Knock

[bjzq8]

I am fascinated that my engine knocks at 9 PSI of boost and 18.75 degrees of advance, at 4317 RPM. The boost built to 15.8 PSI, where I was running 5020 RPM, and had a whopping 3.75 degrees of advance...after FAST pulled 17 degrees of timing. This is with Vortec heads, btw. I replaced the plugs with (identica) NGK TR6s. I replaced the entire distributor. I am running 93 octane gas, and drained the tank once to make sure there was nothing bad left in there after sitting for awhile. I've checked the timing with a timing light, it's right on where it should be. In the cells where it was running, I should be getting 17 degrees of timing. The air/fuel ratio was 11.62 while this was happening. I'm going to try it again with methanol injection tonight...I've had it turned off to try to figure out why it's knocking so much. If I remember correctly, the knock goes away with a medium amount of methanol.

I have only a few ways to explain this:

1. Perhaps the engine got built with the wrong pistons by accident? i.e. high compression instead of dished.
2. My engine is cursed.
3. I am cursed.

I'm leaning towards one of the last two.

So to state a specific question...what else can I be missing here? Why would my engine be pinging at 9 PSI of boost?

Here are the specifics:
4-bolt block
Billet Crank
H-Beam rods
Forged pistons
Big-valve Vortecs
T66/Front A2A
FAST/50lb injectors
Methanol injection (turned off currently)

I've recently pulled this truck out of my garage; I got disgusted with it three years ago, and now I remember why. I've got 7 different FAST log files, all of them show a similar pattern of lots of ping at low boost. I can hear it very plainly, and so far I've had enough sense to back out of it.

 

[NecroWolf]

Re: Knock

false knock? carbon build up? run a compression test and see where you're at and you'll be able to get an idea what the compression is.

 

[bjzq8]

Re: Knock

It's done this since the rebuild, I don't think there would be any carbon to build up. Still possible, though. I will do a compression test and see what I get in that department.

 

[bjzq8]

Re: Knock

I ran it with methanol injection last night; at 12 psi and the knob turned up half way, the knock was gone. I tried 15 psi, and it was the same; the vehicle accelerates very strongly with no pinging. I tried 18 psi, and the first time, it took off fine. The second time (a minute or so later) it began pinging, with the regular falling-on-its-face feeling. I turned the methanol knob all the way up, and a minute later, tried again. Same thing. I guess maybe it's getting heat soaked after multiple runs...but I'm pretty sure I'm not getting any false knock. I didn't do the compression check because it started to rain later that night.

 

[WyoSyclone]

Re: Knock

What sparkplugs and gap are you running? 93 octane is low for these trucks. I dumped a couple of gallons of xylene in my tank because I've had the same problem... it almost eliminated my KR.

 

[bezerk]

Re: Knock

93 octane and 15psi can be a problem,. alsoo the 11.6 isn't that rich does it pull 17 degrees of timing because of knock?
also see if when you tike the 17 degrees of timing out in general, does the knock goesaway?

 

[bjzq8]

Re: Knock

Plugs are NGK TR6. Last I gapped them, they were .030.

It had been running 10.5-11.0 fuel/air and knocking just as much; I thought maybe it had been overfueling. It didn't seem to change the knock much.

When it begins pulling timing, as long as I keep my foot in it, it keeps retarding until it can't retard any more. It goes to 2 degrees BTDC and sits there. The engine is set for 17 degrees of advance at the point that it's knocking most, but it keeps pinging. In fact, I see 20 degrees of retard at one point.

Tonight I'll try to pull the timing at that point back to like 10 degrees and see what a difference it makes. I'll also do some runs at 12 psi to see what a difference that makes.

I guess I'm surprised that I'm getting that much knock at only 15 psi with Vortecs? Maybe it's time I get some 75-pound injectors and convert it to E85. The stuff is $1.49 here.

In a way, it feels good to tune the thing, as well as frustrating. I know there's a solution there somewhere. Thank you for your input.

 

[It's just a six]

Re: Knock

Just a comment, IMO I do not believe that the newer Vortec heads are the cure for removeing knock.

If it pings w/E85,there is definately a problem.

 

[bezerk]

Re: Knock

i agree. i have vortecs and a pt67 and i get knock at 15psi as well. what kinf injectos you have? and do you actual hear it pinging? if so i would get the foot of the pedal because 17kr is engine rebuild time soon

 

[bjzq8]

Re: Knock

I've got 50lb high-impedence injectors. I actually hear it pinging, sounds like a frying egg under my hood. It was a relief to hear nothing but engine when I turned up the methanol. I can't keep my foot in in very long anyway because it falls flat once the timing goes to 2 degrees.

 

[WyoSyclone]

Re: Knock

You might want to re-verify true TDC of #1 then check your timing mark to make sure something didn't get out of whack during the rebuild. I also didn't see any mention of your fuel system - do you have a 255 pump, new filter, correct fuel pressure (base and rising with boost)??

 

[bjzq8]

Re: Knock

I haven't checked TDC since the rebuild, but it does have a new balancer and not the original. I'll certainly put it near the top of my list. I have a 255 Walbro pump, and a fuel filter with less than 5000 miles on it. I checked the fuel pressure with a gauge on my hood. Fuel pressure was a base of 45, rising with boost as it should. Back when this was my "original" problem, I tried fuel pressures between 40 and 50 with no change.

I'll report back on my findings when it stops raining.

 

[Quickstop [UK]]

Re: Knock

how old is your Walbro? cheap chinese copies around recently could be causing you headaches.

What were your original problems then?

Also as mentioned the vortec chambers are less susceptible to knock but not the panacea. You've got something else going on. I am surprised you've not verified TDC in this time though.

Hope you get it fixed.

 

[bjzq8]

Re: Knock

The Walbro was new in 2004, went on with new 50lb injectors and a round-type Ultimate.

I had a new engine built, T66 turbo put on, 422 cam, Vortec heads, FAST installed, etc shortly thereafter. It had a new SFI-type balancer put on at that time. As soon as I got it home, I noted that it had a problem pinging, even at 12 psi. I changed a lot of parameters in the FAST tables, pulling some fuel (it had been overfueling a bit, 9:1 A/F, changed that to 11:1 or so) and it seemed to settle down at 12 psi...but I still could not run 15 psi. At the time, the builder said "it's like we put high compression pistons in it or something." It's really baffling me.

I got disgusted with the truck, got a new job, got busy, and it sat until early this year, from Spring 2006 until Spring 2009. I even offered to sell it at one point, but again got so disgusted with the truck that I didn't come to syty.net for over a year. Even now, I shudder to think how much time and effort I've put into it for such little gain.

 

[WyoSyclone]

Re: Knock

Well, three things I'd do, I guess...
- If it's been sitting that long, I'd get all the gas out of it and make sure things aren't gummed up, although if it was doing back after the build this wouldn't be a cause, but something you don't want.
- Try taking the plugs down to a .025 gap and see if it makes a difference
- take a compression check. IIRC the reading divided by 18 gives you a pretty close CR figure.
My truck reads170 to 172 across all cylinders, which means they either milled the heads too much when they rebuilt it, or has got the wrong pistons in it (which I doubt). I believe 'correct' compression is around 155.

 

[bjzq8]

Re: Knock

I have run three tanks of 93 octane through it since the "resurrection."

I will do a compression check and re-gap the plugs tonight, if I get time.

 

[bjzq8]

Re: Knock

I only had time to check and gap one cylinder last night. I got 135 psi of compression, and the plugs were gapped right at .030. I then checked TDC by rotating the engine until the piston just contacted a wood dowel, marking the balancer, and then rotating it the other direction, and re-marking...it was right on with the balancer. That is, the halfway mark was right on 0. I took it out and ran it with half of the methanol dial turned up, and it pinged at 15 psi this time. Not encouraging! I haven't changed any timing or fuel values in the FAST program yet. If I can't get it to run on 15 psi, I guess I can settle for 12...although it seems as though it will be 12 WITH methanol injection.

 

[Quickstop [UK]]

Re: Knock

I got 160-170 on my newly built engine - your compression sounds low.

what boost gauge are you running? MAP sensor ok? If it is misreading then you'll be getting the wrong fuelling.

Also, "settling" is prob not a great idea as your underlying problem will haunt you and you'll accidentally get into it at some point.

It's just a matter of time if you don't sort it.

 

[bjzq8]

Re: Knock

I'm going by the FAST data for boost. When I set the MSBC for 15 psi, the FAST graph goes to 15 psi and stops, same for 12 psi. I don't have a guage for boost any more. I have a 3-bar map that I ordered back in 2004 when I put the Ultimate chip in. I suppose I could try to replace that, but it's never given any indication that it's bad. I haven't checked more than the first cylinder yet. The engine was cold at the time, how much does that change compression? At this point I'm willing to try anything, including chicken entrails.

 

[Quickstop [UK]]

Re: Knock

the sensor gives that info to the FAST unless you have a separate sensor.

If it was misreading it would tell you it is running at 12 but could be at 15 but the FAST thinks it is 12 becasue the MAP sensor is telling you that.

So you're lean and it all looks ok on the FAST... worth considering.