cuzimanoob

So this is a story all about how my life got flipped.... sorry.. but recently I bought a '90 GTA and what I thought I was getting myself into was just an idle problem, became much worse. Got it on the cheap, has tons of mods and is fairly clean. Brought it home and noticed that it would stall out on me in drive with the foot on the brake. If I had it in neutral it would idle rough but not stall out. So I tried doing what everyone on this board suggests, the IAC adjustment and Minimum Air Idle adjustment. While I was able to do the IAC, the MAI would not adjust, my set screw on the 58MM Holly TB would not open enough to keep the engine running. I also noticed during the rough idle that there was a clear knock happening. It was rhythmic and very noticeable, but as soon as the RPM got above 1200 it would disappear. I talked to my dad who used to build carb drag muscle cars and he was saying it was probably detonation. So I didn't pay it too much of mind. The problem kept happening so I had a friend who knew a lot more engines than I did...even though he was a ford guy... So while going through all of the paperwork for the car he saw it was stroked and he was thinking that the knocking might be piston rock. He suggested that we thicken up the oil a bit to see if it goes away and it might give us better troubleshooting information. So we put some oil thickener in it and I go to start it and it knocks really loud a good 4-5 times and wont turn over.. I let off the ignition and let it sit for a while then tried again, same thing. He suggests that we pull the engine and tear it down to make sure nothing is damaged. In the process of disconnecting everything we discover that the people who built the engine were lazy, some screw/bolts were nice and tight others were barely hand tight, one of the header bolts came out the whole way, only 1 bolt was holding the flex plate on and it was pretty much just thrown together and expected to work. Now a few things about the engine. It did previously have a pro-charger system on it, the mount is still on the engine. So I think its safe to assume that the engine is tuned for a Supercharger. I was told that the Cam that i have installed is too aggressive and the duration is too large at 280. I'll list what I can remember about the engine, but I don't have the paperwork right in front of me.

The engine that was originally in the car was the 305, but a 355 was put in...
Block is a 4 bolt main
355 that was bored .030 over
Accel intake manifold with the Stealth ram intake
Edelbrock Headers to a single pipe magnaflow exhaust with a high flow cat
the TPI/AFI Heads for the L98 that were port matched with the intake or vicea versa
new rocker arms, rods, springs, the paperwork was saying that it was rebuilt just 10k miles ago..
pistons are forged and flat topped
The kid who had it originally dumped some money into the engine, I just want to get it running again and make her pretty. She sounded mean when she was running.
I dont know if its the same auto trans, but the guy that was helping me said it felt like it had some work done to it as well, i'll see if i can find out anything about that too. But my main question is, would all those little things add up to it not being able to start and detonate like that? also does anyone know of a tutorial to tune this thing down to close to stock just so i can get it tuned properly at a shop? I heard somewhere that the knock sensor advances the timing instead of retards it, would that cause some of my issue? I did replace it, but if the engine had so much loose on it would it pick that up as a knock? Thank you for reading it all and I hope with all the knowledgeable people here we can find out what's wrong with my GTA.

Orr89RocZ

iTrader: (20)

Sounds like tune was off. Motors dont detonate at idle

cuzimanoob

I do not know how to tune these engines, is there a tutorial somewhere or something that I can do to fix the tune? Also what do you think about the Cam, do you think the duration is too long for my engine specs? I know that you are very knowledgeable Orr, so any help would be great.

Orr89RocZ

iTrader: (20)

Hard to say without knowing every small detail but in general no, 280 deg advertised is not to big as long as the heads flow well and cam lobe is somewhat fast. Limit overlap. I have tuned cams that big in 350 motors before and they run very well.

You need to read over the diy tuning threads and visit moates.net for tuning equipment. Its not bad once you understand how motors work and what the ecm parameters are in the software but for a novice its intimidating and does take some time

cuzimanoob

ok so I got the paperwork for my car, the cam is from TPiS Hydraulic flat tappet cam.

advertised duration 280 280
duration at .050 224 224
gross lift .495 .495
lobe separation 112

Is this a decent cam for a N/A spec engine? I have all the other mod info if youd need that too.

Orr89RocZ

iTrader: (20)

Yeah aint bad for street car. Once tuned it should run fine. It could be abit more aggressive on the lobe like xe268 or voodoo type grind in that 268-270 adv range