Abnormally lean AFR

[user removed]

Clamp off the vacuum line to the regulator and see if it runs better. It won't run perfect since the regulator requires vacuum to make it run lean enough but even with that it should run a lot better than with raw fuel running into the manifold.

The plug not fouling worse nearest the regulator could also depend on how close it is to the idle air circuit.

regards
mech

[user removed]

https://www.youtube.com/watch?v=mSxpDCr4WCo

lousy video

regards
mech

[California98Civic]

Rented the proper gauge from O'Reilley and the fuel pressure regulator failed the test specified in the FSM. I bought a new regulator for $80 (with tax) and installed it. I took it for a test drive, and the engine ran normally. My DD is back in action for tomorrow morning's commute.

Thanks all, and especially OldMech, who nailed this diagnosis perfectly.

[gone-ot]

Kudo's to OldMech for "...tele-commuting..." diagnostics, par excellance!

[user removed]

Glad it worked out but don't forget to make sure the oil is not diluted. We used to check it by smell and when it was real bad you could light the oil on the dipstick on fire and it would burn.

If it's close to time just drop it and refill with fresh oil.

Your tank mileage will suffer severely.

On the first FI Z cars in 1975 Nissans system was licensed from Bosch. They had a flap air flow meter and all the injectors fired at the same time (not sequentially). Two things would flood that engines out in a very short time.

Open circuit in the water temp sender+massively rich engine died almost instantly. Jump the connection to the sender to daignose.

Fuel pressure regulator diaphragm ruptured, ran very rich but usually would keep running if you flogged the crap out of it.

Saw a live show of the Jersey Boys tonight, tickets courtesy of the two step daughters Christmas present. Great show for those who lived in that era.

regards
mech

[pgfpro]

Nice work Mech

[California98Civic]

Undoubtedly, the fuel pressure regulator change fixed the problem [EDIT: fixed it for a little while]. For two weeks almost everything has been normal, but slightly longer starter motor turning before she fires-up. And I think I was in a little denial, because all the previous issues that started this thread just came back this afternoon with a vengeance. Suddenly, the car sputters, the short term fuel trim leans-out steadily during a pulse at 75-80% load. It will get as lean as -28% short term fuel trim in a single pulse. Does that every time, over and over. Go into neutral and a new symptom is that it will sometimes stall. Stalling events sometimes are preceded by an idle speed that is unsteady: rpms 180 and then 500 and then 900 and then 700, 900, 800, and then stall or... you get the idea. Sometimes it does that and then keep running. The one thing that never returned quite to normal after replacing the fuel pressure regulator was the starting cycle, which required slightly longer cranking almost every time. Pre-priming the fuel pressure with the key only sometimes seemed to solve the problem. I have been meaning to look into it, but there are always a few things with this car, and I gotta live and work too. Haha! Back to testing...

Any ideas?

[j12piprius]

Perhaps the WAI is the issue, since that's when the problems began.

[California98Civic]

If so, then it must be because of air restriction. the IAT temps are not higher in an absolute sense from temps I have seen for years. Today was still a little under 130 degrees. I have seen 145+ with previous WAI configurations. But those were bigger diameter tubing. This is the first that is more restrictive than stock. But even if it is the WAI... why take weeks for a problem to form. Wouldn't the engine react quite quickly?

[j12piprius]

Perhaps it causes some damage that takes a few weeks of driving to get worse.

Idk, but if it was me I'd remove it and see what happens.