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Topic Review (Newest First)
04-19-2013 09:55 AM
oldbogie
Quote:
Originally Posted by fleetsidebob View Post
When I turn the key to the run position, the fuel pump runs for a couple of seconds and shuts off. I was assuming it stopped running because it was pressured up.

How can I test to see if there is actually pressure at the injectors during start up? I hate to disconnect fuel lines and have gas shooting all over the place.

The pump itself is not very accessable, but I'm wondering if I could use a clamp meter around the power wire to the fuel pump and see if we have current while the starter is turning. Would that make sense?
The pump should run from 10 to 15 seconds. What's going on is a pump shut down by the computer if in that time if the computer doesn't see the RPMs coming up from a sucessful start. Additionally, there is a relay on the firewall that can fail. You need to get a wire diagram to checck all this out. There are minor differences of how this curcuit is layed out that appear year to year, model to model.

If it's a sensing problem often the engine can be started with a prime and it will continue running, if it's a relay problem it will burn the prime then stop running.

You can force the issue by jumpering around the relay but then you've got to be sure that if the key is in run position, the engine better damn well also be actually running.

Bogie
04-19-2013 09:54 AM
joe_padavano
Quote:
Originally Posted by fleetsidebob View Post
When I turn the key to the run position, the fuel pump runs for a couple of seconds and shuts off. I was assuming it stopped running because it was pressured up.
This is normal. In a factory TBI system, there are two separate methods for operating the fuel pump. When you turn the key to START, the ECU closes the fuel pump relay for two seconds to build pressure in the system. This is the only time that the fuel pump relay is used. Once the engine is cranking and builds fuel pressure, a separate circuit closes through the oil pressure switch. This bypasses the relay and keeps the pump running whenever there is oil pressure.

Quote:
How can I test to see if there is actually pressure at the injectors during start up? I hate to disconnect fuel lines and have gas shooting all over the place.
The only way to test this is to temporarily attach a fuel pressure gauge to the test port on the fuel line to the throttle body. You should see ~15 psi when you turn the key to START. The pressure should remain there the whole time you are cranking the engine. If it drops, you have a problem someplace, like a bad check valve in the pump or a bad pressure regulator.

Quote:
The pump itself is not very accessable, but I'm wondering if I could use a clamp meter around the power wire to the fuel pump and see if we have current while the starter is turning. Would that make sense?
No. See above. If the problem is a check valve the pump will run but you won't maintain pressure in the system, so an ammeter won't help.
04-19-2013 09:38 AM
fleetsidebob I take it that the pick up coil is actually inside the distributor cap and that it is different from the external coil? When you speak of replacing the module, are you talking about the pick up coil?
04-18-2013 09:18 PM
fleetsidebob Wow, that is some pretty heavy advice. I have a grasp of what you guys are telling me, but you certainly have the technology down better than I do. I'll try the test bulb and see if I am getting the signal.

Thanks to everyone for sharing your knowledge and talents. I'll let you know how it turns out.

Fleetsidebob
04-18-2013 06:01 PM
LATECH If this were mine, I would try another Ignition module.
04-18-2013 05:59 PM
LATECH Here is a pinout on the 8 pin HEI/EFI module for TBI setups with small cap dizzy
04-18-2013 05:54 PM
LATECH Yes...the module handles the signal from the pickup coil, and when cranking ...the ecm sends a 5 volt signal to the module to "bypass" the computer and fire the ignition on its base timing, leaving the signal to the ECM to fire the injectors. In bypass mode I have seen that circuit fail to run the injectors, but once the engine starts and the key is in run , the bypass voltage goes away and the module is now in the run mode and runs from the reluctor signal passed through the module then to the ECM and then back to the module.I Know ...confusing.
Anway...injector pulse is checked at the injector connectors. There is a positive and a ground which is the on/off side of the injector circuit. THAT signal is provided by the ECM which gets it from the distributor Module.
Check for injector pulse by using a small bulb like a 194 . Use a buld and socket with 2 leads, shove the 2 leads into the connector for each injector and crank the engine. If they flash on and off as the engine turns
over then the pulse is fine.If not...that will be the trouble
04-18-2013 05:41 PM
ssmonty FWIW,
I'm pretty sure that the computer(ECM) gets a signal from the distributor's reluctor while cranking to tell the computer to pulse the injectors. Its not a large (less than +5V) pulse that comes from the reluctor. I believe it goes to the ignition module, is amplified, then goes to the ECM, but I'm not certain the module is involved.
Which ever route it takes, a signal gets to the computer from the distributor, sort of like a tach, and the computer pulses the injectors.
Look closely at the reluctor's magnets for cracks, wires/terminals for corrosion, wobbly distributor shaft, and corroded ignition module terminals. A little rust can reduce the signal level enough that its not efective until the running voltage(+14V) increases the amplification just enough to trigger the module or ECM.
There are many different distributors on computer controlled ingnitions. Are you certain the one you have is correct for the harness or ECM?
Hope it helps more than it confuses.
ssmonty
04-18-2013 04:55 PM
LATECH Check injector pulse with a noid light. Dont use a test light as the bulb could draw to much current and burn the injector driver out in the ECM.
You can also use a logic probe (red/green LED test light type deal). They are safe as they draw virtually no current.
04-18-2013 04:53 PM
fleetsidebob Actually, I have a spare ECM so I might try that. In fact, I might first try switching the PROM from the spare to the one in it now to see if that is the problem.
When you suggest check for injector pulse, are you saying check for injector fuel flow to the TB, or are you speaking of an electrical pulse? If so, how would I check that?

PS, I like your 64 Tempest. That was my first car.
04-18-2013 04:27 PM
fleetsidebob Yes I am running a stock ECM although not the one that came from the donor car. That vehicle had the theft deterent system. I replaced the ECM with one from a late 80's truck that didn't have the feature. It coincided with the ECM that Painless said I needed.

The funny thing is that I'm pretty sure the pump is working. I just think the injectors aren't getting a signal to pass the fuel on to the TB. How do I check and/or correct that?

Bob
04-18-2013 04:22 PM
LATECH 2 things: as suggested check for fuel pump running when cranking
Also check for injector pulse while cranking

my guess is no injector pulse while cranking
I had one several years back that the module was bad and wouldnt fire the injectors but would fire the coil.
One other time It was a bad pickup coil...but did the same thing.
I would try a module first if there is no injector pulse.
04-18-2013 03:51 PM
64nailhead I assume you're running the stock ECM. Sounds like the pump is not running during cranking. A quick way to check it is jump power to the pump prior to cranking (for a second or two), and then begin cranking. If it starts, then that is the case.

I have to admit, that I don't know what controls the pump during cranking, but I'm sure I can find out. It must be either the ECM or oil pressure sensor. At least I think.

Someone else on this forum must know. I'm sure someone will chime in.

Good Luck - Jim
04-18-2013 02:59 PM
fleetsidebob yes, I did plumb in a return line. I'll check for power. I'm thinking that the pump might be pumping but the injectors are not getting the command to inject while starting. I'll see if I can check for power to the injectors while starting too.
04-18-2013 02:06 PM
richard stewart 3rd Hi
When you put this together did you run a return line from the throttle body back to the tank?
You can attach a meter to the hot going to the pump at the relay to check for power while trying to start it.

Rich
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