Nissan Repair: 86 Nissan D21 V6 - Running VERY Rough, nissan d21, vacuum leak

Question
Hi, I have an '86 D21 Pickup (v6, 4x4, w/manual trans) with nearly 200K mi.  I bought the truck about a year ago, and have been having trouble with it since day one.  The trouble is that in most cases, it will start without much of an issue, and idles great after a few initial spits (only lasting about 5 seconds).  The trouble comes after any more then 10 mins of driving or just idling.  If I step on the gas, the truck spits and sputters like it's about to die, and sometimes it does die, other times, it's like clearing it's throat and spits a little more, let's a black cough of fuel-rich exhaust out of the tailpipe, and takes off like a bat out of hell.

Regardless of which of the two above mentioned items occurs, in general, it seems to have lost a ton of power.  The biggest, and most annoying of all is that if I'm able to keep it running for a full 10-20 mins, when I shut it off, it's all done.  The truck will not start after it's warmed up, unless it's had a few hours to cool.  This has proven VERY inconvenient.

I've replaced the exhaust as it was rotted out and hanging off when I bought the truck.  When I did the exhaust, I also replaced the Cat and o2 sensor.  The plugs and wires have also been replaced, as upon inspection, the plugs were loaded up with carbon.  The temp gauge is showing that the truck does not like to get up to temp, but since replacing the temp sending unit, it at least budges off stone cold, but not much more then that.  I have not had 6 hours to spare to replace the t-stat, as it's a bear of a job on this truck.

I'm drawing blanks on what could the cause of this whole problem.  I don't know if it could be the EGR valve, Leaky Injectors, or something unknown like a vacuum leak somewhere in the whole mess.  I also saw a part called an Ignition Idle Air Regulator on a replacement parts site, and am clueless as to what that's all about too.

Any help you can provide is greatly appreciated.  With an old truck like this, the only "codes" it throws are light sequences on the ECU, which is of no help in this case.  It seems that all of the parts for this truck are VERY expensive, so I want to avoid just carelessly replacing parts unless I have to.

Any help you might be able to provide would be greatly appreciated.

Thanks,
-Mark D.

Answer
Hi Mark -

Wow, seems like your child is a big headache -

There are 2 things that come to my mind with your description of events, and thank you for being thorough with it. Helps a lot, since I cannot physically be there.

First, have you checked the fuel pump? Sounds like it loses prime after warming up. Check the pressure and volume of the pump, and also replace the fuel filter if you haven't already.

Secondly, it could be your ignition module, located in the distributor. These things fail when it gets hot, and if you wait a few minutes, the engine will start again.

Also, you did not say if you replaced your distributor cap and rotor. A lot of times there are carbon tracks in them and affect performance. If you have an ignition coil, may want to check that too.

Hope this helps - if all fails, give me a hoot again and we can go to the next step.

aloha
calvin