Shaking and no power

[Dirtautoguy]

So lately on my 1996 chevy I have noticed at idle it seems to shake a little not alot but a noticable amount. Also today when I laws headed home I started the truck and it almost died but it stayed running. I drove it home and check the fuel pump relay which was indeed loose (not the first time I have had problems with this) some power was restored but it still doesnt feel right. the truck seems to bog down when I give it alot of gas. I scanned it with my scangauge and don't have any codes, but I have 2 monitors not ready Oh and C.

 

I have two suspects the cat or o2 sensors. The o2 sensors because the truck has 220,000 miles on it and to my knowledge have never been touched. The cat because if I bang on one of them it rattles a little (no emissions testing here) also the exhaust is dueled out the sides one side sounds slightly different then the other, and if I drive it very far I can almost a,ways hear the exhaust popping a little I'm not sure if this means anything important.

 

The truck has:

New distrubitor shaft,cap and rotor

New plugs and wires

New fuel filter,pump,and relay

New air filter

Cleaned MAF a few months ago

Cleaned throttle body about the same time as the MAF

I have also noticed my great gas mileage I had been getting has went back down could it be bad gas?

 

Any suggestions? Thanks

[REVYCHEVY55]

Check gasket under throttle body. They are notorious for disintegrating. Hope this helps. Also a spacer under it will help keep heat of of it resulting in more power & better fuel mileage.

[Dirtautoguy]

So your saying it could be getting un metered air? That makes sense. I have been watching my o2 sensor readings and they seem to bounce around alot but once in a while it stays on one number for maybe just over a second which is a long time considering how fast they bounce around. It seemed to run alot better today but the mileage is still not as good as it was and it still shakes some at idle and goes away driving down the road. The shake also seems worse after the truck has warmed up. Ill check the gasket with some cab cleaner when I get a little extra time.

[Dirtautoguy]

I got my scan gauge to read short and long fuel trims I'm going to watch it a little and see what happens

[Dirtautoguy]

I watched my trims and the never went above plus or minus 7 and rarely hit 7. Altlhough it still looks like one o2 sensor gets stuck for a short time. Another thing a wanted to look at is ignition timing if I remember correctly the closer to 0 the better? My scan gauge can tell me that too, if I can get a hold of a timing light ill check that too.

[Dirtautoguy]

I haven't gotten a timing light but I did crawl under there while it was running and put my ear towards the cats they both sound like a jet with a slight metallic sound. It's not very loud. But noticable under idle anyway I don't know about revved.

 

I went camping a couple days ago and there were lots of up down hills. It did not like the hills it just bogged down some. And befor a had left I took a rubber mallet and beat the cats some. Then on the way back out it was different it was tons better and had better pickup.

 

But a while ago I unbolted the exhaust and looked in there and could see the back of the driver side cat and he back of it looks brand new

 

And last, I have been watching my fuel trims and o2 sensors they both seem to get stuck and not change sometimes and I don't have any codes.

[Dirtautoguy]

So I think in the end it was a bad tank of gas. After I had topped my gas tank off a couple times my mileage and power came back but ill keep an eye on it still

[thx1138v2]

I had a similar problem with my '94 Sierra. I chased it for about a week. What I eventually found was that it was a problem with the catalytic converter. The cat had a cartridge inside that had come loose and rotated 90 degrees so it was blocking the exhaust exit so the engine got higher back pressure on the exhaust side of the head. Mine was not dualed out so it affected both heads. I dissassembled the cat from the exhaust system and I could see the cartridge didn't look right. This was at 190K miles and it had never been touched. I know that for sure because I bought it new and do 90% of the work on it myself.

 

Using a 4' 2X2, I knocked the cartridge out of the cat and bolted everything back up and it immediatly fixed it. I replaced the cat later.

 

My worst symptom was odd shifting but I think that was because of the low power. I would go over an overpass on a highway and it would down shift to get over the hump.

 

Here's a quit test: start the engine and feel the pressure coming out of the tailpipe. I could barely feel mine. You might want to compare it to another car if available.