Yesterday I installed some of the FMS 42lb injectors. The car is running a 355 using the 749 ECM. I changed the BPC down to .063 like someone has previously done, but it doesn't seem to be working too well. Sitting at idle the O2s get down to about 4, and the BLM is shooting up to 150. Why would I be running so lean with such large injectors? Any help is appreciated.

 

Vacuum leak, exhaust leak ahead of the O2 sensor...

 

I'm currently running 60 PPH injectors with the stock BPC.
Be sure to cut the min PW duration down some.
What are your PWs at idle, and are they changing when you change the VE table?.

 

I will check for exhaust and vacuum leaks. Since the O2 sensor is in the collector of the header, would a leaky collector gasket cause me problems?

Grumpy, IIRC the pulse width was around 2ms. The min pulse width has not been changed in the chip. Is there a minimum number this can be taken to, or should I just take it down a little at a time. I was under the impression that the BPC vs EGR table was used as basically the same thing as the injector constant. How are you letting the ECM know your injector size?

 

It depends, some leaks can totally trash the O2's readings, while others don't see to really mess with it.

If you increase the injector size by 50% then you want to reduce the min PW 50%, has been the way I do it.

Yes, it's the BPC vs EGR, is what you want to change.
In an ironic set of circumstances, I have some injectors, I'm evaluating. They are xx (insert large number here) PPH, and I'm using the stock BPC settings. They run just fine at .8 msec PW. Actually one chip was down at .72 msec for the idle PW.

The other thing was I spent some time on the ecm bench working out the VE adder table once I had the main VE sorted out, so that I had a consistant PW from peak torque to max RPM. Then once I saw the shape of that, and that the min entry was 12 there, I took and subtracted 12 from the whole VE Adder Table, and added it to the main VE table. That way I had the largest dynamic range to work with on the VE table.

39.1 40.6 41.0 41.0 43.4 48.0 53.1 54.7 56.6
39.1 40.2 42.2 43.0 46.9 53.5 56.3 57.0 57.8
41.4 44.1 45.7 46.9 52.0 55.9 60.5 62.5 63.7
42.2 45.7 46.9 48.4 52.0 56.6 63.7 64.5 66.4
43.0 46.5 47.3 49.2 53.9 58.6 64.5 66.8 68.4
43.0 47.3 47.7 52.0 54.3 58.6 65.2 67.2 68.8
43.0 47.7 48.0 53.1 55.9 60.5 65.6 68.8 70.7
43.0 48.8 49.6 53.9 57.0 61.3 66.0 69.5 70.7
43.0 48.8 49.6 53.9 57.0 61.3 66.0 69.9 71.1

12.5
12.5
12.5
12.5
12.5
12.5
12.5
12.5
10.5
7.8
6.6
4.7
3.5
2.7
0.8
0.0
0.0

Now, this is just how I did it, I dunno if this will work out as an universal answer, but so far the WB looks right, and the commanded AFR are close.

And these tables are for really large injectors, so you don't see the range of entries you might expect.

 

Woah, in the collector? Are you running a heated O2 sensor? If not get one. That in itself may be the whole cause of the problem.

 

The O2 sensor is heated.

FWIW, I've always had fueling problems with the car. After I finished doing the TPI swap using the 165 ECM the thing always ran extremely rich. The BLM's were always stuck on 108. Finally got tired of that and swapped over to the 749, which after some tuning ran pretty good until the injector swap.

 

I'd say set the Open Loop enable to 250, and try my VE table and see what the O2 reads. Then cut the table entries in half, and see where you are. With the stock BPC, and these entries you should be safely too rich. Then dropping the values should be too lean, so then split the difference. Keep doing that till your close. Might take a set or two of plugs, but if your way off you gotta start somewhere.

 

.8 pulse width was ok? I was thinking of setting my min pulse width to about 1.50, to force quassi mode. Seems my motor is switching back and forth between quasi and sync, and I think the low (> 1.50) pulse widths are misfiring.

42lbs injectors.

Here is a snip of what I'm refering to:
<PRE>
Rec Runtime MPH RPM TPS % O2 mV BLM INT AFR RETARD SPARK BPW Inj DC MAP

2764 456770 26 2025 8.6 40 122 122 14.7 0 28.1 1.37 4.6 37.7
2765 456935 26 2150 8.6 577 122 124 14.7 0 27.8 1.19 4.3 35.3
2766 457100 26 2050 8.6 36 122 125 14.7 0 27.8 1.31 4.5 37.7
2767 457265 26 2175 8.6 27 122 126 14.7 0 27.8 1.28 4.6 36.1
2768 457430 26 2025 8.6 53 122 128 14.7 0 27.8 1.31 4.4 36.9
2769 457595 26 2150 8.6 27 122 129 14.7 0 27.8 1.34 4.8 36.1
2770 457760 27 2050 8.6 648 122 132 14.7 0 27.4 1.22 4.2 36.1
2771 457925 26 2050 8.6 22 122 134 14.7 0 28.1 1.43 4.9 37.7
2772 458090 26 2150 8.6 573 122 135 14.7 0 27.4 1.22 4.4 35.3
2773 458255 26 2000 8.6 75 122 136 14.7 0 27.8 1.4 4.7 37.7
2774 458420 25 2125 8.6 27 122 138 14.7 0 27.8 1.34 4.8 36.9
</PRE>

If you look at the o2, it's up and down like michael jackson.
If you look at areas of the log where theres more inj pw, this issue doesn't happen:

<PRE>
Rec Runtime MPH RPM TPS % O2 mV BLM INT AFR RETARD SPARK BPW Inj DC MAP
2818 465680 24 1900 11.8 537 122 132 14.7 0 30.6 1.53 4.8 44.7
2819 465845 24 1925 11.8 728 122 131 14.7 0 30.6 1.53 4.9 45.5
2820 466010 24 1925 11.8 688 122 132 14.7 0 30.9 1.56 5 46.3
2821 466175 24 1925 11.8 759 122 130 14.7 0 30.6 1.53 4.9 44.7
2822 466340 24 1925 11.4 781 122 129 14.7 0 30.6 1.53 4.9 44.7
2823 466505 24 1925 11.4 506 122 128 14.7 0 30.2 1.59 5.1 44.7
2824 466670 24 1900 11.4 733 122 128 14.7 0 30.2 1.5 4.7 43.9
2825 466835 24 1900 11.4 790 122 129 14.7 0 30.6 1.53 4.8 44.7
2826 467000 24 1900 11.4 648 122 128 14.7 0 30.2 1.5 4.7 43.9
</PRE>




-- Joe