You obviously have a healthy pump. Sounds like a lot of flow. I've never been big on the fuel return test. I typically do my testing with a gauge plumbed into the rail. I know they are two different tests but I find the rail pressure test results more useful. If you were to get good rail pressure readings then you could pretty well rule out fuel delivery as the issue. Sounds to me like your primary injectors are not opening and your 1 second of run time is due to your cold start injector. I believe I would start testing for signal to your injectors.

 

im not saying this is your problem, but I can tell you what caused the same symptom on my 4runner. The first time my MAF was unplugged. The second time the wire that goes from the coil to the injector area was unplugged. Had me stumped for a couple weeks only to find a wire unplugged from when I changed my valve cover gasket!

 

I'll give my 2 cents on this one. Based on the description, when you have the Fp pin jumped and ignition on, you're hearing the fuel flow in the fuel rail (pretty sure it'd have a return line like the 3.4L). Not really a spraying noise, but defo a fluid flowing noise. Jumping Fp basically is a simple test to make sure the COR and mass air flow meter are not the cause. Nothing changed, so logically it shouldn't be them unless you have multi-able problems at once. The next thing is as a been suggested, there's a "I'm running" signal sent back from the igniter and testing it is kind of a pain. In my adventure with a 3.4L, repinning, and causing problems from not checking ecu pinouts for different ecu's, the igniter can act exactly the same way as the COR and mass air flow meter problems. I'd guess the igniter would fix your problem, but don't just throw parts at it, diag it. I saw not far back that the wire color is black with yellow stripe, I think that was the same for the 3.4L. You have to do what is called back probing, basically sneaking the probe end into the back side of the connector to hit the terminal inside. The ecu connector is tricky, I think I used a paper clip. Based on the 3.4L you need to see 6 or more volts for the signal (is running) and under 6 volts when it isn't running. The two test points I was able to reach with standard leads on my multi meter on my T100 (ecu and igniter are on passenger side for my truck). You just need to find the black with yellow stripe and first check if you have good connection/wire (low oems, closer to 0 the better), test with both parts unplugged. Once you validated you have the right wire on both sides and you have good connection (say under 0-10 ohms), you'd perform the back probe test with the parts plugged in and have someone watch the meter while it cranks, fires up, and dies. It should do atleast *something* when it's running. Since you have a friend with an 88 (3.0L right?), might see if you could test your igniter on his truck, just make sure the part number is the same, or validate it interchanges online.

Good luck with the truck!

 

Man if you have a buddy with a similar model, see if he will let you swap ECUs for a minute. It takes no time to do it and you may be able to rule out a computer issue. If you have a bad ecu, troubleshooting is going to be very difficult and pointless at that. The last time I had your issue, I cheated an put my spare ecu in because I didn't have the time to really get in to it. Mine cranked first try and never looked back. Not sure what caused it but I now know I have a windshield leak on that side and wouldn't surprise me if I got a little water on mine and shorted it out.

If that ain't it and he'll allow it. Keep swapping components and see what happens. I wouldn't normally recommend something like this but If you're still having problems after this long, then desperate times call for desperate measures.

 

After giving up on this for a few months, I decided to give it another shot. I changed the fuel pressure regulator, and I'll be, the darn thing runs like a champ.
I think the old FPR was not regulating by allowing too much fuel through. Thanks to everyone for their help.

 

Thanks for the update! Glad to hear you got it figured out