I have a 1991 civic dx with FI that doesn't seem to want to start
when its hot. this problem just started after i replaced the radiator but i can't think of any reason why this would affect it. If you leave it sit for 10-15 minutes it will start right away. any suggestions as to something obvious that i may be missing? thanks in advance.

 

Main fuel relay.....they call for them at Honda all the time. Usually its on Accords but we get the occasional Civics with this problem.

 

Main relays do tend to die in the heat, but they don't seem to care whether the engine is warmed up or not. They're just as likely to die on the first start on a hot day -- even though the engine is "cold." Main relays usually die because of a solder breakdown on their board, and this is affected by ambient air temperature inside the car, not engine temperature.

But here's how to be sure: If you hear the fuel pump kick in when you turn the key to ON, the main relay is okay. If you DON'T hear the fuel pump kick in, then the main relay is PROBABLY bad.

Sometimes, though, the TW sensor (coolant temp sensor) dies, and they frequently die in a funny way on Hondas -- they die "cold."

What I mean is, they track the coolant temperature from cold to hot and they tell the ECU what's going on. I think they put out .5V for a cold engine. As the coolant temp rises, so does the voltage, until it hits around 4.5V, maybe 5V for a fully warmed-up engine. Not exactly sure of the voltages here. But then, for some strange reason, they "go cold," putting out around .5V again, even though the engine is really fully warmed up.

In normal driving, you won't notice the difference. But when you try to RE-START the car, the ECU sees START and COLD, and so it dumps all kinda fuel into the injectors (which it SHOULD, to start a cold engine). This'll flood out a hot engine, though, and so it won't start.

Once the engine (and TW sensor) cools off, everything's fine again. Until the sensor warms up and "goes cold." Then, the cycle starts all over again. You can watch it on a voltmeter.

 

Hello. I having the same problem with my honda not wanting to start when it sits out on the hot sun. This info has been very usefull. Now can you tell me where is the fuel pump reley located? I want to try replacing it right-away.
Thank you
wcac1@bellsouth.net

 

Referrencing :
highwayman32
Junior Member

I have a 1991 civic dx with FI that doesn't seem to want to start also when it sits under the sun and gets hot.
Can you tell me where the Fuel Pump Relay Switch is located?
Thank you

 

The "Main relay" is under the dash... my buddy just sold his EF so I couldn't tell you where it is, but when you find it and take it out, just re-solder all the connections in it and presto. fixed... just make sure you use a desoldering station, a sucker, or wick to get the solder off first to re-float them. it's easier than buying a new one, and cheaper than going to pick 'n pull.

 

I have seen many PGM-FI main relays fail due to contamination on the fuel pump circuit contacts. The main relay is about half the size of a ciggarette pack and a bit thicker. Should be grey if stock. Behind the dash roughly near drivers left knee.

 

I have an 89 accord EXi. I am having problems with hot starts as well. And I have a TW sensor code (Code 6). I have tried the sensor and the resistance at various temperatures is right on target. I used a resistor to "trick" the ecu into thinking the engine was hot and cold. (I tried various resistances). I also tested the wire and found no problems. I have also gotten the trouble code right off a cold start before the engine even began to warm up. If I stop the engine and try to restart right away it will not start. The only thing I haven't tried, which seems important, is watching the voltage accross the sensor with an oscilloscope.

Basically my question is does this sound like the same problem to you ? (anyone)
I am running out of money as I continue to throw parts at this car.

Thanks

 

Ended up changing the coolant temp sensor and the wire which leads to it and the problem is fixed.

Who would have thought, coolant temperature sensor code means new sensor. too easy.