MMGrafx

Hi all,
New to the forum and hoping for suggestions of what to look for to solve the problems with my LS engine.
I have a 2000 Silverado Z71 with a 5.3L LM7 that has about 140K miles. Only modification are a Flowmaster dual in/dual out 40 Series exhaust. I also have a Diablo Sport Intune programmer but do use it because it makes things worse. So I’ve only been using it to monitor the sensor data.

The problem I’m having is a loss of power and torque and a lot of engine clatter after it’s warmed up and in closed loop. I’m not getting any trouble codes either. It feels like I’m always pulling a trailer and is even more sluggish when the AC is on. When cruising down the highway and press the pedal to speed up I get a real loud clatter and it doesn’t stop until the tranny down shifts to passing gear. And the down shift doesn’t happen until the TPS reaches 60%. It also clatters a lot during up shifts and accelerating out of a turn.

Using the tuner to monitor sensor data I can see Knock Retard go as high as 7.8 degs which causes the spark advance to drop as low as 6 degs BTDC. The TPS and MAP appear to be working and are not throwing any codes. I thought the timing chain may be a problem so I brought cylinder #1 to TDC and placed a mark on the crank pulley and with a timing light I noticed at idle the mark jumps around a lot, as much as an inch from one flash to the next. Is this a sign of a bad timing chain or tensioner or is this normal for the LS engines and would this cause my problem?

Has anyone else had a similar problem or have any suggestions?

Thanks,
Mike

JRENIGAR

iTrader: (37)

Try monitoring your front o2 voltages from bank 1 to bank 2 and see if you have one sensor going bad. If so it should not go up and down in voltage as quickly as the other if it does at all. They should go kind of back and fourth from like 0.2v to 0.78v or so if I remember correctly. Look at short and long term fuel trims for any discrepencies from bank 1 to bank 2. My old ls1 car had a front o2 go bad just driving down the road and it ran like crap until I figured it out. Injector pulse width is also a place to look for maybe a clogged injector or one not functioning properly. The older Diablo Predator was a good datalogging tool. The intune should be also but I have no experience using it so IDK. . G.L. and post back what you find.

MMGrafx

Thanks for the suggestion. I've recorded the O2 sensors several times and they are all switching like you would expect, from .026 to .93 volts. Whether the transition is fast enough I don't know. The short term trim ranges from -3% at idle to +6% at 50 mph and the long term trim ranges from -3% at idle to +19% at 50 mph and they're equal on both banks. Also, the more throttle the higher the long term trims climbs. I'm guessing but I think that's normal. I've ran injector cleaner through it but a couple of times but it doesn't seem to have any misfires and again the ECU isn't throwing any codes either. I think it monitors for misfires.
I believe my data log format is the same as the Diablo Predator and may be able to post the file up if anyone is able to decipher the data.

JRENIGAR

iTrader: (37)

Try a compression test. My cousins ls1 6 speed car broke a small piece of the top ringland off one piston and caused it to shake in 6th gear when applying throttle when at lower RPM's. When not in 6th and crusing youd never know anything was wrong.

MMGrafx

I'm getting about 160 psi on all cylinders. I don't have any vibrations just a lot of detonation clatter and no power on acceleration. Like I mentioned before the problem seems to be with timing since it drops everytime press on the pedal. Also, when monitoring the spark advance while idling the timing jumps between 18 degs to 24 degs. Would a loose timing chain cause that or a bad sensor?

99 2500

Check your catalytic converters, one or both of them might be plugged.

MMGrafx

How do you check catalytic converters?

99 2500

Many ways, pressure gauge that screws into front o2 sensor bung, lazer gun to read temp ( I think it should not be over 500 F ), pound on them to see if you have a rattling noise inside.

MMGrafx

I have a laser temp gun so I'll try that. If using the pressure method what would be concidered normal and out of spec?

99 2500

No more than 2 to 3 psi

MMGrafx

I checked the temp of both catalytic converters and at idle they bank 1 was 180 degs and bank 2 was 190. Measured again after a drive and bank 1 was around 200 and bank 2 was 230 degs.

99 2500

Next thing I would check is fuel pressure, should be around 60 psi

garygnu

check your rocker arms ,maybe 1 is loose .or maybe you have a broken valve spring .

RockinWs6

Quickest way to check cats is to pull off the AIR diverter valves and use a pressure gauge attached to the end of the pipe. Good cats will be less than 1 psi even revved up.

MMGrafx

Fuel pressure was the first thing I checked it's setting steady at 60 psi. If I had a loose rocker arm or broken valve spring wouldn't I have misfires and vibration and noise? I don't have any misfires, vibration or any abnormal noises.
I'm not sure what a air diverter valve is or if my truck has one. Is the tube going to the EGR valve?

1FastBrick

iTrader: (16)

Some of the early trucks are prone to false knock. This will pull timing like you described.

The early engines from 99-02 had no coating on the piston skirts They tend to be a little noisy and can even slap at start up or just after start up.

The lifters was also different.

I have 161K on my 2000 silverado and after driving it around sometimes the lifters don't pump up all the way and at low speed you can hear them clatter. It's almost like a miss.

Sometimes carbon buildup on the pistons can make them noisy as well. This can be cleaned up with the use of Fuel injection cleaner.

MMGrafx

How do you tell if its false knock? And if so what is the solution? I do have the typical piston slap on startup in the mornings that these LS engines are known for but it goes away after a few minutes. I guess it could be weak lifters but since it starts so easy and idles so smooth I didn't consider them. I've also ran several injector cleaners and ran some seafoam through the intake with no change. It still clatters and loss of HP.

1FastBrick

iTrader: (16)

You would have to watch the knock counter to see if it's pulling timing when you accelerate.

If there is nothing mechanically wrong with the engine this could be the culprit.

poltergeist 02

iTrader: (65)

I had a friend that was having similar issues. He ended up pulling the cam sensor, cleaning it and throwing it back in. It fixed the problem he was having. This may not be the issue with your truck but it may be something to look at?

MMGrafx

I've tried monitoring the Knock Sensor counts but appearantly that isn't a valid PID for my ECU. But I can monitor the Knock Retard PID and it does kick as much as 7.8 degs under load and that is when I hear the clatter from the engine and that is when I see the spark advance drop. I'm beginning to think I may have a bad ECU.
I'll try the cam sensor cleaning and see if that helps. If I remember correctly it's at the back of the engine next to the oil sending unit, real tough to get to.