kevosiroc

Last night I datalogged my car (see sig), 7727 ECM, $8d using AXCN modified. I was getting spark retard (and high knock counts) all over the place except idle. This was my first successful log where everything supposedly was right.

When trying any acceleration, the engine loses a ton of power which seems to correspond to the spark retard. During one acceleration, I have 17 degrees of retard at 25%tps, 70 kPa, 2600 rpm and BLM is 137.

The EGR and AIR systems have been removed physically and "disabled" in the bin file.

Does it make sense to start adjusting the VE tables and maybe reducing the spark? Or should I do something to reduce the max knock attack rate and then make another log?

RBob

iTrader: (1)

I would burn a test chip with 10° less timing across the board. Do this by increasing the initial advance term in the bin by 10 degrees. IOW, if set to 6°, then set it to 16°.

If the knock counts go away then you will know it is a timing problem.

If the knock counts continue then you know to look for a mechanical problem.

Also double check that the distributor timing has been set correctly.

RBob.

vernw

iTrader: (2)

An exhaust leak will cause lot of false knock counts. Check for that. A loose header bolt was my cause.

Also - you're not running a gear drive instead of a timing chain are you? Those wreak havoc with knock sensors as well.

Or any "noisy" accessory like an alternator going bad, etc., could cause a bunch of false knocks.

Just some additional ideas in case Rbob's idea doesn't help.

Good Luck!

kevosiroc

My base timing is set at 8 mechanically and on the bin file.

My compresison ration is 10.33:1 and I have been running 93 octane.

No timing gears here, just a good ol' roller chain.

Thinking out-loudly here..................

I will recheck the timing and header bolts, then I think I will try octane booster. If octane boost does not help, then I will retard timing as RBob mentioned.

I am going to add fuel in some of the places that the log showed lean (140 BLM or higher) before I drive again. That should be OK, right?

The spark plugs did not show signs of detonation. If retarding the timing does not help, should I take the knock sensor out of the loop and see what happens? There has never been any audible knock noises.

vernw

iTrader: (2)

I wouldn't recommend removing the knock sensor, but it might be okay for a quick and short test. Probably no reason to though, you aren't getting knocks at idle from what you said, so the sensor is probably fine itself. Just make sure you're using a 350's sensor on a 350 or 383, a 305's sensor on a 305, etc. There is supposed to be a difference on block size as well as possibly the year it was designated for. Plus - if it's knocking loud enough to hear it, you've got a major problem. You don't have to hear the pinging to sustain internal engine damage.

Where did you get the BIN you're using? Maybe you have an aluminum head bin (more timing typically) and you're running iron heads. Or a lot more compression than the BIN was originally for, etc.

Are you running the standard AXCN timing table?

FWIW - I'm running 10.5 with iron fast burn style heads and don't have problems like you're seeing. I used AXYC (manual tranny, speed density) as my base - but I also had to drop the timing downs from the factory low compression smog-level timing tables.

Just for grins, throw some cheapie muffler(s) on that open exhaust and see if the problem continues. I wonder of that could cause the knocks.......

BMmonteSS

The ecm is probably heading off the knock before it ever goes audible, so taking the knock senosor out of the loop would be a bad idea if the problem happens to be just too much timing. I would try Rbob's suggestion first and see what happens. With 10.33 to 1 compression you could very well be into actuall spark knock.

DAVECS1

iTrader: (2)

I may be lucky, but I am running the Pete Jackson Quite gear drive and a full aftermarket roller setup, and I barely get any knock retard. I do not believe the knock sensors are as sensitive as people say. They are effective though. The motor I built before this one, sounded extremely healthy, but was experiencing knock retard and I could not pinpoint it. First day of tuning it dropped a valve (too much lift) and the only non-forged piece (the block!) gave way.

1. I would personally double check the timing. Set it mechanically were you want it, and set it the same in the .bin file.

2. Check the fuel injector constant in the .bin

3. Look at the log file and richen up the areas that are seeing the most knock retard.

4. If that is unsuccessfull back the timing down in those areas

5. If non of these steps work start looking for mechanical collisions or noises from the motor, and do not drive it too much until you get it fixed.

Is this the stock motor?????

If it is whay are you starting with another .bin? I would modify the one that came with the motor. If your buddies carburated car ran like stink, but had different heads, cam, and intake, would you use the jets he had in his carburator?

kevosiroc

vernw,

Uhm, Edelbrock heads = not iron. The AXCN is for a 91 L98 corvette. I have a 90 L98 vette. All of the engine components were the same from 90-91. Bin is fine... correct application. Timing tables are about stock, and yes, they are aggressive, but the head design is better than stock.

vernw

iTrader: (2)

Then look for valve and or lifter noise, exhaust leak, etc.

As easy as it is to do, try RBob's idea first and see if that helps.

If it does, then you know you don't have any mechanical problems, right? At least you can rule all that nonsense out if that works...

Z_Ghost

Something to think about if it’s real spark knock.
With the new heads you may not need all that aggressive spark advance, better chambers sometimes like less spark advance.
You need to get the BLMs closer to 128, 140 is way to lean and could be part of the problem and you probably also need to play with the pump shots some.

Once spark knock starts it’s hard to get it to stop.

DAVECS1

iTrader: (2)

Does it exhibit knock with the stock chip? You may have changed the heads but if the cam is stock you may not want to shift your timing events to much.

kevosiroc

OK, set timing to 18 like RBob said (base timing is at 8degrees). Still get lots of spark retard. Goinjg to try putting in racing gas to see if octane number is the problem.

vernw

iTrader: (2)

You went the wrong way!!!!

You're supposed to try LESS timing, not more. Set the distributr to zero and see if the knock is still there. If you advanced it to 18 base EVERYONE would be knocking something fierce.....

Teeleton

I seem to be having some odd false knock on my TBI. If I cruise on the freeway at 2400 rpms, the computer just continuously counts knock. If I cruise at 2200 or 2600, no knock at all. It's really odd. I can go cruise all over town, get home and the whole row at 2400 has knock counts in the 50+, and everywhere else will be a couple scattered 1s and 2s. I have the hiway and PE spark tables zeroed out, and there's hardly any difference between the three rows in the spark table. The most annoying part about it is that 2400 is my typical highway cruise RPM!

Teeleton

dimented24x7

iTrader: (2)

If he set the base time in the prom to 18 then it would have sub'd out 10 degrees across the board. The ecm subtracts the base timing out of the overall timing before its sent out the door to the distributer.

kevosiroc

Exactly what you said. I set the base timing to 18 in the bin file.

there is some lifter noise I think, but that never affected any of my other cars. I am not totally sure that the lifters are making any noise.

I am going to get racing gas and see what happens, then I will try setting "min temp for knock sensor enable" to max and see if the engine runs OK - also maxing spark advance to 35 degrees.

kevosiroc

So here is what I did Yesterday: changed the highest spark advance to 35, 10 gallons of 100 octane racing gas to 10 gallons of 93 octane, plus octane boost (not sure that stuff works), and setting "min temp for knock enable" to 151 degrees C.... results:

car drove the same at idle and very low throttle (which from before was OK). It seemed slightly better at larger TPS, but the whole time it felt like it was not firing on all 8 cylinders. It used to do this before - but WOT was OK, now WOT is just as bad as everywhere else. I have checked everything in the ignition system and it is OK. Pulled a few spark plugs and they looked normal.

Now when he car is really hot (or fully warmed up after a little drive) I hear a small ticking like a lifter is collapsed, but all of the lifters are practically brand new. The engine now probably has about 200 miles on it. There is no oil in the coolant and vise-versa. The headers are tightly bolted up.

Could it be that there is still too much timing? Can someone show me a timing table from an engine with similar components (AL heads, fully ported intake, slitghtly hot cam)??

vernw

iTrader: (2)

Sorry to be the bearer of possibly bad news, but I had to swap out 3 lifters on my 383 when they "stuck" just 400 miles into the new engine. Been fine ever since though (swapped out all 16 when it happened).

Since my heads aren't iron, my table won't help much.

Sorry for miunderstanding your timing changes earlier, I though you changed the dizzy to 18BTDC (not the bin).

Just one thing to think about - if the E heads are "fastburn" style, then they'll typically require a little less advance ("fast burn"). As I understand it, porting work, etc. doesn't affect timing, just the amount of the breathing/HP due to better flowing.

edit: soRRY - MY HEADS ARE CAST IRON....

kevosiroc

My heads are not iron either.

Can I see your lower spark table to compare with mine. I am currently using the spark table from AXCN which is what my car came with, but I limited the max spark to 35 degrees or so.

DAVECS1

iTrader: (2)

Were you having problems before you installed the crane cam in your signature? I built an engine not to long ago. I checked and rechecked the valve to piston clearance, I would of bet my life that I had plenty of room. It ended up when the car was fully warmed up and runnin that the valves expanded just enough to graze the tops of the piston. The car exhibited alot of the same problems you speak of. The way I finally found out this was happing was one night after cruising around and data logging, one of the valves broke and locked up the engine. I remember when I tried to set the valve lash with the engine running, I could feel that the exhaust valves felt different from the intake valves. You might want to pop the valve covers and check it out.

kevosiroc

There was no interference. I found the problem. The spark plug boots were too close to the header (I have straight plug heads and need angle). Cylinder 2 and 5 boots were melted and are arcing throwing off timing and causing all sorts of problems. at idle recently, the car was shaking a bit. Now I have to decide between pulling the headers out and denting them for the plugs, or replacing the heads. I have had my eye on the GM fast Burn head for some time now. hmmmmm.........

What to do. I have cash, but supposed to be for rollcage. And I just got the heads ported from a porting guru (the heads were for my 1992 camaro which needed straight plugs). When the carmaro rolled over, the engine went into my vette. The heads have very little run time on them. I do not know what to do..............

vernw

iTrader: (2)

Try some shortie plugs? The Accels work for me....

kevosiroc

the accel shortie plugs do not have the proper reach for my application

the longest reach they make is 0.460". I need 0.750" reach

vernw

iTrader: (2)

Then you might check out the NGK plugs, they're only 1/8 or so longer than the Accel header plugs.... I used both successfully. Some of the asbestos woven boot covers help as well, used them in the past.

Beats dimpling or replacing the headers....