Engine flooding in "ON" position

I'm finally circling back around to this one after a couple years of aviodance.

When the the key in left in the ON position for more than 30 seconds the engine begins to flood. Years ago when it was left for a couple hours in the ON position it become hydrolocked with fuel. Never did come up with an acceptable explanation.

The injectors are good and it's got a new fuel filter. I'm suspecting the FPR but haven't checked the pressure yet.

Anybody else encounter this or have any ideas?

 

How does it run? It could be a bad FPR but the pump would have to stay on constant with key on. They normally turn off after 5 seconds.

 

Hook up a fuel guage and unplug the FPR while the engine is running you should see an increase of about 10 PSI. If you don't leaking FPR.

How positive are you the injectors are good?

The fuel pump usually shuts off after it builds up pressure. If it keeps running you may have an internal issue in the pump itself.

 

Pull the vacuum line off the FPR while its running. If fuel is coming out of vacuum nipple on FPR the diaphram is popped and that will flood engine. But again for it to flood key on engine off. The pump would have to be staying on constant. maybe the relay is shorted on. The fuel pump relay is called the circuit opening relaty. its under the steering column behind the knee bolster.

 

What engine?

The fuel pump should not come on at all with just key on engine off, momentarily or otherwise. You may have a stuck relay, an issue with the ECU, crank/cam position sensor or the start signal input to the ECU.

The FPR will leak only thru the vent tube, to the outside world or bleed pressure off to the return line. A bad FPR diaphragm on a 3.4 will eventually trickle down the intake tube towards the air filter not the engine, not sure which way it would flow on the 4 cyls.

Also despite the FSM claim there is no vacuum modulation of 1st gen FPRs, 4's or 6's. It was only used on a very few, very early 3.4's (possibly just the T-100) and controlled by the ECU with a VSV.
And no pressure switch.

 

My 95.5 had this vsv for the FPR, my 97 also has the egr set up on it. I have been unlucky with some of the add ons lol. I eliminated the vsv for fpr when I installed a 3.4 from a 99 runner in it. it is a real pita system

 

Yep, not surprising they did away with it.
Interesting to see you had EGR but no controlled FPR in 97 on a 3.4, is that correct? At one time I suspected that the two systems came together.

If any folks need a visual. This is from a Toyota document describing the features of the "new 5VZ".

 

Why do you say the injectors are good? Could one possibly be sticking open bleeding off all the fuel pressure from the rail and line into one cylinder.

 

I honestly haven't done any work to it yet and only noticed the egr system during a cursory glance, I have been too tied up in my 95.5. It very well may have the fpr vsv system as well, I will check and let you know once we thaw a bit here

 

X2, there was a thread a while back where a gal had her injectors bench tested/cleaned 3 times yet several would leak when installed.

 

I've got a 5VZFE.

This has been the one and only time the trucks been to a mechanic. The guy finally figured out that it was hydrolocked after ruling out the starter, which we suspected originally. At the time, back in 2013, he said that he'd cleaned the injectors and tested them. I made the assumption that he'd looked at each in the cylinder, maybe not. It wasn't fixed, just made to run.

Otherwise the truck runs smoothly and isn't throwing any codes.

A couple more observations:
Key OFF - Nothing- normal
Key ACC - Nothing - normal
Key ON - Pump engages and continues to run, not disengaging.

Where is the easiest place to disconnect the vacuum hose from the FPR?

 

Start simple. Find the relay and swap it with a known good (buddies truck?) and see what happens.

 

Relay checks out ok.

 

Yellow arrow is the vent hose, it does not go to a vacuum source.



This may help in trouble shooting. It's a little misleading in that it seems to imply that both the "STA" and "NE" inputs to the ECM are needed to initiate the pump. Only the crank sensor signal is needed. The starter input is used for determining "starting" fuel delivery levels and may override the crank sensor input but it is not required to start the pump.

 

The pump shuts off if you unplug relay? If you're sure it's good then the next step is possible wiring or ecm problem

 

As soon as I figure out how to improv a fuel pressure gauge I'll check back with the function of the FPR.

In the meantime I'll cross my fingers its not the ECM.

 

The FPR wont change by unplugging hose from it. It vents to the air box.

 

This sounds a LOT like this all over again:

https://www.tacomaworld.com/threads...ners-and-tranny-flushes-like-bg.406953/page-4