Hello everyone. This is my first post here. I have just gotten into burning a new eprom for my 1228747. I got the tuner Cat software and there ecu file for my $4f ecm. I have a rather rich running engine at idle / blm fixed at 105, and still wanting to be leaner. I have up'd the fuel pressure to 13psi. But my mid rpm range has a blm of 128, and then at higher rpms I'm at 150. I have a little cam in my 350 chevrolet. My first question is this - If I do the work to calculate all the cells of my ve table to get a blm of 128 or thereabouts, are all other calculations of AFR based on this table? for example, is the Open loop 12:1 AFR based on this table, or straight up calcuations based on the base pulse width, rpm, and map? I am wondering if I fix the table for the close loop operation, will I in fact be correcting the open loop operation as well? Second question - Is there an easy way to force open loop idle operation? I put a heated o2 sensor in my rig, but as the vehicle is running now it doesn't like 14.7:1 AFR at idle. It wants to be a little bit richer. So no matter what is going on, if I am at idle I go straight to open loop operation. Thanks, Marcello

Do you have a scan tool?.
First off, I'd suggest, you see what your idle vac is, and then start by leaning that down in the VE 1 table.
Then at your higher RPM start adding some fuel.

A BL of 105 means the engine is rich, and the ecm is cutting down the PW.
A BL of 150 means it's adding fuel.

Once you get the fuel in the neighborhood you can start worring about the finer details. Lean or rich, causes somewhat false TPS openings, causing the vac signal is somewhat messed up.

And the spark timing is based on engine vac too, so you need to start with getting the fuel close. Some cams even thou mild can raise cane with the vac signal.

Thank you Grumpy.

I do have a scan tool. No problem there at all. In fact I got into the shop this morning and my boss bought another one yesterday. People are dumping their older scantools where I am. Work has been slow so everyone is scrambling for money. So now I think I have at least three to choose from. But I must say none of the scantools we have, snap-on, or otc have the abiltities that something like winaldl has! I made a cable two weeks ago, and hooked up to my laptop. I have been logging every since.
So Thank you for the direction. I will start with getting the fuel trim to where it should be, and then proceed from there. I have 15"hg at idle, which does seem to be causing all my troubles.
I am still wondering How the fuel trim is calculated for Open loop operation? Is it based at all on the VE table???

Thanks,

Marcello

TTT

Yes, and typically the BLM is used as an adjustment. No learning, just using what is already learned.

RBob.

Thanks Rbob,
Now that I have actually done some changes to the VE Table and seen the effects I know it is the truth. I still can hardly believe how much better my landcruiser is running with minimal changes to the VE table. Major difference in acceleration, idle quality, and straight up drivability.
If I am seeing a lean out at the higher rpm's but I am reaching 100% VE in the main VE table, can I bump up the 2d table? OR is anything over 100% considered taboo, and I should be looking for more fuel - either pressure, or bigger injectors? And then lower all the values in the table, bringing them all into range so I am not right at the edge of VE?
My next project is to attempt some way to force open loop at idle. With the heated o2 I've put in, the close loop never times out. I need to run my mixture a little richer than the o2 would like to get the Hydrocarbons down. Anybody have any ideas?

Marcello

I am not familiar with the '8747 ECM, with that if the VE table is the typical two tables that are added together, then 100% in either table is 100% total. Can't go any higher.

As for getting more fuel it depends upon the PW at those RPM's. If there is still room (< 85% DC) then increasing the BPC can be done. If out of PW then either larger injectors or higher fuel pressure is required. Double check the fuel pressure to make sure that isn't dropping off at high load/engine speed.

As for the idle many ECMs/mask allow a change in the O2 window during idle. IOW, an adjusment to the O2 window whenever the engine is in idle.

RBob.