rygi23

My friend's '04 Mach, trying to help a brother out. Car turns over in the a.m. when it's cold but will not start until it warms up in the afternoon. I was thinking the battery dropping a cell (still on the factory one @ 80K!) but the car is turning over strong as if it's not getting fuel. He is throwing the o2 code (o/r h with no MIL elims) but we're foggy on how that would have an effect. Any help greatly appreciated.

MustangBradley

Bad fuel pump? In the morning, can you hear the fuel pump pressurize the system when you first turn the key on? You should hear it plainly make a noise for about 2 seconds then stop. If you don't, then I would bet the pump is on its last leg.

rygi23

Nope. That was my 1st suggestion but he said he could here it.

MustangBradley

I think you are on the right track with suspecting a fuel problem. Next is to check the fuel filter. Also, bad gas could cause problems though bad gas is less of a problem these days. My 5.0 would not start with the tank low once. I added some new gas and it started up. I went to the gas station, filled up and the problem never resurfaced. It acted like it was out of gas but I could hear some sloshing around.

Doc Hawk

What do your plugs look like?

Detailer_Dave

The IAT sensor could be out of spec and not enriching the fuel enough to start engine at real cold temps.

Snitz

what is the actual error code