Hi,
my 2007 GS350 is acting like the fuel sensor is shorting out ( Cranks for 1.5 seconds then will not turn over until 5v resets) However, when I unplug the fuel sensor it makes no difference. Seems like a sensor short but I would welcome input/suggestions

 

So its the actual engine starter cranking over that your having an issue with? How are you resting the 5v?

Could it be something wrong with the actual starter? if you hold down the starter button for longer then 3 seconds will it keep cranking? Or is it just not firing up the engine? Have you checked for the obvious things like gas, battery terminals, battery voltage etc?

 

Starter is fine, Battery is good, engine will start for just a second or two then die. After that I am not able to get the engine to crank over again. I also loose communication with the ECM. This lasts for about an hour then resets. After that I am able to connect to the ECM again until i hit start agan then the whole sequence of events starts again. when I am able to connect it shows 21 faults in the engine section. All faults are sensor related. I replaced the Crank sensor and Alternator. I have tried unplugging the fuel pressure reg sensor but it makes no difference. I have also unplugged multiple sensors trying to isolate the issue.

 

What 5V source are you measuring? How do you know it resets?

I place bets on either the fuel (pressure?) sensor itself or a loose ground cable. It could very well cease to conduct electricity after a few seconds because of vibrations, and then the terminal would fall back in place. Losing communication with the ECU is really strange, and I saw a similar behavior on a BMW (X5 Pine Hollow Auto Diagnostics on YouTube) except it wouldn't even start. The ground cable became brittle and cracked.

It could be the fuel pump or anything else related to fuel supply too, but everything is usually really robust.

But a problem like this will be hard to diagnose anyway. You should consider asking a mobile mechanic about this, otherwise you could throw unnecessary expensive parts at the car or spend weeks and weeks...

 

So I kept having the same issue. start for 1.5 seconds then dies. After it dies the cooling fan will kick on, engine will not turn over and the cooling fan turns on. I unplugged each sensor including the frps and it made no difference. UNTIL I got to the crank sensor. I unplugged the crank sensor and it restored ECM communications/Cranking. Bought a new crank sensor, installed and plugged it in. New crank sensor causes the same issues but as before, when I unplug it all systems are restored.

 

Did you look at a wiring diagram to see if the fuel sensor has any relation to the crank sensor? So the starting issue happen and then you replaced the alternator, and crank sensor. If you installed the alternator before the issue maybe you forgot something unplugged.

All your symptoms sounds like a bad fuel pressure sensor. See if you can buy a used one off a junk yard, I would avoid cheap china ones off ebay. New there pretty expensive, you might luck out on ebay.

The other things you can probably do is put a test light to the main power to the ecu and with a scan tool data log, fuel/idle/timing/rpm/o2 sensors/etc see getting knocked offline. A light on the ecu power can tell you when the power cuts off on the ecu. Or take it to the dealer and pay for an hours worth of diagnostics.