This is true. This is about the time we are getting our summer blend of gasoline around here as well.

 

I cant post up the tune/logs because I dont have the software, otherwise they'd be in post #1. The best I can do is using a scanner tool plugged into the ALDL. It cant record data to be replayed later but does show accurate live data

With the MAF unplugged running in SD mode the STFTs are extremely lean. Start around -20 and drop to around -40

What would cause it to run progressively richer with the MAF/MAP connected sans O2s, but leaner without the MAF?

Fuel blend change shouldnt be this drastic and would suggest a constant issue. IE always running bad. Not intermittent. Right?

 

Well the first thought would be that the tune was off, but I know Mike is better than that. Other than that, maybe a bad MAF (which you checked) or a bad MAP. You're talking about a 30+% fuel swing between SD and MAF.

 

Attached are the .hpl file, .csv file and DTC log. *EDIT* Jon has the excel file, forgot I can't load it here.

This has been odd. Car ran fine after the first tune. It started to have some issues after running it for a few days, we checked it out again and could not get all the missing to go away. The car liked different timing, but still had some issues. Since then it got worse in the same area, then started to act up at WOT (it did fine when we logged and the MAF curve looked very good and calibrated as I would expect). It is also odd to see the differnece with the MAF unplugged as the VE and MAF were both calibrated in the same day. My only question there is if we happened to dialed the VE in with it acting up or doing something different. I can't remember either if this is an 85 mm MAF or not, if it is then the IAT was out of the picture and would throw the trims off. It will default at like -38F if unplugged, it adds fuel, thus the incredibly rich fuel trims. At the start though, they aren't off too much more because sitting at an idle with the last log and the MAF plugged in they were -10%. Then again (not in what I saw today, but what he mentioned while talking over email) even with the MAF it seemed to trim more and more negative as time went on. I just know the AFR errors were +/-5% when we finished the VE up. Honestly at this point though, it seems a lot if changing. The car pulled quite strong when we got all finished up, I was impressed. It is a totally different animal now.

There is a few things I noticed:
-CKP sensor code, which had not set the SES but was in history as immature (I am not sure on the conditions of this code)
-Around 7,500 Hz is when we captured the first issue, but it is not MAF Hz dependent. At one time in the log he was in the same frequency and it did not do that.
-When the issue happens, the o2 voltages still switch around. No excessive TPS voltage to throw it out of PE, still commanding 12.8:1. I question if the CKP sensor is throwing off injector timing/firing (maybe why timing helped at first, but still within what I consider normal for the motor).
-More KR is showing up now (but I left the sensors sensitive). I am not really concerned about this with the settings it has, but this did not show up last time.
-Even through the issues, no misfires even showed up, yet last time we got a few (maybe one of the codes prevents this from showing when set?)
-There is also a voltage code, so I wonder if the computer may see intermittent low voltage causing issues with the control circuit.

So to me I think CKP sensor. The MAF has been swapped out with no luck so the MAF is good. The only thing that could throw the curve off would be repositioning, but the fact that I don't see it being frequency dependent tells me any movement of the MAF did not hurt it.

Maybe you guys can see something else, but this is weird. I have never seen a car go from running so well to that bad after troubleshooting the obvious things (plugs, wired, compression, fuel pressure, etc.).

 

Did you try doing a crank relearn? Like you said, crank sensor might be going bad... if it was an aftermarket crank, I'd say maybe the reluctor ring is moving.

 

If you suspect a crank sensor and/or crank reluctor problem (including thrust bearing), then find someone who has a high-end automotive oscilloscope, and look at waveforms of the crank sensor (and cam sensor while you're at it)... the waveforms will show immediately if there is a problem or if you can eliminate this and move to the next possibility.

 

My MAF is the 85mm truck unit with the incorporated IAT. If an unplugged IAT defaults to a super low value and sets enrichment, youd expect the STFTs to go super rich with the MAF unplugged, not the other way around. I can splice an external IAT on and retry the test if it would help

 

No, that will make no difference. What is going on is not related to the MAF reading, it even happens when it is trimming. No need to waste time on that.

When you unplug the IAT the computer thinks the car is getting much colder air. It dumps in more fuel making it very rich, which means the fuel trims are going to go way negative to pull out the extra fuel. You said they were -20% to start with and went to -40%, I WOULD expect that.

I thought about a crank relearn but the fact that it was perfectly fine for a while and went bad makes me not want to do that as maybe it will only cause more problems if something is bad.

 

I stand corrected

Too much SBC/3rd gen tech on the brain I guess. LO3s and LO5's commonly cook the CTS which defaults to something very negative sending a massive quantity of fuel into the TB

 

Yeah, it gets confusing haha

 

Crank relearn never fixes anything except a crank relearn code. Tired of posting it. It has nothing to do with driveability. Only misfire detection.

 

So what do you think? Crank sensor or undetermined

 

Try replacing the CKP sensor (it's cheap)... also take a peek at the reluctor wheel thru the sensor bore, turn the crank while observing the reluctor [bent/broken/wobbly/loose?] (this is hard to do, cramped space and flashlight blocks vision).

There is the possibility that the reluctor is spinning/walking at higher engine speeds... the only way to check this for sure is with a high resolution oscilloscope.

 

New crank sensor didnt help, but I did find an oil leak I have to attend to. Oil sender adapter isnt sealing so the intake comes off again

Ill see if I can track down someone with an o-scope. Only ones Ive seen were on campus. May have to go lowtech to monitor crank walk with a camera with a flashlight mounted under the hood during a WOT blast

If it does end up being thrust bearings Im going to grab a new long block instead of doing the mains on this one. Cant afford the extended downtime

 

It has to be a DSO with enough horizontal time to see several crank revolutions, and with enough horizontal resolution to allow zoom in on each crank pulse to make sure it is shaped correctly... e.g. Picoscope 3423/4423.

You also want to view CMP.

Need 3 channels: CKP, CMP, and #1 secondary using a capacitive probe.

 

You're right Joe. Time to break out the heavy artillery!

OP, you'll need to at least synch the crank sensor signal, and ignition on a 2 channel scope. May want to see if you can't get your hands on a low amp probe and "see" what the coils are doing too. Primary current waveforms can tell you alot.

Also if it's possible to find someone GOOD at o-scope use and interpreting wave forms, they can tell you far more about what's going on than any amount of scan data.

Edit: Just saw you're in NC. Va Speed is just across the boarder. We/I can get it figured out for you. We have said equipment to properly diagnose it.

 

When I first looked at your wiring harness pics on thirdgen.org, the first thing I noticed was that giant splice-o-rama you did to extend the PCM connections. Scary looking stuff.

 

Every single wire is ohmed out atleast 3 times before its loomed. Anything over 1.5ohms is cut out and replaced. Since the issue came up the harness has been removed and checked a 4th time. Still fine

This issue is not from the harness

 

Good QC and I hope it's not a harness issue, but after you rule out all other causes that's what you're left with.

I've seen O2 sensors get poisoned via coolant contamination (silicates kill O2 sensors big time) and cause the sensor to report rich exhaust, which in turn makes the PCM/ECM set negative fuel trims and lean out the mixture. Exact opposite of what you're seeing from what I can tell, but it's worth some thought.

I'm thinking you either have a bad tune, or a bad sensor.

Tune can be ruled out by rolling back to a virgin bin image with just the un-needed sensors and VATS disabled. I'd do that next. If you have forward O2 sensors, MAF, and the other basic closed loop sensors functional the engine should run decently and show you LTFTs that are useful.

 

Problem has upgraded to cruising now, it feels like Im running in limp mode. Misfire is still present at higher throttle, just doesnt have any good running mode anymore

I picked up a new long block because the price was right, but have a few concerns

Assuming the thrust bearing is bad, how can the reluctor ring move out of view, even partially? Its got about .050" before it contacts a main cap both forward and back. This isnt enough to move away from the view of the crank sensor




Only real solution I can think of is the reluctor contacted the rear main cap and spun ever so slightly out of alignment. The problem with that theory is it would throw the crank signal off for ALL situations, not just X% throttle or engine load

It seems like the crank sensor isnt the problem afterall