Speeddemon777

Let me just say I really appreciate everyones input on this. I am trying to eliminate and do everything you guys suggested. At this point any idea is warranted to be discussed or tested.

I was on the same page as zali0104 after hearing about the timing. I was curious if it could be a bad knock sensor or crank sensor as well. Any good test I can preform to validate this?

Also, did some research and found that the fans on some of these alternators start to rattle or hit the windings at high rpm causing a false knock. I figured I would use a stethoscope and see what I can hear from the alternator. Although a timing chain and tensioner could also be a factor but I really hope not though with only 22k on the car.

The O2 sensors read the same after the cats as well as the temperature of the cats are within 50 degrees of each other I feel like if it was a bad cat one would read different no?

I did try to get a smoke test done from the speed shop I took it too, but they seemed to think if it was a vacuum/intake leak small enough to not show itself at idle it would be negligible at wot, so I opted for the dyno. I have been doing a lot of research on smoke test so I will try and do a DIY smoke test Sunday and report back with my findings.

For now I am completely convinced that I have a band aid tune on the car and do not want to push it unless I have too. I will do one more scan and try and get a video up before the days end. Thanks again guys!

schpenxel

The cat temp that is reported is calculated, not measured.

I had a TON of knock retard when my power steering pump was going out. It was rattling pretty loud though.. easily heard while going down the road.

Have you posted a log and a copy of the tune? It can't hurt. How much WOT timing were they running? I would be very careful messing with the knock sensor sensitivity settings. They are set quite well from the factory

Speeddemon777

He didnt give me details like that. I posted a dyno chart in my previous post. That was all the tuner gave me. On the dyno chart the blue lines are the first run with -22 degrees and -32 degrees of timing. I believe that is what I was told. You can also see the drop in his tune at 4500rpm. He said he couldnt advance timing anymore at this point or he would start to get detonation.

schpenxel

NEGATIVE? Jesus. If that's right, something is quite wrong. I didn't know an engine could even run with it like that.

There's also a max knock retard setting that should have stopped it from going anywhere near that far down. I really can't imagine that # being right honestly.

I'd love to see a log and the tune though. I agree with everyone else.. I think there's a real problem, not just the tune.

Joe_G

Man that is a bad dyno sheet, no offense. If you can get the .drf files from the dyno operator you can download the dynojet software and create a normal graph with HP and TQ numbers as the y axis and use RPM as the x axis.

I'm assuming that's the AFR graph at the bottom, it needs a Y axis legend as well.

If you get the .drf files and email them to me I'd be happy to make the graph for you.

Something is wrong I'm afraid with the car - if the plugs were misfiring that bad, it would set a CEL. Frankly anything that causes it to run that badly in the first dyno should have set a CEL.

Can you get the hp tuners log and email it to me? I'm no expert but I'm happy to take a look and post it up here so others can chime in if you like.

Can you check your fuel pressure? A gauge is pretty cheap at harbor freight. I'm wondering if your fuel pump is giving out or the sock is clogged.

The timing in the stock tune is pretty cut and dry normal - if your scan was showing timing way off, it was due to something mechanical in the car, I'm wondering if you have a broken cat as someone suggested rattling around that the car is reading as a knock event. That would also explain the rattling you hear.

Frankly as I type this that sounds like it could be your problem, it's not hard to check the cats if you have a lift. I've seen them break apart, normally on blown applications, but they do sometimes just break.

Or something as crazy as a IAT sensor going wacky and feeding the computer odd IAT readings which will move timing a lot - this kind of thing would be picked up on the HP Tuners scan.

djbrun

Joe_G,

I just sent him a pm not to long ago telling him to check the cats as well.

I am almost wishing the tune was not messed with, finding the route cause would have been a better way to start in my eyes.

DJ

Joe_G

You can always go back to the stock tune.

I bet it's your cats, did he mention if it there was a lot of knock retard?

See if he'll email you the .drf files and those two hp tuners scans.

Speeddemon777

Yeh I completely agree with everything you said about the first run. I was shocked to say the least, but I kinda knew the car was running awful. I will do my very best to get the .drf from the tuner. I will hopefully be seeing him on Tuesday when they are back from the 4th of July vacation.

Anyone have a way to test a cat. I was reading the GM SI and it wants you to remove each O2 sensor one by one and take a pressure reading with a special adapter. I mean I have a full lathe and mill so Im not to worried about the special adapter if I HAVE to make it. Anyway, pressures should be 3psi on both sides at idle according to GM. If there is an easier way/other way to do it I would love to hear about it.

I tested the resistance of the IAT and compared it to the "resistance to Temperature" chart in the GM SI. As well as did the test the GM SI recommends you do to make sure both the IAT and coolant temp sensor are within spec. They were within 3 degrees of each other with the engine completely cold, which is just within spec.

Both I and the tuner on did a fuel pressure tests on the cars fuel rail port. Fuel pressure was 60-65psi and hardly moved during wot.


I agree guys I really didnt want to put the car on the dyno, but I had 2 different shops tell me they ran out of ideas and the car needed to be dynod. I reluctantly said yes.

UPDATE:

So I took the car for a drive to get the video and a new log after the tune. The strangest thing is happening. When the car is under 200 degrees coolant temp the detonation or noise is either hardly noticeable or gone. Over 200 degrees and it gets more and more noticeable with temp. The tuner really wanted me to put a 180 stat in it. I mean I do like the shop that I had do the dyno. They have always treated me right. So I dont want to make accusations. I do find it strange they wanted me to do colder plugs and colder thermostat and it seems to be working somewhat better. WHY!?!?!!?!

The first video below I had a hell of time getting the car to make the noise mostly cause the coolant was below 200. It wasnt till after it reached 203 that it start doing something. Pay attention to the last clip in the video when I shift to 3rd you can clearly hear the noise. Sounds like marbles. I have another video my buddy took, which you can hear it a lot better. Im waiting for him to send it to me.

Would love to hear what yall think. Sorry for the long post

Log from scanner after tune here: LOG


I recommend headphones
First video go pro hard to hear(pay attention to last pull 3rd gear):

Joe_G

It's tough to hear but it could be pinging...can you scan for knock retard?

If you have a welder you could buy spark plug anti foulers which are the same size as O2 sensors and weld on an adaptor for a cheap pressure gauges...the gauges may burn up if you use it too long. I've seen cats come apart which you can see if you remove them or I suppose if you had one of those cheap boroscopes harbor freight sells. That might be your cheapest way to check actually.

I would think to review the scans before you go to that headache. Hopefully the tuner will give them to you.

schpenxel

Do you have a copy of the tune or can you read it?

96GS#007

Saw this type of thing twice before. Once on an old L98 Gen 1 SBC and a second time with an LS6. In both cases it was a stretched timing chain.

You've pretty much hit the point of guessing. You need to start thinking about being invasive and really checking things. Engines don't drop 100rwhp from a minor issue. Bad sensors set codes. Plugged cats have exhaust pipes glowing red.

I'd check to see if you have some failed cam lobes...unusual on roller cam engines but possible...and then I'd check the timing chain.

Speeddemon777

Happy Fourth of July everyone!!!

I was able to get another video that my friend took yesterday. It is much more noticeable on the audio. I am going to be checking the cats and then also try a smoke test tomorrow, then Ill see if the speed shop can check the timing chain as I have never done that before. Seems pretty crazy if the timing chain when out at 22k though. I do have a scope with an LCD so Ill try looking at the cat with that for any sort of blockage.

HERE is the new video:

Joe_G

We really need to see an HP Tuners scan of this car, it'll tell us what's going on. Do you have a friend who will scan you? It's free if you have the cord. Hopefully the tuner will give them to you.

I don't think your timing chain is a problem. They do break, but then they do they put valves in pistons, the engine dies, and you have a cam sensor CEL. They don't "slip". They work great until they fail and luckily they don't fail that often.

Speeddemon777

I have a friend I can call tomorrow. He may know someone with a HP Tuners that will scan it for free. Other then that I am reliant on the tuner. I tried looking to see if my scanner has a knock feature for checking the knock retard and it doesnt. :/

UPDATE: Not sure if this is relevant, but I figured I would post all things going on with the car. The scanner reported C0035, C0040, and C0281. Strange? Seems to be a bad wheel speed sensor?

schpenxel

Where are you located?

96GS#007

Timing chains most definitely stretch. Nowhere did I say "slip". When they stretch, it affects the actual thing event. The PCM only reports what timing is programmed in a given cell and any modifications being commanded. There's a reason a custom tune with different timing tables radically helped a stock engine. Hint: it's not a bad sensor.

djbrun

22k miles on a stock car, unlikely?


DJ

Joe_G

I think the wheel speed sensor codes are from the dyno. The brake light switch error I can't think how that would cause what you have going on. Do your brake lights work?

Here's a good thread.

https://www.corvetteforum.com/forums...ters-mean.html

Diagnostic Aids
C0035-C0050 18
Under the following conditions, 2 wheel speed sensors input are 0 and DTCs are set:
• The 2 suspect wheel speeds equal zero for 6 seconds.
• The other wheel speeds are greater than 16 km/h (10 mph).
• The other wheel speeds are within 11 km/h (7 mph) of each other.
Diagnose each wheel speed sensor individually.

Speeddemon777

Anaheim, CA
Speaking of...if anyone in the area has an HP Tuner and is willing to scan my car. I would be VERY VERY grateful!


Thank you! I will look into the codes in the link you sent me. Strange I dont remember them being there yesterday when I did the log, but you are probably right and they are just from the dyno. Either way I figured I would post them so everything is logged. I will also go check my brake lights.

schpenxel

That's what I was going to offer, but you're on the wrong coast!

One thing that may help you, is I'm 99% sure that HPTuners owners can scan the car WITHOUT having to license it. So that will be easier on both you and someone with HPT, if you can find someone local.