Ford Repair Questions? Ask a Mechanic for Answers ASAP
We will have to pinpoint what the engine is missing.
All three of these are tested when the engine is being cranked over. There are two way of checking for fuel. Fuel pressure and fuel trigger. Both are very important and must be present for the car to start. Fuel pressure is self explanatory. You just hook up the gage and see what the reading is. Fuel trigger is check with a noid light. The injector gets unplugged and the noid light gets plugged in to the injector clip. With the engine cranking over, this light must blink. This is the signal to the injectors from the computer. You can have all the fuel pressure in the world, but it wont matter if the injector is not pulsing gas into the cylinder like it should! Compression tester, spark tester, fuel pressure gage and noid light are all accessible at your local auto store. All three tests play a very important part in diagnosing a no start condition. Be extremely careful when doing these tests.
Does the check engine light come on with the key in the on position?
Does it go off while cranking?
Lets go to the fuel pump relay and check for power with the key on. There should be two power wires that go into this relay with the key on.
Just for your info... Here is a TSB for a no start condition.
Engine - No Start Condition
Article No. 92-26-8
December 16, 1992
^ NO START - 4.9L, 5.0L, 5.8L, 7.5L - FROM CORRODED OR LOOSE WIRE SPLICE IN 12A581 WIRING ASSEMBLY ^ WIRING - 12A581 WIRING ASSEMBLY - CORRODED OR LOOSE WIRE SPLICE RESULTING IN POSSIBLE NO START LIGHT TRUCK:1987-90 BRONCO, F-150-350 SERIES
ISSUE:A no start condition may be caused by loose or corroded three-way wire splice in the # XXXXX circuit of the 12A581 wiring assembly.
ACTION:Repair the corroded or loose wire splice by using the following service procedure.
1. Disconnect the negative battery cable from the battery.
2. Locate the fuel pump relay, Figure 1. 3. Trace the # XXXXX circuit wire (yellow) from the fuel pump relay into the 12A581 wire harness. 4. Carefully cut away enough harness wrap to expose the splice (about 4 or 5 inches). 5. Examine the splice. If loose or corroded, repair as follows:
a. Cut out the bad section. b. Reconnect the wires together. c. Solder the wires with resin core electrical solder. 6. Use heat shrink tubing (WT5625) to insulate the splice. Tape (EOAZ-19628-A) and put back into the harness. 7. Reconnect the negative battery cable. 8. Test the vehicle for proper operation.
Did you use a test light or a voltmeter? What color wires did you check?
Was the key on?
NO... there is a yellow wire and a red wire that both should have power on them at this relay with the key on. Here is a wiring diagram of this circuit.
Ok... I want you to go to the EEC power relay (main relay) and check for two powers going into this relay with the key on.
This relay is is located at the air Cleaner Support Bracket, Under Plastic Shield. This relay is also in the diagram that I posted with the fuel pump relay. Look at the diagram to match up the wire colors.
THanks for the accept!
I will stick with you until this thing is fixed!
Let me know what you find!
Ok... Sure not a problem.
Talk to you soon!
Here is another picture of the fuel pump relay. The EEC relay should be very close.
The fuel pump relay has four wires: Red, Yellow, Brown, and a Tan with a light green stripe.
The EEC relay has four wires as well: Red, Yellow, Black and white with light blue stripe wire.
According to "Ford", the computer turns off the check engine light on the dash when the computer recognizes the engine rpm. Because you told me the check engine light goes off while cranking, tells me that the pick up sensor is working and the computer sees a crank signal.
Let me know!
Is this light an oil light?
Is there any check engine light on th dash when the key is turned on?
Lets do this.
Turn the key on and check for a 5 volt reference on one of the wires at the TPS sensor.
It is a three wire sensor located on the throttle body.
It will sit right across the throttle body from the where the throttle cable attaches to.
We are on the right track.
This tells me that the computer is not waking up. It is most likely missing a power or a ground. As long as the fuses are good and that the ignition switch (electrical part) is good, then we will need to go straight to the computer and check all powers and grounds there. THis can be a bit of a pain to gain access to the computer and check powers and grounds, but I will stick with you all the way.
If you want to check fuses under the hood as well as inside the car and check the ignition switch for power coming out on the correct wire/wires, then we can do that before checking the powers and grounds at the pcm.
WHat I am going to have you do, is check for power on two of the four wires at the EEC main relay with the key on.
If we have power on two of these wires with the key on, we know that ignition switch is good.
If you need a location or a wiring diagram of the EEC relay, just let me know!
The eec main relay is located At Air Cleaner Support Bracket, Under Plastic Shield
Here is a wiring diagram.
NOw, lets go to the fuel pump relay and check for power on the red wire and the yellow wire with the key on. You might have to cycle the key off, wait 10 seconds and then turn the key on to see if both of these wires are getting power when you turn the key on.
Lets go back to the EEC relay and check for power on this red wire when turning the key on and when cranking. THis is the wire that comes out of the EEC relay if this relay is engaging
This is the red wire coming off of the EEC main relay?
Does the black wire have a ground?
SO lets recap.
The two wires going into this relay have power with the key on? Yellow wire and white with a light blue stripe wire?
THe black wire has ground?
And no power coming out on the red wire?
If what you are telling me is true, you simple have a bad main relay! You will need to replace that relay with a new one. You can try to swap one from another place like the AC relay if its the same. Just be sure not to use one from a place that will cause the engine to not start like the fuel pump relay.
We need to get power to this red wire. Upon turning the key on and cranking this main relay should click suppling power to this red wire coming from the main relay.
Ok... Does this relay click when you turn the key on or when cranking the engine over?
No - Inever hear it click. In review - th two relays I have been working with that (I think) are the eec relay and the fuel pump relay. The eec relay has the following wire colors.
EEC relay - Yellow / Power alt the time
Tan w/stripe/ Power w/ key-on
Fuel pump relay = Green/ Power all the time
White or Tan
These wires are a little dis-colored
According to the diagram, the EEC relay has four wires. THey are as follows:
white/light blue stripe
UNDERHOOD VIEW In fuse box, left side of engine compartment, on top front of wheel well
I'll keep looking and try a couple of things. As you have probably noted, I'm not really very good at this electronic stuff. Send me your ideas and i'll try them out/ Thanks
I think you are doing a perfect job!
We just need to find the correct relay and check for power coming out of this relay when it clicks on the red wire.
When we are sure we are on the correct relay, we just need to run the same tests. We need to have two powers going in (When cranking), one ground, the relay should click and send out power on the forth and final wire.
Well, before you run a new wire, with a test light, just see if you have a good ground on that wire. Or, use a voltmeter and do a voltage drop.
Look for the relay with the four color wires that I described earlier
SOmetimes the wires fad over time. Go to the relays that you were testing and follow the wires down the harness and see if the wire colors change.
THe only other thing I can think of is checking the Vin number to be sure we are talking about the same vehicle. (Year and model).
Well, keep trying! It will sure feel good when we get to the bottom of this thing!
Let me know if you have any further questions!
Glad to hear its fixed!