Need some help from the experts. I just finished wiring in a 7730 ECM into my new TPI setup that is mounted to my rebuilt 350. Cold start idle is great, but I've got this sound coming from inside the engine somewhere. Goes away when the engine warms up. Sound is unrelated to the 7730 as it was making it on the first ECM I tried, a modified 7427. Been all over where I could reach with a stethoscope, haven't been able to pinpoint it.

Car has not yet been driven since engine was installed, just been idling in the garage while I tuned up the fuel and spark map on the 7427 to get it to run.

Any guidance will be much appreciated!

 

Cant get the video to play on my awful satellite internet . Is it a air rushing sound like vacuum leak ?

 

No vacuum leaks. Sharper sound than that.

And thanks for the ECM and chip! That part at least is working fine.

 

So it sounds mechanical not like a iac ? No problem glad it’s running

 

Sounds like a valve cover being hit with a small hammer. Like a dull thunk/ tap but goes away after time and when the throotle is opened. Hmmm. You're gonna have to get your ears in there to get a general location. Exhaust barely tapping something? iac over active?(though I'd think the idle would jump around) fuel regulator tapping? Fuel line pulsation?

 

You could try taking the belt off, or taking the valve covers off and see if it still happens. Should be ok to run the engine for 20 seconds or so that way. Mechanic's stethoscope might help to pinpoint the sound.

 

Thanks guys! Swapped the driver valve cover this morning for one I modified to tighten rocker nuts. Used my mechanic stethoscope probe (what an awesome tool!) and touched each rocker stud. The sound definitely seems to match with the frequency of the valve train, but I did not hear anything unusual that matched up with the louder sound. After dealing with cheap import rocker nuts, I installed a set of ARP studs and their poly locks, so the rocker arms are down nice and tight. About 1/2 turn past zero lash. No unusual chatter on the driver side at least. Will swap the valve cover to the passenger side next. That one is such a PITA with the heater hoses and my Sanden A/C compressor. Hate getting into that side!

I also pulled each injector plug individually to see if that caused the noise to cease. It didn't, so I'm cautiously optimistic that it isn't a rod bearing or main cap. Is that a logical conclusion?

 

I don't recall what you built for a bottom end but in theory, piston hitting the head, valve hitting the piston are possible. Not too likely but certainly nothing you can rule out completely yet. Get underneath it safely and give it a listen. Rod bolt coming loose? Though, none of those things are going to 'go away' when it get warm.

 

Don't think I have valve to piston interference. Had to pull one of the heads a month or so ago after a series of errors lead to me dropping a small mirror attachment into the bore. At that time, I wanted to verify that the piston could not come into contact with the spark plug electrode. The piston sits about 0.020" (going from memory) down in the bore. Cylinder heads are Dart Iron Eagle, I'm running 1.5 rockers and a TPI-friendly cam from Comp Cams. Not enough lift to bring the valve into contact.

Bottom end is pretty basic - factory crank and rods with all new bearings.

I was able to get down a little under the car while it was running and probe around with the stethoscope. No sounds coming from the oil pan or exhaust.

I sent the video clip over to a local engine rebuilder last night. He thought it might be a sticking lifter. I'm watching to see if oil is getting quickly up the pushrods to the rockers during a cold start. Watched it this morning but didn't set a stopwatch. Not sure how long it should take to have something to compare it to.

 

Stick one end of about a 2 foot piece of vacuum line tubing in one ear and probe around with the other end the same as you do with your stethoscope.