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98 Silverado running rough


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1998 chevy 1500
New User

Jul 23, 2011, 10:32 AM

Post #1 of 6 (4640 views)
98 Silverado running rough Sign In

Hi all,
I have a 1998 Chevy Silverado 5.0 with 85000 miles that is giving me problems. I have owned this truck since new and have done most maintenance and repairs myself. It has always ran like a top. However, in the last few months the truck has started running a little rough and it seems like it is loosing power. It seems I have to give it a lot more throttle to maintain speed then I did in the past, the truck is constantly downshifting back and forth. Subsequently, it seems to be using quite a bit more gas then in the past. I drove it to the lake last weekend and it barely made it up the hill to the cabin. Even on a flat road, once the truck kicks into overdrive, it seems as if it starts missing just slightly and will eventually have to downshift back to 3rd.
Well, I changing out the plugs, no difference. I replaced the MAP sensor at someones recommendation, no difference. replaced the fuel filter for the hell of it, no difference. I decided to take it to a local auto shop, they ran a diagnostics and found nothing wrong. They charged me $98.00 to tell me that.
I am going to replace the plug wires this afternoon but after that I have no idea where to start. I thought at first this was a sensor failure (like an 02 sensor) but the diagnostics didn't pick it up. Any ideas??


Kasper
User
Kasper profile image

Jul 23, 2011, 1:37 PM

Post #2 of 6 (4628 views)
Re: 98 Silverado running rough Sign In

How long has it been since you changed the transmission filter and fluid?


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 23, 2011, 2:37 PM

Post #3 of 6 (4622 views)
Re: 98 Silverado running rough Sign In


Quote
How long has it been since you changed the transmission filter and fluid?


Kasper, when someone comes here asking for help with their own car, they are not usually good candidates to advise other people on theirs.

Original poster.....

You might want to have the back pressure tested in your exhaust. You could have a plugged Converter.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Kasper
User
Kasper profile image

Jul 23, 2011, 4:26 PM

Post #4 of 6 (4611 views)
Re: 98 Silverado running rough Sign In

Sorry was just trying to help I thought about the converter too. But thaought I'd ask that first my bad.
Hope 1 or the other helps good luck


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 23, 2011, 4:29 PM

Post #5 of 6 (4609 views)
Re: 98 Silverado running rough Sign In

Even if it was a transmission problem, changing the fluid would not be advised at that stage so it really doesn't matter if it's been changed or not.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Sidom
Veteran / Moderator
Sidom profile image

Jul 23, 2011, 5:41 PM

Post #6 of 6 (4599 views)
Re: 98 Silverado running rough Sign In

The same thought popped into my head to after reading that post.....

If he doesn't have access to a BP gauge, he could look at vacuum under load.....A vacuum reading dropping very low at high rpms would also point towards a restricted exhaust system....

But back pressure is the best way to go....






 
 
 






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