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2G No fuel in #3 or #4

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Jacob_Barnes520GST

5+ Year Contributor
100
8
Feb 21, 2018
Tucson, Arizona
Heres an interesting one, I replaced my throttle body today with new gaskets, and all of a sudden I have no fuel in 3 and 4. I pulled the plugs and 1 and 2 were wet but 3 and 4 were dry. Can anyone give me an idea why the injectors aren’t pulsing? The car will try to start after the first few cranks but then won’t do anything
 
I have completely re wired the cas to the ecu using known good wires and soldering them together, to the same effect. I disconnected the ecu before swapping throttle bodies, and have tested multiple known good ecus as well. I suspected the CAS, so I replaced it to no avail. I have also tested the signal coming out of the cas and it appears to be working correctly. I’m using the 2Ga CAS that’s underneath the intake cam gear (which by the way is a pain to replace/adjust).
 
Are you showing rpm when you are cranking the engine? are you sure the wires arent backwards for the cas signal? Im running out of ideas.
 
Okay then that rules out the wiring to the CPS and the CAS then. When I was cranking I had 2.4 volts at the CPS. I have a 1G CAS on the way with the adapter harness which will go on when it gets here. If the CPS and the CAS are tested good, what else could be the problem?
 
Let’s stop shotgunning parts for a moment and get to the bottom of this one. Lol.
I’m going to message you my number, text me, and we’ll get this sorted out.
In the meantime, here are circuit diagrams for injectors, crank sensor, and cam sensor...

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2.5v is normal when not cranking (since there's a 5v voltage divider inside the ECU). When cranking you have pulses but you should read a voltage average between 0.4-4.0v (mine reads 2.4v).
Not so, the 2.5 comes from the sensor landing on either a gap or a tooth and sitting there with the engine not running, the ecu chipset uses 5v logic circuitry.
 
Not so, the 2.5 comes from the sensor landing on either a gap or a tooth and sitting there with the engine not running, the ecu chipset uses 5v logic circuitry.
Yes thanx, you are correct. I was thinking of the around 2.5v average you get when engine is running but I worded it all wrong. Also now looking again at the internal ECU circuit diagrams (for the CPS or CAS signal input) I see a tie up resistor to +5v and another resistor going off somewhere unknown, and I made an invalid assumption that it was a voltage divider. However the resistor going off is just a series resistor to other input circuitry - not a voltage divider. So the key on, engine not rotating voltage on the CPS (or CAS) is most likely either +5v or 0v depending on whether the Hall Effect sensor is opposite a gap or not gap (fyi not gap is a blade present section in the 2g CPS) as motomattx says.
 
I’m still stumped where the 2.5 volts at rest comes in. Should be 0 or 5 at rest, no exceptions..
Unplug crank sensor and voltage should be 5V. As said before, if not 5v there’s def something screwy going on.

In my opinion. 2.5v plugged in, not cranking tells me there should be something wrong.
Unless I’m missing something. A Hall effect sensor is nothing more than a switch. —> So if it’s not 5V or 0v when you test signal to ground. That tells me there’s current flowing and something’s taking my voltage away. Those resistors in the PCM have got to be some sort of current protection. Nothing more.


Edit: I am not sure how the crank sensor signal’s input would shut off cyl 3 and 4 fuel when there not even a pair cylinder and we’re a waste spark setup. But I can’t imagine anything goin very well if the voltage signal to the pcm isn’t correct.
 
Here’s good news

I installed a 1g CAS and the adapter harness tonight, and it runs on all 4! I think when I installed the sensor I installed it out of time, because it sounds like the timing is retarded. Idles smoothly but stumbles when revved.
 
I’m still stumped where the 2.5 volts at rest comes in. Should be 0 or 5 at rest, no exceptions..
Unplug crank sensor and voltage should be 5V. As said before, if not 5v there’s def something screwy going on.

In my opinion. 2.5v plugged in, not cranking tells me there should be something wrong.
Unless I’m missing something. A Hall effect sensor is nothing more than a switch. —> So if it’s not 5V or 0v when you test signal to ground. That tells me there’s current flowing and something’s taking my voltage away. Those resistors in the PCM have got to be some sort of current protection. Nothing more.


Edit: I am not sure how the crank sensor signal’s input would shut off cyl 3 and 4 fuel when there not even a pair cylinder and we’re a waste spark setup. But I can’t imagine anything goin very well if the voltage signal to the pcm isn’t correct.
The ecu uses a pull up resistor on that input.
 
Small update. Car has a nasty boost leak, and still needs to be timed correctly after the new CAS was put in. Starts and idles, but has a nasty surge. I want to thank everybody that took the time to help me on this. I will post another update when it is back to normal.
 
Pull up resistor? *learning*


Let’s say you have an ECU with one pin configured as an input. If there is nothing connected to the pin and your program reads the state of the pin, will it be high (pulled to VCC) or low (pulled to ground)? It is difficult to tell. This phenomena is referred to as floating. To prevent this unknown state, a pull-up or pull-down resistor will ensure that the pin is in either a high or low state, while also using a low amount of current.
 
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