Troubleshooting Atomic LS EFI System

[67camarols7]

The following are the dash readings we are getting with the
engine:



RPM 2180 (necessary to keep engine running without periodically backfiring)

MAP Varies 9.0 to 9.9

Oil
Press. 50 psi

Fuel Pressure 60 psi

A/F 29.1

Baro 29.5

Timing 29.8 to 30.3 degrees

ECT 195

IAT 59



The compression was checked and we have 170 to 190 in all
cylinders.

After the initial setup with the MSD we started the car and
had backfiring from the beginning at lower rpm.

The fuel pressure on the MSD dash was reading very high (128
psi) and different than the regulator gauge (60 psi).

The ECT was also showing an error.

After checking the connections (unplug and re-plug) the fuel
pressure now agrees with the gauge at 60 psi and the ECT is reading correctly
with no error indicated.

The engine is still rough running and backfires at idle and also
when throttle is applied quickly.



Please note that much of the installation is new with the
following:



LS-7 motor from a 2008 Z06 with about 4000 miles (motor ran
excellent when removed from the car)

Conversion to wet sump

Stainless Works headers with conversion kit

MSD Atomic LS for LS-7

New alum radiator with dual fans

Vintage Air Frontrunner

FAST 92 mm throttle body w/ new TPS and IAC sensors

New MSD coils

New plugs

New MSD plug wires

New Aeromotive fuel tank with Stealth in tank pump

New #6 fuel lines with return and Aeromotive pressure
regulator in return line after the MSD fuel rails

New cold air intake system



There was much more work with this project which included a
TKO 600 trans, new clutch, with hydraulic throw-out, rack and pinion steering,
A/C, and much more but don’t think any of this work will have an impact on the
engine operation.



Any assistance with diagnosing the problem and getting the
engine to run correctly would be greatly appreciated.



Attached files

[lspwrd]

First, i wouldn't keep runnin it like that, until we get it figured out, Don't wanna do any lean damage if thats an issue. That AFR looks crazy lean and off. Check all vacuum connections and grounds from the rails again just to be double sure. What's the iac count during this condition? Also, an 08 corvette is throttle by wire. This will cause a huge conflict running a throttle by cable and "telling" the ecu its a LS7 during initial setup. Did you use the MSD part number for the coils on setup, or does it think the LS7 coils are on there? This will also cause popping and poor running conditions. With the throttle by cable, you'll probably have to use a different engine application that uses cable and 4x cam gear. Lemme know what you find.

Looks great btw. : )

[67camarols7]

We checked the vacuum and all grounds twice already, they were all good, but will double check again. Since the motor is an LS7 and the MSD does not support the throttle by wire, which motor should we identify this as to be compatible with the remaining LS7 characteristics ? At this moment we don't have the IAC reading but will run the motor long enough to get them it you. We did input the MSD coil numbers on the initial setup and about the only thing still stock on the motor are the stock LS7 injectors.



Thanks for the complement on the car and your assistance with helping us resolve this issue.

[lspwrd]

After re-reading the instructions, i forgot it doesn't support the ETC throttle body anyway and DOES require a TBC throttle body. My bad on that one. Been doing some research on the LS7, isn't this a DOD engine? Does the Atomic LS7 kit include a connection for the DOD on the timing cover next to the cam sensor? If so, is it plugged in? I've never seen the LS7 kit so I'm not sure what's included. Also, i believe the DOD motors use a high volume oil pump, what pump did you use on the wet sump conversion?

[lspwrd]

Im sure your throttle body is adjustable for idle. Set it so its just cracked open a hair after completely shut (binding).

The IAC will do the rest for idle control. Don't keep playing with the idle screw just to get it to run, it should do this on its own. Start with the stock cam setting, after you make cam or idle screw setting changes, turn off the key in between any changes for at least 10 seconds for the ecu to pick up the changes on the next key cycle.

[lspwrd]

Did you mess with the car at all this weekend?

[lsxchevelle]

128psi fuel pressure reading from the atomic looks to be the cause to me.

That would cause a lean condition

[lspwrd]

Everything else looks normal? Have you varified the fuel pressure with a known good mechanical Guage?

[lsxchevelle]

I post it says 60psi on mechanical fuel gauge and atomic reading 128psi that may be a open sensor.

[lsxchevelle]

I just reread the post the atomic agrees with the mechanical gauge.(60psi) Need updated readings and iac