Fuel Fuel Pressure and injectors on a 86 Stang with 3.8 TBI

JJacobs

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Feb 22, 2012
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I have to pulse on the Noid light. So you think it is the pip and I need to replace the distributor? Thought I read some where if the PIp is bad I would have no spark also. Is that true? Any Idea why the OBD! will not read codes?
 
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General karthief

wonder how much it would cost to ship you a pair
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That's the thing here, I am not familiar with the 3.8 and not finding much info here, what I did find was of little help in this situation, it will start with starting fluid so it has a fuel delivery problem, if he did the noid light test on the injectors correctly I would say he has a pip malfunction but he is also having problems with getting codes from the computer.
At this point I would replace the distributor.
 

JJacobs

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That is what I am thinking. Please bear in mid that though I am old I am at best a shade tree mechanic. So a 3.8 does have a pip in the distributor?

It did pull codes once. But I cant seem to get it to do it again after I had it run for a bit?
 

Potomus Pete

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The gas in the intake does suggest fuel/ pump. Lots of miles , does or can suggest pump. Maybe a clogged filter if never done before. I dont have any experience with the six
 

JJacobs

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Might be of help to those helping me. For some unknown reason I got it to pull codes today. Code 11 system OK and code 10 the spacer code. What do y'all think replace the distributor or try something else?
 

jrichker

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@JJacobs

1986 3.8 V6 EEC manual - it's a PDF that you can download. http://foureyedpride.com/pdfs/1986_3.8_CFI_EEC.pdf
Download the PDF reader from Adobe.com if you don't already have it on your computer. This is a 47 MB file , so it will take some time to completely download it.

Do you consistently have good spark? Yes/No
Does removing or installing the SPOUT have any effect on the spark? Yes/No.
If you have good spark with SPOUT in and out, then the PIP sensor is suspect. It can have enough output to trigger the TFI and make spark but not enough to
trigger the computer to pulse the injectors.
 
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JJacobs

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Thank you so so much. Yes I constantly have spark. So I think. I can get it running as long as I spray fuel in the throtlee body. Have not check pulling the SPOUT for spark and seeing if I can keep it runining, Can do. Will do, But why?
 

junkyardwarrior

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I used to have an 85, 3.8 CFI. Same issue, fought it for several months.

Found a wire that was rat chewed from sitting outside. I forget which wire it was, but it was a vref issue, basically I could run a separate ground and everything worked and it'd start, but once disconnected still had spark but would kill the cfi injector assembly. Also no codes could be pulled. Repaired the wire and then it started spitting out all kinds of codes, like 15 of them as I recall. Fixed the issues, drove it around a little and dumped it to a guy who needed a race car body.
 

JJacobs

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Mr Richker

And all others trying to help. Yes I have spark with the SPOUT out. It will run as long as I spray fuel in the throttle body. As I am a novice I will order and replace the entire distributor instead of just the PIP. I saw in one of your post it seems to be the way to go.

Is there a good link for distributor replacement and setting the timing I should look at and follow?

Thanks again for your time, expertise and help!

Jake
 

JJacobs

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I am completely lost. Have gone over the manual Mr. Ricker was kind enough to send me. I am afraid I do not have enough smarts or backround to fully use it as the tool it is.

Replaced the entire distributor. Thinking it was the PIP causing my injectors not to fire. Pretty sure I did it right as I can still get the car to run with fuel sprayed in the TBI.

So I went back to Mr Ricker's checklist and started over from spray fuel part. At all the test points I get right about 9 Volts. The battery is new and putting out 12 volts. So there is current but seems to be resistance somewhere. I get no reading at the pink and black wire at the fuel pump relay. Not sure what that means or where I should go from there? I can jump it and the fuel pump runs fine with good pressure at the Schrader valve. But still the injectors don't fire.

The computer was replaced about six years ago along with the fuel pump, fuel pump relay. The car has pretty much just sat since then.

I can't get the car to pull codes again. Does that, the injectors and the 9 volt reading point to the computer?
 

General karthief

wonder how much it would cost to ship you a pair
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Pull the computer out and open it up. Look for a burnt trace (the silver lines on the board will be black in places) or a swelled/leaking capacitor.
While you have it out clean the connections at the computer and the plug.
 

JJacobs

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General and any others who might have an idea.

I pulled the computer and opened it up. Not sure what exactly I should be looking for? Here are the pictures and close ups of what stood out to me. The first two are overviews. The next two with me pointing are what caught my eye, What do y'all think?
 

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jrichker

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I am completely lost. Have gone over the manual Mr. Ricker was kind enough to send me. I am afraid I do not have enough smarts or backround to fully use it as the tool it is.

Replaced the entire distributor. Thinking it was the PIP causing my injectors not to fire. Pretty sure I did it right as I can still get the car to run with fuel sprayed in the TBI.

So I went back to Mr Ricker's checklist and started over from spray fuel part. At all the test points I get right about 9 Volts. The battery is new and putting out 12 volts. So there is current but seems to be resistance somewhere. I get no reading at the pink and black wire at the fuel pump relay. Not sure what that means or where I should go from there? I can jump it and the fuel pump runs fine with good pressure at the Schrader valve. But still the injectors don't fire.

The computer was replaced about six years ago along with the fuel pump, fuel pump relay. The car has pretty much just sat since then.

I can't get the car to pull codes again. Does that, the injectors and the 9 volt reading point to the computer?
9 volts where? What wire color and stripe, what is the location of where you are probing? Was the ignition switch in the Run position?
 

JJacobs

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Feb 22, 2012
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Thanks Mr. Richker.

Yes the ignition was in the run position.

9 volts on both sides of the fuel inertia switch and at the red wires on the injectors. No volts at the pink black wire at the fuel pump relay. and 9 volts at the orange/lt blue wire at the fuel pump relay. When I say nine volts the reading were from the high eights to the low nines.

What do you think. What should I try next?
 

JJacobs

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If anyone has any ideas of what I should try next I would be very grateful. Have no Idea what to do. May have to have it towed to a garage and in theses times I can ill afford that.
 

jrichker

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The title says 87-93 but it should cover the 86 as well. If you downloaded the 1986 EVTM from the link I posted, you should have a specific diagram for your car.

Fuel Pump Troubleshooting for 87-90 Mustangs

Revised 1-Dec-2015 to add fuse links diagram.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 1-3 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the upper LH corner to ground.

Foxbody Diagnostic connector


Foxbody Diagnostic connector close up view


Turn the ignition switch on when you do this test.



If the fuse links are OK, you will have power to the pump. Check fuel pressure – remove the cap from the Schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. A tire pressure gauge can also be used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.

No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – press reset button on the inertia switch. The hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch

B.) Fuel pump power relay – located under the driver’s seat in most Mustangs built before 92. See the diagram to help identify the fuel pump relay wiring colors. Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness.
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect for fuel escaping while pump is running.

88241.gif


The electrical circuit for the fuel pump has two paths, a control path and a power path.

Control Path
The control path consists of the inertia switch, the computer, and the fuel pump relay coil. It turns the fuel pump relay on or off under computer control. The switched power (red wire) from the ECC relay goes to the inertia switch (red/black wire) then from the inertia switch to the relay coil and then from the relay coil to the computer (tan/ Lt green wire). The computer provides the ground path to complete the circuit. This ground causes the relay coil to energize and close the contacts for the power path. Keep in mind that you can have voltage to all the right places, but the computer must provide a ground. If there is no ground, the relay will not close the power contacts.


Power Path
The power path picks up from a fuse link near the starter relay. Fuse links are like fuses, except they are pieces of wire and are made right into the wiring harness. The feed wire from the fuse link (orange/ light blue wire) goes to the fuel pump relay contacts. The fuse links are in a bundle up near the starter relay; you will have to unwrap the wiring harness to find them.

Fuse links
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Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect. Fuse link material is available at most good auto parts stores. There may even be a fuse link already made up specifically for your car. Just be sure to solder the connection and cover it with heat shrink tubing.

Heat shrink tubing is available at Radio Shack or other electronics supply stores.

See the video below for help on soldering and heat shrinking wiring. There is a lot of useful help and hints if you don’t do automotive electrical work all the time.

View: http://youtu.be/uaYdCRjDr4A


When the contacts close because the relay energizes, the power flows through the contacts to the fuel pump (light pink/black wire). Notice that pin 19 on the computer is the monitor to make sure the pump has power. The fuel pump has a black wire that supplies the ground to complete the circuit.

Remember that the computer does not source any power to actuators, relays or injectors, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.



Now that you have the theory of how it works, it’s time to go digging.

All voltage reading are made with one voltmeter lead connected to the metal car body unless otherwise specified

Check for 12 volts at the red wire on the inertia switch. No 12 volts at the inertia switch, the ignition switch is turned off or faulty or there is no power to the EEC (computer) power relay. To be sure look for good 12 volts on the red wire on any fuel injector.
Good 12 volts means the EEC relay is working. No 12 volts and the ECC wiring is at fault.
Look for 12 volts on the red/green wire on the ignition coil: no 12 volts and the ignition switch is faulty, or the fuse link in the ignition power wire has blown. No 12 volts here and the ECC relay won’t close and provide power to the inertia switch. Check the Red/black wire on the inertia switch, it should have 12 volts. No 12 volts there, either the inertia switch is open or has no power to it. Check both sides of the inertia switch: there should be power on the Red wire and Red/Black wire. Power on the Red wire and not on the Red/Black wire means the inertia switch is open. Push the button on the side of it to reset it, and then recheck. Good 12 volts on one side and not on the other means the inertia switch has failed.

Look for 12 volts at the Orange/Lt. Blue wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring, bad ignition switch or ignition switch wiring or connections. There is a mystery connector somewhere under the driver’s side kick panel, between the fuel pump relay and the fuse link.

Turn on the key and jumper the fuel pump test connector to ground as previously described. Look for 12 volts at the Light Pink/Black wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed, or there is a broken wire in the relay control circuit.

Pump wiring: Anytime the ignition switch is in the Run position and the test point is jumpered to ground, there should be at least 12 volts present on the black/pink wire. With power off, check the pump ground: you should see less than 1 ohm between the black wire and chassis ground.


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The yellow wire is the fuel tank sender to the fuel quantity gage. The two black wires are grounds. One ground is for the fuel tank sender and the other is the fuel pump. The ground for the fuel pump may be larger gauge wire that the fuel tank sender ground wire.

Make sure that the power is off the circuit before making any resistance checks. If the circuit is powered up, your resistance measurements will be inaccurate.

You should see less than 1 Ohm between the black wire(s) and ground. To get some idea of what a good reading is, short the two meter leads together and observe the reading. It should only be slightly higher when you measure the black wire to ground resistance.

The Tan/Lt Green wire provides a ground path for the relay power. With the test connector jumpered to ground, there should be less than .75 volts. Use a test lamp with one side connected to battery power and the other side to the Tan/Lt Green wire. The test light should glow brightly. No glow and you have a broken wire or bad connection between the test connector and the relay. To test the wiring from the computer, remove the passenger side kick panel and disconnect the computer connector. It has a 10 MM bolt that holds it in place. With the test lamp connected to power, jumper pin 22 to ground and the test lamp should glow. No glow and the wiring between the computer and the fuel pump relay is bad.

Computer: If you got this far and everything else checked out good, the computer is suspect. Remove the test jumper from the ECC test connector located under the hood. Probe computer pin 22 with a safety pin and ground it to chassis. Make sure the computer and everything else is connected. Turn the ignition switch to the Run position and observe the fuel pressure. The pump should run at full pressure.
If it doesn't, the wiring between pin 22 on the computer and the fuel pump relay is bad.
If it does run at full pressure, the computer may have failed.

Keep in mind that the computer only runs the fuel pump for about 2-3 seconds when you turn the key to the Run position. This can sometimes fool you into thinking the computer has died. Connect one lead of the test light to power and the other lead to computer pin 22 with a safety pin. With the ignition switch Off, jumper the computer into self test mode like you are going to dump the codes. Turn the ignition switch to the Run position. The light will flicker when the computer does the self test routine. A flickering light is a good computer. No flickering light is a bad computer.
Remove the test jumper from the ECC test connector located under the hood.

Fuel pump runs continuously: The fuel pump relay contacts are stuck together or the Tan/Lt Green wire has shorted to ground. In extreme ghetto cases, the pump relay may have been bypassed. Remove the fuel pump relay from its socket. Then disconnect the computer and use an ohmmeter to check out the resistance between the Tan/Lt Green wire and ground. You should see more than 10 K Ohms (10,000 ohms) or an infinite open circuit. Be sure that the test connector isn’t jumpered to ground.
If the wiring checks out good, then the computer is the likely culprit.


a9x-series-computer-connector-wire-side-view-gif.gif


Prior to replacing the computer, check the computer power ground. The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up next to the starter solenoid where the wire goes into the wiring harness

If all of the checks have worked OK to this point, then the computer is bad. The computers are very reliable and not prone to failure unless there has been significant electrical trauma to the car. Things like lightning strikes and putting the battery in backwards or connecting jumper cables backwards are about the only thing that kills the computer.

See the following website for some help from Tmoss (diagram designer) &
Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif