PhoenixFirebird

iTrader: (2)

In an attempt to start up my recently finished 385 TPI build, I noticed that with key on, not cranking, moving the distributor primes the fuel pump. As well as a few relays clicking. Any idea what would cause this? Only tried a few times, but couldn't get it fired up. Would this be related at all?

Tuned Performance

iTrader: (92)

the ecm does the 2 second prime and controls the fuel pump relay when the key goes to the accessory position I would suspect the ecm ground behind the passengers cylinder head.

PhoenixFirebird

iTrader: (2)

Do you think bad ground? Why would turning the distributor to a certain point kick the fuel pump back on? Related to the car not starting up for can break in?

KMdoza7

iTrader: (1)

this is totally normal for your fuel pump to prime when you turn your dizzy. your car isnt starting because your dizzy is alittle off im assuming

Tuned Performance

iTrader: (92)

The ecm controls the fuel pump relay when it is first powered on for 2 seconds. I was thinking when you were moving the distributor it was moving the harness and the ground was making a poor connection resetting the ecm causing it to reprise the fuel system. Just a guess

PhoenixFirebird

iTrader: (2)

We didn't really try to start it too much before, but when we noticed that, we thought it may be an issue, so we stopped for the night. I never noticed it beforehand. I should have mentioned, the rails don't hold fuel pressure anymore. Replaced the fuel pump, and by process of elimination it appears to have a bad check valve. But with the pump on, its a steady 40-45 psi.

Berlinetta00

If the computer senses a change in the magneto position in the distributor (indicating that the engine is running) it would send a signal to the fuel pump to activate if the rail pressure is below a preset threshold. When you are turning the distributor by hand, the computer is sensing the same thing as the engine running (in a sense) and because your fuel check valve was not holding pressure in the rails, the fuel pump is activated.

Tuned Performance

iTrader: (92)

the ecm controls the fuel pump for the 2 second prime, the ops when 4 psi of oil pressure is reached powers the fuel pump. Are you saying DRP will cause the ecm to activate the pump ?

BigBadLou

iTrader: (3)

Ok, it is time for the right answer.
The ECM controls the fuel pump based on the DRP signal from the distributor's pickup coil. Every pulse from the pickup coil resets the fuel pump ECM countdown timer to 2 seconds.

So if you turn the distributor enough to generate a pulse from the pickup coil, the ECM will activate the fuel pump for 2 seconds and if you keep turning the distributor back-n-forth, the pump won't shut off because the ECM sees pulses and assumes that the engine is turning.
(Warning: do not try this because the ECM will also be injecting fuel into the intake manifold, causing a dangerous buildup of gasoline vapors)

Also, our cars do not have any fuel pressure sensors so the ECM does not activate the fuel pump conditionally. It activates it every time it gets a signal from the pickup coil.

Hope this helps clear things up.
Lou

vetteoz

iTrader: (13)

As BigLou states
From the well publicized L-98 Engine Start Sequence
Initial Crank Action:

If you then rotate the key to the start position the engine will rotate.
Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run. The distributor will send a string of pulses to the ECM
in response to the engine being rotated by the starter. These pulses continue as long as the engine turns (both starting and running) and if they are not present,
the engine will not run.

ECM Reaction:

If the ECM sees the reference pulses from the distributor, it will energize the injector drivers which will begin pulsing the injectors on for 4 ms periods.
The ECM will also pull in the fuel pump relay paralleling it electrically with the oil pressure switch to run the fuel pump.
The ECM also monitors the TPS. If it sees appreciably more than 0.54 volts, it will assume the engine is flooded and the driver has pressed the accelerator
to the floor to clear the flooded condition and will restrict the fuel flow as a result.

Assuming the ignition module is good the engine will “catch”.

Tuned Performance

iTrader: (92)

I know the 89 tune take 8 Drp at 400 rpm or higher to pulse the injectors and previous tpi tunes will pulse right away. How fast are you rotating your distributor back and forth with the key on to make a magnetic pulse I learned something new today had now idea the ecm had control other than the 2 second prime and fp voltage monitor .

vetteoz

iTrader: (13)

One could consider the pump relay power as the "Primary" supply and the direct feed from the OP switch as the "Secondary" supply
even though both are active when the engine is running

BigBadLou

iTrader: (3)

I usually explain it the way that the OP switch is a "backup" system so that the driver does not get stranded in the middle of nowhere because a $5 relay failed.
Obviously that is an ignorant explanation (on my side) since there are myriad other reasons why our cars get stranded on the side of the road every day.

Cheers
Lou

PhoenixFirebird

iTrader: (2)

So if one were to continuously crank the motor over with no start, is it causing itself a flooded condition? If the fuel pump is on continuously and the injectors are spraying, and its not catching fire, that would lead me to think the fuel is just flooding it. The reason I ask is that it feels like it wants to fire the first few series of cranking. After that, it won't even attempt to start. The wideband then reads 11-12 AFR. I plan on messing around with it a bit more tonight.

BigBadLou

iTrader: (3)

Not a flooded condition (fuel passes through the engine).
As long as the pickup coil is generating the DRP signal, the ECM will keep injecting fuel. Just like when you normally try to start.

Have you checked that the distributor is not 180 degrees off? That's the first thing I ask when I hear "it almost catches". Happens to the best of us (but I am not admitting anything).

Lou

PhoenixFirebird

iTrader: (2)

Updating this after messing with it tonight. It is indeed fuel related. Oil has fuel in it, plugs are wet, and by switching off the fuel pump, the motor will fire on the existing fuel. Multiple plugs are wet. Ideas? As far as I know, everything is hooked up correctly. The tune is an ARAP .bin, with injector parameters changed to match the 30lb injectors that are in it. Ideas on this or steps to take? First idea is to put in the 19lb injectors for the cam break in, re-flash a chip for the 19lb injectors, and see if that helps. I'm not sure on the condition of the injectors, they were purchased used off TGO. Thanks for all the help thus far.