Explorer swap fuel question

[76Bronko]

Hello all,

I have a 76, 2001 Explorer swap, EFI Guy harness, that's getting pretty close to being done.

My engine only runs for about 5-10 seconds, and then it dies. It's either a fuel pressure issue or a lack of an exhaust issue. My fuel system is a 23 gallon tank, with the fuel pump inside the tank. I am running a supply and return line. I put a 96 Explorer fuel rail on the engine, because I wanted to use a in rail fuel pressure regulator. I get 65 psi of pressure when I test the fuel rail pressure.
The only computer mods I have had done are PATS delete. I kept the stock EGR and emission ECM programming functions, they weren't deleted.

I do get a 3 second fuel pump activation from the in tank pump when I turn the key, and the motor does fire up, but it dies after a few seconds. I can't tell if it's dying because it's losing fuel pressure or if it's because it has no exhaust system on it other than headers, and having no O2 sensor data getting back to the ECM.

I would think that at worse case, the ECM would still be able to keep the engine running in limp mode, without any O2 sensor data, but I'm not sure.

Also, if the problem isn't exhaust related, do I need to have my ECM reprogrammed to not look for the stock in tank fuel pressure sensor, or hace any code written to have the computer always keep the fuel pump on?

Thank you all for your thoughts. Mel

 

[ntsqd]

Doubt it's exhaust related since O2's don't do much when cold. Engine should be in open loop on start-up.

Does your fuel pump have power while the engine is running?

 

[76Bronko]

I will try to check that. Just disconnect the connector to my fuel pump, and see if I'm still getting 12Vs from the computer when I'm cranking the engine over?

Thank you

 

[ntsqd]

I don't know what your system is using to turn off the fuel pump in the event of a crash. The two most common are an inertia switch or an oil pressure switch. If it is an oil pressure switch then you might try temporarily by-passing it to see if the engine will stay running.
It may be easier to put a test light in parallel with the pump. If the light is on then the pump has power, but this needs to be checked with the engine running.

 

[66broncoCT]

It should run fine with no exhaust. I ran mine that way long enough to almost get up to temperature a couple of time when I was doing my swap. It’s loud but runs.
It sounds like you are losing power to the fuel pump or maybe to the ECM. Where are you getting key-on power from? If you are getting the fuel prime when turning on the key then it is not the inertia switch as that interrupts power after the ECM. Who reprogrammed the computer? If it was efi guy then it should be ready to run don’t worry about your different fuel setup the computer doesn’t care as long as it’s getting the right fuel pressure to run.

 

[Broncobowsher]

Might be an airflow issue as well.
Unplug the MAF, it will be in limp, should start and run fairly well. A bad signal from a MAF will make it run bad/stall/bad stuff. No signal, the computer just runs without it. No signal is better than a bad signal.

 

[76Bronko]

I'm using the inertia switch. I will unplug the MAF sensor and see what it does here shortly. Thanks guys

 

[76Bronko]

I unplugged the MAF and nothing changed (stalled out after 5-10 seconds). Tomorrow I will try to see if the pump is getting voltage from the ECM after the initial prime signal. Thanks everyone

 

[onpier55]

Put a fuel pressure gage on the fuel rail to see what’s it’s doing when it dies. Then You can rule out the fuel pressure as the issue.

 

[73azbronco]

what is your engine off voltage on battery? What is voltage with engine/alt on?

 

[EFI Guy]

After the initial prime, the PCM commands the fuel pump anytime a crank signal is present. Since it runs, I'd say the crank signal is good, and since it primes, your wiring is likely okay.
This sounds like an Idle air problem, but I would not waste time trying to diagnose anything without the exhaust hooked up. I doubt that it has adapted enough to cause your problem, but it can definitely begin to use O2 feedback without being up to operating temp. It just won't apply those values to long-term until it's up to temp. I wouldn't want my fresh build to be getting an extra 25-35% of fuel.

 

[76Bronko]

The exhaust is in and I couldn't be happier with it. One minor hiccup is that the O2 sensors are farther back rearward than stock and I'll need some oxygen sensor extensions. Can anyone confirm that the O2 sensors are: passenger side, precat B1PS, post cat HO23. Drivers side precat B2DS, post cat HO24?

Thanks guys

 

[ntsqd]

Why are you keeping the post-Cat O2's?

 

[76Bronko]

Mostly just for driveability and gas mileage. I believe the post cat O2 sensors give additional feedback to the ECM.

I also kept the EGR system to help with cold starting.

It's my first Explorer swap, so I don't necessarily have any experience to go by.

 

[ntsqd]

As I understand it, the post cat O2's mostly tell the ECM how well the cats are working. All of the AFR etc. adjustments are based off the pre cat O2's.

I'd keep the EGR too.

 

[73azbronco]

Post cat monitors cat efficiency, does not control fuel trim.

 

[76Bronko]

Thanks for the knowledge guys. Summit Racing had oxygen sensor harness extensions in stock, so all of my O2 sensors are hooked up now. I let the engine run for about 2 minutes, and I could tell the ECM was trying to relearn everything. Will give it a fresh oil change and top off the coolant and ATF. Then let it have a few more heat cycles. Hoping to let it run for a half hour or so after that.

Thanks. Mel

 

[76Bronko]

Well gents....the exhausting is on and all the O2 sensors are plugged in. Pretty sure they're wired up in the correct spots, but it's never been confirmed.

I have 20 psi at the fuel rail Schrader valve when the pump turns on for 2 seconds when you start the ignition. I then get 60-70 psi when the engine runs.

The engine runs scary rough. Might get 15 seconds, and then it dies. Oddly enough, with the MAF sensor unhooked, it will run for 2-3 minutes before it dies, and it doesn't sound or run as scary as when the MAF sensor is hooked up.

I'm kind of stuck here. As far as I can tell, the MAF sensor tests ok with my voltmeter. I'm currently waiting for my garage air to clear out, it's that bad. I had to abandon ship after 2 minutes lol. Super toxic air.

Kind of stuck here. Any thoughts?

 

[ntsqd]

Excessive fuel pressure. Flooded rich running will do what you're describing while also washing the oil off the cyl walls, so stop that.

 

[76Bronko]

Excessive fuel pressure. Flooded rich running will do what you're describing while also washing the oil off the cyl walls, so stop that.

I think 65 psi at the fuel rail is the stock value for 2001 5.0 explorers. It's around 50 psi for 98 and below