mmather1

I built an engine for my 91 s10, 350, comp cams 268XE cam 477/480 lift 224/230 duration @ 0.050 with a 110lsa. I build a custom short runner upper intake manifold and im running vortec heads with sdpc lower intake. anyhow the Idle hunts really bad like 400 to 1200 rpm and dies most of the time. Other then the idle it runs great lots of power. I am running the saujp bin and want to start working on VE tables but need it to idle first. I already blocked off the IAC by extending it all the way out and unplugging it, Still hunts. This tells me the IAC is not causing it. If i unplug the MAP sensor it stops hunting and idles perfect, but then runs like crap anything off idle. Could my map sensor be causing this?

armos

Is this happening at all temperatures, only after it slightly warms up, or only after it's good and hot? If it doesn't happen cold, then it's probably only happening in closed loop. If you unplug the O2 sensor you'll prevent it going into closed loop, see if that prevents the idle hunting like unplugging the MAP does.
I had a milder case of the same problem on a Fiero and unplugging the MAP "fixed" it, but swapping it out didn't fix it.

If unplugging the O2 or the MAP both "fix" it, then the problem probably isn't either of those sensors. What happens is unplugging either of these sensors will cause the engine to run rich, and running rich can mask the problem. But if you find that unplugging the MAP is the only thing that will fix it, then it's probably worth a try to swap it.
Make sure you don't have any vacuum leaks or fuel pressure regulator issues.

Do you believe the injectors are in good condition?
Are you using the same injectors as expected by SAUJP? There are some settings in the chip which tell the ECM how to expect the injectors to behave at very short pulse widths. If the programming doesn't match the injectors the ECM will have trouble controlling the fuel delivery at idle. I don't know if that's your problem but it was something I found was partly contributing to mine. Changing the programming had an effect on the problem but I never truly fixed it.
Not sure what settings are in your chip, but the settings I'm aware of are injector offset vs BPW, and vs voltage. These are adjustments for the nonlinear response of the injectors, because the ECM wants to assume that there's a 1:1 relationship between BPW and fuel delivered. At low pulse widths (idling) the nonlinearity can become significant.

Make sure you have good grounds. These are critical for sensors to work well.

On my car I found that retarding the timing would stop the idle hunt. It had to be retarded way beyond spec so it wasn't a good fix, but maybe that would be a clue to somebody if you try that.

mmather1

It seems to be happening at all temps, but it also goes into closed loop like as soon as you start the engine. I will try unplugging the o2 sensor tomorrow to see if it makes a difference. I am using ford blue top 24 # injectors and i believe they are ok i omhed them out and they checked out, I have the the bin set to 24# injector offset vs BPW, and vs voltage tables are both there but unsure what to change in the tables, guess its time to do some more reading

armos

I don't know what to suggest for the offsets, I just copied values from another ECM that had my injectors in it as stock. I don't know if that's the correct way of going about it.

Ronny

iTrader: (1)

I believe the MFG of the injector publishes the offsets. A searech here or Google may show the answer.

mmather1

Ok I plugged the map back in and unplugged the 02 sensor to force open loop, still hunting. so I unpluged map at the same time still hunted. I plugged the o2 sensor back in and unplugged the map and idles great. So i grabbed a map senor off a parts car at work plugged it in and didnt make a difference. I also found the table for pulse with vs battery voltage for these injectors and updated the bin. Still not any better.

JekyllandHyde

iTrader: (3)

Did you set the injector constant to 24lb? As for the offsets, see if your injector has a part number on the casings, then do a search for that part number and "datasheet." I'm running 36lb injectors in my car and I was able to find the datasheet for these injectors from a vendor online. Worst case scenario, call Bosch or whoever made the injectors and see if they can send you a copy of the datasheet. More than likely, the datasheet will have the values in mSec and the GM computer uses uSec values. I've put together a datasheet that interpolates the GM values based on what the datasheet provides.

Also, are your spark error tables zeroed out? I had that problem on my GTA where the idle wouldn't stablize for anything, but I had the spark error tables zeroed out. Putting in the stock settings for AXCN cured my idle problem and I have 36lb injectors idling at a stock steady 800rpm in closed loop with a stick.