I recently swapped my 100K+ L03 for a mildly built-up 350. The day I picked the car up it ran fine. Ever since though I've been frustrated by a rough idle -- eventually stalling out.

Which is followed by a hard starting condition. (unless i put the car into "clear flood mode") which then only idles if I manually hold the car at part throttle, say 1500 RPM's or more.

I've replaced the fuel filter, and IAC,
I've taken the fuel pressure at idle: 11 PSI
I've rebuilt the throttle body, serviced injectors, and replaced the thermostat

I have the most recent datalog available here.
http://www.claresco.com/clients/ALDL_Data/AldlData.txt

I only chose these fields to post, however I have the entire log if anyone needs a more complete picture.

Right around the 162 second mark, (less than 3 minutes after start) she dies. I see the IAC is closed ? But I could really use some help pointing me in the right direction.

Any and all help is appreciated !
Thanks.
1991 Firebird
350 sbc
218/224 @ .50
Edelbrock Performer Intake Manifold, heads, and headers
Single 3" Cat, Flowmaster

 

can you put up a log with BLM data, while i can guess what it is doing, the BLMs would be helpfull to see.

also, in your chip, what temp is the closed-loop enable set to?

it looks like as the temp goes up, it adds more and more fuel , BUT with the overlap of your cam, the o2 readings are probably lying to us. knowing your combo, start off of with, i would give the car some more timing at idle, and take some fuel out. but that is only a guess with the limted data.

can you smell gas? with that cam, and a close to stock chip, you should have a stinky smelly idle. the other thing i would do, is disconnect the IAC, and set you idle via the adjustment screw, to about 500, then in your chip, raise your idle from 600 to about 700 or 750, that coupled with a little more timing, and a little less fuel, should help it idle better.

if you can get more detailed logs, i might be able to make a better guess.

 

heres all the data i logged. Raw values, sensor data and the malfunction flags. (its a hefty one!)

http://www.claresco.com/clients/ALDL_Data/AldlData.htm

im not sure what the closed-loop enable is ? if its a setting on chip the, the manufacturer (ed wright, fastchips) would have used the stock value taken from the previous ecm (aptx).

the only time i can smell gas is when its having trouble starting. (after shes died off idle). Then definately.

I figured setting the idle screw adjustment was my next step . . .i guess i was looking for some confirmation that it is necessary.

yeah, thanks again! :rockon:

 

i really do think that it is getting too much fuel, and not enough timing.

BUT, while trying to get through the Oregon Emisions testing, i noticed a few very interesting things about idle, if you go WAY lean (as in WAY (o2 readings in the .050 range)) the IAC goes crazy trying to keep the car running. but judging by your o2 values, i doubt that is it. what injectors do you have on the car? and if ed wright did the chip, i would send him datalogs, and tell him what it is doing.

 

i reused the stock L03 injectors. 40 lb/hr GM5235279. . .fuel pressure reads a 11psi at idle.

sent the datalogs over to fastchips for support.

the build sheet written up by the engine assembeler indicated 'time @ 0d, with the connector disconnected.'

 

Definatly looks like possibly too much fuel and not enough timing. Looks like whenever the ecm goes to idle down, the lack of timing and too much fuel causes the motor to nose over and then it bounces off the stall saver. If the ecm cant catch it in time it stalls. I had the same problem, which was exacerbated by my 8063. Unless it sees 'drive', it dont care too much what the idle speed is as long as its not too fast or too slow. Made it hard to tune. The way to deal with it is to fully seat and then unplug the IAC and force the motor to idle at slow speeds. From there, begin tuning, in neutral and in gear, the timing/fuel and get the idle as good as possible. Repeat for speeds down to around 400 rpm. Have to do it a whole buncha times but this will help in that the motor wont go sour and stall when the idle speed dips.

 

On the advice of the chip company, I tried adjusting the throttle stop with the IAC fully extended and unplugged. I raised the throttle stop until the engine quit sounding like it was on the verge of dying -- according to the log that shows a TPS value of around 5% (.74 volts ?), as opposed to the stock value of ~.5 volts.

I understand this is configurable in WinALDL, and have no idea what my setting is, so i left it at default .54 at 0%. I've posted these datalogs .here

It seems as this adjustment might be a temporary fix. . .but idle RPM's of 950-1100 just seem too high to me.. Any thoughts ?

 

Although I doubt it's the entire source of your problem, you might want to verify that the chip is also intended for the base timing to be 0°.

If for example the chip has base set to -6°, and the engine is set at 0°, then you'll have 6° of retard across the board, compared to what the chip maker intended.

On that note, might want to put a timing light on the engine, and confirm that the base timing is actually what you think it is.

 

Adjusting the stop screw shouldnt cause any immediate problems. IIRC, though, i think there is a certain point where the compter will no longer consider the throttle to be closed and will not use the value at startup as the base tps voltage for its reference. Not entirly sure. Another thing you could try doing is to bump up the base timing. Not the ideal solution, but its a good stop-gap measure in the mean time untill you can get a burner so you can make adjustments to the chip yourself. The 'tuner' wont be of much help as he doesnt have access to the car.

 

so let me see if i've got this right. . .

with the throttle stop set at stock, voltage reads about .5
blms are right where they should be, 128

after a minute or so, the ECM tries to idle down (why, the chip is set to idle at 850-900?) by shutting the IAC valve way down to 0, and unless the ECM can catch it it in time, she stalls . . Hence the 'hunting' at low rpm's

Ok . . so I bumped the up the throttle stop screw to about 1.2%, .59v last night, the car idled ok . .feigned a few attempts at dying, but didn't -- but i also noticed blm's were down in the 114s --

so by this i can deduce, that,
1. by adjusting the throttle stop screw up, this in turn tells the ecm to send more fuel (TPS voltage up a bit)
2. the car knows its running rich, hence the blm's at 114. (computer trying to correct for the excess)

sound good ?
okay, then my questions are,
why is the ecm wanting to 'idle down', if the chip is programmed to idle at 850-900 ?
--and --,
this is where i humbly ask, what changes would i look to make ? to what tables ?