I admitting don't know much about tunning,


I just rebuilt my brothers LT1 which had a spun rod bearing, it's a 97 SS, M6, 410 gear, stock bottom end with cc503 cam, 1.6 roller rockers, 918 springs, SLP shorty headers, BBK throttle body, aftermarket MAF with a Solomon tune. Car was previously stock with the fore mentioned bolt on's and stock tune. Spun a rod bearing because he over heated it. Heads were milled .08 block was cleaned and checked prior to rebuild.

On first start up car ran very rough, would barely idle. Car was running lean and eventually gave me 2-DTC's. Low voltage on bank 1 and high voltage bank 2. I replaced both 02 sensors with Denso's for now. This improved drivability and idle quality a lot but it's still not right. And doesn't have a lot of power. Here's what I know:

Car dies when coming to a stop
Doesn't like to start unless it gets a little throttle
Car will idle all day just a little rough
If I unplug the MAF the car will not start.
TPS is adjusted correctly .67v closed and 4.65v open
Checked resistance on IAC and checks with in spec .51ohms on both circuits
Timing at idle is 30 degree and goes as high as 40 under heavy throttle?....
Fuel pressure is 44 psi with vac line off holds steady at 40ish under heavy throttle (under a load)
No DTC's currently present.
EGR is obviously deleted, along with emissions stuff


I can record some live data with my scanner but I'm not sure what to look for really. It doesn't appear I can read Idle air counts with my scanner? I have faith in solomons tune, I just need help in what to trouble shoot next?

Car is still running lean

Thanks

Paul

 

40 psi is kind of low. With the vacuum hose off fuel pressure should match fuel pressure at wot. Check the fuel trims on your scanner to see if it is adding fuel. Hope that helps.

 

Aftermarket MAFs are known to be more trouble than their worth; do you have a stock MAF (with the screen still in it) to try? Once you start replacing vital sensors like that with aftermarket crap that add little to no HP you're creating more potential problems. They are not a restriction as some believe; certainly not at the cam only level. How old and what opti is in it also?

 

Yeah, it's not my car and I told him buying that MAF was a waste of money. I do have a factory untouch MAF from my car which is in pieces just have to find it in the endless boxes in which my car is packed in. The OPti is AC Delco probably about 3 years old but no mileage and never had coolant run over it.

I'm gonna try a factory MAF and take a look at the fuel trims as 1995 T/A suggested. I believe my scanner lists fuel trims in %, if this is true at 100% throttle should my trims be at near 100%?

 

Switched to stock MAF, no difference.

Both STFT and LTFT's go to zero upon heavy acceleration?

Turned up fuel pressure just a bit, steady 45 PSI under WOT. Still The same

 

would help to see wtf your IAC counts are. BBK TB....if it has not been "drill mod" that could be the idle issue. Advised you have a way of scanning IAC counts before doing any drilling though

 

Might help to reach out to the tuner; everybody makes mistakes! Could have mailed you the wrong PCM by accident or fat fingered something in the tune lol.

I assume the BBK TB worked without any issues before when stock?

 

Did you mean to say 0.008" instead of 0.080"?

 

Positive the valves are adjusted correctly?

 

Yes, while not a lot of experience with LT1 engines, I've built my share of SBC.

not sure what to do next.....

 

Double and triple check all your electrical connections to make sure everything was attached to the correct location. O2 connections, injector connections, the works.

Odd that you would get low voltage on one bank, then high on the other. Makes me think that something between bank 1 and 2 has been mistakenly swapped around.

If the car will not start with the MAF unplugged, one of the inputs for speed density might be missing. Are the IAT, MAP, and coolant sensors plugged up and working fine?

Are any fuses blown? Under the hood and under the dash fuse box cover?

Are you 100% sure that the plug wires from the Opti are on the correct plug?