Help! Flat spot

[captainrags]

Have flat spot an low rpm accelerating usually in second gear. I have only one MIL 1441 non purge. Don’t really think that it has, anything to do with the problem.
C4 1996 LT4 manual 95K miles.
Any feed back would be helpful
Ray

 

[Schrade]

edit: there ARE times when you can ignore some particular DTC - the FSM diags will say in the diags flow chart to check for another code first, and if it's there, go there; reason is, one ignored fault will oftentimes trip another code falsely. So get to closed loop (fully warmed up), and re-scan. There might be the second code now...



The DTC should probably be checked first.

If it's a EVAP cannister non-purge, you can probably do a by-pass to check the function. Pull the vacuum tube that goes into the cannister, and follow it back to the solenoid. Secure it, and apply 12V to the solenoid that controls purge, and check for vacuum - it should hiss. Then you know the switch works. Put your thumb on the end, and if the tube holds.
edit: probably check the ground first, on the solenoid purge circuit

Put the tube back on cannister, disconnect the other tube that's coming from the tank, TO the cannister. It should hiss, to show no blockage in the cannister.

I don't have FSM, so someone else can post next step of diags...

 

[KANE]

Someone jump in and keep me honest... but if I remember correctly... under WOT (wide open throttle), the ECM goes into open loop relying on programming tables instead of the O2 sensor.

If the evap isn't working correctly, it will throw things off as it transitions into open loop. It is likely you are getting leaned out or over rich at a particular time that is causing your flat spot. Your LT4 is not getting a mixture optimal for that engine speed- which is around 14.7 parts air to 1 part fuel. If you get out of that range- it goes flat. My inclination is that you are getting leaned out as the result of an issue with the evap as a system.

So, I would check the evap as a system first. It impacts how much fuel (rich) and air (lean) is present. The ECM calculates what it needs at any given engine speed under given conditions- but it might be off slightly when compared to what is really going on with respect to the evap system.

Remember- the code always identifies an impacted system- which is not always a particular part.

Here's someone's experience on an LTx motor with the same code-
http://numberformat.wordpress.com/2009/08/06/dtc-p1441-evap-system-during-non-purge/


Good luck!