MAT issue and not going to closed loop...

Reply Subscribe

Thread Tools

Search this Thread

Apr 10, 2008 | 11:02 AM

Chris89GTA

Thread Starter

Supreme Member

iTrader: (2)

Joined: Feb 2002

Posts: 1,141

Likes: 0

From: Nashville TN

Car: 1989 Trans Am

Engine: 355 HSR

Transmission: Pro-Built 700r4 w/ 3400 converter

Axle/Gears: 10 bolt w/ 3.42 gears

MAT issue and not going to closed loop...

Car is back together, but I'm having issues w/ the tune currently. I've been chasing a wiring problem from the MAT signal not getting to the ECM. I had reloated the MAT several years back and one of the connectors I had used came loose. So I re-wired and put new connectors in. Still reading -40* to the ecm... but as I was checking the signal to the ECM I found that the car IS NOT GOING TO CLOSED LOOP.

I've searched and it appears that the MAT does not affect too much in terms of fueling except the MAT table, but would it keep the car from going to closed loop if it is reading a constant -40*?

I've got to track the wires as soon as I can get out in the garage to work on the car again... they are good up til the splice point behind the dizzy... but from there I'll have to see what I find...

I wired up the LC-1 and SSI-4 box, and have had issues getting the system to connect through the serial cable so I can't verify if the gauge is correct, but at idle the gauge says the car is running at around 9-10:1 AFR... in open loop... I'm still adjusting a few things, but wanted to cruise around in closed loop part throttle so I could adjust the injectors constant to get as close to 128 BLM before I start fine tuning the tables from there at p/t and idle...

any ideas?

Apr 13, 2008 | 09:00 AM

Chris89GTA

Thread Starter

Supreme Member

iTrader: (2)

Joined: Feb 2002

Posts: 1,141

Likes: 0

From: Nashville TN

Car: 1989 Trans Am

Engine: 355 HSR

Transmission: Pro-Built 700r4 w/ 3400 converter

Axle/Gears: 10 bolt w/ 3.42 gears

Re: MAT issue and not going to closed loop...

Alright... we 0 responses...

I've looked at everything some more and I think the reason it's not going to closed loop is the single wire O2. It has been moved to the header collector, and it IS getting crosscounts, but not like it normally would. It is ranging from .430-.480 or so... so it's crossing, but not a wide enough range to actually get a sense of what is going on. That's the next thing to do is convert that...

Apr 13, 2008 | 11:09 AM

RBob

Moderator

iTrader: (1)

Joined: Mar 2002

Posts: 18,432

Likes: 231

From: Chasing Electrons

Car: check

Engine: check

Transmission: check

Re: MAT issue and not going to closed loop...

The O2 of .430 to .480 is not hot enough. Basically the sensor is still off. Heated O2 is a good bet. Here are the O2 parameters ($6E, ARAP) that need to be exceeded (lower or higher) for the ECM to believe that the O2 sensor is active enough for closed loop operation:

Code:

        ;
        ; o2 RDY HYST PAIR
        ; (CAL = vdc * 2260
        ;
LC44B   FCB  158    ; 699 mvdc, IF o2 GT THRESH, o2 READY
LC44C   FCB  45     ; 199 mvdc, If o2 LT THRESH, o2 READY
                    ;
LC44D   FCB  50     ; 10 Sec, IF o2 IN WINDOW ABOVE GT 10 SEC'S
                    ;   o2 NOT READY
                    ;       cal = (sec/5 sec)
                    ;

I'm not saying to change these. They are just for reference as you check the data log.

RBob.