91 explorer vapor lock issue.

[jyro]

I'm just going to toss this in, see what you guys think. First, mine is not vapor lock, it happened 2 nights ago in below freezing weather.

If conditions permit (engine temp, so forth) can the engine start directly into closed-loop mode? I can probably research that myself this week, just wondering if anyone has a quick definitive answer. If so, then I start thinking my oxygen sensors are too slow to heat up, or the bandwidth is just too wide due to sensor age. Any thoughts?

I'm going to hook up a fuel pressure gauge next week and see if I can get definitive readings.

Open loop till the coolent temp is correct and I think till the o2's are up to temp. Till then it will be open loop.
Problems with below freezing can be water in the fuel, there is a fuel treatment to allow it to mix with the fuel. typically gas drier or fuel line drier will be on the bottle. it only takes a slight amount of moisture to cause problems.

cold also affects a sticky idle air control (IAC) more, allowing it to not respond to the engine rpm quick enough.

 

[jyro]

kind of like a doctor

Not much to go on since I think you have it set in your head that your 4.0 OHV is suffering from vapor lock.

I just look at the symptoms and try to match them to the most reasonable explanation. Thank God we don't have to do MIR's and CAT scans on cars.