Will not start with key only when roll started whats wrong?

[soto 95 gsx]

Its a 95 gsx... If you roll start the car it will run and drive fine but by starting with the key it wont start it will turn over but never start. It has a optima battery which is fully charged, new battery cables and a new starter which we have only attempt to try and start it twice with it.
but heres the interesting part awhile ago this summer the car stopped starting when you turned the key nothing would happen couldnt figure out why put a new starter relay in and nothing happened still. but by bridging 2 of the wires without the starter relay in the car will start but now it will attempt to start just wont unless you roll start it.

I know thats a two part question but maybe help with either one will help me figure it out.

[JoeShmoe]

Hwo do you know they relay is good?

[soto 95 gsx]

the relay is new but still noting

[soto 95 gsx]

new starter relay

[JoeShmoe]

Well if its attempting to start but not turnover, have you checked to see if your fuel pump is any good? Worth a shot.

[soto 95 gsx]

but if the fuel pump wasent good after roll start it would not right but it does?

[JoeShmoe]

Shit, your right.........

[JoeShmoe]

When was the battery bought?

[Black99GST]

electrical problem... check for a floating voltage... anything like a ground or something simple... do you have a kill switch on your alarm? makesure that is disarmed...

[kjewer1]

I can't think of anything that would cause this. It has to be something not common to both pop starting it and roll starting it.

The ignition switch provides the start signal to the starter, power on signal to the main power distribution system, and a cranking signal to the ECU from the "start" position. The latter is the only one not common to pop starting it. But as far as I know, that really only forces timing to 5 degrees. It could also be the signal for crank fuel inject, etc, but that could also come from the fact that it starts to see RPM, not sure. I guess I would grab a meter and look for the cranking signal at the ECU to at least rule it out.

What's the compression on the motor? If it's low pop starting may turn the motor faster than the starter and give it the compression it needs to fire up. Is it starting immediately and easily on pop starting? Is someone just pushing it, or is it flying down a hill when you start it? Etc.

[JoeShmoe]

Originally Posted by Black99GST

floating voltage

Oh yeah, your battery might read 12V, doesn't mean its good. I believe you need to use a specific gravity feed IIRC.

[kjewer1]

Checking SG was done on the old batteries that needed water added periodically. On newer maintenance-free batteries, you test it under load. Most autoparts stores have the machine to do this. A battery may be able to supply 12 volts to a meter, but have no current capacity for real work like turning the motor over, so voltage drops under load. Internal resistance is the cause, usually from build of crap and byproducts on the plates. Same for terminals and wires. You may not be able to read the resistance with a meter, but when you put a couple hundred amps through it...

[soto 95 gsx]

battery was checked under a load, when its rolled started its usually down a hill but by people pushing.