Basically I have a goodwrech 350 with a performer plus cam. The engine has around 8.5:1 CR and the cams specs are 204/214@.05 with 112 LSA with a very lazy profile. Edelbrock states that it has an advertised duration of 278/288. I also kept the new but stock timing set that came with the motor. That could also be the source of the problem there.

What Im seeing and have seen is that the engines vacuum falls from around 19 inHg at 1k to around 16 inHg at 700 rpm where it idles and the ECM indicates there is alot of O2 sneaking past the O2 sensor. As far as I can tell, there are no exaust leaks. The headers and bolts are snug at the cylinder heads and there is also a new doughnut gasket on that header with the O2. The motor has always had a stinky idle since I put the cam in. Everywhere else the motor is rich and the exasut stinks at idle so I dont think its a lack of fuel. This motor willingly does everything but idle. Its always been like this.

Is it possible for the long advertised duration to be allowing the exaust pulses to steal some of the intake charge and/or let the cyl. pressure bleed off? Or, is it more likely to be that the timing set is off and the cam is retarded.

 

If the motor is actually rich but the O2 sensor is saying it's lean, then it's lying.

Try a new O2 sensor.

 

The O2 sensor is reporting the engine as being rich everywhere but idle.

 

To add to this I added fuel in across the board.

 

Intake manifold vacuum leak.

 

Checked the manifold and carefully looked over the headers last night. Found the cause to one of my problems. The hairline fracture thats been in the d/s header for the longest time turned into a big 'ol crack. I shoudl recheck everything rather then entertain my wacky theories. Theres probably something ive been missing this whole time.

 

Somehow this isn't making a whole lot of sense....

The exhaust stinks at idle and the motor is rich everywhere; so you added fuel.

The motor is rich everywhere, yet the O2 sensor reports lean.

16" of vacuum is ALOT. Plenty. It does not indicate a problem. Think about what "vacuum" actually is, for a moment: the motor is a giant pump; it's doing its damnedest to pump all the air out of the intake manifold and put it in the exhaust; but, there's this leak on top of the manifold that lets air back in, called a "throttle"; so the pressure in the manifold reaches some value at which equilibrium is established between how fast the engine can empty the manifold, and how fast it refills through the throttle. Atmospheric pressure is about 30" (watch the weather report tonight on TV for the exact value at your locale at the moment, might be something like 29.95 and rising, or 30.1 and steady, etc.); so 16" means the engine is able to maintain about ½ atmosphere of vacuum in there. THat's about normal for a motor with a stockish cam at that RPM. A bigger ccam will make the idle vacuum drop.

Looks to me, you need to put in a new O2 sensor that reports the truth; take out the extra fuel "across the board", either with FP or the PROM; and maybe put more fuel in at idle ONLY.

Also, check your timing. Retarded timing will cause a very poor idle. I don't mean just shine a light at that stupid mark that isn't really connected to the engine, but rather is only loosely associated with it by a blob of 15-year-old spooge; actually verify that when the #1 piston is at TDC, the mark is at 0.

Also, check for an ignition-related misfire. A cyl that's not firing will allow both raw fuel and fresh oxygen into the exhaust, and the ECM will be very confused. A FUNCTIONAL O2 sensor will report that the mixture is lean under those conditions, and will add fuel; the other 7 will run pig rich; and the ECM will still see "lean".

 

Lets take a step back. No, make that two...

I switched my tbi over to use a maf to do the fueling. Its a long story but the net effect was that I was concerned that the fueling would be off. I saw 160+ blms indicating an extremly lean condition around the areas taht it idles so I added more fueling everywhere. Richened up everywhre, resulted in the computer reporting rich conditions under normal operating conditions. But, at idle it was still reporting a lean condition and adding fuel on its own even though it was obviously rich. I checked the headers over one more time and found the large split that had formed. That explans the false lean condition at idle since the exaust pulses are pulling in air behind them. Problem solved.

Now I do know that the engine is a large air pump. Im slow, but not quite that slow . my impressions are that the motor should be able to pull around 18-20 inHg and idle smoothly at 600 rpms with this cam since its advertised as 'smooth idling' crappy stock profile. It only does around 16 at lower rpms, doesnt like idling below 750 or so, and has a roudy exaust note. Been like this since I put it in. Maybe thats the way it is but to me it should seem like it could and should do better.

Edit: No misfires or anything. After a week of messing around with teh tune I got it to idle properly. Didnt have to do much else but the idle was a pain as usual.

 

What cam is it? What ICL is it installed on?

 

edelbrock performer plus. 204/214 112 LSA. Installed with the stock timing set so the timing is whatever it would be with a stock timing set .

 

Whose "stock" timing set?

A GM set will put the cam at 4° retarded from where the timing set that it's supposed to be used with, will put it.

A used GM set will add to that.

A "truck roller" chain (the "roller" sets that cost like $20, because it's not a roller, it just sort of looks like one from the outside) will let it retard even more than a typical worn-out stock one, within the first couple thousand miles.

Cam timing retard lowers idle vacuum. It improves top-end HP, in situations where "top end" is available. Probably not applicable here.

Sorry to hear you paid too much for your cam. Seems to be a common mistake. You could have got it for alot less. Or, you could have paid the same, and got a modern, much better cam instead. http://store.summitracing.com/partde...art=SUM%2D1102 as compared to http://store.summitracing.com/partde...art=EDL%2D2102 Next time, feel free to ask, before you make your final choice.

 

i didnt pay a dime for it actually Relative gave it to me two years ago and I didnt know any better at the time so I just threw it in there with the new gm stock timing set that was already in my crate 350. IIRC I think it had a 929 in it to start with. As I stated above, my suspitions mainly lie with the timing set. Im thinking of going in there and swapping the timing set out. While Im at it Ill see what I can do about the present heads and cam. Maybe even degree it this time around.