Engine Engine starting issues

Swhitney

Active Member
Feb 11, 2019
103
3
28
Oregon City
As long as I can remember when my 1992 mustang gt is warm, and after it's been shut off the engine will not start unless I hit full throttle. I'm curios if anyone has seen this failure mode, and if there is a known fix, of things I might look for?

The strange part is when the engine is cold it will fire on initial try every time, which seems strange to me.

>347 stroker
>victor jr cylinder heads
>performer RPM II intake
>24 lbs injectors
>stock computer
>matched MAS for injector size
>fuel pressure is stable when looking at a fuel pressure gauge


IMG_2729.jpg
IMG_2303.jpg
 
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HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
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Memphis TN
its probably got a leaking injector....after you turn engine off it leaks and fills engine w vapor which has to be cleared before it will start....Do you have to prime the pump twice ever? Do it hold fuel pressure when turned off?
 

Swhitney

Active Member
Feb 11, 2019
103
3
28
Oregon City
its probably got a leaking injector....after you turn engine off it leaks and fills engine w vapor which has to be cleared before it will start....Do you have to prime the pump twice ever? Do it hold fuel pressure when turned off?
The fuel pressure does leak down over time, but not immediately. Is there a way to test fuel injectors for this problem?
 

mikestang63

SN Certified Technician
Aug 27, 2012
10,470
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In the garage
Where's a good place to buy 24 pound injectors that are not 300 dollars?
check the classifieds here and on.... ahem... other not to be named mustang sites... there are also a few guys who sell parts like HorsePLay Auto, MPS, Out to Pasture Parts, Fakebook groups... FleaBay
 

HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
764
288
73
58
Memphis TN
The fuel pressure does leak down over time, but not immediately. Is there a way to test fuel injectors for this problem?
only way to test them is to pull the fuel rail/injectors out of the intake and pressure the system and see if any leak, or pull them and send them off.
 

mikestang63

SN Certified Technician
Aug 27, 2012
10,470
7,249
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In the garage
only way to test them is to pull the fuel rail/injectors out of the intake and pressure the system and see if any leak, or pull them and send them off.
you can test them on the car with an electric drill battery and two wires. If you energize them and you hear them clicking.. Also can use a DVOM while on the car to check the resistance. Bring a can of Carb cleaner and buy a $10 injector tester off Ebay. Those will get you in the right direction
 

Swhitney

Active Member
Feb 11, 2019
103
3
28
Oregon City
you can test them on the car with an electric drill battery and two wires. If you energize them and you hear them clicking.. Also can use a DVOM while on the car to check the resistance. Bring a can of Carb cleaner and buy a $10 injector tester off Ebay. Those will get you in the right direction

Before putting them back in the car I did the battery test, and they made a clicking noise. They all work while running, but I think from the first comment that one is bleeding down after the car is shut off.

Who would be a person that can rebuild injectors?

Might be easier to simply bite the bullet and buy a new set. I worry about stripping them from a junk yard car and having some other issue.
 

jrichker

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As long as I can remember when my 1992 mustang gt is warm, and after it's been shut off the engine will not start unless I hit full throttle. I'm curios if anyone has seen this failure mode, and if there is a known fix, of things I might look for?

The strange part is when the engine is cold it will fire on initial try every time, which seems strange to me.

>347 stroker
>victor jr cylinder heads
>performer RPM II intake
>24 lbs injectors
>stock computer
>matched MAS for injector size
>fuel pressure is stable when looking at a fuel pressure gauge


IMG_2729.jpg
IMG_2303.jpg
Dump the codes and look for an ECT failure... Codes 21, 51

Code 21 or 116 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.

[color= blue]Revised 6-Apr-2017 to add diagrams and resistance check for ECT wiring.[/color]

Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error. Warm the engine up until you get good hot air from the heater and then dump the codes again.

The computer Engine Coolant Temperature sensor has absolutely nothing to do with the temperature gauge. They are different animals. The ECT sensor is normally located it the passenger side front of the engine in the water feed tubes for the heater. It has two wires that connect by a weathertight plastic connector.

The water temperature sender for the temp gauge is located in the driver's side lower intake manifold. It has a single wire that connects by a push on connector on the temp sender.

Code 51[/B] Engine Coolant Temperature (ECT) sensor signal is/was too high [/b]

[color= blue]Revised 6-Apr-2017 to add diagrams and resistance check for ECT wiring.[/color]

Possible bad ECT sensor or wiring. Possible missing signal ground – black/wire broken or bad connection. With the power off, measure the resistance between the black/white wire and battery ground. You should see less than 1 ohm. Check the same black /white wire on the TPS and MAP sensor. More than 1 ohm there and the wire is probably broken in the harness between the engine and the computer. The 10 pin connectors pass the black/white wire back to the computer, and can cause problems.

The computer Engine Coolant Temperature sensor has absolutely nothing to do with the temperature gauge. They are different animals. The ECT sensor is normally located it the passenger side front of the engine in the water feed tubes for the heater. It has two wires that connect by a weathertight plastic connector.

The water temperature sender for the temp gauge is located in the driver's side lower intake manifold. It has a single wire that connects by a push on connector on the temp sender.


If you have replaced the ECT sensor and are still having ECT like problem symptoms, check the ECT wiring .

a9x-series-computer-connector-wire-side-view-gif.71316


eec-iv-computer-connector-for-5-0-mustang-gif.88243


See the graphic for the 10 pin connector circuit layout.

salt-pepper-10-pin-connectors-65-jpg.68512


Check the resistance of the green wire on the ECT connector to the green wire on pin 7 of the computer connector. You should see less that 1 Ω (ohm)

Use Pin 46 on the computer for ground for both ECT & ACT tests to get most accurate readings.

Pin 7 on the computer - ECT signal in. At 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. At 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer.

50 degrees F = 3.52 v
68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms

Diagram courtesy of Tmoss & Stang&2birds
88-91_5.0_EEC_Wiring_Diagram.gif


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

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/88-91_5.0_EEC_Wiring_Diagram.gif
 

Swhitney

Active Member
Feb 11, 2019
103
3
28
Oregon City
Here are the wires that you referenced above. The color codes seem to no line up with the write up. Can you tell which one is which? The white/yellow wire is not plugged into anything, so I'm not sure what this one does. :(

Photo Jun 09, 1 07 24 PM.jpg
Photo Jun 09, 1 07 39 PM.jpg
Photo Jun 09, 1 07 47 PM.jpg
 

Swhitney

Active Member
Feb 11, 2019
103
3
28
Oregon City
Where is the yellow red wire plug supposed to be plugged into? I bought this car years ago and the previous owner had been tweaking some electrical not in my favor....

Also, I am swapping the ECT, and ACT sensors out today, so I hope to see how she runs after that.

Photo Jun 10, 8 03 14 AM.jpg
 

Swhitney

Active Member
Feb 11, 2019
103
3
28
Oregon City
Holy crap! this totally fixed the problem! I replaced the ECT and the ACT sensors. This has been a problem for many many years, and these sensors were the culprit. :)