383 rattles under load

[haysonj]

My 383 when pulling a hill will start to rattle really bad. I'm using 91 octane on a 9.5 compression. What I'm wondering is if this is a mechanical problem or is it in the computer. Oil pressure is fine and temp stays around 195. If I put it in neutral it will rev to 5000 with no noise at all. It will only do it when towing under load. I'm thinking maybe the timing is off somewhere. Anyone have an idea on this. Thanks John

[kwmech]

Carb? fuel injection? where is the timing at?

[cableguy0]

Pinging or spark knock. Either the engine isnt getting enough fuel,octane isnt high enough or the timing is too far advanced. Are you sure compression is only 9.5-1? Do you know where the timing is set at? How much total advance do you have?

[68GMCCustom]

get a timing light and see where your timing is.

[haysonj]

Originally Posted by cableguy0

Pinging or spark knock. Either the engine isnt getting enough fuel,octane isnt high enough or the timing is too far advanced. Are you sure compression is only 9.5-1? Do you know where the timing is set at? How much total advance do you have?

Its a Edelbrock tune port injection timing was set at 10 degrees per instructions. I'm sure of the 9.5 comp as I built the motor at cruise speed the total advance is 48 I really haven't checked it with a light yet I'm pretty sure it is spark knock as it doesn't sound like pinging. Also the truck has no power under load but without the load it will smoke the tires in low gear.

[cableguy0]

Pinging and spark knock are the same thing. Its a rattling noise. I would be suspect of fuel flow. What are the specs of the rest of the engine? Estimated horsepower? A healthy 383 pushes the limits on the capabilities of that system. Have you been running this system long? Is this a new problem? Is the fuel filter new?

[haysonj]

Originally Posted by cableguy0

Pinging and spark knock are the same thing. Its a rattling noise. I would be suspect of fuel flow. What are the specs of the rest of the engine? Estimated horsepower? A healthy 383 pushes the limits on the capabilities of that system. Have you been running this system long? Is this a new problem? Is the fuel filter new?

Estimated HP is around 400 and System is good to 500 It has Scat steel crank, KB forged flat top pistons world 72 cc heads with headers I'm wondering if I may have got Gasket sealer on the injectors when I put the manifold on. I actually had the system on my 300HP 350 for about 10,000 miles and it did fine.

[Ticker]

It's almost certainly timing - either mechanical advance or (since it's happening under load) either an incorrect vacuum advance curve or the vacuum advance isn't working at all.

[haysonj]

Originally Posted by Ticker

It's almost certainly timing - either mechanical advance or (since it's happening under load) either an incorrect vacuum advance curve or the vacuum advance isn't working at all.

There is no vac advance it is all done by the computer. I can change the advance at different RPMs and Different Vac levels But I don't have enough understanding Of why I'm doing it so I may have to take it to someone that has a dyno and let them tune it. The hand held that connects to the computer has a light that changes from red for lean to green for rich on the fuel and it is almost always green except when I let off the throttle it will go red.

[Ticker]

Originally Posted by haysonj

There is no vac advance it is all done by the computer. I can change the advance at different RPMs and Different Vac levels But I don't have enough understanding Of why I'm doing it so I may have to take it to someone that has a dyno and let them tune it. The hand held that connects to the computer has a light that changes from red for lean to green for rich on the fuel and it is almost always green except when I let off the throttle it will go red.

I missed the post that it was Edelbrock TPI But as you note, even though it's computer-based there is still RPM and vacuum-based advance.

Which unit is it specifically (P/N)? Do you have a pointer for the manual on the Edelbrock website?

If there's a simple way to just turn down the amount of vacuum-referenced advance, that's where I'd start.

[haysonj]

Originally Posted by Ticker

I missed the post that it was Edelbrock TPI But as you note, even though it's computer-based there is still RPM and vacuum-based advance.

Which unit is it specifically (P/N)? Do you have a pointer for the manual on the Edelbrock website?

If there's a simple way to just turn down the amount of vacuum-referenced advance, that's where I'd start.

Its the Pro Flo I 3500 series which I believe has been replaced with the Pro Flo II I can turn down the advance at certain points but I'm not sure which points to start with. I tried doing it on the global screen which retards it across the board and the truck didn't run very good. I should take it out and watch the screen and see where the advance and vac are when it starts to ping. Here's the link to Edelbrock
http://www.edelbrock.com/automotive_...oft-tech.shtml

[cableguy0]

can you post up where your timing is in 500rpm increments starting at idle? The curves in a mild 350 will be a good bit different than in a 383. Basically the pinging is stealing your power.The mixture is igniting before it should. Sometimes it will occur before the piston is even at the top and try to push engine backwards. Its definately not a good thing at all for the engine and can cause serious issues. burnt/broken pistons trashed bearings etc etc. Does that system have the ability to show you where the timing is when your under load at a given rpm?

[haysonj]

Originally Posted by cableguy0

can you post up where your timing is in 500rpm increments starting at idle? The curves in a mild 350 will be a good bit different than in a 383. Basically the pinging is stealing your power.The mixture is igniting before it should. Sometimes it will occur before the piston is even at the top and try to push engine backwards. Its definately not a good thing at all for the engine and can cause serious issues. burnt/broken pistons trashed bearings etc etc. Does that system have the ability to show you where the timing is when your under load at a given rpm?

Yes I have a hand held unit that gives me RPM Vac Fuel Timing in real time I will have someone ride with me and see if I can write down some of the numbers. I can only change them at every 1000 rpm and it phases in between. I'll try to get some numbers and get back on here.

[cableguy0]

1000rpm increments will be fine it should just gradually climb to the next point.

[haysonj]

Originally Posted by cableguy0

1000rpm increments will be fine it should just gradually climb to the next point.

I found my problem, after lots of reading the Manuel I figured out the fuel and timing tables. When I went in and looked at them I had 8 degrees of advance at 6 in of vac all the way to 5000 Rpm. I took it back to 0 across the board and it runs a lot better. Now I just need to hook up the boat and see what it does. Thanks for the interest in my problem. John

[cableguy0]

Good deal. At least it was a simple cheap fix.

[LONGHAIR]

While I am surprized that no one picked-up on and asked about the "computer" comment....the burden of disclosure is on the original poster.
Having an aftermarket fuel injection system that is in total control of ignition timing would have been nice to know from the begining.
No one is going to assume something like that. Many of us are here to help.....help us help you.