Unique Tuning problem.

[tmoore8828]

I'm trying to tune my 91 GS turbo conversion running 5-10 #'s of boost. The car is running the oem 9:1 pistons. I have all the supporting mods 255 pump, afpr, knock, maf, boost and egt guage, 2 1/2" exhaust, eprom ecu (rebuilt by steve, outstanding job!!) and dsmlink coming this week.

When I log w/ fuel pressure at the stock turbo level 36-37, the Low fuel trims are maxed at 140 and the high fuel trims around 120. When I raise fuel pressure to 40-41, I can get the low trim down to 118 but the car seems to run PIG rich at idle.

I'm a little confused, I've read all the trim articles and tuning articles, But my question is this.

The ECU lookup tables are designed for a turbo motor w/ lower compression. So when its adding fuel to get to 100% can I really use that as a refeence or should I be using O2 sensor voltage to determine rich / lean.

Once I get the DSMlink, should I keep the higher fuel pressure and just subtract fuel during WOT? And I think I could basically use the 2G timing table because they are very close as far as compression.

 

[tom04841]

Sounds to me like you have a leak and unmetered air is causing your high trims. Do a boost leak test to make sure. Do you have the barbs on the intake tube capped, or are they running to the valve cover and vapor canister?

I did this conversion on my first eclipse, and had the same problem. Turned out to be the line to the vapor canister under the battery had come off and i was sucking unmetered air thru there. Your best bet is to cap off the nipples and run those lines towards the ground or a catch can to eliminate that as a problem down the road.

I didn't have a problem with my trims after that.

I wouldn't go by 02 valtage.....its a narrow band and innacurate for tuning.

You could use the 2g timing maps since it is closer to what you have than the 1g maps. I would also pull an extra degree or two to be on the safe side. You are using higher comp pistons that weren't designed to see boost (very thin top ring land). Detonation is going to be the death of those pistons. When it happens over an extended period, it cracks the ring lands and you lose compression on that cylinder. so your main concern is to get ZERO knock.

Do the boost leak and post back.

 

[tmoore8828]

I did a boost check and sure enough, I had a pretty decent leak between the upper intercooler hose and the SMIC. I haven't had a chance to take it for a drive yet. But it sounds as thought the idle smoothed out and I gained a little vacuum on the boost gauge.

As far as the OEM pistons, I did the conversion to the NA motor so I could get all the electronics squared away while I'm building the actual turbo motor.

Tom, what did you run for fuel pressure on the OEM pistons? I'm just wondering if I set it for 43 , I know the fuel trims will lean it out during closed loop, I'm just worried about dumping fuel out the tail pipe during boost!