X-Ravin

Ok so I've been trying to get my idle to be a bit better and it just seems that from what I've read I really shouldn't have much issue with tuning my setup since it's pretty mild. Here's what I've got:

Comp Cam 08-500-8
Pro Mag roller rockers (not sure of ratio, installed by PO)
Mid length headers
No cats, flowmaster exhaust
Airfoil
Gutted airbox
2000 stall
3.73 gears
6E AJUM tune (cold start inj unplugged)

And numerous other non-engine related things. Basically from what I've read this shouldn't even have a lopey idle. But my idle is pretty rough. Open loop runs super lean, I know some of that is from the unplugged cold start inj. Closed loop idle started with super lean BLMs but I upped the idle fuel and now they are close to 128. Cruising BLMs are all close to 128, but if I give it any more than about 40% throttle I start getting consistent knock retard.

So do I need to look for something that is causing the bad behavior? I've replaced all the vaccuum lines and fittings so I don't think it's a leak. Then engine was rebuilt about 9 months ago so everything should be in good shape. One idea I had was that maybe the rockers aren't set right, I do have a ticking under load. O2 sensor is new, and heated.

L98IROCZ1987

check your timing and make sure you unhook your dist. electronic advance plug along the fire wall in the harness on the passenger side before you check or adjust . make sure your distributor hold down didnt come loose.

GreekItalianMan

A rough idle could also be caused by many things, best thing to do is keep eliminating the possibilities. My idle is a bit rough too,and my cars performance is sluggish when accelerating. I'm at the gas part. Seeing if the fuel injectors are clogged. Also you might want to do the engine code test.

Orr89RocZ

iTrader: (20)

what ecm setup did you start with? Did you do a conversion to 6e?

that cam is not bigger than stock really, just a more modern version with higher lift and abit more aggressive lobes. It should run fine on a stock tune MAF setup. Sure the cam was installed right?

Try an ARAP bin without the aggressive timing table and see where that gets you. That bin surprised me on another setup with a big cam and heads on stock L98 with HSR. Runs great with little changes made to the bin.

X-Ravin

Timing is properly set at 6* to match bin. I do need to check fuel pressure which I may get to this weekend.

I think I'm actually running AJUM with the ARAP fuel tables, but I'll try ARAP with the lower timing and see what happens. I originally tried ARAP, but was getting too much knock with the agressive timing tables.

I upgraded from 32b I believe, the PO had a chip burnt by TPIchips to match the mods, but I'm pretty sure it was just a Corvette tune, the timing was more aggressive than ARAP!

Orr89RocZ

iTrader: (20)

You dont need alot of timing with these motors, especially the iron head setups. Vette heads seem to like the high timing but not all aftermarket aluminums like the higher timing because they are more efficient heads than factory l98's.

You can try ARAP base bin but copy and past another timing table in it, like AUJL or another bin. But smooth the table out abit, there are alot of peaks and valleys in the stock tables.

try to work from main spark table and zero out the PE mode advance. Makes it easier IMO.

Set it up fairly conservative for now and then work your cruise cells. Running more timing there will help with mileage and such and with lower rpms and lower loads on the motor, you can run a good bit of timing. Just setup a nice smooth table and then slowly add a deg or 2 across the lower load/lower rpm ranges where you cruise at, and watch for spark retard and watch the BLM/INT's. Changing the timing can alter what the o2 sensor sees but doesnt mean the chamber is seeing a change in air fuel. O2's read the aftermath of a burn, the actual air fuel mixture in the chamber is a set amount. So the car may run better with higher timing at cruise but the blms may not read 128 exactly. Dont be alarmed.

X-Ravin

Thanks for the tuning tips. I'm just trying to make sure that something else isn't wrong before I start trying to run down tuning problems.

X-Ravin

Just an update. I replaced the injectors with Bosch III's, 27lb. Also put in a BBK AFPR (bad choice since the plenum contacts the adjustment screw... Even without adjusting for the bigger injectors I'm still seeing 4.44mV in open loop and idle BLM's of about 146, all other BLMs are trying to lean out the injectors. Still seeing lots of knock at partial throttle, but WOT is clean.

The tune is now ARAP with the AJUM timing table. So it looks like I'm back to hunting down the phantom lean problem. I'm wondering if my timing tab is off really bad and I'm running more timing than I think.

Orr89RocZ

iTrader: (20)

Let it idle a bit and then check the spark plugs to verify if its lean or not.

Is the MAF working properly?

X-Ravin

I've checked the plugs, they are white so I do believe the lean condition is true. As for the MAF, I don't really know how to check it. It seems to be reading like I would expect.

Orr89RocZ

iTrader: (20)

I'm not sure why its reading so lean then. That combination is not all that wild. Stock ARAP tables should handle it well.

Are all the sensors new and working well? Fuel pressure up enough?

What heads are on it and what is the compression?

X-Ravin

Tried stock FP and bumping it up a bit too. Replaced the O2 sensor twice, both times using heated sensors. I don't know the compression, is there a way to find out? Heads are 87 IROC heads AFAIK

Orr89RocZ

iTrader: (20)

what pistons are in it?

X-Ravin

No clue. I do know the PO rebuilt it to be a daily driver and get decent mileage so my guess is stock style bottom end. Another symptom, apparently the exhaust smells bad. My wife drove behind me for a few hours and she said it smelled nasty, not rotten eggs nasty though.

X-Ravin

Ok I adjusted the tune for the new injectors and it's running a little better. It seems my knock is gone in both partial and WOT. Other than a 1* spike when I jab the throttle but I think that's pretty normal. Still seeing 0V in open loop and idle is still trying to richen out in closed loop. I think I'm going to try and back the timing down and see what happens, see if I can get open loop to show more than 0mV.