96LT1355Z28

iTrader: (2)

Well I finally got my new engine together and in the car but I can't seem to figure out whats wrong with it. On the dyno it made 429/399 rwhp/tq but was at lean at 15.6 per the Dynojet wideband, I know they generally show leaner than the car actually is. It would pop and backfire if you tried to hold 2500 or 3000 rpm in neutral. And it had the strong rich smell that burns your eyes. The fuel psi was at 50 w/o the vacuum line and 46 with it. The long term fuel trims were at -15.8 on both banks almost all the time. After several emails with Bryan at pcmforless I've turned the fuel psi down ti 43 w/o vacuum and the eye burning smell has gotten much better, the idle isn't near as "choppy" as it was. Now the LTFT's are at -14.3 in bank 1 and -11.1 in bank 2 at 3000 rpm driving in 4th gear, the O2's show .930v. It pops like I'm microwaving popcorn in the muffler durring a decel in gear and will sometimes backfire or pop between shifts. Now at idle the LTFT is -14.8 to -15.6 in B1 and +25.0 for B2! After talking to Lloyd Elloitt, the engine builder (short block), Bryan and Keith at pcmforless, and Ed Wright I'm lost as to what else to look for! Durring the last few weeks I've:

-replaced fuel filter
-replaced plugs and wires (Autolite 104 @ .030)
-adjusted the rockers from 1/4 to 1/2 then back to 1/4 turn past "0" lash
-cleaned the MAF and tried one from another LT1 car
-checked all exhaust bolts (all tight) no signs of exhaust leak
-replaced a slow responding O2 sensor (new AC O2)
-tried the brakeclean, starting fluid, and propane method of finding a vacuum leak, nothing found

There are only 2 things I've noticed that are puzzling me and I'm sure they're part of the problem. I've got a filter in my PCV system and it keeps filling up (about 1oz per 30 minutes of run time) with a fluid. It doesn't smell like fuel, oil, or coolant, it is somewhat transparent and tanish yellow in color. It's thicker than water but not as thick as oil, my guess is oil and coolant but don't know where it's comming from. The other thing is I've only got between 8-10 inches of vacuum at idle (960-1050 rpm). Lloyd said I should have between 12-14 inches. Sorry for the long read, this has been ongoing for almost a month now! Here's a rundown of the engine:

Short Block:
4.040 bore X 3.75” stroke 385CID
Splayed 4 bolt mains
4340 Callies crank
4340 6” Compstar H beam rods ARP 2000 bolts
4032 -5cc SRP pistons file fit Total Seal rings
Melling M55hv oil pump
Moroso 7qt oil pan and windage tray and pickup
Pioneer SFI balancer on stock 3 bolt hub
balanced and assembled by Todd Maschmierer

Top End
Stock LT1 ported heads (LE2, 205 cc intake)
.026” Mr. Gasket head gaskets 12.1:1 static compression
Manley 2.00/1.56 6000 series valves
Stock LT1 intake ported to match heads by Lloyd Elliott
Lloyd Elliott HR cam (236/244 @ .050, .592/.592 lift, 112 LSA)
Stock GM HR lifters
Trick Flow 7.2” pushrods
Crane 1.6 SA rockers (0 lash +1/4)
Patriot Gold Extreme valve springs (155# seat/400# open)
Professional Products 58mm TB
3.5” 90 degree air intake with K&N filter
Stock MAF w/ screen

Ignition:
Stock coil and ICM
MSD 6AL
Dynaspark II optispark distributor
Accel Extreme 9000 plug wires
Autolite 104 plugs (.030” gap)

Fuel System:
Racetronix 255 lph in-tank pump
Racetronix hotwire fuel pump kit
Stock 3/8” feed and 5/16” return lines
Stock in line filter
Racetronix 42# low impedance injectors
Aeromotive adjustable fpr
Stock fuel rails

Exhaust:
Paceseter LT headers 1.75” primary, 3” collector
3” Y-pipe merged to 4” single pipe
1 chamber Flowmaster with turndown at rear axle

PCM4LESS tune, I know I need a dyno tune with this setup. I need to figure out if it's mechanical problem before I go back to a dyno or the track!

Thanks for reading my long A$$ post.

b4cz2896

may sound funny, but check your plug wire routing. 2 switched wires will cause alot of funny things. Also, if you have some type of scanner check misfire counts around 2000 rpm. May help narrow down which cylinders are missing. On my old lt1 i had a loose rotor in the opti and it would do what your describing.

96LT1355Z28

iTrader: (2)

Gone through 2 sets of wires and checked wore routing countless times for peace of mind! I'm getting a hold of a better scan-tool tomorrow hopefully it will reveal something. I've using a Dynaspark opti, it's sealed from the factory so I can't open it. Thanks for the response though!

aboatguy

Internal vacuum leak...
Check your intake gaskets.

I'm going through the same thing and I finally bit the bullet and pulled my intake a couple of hours ago and voila wet gaskets (even though the intake was pretty dry...the intake ports in the heads were a different story...

Oh yeah leanish drivers side pig rich on passengers side..

Last week I redid the header gaskets exhaust, changed O2 sensors, vacuum check, compression tests, two different dyno shops..... for wideband testing.
Almost same story as yours. So maybe your problem is the same too.








Mike

jaycenk

iTrader: (1)

Are your valves adjusted ok? To be honest with you I have the pop and some back fire on mine as well and already had to change plugs because it became a miss that set in a bit later. Mine I think is the tune. It is close but not quite. your fuel pressure looks right on and if you don't have idle problems then I would say the tune. Also have you set you TPS voltage yet? you have an aftermarket TB so you need to set the TPS sensor to the correct voltage and adjust you idle if when you do it.

96LT1355Z28

iTrader: (2)

Update, with a lot of searching I figured out my problem with the split long term fuel trims (BLM's). There's a separate passage for idle air in the LT1 intake separate from the main plenum. This link below explains it much better, I did these modifications and it seems to have helped my fuel trims drastically. It still runs a little rich but from what I've found that's pretty common for a mail order "safe" tune, plus I can't expect a mail order tune to be perfect on a setup like mine. So if your having split blm's or fuel trim issues and you've got an aftermarket TB you may thing about trying this:

http://members.***.net/chipsbyal/page/idle/index.html

P.S. I also found a small leak in my fuel pressure regulator, there was no liquid fuel in it but the vacuum hose had a fuel smell. I found this after pulling the TB and seeing moisture and smelling fuel inside the main plenum near the pressure regulators vacuum port. This thread helped me, lots of good info.

https://ls1tech.com/forums/lt1-lt4-m...an-oem-tb.html

Mike I was just getting ready to pull my intake but I figured I'd address the TB issue first!

Jaycenk, been through the rockers 3 times with no change, TPS is at .67 after playing with the TB blades which are barely open now at idle.

Thanks for the responses!