Knocking, losing power, mileage falling

officegig · January 27, 2007

2000 GMC Sierra, 5.3, 76,000 miles.

Purchased used at 72,000 miles. (5 months ago)

At purchase changed all fluids, fuel filter, trans tuneup and sparkplugs.

My truck ran perfect, the engine was very responsive, never making any noise. So smooth and quiet that you couldn't hear or feel the engine running unless you focused on it. So nice I tried to start it a few times while it was running.

Over the last 500 miles or so, the engine has lost power. It is still okay but it is very different from 500 ago. The fuel economy has gone from 14.3 +- to 10.0 +- miles per gallon. Also my engine is knocking at startup. Sometime loud and sometimes not at all. There is knocking after warmup now but not all the time and sometimes even at speed. I changed the gas station I usually use but did not increase the octane. The knock I am hearing is not from low octane. It's more like in the olden days if you turned a distributor to far off the mark but not exactly. At times it is pretty loud.

This engine burns no oil between oil changes(3000 miles) and leaks nothing. There is no check engine light on. All fluids look and smell correct. The oil preasure is 55 - 60 psi and always has been. There is no smoke, blue or black at startup or anytime. I have a remote start and have watch the tailpipe on the coldest days and no smoke at all.

Variables:

1) I changed my oil and filter about 750 - 1000 miles ago.

2) My brakes pulsed and I had to push on them double as hard as normal to stop, that problem repeated one time and hasn't happend again in the last 400 miles.

3) My engine stumbled twice for no reason, I was sitting at an idle and it missed on two different occassions.

4) My engine runs a couple degrees hotter then before. 208 degrees, on my guage it is just below 210. It used to be a litte lower by a couple degrees.

If you have any ideas or solutions it would be greatly appreciated.

pm26 · January 27, 2007

2000 GMC Sierra, 5.3, 76,000 miles.
Purchased used at 72,000 miles. (5 months ago)

At purchase changed all fluids, fuel filter, trans tuneup and sparkplugs.

My truck ran perfect, the engine was very responsive, never making any noise. So smooth and quiet that you couldn't hear or feel the engine running unless you focused on it. So nice I tried to start it a few times while it was running.

Over the last 500 miles or so, the engine has lost power. It is still okay but it is very different from 500 ago. The fuel economy has gone from 14.3 +- to 10.0 +- miles per gallon. Also my engine is knocking at startup. Sometime loud and sometimes not at all. There is knocking after warmup now but not all the time and sometimes even at speed. I changed the gas station I usually use but did not increase the octane. The knock I am hearing is not from low octane. It's more like in the olden days if you turned a distributor to far off the mark but not exactly. At times it is pretty loud.

IIThis engine burns no oil between oil changes(3000 miles) and leaks nothing. There is no check engine light on. All fluids look and smell correct. The oil preasure is 55 - 60 psi and always has been. There is no smoke, blue or black at startup or anytime. I have a remote start and have watch the tailpipe on the coldest days and no smoke at all.

Variables:

1) I changed my oil and filter about 750 - 1000 miles ago.

2) My brakes pulsed and I had to push on them double as hard as normal to stop, that problem repeated one time and hasn't happend again in the last 400 miles.

3) My engine stumbled twice for no reason, I was sitting at an idle and it missed on two different occassions.

4) My engine runs a couple degrees hotter then before. 208 degrees, on my guage it is just below 210. It used to be a litte lower by a couple degrees.

If you have any ideas or solutions it would be greatly appreciated.

It is possible that the EGR valve is malfunctioning. When the valve does not open, the engine will usually run a few degrees hotter and typically ping with low octane.

Check the EGR valve for proper operation.

If the EGR valve gets stuck open, you will get very bad mileage and the engine will be low on power, as too much burned exhaust will be pumped into the intake manifold. This failure mode is not common, as the valve is spring loaded , but it can happen and it did happen to me on an old Pontiac Boneville. The reason is carbon buildup on the valve stem.

Try 93 octane as see if pinging disappears.

Another possibility is that you may have a loose timing chain which has jumped a tooth.

Also, if this is a distributorless engine, I would check the crank and cam position sensors.

spackelman · January 27, 2007

Check the air intake tube connections (after the MAF) and clean your MAF. A slight air leak will give similar symptoms as your are describing.

Happened with my truck. Cost me $50 at the dealer for them to tighten the connections.

officegig · January 27, 2007

Thanks, I am going out in the cold now and checking and following your advice. I don't think it is timing chain. It would not fluctuate so much. Cam and crank sensors, maybe, MAF that would be great if it is that easy. I will let you know. Thanks

unsolved · January 31, 2007

Might want to check anti knock sensor also. If it is bad the engine will knock under load. Easy way to tell is to de advance the timing a few degrees. If it stops then you know what to look for. If it was EGR you would have a check engine light on. 210 is pretty hot considering temp gauges are off and sensors fail. 280 boils antifreeze.

I would also throw some premium in it and see what it does. Good Luck

officegig · February 2, 2007

Well, after all these year I have personally never seen this happen, I have heard about it but never experienced it. My Fram oil filter was defective. I went over everything and just decided that the filter was worth a shot and that was it. I replaced it with a Purolator filter and the power came back as well as the gas mileage. The knock/tap is mostly gone except when accelerating cold or when I really jump on it. So because of a filter my engine has suffered permanent damage and I am sure 1000s of miles of use are also lost.

Thanks for all the advice. I really appreciate the efforts.

spackelman · February 2, 2007

Well, after all these year I have personally never seen this happen, I have heard about it but never experienced it. My Fram oil filter was defective. I went over everything and just decided that the filter was worth a shot and that was it. I replaced it with a Purolator filter and the power came back as well as the gas mileage. The knock/tap is mostly gone except when accelerating cold or when I really jump on it. So because of a filter my engine has suffered permanent damage and I am sure 1000s of miles of use are also lost.

Thanks for all the advice. I really appreciate the efforts.

How did (does) the oil filter affect the engine like this? What made you suspect the oil filter?? I'm no expert, but in all my yeasrs of tinkering around vehicles, this is a new one.

Appreciate the feed back. I will certainly look foward to any expliantions.

Thanks...

Z71Rider · February 2, 2007

Well, after all these year I have personally never seen this happen, I have heard about it but never experienced it. My Fram oil filter was defective. I went over everything and just decided that the filter was worth a shot and that was it. I replaced it with a Purolator filter and the power came back as well as the gas mileage. The knock/tap is mostly gone except when accelerating cold or when I really jump on it. So because of a filter my engine has suffered permanent damage and I am sure 1000s of miles of use are also lost.

Thanks for all the advice. I really appreciate the efforts.

Naawww. I've never heard of anything like this. I think changing the oil filter and the symptoms going away are merely a coincidence. I guess the filter could be clogged, but that engine has a bypass around the filter...just in case that does occur.

I don't even know why you'd suspect the oil filter unless I'd changed out a bunch of other things...sensors, etc.

How'd you verify the filter was bad?

This is really interesting. Please keep us posted.

officegig · February 3, 2007

Here is my reason. I have been working on my own vehicles since I was a kid. However this is the first vehicle I have owned that is controlled by a computer. When I had it inspected in New Jersey when I bought it used, they didn’t test emissions, they just connected it to a computer and it passed. For New Jersey to except this system I thought that it must be very controlled by the computer. During the time that it was running poorly I kept waiting for the check engine light, never happened. Then I asked help here and went out the next day to check the suggested possible fixes. I thought that a crank and or cam sensor is either on or off. I thought that if it were the egr valve then I would have a light on my dash. I did replace the plugs that day and I cleaned the mass airflow sensor. None of these things made a difference at all. Now I am standing there thinking that the only thing that I have done pre it knocking was change the oil and filter. I drove to the parts store and purchase a new filter drove home and installed it. On startup it knocked for a few second loud and calmed down and sounded much better. I took it for a test ride and full power was restored and based on the amount of fuel used since then and my trip meter, my fuel mileage is back or at least very close to it.

It may be a coincidence. I don’t know about the bypass for the filter all I know is that the engine is back other than the cold knock and the jump on it knock/ping, but it feels like it used to.

Before this vehicle I drove a Jeep Grand Wagoneer 1990. I had a problem with the pickup coil and just decided to replace the distributor because it had over 200,000 on the engine. Everything was fine for a while then on day while leaving work the engine would start but I couldn’t accelerate until it was completely warm. I made it home and was checking on the problem and found that it I disconnect the vacuum advance it ran fine except the timing would not advance via vacuum. After checking timing chain and gear, vacuum and everything as well as endless hours of agonizing thought and said to myself, what is the last thing I did before this happened. That was the distributor. I started doing voltage tests from the spark controller to the distributor and on one of the test I had no reading. I unscrewed the pickup coil and found one of the wires from the pickup coil under the plate. Every time the distributor advanced it moved the pinched wire until it broke. It touched when the timing was not advanced and the truck ran fair. This is one of the reasons I think about mechanical things the way I do and why I decided that for a few dollars more it was worth a shot.

I don’t know what else to say about it. I got lucky.

Let me ask this. Is it possible that I have a clogged filter bypass? How big is that bypass? There is no doubt about it, my engine is back. But I may have new concerns. My engine is so clean, there is no muck on the stick or in the cap. If there is something blocking the bypass it is not muck and sludge, something must be in there blocking that passage.

What do you think? I am a graphic artist not a mechanic. So I am listening to what you all have to say and I really appreciate your advice.

I love my truck and wanted it to last for 10 more years or more.

spackelman · February 3, 2007

By coincidence, on other forum, a guy blew out the oil filter seal. Re-seated the seal, started up again and blew it again. Oil changed every 3k, ran like new (90 something Grand Am). Waiting for a explain on that one!

Clogged oil filters beyond our control??

Another new one for me.

Is there a secret life to oil filters that is ......??

officegig · February 3, 2007

Let me ask this, where is the oil pressure sensor on my truck? I would think that the engineers woudl have oil pump, oil filter, pressure sensor. Why would my oil pressure guage read 60# if the filter was defective? Anybody have an answer to that?

Z71Rider · February 3, 2007

Here is my reason. I have been working on my own vehicles since I was a kid. However this is the first vehicle I have owned that is controlled by a computer. When I had it inspected in New Jersey when I bought it used, they didn’t test emissions, they just connected it to a computer and it passed. For New Jersey to except this system I thought that it must be very controlled by the computer. During the time that it was running poorly I kept waiting for the check engine light, never happened. Then I asked help here and went out the next day to check the suggested possible fixes. I thought that a crank and or cam sensor is either on or off. I thought that if it were the egr valve then I would have a light on my dash. I did replace the plugs that day and I cleaned the mass airflow sensor. None of these things made a difference at all. Now I am standing there thinking that the only thing that I have done pre it knocking was change the oil and filter. I drove to the parts store and purchase a new filter drove home and installed it. On startup it knocked for a few second loud and calmed down and sounded much better. I took it for a test ride and full power was restored and based on the amount of fuel used since then and my trip meter, my fuel mileage is back or at least very close to it.

It may be a coincidence. I don’t know about the bypass for the filter all I know is that the engine is back other than the cold knock and the jump on it knock/ping, but it feels like it used to.

Before this vehicle I drove a Jeep Grand Wagoneer 1990. I had a problem with the pickup coil and just decided to replace the distributor because it had over 200,000 on the engine. Everything was fine for a while then on day while leaving work the engine would start but I couldn’t accelerate until it was completely warm. I made it home and was checking on the problem and found that it I disconnect the vacuum advance it ran fine except the timing would not advance via vacuum. After checking timing chain and gear, vacuum and everything as well as endless hours of agonizing thought and said to myself, what is the last thing I did before this happened. That was the distributor. I started doing voltage tests from the spark controller to the distributor and on one of the test I had no reading. I unscrewed the pickup coil and found one of the wires from the pickup coil under the plate. Every time the distributor advanced it moved the pinched wire until it broke. It touched when the timing was not advanced and the truck ran fair. This is one of the reasons I think about mechanical things the way I do and why I decided that for a few dollars more it was worth a shot.

I don’t know what else to say about it. I got lucky.

Let me ask this. Is it possible that I have a clogged filter bypass? How big is that bypass? There is no doubt about it, my engine is back. But I may have new concerns. My engine is so clean, there is no muck on the stick or in the cap. If there is something blocking the bypass it is not muck and sludge, something must be in there blocking that passage.

What do you think? I am a graphic artist not a mechanic. So I am listening to what you all have to say and I really appreciate your advice.

I love my truck and wanted it to last for 10 more years or more.

Your reasoning is sound. I just have never heard of such a thing. Do you still have the suspect filter? Keep it. There is 1 thing you could try...assure that the truck's running right, and put the old filter back on. Don't try to trash your engine if it is defective, but, if the symptoms re-appear, then you've nailed down to like 99% certainty what the issue was. If not, then the filter change was merely a coincidence and you still have some problem.

Keep us posted...this is too weird.

spackelman · February 3, 2007

Let me ask this, where is the oil pressure sensor on my truck? I would think that the engineers woudl have oil pump, oil filter, pressure sensor. Why would my oil pressure guage read 60# if the filter was defective? Anybody have an answer to that?

If the oil pump is ok, you will have pressure. If the filter is clogged, that will only affect flow or volumn of oil pumped to the system. With low flow, the system will take longer to build the pressure.