ULTM8Z

Rbob has been working with me lately via e-mail on this idle problem (thanks RBob!).

He recommended I do this: Took a factory AUJP calibration; only mods are disabled AIR and EGR, zeroed out the AIR offset in the constants table, and changed to 24 #/hr to match my injectors.

I then started varying the O2 idle rich/lean threshold by .050 mV up and down, took a boat load of AutoXray scan data. Today, I took some gas analyzer data too. Not with as much fidelity, but some data in order to see any trends.

Keep in mind I have no cats (yet...).

If anyone here is good at reading gas data????

At the factory .598 mV
-------------------------------------

In Park, idling at 750 rpm:

HC 1400 ppm
CO 2.7%
CO2 10.6%

In Drive, idling at 650 rpm:

HC 640 ppm
CO 1.9 %
CO2 11.9%

In Park, 2500 rpm

HC 520 ppm
CO 2.6%
CO2 12.0%


At 700 mV
-------------------------------------

In Park, idling at 750 rpm:

HC 2000 ppm
CO 4.0%
CO2 9.8%

This was so bad, I stopped here.


At .300 mV
-------------------------------------

In Park, idling at 750 rpm:

HC 1000 ppm
CO 1.3%
CO2 5.4%

In Drive, idling at 650 rpm:

HC 400 ppm
CO 1.0 %
CO2 6.1%

dimented24x7

iTrader: (2)

Wow, looks like it runs considerably cleaner when its going lean. Dont know what the NOx look like though. How did it idle at each offset?

ULTM8Z

Idled terribly at .700 and makes your eyes water!

At .300 mV, it idles not much differently than at .598. Only thing is, you can see that the combustion efficiency is terrible (way less than 10% CO2).

Leaning the mixture out kind of band-aids the HC's and CO. But it doesn't appear to make the engine run "better".

I suppose none of this takes into account ignition timing, since factory TPIs will likely require a very different initial timing than my setup.

ULTM8Z

BTW, no matter how rich I made it (went up to .850) when I was taking the scanner data a while back, it never spit out one puff black smoke, even though it idled so bad it made my current misfire look smooth!

funstick

2 things come to mind. a bit more timming will help lower the HC. the second thing is physics. if your running a small engine i belive a 5.3 (327ci) then youve got to deal with overlap. it will cuase considerable trouble at idle. not reversion as much as overlap throwing raw fuel out the pipe. so you have 2 options. change the cam for one with less overlap and the same duration and lift or change the cam profile entriely. you're not going to get a stink free idle with out craps loads of advance a higher idle and a very lean mixture to keep things clean. my strategy would be to rethink your current cam profile.

ULTM8Z

funstick, the cam is only 212°/218° duration with a 112° LSA. The engine is 350 cid. I can't believe that's considered a radical combo??

dimented24x7

iTrader: (2)

That thing should idle smooth. Have you looked at the ignition at all? Definatly worthwhile if the car is misfiring.

ULTM8Z

Oh man! I've been through that ignition like the IRS through Willie Nelson's tax return!

What's really odd is that the car feels smoother in Park, but according to the gas data, it's running worse in Park!

eric305TPI

Are you able to get O2 percentages with the other gas data so I can see the whole picture.

ULTM8Z

I wish! The O2 portion of the analyzer was malfunctioning.

He says he's going to get it fixed fairly soon...

Any guesses with the data that I have?

JPrevost

Hold up. Where does the gas data show it running worse? I hope you're not looking at the sensors and saying, hey, the engine should run better with this blah blah blah because face it, engines are funny animals. None of them EVER do exactly what you want or think they should do. They come close but most of the time you'll just be giving yourself a headache trying to get the data to match up. Get the engine running good, then analize the data, get it running better, THEN analize THAT data. My engine is similar to yours except I don't know if you've got fastburn heads or not. The cam is similar enough and my car liked running slightly rich at idle. Sometimes, like in my case, the cam specs are misleading. I've got a TON of advertized duration. This being said, my idle is rather ruff at low engine speeds hence the "loopy idle" advertized with this motor even though it has a 212/222 @ 50 thou rating! I couldn't get it to run well at stoich let alone lean.
I've attached a diaghram that should help you somehow or another.
One other thing, you say at .700 your eyes water. That's really odd and the fact that you don't see any black smoke... sounds like a no spark situation. Looking at the spark plugs will tell you if you're even getting spark in the cylinder. Clean all the plugs or get new, run for a little while at the problem area, shut off ignition completely, pull plug and if it looks like it did before (clean) but wet, there's your problem cylinder. If it's wet and black it's firing but not very well. Have you done the old turn off the lights and look for blue sparks trick? You might have a bad wire (coil wires go bad too).

ULTM8Z

I'm comparing:

In Park, idling at 750 rpm:

HC 1400 ppm
CO 2.7%
CO2 10.6%

In Drive, idling at 650 rpm:

HC 640 ppm
CO 1.9 %
CO2 11.9%


In park, HC's are over twice as high, CO is almost 50% higher, and CO2 is significantly lower. This tells me that combustion efficiency is way lower in Park than in drive. Am I off base in my analysis? I'm definitely no expert...

I have AFR 180cc street heads. That cam is exactly what I have.

That's just it. I've been through three sets of plugs running that very experiment. Each time, all the plugs come out looking all exactly the same: light to dark tan, no strange deposits, and dry as a bone. Plugs are ACDelco FR3LS (what GM recommends for ZZ4's) and I have had them gapped from .035 all the way up to .060. Currently, all are gapped to .045.


Actually a guy on corvetteforum suggested the same thing today. I'm going to do that tonight. Also, I'm running a Corvette large cap distributor, so no coil wire to speak of.

ULTM8Z

Looking at your graph, it appears that I'm running rich as it is. Though, my HC's are way off the chart.

But it would explain why when I lowered the O2 threshold to .300 mV, the HC's went down significantly. Only problem is that CO2 also decreased signifcantly. As I understand it, CO2 is a good meaurement of combustion efficiency.

funstick

was the camshaft degreed in ??? if so is it advanced or retard over the ideal position ???? if it was significantly retarded that would cuase all of the above problems.

dimented24x7

iTrader: (2)

That holds true for AFRs above 14.7:1, but below that, your leaner then stoich, so theres less fuel available to burn, and hence, less CO2 being produced. It may even be burning more efficiently even though there is less CO2 present.

I too vote its some other problem then the fueling, especially with a misfire present.

ULTM8Z

Funstick, it wasn't degreed in. Comp Cams however does grind 4° advance into the camshaft such that if one installs the cam "straight-up", it'll actually be 4° retarded.

At one point I was chasing a rumor that GM built 4° retard into their timing chains. I thought perhaps the ZZ4 timing chain was cancelling out Comp Cams valve timing spec. Chased that one for a few weeks asking everyone from Scoggins Dickey Chevrolet, to Comp Cams, to Crane Cams, etc... did internet searches on it and couldn't confirm or disprove it.

I suppose what I could do is put a dial indicator on the pushrod side of the #1 intake rocker and a degree marker on the damper. Then slowly rotate the engine by hand and see where the intake centerline is. If it corresponds to what Comp Cams has on their cam spec card, then I know I put it in correctly and GM's "phantom 4° retard" is truly false.

How much would a cam have to be off before you start noticing problems like this? Is 4° really that much? I'm no expert, so I'm asking a honest question.

Thing is, once I get off of idle, this car hauls a$$ with really no driveability problems. In fact, just yesterday, I made really short work of a 350Z going up a freeway on ramp. Wouldn't a retarded cam cut down on low speed torque too? Or perhaps, if it's not degreed in correctly now, then I have more torque to gain by degreeing it in right???

Craig Moates

Cams are designed to run at a certain synchronicity with respect to the action of the pistons and what-not. The dynamics have to be right. Even a degree or two will make a big difference.

On my own engine, I made sure it was within 1/2 a degree using the offset bushings. It does right what it ought to with the heads it has, and has a nice tapering plateau powerband up through 6500+, never falls off.

A friend of mine set up his (nice) 406 engine, with massively ported heads and huge cam, and didn't get his cam degreeing correct. He assumed that it was good from Comp, installed it straight up, and the motor (single-plane MPFI setup) falls flat on its face above 5500. It should go straight to the sky up through 7k. The tune is dead-on, spark is right. Plugs look great. But the cam timing is just a little off. Makes a big difference up top. I mean it drops OFF up there.

You're right, that's a ***** cam, it should idle like glass. How much vacuum are you pulling?

What is your spark advance at idle? One good idea is to 'tune for vacuum'. Adjust your spark advance to achieve max idle vacuum. Then adjust your fueling to achieve the same. Go back and forth, and let your IAC make up the adjustment. By doing this, you will be making sure that your engine is running at the most efficient combination of fuel/spark at idle. I mean, if you're at a particular RPM setpoint (say 1000), and you make adjustments to fueling and spark until the vacuum reaches a max, you've achieved optimum efficiency. No questions asked.

You can NOT believe the O2 data at low RPM, especially around idle, with larger cams. The amount of fuel that just gets dumped out the pipe along with unconsumed air is enough to offset the readings. You saw some of that in the HC readings I think.

Have you tried leaning out your idle range to see what happens? I've gotten very nice results from doing just that. Leave the fuel in up top, but starve it down low. Cleans up amazingly well if you put some timing in there.

ULTM8Z

I'm pulling about 16 inHg at 750 rpm in Park, and about 13-14 inHg at 650 rpm in drive. Nothing I've done has been able to improve that (aside from changing to a AC Delco O2 sensor which picked up 1 inHg of vacuum and did help out the idle a little).

I think I need to check the installation of the cam and verify that it's installed correctly.

Craig Moates

You tried tuning in open loop?

Disconnect the IAC and the O2 sensor, grab that distributor, and twist it around for max RPM. Check the advance and that's where you'll want it.

Do the same with fuel via adjustable FPR or diddling your FI constant.

Then you hook up your IAC and you'll get max vacuum.

funstick

well thats very hard to say. let me share my experence with the stealth ram on a large engine ( 427ci with big ported heads etc etc etc )

you have an intertial supercharger on your engine. inertial through helmholzt harmonic tunning. ive had similar issues with good headers t can actually create overscanvengning at idle and low rpm with good TQ output and reasonable drveability. the problem lies in the amount of overlap in the cmashaft.

the other possiability is that yes the cam is not properly degreed and 4 degrees could cuase big trobule for sure.

ULTM8Z

Somehow I don't think overlap is a problem with my cam, as small as it is. I wanted an upgrade from the ZZ4, but maintain excellent driveability.

Speaking of headers... hmmm.... mine are not equal length, but that #2 primary header pipe is rather long compared to the others (though, #1 is also fairly long). Since #2 is the one misfiring, maybe there is some overscavenging going on in that cylinder? I don't know... maybe I've stumbled upon some engine combination where all factors combined contribute to a very poor overall distribution pattern at idle speeds.

I guess we'll know more when I check the cam timing.

BTW... how do you like the Stealth Ram? If I can't get this MiniRam running right, I may be looking at one of those...

ULTM8Z

Craig, thanks. I'll put this on my to-do list for the weekend that I do my cam timing check. Hopefully next Saturday or Sunday.

dimented24x7

iTrader: (2)

Thirdgen aftermarket headers suffer from the same problems. Unequal primary lenghts. Havnt noticed any ill effects from it at idle. I think the MR will alter the engines VE, but it still should idle well and pull good vacuum.

I still think you should go ahead and check all the basics like the ignition system and timing at idle before going and chasing other theories.

PS, have you checked the actual AFRs yet? All the injectors working properly?

ULTM8Z

Agreed. What you said...


I'm assuming you mean Air Fuel Ratio and not my Air Flow Research heads... In that case, the only "real" measurement I have is DynoDon's and Kevin91Z's wide band O2 sensor telling me that the passenger side is running at around 19 or 20:1 at idle. But I get conflicting data when I inspect the spark plugs and they show up medium tan and how have a CO readings showing up at around 4%.

Yes the injectors are in fact working properly. Verified that with a different set of injectors and by swapping injectors around, putting noid lights on the plugs, and ohming out both sets of injectors. I'm absolutely positive there's no fueling problems with this system. It's either something mechanical or ignition related. And given how much I've gone through the ignition system, my money is on something mechanical.

One thing I just did was to order another AFS74 spark plug to go on the passenger side. I have a Delco on the driver side and a Bosch on the passenger side. So when I compare BLMs (with ECM controlling side then the other) I'm wondering if the Bosch is giving accurate results for the passenger side. Especially since the Bosch doesnt' go into closed loop as readily as the Delco. Anyway, it'll be curious to see (with a true apples-to-apples) what the BLMs are doing from side to side.

I can also take a voltmeter to the non-controlled O2 sensor while the ECM is controlling other side and see what's happening. For instance, hook the driver side O2 up to the ECM and put a voltmeter on the passenger side. If the ECM is holding the driver side of the engine to 128 BLM, but the passenger side O2 is pegged at really high mV or really low mV, it'll be a good clue. Then I can switch it around and see what the driver side is doing with the voltmeter.

funstick

oh you have a minram. uugghh. answer this. how many iac counts do you have at idle ?

ULTM8Z

Looking at my scanner data...

In park, IAC steps are 31 at 750 rpm.

funstick

try cutting those back to close to zero in park by opening the throttle and get back to me.

dimented24x7

iTrader: (2)

Theres a possible problem that could do it, 20:1 at idle. Assuming there are no large exhaust leaks to skew the data, that will cause all the above symptoms. Have you checked for vac leaks at the intake yet? If not, that number 2 intake runner is probably a good place to start

ULTM8Z

Adding it to my list... <scribble, scribble, scribble....>

ULTM8Z

Been there, done that, got the lousy t-shirt!

dimented24x7

iTrader: (2)

How was the reading on the drivers side, if one was taken?

ULTM8Z

It was pretty normal... about 14-15:1.

dimented24x7

iTrader: (2)

That definatly indicates a problem on the pass side cylinder bank. It could either be from a vac. leak, or from the misfire itself. The fact that the d/s bank was ok points to something other then the tune.

dimented24x7

iTrader: (2)

Id start looking closely at everything associated with that cylinder bank. If you know it is indeed the #2 cylinder misfiring, then concentrate your efforts on figuring out what is causing that cylinder to misfire. IMO, the computer is totally out of the equation now, if the WB O2 readings are correct, which Id bet they are given how the motor is running.

Craig Moates

With a cam like that on that engine size, I'd like to see like 17:1 or so at idle via WB. Since they're different on both sides, yeah, you've got an issue.

Read your plugs, check for exhaust leaks as well. Might try swapping plugs/injectors left to right if you can't trace it down rigth away.

ULTM8Z

Yeah, it would appear that way...

But like I've been saying, there's no indication that there's any issue with any particular cylinder.

Air Flow Research evaluated the cylinder heads => No problems

Ran compression tests => No problems

Ran leak down tests => All cylinders within 10-15% of eachother (In fact #2 was one of the better ones!)

Inspected all spark plugs => All identical... clean, dry and a medium tan color (I've actually replaced and tested every component in the ignition system (including the entire distributor assembly)

Been through the entire fuel system (like I said earlier) => No problems

Engine doesn't loose coolant or oil and there's no peculiar colored smoke coming out of the tail pipes.

The whole frustruation of this thing is that I just can't seem to get a perponderance of evidence pointing at anything. The data and evidence are just all over the place!!

Any rate, that cam timing thing has got me real curious. Hopefully next weekend I can poke at that a little.

Z69

Cam timing wouldn't make one cyl screwy.
Unless that lobe only had a problem.
Didn't I bring that up a while back?

Have your tried individual header tube temps.
An infrared gun will give erroneous results unless you point it at similar color areas on each tube.
And the actual temp reading may or may not be correct.
But they should all track.
If you can get a hold of a contact pyrometer.....
I have one at work but you probably don't want to drive up here.

Have you looked at those little passages in the runners?
I'm not sure if they are for egr or IAC. MR probably doesn't have them. LT1 does.

ULTM8Z

I'm not ruling that out at this point. This misfire could very well be a symptom of a larger problem.

I already inspected the cam lobes when I changed the lifters. Besides, I've never heard of a roller cam lobe going bad.


Haven't actually measured individual tube temps. All I've done is to spray a little water on each tube. The #2 cylinder definitely is cooler than the others.


Right. MR doesn't have any passages like that.

dimented24x7

iTrader: (2)

I too agree that cam timing wouldnt make just one cyl. run bad, unless it was misground or something. I wouldnt chase that at this point. The easy stuff are things like the plug wire or the spark plug. An inspection and swap with an ajacent cylinder would rule that out. The other easy possibility is a carbon tracked, or otherwise faulty dist. cap. Try those first...

funstick

im cursious to see what happens when the iac isnt controlling the idle so much. could be air distrobution inside the plenum.

funstick

im cursious to see what happens when the iac isnt controlling the idle so much. could be air distrobution inside the plenum.

ULTM8Z

If one looks at a cam sprocket, there are 36 teeth on it. The crank one has 18 teeth. If I somehow installed the timing chain one tooth off, that would be 5° right?

Looking at the cam gear, one tooth equals 10° rotation? 360/36=10. However, the cam rotates at half the speed of the crank, so in crankshaft degrees, it's 5. Correct?

If so, then if the cam was one tooth retarded, it would negate the 4° advance the Comp cams built in, plus put me 1° more retarded than that. Hmm...

Guess I'll find out this weekend where it's at...

Craig Moates

You need to be pretty inebriated to install the cam one tooth off. However, it's been done many times (not coincidentally). That'd have it running real bad!

ULTM8Z

Depending on what I find this weekend, it may be...

"HEY! I resemble that remark!!"

dimented24x7

iTrader: (2)

The engine will rotate twice what teh cam will rotate, so its 20 degrees, or something close to that. Its possible, but that wouldnt cause just one cylinder to run poorly, the entire engine would run like puke, if it really ran at all.

I wouldnt take the timing chain cover off just yet, or entertain any other sorts of theories at the moment.

Id start off by first checking the spark plug wire on that cylinder by hand and with a DVM to make sure its ok. Id also inspect that plug to make sure its not faulty, and then swap the wires and plugs with an adjacent cylinder. If that doesnt fix it, then Id pull the cap and carefully inspect that for any sort of carbon tracking or damage. After that, Id look it the injector and verify its firing and there arnt any faulty connections or intermittent power issues. After that, Id look at the intake again, inspecting everything that has to do with that cylinder thats misfireing. Any leak along or near that runner/intake runner can take out the cylinder.

That what Id do, anyway. Good luck trouble shooting this weekend Id suspect its something stupid thats causing the trouble.

dimented24x7

iTrader: (2)

Really have tested alot so far, probably eliminates any igntion or fuel issues.

All the evedence seems to be clearly pointing to an individual cylinder misfire. Cool header primary, high HCs, large disparity between AFRs on the pass. and drivers side banks. All of this is indicative of a misfire. If the car only really misfires under low loads at high vacuum, but runs well under load, then thats a strong indicator of a vac leak.

jwscab

You could try diabling the IAC to see if the 'screwy airflow' is a problem. Do the jumper on A and B thing, wait till the IAC is extended, then unplug it. (remove jumper from AB then start it up) Then crack the throttle blades slightly more, and set your idle. Try your tests with AFR and listen for roughness.

BUT.....It really does sound like maybe the cam has a lobe or two that might be 'off' compared to the others, if your testing so far is as exhaustive as you've mentioned.

before tearing into the motor again, you could pop the valve covers off, put a dial indicator on the tips of the rocker arms, get yourself a degree wheel, and get real familiar with the timing events of the engine. of course, you will have lifter bleeding to account for, but some gross mis-grind, or wiped lobe will show up pretty quickly.

just a thought. good luck with it....

ULTM8Z

I was thinking about it a little more and I think you're right. So if I was off by a tooth, there's no way it would run as "good" as it is... the cam timing would be out by almost 20°.

Then there was a rumor I heard a while ago about GM building 4° retard into their timing chains. But, if that were the case, then everyone with a ZZ4 who swapped out the cam (and didn't change the timing chain) would have a similar problem.

Starting to think it's a waste of time to go after the cam timing.

Back to square one...

dimented24x7

iTrader: (2)

Id go back and take a fresh look at everything. One thing about these problems is alot of times the cause is right under your nose. I had a misfire from an internally carbon tracked wire. Looked fine externally but it was all burned up inside. Another ignition problem was due to a dirty dist. base. Caused lots of misfiring and later a completly dead car. Rebuilt the entire distributer, spent lots of money, did lots of diagnostics, and in the end realized that the entire problem was due to a greasy dist. base blocking the ground path. All I really needed was some mineral spirits to clean it off. Sometimes it seems that the easiest problems are the hardest ones to find

Has the car been doing this since day one? Or was it a problem that appeared over time?

91L98Z28

since you've had this problem for so long now, and (if my memory serves correctly) you've pretty much replaced everything except the intake itself, I'll vote (again) for an intake swap - to <i>anything</i> else. stock TPI, stealth ram, super ram, whatever - anything but that miniram. I recall reading before on the forums that it has known distribution issues, maybe your particular combo amplifies them. who knows.

hell, I have a stock lower and runners that you're welcome borrow for a while if you're willing to foot the shipping cost. You'd have to supply a plenum and fuel rails, though...I don't have spares of those. just the runners and lower is what I have, after I went to an accel lower and AS&M siamese runners.