96 K1500 shudder at hwy cruise

[Shortbus]

1996 k1500 305 300000 miles

I bought this truck to use around the farm for chores and stuff knowing it had a few issues. The first issue was #5 misfire code and bank two rich

I changed the autolite plugs out for delcos and tested the wires which were aftermarket but all were in spec. I changed the cap and rotor with oreilly brand.

After all that the misfire went away and the rich code was still there it was obvious it was burning to much fuel so I changed the temp sensor with no luck there either.

I had a coolant leak somewhere and chased it down to the manifold seal at the front, so I did the upper and lower seals and gaskets and while in the upper section I noticed the fuel pressure regulator had been leaking for some time since the inside of the plenum was clean all around it. So I put a new regulator on the spider and looked at the nozzles which all looked like they had been firing okay. It was the old design spider though and looked original.

After doing that the ses light went off and it runs perfect. It even starts now after being warm without holding the accelerator down.

Now my problem is a shudder in overdrive at highway cruise speeds during tcc lockup. Before I did all of the aforementioned it would shake the dash and entire truck like crazy.

After I did this work it still shudders just not as bad. It only does it in overdrive with tc locked and minor pressure on the foot pedal. Giving it gas or letting off the gas stops the shudder.

Anyone have any ideas?

[Shortbus]

Oh there is no codes now and I never checked the plugs after fixing the rich problem I put about 500 miles on it in 4 months with it running rich. I thought it may come out of it if I fixed the issues and drove it. I did run some sea foam in the tank and that didn't make a difference.

[j cAT]

Originally Posted by Shortbus

Oh there is no codes now and I never checked the plugs after fixing the rich problem I put about 500 miles on it in 4 months with it running rich. I thought it may come out of it if I fixed the issues and drove it. I did run some sea foam in the tank and that didn't make a difference.

I would check the exhaust back pressure. running too rich will plug up the cat converters.

if the coolant was entering the combustion chamber the O2 sensors get damaged.

remove the upstream O2 sensors [hole open] see if the issue is gone.

[Shortbus]

I never did smell any coolant coming out of exhaust but I will check the sensors and try pulling them to see if there is a difference.

The guy that had this before me put a new thrush muffler of some sort on it and the complete tailpipe is laying in the bed. Could this cause some issues with not enough back pressure if say the cat is not plugged?

Throttle wise it is just as snappy as my 03 silverado so it leads me to think its breathing okay.

[Shortbus]

Thought I would update this thread. The shudder was a huge issue for me so I went to oreilly auto parts and found some dr trans transmission shudder fix. It came in a two ounce tube and I put it in the trans and the shudder is gone. I don't believe in additives but so far that has masked the underlying problem for now.

I did want to point out that after fixing the fuel pressure regulator a few weeks later I finally got a new code which had to do with the cat convertor efficiency.

At this point the truck runs great but it has the engine light on. I am considering putting a new cat on it. This truck gets about 400 miles a year on it so it is not a big deal at this point.

[tempfixit]

Originally Posted by Shortbus

Thought I would update this thread. The shudder was a huge issue for me so I went to oreilly auto parts and found some dr trans transmission shudder fix. It came in a two ounce tube and I put it in the trans and the shudder is gone. I don't believe in additives but so far that has masked the underlying problem for now.

I did want to point out that after fixing the fuel pressure regulator a few weeks later I finally got a new code which had to do with the cat convertor efficiency.

At this point the truck runs great but it has the engine light on. I am considering putting a new cat on it. This truck gets about 400 miles a year on it so it is not a big deal at this point.

IF you have the means to do so I would monitor how the upstream oxygen sensors are switching, a lazy upstream 02 sensor can cause a converor efficiency problem. (WHat is the specific code number)

[j cAT]

with your 400mi use / year the fuel is a big problem. this will create cat converter code issues. the gasoline we use today even with the use of stabilizers is only good for about 14 months or so. the lower the fuel level the greater the air/mositure that damages the fuel. fuel filter needs replacing much more often ....

when refueling always use stabilizer at the max amount.

prior to 1998 when I used dexron III in my vehicles, I always added transmedic a one pint amount ,to the transmission . Prior to replacing the fluid and filter. this product cleans and conditions the seals .

after 1998 using mobil synthetic transmission fluid this was not required.

shudder issue starts with getting the engine issues resolved. bad .old, contaminated fuel manufactured today is a good reason for this.

my experience comes from inboard boat engines.

there are products that do clean the cat converter with poor effeciency.

it is possible with your limited use the vehicle needs this , and run for a time at a good speed the clean out excessive deposits coating the converter internal surface.

[Shortbus]

I put a 1000 miles on it driving back and forth to work. Fuel economy is average I would say. Engine light still on I haven't pulled codes since last post. It runs great but the engine is tired. I also think the 4l60 is is on its last leg it slips occasionally usually when it's cold. Never noticed that until I started driving it on the highway. I'm just glad it's not my daily driver.