just bought my first mustang, have a few questions already!

jzauner

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*TL;DR at the end*
So first off, I bought my first mustang, a 91 LX (4 cyl) convertible yesterday I attached a picture so you can see what I'm working with here. So far I'm having a blast with working on it. I'm no strangers to wrenching on cars at all as I have been through 4 VWs (2 buses, a thing, and a beetle), a jeep, helped my dad on his 1950 chevy truck, and a 1978 AMC AMX and a 1973 Plymouth Duster, and a few new cars that I just drove without working on them. I swear, I am no stranger to the "search" button in forums as well. I've always been the one where I prefer to learn hands on from a guru. I had a VW buddy teach me everything about the VWs and same thing about the jeep. Haven't met a mustang buddy yet. Though... I'm in Dallas, so I'm sure I will soon.

So a little about the backstory on this mustang. It was only driven a few days a week for the first 10 years or so of its life. It was then sold to the second owner, who I bought it from. He lived, worked and played within 1 mile of his apartment. He told me that he did quite a bit of work on it over the years for maintenance and preventative stuff. He then bought a new car when he had a kid, and loaned the car to his niece. She drove it for a while, then the transmission "quit working". I asked him what that meant, and he had no idea. So I honestly have no idea if it is the transmission or what.

So It sat for about 6 years. No gas in the tank. There was a rat living in it, but he has been evicted. When I got to the mustang, there was no battery, and the positive terminal clamp was gone. So I got a battery and that cable, and hooked it up. Everything electrical worked minus the back passenger window. Not a concern at this point at all. Also the passenger headlight (it is full of water... I guess the blinker fluid thing is real!). Again, not a concern. So look over the car and there is no rust in the strut towers, the frame looks good, and the engine turns over by hand. So I put air in the tires and trailered it home.

I make sure there is no gas in the tank, throw some gas in there, replace the fuel filter, and see what happens. It cranks freely, but doesn't start. Not surprised, but hey.

So I started going down the list of "it cranks but doesn't start". Tried the ether test and it started for about a second, then turned off. I pushed down the valve and no fuel came out with pressure, but a drop or so came up out of the valve and sat in the body of the valve. Or do I need to test that with the fuel pump jumpered on? Currently at the step 4 (no fuel pressure), part B (fuel pump relay) I look under the drivers seat, and there is a green connector with a black cap on it. I pull the black cap and there is an orange tip to the connector. Is the relay actually supposed to clip in there, or is that a test socket? I have 12 volts to the pink/black wire. Is that the only thing to check there? There is sound from the rear (I assume the fuel pump) for about a second when I turn it on. I assume it is priming the pump.

TL;DR- Bought a mustang, been going through the checklist step by step. for the fuel pump relay, is that just a test socket under the drivers seat or should there be a relay plugged in? Also, does the fuel pump need to be jumpered on to test the valve?
mustang.jpeg
 
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jrichker

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The 91 should have fuel pump relay under the driver's seat.

Fuel Pump Troubleshooting for 91-93 Mustangs

Revised 6-Feb-2016 to add fuse link diagram

Ignition switch in the Run position, engine not running tests.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on.
It should run for 2-5 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the upper RH corner to ground.

Foxbody Diagnostic connector


Foxbody Diagnostic connector close up view





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 Relay:
On 91 cars, it is located under the driver's seat.
On 92 and 93 cars it is located under the MAF. Be careful not to confuse it with the A/C WOT cutoff relay which is in the same area. 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.

Theory of operation:
Read this section through several times. If you understand the theory of operation, this will be much easier to troubleshoot. Refer to the diagram below frequently.

Diagram of the fuel pump wiring for 91-93 cars.


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

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.

Control Path
The control path consists of 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 relay coil and then from the relay coil to the computer (light blue\orange 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.

Computer power path
The computer power relay must properly function to provide power for the fuel pump relay. That means you must check the operation of the computer power relay (PCM Power Relay) before chasing any problems with the fuel pump circuit. The computer power relay is located above the computer under the passenger side kick plate cover. . It is not easy to get to, you must have small hands or pull the passenger side dash speaker out to access it.
With the Ignition switch in the Off position, check the resistance between the black/white wire and a clean bare spot on the car body metal. You should see less that 1 Ohm. More than 1 Ohm is a broken wire, or bad connection of the black/white wire and the car body metal.
Check for 12 volts at the yellow wire. Good 12 volts and the fuse link is OK. No voltage or low voltage, bad fuse link, bad wiring, or connections.
With the Ignition switch in the Run position, look for good 12 volts on the red/green wire. No voltage or low voltage, bad fuse link, bad wiring, or connections.
Good 12 volts on the red/green wire, look for good 12 volts on the red wire or any of the red fuel injector wires. No 12 volts or low voltage and the relay isn’t closing, or relay socket contacts are dirty/corroded. Water has been known to run down the radio antenna wire or leak from the windshield and get into the relay and relay contacts.

Fuel pump 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 (pink/black wire) goes to the fuel pump relay contacts. When the contacts close because the relay energizes, the power flows through the pink/black wire to the contacts and through the dark green\yellow wire to the inertia switch. The other side of the inertia switch with the brown\pink wire joins the pink/black wire that connects to the fuel pump. The fuel pump has a black wire that supplies the ground to complete the circuit.

Fuse links at starter solenoid
64326.gif


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

Power feed: Look for 12 volts at the pink/black wire (power source for fuel pump relay).
No voltage or low voltage, bad fuse link, bad wiring, or connections. Remember that on 92 or later models the fuel pump relay is located under the Mass Air meter. Watch out for the WOT A/C control relay on these cars, as it is located in the same place and can easily be mistaken for the fuel pump relay.

Relay: Turn on the key and jumper the ECC test connector as previously described. Look for 12 volts at the dark green\yellow 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.

Inertia switch:
The location for the inertia switch is under the plastic for the driver's side taillight.
There should be a round plastic pop out cover over it, remove it to access the switch button.
With the test connection jumpered and ignition switch in The Run position as described above, check the brown/pink wire. 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 dark green\yellow (inertia switch input) and brown/pink wire (inertia switch output). Power on the dark green\yellow wire and not on the brown/pink wire means the inertia switch is open.
Press on the red plunger to reset it to the closed position. Sometimes the inertia switch will be intermittent or will not pass full power. Be sure that there is 12 volts on both sides of the switch with the pump running and that the voltage drop measured across the switch is less than .75 volts.

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.

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.



49675.gif


Control path:
Relay: The light blue/orange wire provides a ground path for the relay power. With the test connector jumpered according to the previous instructions, there should be less than .75 volts.
Use a test lamp with one side connected to battery power and the other side to the light blue/orange wire on the fuel pump relay. 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. Remove the test jumper from the ECC test connector.
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.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)
for help on 88-95 wiring Mustang FAQ - Engine Information

Fuel pump runs continuously:
The fuel pump relay contacts are stuck together or the light blue/orange wire (pin 22) has shorted to ground. Remove the fuel pump relay from its socket. Then disconnect the computer and use an ohmmeter to check out the resistance between the light blue/orange 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.

The picture shows the common ground point for the battery , computer, & extra 3G alternator ground wire as described above. A screwdriver points to the bolt that is the common ground point.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972
ground.jpg
 

jzauner

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I did do the valve check and tricked the fuel pump into running. No gas shot out, but a very small amount did come up and pool inside of the valve. I'm thinking the fuel pump just isn't pumping enough at this point. Am I correct in this? Sorry again for so many questions!
 

90sickfox

I didn't really have an issue with the stink...
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There should be a relay plugged in there. The relay is missing so once you get one it should power the pump. Without it there should be no power going to the pump at all. The noise you heard had to be something else. Even though there's nothing else back there to make noise.

Before you replace the relay unplug the round black connector behind the bac bumper. It's to the passenger side a little from center between the tank and rear bumper support. When you plug in the relay and jumper the test connector check the pink with black wire at that connector. The reason I say disconnect it at first is because if you heard it the pump could be boot leg wired.

Check around the tank for any wires.
 
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jzauner

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Great! That is what I assumed and exactly why I checked. I didn't want to take off the gas tank if I didn't have to. What is weirder is that there was a black cap over it. had a ford symbol and a part number. but it was not a relay, just a dust cover of sorts. I will crawl back and look at the tank for any fishy looking wires.

However, when I jumper the test connector and hit the valve, a little gas pools up inside the valve. So... something is going there, which confirms the sound I can only assume is the fuel pump
 

90sickfox

I didn't really have an issue with the stink...
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Of it had a ford cover on it check the fuel cut off switch wiring. It's in the trunk behind the interior panel that runs across the back by the latch. It will also have pink and black stripe wires. Jump the test connector under the hood and verify 12v in and out of there. It's in the check list.

It may be worth it to drop the tank anyways. No telling what is going on in there. Atleast, you'd have peace of mind. Rust can clog a pump up pretty good. The new ethanol mix wreaks havoc on metal tanks.
 

jzauner

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I did check the inertia switch and the hood. Both checked out. When I got to the relay, I was confused because there was in fact no relay plugged in, just a cap over it. Was there a Ford option to bypass the relay for some reason?
 

jzauner

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Ah! That is good to know! The “crank but won’t start list” just said to check under the seat. So I’m back to my initial thought of replacing the fuel pump (and tank while I’m at it). If mine is stock and a 4 cyl, is there any reason to upgrade to a higher flow fuel pump?
 

91TwighlightGT

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No the pump is more than enough for a 2.3l.

If you are dropping the tank I would also replace the filler neck seal while you are at it.

Edit: A new tank doesn’t come with that seal, either. At least, mine did not.
 

91TwighlightGT

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Just a couple of things to note. You mentioned at the beginning that you could hear the pump priming. If that is the case, then it is unusual (although not unheard of) for the pump to not make enough pressure to start. However, there is a rubber hose on the fuel pump assembly that can rot out which will cause the fuel to recycle back into the tank instead of through the fuel line, so pulling the tank may ultimately be the correct thing to do. At this point, you probably just replace the fuel pump assembly and move on, rather than fix the hose on an old pump.

I had a similar no start situation with my vehicle that sat for a long time, and ultimately ended up replacing all four injectors. If you have rough running or a no start and have fuel pressure, I wouldn't rule out that the injectors have become clogged. They are super cheap on ebay for some remans if you want to save some money, they are pretty pricey at the parts store.
 

Boostedpimp

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I would verify the pump is in fact working and then pull the fuel filter. It's simple and cheap and probably needs to be changed anyways maybe you'll get lucky and it'll be clogged.
 

90sickfox

I didn't really have an issue with the stink...
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Didn't notice the fuel pump relay ran through the ccrm on 4 cylinders. During my swap it was under the seat...I think...but that was a 1988.
 

jzauner

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Thanks! I will order a new fuel tank and fuel pump. I changed the fuel filter before I ever tried starting the car. If this doesn't work, I think the injectors are last on my list of what it could be. I will probably go ahead and replace the vacuum lines and such while I'm at it. Basically anything that could have dry rotted over the last 6 years. The soft lines that connect to the fuel filter look to be good. In you guy's experiences, is it worth it to change those out, or are they usually pretty good? it was stored in a garage if that helps.
 

91TwighlightGT

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Just a couple things...

I am not advocating that you replace the tank unless you have physical damage, it is leaking, or obviously rusted. Usually these things are just fine and don't need to be replaced. On my car the tank had damage at the seam and it leaked, so I had to replace it. Sometimes baffles and things can break loose, but again it's an extra 100 bucks that you may not need to spend.

I still recommend the filler neck seal, though, as it is commonly bad and can cause leaking and fumes.

Vacuum lines are easy and cheap, so knock yourself out there. I haven't seen the rubber fuel lines go bad, but anything is possible. It would be unusual, though.

Anyway, I agree with your plan of action. Fuel pump first, hopefully that cures it. Injectors are simply a possibility.

After you get that knocked out, I would consider doing a timing belt. These are not interference engines, so you aren't going to have a catastrophic failure if it breaks, but it will strand you. Timing belts will dry rot over time, so it's not a bad idea to do it if you are unsure.

Also, is this an Automatic transmission? If the previous owner said it was having transmission problems, I would be apt to believe them. The A4LD in the 2.3L cars is a problematic POS.
 

jzauner

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Thanks for the heads up! I'll drop the tank out today or tomorrow and see what it looks like. I was planning on just doing all new to save myself the headache of messing with it all again, but if the tank seems fine, I'll just do the sending unit fuel pump, and all new seals.

I did not know that about the automatic transmissions. Crap. The PO wasn't driving it when the transmission issues started, and he wasn't able to tell me what said issues were. I have always driven/worked on manual transmissions, so I am honestly unfamiliar with automatics. Hopefully in a week or so, I can start looking into that. Is this something I would be better off just having a transmission shop rebuild it for me? The mustang does have less than 100,000 miles, so that is why I was hoping the transmission was okay.

I did order the fuel pump and such, so as I am waiting on those to arrive, I will start inspecting the brakes to see what condition they are in.
 

91TwighlightGT

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Thanks for the heads up! I'll drop the tank out today or tomorrow and see what it looks like. I was planning on just doing all new to save myself the headache of messing with it all again, but if the tank seems fine, I'll just do the sending unit fuel pump, and all new seals.

I did not know that about the automatic transmissions. Crap. The PO wasn't driving it when the transmission issues started, and he wasn't able to tell me what said issues were. I have always driven/worked on manual transmissions, so I am honestly unfamiliar with automatics. Hopefully in a week or so, I can start looking into that. Is this something I would be better off just having a transmission shop rebuild it for me? The mustang does have less than 100,000 miles, so that is why I was hoping the transmission was okay.

I did order the fuel pump and such, so as I am waiting on those to arrive, I will start inspecting the brakes to see what condition they are in.


Well, naturally I would say sort the running problems, then assess the transmssion. It is certainly possible that the car began to run poorly and the driver diagnosed it as "transmission" when it was actually something else. That happens quite frequently, however the track record for the A4LD is very poor so again I wouldn't be surprised at all to hear that it was having an issue.

As far as rebuilding it, I would do a little research on the options for the 2.3L Automatic. My cars are all manual transmissions, so I've done only mild research on what to do for the Mustang automatics. There may be shops that know those transmissions well and can rebuild them with quality parts to make them last longer, which I would definitely be in favor of doing rather than a stock rebuild - again, these transmissions aren't known for their longevity. If you don't have any luck there, then I'd say that a standard rebuild would be the best bet. I would not trust a used transmission based on their track record, and the fact that these cars are very old now so often the reason they end up in the yard is because of a mechanical failure.
 

jzauner

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That was the plan! Get it running, make sure brakes are good to go, then start diving into the transmission. I'm thinking I will drop the tank tomorrow. Too many mosquitos outside tonight, and its too stuffy in the garage to have the door closed. I'll let you know what I find.