I've got everything tuned in pretty well. After the FPR fiasco I'm reading to do some tuning again...

I get some serious spark knock when I first fire the engine up. I know that too much SA will cause the knock, but where do I take it out?

I can't really watch the scanner as it's not doing anything while cranking.

I don't want to start taking timing out everywhere because I have no idea where to start. I'm assuming it will be in the 90-100 kPa area and 400 rpm...or something like that. I'm not even sure if the ECM has control of the timing during cranking...or if it's purely where the dizzy is at.

Maybe I could take it out of the the cold SA bias table? ...at 0 vacuum?

 

If I remember right, you're using the '7747? If so, maybe try taking some out of Startup Spark Added and/or adjusting the Startup Spark Decay? I'm no expert by any means, but it looks like a good place to start.

 

Yes I'm using the 7747.

I seem to remember that the start-up SA didn't come in until AFTER the engine was running. The start-up SA was there to burn off all the choke fuel.

...I think...

...can anyone clarify?

 

I am not familiar with the 7747, but with my 7730-8D, the starting cranking does not show rpm or spark advance until the engine fires. Then, at engine start, there are always knock counts. After starting, no further knock counts appear until the next start-up.
So, unless some severe knocking is bothering you, I suspect what you see is normal.

 

Yeah a few knocks is ok...but this knock sounds like a diesel engine starting.

I had the engine cover off while I was starting it...which basically means my right foot is less than 12" away from the engine. You can really hear it...it sounds terrible.

This is only on hot restart...

 

check your main spark table for a really high value around 100kpa or so at 400-600 rpm. just a random thought.

 

When is it knocking?.
During cranking ie less then 400 rpm-ish your just on the module, no ecm involvement.

If you mean the first 30 secs or so after starting there is an addtion SA table.

FWIW, you should give any engine a full 30 secs at idle on start up before engaging the boiler room.

 

It knocks the second the engine fires up. The scanner is recording these knocks at 1000 rpm x 80-90 kPa.

BUT I know it occuring before that, WinALDL is just recording it there at the time it gets the info.

The best way I can describe it is to say it knocks real hard the instant you let off the key from cranking.

thanks for the input everyone

 

Add more starting fuel for the warm coolant temps?

 

Guys, does the 747 do the same Knock sensor test that the 730 does??(apon startup I mean)

 

If I understand correctly the 7747 does the KS test the first time it goes into PE mode. Until the test is passed you don't get PE SA....I think.

I dinked with some things...took a look at Grumpy's 747101.bin to see if I could spot any trends. I noticed that the cranking AFR and the choke AFR was ALOT richer than mine.

I tried turning the fuel up a bit on mine. It got better so I gave it some more. It was almost completely gone so I set my base timing from 8* to 6* and now I don't have any problems.

I still get a couple counts on WinALDL...but it doesn't sound like it's gonna blow on start-up...that's how loud it was.

 

Look at the CTS spark adder, at cold engine.
And maybe try dropping the IAC max down a LITTLE bit.

Your first couple revs might just be too high before the oil pressure comes up.

 

Thanks all. I also tried turning the IAC park position down from 140 to 120 and now it starts great!

 

Good to hear.
Thou for those listening in.
When you play with the max park and various park positions of the IAC, you need to watch what effect it has on what the crank pulse width does. As you lower the available air supply, you in a fashion richen up the cranking AFR.

And when you start fudging with the IC, and changing injector sizes, you can really screw up the cranking prime strategies.

So you'll also want to get clear on the clear flood strategy you chip uses, and make sure it's what you think it is, and works the way you want it to. GM uses several different clear flood modes so you need to figure out which one you have. Not often a critical thing, but just one of em lil things that makes a difference from close to CORRECT.

 

This is all I found on clear flood...
So when the TPS reaches 65% it goes into clear flood mode. Then it uses 6.0:1 AFR?? I thought clear flood was to get the fuel out of the engine. How does going to 6:1 AFR do that?

I guess there's something I'm missing....

 

While in clear flood the AFR value at LD2C7 is added to the crank AFR. Thereby making it leaner.

Note that there are hot restart AFR/IAC/CTS terms at LD300 - LD305. Unfourtunately the '747 does not have any hot restart SA retard functionality.

RBob.

 

I have a bad knock now exactly the same as your describing.I just figured It was the crank slapping the block the first few seconds of startup.It only happens on the first start of the day in cold weather.This seem to started happening after the 1:6 rocker upgrade.I will try to change my base timing to 6d and slight lower max iac.But what else ,I have 730 ecm 400sbc and stock s/a tables/cold startup.