high petrol usage and wont start for 5 mins

[soothsayer]

hi i have everything else sorted on my new car except its using about twice as much fuel as it should approx 20 mpg and unsure wether related or a different fault if i turn the car off when warm eg stop at the shops or put petrol in i can t start it for 5 mins it just turns over then after 5 mins of either turning it over or left it will start fine ... when running everything seems great except juice usage of course any help esp on fuel usage would be grateful

[spiffyguido]

Sounds like it's running too rich when hot. Whenever I've had this problem, it's always been the coolant temp sensor.

Is your ECU throwing any error codes?

Next time you have trouble starting the car, go under the hood and pull the electrical plug off the coolant temp sensor (round, in the thermostat housing I think, 2 wire?). If the car starts right up after doing that, then the coolant temp sensor is probably to blame.

[RedRacer]

Just throwing this out there ..... if you're driving a 4th gen 2.2 or 2.3, (si or vtec) the mpg is actually around 19 mpg city and 24 highway, giving you a combined mpg of about 21. So if you're getting 20 mpg in stop and go (city) driving, that's about what it should be based on the recently modified US mpg standards. When I keep my foot out of it and don't engage boost, my mileage is around 19-20 around town. We won't talk about the Hummer style mpg I get when I spin the turbine and have my foot through the floor.......not a pretty sight.

The S model isn't quite as thirsty with around 23 city and 26 highway or a little higher. Combined would land somewhere around 23mpg.

Preludes are sports cars, they're not economy cars and they do love their premium fuel.

I'm wondering if the starting issue you're having is the main relay perhaps? Did it just start doing this? You said it only refuses to start when it's warm? My Accord would do that after stopping for fuel. Occasionally it would refuse to run after other stops, but it seemed more prevalent at gas stops. And it only happened after the car was warmed up and if the outside air was warm too. Turned out to be the main relay. But since I think your mpg is about what it should be, the other signs, to me, are indicative of the infamous Honda relay problem of having a crack in the solder points on the board. The cracks expand, continuity is lost and the fuel pump stops running. Cools off, the board shrinks a little, contact is made again and the car starts.

As for improving the fuel econ, just stay off the throttle, don't use the AC unless you have to, avoid hard stops and starts and don't drive over 55 on the highway. Make sure it's tuned properly, air filter is clean and breathable, pvc filter is working properly, oil is good and changed regularly and that your tires are at 32 psi or no higher than 35 psi (when cold)

And keep those windows rolled up on the highway too, use the fan and vents for fresh air...windows rolled down at high speeds creates huge drag on the car.

[soothsayer]

cheers for replys i ll change main relay ..i was expecting for a 2.0 ltr auto 30/35 as i had a probe before 2.5v6 that returned 38 but if thats what it is ok

[AyeZer]

My car won't start also, and I have the same car like a soothsayer. I am so thankful that I visited and read this discussion. I will try the suggestions and tips also of you all said. I really hope this will work to my car.

[samboman]

i have this same problem, would you please be able to describe what the main relay is and what should be replace/fixed?

[spiffyguido]

i have this same problem, would you please be able to describe what the main relay is and what should be replace/fixed?

This may help:

viewtopic.php?f=3&t=400

[samboman]

thank you very much, i had been putting up with it for past 6 months and had it looked at by a mechanic a few times. after struggling to remove the main relay we resoldered the connections and since then it has been working a charm, thanks again