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Discussion Starter #1
My 99 Odyssey starts fine unless the outside temperature is hot. Anything above low to mid 80's and parking it in direct sunlight will possibly lead to this problem. It will turn over and almost start and then just crank as if it's not getting any gas? If you floor it and keep turning it over, eventually we can get it started, but it won't idle for several seconds. You have to feather the throttle and rev it up to keep it from dying for about 20-30 seconds. Then it is usually ok and will drive fine? Any ideas?
 

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Look for burnt solder connections on the main relay. Look in the 99-04 section for threads that have the location/photos. I'm not positive that is your problem, but it is common in older Hondas. The main relay powers the fuel pump.
 

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A defective coolant temperature sensor could cause the PCM to deliver too much fuel at hot startup, thus flooding the engine.

Do you have an OBD tool (e.g. ScanGauge) to read the temperature the PCM is seeing at startup? (The dash temp gauge is uselessly inaccurate for this kind of diagnosis.)

How long do you park in the hot sun and get the hard start problem? Long enough for the engine to cool down? If so, the above sensor is less likely at fault.

As the engine cools, the interior warms on a sunny day. The main relay mentioned by egads is inside the van, so it becomes the prime suspect in hot weather performance issues. (The only atypical symptom you have is that you seem to be successful in coaxing it to start, even if unevenly. A failed main relay usually results in no sign of starting due to an absence of fuel supply.) Nevertheless, it is a common failure point.
 

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Discussion Starter #4
A defective coolant temperature sensor could cause the PCM to deliver too much fuel at hot startup, thus flooding the engine.

Do you have an OBD tool (e.g. ScanGauge) to read the temperature the PCM is seeing at startup? (The dash temp gauge is uselessly inaccurate for this kind of diagnosis.)

How long do you park in the hot sun and get the hard start problem? Long enough for the engine to cool down? If so, the above sensor is less likely at fault.

As the engine cools, the interior warms on a sunny day. The main relay mentioned by egads is inside the van, so it becomes the prime suspect in hot weather performance issues. (The only atypical symptom you have is that you seem to be successful in coaxing it to start, even if unevenly. A failed main relay usually results in no sign of starting due to an absence of fuel supply.) Nevertheless, it is a common failure point.

I've had it parked in the garage for an hour when its in the 90's and it wouldn't start at first. I did pull the main relay and re-solder a couple even though none of them looked bad, just hoping. IT does behave like a flooded engine though so that may be worth investigating? Thanks to both of you for your advice, this van is on it's last leg and I'm proud of it's 20 years of reliable use. At this point, I'm hoping to get another year or so out of it. I'm somewhat handy, if it isn't to indepth, I'll try anything.

Thanks
 

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If it sounded flood look into no spark issue. Main relay also a potential problem. Sounds electrical.
 
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