Sluggish engine performance after distributor replacement. on 1995 Nissan Pickup (D21)

Just had my distributor replaced for the second time in the last 2 weeks. The first replacement distributor ran good for 7 days then died. The second replacement distributor is causing my truck's engine to run rich: I smell and see unburned gasoline leaking out of the exhaust. The engine's performance is sluggish. When I accelerate, the engine revs up slowly. The engine is not misfiring. What could be causing this problem?

by in San Diego, CA on January 25, 2011
2 answers 2 comments
ANSWER by on January 25, 2011
you have one or more of the wires crossed, this engine uses 2 spark plugs per cilynder and must fire in sequence not at the same time.
COMMENT by on January 26, 2011
No, this engine only has one spark plug per cylinder. It's not a staggered fire ignition, which was common with Nissan trucks from the 80's. The firing order is correct: 1,3,4,2. I inspected the spark plugs last night, all looked good. Each cylinder is firing. There was no unburned fuel on the electrodes. Each plug had a smell of burned kerosene, similar to the smell emitted from a Coleman lantern. Coloration on each spark plug appears normal. I noticed the replacement distributor is different then the original. I know there are two models of distributors for this engine: a Hitachi and a Mitstubishi. I am uncertain if they are interchangable, but the distributor currently installed is not the same model as the original. I'm not sure if this may be the root cause of the problem.
ANSWER by on January 25, 2011
Check this link for the firing order of your vehicle, http://www.wellsve.com/custom_searches/ds_firing.php
COMMENT by on January 26, 2011
Thanks for the link. The firing order is correct. As I mentioned in another reply, something is causing the mixture to run rich. Could be a sensor gone bad? With computers monitoring and adjusting the mixture, it could be anything. I probably will be taking the truck to a shop and have them look at it. Thanks for your response.