Cranks but des not start

saltydawg2112 · Jun 11, 2015

94 Ranger 4.0 While cranking I probed the valve on the fuel rail and found no pressure. Checked the voltage to the impact switch and found no voltage there. So I went to the relay. With the key on engine off (koeo) found voltage on coil pin and contact pin. When plugging relay back in and unplugging it, I did not feel the contacts clicking. Replaced the relay but it still will not start. I jumpered the contacts at the relay and the pump will come on and I will have pressure at fuel rail. Keeping the jumper on the contacts and the pump running, pressure in the fuel rail, it still will not start. Checked the spark plugs and I do have spark. Also I noticed that the check engine lite (cel) does not come on when cranking. Can't remember if it did come on before this problem popped up. Changed the EEC relay just because I had another handy. Disconnected the negative cable to battery for awhile to see if resetting EEC module would help but still no luck and cel still does not come on. Any ideas?
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Earl43P · Jun 12, 2015

Could be the ECM Power diode.

If your CEL does not come on when you turn the key to Run (don't crank), then there is your problem. Fuel pump will never get powered until the ECM relay energizes.

http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Enginecontrols4_0_3_0_1of3.JPG

Take a look at that ^ schematic. Yours is similar.

saltydawg2112 · Jun 12, 2015

Thanks. I'm suspecting the same thing considering the negative of the fuel pump relay goes to the ecm. Just looking for any other possibilities. ECMs are kind of pricey.

RonD · Jun 12, 2015

Fuel pump power runs like this

Battery-------fuel pump fuse(30amp)------fuel pump relay---------inertia switch(impact switch)--------fuel pump

Fuel pump relay power runs like this
Battery----EEC fuse(30amp)----EEC relay-------fuel pump relay coil---------computer------ground

If you remove the fuel pump relay, with key off, there should be one slot in the relay socket that has 12volts, that is from the fuel pump fuse.
With key on a second slot will have 12volts, that is from the EEC Relay, next to fuel pump relay, this EEC relay powers the computer(EEC/PCM/ECM), fuel injectors, spark system and fuel pump relay(not fuel pump).

yes, the computer uses the fuel pump relay's coil Ground to close relay, assuming EEC relay is closed(on) and other side of coil has 12v.
Computer ONLY grounds the fuel pump relay for 2 seconds when key is turned on, computer will not ground the relay again until RPMs are above 500(engine started), OR unless you turn the key off and then ON again, and again computer will Ground the relay for 2 seconds.
This is a safety feature in case fuel line breaks, engine would stall or engine is shut down for another reason, roll over, ect..........fuel pump power is stopped so gas doesn't continue to pump out when engine RPMs are 0

saltydawg2112 · Jun 13, 2015

Thx Ron. With this info I had my helper crank the motor while I help the fuel rail schader valve open. Did not even get a squirt of oil. If I jumper the contact out the fuel pump will run and I have fuel pressure. Double checked to ensure I had spark. Checked the resistance between the negative and ground of fuel relay coil. Found 0 ohms for a couple seconds then it increased up to about 10k ohms. Just can't figure out why I can't get fuel pressure when cranking. Tried cussing at it and threating it with a very large hammer. Picked up a voltage probe and will see if I get cel codes at eec test plug.

RonD · Jun 13, 2015

If you look here: http://www.therangerstation.com/tech_library/OBD_I.shtml

There is a diagram of the EEC test plug..........with Fuel Pump slot labelled
That slot's wire is connected to the Computers wire that goes to the Ground for the Fuel pump relay's coil.
So if key is on(FP relay coil has 12v) and you Ground that slot you should hear the Fuel pump relay "click" and fuel pump should come on, same as if computer grounded it.

saltydawg2112 · Jun 13, 2015

Grounded the fuel pump pin on the eec test connector and the relay clicked and pump ran. Also did an eec test with my voltage probe at the ees test connector. It showed nothing. My cel did not lite up and iether did my probe during crank. With the key on I pulled the eec relay and plugged back in several times and I can hear the relay click. I just hve to find the power ire to the eec to ensure there is power going to it.

saltydawg2112 · Jun 13, 2015

Correction. Did eec test with key on and not cranking

RonD · Jun 13, 2015

Good pin diagram here for EEC-IV(pre-'95) Ford computers
http://www.auto-diagnostics.info/ford_eec_iv

Cranks but des not start

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