Program differences?

[2seater]

Does anyone know if there are ECM programming differences between the 1988 and 1990 model years, specifically relating to the fueling in the (16) operational cells? The reason I ask is the BLM is stubbornly stuck in the high 140's to 150 in all cells, although the Integrator is operating in the normal range. This is my stock 1990 engine with the 1988 cam installed. The only other modification is a larger plenum on the intake manifold. I have tried both the stock throttle body and the 0.2" larger diameter one with the same MAF sensor installed and it is slightly worse with the larger throttle body. Raising the fuel pressure to 46# did help slightly. It acts like it wants larger injectors, but the engine is otherwise bone stock. Stock manifolds, ceramic coated, rear outlet opened up, no cat. and straight through muffler. Idle vacuum is good at a steady 18", O2 sensor is good and active, overiding the injectors individually yields similar vacuum and rpm drops. The engine runs very well overall, starts instantly and cruises easily. Any thoughts?

[Guest Greg Ross]

Hal,

Do you have a spare ECM PROM/ or and spare ECM. I have never seen BLM numbers that high, ever

[padgett]

To me it sounds like an O2 sensor that is working but rong. What is the colour of the insides of the tailpipes ?

[2seater]

Greg,

Well, I have seen readings that high before but only when fiddling with the tuning when turbocharged. I do not have a spare ECM or stock chip, although I have a few different turbo tunes. The chip is a copy of the stock ANWU, but it is not the stock EEPROM. I have a zif socket installed to reduce the cost of chip programming. A flaw in the copy?

Padgett,

Good idea on the O2 sensor. I do have a few others so I will try switching it as suggested. The tailpipe is black although it doesn't smell too bad even without a cat. When I swapped back to the stock engine I did find I had blown the vacuum modulator and it has sucked down over a quart of fluid over some time. I have several hundred miles on it after the switch and repair, so I would think that residue is no longer present.

Thanks for the replies. I was guessing the slightly more aggressive cam has affected where the ECM is running as far as load cells go?

[2seater]

Follow up: I changed the O2 sensor but it operates exactly the same. Cross counts look good, 70 mph cruise shows high teens to over 20. Integrator still looks good. Runs very well overall, but blm sits @ 150 while cruising. Roll into the throttle a little and it drops to 149, so it isn't stuck there, it just wants to be there. Will check for vacuum or exhaust leaks again. Going to try my remote mount MAF to see if it the operation changes. Thanks for the suggestion.

[DAVES89]

Hal, I have three tested MAF's at my house. email me if you want to try one...

[padgett]

Any chance you have an "L" MAF ? That could confuse things but a 150 BLM (long term) is waaay rich (at the limit). My understanding is that the 88 had a different cam and you might want an ANCX (88 revised) PROM.

Edited November 15, 2010 by padgett (see edit history)

[2seater]

Dave, Thanks for the offer, but I have several MAF's as well, all tested on the flowbench.

Padgett, I have the original equipment MAF sensor in place, although I do have an "L" (snakes) sensor in my collection as well. The "L" sensor looks the same from the outside but it is different where it inserts and cannot be interchanged into the "C" housing. However, the "C" will install in the "L" housing, although I don't know how accurate it would be since the flowpath at the sensor would not be smooth?

In any case, I believe I have corrected the problem, although not certain of the cause? I noticed the problem got worse with the larger throttle body, coupled with the larger plenum on the intake. My surmise was this combination somehow affects the flow through the sensor portion of the MAF assembly. Even though timed acceleration runs were slightly faster with the larger T/B, the MAF read about 7% lower (same sensor). I had constructed an adapter to allow location of the stock MAF housing to the inlet side of the turbocharger. I transferred the same sensor to the remote housing and coupled that upstream of the stock setup. It took a little driving but the BLM has dropped to 130 at the same 70 mph cruise and it moves around slowly in the expected range. The original question was I suspected the calibration of the various cells in the PROM was different but I think now that my modifications have caused it to read a different cell than the ECM expects. I will know if the operating cell has now changed when I get a chance to drive it with the scanner connected. Should have done so today but I didn'g expect such a large change. Thanks guys.

[padgett]

Probably is going to need to learn but is a feedback system that is constantly updating and should find a new level, just not 150 - 123-133 is more like it