Detonation

[djmac]

I have a 82 Jeep J10 with a Ford 460 engine and a Custom EFIS Multiport (91 camaro ECM). I have a problem with pinging or detonation since I started her up this spring and I have no clue why. I am not a tuner but rather I record a datalog and then burn my chip with the file created by my tuner. I have checked the base timing (6* before TDC) added 110 octane fuel, and nothing improves the situation. I can get a ping by merely reving the the engine in the driveway! It has a steady ping under almose any pedal pressure under load. my tuner says it can't be be spark knock because he has zeroed out the table? Not sure what that means but I am not recording much in the way of knocking in the datalog . My ECM controls my timing as well and I was wondering if someone could explain how exactly that the timing adjustments are made. Is it strictly an eletronic function or does the ECM control the base or breaker plate in the dizzy? The reason I ask is because I am trying to figure out if something mechanical is sticking (breaker plate) or is it a tuning problem or another mechanical problem. It pings in open or closed loop but seems to get worse as it warms up. Any help regarding this matter would be appreciated.

[EagleMark]

Timing is all havdled by ECM depending on what you did to convert the distributor on your Ford.

Also a 460 would need some big ass injectors, what do you have and what presure are you running?

You can check with a timing light.

What happens if you disconnect the timing bypass wire? Usually brown with white stripe and has a disconnect built in. Disconect it, check timing, what is it?

Unless you have a mechanical problem like a bad piston...

[1project2many]

Please enlighten us about your engine and the setup you're running.

Stock 460 or built? Used engine or fresh overhaul? Cam size? Compression ratio? Injector size?

If I read this correctly, you're hearing knock when the engine's running but the knock sensor isn't detecting knock. Is this right?

The knock sensor and to a lesser degree the knock filter circuitry in the computer memcal are designed for a specific engine and it's really based on cylinder diameter. You can install these parts on different displacement engines but it will change how the sensor and the ecm responds to real knock.

If you think you are are hearing knock and the sensor isn't reporting knock the first step is to confirm the sensor can report knock. A tried and true method is to tap on the block with a hammer while the engine is running and watch to see if the scantool / laptop reports knock. If no knock is reported you need to diagnose why.

If you are hearing a noise which only sounds like detonation you need to confirm what that noise actually is. Timing can be set at a fixed value to help eliminate spark advance as a cause. Tools are available to listen at different points on an engine to help locate where noise is coming from. Spark plugs can be removed and checked for signs of overheating or detonation. Individual cylinders can be disabled to try and isolate a specific cylinder. And inexpensive cameras are available for looking into a combustion chamber to possibly ferret out signs of mechanical damage or contact.

Good luck.

[EagleMark]

Good information! Shannon?

Another point a lot of people overlook when they do GM EFI conversions is the knock sensor besiades what was said above, is designed to be in a water jacket. Now think of what it can hear through water right next to the cylinder wall.

I have done many conversions on many differant engines and use a knock sensor as a tool, if I can? Sometimes I can make an engine knock and hear it by ear and the knock sensor never sends a signal.

[RobertISaar]

a 460 has a 4.36" bore.... might be difficult to match up a filter for....

a BBC 427 has a 4.25" bore, that's the only one i can think of.

[djmac]

Thanks for all the input guys:


Disconnected the timing bypass no change

Pulled each plug wire one at a time the ping remained for each cylinder

Checked the timing (6*) Moved it around a little bit ....no change

Hammered on the block....no knock count

Pulled all the plugs and performed a compression test...BINGO looks like a blown head gasket on the right bank between the 2 center cylinders. I ordered the head gasket and will put it in this week. Hopefully this will take care of my low vacuum too.

As far as my engine goes it is nothing wild but it has a few mods:

milled ported polished heads punched out with large valves

Compression is around 9.5:1

26 pd injectors

Fuel PSI 45lbs (adjustable regulator)

MSD 6A CDI and a Blaster Coil

Cam: Voodoo part number 61602. 219/227 @ .050" lift.

.540" / .552" lift

Bored 60 over

It's actually quite a hybrid between the Jeep Body/Frame GM ECM, Ford Motor, Trans and 1 ton axles from a 78 Ford Pickup. Gets about 9 mpg downhill with a tailwind.

[EagleMark]

Glad you found a problem, hope it,s the one your looking for!

Wonder if the block and head a true?

Those cams specs, even in that big a cubic inch motor are still going to produce a lower vacuum. So chip tune will be mandatory even just for idle.

Sounds like a sweet truck, but you know the rules?

[1project2many]

Well, you might want to get with your tuner to find out what settings if any have been changed relating to the knock sensor. The factory manuals can do a good job describing tests for the sensor which will help you narrow down the problem. Tests are generally fairly simple: Check resistance through the sensor, check for voltage from the ecm, and check for fluctuating voltage at the sensor with the wire connected when tapping on the block.

You might want to look at the Marine world for a knock sensor which matches your engine. Some of the boat makers used 460 engines and there's a good chance they had a Delphi or GM engine management system installed.

[EagleMark]

You have any links to Marine injection?

I have worked on a few and none had knock or O2.

Since your introduction turned into a tech discussion I am going to move it into the GM EFI section as that is the EFI system you are using.

[djmac]

Glad you found a problem, hope it,s the one your looking for!

Wonder if the block and head a true?

Those cams specs, even in that big a cubic inch motor are still going to produce a lower vacuum. So chip tune will be mandatory even just for idle.

Sounds like a sweet truck, but you know the rules?

Here is a link to a photo before I added another 5 inches of lift.




I put a straightedge on the block and it looks good. I just dropped the head of to have it resurfaced just in case.

[djmac]

You have any links to Marine injection?

I have worked on a few and none had knock or O2.

Since your introduction turned into a tech discussion I am going to move it into the GM EFI section as that is the EFI system you are using.

I have no links but I would like to check it out. I know the guy who at CustomEfis acknowledged that the 350 small block knock sensor may or may not work well in BFF.

[1project2many]

No links handy. Google is your friend.

MEFI controller is capable of knock and O2 control. O2's deleted on marine apps due to water cooled exhaust but control system was capable of using it. Knock sensors used in Mercruiser and OMC Apps among others. 305, 350, and 454 MAG EFI and Scorpion engines are a coupe apps I can think of. Trick will be finding 460 engine running MEFI or using a GM knock sensor. Mebbe the 470 Merc engine?

[1project2many]

The 350 knock sensor probably isn't the best match for your block but I would expect it to report knock if you hit the engine block. Check your sensor and figure out why the ecm isn't reporting anything.

[djmac]

The 350 knock sensor probably isn't the best match for your block but I would expect it to report knock if you hit the engine block. Check your sensor and figure out why the ecm isn't reporting anything.

Here is a comment I got a while back from my tuner. Did his change stop the sensor from recording?

You're not getting any spark knock, because zero'd your knock table out some time ago. took a liitle fuel at idle, but really suspect something else is amiss.

[Six_Shooter]

You may not be getting any knock induced retard, but you can still have knock counts.