pwdbychevy

Here's a problem that's been bugging me for quite a while now and I can't figure it out. When I start my car early in the mornings my AFR hovers around 13.4 (engine hates anything higher than that). After a drive to AutoBone-heads to return ANOTHER defective part(sorry, I had to throw that in there) I get into the car and restart it and my AFR will lean out 2-3 points higher(15.4-16.7 sometimes in the 17's) for about a minute or so and then it'll go back down to the 13's again and settle. I'm using SAUJPV4 $8D mask. I've tried increasing Startup Enrichment vs. Temp but it still does it. Does anyone else have the same experience or any insight on what may be causing this?

JP86SS

iTrader: (1)

Might want to look at the 100 Kpa cells in the main SA table.
The 100 cell vs RPM is used for idle until warmup, then the closed throttle table and the regular idle SA will come into effect. I believe the threshold value for when the transition is made is at location $8032. Might be others but I just don't remember.
Could reduce the CL delay timers for hot start if that helps get it inline faster too but that would mean actually the OL settings need tweaked somewhere for temp.

pwdbychevy

I'm running constant open loop. I did not know that the main SA table at 100 kpa was used for idle until warmup. I learn something new everyday. Would you suggest increasing timing in those cells?

pwdbychevy

ttt

305sbc

iTrader: (3)

You didn't say what ECM you were using but I think I'm assuming a 730 ?
No, advancing the SA will not make you run richer.

After I had eliminated all possible mechanical causes - blocking all vacuum lines & eliminating possibilities of air leaks, watching the fuel pressure at the rails, eliminating the possibility of fuel boiling in the lines, etc...
I would start going through the tables in the calibration and testing things to eliminate them one at a time.

A good look at some datalogging should steer you in the right direction. Is the commanded AFR and/or the injector PW reading different when this problem happens?
In other words is the ECM commanding less fuel? and why?
Is the IAT table causing it to do this because of heat soak?

If the commanded fuel is the same, then either you are physically getting less fuel through the injector or you're getting too much air.
Is the IAT position different when this happens?
EGR commanded?

???

iTrader: (5)

mine does.. haven't had much time to work on it since its sitting in a body shop. but I think its the MAT. on a hot restart the intake is really hot. say driving around it read 35c on a restart it will be atleast 50c. the mat table is weird, its based on air flow. which makes sense to do that, since we have long runners and the slower the air the more heat added. but I don't have a clue how to change the numbers to do what I want. which is not lean the crap out of it at hot temps, not at a air flow amount. so I'm lost.. once I get the car back. I'm going to throw some random numbers in and see if the changes make any sense to me. but yours sounds just like what I'm chasing. any small change in mat temp, makes a huge diff in a/f. makes it hard to tune the ve table, since I spend more time trying to get the temps at the same as the last time, so I know if my changes did what I want.

pwdbychevy

It's a 7730 ECM. When you say IAT do you mean IAC or are you referring to to Manifold Air Temp? I wasn't sure if you mistyped it or not. EGR is disabled.

RBob

iTrader: (1)

There are several threads in the Tuning Book sticky on the MAT tables and how they work. One of the threads also discusses the changes made when relocating the MAT to be an IAT sensor.

RBob.

305sbc

iTrader: (3)

MAT for you - I was thinking Intake Air Temp IAT.

What does yours look like?

pwdbychevy

That's what I thought. It screws into the bottom of the plenum and is about the same size of a coolant sensor but has a cage surrounding a little sensor inside.

305sbc

iTrader: (3)

I meant what does your MAT table/calibration look like?

pwdbychevy

Oh The one on the left is the MAT Inverse Term Lookup Delta Mult. Vs. Airflow table and the one on the right is the Startup Enrichment Offset Vs. MAT table.

???

iTrader: (5)

yeah, and i've read thru everything twice, but i'm dumb and i can't wrap my head around it. i mean it seems to make sense when i'm reading thru and following along, them i get to my car and i'm like.. huh? blah.



i'm hoping someday it makes sense. or i just give up on it lol

???

iTrader: (5)

i'm pretty sure thats not the kinda of sensor the stock cal is meant for. the stock ones i've seen are a big chunk of brass and change temps slowy because of this. where your's is prob the better sensor. it will prob need some tuning for it.

i say that and i have the stock sensor and mine doesn't work right either on the stock cal and intake setup. so i'm prob worng, but just throwing that out there. i think i read that you have a v6 style sensor now.

305sbc

iTrader: (3)

It's the 2nd table you posted there.
I'm not sure what the "offset" is for zero change, but I think I would start by putting in zeros in the temp range from 80*C and up and see if it has the effect you're looking for.
My logic is that if there is no offset the multiplier in table one shouldn't matter.

Hopefully someone will correct me if I'm wrong.
If you try it please post your results.

pwdbychevy

I'll test it today and post the results. Thanks!

pwdbychevy

The factory sensor has a brass tip? I have a V6 style intake snorkel to where you can screw the IAT into it. I didn't know they were different. That could be the cause of my problem.

???

iTrader: (5)

as far as I know the v8 tpi MAT sensor that goes in the intake is the big brass one. but I wouldn't put much hope in putting that sensor on your car and it fixing your issue, since yours sounds like what mine does with the brass sensor. oh and that 2nd table your going to try, from what I've read and what I've tried on my car, doesn't really do much of anything. I think its pretty much going to be that grams of air flow one that needs tuned.

pwdbychevy

I zeroed out those numbers like you said and it didn't do anything so you're probably right.