This is a little long but here goes. I have a 1993 pick up X cab with the 3VZE engine. It was extremely overheated and had to be replaced. It was running well at the time. I replaced it with a known good used engine and after replacement will not stay running. Key on, the fuel pump is running and the truck starts right away but stalls immediately. I've tried jumping the FP and B+ terminals but it still doesn't stay running. I've also opened the vane in the VAFM and that did not work either. I even jumped the FP port straight to the battery and it does the same thing. When it starts it sounds perfect so I do not think there are any mechanical issues. Considering this, are there any fuses to look for or fault codes that would prevent the truck from starting? Or are there any other suggestions? There are many other threads as you all know and I have read a lot of them.

 

Here's what I know about the VAF-COR circuit: https://www.yotatech.com/forums/f116...-quits-312747/
I would expect that jumpering FP to B+ would rule all of that out. But just for fun, measure the voltage to ground at FP, then open the VAF vane with key-on (not start). The voltage should go to battery with the vane open; if not you could have an open coil in the COR.

If you have a connection problem with IGF (igniter) to ECM, the ECM is supposed to stop the injectors after 6 revolutions. That is supposed to throw Code 14. (You don't have any codes, do you?)

 

I have not checked for codes yet but I will tomorrow and open the vane to see if there is voltage. I know for sure that the vane opens freely and the truck starts immediately. Thanks for the information. This truck is driving me nuts.

 

Opened the vane and I have power to the FP. Code 24 but that can be just from trying to start it with the unit unplugged.

 

Am I looking for a ground?

 

Am I looking for a ground?

 

You could try disconnecting the fuel return line from the Fuel Pressure regulator, and replace it with a 6mm/1/4" clear vinyl tube to a suitable container. First, try jumpering FP to B+ to run the pump. There is no spec, but I get about 1/2 liter/min. If that seems okay, pull the jumper and try starting it. If you keep getting return flow until right after the engine dies, then fuel pressure is not your issue. But if the flow stops before the engine dies, then you don't have enough flow/pressure to keep it running.

Be careful, especially with the second test. Don't splash gasoline onto an engine with live ignition.

 

I'll give it a try thanks

 

I checked for return pressure like you said. The flow is steady jumping Fp and B+ but I do not know what the correct flow should be. It flows during start but obviously stops when the engine dies. Approximately 2 seconds. The main and cor relays seem to be working correctly as they click when excited. The main problem I have is that the car ran before this engine was replaced. The battery was removed first and replaced last so there should have not been any electrical problems. Leads me to a fuel problem with really no way to check pressure. If I spray accelerant in the vent tube, it runs.

 

Are you saying you’re jumping Fp and B+, then starting it and it will stall with no more fuel flow through the return line after two seconds?

 

No I had fuel flow with the fp jumped and also when it starts until stall which is about 2 seconds.

 

Start it with the jumper across Fp and B+. See if it stays running.

 

it does not stay running

 

If the key is ON with Fp and B+ jumped and the pump isn’t running indefinitely then I’d think the pump or associated wiring given everything else you verified. Did you check all the components according to the link provided?

 

The pump is running (at least most of the time) because he is able to start it. If the fuel flow stops sorta-after the engine stops, that's because the lack of air flow through the VAF allowed the FC switch to open, opening the COR, stopping the pump. What I was thinking of is if the fuel flow stopped sorta-before the engine quit, it might be the cause of the engine quitting.

So I don't think you have a COR-VAF or other fuel flow problem. You might have a stuck-closed injector (or several). The engine starts with the fuel from the CSI, but that shuts off when the key moves from start. Try disconnecting the CSI electrical feed and see if that makes a difference.

 

The fuel pump runs jumping the Fp and B+ constant but does not run after start. The engine starts and runs smooth for 2 seconds and shuts off. Also, the original engine did run with the exception of a cracked head. All I did was transfer parts from that engine to this one. I will check the CSI tomorrow. Thanks for all the help.

 

Definately sound like the COR Run side. It has 2 sides, Start and Run. Essentially 2 relays in one body. Absolutly an essential system for yor safety. It stops the fuel pump instantly if the engine stops. Like in an accident. Keeps you from developing a nice puddle of spilled fuel in an accident, threatening both you And the first responders with a nice toasty fire. HUGELY important safety system.

Pat☺

 

First of all thanks for your and your families service. I did all the checks on the COR relay and it appears to be working correctly. Does the fuel pump circuit rely on power or does it rely on the ground side? My 35 years experience is mostly GM which is totally different than Toyota. Similar but less complex. The injectors were taken from the replacement engine and the left side stayed untouched while the right side injectors were removed form the current fuel rail and the newer ones put in place with new seals. I didn't want to disturb the current fuel line on that side. I will unplug the CSI and see if that makes a difference. a lot of questions sorry.

 

I unplugged the CSI and the truck turns over and will not start. Plugged it back in and it starts and stalls.

 

What that "points to" is no fuel through the injectors (you're starting with CSI fuel, which cuts off with key-to-on.)

Remember that the injectors are opened when the ECM grounds one lead. So if you measure either side of the injector to ground with key-on, you'll get battery voltage. You could try a "noid" light to see if you get flickering. You could try checking the igniter for obvious harness damage. If the IGT signal doesn't make it to the ECM, I don't think the ECM knows when to open the injectors.