well i bought a 1990 allante with the 4.5 and i have to say it is pretty damn good! i have put over 2500 KM on the car since i got it... so about 2 weeks and all i can say is SWEET average at 21.6 mpg ( 70% in town ) it has some power behind it and the allante handles very well. 86,000 clicks on the car too.
but one question i would like assistance.
every so often i have a smell of gas just a bit of it.. i think it might be a leaky fuel rail or something. i have to check it out.. but i wanted to know if this is a common issue on ageing 4.5s or its just a worn item?
I dont know about an allante, maybe in one of the front fenderwells. Its pretty big, about the size of coffee can and has numerous vacuum tubes and one electrical connector on top of it. Try the Allante forum. You could also check fuel pressure bleed-down with a gauge to check for a leak.
Also, I see you are from Canada which nominates the car for corrosion issues. One problem with my Eldo I had was the vent/filler pipe to the fuel tank had a small pinhole in it that caused occasional fumes... Easy as pie to repair if that's the case.
If the fuel tank was still steel on those, rust at the top of the gas tank is also a possibility.
You'll just have to sniff around a little on a calm day and try to guestimate the area it's coming from.