Hi All,

I need some help on this, I just installed a new motor, got it running and ran very good. Than later in the day I started and it would fire than slowly rpms would drop than die. I would start it again and would pump the pedal to get it to idle properly and it would idle properly. Now it cranks fine, gets gas (plugs are wet), gets spark but wont fire...confused.

It'd probably help to know the year/engine. The problem could be one thing on a carbureted 2.6 and something completely different on a fuel injected 3.5.

I would think it could be narrowed down to fuel delivery or air intake though. But I'm pretty new to these beasts.

Whoops...Sorry forgot to tell you what model. Its a 91 LS 3.0. It has a new motor and otherwise all stock. Can it be a bad ecu and still get spark & fuel? When it cranks it just doesn't sound like it even wants to fire.

Did it sit long enough for the fuel to go bad?

I don't think so, it sat for about a couple months. New gas, fuel filter installed before it was fired up.

If your sure its got good fuel (spaying starting fluid in intake easy test), its getting spark all the time and your timing is still good, should run. You could pull off the right (driver side) plastic cam sprocket cover and turn the crank clockwise to TDC to check the timing.

For the ECU you can check it with an analog meter as described HERE and in the factory service manual available at Mitsubishilinks
I believe the picture on the first link under "Cracking the code" and the pic in the FSM show where to put the meters leads looking at the back of the test plug where the wires are going into it. Also the test plug was moved on my 90 to under the glove box rather then behind it as shown for the 89. Likely the same for your 91.

Here's where I'm at. I have spark and fuel (I can smell it) As I was getting the timing marks lined up I was able to crank the engine by hand real easy as if no compression. I was thinking the fuel could have washed away the oil and not let the rings seat so I have squirted oil in the cylinders disabled the injectors and still no change. Can the lifters on a 3.0 pump up too much and hang open the valves? Did something major happen and the motor comes out again? Any suggestions?.... Help Frustrated!!