3TAS4ME

Hello everyone. I haven't been on this board in a very long time. I have a question about my 93 T/A. It is a M6 car. It had an engine fire back in 2006due to an animal piling leaves and sticks on the exhaust manifold. Long store short, I fixed it and one thing I replaced was the intake that came from a '94. I also used the '94 injectors since three of mine had melted from the fire. I believe the '94 injectors are a different part number than the '93, and also the '94 went with a MAF sensor instead of speed density of '93. Any problems running the '94 injectors? It seems to run fine under full throttle but fuel economy is not nearly as good as it used to be. I used to get 26-27 on the hwy and now I can only seem to get about 22. Injectors? Engine is stock otherwise.

Injuneer

93 injectors were 22 #/Hr. 94-97 injectors are 24 #/HR (programmed as 24.9). With the 93 ECM and a stock program, the 94 injectors are flowing up to 13% more fuel the the original injectors. The ECM can compensate for this to some extent, using the long term fuel corrections. But to eliminate this issue, you need a new chip burned for the larger injectors. It's going to run rich at WOT (PE mode) with the larger injectors.

3TAS4ME

Thanks for the reply. That is kind of what I was thinking. Could the higher fuel/hr rating affect part throttle as well thus explaining the much worse fuel economy? How does this show up, on the block learn? I have a Tech 1 and can check.

3TAS4ME

Also, if I choose to install the correct injectors, is there a supplier for these that is reasonably priced? I see that GM has discontinued these injectors.

Injuneer

Use your scanner to look at the "BLM" (LTFT) for each fuel cell (there are 18 cells). The ECM would reduce the LTFT's below 128 (0 correction) to correct for the increase flow through the larger injectors.

The LTFT's can only go down to 108, limited by the program. That would pull about 15.6% of the normal fuel flow. If your ECM was already using the LTFT's to pull a bit of fuel, it is possible that it could affect the fuel mileage. The ECM can also use the short term trims (STFT's) to pull fuel, but that tends to be hit or miss, because the ECM is already toggling the A/F ratio back and forth between slightly lean and slightly rich so the cat will work.

When you go into PE (power enrichment) mode, roughly WOT (it's actually a table of throttle position vs. RPM), the ECM will default the LTFT's to 128 (0 correction) if they were pulling fuel out in closed loop.

Not sure on a source... you could try the "parts for sale" and "parts wanted" in the Marketplace forums.

3TAS4ME

Ok, thanks. I will take it for a ride with the Tech 1 and see what I have for readings on the block learn.

Injuneer

Those are stored in volatile memory. Can't the Tech-1 pull them up at any time?

3TAS4ME

Yes, it probably can. I haven't checked yet.

3TAS4ME

Just went out and check. BLM is right at 128. Now I am confused!

Injuneer

Which BLM in which of the 18 cells? Was your battery unhooked recently, clearing the BLM's?

3TAS4ME

I didn't look at any individual cells, just on the data stream that is what it shows. I have not unhooked the battery since it was put away for winter. Took it for a several hundred mile drive this last weekend along with six passes down the drag strip. It should be reading what it really is.

Injuneer

But there are left and right BLM's for all 18 cells = 36 independent BLM's. If all cells are 128, "learning" is disabled. Or it's simply not going into closed loop. It would be virtually impossible for all BLM's to be 128 if the system is going into closed loop, and learning is enabled. The scanner can check the flags for closed loop, and for learning.

3TAS4ME

Do I need to take it for a drive and see if the ECM goes into closed loop? How do I tell if it is "learning" or if that is disabled?