Been chasing a gremlin (code 25 lean) for a few weeks. Checking vacuum leaks, used propane torch, changed plugs wire cap rotor (they were over due anyways), But whats been getting me 3x's now is at random, I loose 99% power and can only limp off the side of the road with an idle. I can throttle to 1500 rpm's but it falls back flat to a few hundred, then finds its idle.

To fix. Shut off, count to 10, turn on and drive off like nothing happened.

Today it happened again so I suspect Fuel pump. Changed filter first, then check rail Pressure, and according to FSM I have 44PSI with connectors jumped AND at idle, it does not drop with FPR unplugged(but not too worried about that yet), But whats bothering me is the rail will not hold the 21PSI for 5 minutes. It goes to Zero immediately when stop engine. Now this could possibly not be my power loss issue, but its defiantly related to my hot start crank for 3 minute issue. New to the 3vze

92 4 runner auto, v6 85k. Ideas? Cant find alot on google search for this rail pressure loss issue.

only re occuring code is 25 and not always present when power goes out.

 

Update and new Questions - Seeing my truck has a Safari Snorkel and Flowmaster No Cat Exhaust, Is this alone enough to trigger a lean 25 code? Can VAFM adjustments be made to compensate for the added air flow which could possibly be causing the lean running?

 

There is a check valve in the fuel pump to hold the fuel pressure. If that check valve fails, as soon as the pump stops the rail pressure falls flat.

But you can lose fuel pressure anywhere after the pump, so before I suspected the pump I'd look at the Fuel Pressure Regulator. If it was "stuck open" it would drop the pressure as soon as the pump stopped. Also, the fuel pressure would generally be too low, which would give you .... code 25 (too lean).

(The fuel pressure is lowest at idle when the vacuum is highest. If your FPR does not track the intake manifold vacuum, and it's somehow the correct mixture at idle, it will lean out with the throttle opened. And if the FPR is not working, the pressure may not jump with FPR unplugged.)

 

So this can make the check valve on the pump look like the culprit

This makes sense after reading it a few times.

Highest vacuum at idle = lowest fuel pressure.(38-44)
Stuck FPR = no FP increase + throttle = more air same fuel = lean

38-44psi is what FSM shows for idle, I'll toss on my FRP off my parts truck and do the tests again. Thankyou

 

You can can plug the FPR output for the moment and see if the pressure drops off emediatly after pump is off.


I wouldn't hold to long because who knows how much over max pressure aged fuel injectors seal will hold.
Also a bad injector can bleed off, But you wouldn't be getting code 25 then.