420a no start....possible fuel system problem

[VelocitàPaola]

Read this post for more ECU-diagnosing tips...
http://www.dsmtuners.com/forums/showpost.php?p=151008846&postcount=16

Read this post... you're looking for a +9V signal at the CMPS and CKPS sensors.

 

[DSMcrazy3]

I tested my cam sensor to tell whether or not my ECU was blown. I don't remember which of the wires it is, but one of them should be a 5v signal. The other of course is the 9v.

*Just so when he see's less than 9v on one he won't worry*

 

[Talon ESI-T]

Wow, sorry guys been away for a lil bit.

Ok most of the info is in this thread and its good. So let me recap to just make searchng a bit easier.

ECU's are known to fail, symptoms include poor running and idle performance. They also include the momentary dieing condition where the car cools off and restarts. Here are some things to test before buying a new ECU and Help out troubleshooting a No start.

1. Fuel pump prime and pressure. As you know the fuel pump should prime for a second or so when the key is turned on. You might not be able to hear it, i have one thats silent. So the next best way is to take out the gas cap and have a friend listen. Make sure the key is off for 2-3 seconds, then turn it on. No sound? Test for power then.

To test for power at the fuel pump you need a test light. If you unplug the connector by the fuel lines on the passenger side of the gas tank, there will be 2 wires there. One is ground and one is positive. Connect each probe of the test light to each and turn the key on or in the start position. The test light should light up. No power? Test the relay.

To test the relay you can do one of 2 things. You can jumper the pins to feed 12v+ to the pump and try to start it or you can test it per the haynes manual, this i dont trust because all the haynes has you testing is the small coil in the relay, the contacts can flash over causing the relay to not allow current to the fuel pump. Ok you can also replace it with a known good one, so there are 3 things to try. Depending on your level of expertise, you decide the one that fits you. I choose the industry standard approach.

The fuel relay has 4 wires. ECU wire, 2-12V+ wires, and the fuel pump wire. When you turn the key on, the 2 12V+ wires should have 12v+. The ECU wire should get a neg pulse for about a couple secs. If your not getting the 12V+ on 2 wires then you have an issue relating to fuses or fuseable links. If the ECU is not providing a NEG pulse on the ECU wire then you might have a bad ECU. The fuel pump wire which is the rearmost pin will test like a ground wire so dont confuse that with the ECU wire.



Next thing to test to narrow down the ECU failure are the outputs. The ECU has 2 regulated voltage outputs. The ECU puts out 5v and 9v, the 12v output of the ECU is not regulated. At your cam and crank sensor you will have three wires. Ground, 5v, and 9v. Test for each. if one is missing then you have a harness issue or poss bad ECU.

Test for injector pulse. Each injector has 2 wires. You guessed it, one is ground one is 12v+. With the key on and cranking you will have 12v on the green/red wire. if your 95 has different colors or the wiring is black from age, the 12v wire will be the thicker of the two. Make sure you have 12v there. if you dont then you may have a ASD relay failure. If you do the use a testlight on both those wires (clip to one wire and probe to the other) to see if the testlight will flicker during cranking.

One ore thing before you head out to buy another ECU. What about spark? Do you have 12v on the middle wire of the coil pack electrical harness? you should. Do you have spark?

Now if you dont have 12v at the coil pack and injectors then lets test the ASD too. Just like the Fuel pump relay the ASD will have 2-12v wires, an ECU wire, and the last wire will go to the injectors and other accys. With the key on for a few secs the 12v wires should show voltage. One will stay on as long as the key is on (at least on my 97 it does). Test to see if the ECU is sendign a neg signal on the ECU wire when the key is first turned on. The ECU will shut off the ASD relay if the car is not started after a few moments so dont be surprised if the signal goes away shortly after turning the key. If the ECU wire tests ok then plug the relay in and turn it upside down. Test the last wire that feeds the accys for 12v+ while someone turns the key to the on position. Dont know what wire it is? Use process of elimination to find it. If you found the 2-12v wires and the ECU wire then the last one is the accy wire.

On ECU's i have seen take a dive like this, (my 96 would die intermittantly) the 5v or 9v regulated output would crap out. No fuel pump Neg signal from the ECU. No spark signal from the ECU.

Terry

Now normally i would provide you with wire colors to test. Since you know more about what your doing i feel safe explaining this to you in this manner. This winter I have a lot of writeups to complete. Testing of components is a great deal of it. Paul, i will be sending them to you to post here and I will be placing them at 2gnt as well.

For those of you that took time to read this, I appreciate it and give you a lot of credit.

 

[VelocitàPaola]

Paul, i will be sending them to you to post here and I will be placing them at 2gnt as well.

Thanks Terry. I'm trying to get together a comprehensive 420A FAQ over here, and I'm sure your contributions will be invaluable.

 

[1995eclipserst]

i have a 1995 eclipse rs and the fuel pump will not turn on and i have no fire from the ignition both relay's are good and the fuel pump runs on a 12v source please help