I haven't had a chance really do very much on this car since my last post about the gas analyzer data... still want to rerun the compression and leak down tests... just need to get over to my friend's house to borrow his stuff.

But with the stuff I could do at my place, I checked the cam timing with the dial indicator and it's right on the money.

However, being sick of the smell, I ended up putting cats on the car so I could at least drive the bloody thing around without choking. If I solve the problem, maybe I'll take the cats off later.
One thing though, the car actually idles a bit smoother with the cats on. Not sure how much better I could quantify it than that.

With that seemingly minor improvement, I went back and bought a 30 lb injector for the number 2 cylinder to rerun that test I ran before but didnt' get anything positive on. This time, with the 30 lb injector on #2, when I disconnect the injector plug at idle, the engine responds just as strongly as it does on other injector plugs. The engine RPM goes down, with a pronounced miss on #2 just as with the other cylinders. That's a seriously positive development! Before, it wouldn't respond at all.

I'm now getting a pronounced sulfur smell at times (not rotten eggs as in other posts that I've searched through) very similar to a bured out match. I believe this indicates an overly rich condition?

I started to play around with the idle fuel, spark timing, and idle speed again. I lowered the idle speed to about 625 rpm, down from 650-675, put the O2 idle threshold at 325 mV (was .450) which significantly reduce the sulfur smell. I then started playing around with the timing. I'm currently up at around 33 deg BTDC at idle speeds and it seems to help. The idle is sitll definitely rougher than it should be in drive , but I picked up 1" of vacuum and the low speed bucking has been reduced by about 50% I'd say. In neutral, the engine is really smooth now...no detectable misfire.

Only thing is, now, when I'm neutral and put in gear, the engine wants to stall, but it then recovers and jerks the car forward. I'm thinking 325 mV is too lean?

Question: I've read all of the statements about giving the engine what it wants, but would anyone suspect that this engine would require >30 deg of timing at idle just to idle somewhat smoothly? I'm going to go higher and see what happens. But what would it indicate if say I needed close to 40 deg of idle spark timing for a smooth idle?

 

The caveat to playing with the O2 stuff is that the r/l threshold isnt the only thing that governs how the PID routine handles the fueling. There are also additional setpoints that must be adjusted. Changing just one parameter can have undesired effects. It could even cause it to go richer if the various calculated correction terms are fighting eachother. Id set it back to .450 V, or just disable closed loop altogether for now untill its fixed.

Also, as a refresher, is this car MAF or MAP?

From what you describe, this isnt really as much of an issue as giving the engine what it wants, it sounds like theres something very serious going on, although from previous threads that has yet to be determined. It also shouldnt need 30+ degrees to idle. Should do fine with around 20 if its a mild combo.

 

I agree that 30+ degrees of timing at idle seems to be too much.

One thing grumpy has often pointed out, It's easy to get caught up in a "too much timing and fuel" loop.

For reference, the 406 in my '71 (which still has one of those pesky Holley "mechanically-controlled fuel leaks" aka carburetor on it) has a mechanical roller cam with 240* intake duration (at 0.050"), 248* exhaust (at 0.050"), and 110* lobe sep.

It idles dandy with 18-20* of timing and the exhaust only burns your eyes when it's running in a closed space (such as a garage). The 232/240 112* lobe sep cam I ran before, didn't burn the eyes.

First, my preference and suggestion is to bring the idle up. 600 is pretty darn low even on a stock cam, and while you're not running a thumper, there's still no reason to be down that low (in my opinion). I'd aim for 750. Plus, you'll find better efficiency with a bit more RPM and probably less exhaust smell issues.

Secondly, take a jump down to 20* timing at idle, and re-adjust fueling if needed and see how it does to make sure you haven't gone too far and missed the boat.

I think I read that you're going to dump the miniram and go with another intake. You might find that you have to re-do some of this work once you swap to another intake, as it might change what the engine wants. Right now you're sort of tuning for an extreme high rpm intake on a tame motor and that is probably complicating things.

Did you ever get the chance to bolt on a carb setup just to see what happens?

Personally, on my 406, I plan to run a holley stealth ram, provided it clears the hood (no cowl hood and don't want one).

 

your forgetting that carburators unlike efi turn the whole intake manifold into a giant mixture chamber. with port efi the fuel doesnt normally wash its way back up the runner. this is one advantage TBI has over port.

 

I'm not sure I follow / understand? I agree that there is a difference since you now have a 'wet' manifold with a carb (or TBI), but even with port if you change the intake design/size/geometry you end up re-tuning a bit. I'm assuming that's what you were referring to - the re-tuning for different intake?

 

Im reffering to mixture distrobution differences between EFI and TBI/Carb.