Another "cranks but no start" thread.

HISSIN50 said:

You might want to use a spark tester or an old but clean plug for the spark testing. This helps remove variables.

I'd want to test the rest of the TPS wiring. You want to ensure there is not an issue with VREF or sig-return circuits.

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HISSIN50 said:

If you disconnect the TPS, you could ohm it out to see if the resistance changes with position/displacement. If not, the TPS itself is probably bad.

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jrichker said:

Getting started:
Verify that VREF is good:

1.) The fist step is to dump the codes: if one of the sensors is shorting VREF to ground, you will get codes 22 (MAP/BARO sensor), 63 (TPS sensor), and 31 or 32 (EGR sensor). You will get all the codes if VREF is shorted to ground, not just one or two of them.
Codes don't exist - the car hasn't run in 2-4 weeks, and I disconnect the battery whenever it's parked b/c something drawing on it.

2.) The next step is to determine which sensor is causing the low VREF voltage.

A.) All sensors connected and installed correctly. Ignition off:
Locate the MAP/BARO sensor on the firewall behind the upper intake manifold. Insert one safety pin in the rear of the electrical connector where the black/white wire is connected. Insert another safety pin in the rear of the electrical connector where the orange/white wire is connected. Make sure the safety pins do not touch each other or metal parts of the body or engine. Connect the DVM or meter to the safety pins. If your meter is polarity sensitive, be sure that it is connected correctly: positive to the orange/white wire, negative to the black/white wire.
All installed and connected correctly.

B.) Turn the ignition switch to Run, but do not start the engine. Note the voltage: it should be between 4.5 and 5.5 volts. If it is within range, go to step 5. If it is over 5.5 volts, go to step 7
5.09V

3.) TPS sensor connected and installed correctly. Ignition off:
The TPS is mounted on the top side of the throttle body. Insert one safety pin in the rear of the electrical connector where the black/white wire is connected. Insert another safety pin in the rear of the electrical connector where the orange/white wire is connected. Make sure the safety pins do not touch each other or metal parts of the body or engine. Connect the DVM or meter to the safety pins. If your meter is polarity sensitive, be sure that it is connected correctly: positive to the orange/white wire, negative to the black/white wire
All installed and connected correctly.

A.) Turn the ignition switch to Run, but do not start the engine. Note the voltage: it should be between 4.5 and 5.5 volts. If it is within range, go to step 4 to check VREF on the EGR sensor.
5.09V

4.) EGR sensor connected and installed correctly. Ignition off:
The EGR is mounted on the back side of the EGR valve. Insert one safety pin in the rear of the electrical connector where the black/white wire is connected. Insert another safety pin in the rear of the electrical connector where the orange/white wire is connected. Make sure the safety pins do not touch each other or metal parts of the body or engine. Connect the DVM or meter to the safety pins. If your meter is polarity sensitive, be sure that it is connected correctly: positive to the orange/white wire, negative to the black/white wire
All installed and connected correctly.

A.) Turn the ignition switch to Run, but do not start the engine. Note the voltage: it should be between 4.5 and 5.5 volts. If it is within range, go to step 5.
5.08V

5.) VREF less that 4.5 volts with all sensors disconnected or VREF OK only at MAP/BARO sensor:
Disconnect the battery negative cable at the battery. Remove the passenger side kick panel and then loosen the 10 MM hex bolt that secures the computer wiring harness connector to the computer. Measure the resistance between pin 26 on the computer and the orange/white wires on the MAP/BARO, TPS and EGR sensors. You should see less that 1.5 ohms on each of the orange/white wires and pin 26. More than that indicates wiring problem.
Did not complete this test, since all VREF were >4.5v

6.) At this point, you have verified that all the sensors that use VREF have the proper supply voltage. If you still do not have proper VREF, then the problem is inside the computer. This is a replace the computer with a known good unit and retest to see if you get the same codes 22 (MAP/BARO sensor), 63 (TPS sensor), and 31 or 32 (EGR sensor). All the codes should have cleared unless you have some faulty sensors.
I'll try to find a known-good computer nearby to borrow...

7.) VREF exceeds 5.5 volts:
Disconnect the battery negative cable at the battery. Remove the passenger side kick panel and then loosen the 10 MM hex bolt that secures the computer wiring harness connector to the computer. Pull the wiring harness connector down so that it disconnects from the computer. Then measure the resistance between the orange/white wire on any of the sensors and pin 1. Then measure the resistance between the orange/white wire on any of the sensors and pin 37. You should see greater than 1 Megohm or an infinite open circuit in both cases. Less than 1 Megohm indicates a wiring problem.
If the resistance check is good, then the problem is inside the computer. This is a replace the computer with a known good unit and retest to see if you get the same high voltage readings. If you do, then your DVM may be whacko…
Tested orange white on TPS to pins 1 and 37, and both were infinite open.

VREF is verified as good, sensor output is still low:
8.) One or more sensors get a low output voltage code (63 - TPS sensor, or 31 or 32 - EGR sensor). After you have replaced the sensor and are still getting a low voltage code or low voltage reading, it is time to go hunting. By completing steps 1-7, you have verified that you have good VREF and it is not a cause of your problem.
Disconnect the battery negative cable at the battery. Remove the passenger side kick panel and then loosen the 10 MM hex bolt that secures the computer wiring harness connector to the computer. Pull the wiring harness connector down so that it disconnects from the computer.

Make sure that the TPS & EGR sensors are disconnected while performing the following tests. If you don't disconnect them, you will get incorrect measurements.

A.) TPS sensor: measure the resistance between the TPS green/lt green wire and pin 47. You should see less than 1.5 ohms. I got 0.2 ohms.More than that indicates a wiring problem. Then measure the resistance between the green/lt green wire on the TPS sensor and ground. You should see greater than 1 Megohm or an infinite open circuit.I got an infinite open circuit.

Adjust the TPS sensor as follows:
Set the TPS voltage at .5- 1.1 range. Because of the variables involved with the tolerances of both computer and DVM, I would shoot for somewhere between .6 and 1.0 volts. Unless you have a Fluke or other high grade DVM, the second digit past the decimal point on cheap DVM’s is probably fantasy. Since the computer zeros out the TPS voltage every time it powers up, playing with the settings isn't an effective aid to performance or drivability. The main purpose of checking the TPS is to make sure it isn't way out of range and causing problems. Put the safety pins in the Dark Green/Lt green wire and Black/White wire. Make sure the ignition switch is in the Run position but the engine isn't running.
I cannot get my TPS to read any higher than 0.12v today; and that's only when I ground out to the battery. When grounding out to the black TPS wire, I only get 0.02v

B.) EGR sensor: measure the resistance between the EGR brown/lt green wire and pin 27. You should see less than 1.5 ohms. More than that indicates a wiring problem. Then measure the resistance between the brown /lt green wire on the EGR sensor and ground. You should see greater than 1 Megohm or an infinite open circuit.
I got 0.03 ohm at pin 27, infinite open at ground.

C.) If both the above tests pass, then the problem is inside the computer. This is a replace the computer with a known good unit and retest to see if you get the same low voltage readings. If you do, then your DVM may be whacko…

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jrichker said:

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

1.) Remove push on connector (small red/blue wire) from starter solenoid and turn ignition switch to the Run position. Place car in neutral or Park and set the parking brake. Remove the coil wire from distributor & and hold it 3/8” away from the engine block. Jumper the screw to the big bolt on the starter solenoid that has the battery wire connected to it. You should get a nice fat blue spark.
Most of the items are electrical in nature, so a test light, or even better, a voltmeter, is helpful to be sure they have power to them.
I do get a spark. Not fat, but a blue spark.

No spark, possible failed items in order of their probability:
C.) TFI module: use a test light to check the TFI module. Place one lead of the test light on the red/green wire on the ignition coil connector and the other lead on the dark green/yellow wire on the ignition coil connector. If the TFI is working properly, the test light will flash when the engine is cranked using the ignition switch.
I've got flashing.
D.) Coil
Brand new.
E.) No ECC or computer power - ECC or computer relay failure
86-93 models only: ECC relay next to computer - look for 12 volts at the fuel injector red wires
I've got 12v.
G.) Ignition switch - look for 12 volts at the ignition coil red/lt green wire. No 12 volts, blown fuse link or faulty ignition switch. Remove the plastic from around the ignition switch and look for 12 volts on the red/green wire with the switch in the Run position. No 12 volts and the ignition switch is faulty. If 12 volts is present in the Run position at the ignition switch but not at the coil, then the fuse or fuse link is blown.
Note: fuses or fuse links blow for a reason. Don’t replace either a fuse or fuse link with one with a larger rating than stock. Doing so invites an electrical fire.
Ignition fuse links may be replaced with an inline fuse holder and 5 amp fuse for troubleshooting purposes.
I haven't done this yet!
H.) Missing or loose 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
I.) Computer.
J.) Bad or missing secondary power ground. It is located between the back of the intake manifold and the driver's side firewall. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges.
Feels good, clean, tight.
K.) Engine fires briefly, but dies immediately when the key is released to the Run position. Crank the engine & when it fires off, pull the small push on connector (red wire) off the starter relay (Looks like it is stuck on a screw). Hold the switch in the crank position: if it continues to run there is a problem with either the ignition switch or TFI module. Check for 12 volts at the red/green wire on the coil with the switch in the Run position. Good 12 volts, then replace the TFI. No 12 volts, replace the ignition switch.
Haven't done this yet actually...

2.) Spark at coil wire, pull #1 plug wire off at the spark plug and check to see spark. No spark, possible failed items in order of their probability:
I have spark.
A.) Moisture inside distributor – remove cap, dry off & spray with WD40
Was dry
B.) Distributor cap
Replaced
C.) Rotor
Replaced
D.) Spark Plug wires
Replaced
E.) Coil weak or intermittent - you should see 3/8" fat blue spark with a good coil
Get spark, but not a fat spark.

3.) Spark at spark plug, but no start.
Next, get a can of starting fluid (ether) from your local auto parts store: costs a $1.30 or so. Then pull the air duct off at the throttle body elbow, open the throttle, and spray the ether in it. Reconnect the air duct and try to start the car. Do not try to start the car without reconnecting the air duct.
Car starts with ether, but immediately dies. This is a MAF-converted car.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 5-20 seconds and shut off. To trick the fuel pump into running, find the EEC test connector and jump the connector in the Upper RH corner to ground. The EEC connector is near the wiper motor and LH hood hinge.
Fuel pump primes OK.

If the relay & inertia switch are OK they 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. Fuel doesn't "squirt" out, but pours out rather quickly. If you have any doubts about having sufficient fuel flow/pressure, rent a fuel pressure test gauge from the auto parts store. That will tell you for sure if you have adequate fuel pressure. I can't get my AutoZone-rented guage to depress the Schraeder valve enough.


4.) No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – Coupe & 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 OK
B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter. Look for 12 volts at the Pink/Black wire on the fuel pump relay.OK
C.) Clogged fuel filter New, but could be clogged I Suppose.
D.) Failed fuel pump
E.) 86-90 models only: Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue wire on the fuel pump relay. How do I know if it's blown, the link doesn't appear to open at all?
F.) Engine seem to load up on fuel and may have black smoke at the tailpipe. Fuel pressure regulator failed. Remove the vacuum line from the regulator and inspect for fuel escaping while the pump is running. If fuel is coming out the vacuum port, the regulator has failed. Check the regulator vacuum line for fuel too. Disconnect it from the engine and blow air though it. If you find gas, the regulator has failed. No fuel in either instance.

5.) Fuel pressure OK, the injectors are not firing.
A.) The PIP sensor in the distributor tells the computer when to fire the injectors. A failing PIP sensor will sometimes let the engine start if the SPOUT is removed.
A noid light available from any auto parts store, is one way to test the injector circuit to see if the injectors are firing. The noid light plugs into the fuel injector harness in place of any easily accessible injector. Plug it in and try to start the engine: it will flash if the injector is firing. Noid light blinks as it should.
B.) I like to use an old injector with compressed air applied to the injector where the fuel rail would normally connect. I hook the whole thing up, apply compressed air to the injector and stick it in a paper cup of soapy water. When the engine cranks with the ignition switch on, if the injector fires, it makes bubbles. Cheap if you have the stuff laying around, and works good too. I don't have any old injectors...
D.) Pull an injector wire connector off and look for 12 volts on the red wire when the ignition switch is on. Have 12v.
G.) TPS voltage exceeds 3.7 volts with the throttle closed. This will shut off the injectors, since the computer uses this strategy to clear a flooded engine. Use a DVM, a pair of safety pins, and probe the black/white and green wires to measure the TPS voltage.
It should be .5-.1.0 volts with the key on, engine not running. Note that if the black/white wire (signal ground) has a bad connection, you will get some strange readings. Make a second measurement using the battery post as the ground to eliminate any ground problems. If the readings are different by more than 5%, you may have a high resistance condition in the black/white signal ground circuit.
Can't get TPS over 0.08-0.12v.

6.) Spark & fuel pressure OK.
A.) Failed IAB or improperly set base idle (no airflow to start engine). Press the throttle ¼ way down and try to start the car. See the "Surging Idle Checklist for help with all your idle/stall problems. Car won't start even w/1/4 throttle.
.

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