silvernblack

Ok, so I burned myself a chip from an AXCN bin, removed the VATS, EGR; etc.

Engine seems to run just fine. Winds up pretty well, takes off fine, and idles well, but lean.

That is it idles just fine until I go out on the highway cruise for a while at 60-70, Air/Fuel ratio hanging at about 12.8:1 @ 2300 RPM. So everything looks fine until it comes time to slow down and stop. As I decelerate and approach a stop sign the engine idle goes extremely low and then the car dies. Starts right up again, but that slow down and die thing is quite annoying.

Any ideas here?

RBob

iTrader: (1)

Is there an operational VSS hooked up to the ECM?

RBob.

silvernblack

Old car, mechanical speedometer, vss flag switched off.

RBob

iTrader: (1)

Good possibility a VSS would fix this. Otherwise it may take some parameter tweaking to reduce the problem. I'll bet that there isn't any IAC throttle follower w/o an operational VSS.

You mentioned that it is a little lean at idle, try a tad more fuel. Raise the idle speed and the stall savers. Maybe a little more SA at idle (closed thottle table). Can also add a degree or two more SA right below the desired idle RPM. This can help catch a falling idle.

The 12.8 at cruise seems rich, is this an open loop system?

RBob.

silvernblack

And my Autoprom indicates that the O2 sensor is responding. I want to do the system tweaking but I thought I'd get the idle thing fixed first.
The RamJet computer used to run the engine completely pegged rich at less than 12:1, so I was feeling kinda happy that the 730 was maintaining 12.8:1. It maintains it pretty steadily too.

I'll look into the timing and see if I can understand and do the other manipulations that you mention. the Ramjet computer also had the timing set at 10 BTDC.

I don't understand the 6 BTDC distributor timing issue along with the '730 also having a 6 degree setting in the computer. Could someone explain that?

Thanks for the help.

jcj

RBob

iTrader: (1)

The 6 degrees BTDC for the distributor (base timing) and the 6 degrees initial for the ECM is to balance out the SA. The 6° initial ECM is subtracted off within the ECM calculations, while the physical location of the distributor adds it back in. It ends up a wash. And is why both the distributor and the ECM initial SA terms/values needs to be set the same.

While in closed loop have you set the O2 window values different? Or possibly have removed the AIR system? I ask becasue running 12.8:1 in a stock closed loop setup isn't correct (AFIK).

RBob.

silvernblack

I also adjusted the air injection compensation(or thought I did), I'll look again.
Why would it be running more lean that 17:1 at idle?.... and then right away, I mean as soon as I give it a little throttle, it comes off the peg and heads for rich, actually runs quite nice....well, 'cept for when I'm coasting to a stop and it dies.

Where can I find a VSS to convert my mechanical signal to the appropriate pulse count?

silvernblack

no message, just correcting the post subject.

RBob

iTrader: (1)

I's venture to guess that the AIR isn't completely off -or- the O2 sensor calibration tables/values are incorrect.

In order to shut down the AIR system I would change these two parameters to the values shown:

Then rework the O2 idle terms and the O2 window tables.

If you have headers is the O2 sensor a 3-wire heated?

An inline VSS may be purchased from places such as Jags-that-run.

RBob.

silvernblack

thanks for the specifc pointers. I've gotta finish working on my Bronco then I'll start playing with the RamJet.

Dyno Don

iTrader: (7)

Turbo City has one and so does Painless.

silvernblack

I'll give them a yell. Hopefully I can play with some of this tomorrow.

Annother question: Do I have to do anything with the Park/Neutral wire if I'm using the Corvette manual bin?

RBob

iTrader: (1)

Leave it open. Scan tool should show it as 'in drive.'

RBob.

silvernblack

I performed the following.

--------------------------------------------------------------------------------
L839A: FCB 255 ; IF COOL < 151C, DIVERT
L849D: FCB 0 ; 0 mvdc, DIFF R/L WHEN AIR DIVERTED
--------------------------------------------------------------------------------

Not sure if I am supposed to notice anything yet. But after a run on freeway it didn't die....just idled VERY low at ~ 575 rpm.

My Autoprom tells me that my Air/Fuel ratio is swinging from rich to lean at idle. My analog A/F gauge however just indicates lean...I suspect that the analog gauge cannot react to the quick changes at idle and so just fails lean.

What would be an normal expected value for the O2 voltage swings at idle?

silvernblack

and it runs best there.

I tweaked the lower VE table such that I could get BLMs near 128, but the car ran worse. Tomorrow I'll check to make sure my fuel pressure isn't too high. I set it at 43 psig at idle last week but haven't rechecked it.

I still haven't gotten the VSS. Tomorrow I'll call Turbo City and see what they have for old trannys....and I'll check my fuel pressure too.

Does anyone know if VSS has an effect on BLMs somehow? And if so, what effect?