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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
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It could be bad gas. If I were to see this I would first suggest a power balance test. Since it is running rough, disconnect one spark plug at a time and see if there is a change. If nothing happens, you may have identified a malfunctioning cylinder. You can also do this as well with the fuel injector wires (same way, one at a time).
You may have a sticky/bad or grounded fuel injector. Noid lights help here ase well.. Also, it would be nice to see what your Fuel trims are as well as what your O2 sensors are reading. Do you have a scanner that can read these?
The only O2 sensor I would be concerned with at this time is the upstream (A/F) sensor and what it is doing. The downstream O2 sensor just tells the computer the condition of the CAT (I won’t go into all the details here) but I have seen GM CATS be pretty trashed and not throw any Emissions (I.E. P0420) codes. But you could be right, there might be an exhaust blockage issue…
So I would start with the simple and see where this leads you. After all you have replaced, I would suspect something in the fuel delivery system (fuel injectors)….
Good luck
Karl
I have both a scan tool and a scan gauge 2. The scan gauge 2 can read and tell me what the o2 sensors are reading. The injectors are the spider injectors that are inside the manifold so I can’t unplug one at a time. Won’t I get shocked if i unplug them while its running?
Ill post what I find thanks!
To remove the spark plug boots while firing, use a leather boot tool… If you don’t have one, just insulate your hand/arm and use a tool to remove the boot. You may get zapped a little, but it wont hurt you (unless you are not a heathy person and have a pacemaker or something).
Also, this may help…. You might be having an issue with the fuel injection spider or the pressure regulator….
http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/testing-the-spider-fuel-injector-1
Today I got in the truck it starts fine and ran fine so I drove it. After it warmed up the shaking got worse and the mileage still isn’t what it was. So I watched the o2 precast sensor readings on my scan gauge 2 today. They bounced around from high to low putty fast but would get stuck sometimes always on the rich side around 78 for just over a second maybe. Or it will change but hover around 72-78 for a minute which is rich. Someone on another site suggested I check the upper intake plenum gasket so I plan on doing that and pulling the plug wires tomorrow.
Definitely inspect for vacuum leaks somewhere!
Check your LTFT if it is high and what your STFT is doing and let us know…
1996 chevy
the truck has 220,000 miles on it
Might be time for a new timing chain + water pump. Flash it with a timing light and see if it is within spec. Learn the specific procedure for setting timing for your engine.
http://www.youtube.com/watch?v=asGttQF_0wk
[video]http://www.youtube.com/watch?v=asGttQF_0wk[/video]That would make sense it is alot of miles. And I’ll see if i can find a way to look at the fuel trims. Although yesterday it ran great but the mileage was still different but that could be a number of different things. I checked for vaccuum leaks but didn’t find any although I do hear what sounds like a leak by the vapor canister but I can’t see any.
I’m going to guess that you have a catalytic converter problem. If it rattles when you tap on it chances are that it’s coming apart inside and causing the issues with the truck.
That makes sense. What is a good brand for cats? Maybe ill look into it and only one of the two rattle. I was also wondering if a bigger diameter cat would be better? We don’t have emissions testing here but I’m only 19 and should I move in the future to where there is testing I would like to be able to pass. ( I plan on keeping this truck for as long as possible) its kind of been my project truck that was also my daily driver through high school.
I programmed my scan gauge to read me short and long term fuel trims ill watch them a little and see what they say
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.
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.
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