1993 Isuzu starting problem

Hello all
I have a 1993 Isuzu pickup, 2.6L MFI engine. When ever it sits for more than 1 1/2-2 hours I need to give it a shot of starter fluid to get it to start.
It cranks fine just won’t start. I have checked for spark and I am getting it. I replaced the fuel pressure regulator and it did start correctly 1 time.
I replaced the fuel pump and it did nothing. I am going down the road of a bad fuel pressure regulator out of the box. Does anyone have any idea what this could be? I have replaced all the vacuum lines also.

The one sensor that would cause your cold start problem would be the Engine Coolant Temperature sensor. This is not the sensor for the temperature gauge or the overthem idiot light. It is the one that the ECM uses to decide how much fuel to inject for the temperature of the engine.

You can either measure the resistance of the sensor and check it against the calbrated value in the service manual for the temperature of the engine at the time or just replace the sensor on suspicion. Also, check the wiring to the ECM as a short to ground will mimick a fully hot engine signel to the ECM causing too lean injection mixture.

Hope this helps.

Also, try turning the key from Off to Run (not all the way to Start) a few times, pausing to hear the fuel pump run for a moment each time. This will bring fuel and fuel pressure to the engine. Then try to start the engine.

Could be the temp sensor as mentioned above, but my guess is that the fuel rail is leaking pressure. It can go one of two way. Either back into the gas tank, due to a faulty check valve. Or out a faulty injector into the engine. By your description, more likely it is a faulty check valve. A fuel pressure leak down test would confirm one way or the other.

I have tried the turning key to on and back off. Sometimes it works if I do it about 30 times. Unfortunatly It doesn’t have a fitting to check the fuel rail pressure. The only thing it has for a temp sensor is a thermal vacuum switch. This is old vacuum controlled mechanical fuel injection. I will try pinching off fuel lines to see if it makes the problem go away.
I’ll price a new thermal switch but I don’t want to throw parts at it.