We are having a heck of a time diagnosing my friends 355 tpi.

Here is the run down on the motor. Freshly rebuilt 355 with mildly ported stock heads, eldelbrock headers, and mild cam.

We have been chasing a noise that seems to be coming from the throttle body. Almost like a knocking noise. If you bring the rpm's up slow, no noise, you goose it and you hear a rapping/knocking noise??

We just spent all day going through the exhaust, no leaks there. He is also getting blue smoke on startup, and sometimes when hitting the gas hard, even though the heads were re-done with the motor?

Any idea what could be causing this? We have already pulled the valve covers and could see nothing wrong regarding valves(from what we could see. It is def coming from inside the motor, it gets tons louder when you pull his air ducting off.

Any ideas?

 

im kinda having the same problem on my lt-1... it will idle just fine, but when i give it a good amount of gas it will knock like crazy till i let the gas off... no idea though! good luck man!

 

Odd thing, the motor has been set at 6* BTDC, idles better and runs stronger at 0* BTDC. Found that out today, kinda funky. I can deal with that, but the car still pings like crazy under load. That is some loud *** detonation.

After seeing the effects of setting the motor at 0* I tried it a little more retared, but it began to idle really bad, so I set it back to 0*.

Found out the #4 injector is not fireing at all. Disconnecting the injector has absolutely no effect on idle at all. Also verified that #4 has spark, it does a pretty healthy spark too.

Stupid motor......

 

yeah, number 4 being dead should still not give me that nasty detonation i am getting.

We are getting closer though, one step at a time.

 

you're too smart for me, i give up

 

Why did you already mention everything we just talked about in the first post ede?

Rather than state the obvious as we have already done, why don't you explain just HOW to check those because I sure as hell don't know where else to look after this.

We've already played with timing, when I set the initial timing back to zero. The chip currently has a stock timing curve. Setting it below 0* didn't reduce the knock and only made the engine perform even worse, barely idling. Massive surging issues when it was at 8* BTDC, 6* BTDC didn't change anything either. 0* BTDC is where it likes to be, best idle, and best power there.

We've already discovered that the #4 injector isn't firing. And we can't do anything about that till we replace it and get it running.

The motor is as follows:
355sbc
L98's with a bowl job and upgraded springs
stock plenum, runners, and intake (for now)
212/218 camshaft with about .500"/.510" on a 112lsa
Edelbrock headers, y-pipe, no-cats, stock I-pipe, flowmaster muffler.

The exhaust has been checked over for leaks multiple times. The headers are sealed damn good.

 

ttt

 

what compression ratio is he running on the motor?

 

It was built to run near stock compression with 64cc heads. But I don't know the details of that exactly. The block was originally a L98 out of a 91 formula 350. The heads are 081's off a 88 L98 GTA that have been given a bowl job, and valve job.

I do know the pistons are forged though.

 

maybe with the mods the stock style timing curve is just not right for what you have done to the motor

maybe with the #4 injector being dead it still might be letting enough fuel to let the motor run uber lean on that cylinder under load


have you checked the fuel pressure?

what tune is the chip in for fuel?
maybe your running lean enough to cause the detonation for all cylinders.

what about vacuum leaks?

 

Just a thought... did he use the right style timing pointer with his balancer...

I know some are straight up, some are off to the side at like 2 o'clock.

I heard someone else use the wrong pointer and thought they only had like 6* timing, when they had more like 20*

edit:
Maybe since 1 injector is gone, others are on their way, which may mean that you're getting less fuel out of some of them, causing you to run lean here and there.

I would replace the injectors and see if it clears up, then work from there.