I'm working on a problem where I get a lean spike on accel at low throttle openings. While I am waiting for a fuel pressure guage to be delivered, I thought I would get familiar with the AE tables... however there are 8 tables and over a dozen constants in the code. Does anyone want to share experience on how these tables interact? I am working through the code but would appreciate any help.

 

I went through most of the code regarding all the AE function. Ill look over it tonight and email the updated hack if you wish to see it. Its been awhile since Ive looked at it so I dont remember much about how it worked.

 

Actually, to make it a little easier, whats the exact problem your having? Does it go lean right away? Is it ok, and then goes lean after you open the throttle?

Another thing to keep in mind is that at low throttle openings, there is little or no AE as the TPS AE may not be present and the MAP AE may not provide very much. If youve done some mods then some things may need some tweaking.

Luckily, in the PCM just about everything is transmitted through the ALDL so there is plenty of diagnostic info to guide you if it does prove to be an actual issue with the AE.

 

When under low throttle opening cruise I get the following:

- Slight open (<25%) produces a short lean spike but it recovers fast enough that there is no hesitation.
- Moderate open (<50%) produces a lean condition and a stumble which cleans up in a second or two then the truck accelerates.
- >50% opening produces a lean condition and then a pop as (I assume) the over compensated fuel is dumped in.


The percentages are obviously guesstimates. I am assuming 'pump shot' is low because of the increased surface area of the GMPP intake and the higher flow rates of the vortec heads compared to the original L05 engine. This should dry out the buffer charge in the intake and cause then engine to go leanuntil the PCM can compensate. Although I'm not ruling out loss of fuel pressure until I get a gauge attached.

I also get the same stumble/pop effect during shifts when the engine is cold. My coolant comp tables are not correct yet.

I was just looking to start understanding the tables since I don't have much else to do and I dislike making 'shot in the dark' type modifications.


If you have a better hack than the public one I'd love to see it. I have been annotating the code as I start to understand it (mostly variables at this point), but more information is always better.

You can send it to:

spam (hyphen) trap [at] austin {dot} rr "dot" com

 

You're probably going to have to add some. What I don't understand is, how do you decide when to add more MAP or TPS based AE? Either way, to really fine tune it, I can't see getting away without a WB. You may be able to get close with the feedback from a narrow band O2 (integrator?) and a fast enough ALDL frame rate (EBL would be great here), and "close" may be at least good enough to drive the car...

I just went through and tweaked my AE vs CTS table (had to lean it out from stock, oddly). I didn't touch the TPS or MAP tables, just the global multiplier table based on coolant temp. Anyway, my AE was so rich after a few small pumps of the gas that it would actually cough and sputter for a few seconds until the engine consumed the excess AE fuel. That was enough time for my slow-*** 160 baud ALDL integrator to show rich. Surely on 8192 (or faster), you could do a lot more.

It should go without saying that your VE tables should be right on before adjusting AE.

 

Sounds like overall its just lean on tip in. The pop is the engine going really lean from a total lack of fuel. Like you implied, first check the fuel pressure to make sure the pump is still keeping up.

Since I want to convert this PCM over to use a MAF if possible, Ive gone through and commented most of the code and the calibration portion of one of the $0D. I think I hit on all the code that handles the AE and DE/DFCO. From what Ive seen on the bench, the stock routine seems to use the TPS to generate most of the AE with the MAP providing a smaller portion of the AE. Probably the TPS AE would be the thing to concentrate on. As for what to adjust, well, you can both adjust the duration and the magnitude of the AE via all the tables they give you. Id suspect that it probably just needs more with the new intake.

I havnt used the actual TPS AE routine much since my old ECM primarily relied on MAP AE with the TPS AE just providing a shot of initial AE to cover the manifold filling. Basically Ive figured out how the PCM works, but not how to work it.

Whats that e-mail addr. again? Maybe Ill just hit Craig up and see if I can repost the most recent version on the FTP.

 

Would it be correct to say that a pop from the intake means a transient lean condition and a pop from the exhaust means transient rich? That seems to be the way my car responds. With my too-rich AE, I could rev up the engine and I'd get nice pops from the exhaust as the mixture completed the burn outside of the combustion chamber.

Hey, what did people do before electronic data logging equipment?! SOTP and track data (and vacuum gauge), I would assume.

 

I basically went into a parking lot, opened the door, and watched out the back as I accelerated. Stumbling/hesitaion with no smoke, need more. Bogging with black smoke, too much.