engine chatter that goes away when engine is HOT ? lean?

CBradio · Post by **CBradio** » Mon Oct 26, 2015 6:21 pm

Finally have the car running decent!!

But please, analyze this:

If I'm driving around and feather the gas pedal, between about 1600-2200 rpm I get a "chatter" from the engine. Above this, seems to dissapear. This happens only under load, and don't hear it if revving in neutral or park, AND it seems to completely go away when the engine is HOT (not just warm, and this only happens if I retard the timing). I don't know if this is pinging, or some type of valve chatter, or possibly a leaky exhaust, but if it is "pinging," it doesn't seem to me its due to timing, but maybe mixture. A lean condition?

SO, I've been messing with the AFM mixture, and timing.
It seems that the noise gets slightly quieter with less advance and/or more fuel...

BUT even timed to spec or more retarded, I still get that chatter; even running so rich that the car wont run when cold unless I keep pumping the brakes to give it more air..

Do other members experience this until the engine gets past the second white line? (which only happens if my idle is retarded)
go from A to B.

CBradio · Post by **CBradio** » Thu Oct 29, 2015 2:01 pm

The clatter almost goes away completely with very retarded timing (vacuum disconnected!), but then again the car doesn't really move at all.

The car really opens up if I put it in "2" and pull at ~3500 rpm
WOW.

I'm thinking the clatter is:
1. Timing chain related, maybe I didn't bleed my tensioner
2. I need a valve adjustment (did one a 1,000 miles ago)
3. Exhaust manifold or downpipes making noise

MAYBE:
4. Car running lean in this range
5. Carbon build up (premium gas made no difference tho)

I'll post when I chase this down.

CBradio · Post by **CBradio** » Fri Oct 30, 2015 5:11 pm

Pulled the cover...

So I did the valves before I put the head back on a while back, and adjusted the valves, and now when I measured it turns out somehow the valves got *tighter* (.008 guage wouldnt slide in on cam side). Anyways I adjusted them all again

CBradio · Post by **CBradio** » Sun Nov 08, 2015 3:16 pm

Okay, too clarify, the "chatter" only goes away when the needle temp points to 2 o'clock and that really only happens when I set the timing so that the idle is too retarded (seem to be spec ATDC with vacuum retard connected, but this really causes the engine to run warm and I've noticed most m30s idle 8-10 degrees BTDC).

So if if timing is set not too retarded, I always get the chatter, because I won't get the temp needle that high.

Anyways, I pulled the cover, adjusted all the valves, re-primed my chain tensioner, confirmed cam timing and put everything back together. Valves are actually just a touch louder now, but idle is smoother, BUT that "chatter" is still there when driving under light load, ~1700-2200rpm.. and still NOT present when I rev in park or neutral. I do get a very slight miss around this rpm however. What does this mean?

I'm stumped. I thought maybe it was the lack of a "thermovalve" aka "green thingy" that shuts off the vacuum advance until the car is hot, but even with vacuum advanced plugged I get the chatter. I also tried two different distributors (and checked weights are functioning and springs are intact and doing what its supposed to)

I guess I'll just live with it and drive the car. If its "pinging" than the engine seems to tolerate it. I know I have a pinhole size hole on weld seam where they cut turned the downpipe flanges to fit my bav manifolds, maybe thats it; short of this I'm out of guesses.

RonDwyer · Post by **RonDwyer** » Sat Dec 05, 2015 8:00 pm

Get a really long screwdriver and when it is chattering pull over, open the hood and place the blade on the edge of each injector one at a time. Put the handle to your ear to listen to the injector. This is the easy stethoscope method. If any are misfiring (sticky) they will sound different than the others. It's a quick and easy test.

If any of the injection hoses are hard, brittle or cracked, replace them all.

CBradio · Post by **CBradio** » Sat Dec 05, 2015 8:31 pm

THANKS FOR THAT. I did the screwdriver test to see if they are all firing, but didnt think to see whether some sound different...

Actually this week was thinking it may be the injectors too!

RonDwyer · Post by **RonDwyer** » Sun Dec 06, 2015 12:19 am

WHat you will likely find is an electrical connection that has gone bad. I've even seen the connectors wired on with baling wire. You don't even want to know what the rest of the car looked like. And change your hoses. New hoses solve tons of issues.