1995 D21 Pathfinder V6 engine running rich

[carbotdude]

Hello

I am new to this forum.

I purchased a 1995 Nissan Pathfinder SE-V6 with the VG30e engine with a manual transmission and transfer case last year.

I upgraded the coolant reservoir and battery after purchasing the vehicle.

 

I had my valve cover gaskets replaced as they were leaking oil onto my starter motor and killing the starter June 2026. I mentioned to the mechanic that I noticed a 51 ECU LED engine code, which my research tells me points to fuel injector issues.

After the repair was completed, the engine started running rough and dying after a few minutes. This first mechanic gave up on the car and told me to take it.

The first mechanic said that he replaced the fuel injectors as well as the valve cover gaskets.

I noticed that the exhaust is much darker than usual. This tells me the engine is running rich.

 

I had a different mechanic take a look at the engine. After replacing a few hoses, the engine ran a little better, but not much better.

The second mechanic mentioned to me that the engine is running rich on all cylinders by checking all of the spark plugs.

This same mechanic conducted a smoke test and did not find a leak. I think he mentioned something about messing with an EGR valve/baffle or something and that did not change the engine behavior (I need to find a good picture of that part).

At this point the mechanic told me he doesn't have time to look at the car. His biggest suspicion is that there is an undiagnosed vacuum leak.

 

What do I do next to fix the rough engine? As far as I can tell, the rough running is at all RPMs, not just idle.

I have never had so much fun driving until I got this car. I would like to get it running again.

Is there a guy/shop in the New England area that knows how to work on these older Nissans?

At this point, I am willing to sell the car to somebody that has the tools to work on it.

I am beginning to think that specialized tools are required that I don't have, especially if the valve covers or engine block are warped in any way (how does one know)?

The vehicle is sitting at a friends place 30 minutes away as I don't have room for a broken car.

Edited September 13 by carbotdude
Clarifying vehicle information

[Strato_54]

Check either MAF connection, O2 sensors or base ignition timing. These are the big 3 that will make it run rich. Assuming (never assume) there's no vacuum leak and the injectors are good from factory. Rich is usually a sign of bad combustion or too much air so if it thinks its getting too much its gonna freak out or If it seems improper timing it will dump fuel to keep it safe.

 

only fancy tools you'll need is a timing light and maybe a volt meter to check some wiring. otherwise you can fix this thing with basic tools. Welcome to the forum

Edited September 13 by Strato_54

[Strato_54]

https://www.nicoclub.com/nissan-service-manuals

[carbotdude]

Is it possible that an exhaust leak would cause too much fuel to be dumped into the engine?

The first time I tried to remove the starter, I had to undo 2-3 bolts on the exhaust after the header on the passenger side.

That connection might be before an O2 sensor now that you mention it.

 

I forgot to mention this is the 4WD 4 door variant of the SE-V6.

Edited September 13 by carbotdude
missing content

[Strato_54]

yes if its leaking before the O2 its going to affect the AFR. Anything between MAF and O2 should be a completely closed system. Try and patch that up and see how it runs. if its still off then I would check the base timing. I think its 15 degrees at idle with the lower throttle connector unplugged at operating temp. +/- 2 is fine but anything more than that is going to cause issues.