chevyboy07 91

Some of you may or may not have seen the few threads about my mystery surge. Well, i just thought it would be a good idea to ask if an experienced PROM guy would be nice enough to let me send them my Datamaster scans and see if they can use the #'s to find my problem. Also, the car has been tuned by Alvin @PCMs for less. He's a nice guy, but isnt being to helpful with me at this point. I asked him if he changed my injector constants, etc and got no response. When he first tuned the car it was on a stock fuel system. When i stepped up to the new motor, i went with a good pump and 24# injectors also. I told him about it, but am not sure he "copied my transmission" to him LOL.

Symptoms and some discussion is in this thread:

https://www.thirdgen.org/techbb2/sho...hreadid=218042

there is a similar thread started by me in the General section also, but this one seems a bit more concise.

Pretty much right now i have a start up and cruise w/ one WOT series file i can send. I can get any particular data runs you want if it will help (ie: only idle, etc etc)

THANKS!!

ULTM8Z

Assuming your fuel and ignition systems are in good working order, here's what I would do.

Credit Grumpy for this one- Mechanically set your idle speed to about 50 rpm above the requested speed in your PROM. You can do this by opening the throttle blades with the stop screw until you see 0 steps on the scanner. For me, I set my requested RPM to 600 and my stop screw to give me 650 rpm.

Also, the ECM is constantly trying to adjust RPM with spark advance. There are two values in the $8D code for idle speed corrections via spark advance and retard. Set these to zero. This will keep the ECM from adding/removing spark which can cause idle speed surging.

By doing these things, you take the ECM out of the idle speed equation.

What BIN are you using? AUJP? ANHT?

Grumpy

Send me *one*.
Large objects take along time to download in parts of OH.

chevyboy07 91

wow...thanks ULTM8Z and Grumpy!!

Grumpy, I am sending it now...thanks again

BTW: Ult: I dont have a tuner anymore man...plus i am not so great with the actual tuning :/

edit: actually, i have it on disk at home...ill have it sent within the next 30 mins or so....

Mangus

Chevyboy -

Out of curiosity, how "quick" is the surge? I'm having what may be a similar problem with my car, in that when its warm and idling at its lowest RPM in the idle table, it kind "rocks" (steady jump) but only fluctuates 50 RPM or so. Its even hard to see on the scanner. Now, with moates software (and TunerPro), at one point I could see the BLM cell bouncing back and forth at idle and the two cells containing very different BLM numbers (I think it was like 128 and 117), almost as though the idle RPM was straddling two BLM cells. Since the numbers were so far apart (no idea why, as they should be pretty close to one another in adjacent cells, I would think), it was adding fuel in the lower cell, causing the engine to speed up a little, causing it to hit the other cell which took out fuel, causing the RPM's to drop, hitting the first cell which added fuel, ad infinitum...

Ronny

iTrader: (1)

please enlighten me on this. why cannot you burn a new chip to take some fuel out of 117 cell? the blms are long term what does the INT look like? i too have a surging but it seems intermittant. blipping the throttle allows it to settly down to 700 and very smooth them. B4 at idle surges 800-900 and again bouncing cell to cell on map which i expect. i am questioning whether my throttle cable is worn holding in higher cell/rpm.

Mangus

The first question is, why are these two *adjacent* cells so far from each other? Also, why is the BLM cell boundary so low (its not set that low in the bin). I don't want to chase the wrong problem. (look for a horse when you see hoofprints, not a zebra).

These two questions lead me to believe there's more to the problem.

I did a bunch of other stuff with the spark and fuel tables (for unrelated reasons - had some bucking between 1100 and 1600 RPM at mild LV8s), and the problem seems to have gone away (the bucking hasn't though), so it seems it was either fuel or spark (or both).

chevyboy07 91

Hey Magnus, let me give you the typical run down of "the process"

Lets say I'm cruising to a stop. No brakes applied yet. The car will surge the whole time about 100 rpm or so. When i get closer to a complete stop and then finally do stop it will start getting worse and worse(surge 1-1500 rpm at times), sometimes even bucking so bad it finally stalls on the low end of the surge (400 rpm or so). Immediately one would think "vaccum issue" b/c of the applied brakes. I WOULD agree (let me finish) BUT, i have went out on an open road and came to a dead idle cruise(=2mph or so) and the same damn thing happens! No brakes applied whatsoever.

SO, i dunno what to tell you. And very very rarely, when the stars line up, it behaves much better, but still has a hint of surging in it.

Grumpy says my IAC #'s are all over the place, so im going to follow some advice from there and see what happens.

All the technical stuff that has been mentioned....let it be known, it is still out of my league. And now i cant practice anymore b/c the tuning equip. "has left the building"

Ronny

iTrader: (1)

i there a deaccleration enleanment or deacceleration fuel cutoff issue here? my situation may have been different BUT i experienced that same problemsyou did day one of my mods(all done at once) with stock eprom and ecu. would buck so bad at the slow down(say a u turn) car would lay rubber and jerk so bad i had to disengage clutch. fix was 7747 and tuning. to best of my knowledge the above two areas were disconected in eprom as well but that was done only due to car stalling at stop sign from a prolonged slow down or a sunnen braking on xway car could stall out.