Truck loosing power

[ASkipper]

I got a 2005 Silverado Crew Cab Z71 w/5.3. I have 295/70r17 Toyo Open Country MT tires on it. I was driving it Saturday on opening day of deer season- which means I had a lot of stop and go driving with a lot of mud, water, and dirt road driving. Truck started acting funny about mid day. I could press the gas pedal and it would not hardly go. When it got to about 2000rpms it seemed to take off. I noticed it did not have any take off power. It would not even spin the wheels over on a dirt road. I had to lock it in 4wd low one time and it still did not want to take off. It had the SES light burning and I checked it when I got home and it was for one of the knock sensors not responding. The SES light had been burning for awhile as I have not had time to fix it. I cleared the DTC's with HP Tuners and the power was back. I drove it Yesterday and it was fine till later on in the afternoon. Then it started doing the same thing. I know I could try taking out the Torque Management. I dont understand why it would be fine one minute and then no power the next. The SES light has not come back on and still the power is gone. What could I try the truck is bone stock down to the paper filter. Only changed the tires.

[MonteC]

fix the knock sensor.

[TurboWS6]

fix the knock sensor.

^This.

A bad knock sensor will make the computer pull timing like crazy, all it has to do is tell the ECU you have knock and your timing goes away (if its bad its telling the ECU your knocking) along with that, your power. Chances are its got water or oil under the grommet in the valley pan, not saying you had the truck in water though, it accumulates over time due to the high humidity of the south and heat cycles. When you change it make sure you seal the rubber grommet with some silicone and seal the other one while your there to and this shouldn't happen again.

[LXtasy]

Yup. Could look like this.
https://fbcdn-photos-a.akamaihd.net/hphotos-ak-ash4/s720x720/374291_2893625345059_5774098_n.jpg

[ASkipper]

I was told while I had the intake off that I should replace both sensors and the wire harnesses. That is around $150 in parts. What do yall think.

[BigdaddyDupree]

If you are going to do it swap them both and the harness. I can sell both knock sensors and the harness for about 150 through the dealership i work at. Get a good silicone to seal around the top of knock sensors also.

[ASkipper]

If you are going to do it swap them both and the harness. I can sell both knock sensors and the harness for about 150 through the dealership i work at. Get a good silicone to seal around the top of knock sensors also.

Is the harness you can get plug and go or do you have to splice it in. The one at Oreily's is one you have to splice.

[TurboWS6]

The GM one Dupree is offering is plug and play. Make sure you get the GM intake gaskets to, the aftermarket ones are hit or miss, I bought a set of aftermarkets and couldn't get them to stay in the intake long enough to bolt it down, thought I had it and one popped out didn't notice it, started the car and had a bad vacuum leak because the intake cut the gasket. Bought GM they stay in like a charm. You might get lucky and not have to change them too just depends on whether or not they a smashed once the intake comes off.

Another pit fall is the oil pressure sending unit, when you pull the intake makes sure it only comes up and forward, if you let the intake go back toward the fire wall the sending unit will break, and you will be out another 50 dollars to replace it.

[BigdaddyDupree]

The one i have is plug and play

[ASkipper]

The one i have is plug and play

I wish I was closer to you I would jump all over it. Sadly enough Im in Conway. Do you happen to have the part #'s and maybe I could get them through my local dealer here for a decent price.

[BigdaddyDupree]

12601822X1
12589867X2

[ASkipper]

12601822X1
12589867X2

Thank you sir.

[AverageJoe]

I had a knock sensor code on my 01 and found one of the sensors unplugged. Plugged it back in, new intake gaskets and it was gtg. I guess the factory must not have snapped it on all the way and it worked its way off in 9 years. Been a couple years and ~40k and still no codes. Good Luck!

**Edit: I wish I had replaced the oil pressure sensor while I had the intake off, I am getting some erroneous low or no oil pressure readings sometimes. That is some extra money I would recommend spending, not so much the harness (unless there is damage, of course).

[schardbody]

knock sensor code wont cause timing to be pulled, atleast on my truck it doesnt. i've verified with HPtuners that it runs exactly what my map says with the code on or off.

the felpro gaskets are fine, and i actually prefer them over OEM in truck applications (totally different gaskets than car).

DO NOT take the intake off without replacing both sensors and harness with OEM parts, or you'll be doing it again.

remove the foam from the bottom of the intake. use RTV (i prefer grey) to build a dam around the knock sensor connectors after install (you'll see what i mean when you get the intake off). the rear sensor will be rusted and have water/mud sitting in the valley. the foam prevents moisture from getting out so its got to go, the dam/sealant is to keep the moisture out.

take a GOOD look at your steam vent line/s i've seen quite a few rusted through or about to rust through.

leave the fuel rails on, no need to remove them. you will have to feed the evap purge solenoid nylon hose/line through the drivers side but its easily done.

i use a wet/dry vac to clean the heads intake mounting surface as soon as the intake comes off, you'll see why.

[2001hawk]

knock sensor code wont cause timing to be pulled, atleast on my truck it doesnt. i've verified with HPtuners that it runs exactly what my map says with the code on or off.

the felpro gaskets are fine, and i actually prefer them over OEM in truck applications (totally different gaskets than car).

DO NOT take the intake off without replacing both sensors and harness with OEM parts, or you'll be doing it again.

remove the foam from the bottom of the intake. use RTV (i prefer grey) to build a dam around the knock sensor connectors after install (you'll see what i mean when you get the intake off). the rear sensor will be rusted and have water/mud sitting in the valley. the foam prevents moisture from getting out so its got to go, the dam/sealant is to keep the moisture out.

take a GOOD look at your steam vent line/s i've seen quite a few rusted through or about to rust through.

leave the fuel rails on, no need to remove them. you will have to feed the evap purge solenoid nylon hose/line through the drivers side but its easily done.

i use a wet/dry vac to clean the heads intake mounting surface as soon as the intake comes off, you'll see why.

Why your vehicle would not pull timing when the knock sensors detect detonation is NOT normal. Every GM vehicle I have seen lays down like a dog when the knock sensors tell the PCM. Usually 12 degrees of timing is pulled and that is noticeable. Some of the guys rely on the knock sensors to pull timing for there nitrous. It is a little strange because if the knock sensors had been tuned out at some point it shouldn't be able to set off your MIL.

[2001hawk]

Loosey you got some 'splaining to do. LOL.

[BigdaddyDupree]

if you need to get a good deal i could always mail them to you

[schardbody]

Why your vehicle would not pull timing when the knock sensors detect detonation is NOT normal. Every GM vehicle I have seen lays down like a dog when the knock sensors tell the PCM. Usually 12 degrees of timing is pulled and that is noticeable. Some of the guys rely on the knock sensors to pull timing for there nitrous. It is a little strange because if the knock sensors had been tuned out at some point it shouldn't be able to set off your MIL.

working knock sensors detect abnormal knock and send that information to the PCM to make changes to ignition timing. under these circumstances a code is not set.

knock sensor codes are set when the PCM does not get input from the knock sensor/s either because the sensor is bad or the circuit is bad.

there is no code for "too much knock".....


when my truck had a knock sensor "A" code i was wondering how much timing was dropped because of the code so i logged ignition timing, then replaced the sensors and harness and logged again. no change in ignition timing so i compared the numbers to the map and it was the same.

the PCM has the ability to advance the timing based on input from the knock sensors, i believe the PCM might not do this with a KS code, but Jaime would probably have a better understanding of this part. i've never looked at adaptive ignition, i tune for zero knock retard and then let the PCM do its own thing.

[TurboWS6]

So out of curiosity, doesn't the SES light throw car/ truck in limp mode, and use that timing table. Hense reducing the timing?

[2001hawk]

I know there is no code for the knock sensors pulling timing. I have had to pull an intake off before because the little harness had been smashed and eventually chaffed through grounding out which threw a code.

[LXtasy]

Just shoot it with all that timing pulled

[RoadconeTuning]

MASH DA MOTOR

[schardbody]

So out of curiosity, doesn't the SES light throw car/ truck in limp mode, and use that timing table. Hense reducing the timing?

From what I seen the base timing table was still used with or without the code or error present. People think dtc's put the car in open loop but that's not the case with most codes the vehicle still runs closed loop, so the pcm is still receiving data from input sensors and making live changes. A lot of older pcm's didn't have this ability and would go open loop in the event of an error code.

If he has hptuners it would be very easy to see if I'm right just log ignition timing and compare it to your map like I did.

[ASkipper]

I was tolod at dealer that it may be the fuel pump. I drove truck all day Monday and it lost power around 4:00 and the SES light is not burning. I am wondering if it may be the fuel pump. I hear it cost a lot to get it fixed.

[LXtasy]

remove bed. replace pump yourself. put bed back on.

[bwelch]

just put a walbro in the stock bucket....$100 is better then $300 ish

[Dride76]

Fought the same issue for months. Put in 2 fuel pumps. The whole time it was crank position sensor. Didn't throw the code when you weren't driving.

[ASkipper]

I think I have found the culprit. I put my fuel pressure gauge on the truck- 60psi even when driving and still no take off power. The SES light was not lit so I checked the DTC's and low and behold P0336 code but no light. I cleared it and drove it down the road to a dirt lane near my house. It would take off good. I drove it around more and noticed the power gone again. No light- Checked the DTC's and the P0336 code was back. cleared it and power was back. When I day power is gone I mean think of it as TM times 3 it is dead until about 2200-2500 rpm. If I have time tomorrow I am going to log it with HP and see what happens with and without the code.

[schardbody]

crank sensor on an LS motor is unlikely but a possibility none the less.


it is common for the fuel pumps to break down over time, usually cause higher amp draw and burn up the stock connector first though (usually diagnosed as a fuel pump). normally wont cause a low rpm issue though, more than likely you'll see the problem going up a steep grade or other high load situations. based on what you said its probably not a bad fuel pump.

[schardbody]

posted at the same time as me... wonder if you got some water in the connector from the hunt club.

[ASkipper]

posted at the same time as me... wonder if you got some water in the connector from the hunt club.

Light has been on for 6 months for the Knock sensor. It is a good posibility about mud and water as I was going through a lot of mud.

[gearmesh, inc.]

When you are losing power, take a look at your fuel trim parameters to see if fuel is being added. You mentioned fuel pressure stays at a constant 60 psi like it is supposed to, so that should rule out the pump.

Fuel trim values typically run +/- 10% when things are running right. Since you have enough fuel pressure, a abnormally low reading MAF can under-report how much air is actually coming into the engine. As a result, fuel delivery won't be enough to mix with the actual air mass going in the engine. This causes the HO2s to read lean, so the PCM will add more fuel in order to get the HO2s to switch rich for a moment. The more fuel the PCM adds, the greater the positive fuel trim correction percentage. MAF sensors don't always set a code unless they crap out all the way.

Another way to check to see if a MAF is reading what it should is to watch how many grams/sec of air are reported from the MAF sensor when you run WOT to the top of the tach. The max number of grams/sec should be approximately 80% of the horsepower the engine is normally capable of. For example, if the engine is advertised at 300hp, you should see around 240 grams/sec of air coming into the engine at WOT redline.

[ASkipper]

When you are losing power, take a look at your fuel trim parameters to see if fuel is being added. You mentioned fuel pressure stays at a constant 60 psi like it is supposed to, so that should rule out the pump.

Fuel trim values typically run +/- 10% when things are running right. Since you have enough fuel pressure, a abnormally low reading MAF can under-report how much air is actually coming into the engine. As a result, fuel delivery won't be enough to mix with the actual air mass going in the engine. This causes the HO2s to read lean, so the PCM will add more fuel in order to get the HO2s to switch rich for a moment. The more fuel the PCM adds, the greater the positive fuel trim correction percentage. MAF sensors don't always set a code unless they crap out all the way.

Another way to check to see if a MAF is reading what it should is to watch how many grams/sec of air are reported from the MAF sensor when you run WOT to the top of the tach. The max number of grams/sec should be approximately 80% of the horsepower the engine is normally capable of. For example, if the engine is advertised at 300hp, you should see around 240 grams/sec of air coming into the engine at WOT redline.

I drove it all day today and it lost power once and then the SES light came on. I cleared the P0332 code and the power was back. Last week I was burning a lot of gas. This week it did not burn near as much. I know I am going to change the knock sensors tomorrow. Then go from there.

[98z-28camaro]

HAVE YOU REPLACED THE KNOCK SENSORS YET??? ITS NOT A BAD JOB.....

[ASkipper]

Got it fixed today.

Intake off
http://i79.photobucket.com/albums/j136/askipper/1347237533.jpg

A little dirty
http://i79.photobucket.com/albums/j136/askipper/1347238046.jpg

Rear sensor
http://i79.photobucket.com/albums/j136/askipper/1347237600.jpg

Front Sensor
http://i79.photobucket.com/albums/j136/askipper/1347237955.jpg

Front sensor plug
http://i79.photobucket.com/albums/j136/askipper/1347237859.jpg

Rear Sensor Plug Notice the stud is rusted completely into. That's supposed to be in sensor.
http://i79.photobucket.com/albums/j136/askipper/1347237808.jpg

Rear sensor out
http://i79.photobucket.com/albums/j136/askipper/1347237673.jpg

http://i79.photobucket.com/albums/j136/askipper/1347237748.jpg

Took me about 2 hrs to do it. It would not have taken that long if I could have found my fuel line tool. For some reason it has disappeared. I had to make a tool out of some hard round plastic to get the fuel line off. If it hadn't been for that I could have had it done in a little over an hour. No wonder that it was throwing the P0332 code for the rear sensor the stud for the harness was rusted into and not getting a good signal. Now to see if that's the only problem I have. Fingers crossed.

[TurboWS6]

Pretty nasty in there. Seems this rusty knock sensor is becoming a common problem.

[schardbody]

its been a problem since LS motors went in trucks in late 99, i assume its because the engines sit at an angle in the trucks as compared to the cars, could have something to do with the intake aswell.

as long as you take the foam off and use RTV on the sensor plugs you shouldnt have a problem with them again.

i havent seen one with the top rusted off like that, i could see that sending a false knock signal to the PCM and pulling a ton of timing, but i'm still skeptical.

[2001hawk]

LOL at tags.

[schardbody]

Anonymous tags = no balls.

If you want to dispute something I said lets see who has the knowledge and experience. Post up!

[2001hawk]

I am not responsible for the tags, but find them funny nonetheless. I could call you a dumbass, or a stupid fuck, or a moron, or a lot of other things, but what would be the point.

[schardbody]

the tag doesnt bother me, everything i posted was based on personal first hand experience.

i wish someone would get bored and go unplug their knock sensor harness at the intake and see how much power they lose, hell even log timing then unplug them and see if it changes. maybe it was just my truck but it didnt change, neither did power.

if the CKP sensor connector got water in it it would cause his problem but would probably fix itself after a few heat cycles dry it out so its possible we will never know what was wrong with it. cars are assholes sometimes.

[2001hawk]

Electrical gremlins can come and go, but there was obviously also a problem with the knock sensors. Guess it would be better to wish Andy best of luck and hope he has nipped this in the bud instead of guessing what was causing the power loss.