Hi guys, I posted a while back on the following:

My 1967 327 came with an Isky 280HL flat tappet hydraulic cam. Spec'd 232@0.05, .485" gross lift, 280 adv. duration -- single pattern, 108 LSA. I had 6E MAF and a Stealth Ram. The car always had a terrible rich smelling idle, so bad you could smell it in the car at a long stoplight, and so bad it would stay on your clothes if you stood outside near the car idling. The O2 readings would be normal at all rpms above idle, with near 128 BLMS. However, at idle O2 voltage would be very low, near zero sometimes. O2 sensor was a brand new AC Delco 3 wire. Headers were brand new. I verified there were no exhaust leaks at all. I changed the 3 closed loop O2 tables in Tunerpro (upper, lower, middle swing value) to move the O2 swing point / swing band down significantly, thinking this would effectively lean the idle out by making the car think it was closer to stoich. This did not make much of a difference -- BLMS would still max out at idle and the smell was awful. I believe the large amount of overlap (64 degrees of overlap on the Isky cam!!) was fooling the O2 sensor to thinking it had a lean condition at idle (the cam did lope a lot)

Fast forward to a few weeks ago-- I changed the cam for 2 reasons -- 1 to move the power band down a little (the Isky was making peak HP at 6000 rpms, but was down less than 10 hp out to 7000 rpms, which I have revved this motor to, but my heads are at max hp probably around 6K) 2. to get a little less overlap

Current specs for the new cam are:

Comp DEH275, 219 @ 0.05 intake, 229 @ 0.05 exhaust, .462" gross lift intake, .482" gross lift exhaust, 272 adv. intake, 279 adv. exhaust (the adv. figures are off the top of my head and might be a couple deg. off). 110 LSA. So we have a little wider LSA and a milder intake lobe w/ less lift and significantly less duration. I figure this can't hurt. Peak hp is around 5500

On a desktop dyno with my head flow #s it shows that I have around 30 hp more across the entire lower band with the new cam vs. the Isky. The car shows it driving, it is crisper and has more bottom end. It really doesn't nose over at high rpms either, I am shifting a hair over 6K, it will spin out to 6500 no problem though.

BUT the idle still maxes out the BLMs, has very low to near zero O2 voltage only at idle, and smells TERRIBLE. The new cam idles very similarly to the old one, not surprisingly , because the exhaust lobe is similar. However this cam has less overlap and less duration, so I figured the idle would clean up a little bit.

WHAT GIVES? I know I have no exhaust leaks causing erroneous O2 readings, I was meticulous about flange preparation and gasket selection. I actually welded the collector rings on the headers so they are rigid and do not flex.

What can I do? I will get a wideband sometime in the future, but if cam overlap is still fooling the O2 it will probably fool the wideband too. Should I cap the BLM at 128 max and start taking fuel out of the MAF tables around idle and see what happens? Lowering the O2 upper/lower/middle closed loop values do not help me because the O2 is so fooled by the cam that idle is just about "off the chart" of what the narrow band can see. Therefore it is not setting up cross counts, since the cross point at idle is actually below what the NB shows as 0.00 mv. I should stop wasting all this money on the gen I and get a 350 roller to build so I can get lots of FAST lift without the duration that flat tappet hyd. cams need so the ramps aren't excessive. I hate hydraulic flat tappet cams!!!! hate hate hate hate

 

From what I know an o2 need hot eonugh to work right. Mabe your o2 is not close enough to the block to keep it warm enough to give a proper signal at idle?

Maybe even more so with headers, ya know 4 less cylinders keeping it hot and reding right. Why people run 3 wires, so it heats up and reads right sooner. Must not be hot enough at idle in its position???

 

Try letting it get cross counts. Change something to let it get them, such as the BLM limits, or MAF tables. Seems a lot of people get lean exhausts, it smells from misfire, think it's rich, and never let go of that idea. Rich doesn't smell much until it's nearly smoking. All signs are pointing lean on your setup.

 

Thanks RednGold. I will see what happens with some MAF table mods. I remember richening up the MAF tables substancially a while ago and I still could not get cross counts.

 

May want to try a cylinder balance test - pull injector clips on each cylinder seeing if they all make the same difference. Maybe there's one or two not pulling their weight, and misfiring.

 

First thing is to disconnect the O2 sensor and compare pulse width. See if that changes anything. Too much overlap (+no cat) and can make it more reasonable to run open loop full time. You are most likely getting lean misfires. Richen it up some and see if idle quality increases. Running too lean "smells rich".

The other thing I would check is vaccum at idle. If there is little vacuum, the regulator will raise fuel pressure (only at idle). In that case you'll have to cut back ALOT of fuel in that one area.

Big cams just stink at idle, I just lean it out to 15:0 and add timing to compensate. Makes for a rock solid idle, even on big cams.

 

I pulled 10-11" vac idling with the Isky 280 I took out. I probably pull around 12" with the current cam. The idle quality, as far as smoothness and consistency, is fine. The cam has a choppy idle but it doesn't really hunt. However I will work on richening up and see what happens. Thanks guys

 

Here's the update. I am definitely correct. The car is definitely rich, it is not a lean miss condition appearing/smelling rich. I tried your suggestions and added fuel in the MAF table until the idle/low speed operation actually made the O2 happy with the stock O2 bounds. I got it to the point where the BLM at idle was 128 or thereabouts instead of the usual maxing out at 160. The idle was sooooo overrich with the BLM reading 128 that under light load the engine would stall out and take a bunch of cranking to restart. I went back to stock maf tables and all was well again, except for the usual near-0mv reading at idle from the 02 sensor. I brought the O2 cross point down to 100 mv and the upper/lower bounds +/- 45 mv either direction, and that gets the BLM to at least not max out at idle. I wouldn't have thought that the cam I am running would still be way too big for the O2 to read accurately at idle, but it is. I don't know that a wideband would even be accurate if the overlap is fooling the NB by a ton. I am probably running around 12-13:1 idling when the NB reads 14.73. The car barely runs it's so rich under these conditions. When I lock the BLM so it can't runaway idling, and the O2 reads 0 mv, the car runs excellent and idles great. It still smells too rich. I guess I am going to have to keep tuning by plug reading and smell for now. The plugs still look overrich even with the O2 indicated "lean" condition. The exhaust valves were all quite dark when I had the heads off recently. I think a frieking Quadrajet would get my AFR closer to ideal than the EFI with the brand new heated genuine delco O2 sensor that doesn't like me. As I said, absolutely new exhaust and gaskets with no leaks. All injectors check good, fuel pressure is stock. AGH!!

 

You went from a cam with 16* overlap to a cam with 8* of overlap. A stock TPI cam is in the -20* to -30* degrees of overlap range. I have a MAF engine with -2* of overlap and the BLMs climb to 160 at idle. The only way I found to cure it was changing the O2 constants for closed loop or go to open loop mode. You could also change the code to run open loop at idle and closed loop under part throttle. It wasn't worth the effort for the cam I have.

 

Have you considered that?

 

Would I still have highway mode fueling and highway mode spark in open loop? I need both of these. I am getting almost 25 mpg highway with a cammed up 327 and 3.73 gears with O/D because of highway fuel/spark. I will not give this up!

 

do as junkcltr said, set it up to idle in open loop & go to closed loop once on the gas, you'll have best of both, good idle & full use of highway mode

 

Guys I am running MAF 6E. I am not aware that there is an easy way to go open loop idling only -- I was of the belief this is for SD setups only. Am I wrong?

 

i don't know much about MAF systems, but as far as i know you can set it to run open loop at idle on a MAF system.

these may help if you haven't read them already

[url]https://www.thirdgen.org/techbb2/showthread.php?s=&threadid=310130

[url]https://www.thirdgen.org/techbb2/showthread.php?s=&threadid=289489

 

I've read these threads already. I don't think you can run 6E open loop at idle only, I've already been through this before.

 

Disconnecting the IAC, and/or the bypass line makes that test alot more effective.

 

This engine is fresh, cranking psi is within 5 psi from highest to lowest cylinder. Cyl dropout test shows all 8 are pulling their weight.

 

If you like closed loop then you need to change the code to do open loop for low rpm (idle). The easiest route is to lower the RL )2 thresholds like the stickies talk about. The BLMs will stay near 128 if you do that and not give it too much fuel.

I did that with the $58 code that I am running and it seemed to work OK, not great but got me by for the time being.

 

I have already adjusted the 3 R/L thresholds!!!!! The narrow band O2 reads 0.00 mv idling because the overlap from my cam puts me off of its readable scale. Did anyone read my post? I can not take out enough fuel using the O2 thresholds to make the idle not over rich. Also as I do take out fuel the tune looks even worse to the NB sensor. It looks like the best I can do is remove fuel in the MAF tables such that, with the BLM maxed out, the fueling is where I need it.

 

Sorry I can't give any more help on the 6E setup, I'm all $8D myself.

When you get a chance, what is the cylinder drop out test you mentioned? Is that just pulling a plug wire and noting changes?

NEVER MIND, figured out what the cyl drop out test means

 

I think your only option then is open loop or learning how to code assembly.

 

There are 2 INJECTOR values in the $6E BIN. They're in the "Constant" section. If you have put in larger injectors and have modified these 2 values to reflect those injectors, then you may be have the same problems I incounter. These 2 values seem to control Pulse Width. Warm up your engine and get it into closed loop. Then while idling, slowly reduce these 2 values using emulation. You should notice the engine idling differently, a decerease in pulse width which should lean put the mixture at idle. I went from 22LBS to 28LBS injectors. I went in and changed these values to reflect the new 28LBs and started noticing a rich mix at idle. It idled ok, but!. Then I slowly back off the values in these locations the idle smoothed out. I'm running a 24 in these positions and I have a nice idle and no smell.

Play with it just to see if it makes a difference.

 

Yup, that is why emulators are a bad thing. This is a bad way to learn how to tune using a stock ECM. You may not think so, but as you learn more you will understand what I am saying.

 

Emulation is great as long as you understand everyting going on. Beside, emulation is how I found out what to do to fix teh problem. The 28lbs value did not work correctly because I had the fuel pressure cranked up as well causing more fuel to be added then the ECM was tracking. Not a bad problem at WOT where more fuel is needed, but at Cruise BLMs where low and idle was not right. 28 would have been fine if the fuel pressure was left at 40lbs,

 

r_wells - lowering the injector constants actually RICHENS the mixture. Telling the computer that the injectors are smaller than they are only makes the computer open them longer to try to get the same fuel.

 

Crazy question 327, but what kind of ignition are you running, you may have a problem at idle if the ignition you have is not burning the fuel because of the lower voltage at the coil, just an idea, it caused and over rich smell in my car at one time. As the rpm increases the alt. puts out more voltage and will let the ignition put out a stronger spark. Are you running an MSD if not I would suggest it, I have seen a bad cell in a battery that the alt. would not keep up with cause all kind of idle problems, especially if your runnig electric fuel pumps/fans/water pump etc. Its just an idea that maybe the ignition/plugs may not be burning the fuel at idle. I had a semi issue like yours on my PRO STREET VEGA and installed and OPTIMA battery and you could really tell a difference in the way it started idled and smelled. Maybe this will give you something else to look at. Good Luck.

 

For what it's worth I have had the same idle problems. Though mine idle's great with a low reading. I have heard of other people having the same problem. I only hear about this problem on cars that have long tube headers or shorty headers with the O2 sensor further back.

 

I'm running a remote Accel super coil. The idle quality is fine, it is consistent, just smells extremely strong.

 

I was having an idle problem with my hotcam and lt4 intake ($6E). I replaced the entire ignition system, had my injectors checked, added fuel, took out fuel, added timing, nothing helped. I read something in an lt1 forum about reversion from cam overlap causing one bank to run lean and the other rich at idle. (I only have one 02 sensor so I would never know this) They solved the problem by backing out the idle adjuster screw to close the butterflys so most of the air entered through the IAC valve. I tried it and it worked for me. (I've been known to try about anthing short of calling Miss Cleo!) The iac steps are about 120 , but It will idle down to 600 rpms and not stall. I can now stand behind the car without my eyes burning from the fumes. Don't ask me why this works because I don't know.

 

Thanks LARRY, That is some good info to know, I was currious about what I would have to do if I ran into this problem, im about to have my engine set up soon and have a semi large cam, I have the moates APU1 but did not know that to do if that does not adjust it out, so I guess we just revert to the old mechanical adjustments......LOL. Thanks