spark? Maybe fuel issue?

[outkastracing]

alright well i just did a r&r of a 6 bolt in a 91 talon awd after everything got it going went to drive it and it straight falls on its face like massive fuel loss or loosing spark! so in testing the circuits i found the fuel pump has no power on the black wire with the white stripe so we decided to do the fuel pump rewire to see if that helps well no it does not. so we took a 12v wire straight from the battery to the fuel pump and the fuel pump is working! so my question is what could it be im completely out of ideas? we've even taken my mpi out of my car to try in this one, also swapped ecus and still nothing ive worked on this thing all day and im done so please help me with ideas!

 

[ilikespeeding]

Bust out a multimeter. Figure out where the source of the power loss is. See if you're getting power to the relay, then after the relay.

 

[luv2rallye]

FP relay is only activated (by ECU) while cranking and getting spark. It does not activate with just key on with engine not running.

 

[outkastracing]

ok thanks so what would cause this thing to just flat fall on its face??? i know its getting fuel because it starts everytime it just is like running out??? has anyone had a problem like this before??? new air filter, new fuel filter, new spark plugs ngk. ive replaced all this!

 

[ilikespeeding]

FP relay is only activated (by ECU) while cranking and getting spark. It does not activate with just key on with engine not running.

Should be active when the car is in the on position for about 3 seconds. The system has to prime.

Any noises coming from your fuel pump when the pump is priming?

 

[spyderturbo007]

The only way you can turn the FP on without starting the car is with DSMLink. As luv2rallye said, the ECU won't energize the fuel pump until it receives feedback from the CAS.

 

[luv2rallye]

Fuel system in dsm's need to maintain pressure (even for hours after turning off). You might try measuring the fuel pressure at the fuel rail while cranking. A leaky fuel pressure regulator would affect this (sometimes even a leaky fuel cap).

ilikespeeding: Although most other cars prime their FP when key is turned to ON, the 1g's and 2g turbos do not (2g NT does however). Many people have this wrong because they hear a click. The click you hear when key is turned to ON is the MPI relay and IAC, not the FP relay. The ECU (pin 8 on 2g, 56 on 1g) gets pulled low to provide the FP relay ground (which activates it) when the ECU detects the coil firing. This statagy I'm sure was for safety reasons in a crash. Fuel pressure is expected to last for hours (even days sometimes) so fuel will be there when starting. If it isn't, it will be very quickly when FP kicks in, since fuel is still in the lines so slightest pressure will start it moving immediately. Of course if the FPR is faulty the correct fuel rail pressure would not be there so engine could die and it would dissipate quickly when turned off.
If you don't believe fuel pressure stays there on a properly working dsm, just try disconnecting the fuel connection to the fuel rail a few hours after you turn it off and you will get convinced very quickly. This is why one should always twist fuel cap off/on before disconnecting any fuel lines to relieve the pressure.

 

[outkastracing]

so i know that the fuel pump is coming on!!! i can hear it and the car runs but when the car is running and you rev it up and wait 10-15 sec the car starts to say idle down!!!! and thats even though you dont take your foot off the gas! so my question is could it be a spark issue or are you guys saying more that it could be the pressure regulator??? has anyone had a problem like this before??? and also could this be a bad cas???? im curious because i got a spare maybe i should try that????