dyno results and A/F ratio

[Craig 94 TA GT]

Thanks Joe. I had a compression check after someone dumped sugar in my tank around 3/04. The results were 130 all the way around, except #2 was at 160 according to the shop. But that was 1.5 years ago, and maybe something changed.
I did just remove #3 plug to see what it looks like after 2 weeks of regular driving.



It's a bit blurry, but you can see that the ceramic insulator at the top is half black. And the electrode also contains black marks at the base to the middle (but not at the very top/tip). Is this is a sign of detonation or other problems?

EDIT: I forgot to mention, the motor eats 0 oil after 4000-4500 mile oil change intervals. And the throttle body is spotless everytime I get in and check it. Hopefully those are at least some signs that the motor is OK.

[Injuneer]

Fred, I have a few questions, if you don't mind. What are the requirements for getting into cells 17 and 18 in closed loop? < .3 MAP and low RPM?

Also, I scanned the PCM after several days of running after the injector swap. I noticed something in cells 1 and 2: after a few minutes running in closed loop, the BLMs are around 120-125 for the right, and 122-117 for the left. However, as time progresses (maybe 10-15 minutes later), the BLMs drop: 116-127 for the right, and 114-109 for the left. Is this indicative of a fuel injector leak? Or indicative of something else? In cells 5, 6, 7, 10, they all show roughly 140/128.

Lastly, would it be worth something to unplug the MAF and see the BLMs in speed density mode?
Thanks in advance.

As best I can tell, Cells 17 and 18 are "synthetic" cells. There are arrived at by the PCM somehow calculating the BLM values from the other cells. Cell 18 is the open loop "load" cell, and Cell 17 is the "decel" cell for both open and closed loop. Cell 18 will sometimes be used in Power Enrichment mode (WOT) but I can't figure out why sometimes it will select Cell 15 and lock the BLM's at 128 (because the PCM was cutting fuel in that cell in closed loop) or other times it will go to Cell 18 at WOT, and use 128 for the BLM's. Not sure why that happens.

Are you saying the Cells 1 and 2 have lower BLM's on the left side, while the upper cells have 140 left/128 right? Generally, you type the left cell on the left/right cell on the right. Just trying to make sure I understand what you typed.

I guess you could try running in speed-density. I never tried that when I still used the stock PCM. My learning on the stocker stopped at least 5 years ago when I eliminated most of it.

[Craig 94 TA GT]

Thanks for the answers Fred.

The reason I asked about cells 17 and 18 in closed loop was that I constantly see both in closed loop. In fact, I see 18 a whole lot. It seems that it uses cell 18 under the conditions of 650-900 RPM and .3 to .42 MAP under low speeds. I wasn't sure if it's supposed to be used in this case. I've also seen it at WOT, sometimes, just as you mentioned. However, I generally see 15 more under WOT.

Sorry for the confusion about the BLMs in cells 1 and 2. Please disregard what I wrote before. Generally, in these cells, the BLMs seem to be way low. On the left, it ranges between 122 and 127. On the right, it ranges between 109 and 120. In other cells (5, 6, 10, 11), the BLMs are generally 139/128. Then on cells 16 and 18, they're at 140/120. I'm not sure if there's a pattern here, or not?

And I'll try to run speed density just to see the BLMs. I guess just to eliminate the possiblity that the MAF is somehow affecting the readings. Probably not the split, but maybe something else

Lastly, at 550 RPM, idle MAP is .42 and baro is 1.03. .42/1.03 is .408, which seems a bit higher than the 1/3 it's supposed to be. Is this within "tolerance"?

[Craig 94 TA GT]

I just got back from testing the motor in speed density mode. The BLMs are MUCH higher than with the MAF plugged in. Here's a small chart:
Cell -- MAF plugged -- MAF unplugged (speed density)
18 --- 140/119 --- 160/138
16 --- 138/121 --- 157/134
10 --- 139/128 --- 147/136
6 ---- 135/125 --- 143/130
2 ---- 123/115 --- 133/130
1 ---- 123/112 --- 144/131

I'm not sure if this means anything or not...the split seems to be the same difference, about 10-20 depending on cells. However, I have no idea why, in speed density mode, it is adding a whole lot more fuel. Maybe, though, this means nothing?

[Z Ya Later]

Hmmmm. I'm not sure how the 94+ PCM responds to running it without the MAF. If it is programmed to run like the 93, then it looks like you might have either a bad MAF or the harness to it is giving up the ghost. Not sure how much help I'll be, but I'm sure Fred and Joe can give you some better advice.

[Injuneer]

MAF mode measures air flow directly. If you make a change that improves breathing ( = improves voumetric efficiency), the PCM knows about the improved air flow directly from the MAF reading.


That's not the case with speed-density. Speed-Density caluclates air flow with:

RPM/2 X displacement X Density of air X Volumtric Efficiency = Mass air flow.

The fly in the ointment it "Volumetric Efficiency" (VE)..... that is a number pulled from a lookup table based on load and RPM. If your PCM is still stock, and you have improved breathing, the VE picked from the table will be too low, resulting in air flow calcualtion that is lower than actual.

In S-D, the PCM is calcualting fuel based on the air flow for a stock engine, but you have improved breathing, so there is more air flowing than the PCM clculates. So the fuel it adds based on the calculation is inadequate. So the O2 sensors tell it to add extra fuel = high BLM's.

I'm a bit surprised that with the mods you list you are seeing that much improvement in air flow. It may be a problem of the MAF also being a bit "off" as well.

The 94 and up PCM has all the same capabilites as the 93 ECM.... it can run fine in Speed-Density mode. It just adds the ability to get the acutal air flow directly from the MAF, rather than having to calculate it.

[Joe 1320]

I'm curious if you reset the PCM before you ran it in the Speed Density Mode. Did you notice any difference in seat of the pants performance? Here is an instance where I would love to see exhaust temperature readings from bank to bank. That would actually be a better indicator of the state of the combustion events.

[Z Ya Later]

Also, did you happen to reload the header tune or are you still running the stock tune that we reflashed a few weeks ago?

[Craig 94 TA GT]

Joe, I didn't reset the PCM previous to running in S-D. I didn't notice any difference in performance. In fact, if anything, maybe slower but I really didn't get on it at all, so I can't much about it.

Thanks for the info on S-D, Fred. I'm guessing the reason the left BLMs are so high is because there's still some kind of exhaust leak that keeps feeding air to the left O2. Although I can't figure out where it is and how to fix it. Otherwise, the right BLMs are on par with the stock VE formula + these mods, correct? Although I see what you're saying about the overall increase from bank to bank, cell to cell. Maybe it's worth getting a new MAF, or could it possibly be the injectors? The MAF readings, though, seemed to be "on-par", at least from the csv files I have. Is it possible for the readings to "look" ok, yet the sensor still be screwed up?

Steve, that's the stock program. I'm not going to load the PCMforless one because I already have lots of "before mods" csv files, so I'm trying to compare what was going on previous to each mod.

Also, scratch what I asked earlier about the plug. I think the black is deposits from running rich, rather than detonation. So maybe that proves that the driver's side has a "false lean" condition.

EDIT, I screwed up on cell 10 above. They should be switched. It is correct now. Sorry.

[Craig 94 TA GT]

I ran it in S-D one more day and noticed that the BLMs were rising even higher. Cell 16 was 160/133, 10 was 150/133, etc.

I have a couple thoughts though. If it it's an internal problem, would I notice it by reading the plugs? I mean, if the head gasket was blown adjacent to a bolt hole, would I be able to tell by reading the plugs? I haven't removed all of them yet, just 4/8 (3 on driver's, 1 on pass). I don't know what other internal problems there could be since there's no oil be burned, no coolant loss, etc.

I also have to get new motor mounts for sure, as the 1800 RPM vibration is getting worse. I just hope that it is the headers rubbing on something that's causing the vibration. Then, I'll probably do a compression check if the plugs show OK. I'm also getting a new header-y-pipe gasket courtesy of SLP. So I'll attempt to re-install that, sometime, or possibly have the y-pipe flange gasket holder recentered in order to truly eliminate the possibility of an exhaust leak. Just one step at a time, as you said Joe.

[Craig 94 TA GT]

I finally got to doing a compression test on the driver's side bank. I will try to follow with a leak-down test later. This is the first time I've done a compression test, so couple things to note are:
- The engine was fully warmed up, but it took a while to remove the header and driver's side plugs. So it was only a tiny bit warm by the time I got to testing. I didn't have time to remove the passenger's plugs because the motor would be cold by the time I got them out.
- The TB was wide open, the radiator cap was removed, and the PCM fuse was pulled.
- I counted 4 compression strokes by looking at the gauge. Each time the needle jumped or increased, I assumed a compression stroke occurred.
- The way I read compression on each stroke was by video recording. The needle would usually initially read ~30 psi higher than the actual reading (then bled down a bit), so I recorded about 30 psi lower than what the needle showed for the first 3 strokes.
So for example, on cylinder 1, the first stroke occurred, and the needle shot to 150, slowly bled down to ~130 (it would eventually have bled to 120), then on the second stroke it hit 210, then about 220, and lastly about 235...and eventually bled down to 210.

Here is the chart:


Is this the correct way on reading this? If it is, it seems like the compression test shows nothing wrong, as all cylinders are within < 5%. Of course, I still have to do a leak-down test.

[Craig 94 TA GT]

On another topic, I'm carefully looking at the header gasket for possible leaks. I'm wondering, does this look like a potential leak, or does this seem contained?
Either way, I'm switching to Percy's aluminum since they're reusable.
Thanks in advance as always.

[Joe 1320]

To me, that gasket looks like an eventual failure. you can see the direction the carbon tracking is going and eventually it will consume everything except the perforated metal core and that won't stop the exhuast gas. It may have been contained for the moment, maybe not. I don't know how much use the motor has seen since the install and there could have been a slight leak from day one. What I don't like is what appears to be unequal crush of the gasket by the header. I think you;ll like Percy's They are thicker and crush to conform.

I'll wait until I see the leakdown numbers for anything else.

[Craig 94 TA GT]

Thanks Joe. I'm following your advice on the Percy's...they sound to be the best! Especially for not perfect flanges. You can see an ever so slight gap in the header Drivers side flanges and thats exactly where the carbon was starting to build up in the gasket. I've had these gaskets for under 5 months, and have driven less than 800 miles.

[fastTa]

I agree with Joe, that gasket was already looking for failure. It's a little hard to tell in your pics and who knows how truly straight that level is, but those look to be fairly significant distortions in the header flanges. Sure some of that will "true up" once they are torque'd down, but still looks like a bit much.

You might want to consider a copper exhaust gasket. Also you can take your headers to NAPA or any local machine shop and have them either machine the flanges to be square or if it's not too bad they can put them on their belt sander. I would just pay the $20-$25 bucks and have them machine'd. .015"-.020" should do it.

But again, it may not be as bad as that picture makes them look.