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1988 Ford Thunderbird Won't Start - Fuel System
Question: After replacing the fuel pump and regulator I still have good pressure and flow, but when the key is turned to the ON position you can hear the fuel pump run anywhere from a couple seconds to 90 seconds depending how long it has been since the car was shut off. During this time the car will not fire. Once the fuel pump quits running, the car will start immediately.
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Technican: Hello, Thinking out loud it is the check valve in the fuel pump that is responsible for maintaining fuel rail residual pressure to facilitate engine restart with minimum crank time. The computer will command the pump to run a couple seconds to rebuild the fuel pressure so that the injectors will work.
What engine do you have, please?
Have you considered leaving a fuel line gauge connected to the rail to test pressure leakdown when you turn the key OFF?
Is this a new problem after pump and regulator replacement, or a continuing condition?
Owner: It isn't the fuel pump check valve as I've put in two new fuel pumps. I have a fuel gauge on the car all the time now. It builds to about 35psi and fuel will flow immediately upon turning the key to Run. This happened with the original pump and two replacements. Pressure holds for 10s of seconds when the key is OFF. What seems to be happening is the control voltage to run the fuel pump continues long after the pressure has built up, and during this time I'm guessing the fuel injectors aren't operative, therefore it won't start if cranked. As soon as the pump quits running, the car will then start immediately. Beginning to think it has something to do with the Electronis Engine Control electronics or a sensor feeding it.
Technican: What engine do you have, please?
You stated "pressure holds for 10s of seconds when key is OFF"? Will you please restate that? Did you mean 10 seconds?
Your car's computer does have the driver module within it that will time the pressure initialization when the key is switched ON. Critical sensor value from the coolant temp sensor (CTS) and crank position sensor (both inputs) along with oil pressure after engine start factor when, and for how long fuel will be called for.
More when I know what we are working on. It will tell me where to look for answers.
Owner: The engine is the 3.8L V6. The pressure as measured by a fuel pressure gauge I have on the rail valve shows the fuel pressure holds at about 40psi for upwards of several minutes and then slowly bleeds down. This is similar for the original fuel pump and two replacements. I get this measurement after the pump stops running when I just turn the key to the Run position and do not start the car. Same readings if I drive the car, stop, and then watch the gauge. Even though the pump continues to run when you just turn the key to the Run position, the pressure immediately jumps to 40psi and holds. This noon after driving to work, letting the car sit in 70 degree weather for 4 1/2 hours, took almost 4 minutes for the pump to stop running after the key was turned to the Run position. Once I heard the pump stop running, I tried to start the car and it started immediately. The car will crank but not start as long as you can hear the pump running once you turn the key to the Run position. Also, once the pump stops running and you turn the key OFF instead of starting the car, the pump only runs for a couple seconds when you turn the key back to the Run position. As far as I know this Thunderbird has no crank position sensor as it has a normal distributor.
Technican: Excellent information! I'll get to work.
Owner: This morning it only took 23 seconds for the fuel pump to stop running and the car started immediately, whereas, yesterday it was close to 60 seconds. I think you're on the right track by looking at whatever controls the fuel pump, especially, when the key is turned to the Run position, but the car is not started. At this time it should make no difference to the EEC what the coolant temp, oil pressure, or vacuum is as the car isn't running.
Technican: I believe your car needs the Electronic Control Assembly (ECA) replaced. After studying The Mitchell I Auto Repair Data Base I submit the following text quote:
FUEL PUMP RELAY, THEORY OF OPERATION
"Fuel pump relay and ignition is activated by ECA when the ignition switch is in the "ON" or "CRANK" positions. When ignition is turned on, the relay is activated to supply initial line pressure to the system. The 2.3L Turbo MPFI, 2.5L CFI, 3.0L MPFI, and 3.8L MPFI (FWD) engines use an Integrated Relay Controller Module (IRCM). The IRCM incorporates the fuel pump relay."
FUEL PUMP CONTROL
"When ignition switch is turned to "ON" position, EEC power relay is energized (contacts closed). Power is provided to fuel pump relay and to and to timer in ECA. Fuel pump receives power through fuel pump relay contacts. If ignition switch is not turned to "START" position, timer in ECA will open ground circuit after approximately one second. ECC senses engine speed and shuts off fuel pump by opening ground circuit to fuel pump relay when engine stops, or when engine drops to less than 120 RPM.
Opening ground circuit de-energizes fuel pump relay (contacts opened) and de-energizes fuel pump. This function allows pressurization of fuel system. When ignition switch is turned to "START" position, ECA operates fuel pump relay to provide fuel for starting engine while cranking."
The ECA is located behind the right side kick-panel.
Your distributor uses a PROFILE IGNITION PICK-UP (PIP) with a HL EFFECT SWITCH to provide the reference signal to the ECA that a crankshaft position sensor does on engines without a distributor.
Normal fuel pressure for the 3.8L V6 is 35-45psi. I did not obtain a time window specification for fuel rail pressure leak down after the ignition is turned off.
Owner: Don't suppose they sell just an IRCM? Anyway I think you confirmed my suspicions,
sam
Technican: Well, what is key here is that the timer is intregal with the ECA. Your IRCM (fuel pump relay inside) is doing what it is told by the ECA. I don't think you need the IRCM. I want to fault the timer and that calls for an ECA.
You can always shop this. National auto parts chain stores will have rebuilt ECAs available with a core exchange. Ford will have one butprobably have to order it! Salvage yards just might have a good one (careful here). One of these sources should be able to tell you the useable-on range of years your ECA fits to help you shop.
has a parts finder link. I've used it. It works. Your request does not cost you to put the wheels in motion, several vendors will ask for your business if they have your part. They will quote their price. No obligation. No strings, and there is nothing in it for me to suggest this path to you.
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