Knock, Knock, Knocking on heavens door!

[EagleMark]

Well that's all I get with this new built cammed 5.3L 2000 LS engine. Even with a flushed tank on high octane fuel it's pulling 8* timing at WOT and pulling some timing even if not at WOT.

The knock sensor were replaced along with the harness from them during the rebuild because they were oil soaked and nasty.

Can't hear a ping. Even with Low Octane table it's pulling timing. Motor is a quite as could be.

Any ideas on how to diagnose them, things that could be done wrong, did we get some bad AC/Delco knock sensors, etc... any ideas. We've done all the regular stuff like looking for something loose or rattling...

[Fast355]

Well that's all I get with this new built cammed 5.3L 2000 LS engine. Even with a flushed tank on high octane fuel it's pulling 8* timing at WOT and pulling some timing even if not at WOT.

The knock sensor were replaced along with the harness from them during the rebuild because they were oil soaked and nasty.

Can't hear a ping. Even with Low Octane table it's pulling timing. Motor is a quite as could be.

Any ideas on how to diagnose them, things that could be done wrong, did we get some bad AC/Delco knock sensors, etc... any ideas. We've done all the regular stuff like looking for something loose or rattling...

Did you torque the sensors? IiRC the LS sensors are torqued a bit differently than the old 350s.

When I 0411 swapped my Express was showing knock like crazy. I have had knock retard turned completely off for over a year.

[brian617]

Are the rockers audible? I know a guy who gave up on aftermarket cams in favor of a GM cam because of all the noise he was getting. Even tried different length push rods recommended by the cam manufacture.

[EagleMark]

No, it's as quite as can be and the cam is in mild range. I've listened to everything my self from under hood to bottom of engine on a lift and we even brake/loaded the engine till the wheels spun. There's no noise. Motor was pro built and installed by owner of the repair shop so it's been gone over well. We're just scratching our heads with the knock?

Fuel was even checked yesterday...

[dave w]

I think it's too much oil in the combustion chamber. Check the plugs? How does the oil smell, gasoline ordor? To much oil in the combustion chamber will "rock" the piston around at / or near TDC.

dave w

[Fast355]

I think it's too much oil in the combustion chamber. Check the plugs? How does the oil smell, gasoline ordor? To much oil in the combustion chamber will "rock" the piston around at / or near TDC.

dave w

Might be onto something Dave. Does the engine have the newer design fixed orifice PCV valve?

[mecanicman]

How much timing we talking wot? What afr you at?

[Fast355]

How much timing we talking wot? What afr you at?

Also a valid point, but it seems as if he is trying to run the stock low octane map and there is not much timing there. The last 4.8 I tuned only used 28* of total timing at WOT.

[mecanicman]

Also a valid point, but it seems as if he is trying to run the stock low octane map and there is not much timing there. The last 4.8 I tuned only used 28* of total timing at WOT.

You must have better fuel, stuff out of the pumps here I usually end up more like 24-26

[steveo]

i helped tune a 5.3 the other day. they really dont seem to like (or require) a bunch of timing, probably because they have a pretty damn efficient combustion chamber. 28 degrees wot all-in is sooo much for that engine imo

[Fast355]

You must have better fuel, stuff out of the pumps here I usually end up more like 24-26

i helped tune a 5.3 the other day. they really dont seem to like (or require) a bunch of timing, probably because they have a pretty damn efficient combustion chamber. 28 degrees wot all-in is sooo much for that engine imo

Shell/Chevron 93 is the only thing I recomeend people around here to use. Well E85 is better in a Flex Fuel.

The truck I tuned was 4.8 with milled ported 243s in a RCSB truck.

The 5.3s I have tuned are as you guys have said 24-26* total. I think the short stroke/long rod makes the 4.8 want a little more timing.

The old L31 engines do not like a whole lot of timing with the stock cams either.

[Fast355]

We did however recently have some kind of gasoline reformulation. I had been running 89 octane, KNOCK FREE on 32-33* total timing in my Titan. Suddenly it was picking up knock activity at WOT, no actual timing retard yet though. Nothing more than a few months time and a noticeable change in gasoline quality. Computer even picked up the change and adjusted the ethanol % accordingly. I am thinking we are getting more than 10% in most batches here. I am glad that I logged it, moved up to 93 octane and retarded the timing 2*, before I hit it with the 75 shot.

[brian617]

I am thinking we are getting more than 10% in most batches here.

Buddy at Chevrolet dealer said he tested a truck with 14% recently (Walmart/Murphy station).

[EagleMark]

I'd have to look at the calibration but it is the stock High Octane table timing... by rights it should not be knocking, on stock motors that have been running high octane I've seen no knock retard to 1*. At one point in a log it was only getting 10* and pulling 8* timing.

The GM.ASPARK PID is still at 70% as well, so thats 70% High Octane and 30% low octane table for spark advance. Don't think the knock sensors were over tightened, the owner of the rig is a certified tech and owner of the shop as well as aware of knock sensors being sensitive to torque. He checked today and the were not AC/Delco but Delphi replacement sensors.

AFR is about 12.5, I've set it up VIA EQ Ratio at 1.16.

The oil is interesting! We'll be pulling plugs tomorrow for a look. This is a brand new motor and maybe 500 miles on it. No notice of any oil burning or loss. Also going to try turning off the knock sensors and see if they are the issue...

[ony]

maybe plugs to hot?