happyhapka

Will adjusting my fuel pressure adjust my air fuel ratio?..

86 LB9 ... Holly afpr..

Am running really rich at 10.0-10.5 and am at 44lbs.

If I turn it down more will my afr come up where I want it. 13.0afr.?

GeneralDisorder

iTrader: (1)

No. Changing the fuel pressure will change the *size* of the injectors and that will just throw off the computer's fueling calculations which will result in the computer adjusting the fuel trims (BLM) till it's back where it was before you changed the fuel pressure.... So other than making it run like dog **** till the O2 comes online and throwing off your BLM ultimately it will do nothing.

44 psi is normal. Your problem lies elsewhere. And where are you getting this AFR number from?

GD

happyhapka

My wide band O2 ..

So if I lowered it it wouldn't do anything... If I raised it it won't do anything or will it atomize the fuel better and that's it?.. it won't add more... There the factory injectors I think..

There not leaking that I'm aware of ... Hmm?

GeneralDisorder

iTrader: (1)

Sounds like you should look at the narrow band O2 readings. The ECM uses it to target closed loop idle AFR.

GD

happyhapka

No, at idle and cruising I'm right on 14.7 afr Wich is perfect.. it is when I go WOT is when it goes to 10.0-10.5 afr...

It's perfect everywhere else but wot.

86LG4Bird

iTrader: (1)

Actually in this case, you CAN alter your AFR at WOT by adjusting the FP lower.
You reduce it to a level low enough that the ECM hits its upper limit on long term fuel trim, limiting the AFR to something better (higher) than your current 10.X.
Just pay attention that you don't reduce it so far that it begins to affect your idle and cruise AFR. This is not likely since the factory base calibration targets 14.7 for idle and cruise but targets a much richer WOT AFR. So you have some room in there to play with.
I did this successfully way back in the days before I did my own programming.

GeneralDisorder

iTrader: (1)

Problem with that approach is that under cold startup, when you are in open loop idle and cruise, it will be massively lean and run like poo till the O2 sensor comes online and then your BLM's will be adding fuel like mad. Its generally a bad idea to run the computer way out in left field like that - it reduces it's ability to further compensate when it's already jacked all the way rich.

10.0 - 10.5 is what mine was at with stock tune also. Seems to be normal for the 86 LB9. I thought it was odd also but your's confirms that this is likely how it was mapped. I went in and changed the MAF tables using 89 $6E and moved mine to about 12:1 at WOT. It didn't seem to make any significant difference in performance. The engine is just a turd and mine seems to be prone to false knock. I've played with the AFR and the timing up in the WOT range and even pretty significant changes don't do anything you can really feel. The engine just doesn't flow air up there - the stock heads and exhaust are the restriction. It hits the wall a little before 5,000.

GD

ULTM8Z

Overly rich at WOT is standard fare for GM in the 80's and 90's.

It was an engine safety thing...

The only real way to help it is to get a WB O2 in there (which sounds like you already do if you're reporting actual AFR's) and start leaning it out to about ~12.5:1.

happyhapka

I did reach a 12.5 afr.. though runs hard at work it runs lean during idle but is 14.7 WHILE cruzing... Thought it was a minimal idle thing but it isn't..


any ideas or would that just be the tune?

GeneralDisorder

iTrader: (1)

Are you tuning or are you messin with the fuel pressure? Don't do that!

You need to tune it. Lowering the fuel pressure has all kinds of implications for the injector flow characteristic, atomization, throwing your tune in the sh1tter, etc. The injectors are rated at a specific pressure for a reason.

It probably leaned out because the BLM's were maxed rich and that's a software limitation. These older ECM's did not have the capability to add/subtract 50-100% fueling like the newer stuff does. They have only BLM/INT ranges from 108 to 150 and that's about a total of 15%. So if you modify the fuel pressure by enough to rail the BLM and the INT full rich your going to get *at most* 15% more fuel and if thats not enough then it happily ruins your engine without any warning lights.

GD

happyhapka

Ok so my tuner told me it's tuned for 44 lbs.... So I will set it there and leave it and wrk from there... I originally had it at 50 lbs..... She ran great... Just rich at wot.. +\- 10.0 afr.. so I will put it to 44.. and talk with him more about it to get it right...



Or is 48-50 better.. or keep it at 44.

GeneralDisorder

iTrader: (1)

44 is perfect. That is stock and the injectors were engineered to perform best at this pressure.

86LG4Bird

iTrader: (1)

Well, if in fact the OBD1 control on these 3rd Gen's is different from the OBD1 control on the 92-95 LT1 platform, then you could be correct.
The (higher value) BLM's are saved and used for next startup and running until O2 sensors come online and resume corrections to the saved BLM adjustment. So no, it does not run lean in open loop. It runs very close to the 14.7 stoich before it engages closed loop.
I'm not arguing that a proper tune isn't the way to go (that's they way I do it too ). But the answer to his questions is: It does work.

GeneralDisorder

iTrader: (1)

No - they're dumb as dirt. They do not store anything between startups. The 7165 ECM does not have the capability to store anything between drive cycles - or for that matter to learn anything beyond the 15% rich or lean it can adjust over the course of a drive cycle. When you start it up it relies on static mapping till the O2 comes online then it will go nuts with the BLM trying to adjust.... every time you start the engine the BLM map is locked to 128 till the O2 comes up. So if your mapping is screwy you can cause serious damage if you mash on it before it learns.

GD