idle correct, fuel trim or idle quality more important?

[MyBeatGSX]

Here's my issue. At -21% on the AFC my fuel trims are perfectly zero'd at idle. My idle is also the worst its ever been. Crazy missing, extremely rough, low vacuum. Now if I turn the AFC way up beyond the ECU's ability to compensate it back to stoich (around +10%, but the richer I go the cleaner it runs up to +25%), the engine purrs and pulls 20-21in/hg.

What's the deal here? Why do I have to run stupid rich to have a clean idle? Why do I have to go +10% on 550's to get a good idle? I should be taking fuel away not adding it. Is it possible that my O2 sensor is not calibrated correct and so its sending signals to the ECU that are way off?

My bottom line question is, what's more important, adjusting the idle to be clean and smooth or adjusting so that my fuel trims are zero'd? I'm afraid if I go with the very rich but clean idle setting I'm going to be fouling plugs like mad and my gas mileage is going to take a shat. When idling smoothly its so rich that the O2 no longer cycles, its just pegged rich. Keep in mind, ANY setting within the ECU's ability to pull it back to stoich results in a rough idle.

 

[GVR4592]

If the O2 sensor is functioning properly, I would start by verifying that base ignition timing and fuel pressure are correct. Then check for boost leaks if you haven't already.

Can you post a datalog of the O2 sensor cycling at idle?

Is cam timing correct?

 

[andymoraitis]

I would start by verifying that base ignition timing and fuel pressure are correct

2G timing is controlled by the ECU. Also I had Tyler bump his fuel pressure from 40 to 43 with the vacuum line off in another related tuning post.

Just offering some info...

 

[tstkl]

so even if you rotate the cas it will still have the correct base timing? thats nifty, what does it use to test base timing?

 

[MyBeatGSX]

'95-'96's have a grounding plug, at least my car does. Timing is at 5*. Cam timing is correct. Fuel pressure is at 43 base, 41 w/vacuum. It will not go below 41psi now that I've rewired the pump. This is meaningless however because it did the exact same thing before the pump was rewired and I had 35-38psi w/vacuum.

The fact that my idle fuel pressure WITH vacuum on it is still 41psi would seem to indicate I'm running too rich already, but yet it wants to go richer...WTF

I'll try to get a log tommorow but it looks like a perfectly square up down, up down on the graph at regular and fairly tight intervals. Also the sensor is almost brand new, I got it last summer. Its done this crap idle ever since I put the 550's in.

 

[GVR4592]

Are you sure they're 550's? I had a set of RC injectors that were supposed to be 550's but they acted like stock injectors. I later found out they were 440's.

 

[MyBeatGSX]

That would really suck @$$ huh? Yea but if they were 440's or smaller than 550's my fuel trims would be zero'd when the AFC was zero'd wouldn't they? Based on my other topics, a few people here have suggested I might actually have 650's. But looking at where my low throttle is at now I'd say they probably really are 550's. I'm in the -14% range for the rest of the RPM range, so that's close enough I think.

Is there something I'm over looking? My idle fuel pressure is too high, that's why I have to go to -21% to get the trims right, so I definately have lots of fuel. But yet the motor wants at least +10% to run right? Why so rich? What could be wrong with it that I need like a 12:1 or richer A/F to idle correctly?

And please note, it did this the second I put the injectors in and it hasn't stopped since.

 

[MiSFiTz]

Mines doing the same thing... i put 660's in..

Im like -9 / -5 area to have a perfect idle.. for whatever reason... did it when i put the injectors in.. 190 fuel pump..

Im like -20 / -30 throught after that doesnt make sense does it..

 

[MyBeatGSX]

Glad to know I'm not the only one. What does your O2 voltage look like at idle? Are your fuel trims zero'd? Mine doesn't run right even when the trims are zero'd.