5.3 Knock Sensor Replacement

jtupper · September 25, 2009

The parts finally arrived from GM Parts Direst today so I started to tackle this project this evening. I have the new sensors and boots installed and I will let the RTV dry overnight and put it all back together tomorrow morning. I have a couple of questions though...

First, can I clean the intake manifold? I mean really clean it...like take some degreaser and a hose to it. I imagine it would be pretty difficult to get all of the water out if the inside. Would that hurt anything if there was a little water in there?

Also, the inside of the intake and the walls going down into the head are just covered in carbon. Is there anything I can do about that? Here are a few pics of the process. Youy can see all of the carbon build up in the first pic.

jtupper · September 25, 2009

Job is all done now. I ended up just using engine degreaser and a hose on the outside of the intake plenum, then I used a whole can of intake cleaner spraying in the inside out as good as I could. I just left the intake ports on the head alone. I didn't want to screw anything up.

All in all, this job took me about 6 hours. If I had to do it again, I think I could knock it out in 2-3 hrs. It wasn't too difficult, just tedious. I'll report back in after about a week or so and let you know what kind of gas mileage improvements I get.

MT952 · September 26, 2009

What was oringinally wrong with the engine? i have a knock in my 5.3 but i thought it was a lifter making the noise.

MT

alwcurlz · September 26, 2009

Job is all done now. I ended up just using engine degreaser and a hose on the outside of the intake plenum, then I used a whole can of intake cleaner spraying in the inside out as good as I could. I just left the intake ports on the head alone. I didn't want to screw anything up.

All in all, this job took me about 6 hours. If I had to do it again, I think I could knock it out in 2-3 hrs. It wasn't too difficult, just tedious. I'll report back in after about a week or so and let you know what kind of gas mileage improvements I get.

I changed mine out a few weeks ago just to make sure I would be able to get them in without troubles, and before winter. I used about half a dozen cans of carb cleaner and a brush and scrubbed the intake ports out and also the head intake ports. It's more important to get the buildup in the head ports where the fuel is expelled since the carbon buildup will absorb the fuel more giving a leaner run and possibly less fuel efficient. I noticed there is a better throttle response but, haven't taken it on a road trip to see what the fuel economy is like.

jtupper · September 26, 2009

Job is all done now. I ended up just using engine degreaser and a hose on the outside of the intake plenum, then I used a whole can of intake cleaner spraying in the inside out as good as I could. I just left the intake ports on the head alone. I didn't want to screw anything up.

All in all, this job took me about 6 hours. If I had to do it again, I think I could knock it out in 2-3 hrs. It wasn't too difficult, just tedious. I'll report back in after about a week or so and let you know what kind of gas mileage improvements I get.

I changed mine out a few weeks ago just to make sure I would be able to get them in without troubles, and before winter. I used about half a dozen cans of carb cleaner and a brush and scrubbed the intake ports out and also the head intake ports. It's more important to get the buildup in the head ports where the fuel is expelled since the carbon buildup will absorb the fuel more giving a leaner run and possibly less fuel efficient. I noticed there is a better throttle response but, haven't taken it on a road trip to see what the fuel economy is like.

With my limited knowledge of engine internals, I was worried about screwing something up my doing anything with the intake ports on the heads. Specifically, I was concerned with knocking off a big chunk of cartbon build up in the combustion chamber causing damage to one of the cylinders. Lesson learned I guess. I alos notice the throttle to be a bit more responsive, albeit not by much.

MT952 - I was getting a serive engine soon light with a P0032 error code if I remember correctly.

jtupper · October 9, 2009

Well, the gas mieage results are in and they are underwhelming to say the least. My gas mieage went up from about 12 to 12.5 MPG. I guess I was hoping for something in the range of about a 1-2 MPG impovement. It used to get 14-14.5 MPG with stop and go driving (which I do a lot of), but over the last 40k miles that has begun to drop off to about what it is now.

Oh well, the important thing is that the repair was completed and I no longer have that issue to contend with.

txab · October 9, 2009

How many miles on engine? Are you still running the original O2 sensors?

jtupper · October 9, 2009

I kind of suspect that the O2 sensors need to be replaced. I've got 152k on the clock and I'm still on the original sensors and catalytic converter.

What is the change interval on those sensors. I thought it was just when they went bad.

txab · October 9, 2009

I've heard various mileages suggested for changing. I know they can get lazy as they get older. I've got a older s-10 blazer that I've put 2 in over the years. It's got 190k or so on it. Changes it the first time at about 100k, then again at about 160k. It started being a little rich, you could tell by smell. Of course it doesn't use the heated O2 sensors like these engines of today, also only has one.

jtupper · October 10, 2009

I hear ya, but with 4 of them at $75 a pop, I'm not inclined to change them unless I really need to. I don't want to just throw money at it and I don't know how to truly determine if they are going bad or not.

txab · October 10, 2009

The 2 front ones are the sensors that monitor engine performance. Back ones are there to monitor cat performance.

What about plugs and wires? How long since they were serviced? Cleaned the MAF?

jtupper · October 10, 2009

The 2 front ones are the sensors that monitor engine performance. Back ones are there to monitor cat performance.

What about plugs and wires? How long since they were serviced? Cleaned the MAF?

I did a full tune up at about 110k...changed plugs, wires, PVC, fuel filter and coolant flush. I had the injectors cleaned a few months ago. I just cleaned the MAF and throttle body when I did this repair and also replaced the PVC again.

txab · October 10, 2009

Sounds like you've done got things covered. Cats still free flowing? Are you running a heavier weight oil now than you were before? Are you comparing MPG by taking onto account the proliferation of ethanol added fuels? I'll easily lose 1.5 mpg running the 10% blend. Have you gradually added weight to the truck over time, like toolboxes and such? Bigger tires, heavier tires? It can be as simple as engine and drive train wear causing a loss of efficiency

chrisfrost · October 17, 2009

Job is all done now. I ended up just using engine degreaser and a hose on the outside of the intake plenum, then I used a whole can of intake cleaner spraying in the inside out as good as I could. I just left the intake ports on the head alone. I didn't want to screw anything up.

All in all, this job took me about 6 hours. If I had to do it again, I think I could knock it out in 2-3 hrs. It wasn't too difficult, just tedious. I'll report back in after about a week or so and let you know what kind of gas mileage improvements I get.

I changed mine out a few weeks ago just to make sure I would be able to get them in without troubles, and before winter. I used about half a dozen cans of carb cleaner and a brush and scrubbed the intake ports out and also the head intake ports. It's more important to get the buildup in the head ports where the fuel is expelled since the carbon buildup will absorb the fuel more giving a leaner run and possibly less fuel efficient. I noticed there is a better throttle response but, haven't taken it on a road trip to see what the fuel economy is like.

With my limited knowledge of engine internals, I was worried about screwing something up my doing anything with the intake ports on the heads. Specifically, I was concerned with knocking off a big chunk of cartbon build up in the combustion chamber causing damage to one of the cylinders. Lesson learned I guess. I alos notice the throttle to be a bit more responsive, albeit not by much.

MT952 - I was getting a serive engine soon light with a P0032 error code if I remember correctly.

Heaven-o again, next time, spin engine around until the intake valve in the port You want to clean is closed, clean the port really good, then blow out with compressed air, while it is drying at same time. The intake runners being good and clean can and usually does make a huge difference with throttle response and fuel economy. But the offending carbon diminishes those mostly via compromising air flow volume and different turbulence characteristics.

jtupper · October 17, 2009

Heaven-o again, next time, spin engine around until the intake valve in the port You want to clean is closed, clean the port really good, then blow out with compressed air, while it is drying at same time. The intake runners being good and clean can and usually does make a huge difference with throttle response and fuel economy. But the offending carbon diminishes those mostly via compromising air flow volume and different turbulence characteristics.

Good information! I wish I would have known this when I did the repair. Maybe this will at least benefit the next person wnating to do this.