Hi guys, I have a .462/.482" 219/229 @0.05 110 LSA flat tappet cam in my 327 with a HSR, 24 lb/hr injectors, 6E MAF. This car has always had a very strong smelling exhaust idling, even carbed (although carbed wasn't quite as bad). I get near-0.00 mv idling with my 3 wire heated, brand new genuine Delco AFS-73 O2 sensor. My blms max out idling.

I thought that my very lean idle O2 readings were caused by my lazy, high overlap cam fooling the O2, and that I was actually rich. However, removing fuel in the MAF table at idle made the idle quality (which is normally very stable and good, but just strong smelling) worsen significantly. I have slightly boosted MAF tables around idle for richer fueling, which I tried putting back to stock, making the idle quality suffer.

I just tried running 32 deg idling instead of my normal 26 deg. The smell in closed loop got worse, and the idle when I backed into the garage literally left a chemical-smelling stench that, with the door open, was making my eyes burn and water so bad I had to leave the garage, even with the car turned off. It was burning my eyes like peeling onions. The exhaust smell is not like gasoline, it is a toxic chemical smell. The best I can describe is that it smells somewhat like a very strong permenant marker smell. It stays on my clothes just from being near the car idling until they are washed, even days later.

Is it possible that a) I have too much timing at idle, and that I need less than 26 degrees?

OR

b) I really am too lean at idle. Advancing the timing but leaving the fueling the same made the smell worse because advancing the timing effectively makes the engine act leaner, whereas retarding would make it act richer?

I noticed that my CEL threw much sooner during prolonged idling (lean code) than it did with the 26 deg idle timing.

The car runs so good other than the awful reek/eyes burning at idle that this is driving me insane. It will idle all day in traffic but it smells so bad!

Help!

I don't have a wide band O2 yet (although WBs are not necessarily entirely accurate with a lazy cam like this idling anyway)

 

Read all you can on the 02 constants(thru searching and sticky).

Tends to be a fairly common problem with higer-ish duration cams and LSA under the 112 mark.

Prolly going to have to lean them out some at idle, experimenting will give bnest results

later
Jeremy

 

I already know about the O2 constants. I have been going down this road for quite some time now. Think about it. I am off the NB scale. 0.00 is 0.00 no matter how you look at it. You can make the slow and fast O2 bounds, and the cross point, anything you want, and it doesn't matter, 0.00 is full lean and it will max out. So I have a lot more to do than just O2 bounds.

 

Welcome to the world of Philly gas. Having cats on the car helps a lot, once they light off the stench goes away. Can also try a different location to purchase fuel. Seems some stations fuel reeks less then others.

RBob.

 

I'm actually not in PA anymore, I'm in VA. Location doesn't matter, this is a tuning issue I've had for years, whether in NJ, CT, PA, MD etc. I have other un catted small block chevies that do not smell like this running, this particular cam is not very friendly to tune at idle.

 

Time to do or re-do a cylinder drop test. Or, squirt water on the header pipes at idle.

 

I have checked cranking compression on all 8 and I am within a few psi deviance, max. The only things that could possibly cause a problem for one cylinder would be spark or fuel. The plugs all look the same. Can I drop out one cylinder at a time using the injector harness? I hate pulling plug wires and electrocuting myself.

 

Yeah, the injectors are the safer way. One other way is to loosen the wires at the cap before starting, and use plastic toy pliers to lift each one in turn.

 

I have an Accel 50k volt coil, I don't want to go anywhere near these plug wires running! I tried doing a cylinder drop out test before and even wearing welding gloves, I got hard core shocked.

 

I would go the injector disconnect route.

So when you start the car, the NBO2 reads 450mV and then drops to 0mV as it warms up? I have seen NBO2 drop into the 20mv -100mV range but never down to 0mV exactly. Strange. Did it stay at 0mV when you ran open loop and gave it more fuel?

 

The O2 starts generating cross points only 3-4 seconds after a cold start up. It is heated and warms up very fast. Reading 0.00 is not all that hard to believe. The O2 was designed to be a switch with a very steep slope on either side of 14.73:1, for catalyst activity. With my exhaust stream being obscured by the cam overlap, the sensor is way out of its range. If I intentionally over-richen the idle by cranking the maf tables way up or running open loop, I can get the O2 to read near normal values at idle, but the car runs awful. This is not a problem I have failed to investigate.

 

I am with junk, when mine wasn't tuned well in closed loop, idle for a while, learn kicked in and would stall the engine, with low O2s around 100, to 200mv's....

Omv sounds like a bad sensor or wire, but the question is why isn't the computer complaining, mine did with my low mv's...

Lean error, swing points where too high for overlap (cc306) but I'm sure you know that part

if the engine runs like you say... the O2 is probably shot (i would say) but some cams DO come with a gas station perfume, but yours looks pretty tame from your sig...

maybe they are too cold, maybe a three wire is needed?
being too far away from the head?

 

I have never seen a NBO2 respond in 3-4 seconds after cold start-up. They usually just hang at 450 mV until hot. They usually don't switch when cold. They do have a steep slope at the switch point but it flattens out around 100mV (I had to CAL the WBO2 to match the NBO2). The only reason that 0mV is hard for me to believe is because I have never saw one do that. Learn something new everyday.

I read you other posts and I know you have looked into this. I am sure that you read the NBO2 with a voltmeter with it un-connected from the ECM to ensure that the ECM isn't bad. Sorry I can't be any help.

 

Fun Pain,
Your CC306 has NBO2 values like I would expect. Your 230/244 @ .050" cam is much larger than the 219/229 that is in the 327ci. The smaller cam will act larger with the smaller ci, but I still can't figure out why it would read 0mV. All I can think of is testing it with a voltmeter with the NBO2 disconnected and seeing if the sensor is bad or the ECM is bad or the NBO2 ground /reference is bad (O2 has it's own ground wire).

 

Where is the O2 located in exhaust? Can it be relocated to sample both banks? I've had some customer's cars read 0.00. So I know it can happen. Are 24lbers right for 327cid N/A? I use 24's for 383cid. Have you tried 19's?

 

Are you using a voltmeter with high impedence?
You could be loading down the signal with a cheapo DVM.
Are the readings with the meter consistent with the datalogs?
My idle was similar to that earlier this summer but shifting the constants and adding a bit of timing cleaned it up allot. Idle quality could still be better but the eyeball washing is gone.

 

24s are definitely not too large for a 327 operating at up to 6500 rpms. 24s are on the small side for a hot 383 if it is built to run to 6000+. I haven't read the O2 with a voltmeter, just through the datalog.

Fun pain, read my post. IT IS A HEATED O2. Genuine delco. Brand new. Wiring harness is all new Painless with weatherpak connections.

It does flag a lean CEL after prolonged idling. ARGH!

It doesn't sit at 0.00 100% of the time idling, it does swing above it, but not by much.