only make around 210 HP at 4000 maximum RPM when it was brand new. That does not leave a lot of extra power if you are driving a 6000+ pound truck with a cargo load and pulling a trailer up long hills into a headwind at 75MPH. I think Chevy engine RPM and HP were increased in 1996 model year.

Did you take Interstate 80 across Iowa? That road has a lot of long hills as you seem to cross a river valley every 3 to 5 miles in the western half of Iowa. A more level alternate route could be I-90 across southern Minnesota, Highway 60 and US 75 along the Floyd River Valley to Sioux City and I-29 down the Missouri River Valley to Council Bluffs. Other more level routes could be US 20 to Sioux City; or US 20 to Early IA, and either Hwy 175 along the Maple River to I-29 at Onawa or US 30 along the Boyer River and Union Pacific RR from Denison to i-29 at Missouri Valley.

mmfan55 · Jan 23, 2019

May be perfectly normal to operate that way. Using tow mode may alter shift points. Older smaller gas engines will have to develop power thru rpm. Hard acceleration to develop power requires rpm. Don't know how sophisticated the computer system is on your vehicle but what you describe may be normal.

Bob · Jan 23, 2019

When's the last time the fuel filter was changed?

D beatty · Jan 23, 2019

If your stomping on it there will be a little hesitation because you are making transmission drop a gear. At 75 MPH transmission should not be kicking out of overdrive on its own till it gets down to 45 mph. I think you can make the overdrive kick out manually by pressing gas pedal.If you really want to know if there is a problem find a competent transmission shop.

Roger Tomfohrde · Jan 23, 2019

Fuel filter has not been changed yet, it was on my list. The rest of the engine had a tune up 3-4000 miles ago. We were on I 90. If it only did it once I would think a fluke but it is getting worse. Will do it on a flat stretch of I 94 empty and it is not just hesitation but will drop 20mph if you let it go with the pedal down and not let up and it will shift quickly then. I am guessing I will have to take it in when it gets warm. It did it last year for a spell and then seemed to work its way out of it.

Bob · Jan 23, 2019

(quoted from post at 15:06:52 01/23/19) Fuel filter has not been changed yet, it was on my list. The rest of the engine had a tune up 3-4000 miles ago. We were on I 90. If it only did it once I would think a fluke but it is getting worse. Will do it on a flat stretch of I 94 empty and it is not just hesitation but will drop 20mph if you let it go with the pedal down and not let up and it will shift quickly then. I am guessing I will have to take it in when it gets warm. It did it last year for a spell and then seemed to work its way out of it.

With an issue like this, I would connect up a fuel pressure gauge with a long enough hose to sneak out under the back of the hood, and use a wiper to hold it against the windshield where you can see it and go for a drive, and verify that fuel pressure doesn't fall off under the conditions that are causing your issue.

Roger Tomfohrde · Feb 19, 2019

Finally got to work on the Suburban. Found a partially plugged fuel filter. Yeah the videos say 5-10 minutes but try that laying on a icy surface at 10 degrees out. It took awhile to get feeling back in my fingers

Definitely will help and I will find out when I pull a trailer this weekend. This is some of what I dumped out of the filter.

Suburban not shifting at WOT

Roger Tomfohrde

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ss55

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mmfan55

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Bob

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D beatty

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Roger Tomfohrde

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Bob

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Roger Tomfohrde

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