ULTM8Z

Guys,

As a point of reference (in order to eliminate my own calibration from the misfire diagnosis)...

What would you expect to see as far as Block Learn as a result of running AUJP on my setup:

ZZ4, AFR heads @ 10:1 compression, Comp Cams 212/218 @.050, MiniRam intake, full length exhaust headers.

With a bone stock AUJP calibration, the BLM is pegged at 108 on both sides of the engine at idle speed.

What I'm getting at is tihs, if a BLM of 108 is not expected for this engine combo, then it may be a valuable clue that could help point me to the cause of the rough idle/misfire problem.

I'm very much leaning toward a system level problem rather than a localized problem at any one cylinder. The fact that I get the same readings on both sides of the engine is one cluse. In addition, all the spark plugs look exactly the same, whereas with other past problems (loose injector plug, broken valve spring, bad plug wire, thrown push rod) the spark plug on the offending cylinder always read very differently than the others. In this case, they're all the same. So with these two observations, it would appear that what ever the rough idle/misfire is, it's a symptom and not a cause which to me would eliminate mechanical probelms in the cylinders.

JP86SS

iTrader: (1)

When you ran this test, was the injector constant recalculated for your setup?
Higher fuel pressure or larger injectors would give that rich indication right off the bat. You said "at idle speed", did you drive around or just sit still? There needs to be movement for the learning to ocurr IIRC and you may just be seeing the cleared BLM reaction from an initial startup with clean memory.
If that is not the case, I wouldn't think that cam is aggressive enough to cause that condition to happen. Possibly something over 220 might begin to give a rich reading with the stock cal.
I know you've been chasing that miss for a long time, wish I could be more help.

RBob

iTrader: (1)

I'd expect that with a stock AUJP. What is the LDA on the cam? What is the idle MAP value?

Set an idle SA of 26 deg BTDC, then increase the O2 idle terms until the skip goes away. Ignore the O2 except to see what it is doing. Don't do any adjustments based on the O2.

Make adjustments according to how the engine is running. Keep increasing the idle O2 terms 50mV at a time. Observe how the engine idles. There should be a sweet spot, then as the idle O2 values are continued to be increased the engine will get a little rougher.

RBob.

Here are the idle O2 terms:

Should also zero out this one (no air pump, right?):

And set the air to always divert (set to 255):

ULTM8Z

Oops, yeah I forgot, I did in fact alter the injector constant to 24 #/hr since that's what I'm running. Everything else though, I just wanted a pure AUJP data point for reference.



RBob, the cam has a 112° LSA (I'm assuming your "LDA" is a typo), idle map is about 2.15 volts (approx 15 inHg vacuum) at 700 rpm.

Man, I've been through those O2 constants so many times... but, considering your EFI experience vastly out weighs mine, I'll rcertainly run the test. I suppose this is good though since we're now coming from a common reference point, namely the AUJP cal.

I'll know when I have this problem licked... the bucking/jerking during low speed crawl (<1 mph, brakes partially applied) will disappear.

BMmonteSS

This sounds simple, but it's worth checking. I've been having misfire problems lately too, It seemed to go away everytime I swaped to a new module. I was getting the parts store cheapies so I just exchanged them and everything was fine for a while, then the miss would come back. It ended up being a loose screw. The screw that holds down the condensor in the dissy also grounds the system. Everytime I changed the module I would wiggle this connection and walla it worked fine. The car now runs much better, although I now have to completely retune my VE's. My AFR has changed as much as a half a point in some places and a full point on the top end.

RBob

iTrader: (1)

That is about 51 KPa which is decent. Shouldn't have much trouble getting this engine to idle well. 112° is also on the tame side.

LDA Lobe Displacement Angle
LSA Lobe Separation Angle

Two terms for the same thing.

Starting over with a stock AUJP is a good idea. As you run the test keep a note of what the BLM and INT is once they stabilize. Again, don't change anything based on them, just continue with each +50mV change and re-test.

Low speed crawl may not be affected by the idle O2 terms. Will depend whether the TPS% and MPH thresholds for 'in idle' are exceeded or not. If the above doesn't some up with anything then I'd recommend a 4-gas analyser and an ignition scope be hooked up.

RBob.

ULTM8Z

Couple of other observations-

The low speed jerking seems to correspond to the lope or miss of the engine. That is, whenever there is a lope in the engine, it will result in a corresponding jerk forward/backward in the vehicle

The idle speed holds steady within about ±50 RPM. There is no hunting up and down or anything like that.

I have an AutoXray. RBob, would it be worth it to post the data at various O2 constant values? Maybe a data scan every .100 volts up or down? Maybe one or more monitored parameters may stick out or vary more than expected, or give some further clues.

RednGold86Z

iTrader: (1)

Are you using a manual transmission? If so, can you get it to run at 800 RPM and 80-90 kPa for a few samples, see if it bucks in steady state there. I recently found a cracked spark plug that would only buck at low RPM high load. The late timing combined with high cylinder pressure makes for a difficult gap to jump, so it finds any weak points, like arcing from the coil to a ground, or arcing across a crack in the porcelain of a plug.

It could be bucking from the extra fuel of leaving a cell with 108 and going to a cell with 128.

Could be IAC swinging open quickly.

Could be going from misfire to good fire.

I'd try removing all transient fuel for a test to see if it's still there, then figure out what can be done to put it back without it screwing up.

That small of a cam shouldn't be giving lots of trouble.

ULTM8Z

It's an TH700-R4 automatic trans with a factory '96 LT4 Vette torque conveter.

Idle speed is set for 625 rpm. Like I said, the idle holds steady and stable, and never wants to stall on me. If I raise the idle to say 800, the bucking starts to go away, but it's alot more difficult to hold the brakes. Way before when I had my ZZ4 cam, and before the misfire started up, the idle was silky smooth at 600 rpm.

I also know I don't have cracked spark plugs since I've already borrowed two other sets from some friends and always got the same result.

RednGold86Z

iTrader: (1)

Any header tubes hotter or colder than the others?

A dead lifter on an exhaust may show a hot tube, for example. Loosening it (the rocker nut) until it has noise may bring it back to normal temps.

Probably not anywhere near your issue, but it's a small cam, should be no problem with the tune.

ULTM8Z

#2 cylinder tube isn't cold, but it's colder than the others. That's with a simple water squirt test. I haven't actually mapped out the exhaust temps. There may be deltas between the other tubes as well...

ULTM8Z

Rbob,

Haven't forgotten about running that test... just trying to find the time!!

I'm definitely interested in getting your opinion on the AutoXray data if you're up for it.

Thanks.