After tuning my closed loop BLM's to near 128. (87 TBI 350, 747 ECM, headers,injector spacer). I am getting a lean knock when accelerating heavily from a stop. I Doubled the accel enrich Vs TPS values and this got rid of the lean knock till the next time I drove the car. I think the ecm is subtracting the extra fuel and causing the lean knock. Is this possible? And how can I fix this? -Rod-

 

U said u tuned your fuel tables to 128. Have u done any tweaking to the spark tables?

Getting the fuel to 128 is only the first step.

U must also make sure the knock is real and not from a false source as a bad tensioner or resonation.

If u increase AE and it doesnt help, it could be from another source and the sensor is picking it up or you have too much timing there for your combo.

To accurately work on the AE stuff you will need something like a wideband to get a better understanding of what is truly going on.

U may need to take out some timing as well as add/subtract AE depending on the particular area of the table you are in when the "knock" occurs.

later
Jeremy

 

Yes I have also tried taking out timing at the low RPM ranges where the Knock is happening this did not help. I also increased the amounts of timing the ECM can retard the timing when knock does occour but i still get audible loud knock. I am using the stock spark table. In addition to the knock I am also getting a hesiitation when I accelerate from a stop. The hesitation lasts 1-2 seconds then the car will take off, no stalling just does not accelerate. Does this when the engine is in closed loop. Open loop no problem.

 

Does this heavy knock only occur once or twice after each time you start the engine? The reason I ask is that there is a forced knock routine that is used to test the Detonation Control System (or in GM-ese, Electronic Spark Control, ESC).

RBob.

 

It Knocks at least 1/2 the time If I accelerate with about 1/2 throttle from a stop. The hesitation is always there. Unless I am real light on the throttle. The the check engine light comes on with a ESC code. Is it possible the O2 sensor is making the engine run lean. It is a bosch 3 wire about 3 months old. I increased the A.E. and it went away till the next time I drove the car. Could the ecm take out fuel that is added in A.E. based on O2 sensor readings? -Rod-

 

Yep, forced knock test. . . Go over to the diy-efi site and get the esc_done.zip patch. Apply that and finish your AE tuning.

RBob.

 

So you think the ECM is testing the Knock sensor or ESC by advancing the timing when i get on the throttle hard. I would like to try out that patch to see if it would work.
Is it on the DIY EFI or GMECM? When I click on list of files on the DIY EFI I get "Page not found"
The GMECM site just had a lot of bins unless I am missing it somewhere.
Can you help me out finding that file Rob I searched high and low, all I could find is a whole lot of bins. Thanks -Rod-

 

Actually I know the ECM is adding timing to force knock while in PE mode. For the patch I gave the wrong filename, it is: ESC_747.zip (sorry about that). Found here:

ftp://ftp.diy-efi.org/uploads/ESC_747.zip

Note that that server is case sensitive with the filenames.

RBob.

 

Thanks for all the help RBob. I downloaded that file but I am not good at figuring out line command stuff. So I decided to change the Knock Sensor (18 years old). That took care of the problem. I should have changed it when I put the engine in.
After that I decided to set the A.E. 's back to stock. I doubled them thinking I was getting a lean Knock. The stock settings are better. I also cut the stock settings in 1/2 and the engine still accelerated fine to my surprise. Must have a lot of wiggle room on those A.E. settings.
Again Thank you very much for the help in solving my problem.
-Rod-

 

Good to hear you got it going.

RBob.