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Rangers are good reliable trucks.
3.0l V6 Vulcan engine was used in many Ford cars and in the Rangers, 1991 Ranger was the first year, although in 1995 3.0l got distributorless spark system which has less problems.
1990 Rangers got the 4.0l OHV V6 alot more power than 3.0l and MPG is close, IMO 4.0l would be a better choice, it was distributorless since first used.
2.9l V6 was a good engine, rangers had these from 1986 to 1992, they did get low oil pressure as miles got higher.
In 2001 Ranger got the 4.0l SOHC V6, this was a completely new 4.0l, no relation to the 4.0l OHV, early years had timing chain issues.
Ranger leaf spring hangers tend to rust out, so check those.
You can look here, just click on this>>:
http://www.therangerstation.com/tech_library/axle_codes.shtml
On the door tag there will be an AXLE code, that will tell you the gear ratio and if it is OPEN, or L/S(limited slip), Ford calls it Trac-lok, Chevy calls it posi-traction, samething
A letter then a number is L/S, like F6 or R6, two numbers like 86 or 96 will be OPEN(car differential), that should save you some time when looking.
Also click on this>>:
http://www.therangerstation.com/Magazine/Summer2009/federal_sticker.htm
This is the rest of the info from that door tag, if you have to drive a bit to see a Ranger have seller take a picture of the door tag and send it to you.
VIN is also there so you can check that out as well.
And don't forget the Mazda B-series, same truck but often sells for less used, B2300/B2500 had 4cylinder engine, B3000 has 3.0l, B4000 has 4.0l
Super cabs or extra cabs won't have 7ft beds, 7ft beds were only available in regular cab models, I think pre-1998 long beds had 114"(113.9") wheelbase, and 1998 and up long beds had 118"(117.5") wheel base