[Arctic700cat]

I have a 1999 Gmc suburban with a 5.7l. When im driving on the highway going up a hill just as i get to the top i feel a bang!!!! I took it in to have it checked out and they said it was the EGR valve. I replaced that and it still did it. The truck has 123000 miles on it. I dont know if its still the stock trans or not. Any ideas??????

 

[silveradotrailblazer]

Has it thrown any codes??

 

[stephan]

Are you hearing this bang like it could be from the exhaust backfiring, or are you feeling it like something in the transmission letting go?

 

[silveradotrailblazer]

when you say you heard a bang, do you mean like a explosive backfire or a bang like metal hitting metal? A little more detailed info please.

---------- Post added at 12:59 PM ---------- Previous post was at 12:57 PM ----------

stephan, as we said before, all great minds think alike!!:lol:

 

[stephan]

Yep ...I have no clue on this one without more info.

 

[Arctic700cat]

Sorry guys yeah i feel a bang it shakes the truck. its not a backfire. the only codes im throwing are a O2 sensor and fuel tank pressure sensor. To me it feels like the trans is slipping but not sure.

 

[stephan]

What the mechs did first --> I took it in to have it checked out and they said it was the EGR valve This tells me they thought it was a backfire, because an improperly functioning EGR valve can cause a backfire (even though replacing the EGR didn't fix yours.)
A back fire can also make your truck shake pretty good depending on just how much fuel is exploding. I'm guessing that you're throttling your truck pretty good to get to the top of this hill, but as you're cresting it you're letting off a little..right?

 

[Arctic700cat]

yeah kinda well I try to use the cruise control as much as possible. But your right the truck runs fine up until i let off or the cruise backs down alittle.

 

[Ethan]

Does the truck jerk real hard when it goes bang? If so it might be the TCC solenoid slipping. My truck was doing something similar. It started to go away after I replaced almost everything to do with the ignition system, guessing with the engine constantly jerking from bad cylinder fire, it wore out the TCC real bad, but after, it calmed down, still does it every once in a while.

A way I've found to get around it is to drive the truck in the Drive gear until the engine warms up, then put it into overdrive. It seems to help.

 

[Arctic700cat]

Ethan.....how did that work out for you on gas milage?

 

[Ethan]

No real difference, the tranny wont go into 4th gear anyways until it warms up to at least 140 degrees. I guess letting it warm up to 210 degrees helps loosen everything up more.

Even with my bad TCC I still get 17 mpg in the city and 20-21 mpg on the highway. You just gota go easy on the gas, and just let the engine do its thing, I know most people like to get to speed as soon as possible, but when the TCC is going bad, it just makes things worse trying to always force the engine to work hard.

From what I'm told, replacing both TCC solenoids is pretty easy, just drop the pan and they are both right there, and I'm hoping they are not too expensive.

 

[cbdbcbdb]

Check the crankshaft position sensor connection to the distributor and/or the sensor itself. I just replaced my distributor and forgot to plug the sensor back in, took it for a test drive and just as I let off the gas after accelerating... "bam"... it really startled me. Plugged it in and now it's smooth.

 

[Arctic700cat]

thanks cbdbcbdb i will look into that cause that sounds like what my truck is doin.