I got an 88 iroc with a 383 (heads/c/edelbrock full intake) to start. I started prom burning after the chip i got from pcm for less was running the car way lean up top and causing bad detonation. So i started tuning myself, had some issues here and there but so far its gone ok. The car was orignally a 305 so likewise i had been using that bin as a starting point. Recently i decided to switch to the 350 bin of that year and its shown some much better results and is far easier to make changes too and see results. However no matter WHAT i do. the car always seems to get detonation up top. With the stock 350 bin burned it will detonate real bad up top. So i modded the pe tables to add instead offff 15% fuel? to dump 25%. I figured i was detonating because the maf was being maxed out at like 3K. Now this did help alot, but it was still there. So i upped it to 30% and i dont see any change at all..its still there. I sent some files to a friend and he said the o2 is showing rich at those rpms...so whats going on then? My timing is set at 10 base and the timing tables have not been touched...so i figure its not a timing issue either?

I know the car has some valvetrain noise so at wot im losing 10 degrees of timing as well..unless it really is hearing the detonation? Or on the other hand that im not hearing detonation at all and its some sort of valvetrain noise but im pretty sure its detonation. I tried pulling the plugs...they dont show anything wrong really..color looks ok. The first time i pulled em with the chip from pcm for less they were white so i knew i was running lean up top. Its really starting to drive me crazy, the car is just no fun if i cant beat on it every now and then.

engine specs:

383
edelbrock performer heads
comp cam (.495 in, 503 ex., 218/224, 112 lsa)
full roller rockers
Full edelbrock tpi intake
30lb ford motorsport injectors

Am i possibly running out of fuel pump? I figure that would show up on the o2 though...Fuel pressure looked good (at idle at least) 41psi with vacuum off. If anyone would like to see a fairly new run from today...i can plot it on an excel graph and send it your way. If you need anymore information just ask

thanks guys

 

What's your compression ratio (there's some edelbrock heads with small 58cc chambers that would require some dish in the piston)? What octane fuel are you using? What is the total timing when in PE mode at the point of knock?

Should really try to determine if what you're hearing is knock or not, and fix whatever is ticking. Also should get a wideband in there while you're at it. Also should put in the 350 knock sensor.

 

i believe the heads are 60cc and compression ratio is 10:1. I am running 93 octane all the time. In tunerpro max advance is set to 40 but i think all i ever hit is 35?

I have the updated esc module from a/c delco. I heard it was good at ditching false knock. Originally the car was pulling 17 degrees out up top and when i switched it to that it went to 10 degrees. I have yet to put in the 350 knock sensor though.


Now on data master, i see the timing reach 31(?) degrees at wot...however the knock retard is 17 degrees. Does that mean the car wanted 31 and then computer pulled out 17 so it was really running 14 dgrees at wot? or does it mean it was running 48 degrees advanced an the computer lowered it to 31? because then somethings gotta be wrong there

 

another thing i noticed when i took it for a drive today...i popped it into 1 and accelerated all the way to redline..no noise, then i shift into 2..and a couple of seconds into 2 it starts making the noise...?

 

Yeah, I think what you're seeing is the calibration trying to give the engine 31 degrees, but the knock sensor/system pulling out 17, thus the engine gets 14 and still knocking, or something close to that.

I would get a timing light out, again (if that's how it is), and make 200% sure you set the base timing to whatever your calibration shows (i.e. 6 is stock, 10 is what you stated, bypass wire disconnected). The base timing on the car and calibration MUST be the same if you want things to jive.

What RPM does it start "making noise" and is it consistantly at that RPM?

That behavior of the noise starting in second gear favors that it's real knock. I'm surprised that a stock-ish calibration is causing that. What is your base calibration, and what changes have you made to the spark tables?

The Edelbrock heads may burn a little faster, too. I had a set of the 60cc (stolen before I could install), that have a very pretty chamber. With those and ~10:1, it very well may like less timing. For that - you'd have to change the main spark advance table at the higher loads, down until knock is primarily eliminated (read up on how to step down the timing, without overdoing it).

 

ok i put in the 350 knock sensor...car feels much better and detonated a hell of alot less...especially when i nailed in on the highway..i didnt hear a thing. But as i accelerated into second from 1st i could still hear it. I havent gotten any data logs on how it looks now, that will have to wait until tomorrow.

I have made NO adjustments to the timing tables at all...which is what bothers me. The engine is from engine factory, i bought the car with it in it and they suggested base timing be set to 10 degrees..maybe i should back it back down?
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and i would say its about 4k that it starts making the noise

 

the timing should be set at 6 degrees, thats what the prom is configured for, set your base timing to 6 and see what happens

 

Engine factory may have been giving you specs for a Vacuum/Mechanical advance HEI distributor - not computer controlled, where they want something like 10 degrees at idle, and 32° at 3000 or something like that.

With computer controlled, you can set the base to 10° but you MUST change the base timing in the calibration bin to 10° also, in order to actually get what the computer says it gets, otherwise you'll be giving it more than that, unknowingly.

 

nope it the dizzy came with the car and was intended for fuel injection and a computer controlled set up.

I set base back down to 6 and its improved quite a bit. I also just went into the spark advance at wot table and zeroed them out...well see how it goes tomorrow when i drive it. IF it still does it, should i start messing with the advance tables?

and yea when i was running 10 degrees base i had it set in the prom that way as well

 

well i messed with the advance tables...i lowered alot of values past 160 load and above 3600rpm...it def cured alot of it..i still get a slight spark kncok when it first goes into 2nd but other then that..its getting better. However i had to lower many of the values down to like 20 degrees advance from basically 3600 up to 4800...that seems a bit excessive doesnt it? thats around 7 degrees of timing removed at some points..

 

Give the motor what it wants. Just keep adjusting the timing until you get it running right. You have a short duration cam, 383 cubes, and 10:1 comp so the cylinder pressure is higher than stock.

Be sure to put a fuel pressure guage on the car and put it under the driver's side windshield wiper and make a blast down the street. I was having the same problems as you and the fuel pressure was dropping from 45 to 32 at wot. I was using the stock pump and added an in-line pump to cure it.

 

Well finally decided to take some of the advice of a couple friends and try a colder plug. The manufaturer of the engine suggested RC12YC champion plugs which i didnt want to put in there from the get go but i did anyway. Well i swapped over to an FR5 NGK plug..roughly a heat range or 2 colder. I also that same day removed the cat from the car which i found out after cutting it off that i was clogged pretty bad..all the internals had fallen apart on the inside. Well whatever it was, the detonation is gone..WITH full stock 350 timing tables

thanks for all the help guys!

Im still going to look into the fuel pump as well though, i have a feeling it wont be keeping up much longer