Engine Turbo fox build hot start issue

89turbofox

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Mar 26, 2020
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Hi new to the page and in desperate need of some guidance.
I have a 89 fox 5.0 with an on3performance turbo set up and for the life of me cannot figure out my hot start issue. Car has 60lb injectors, 340lhp fuel pump, new high torque starter, new coolant temp sensor, new plugs, wires, cap, rotor, new calibrated maf for injectors,new adjustable fuel regulator. And more I’m forgetting but the car will normally start cold fine and runs great no noticeable surging or anything like that and drives and pulls hard. But ones it’s warm it doesn’t like to start back up and have to let it sit while. I changed tfi modules several times and seemed to get junk ones out of the box so put original motor craft one back in. I had the car tuned and has an sct chip.
I pulled the codes and where getting codes 15,26,85. All the emissions stuff has been taken off. So leading to a possible ecu failure? I’m honestly stuck and Just wanna enjoy my car lol any help is appreciated and i may have missed something I changed but all ears.
(I believe I’m posting in the right area)
 
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John Dirks Jr

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Jun 28, 2013
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Have you tried holding the throttle wide open on a hot start? If everything is correct you shouldnt need to do that but sometimes it will get it started and maybe give you a clue.
 

Mstng93SSP

You have a nice rear end there Dave.
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Nov 29, 1999
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If you paid to have your car tuned, and it has a hot start issue then the tuner should straighten it out. If they won't, you need a new tuner. Don't know if you have any money in your budget but a megasquirt setup and a good tuner would change your life. @a91what is a member here and he tunes me remotely. His tuning ability is pretty amazing.

Chris
 
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jrichker

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Hi new to the page and in desperate need of some guidance.
I have a 89 fox 5.0 with an on3performance turbo set up and for the life of me cannot figure out my hot start issue. Car has 60lb injectors, 340lhp fuel pump, new high torque starter, new coolant temp sensor, new plugs, wires, cap, rotor, new calibrated maf for injectors,new adjustable fuel regulator. And more I’m forgetting but the car will normally start cold fine and runs great no noticeable surging or anything like that and drives and pulls hard. But ones it’s warm it doesn’t like to start back up and have to let it sit while. I changed tfi modules several times and seemed to get junk ones out of the box so put original motor craft one back in. I had the car tuned and has an sct chip.
I pulled the codes and where getting codes 15,26,85. All the emissions stuff has been taken off. So leading to a possible ecu failure? I’m honestly stuck and Just wanna enjoy my car lol any help is appreciated and i may have missed something I changed but all ears.
(I believe I’m posting in the right area)
You have one code that is a problem... Code 26 points to the MAF and it is not an emissions control part.
Mass Air Flow is used to help the computer measure the amount of air entering the intake so that it knows how much fuel the engine needs to perform properly. Mass air flow measures not only the amount of air, but to a limited extent, also its density. Changes in humidity, barometric pressure and inlet air temperature also affect air density. The Manifold Atmospheric Pressure or MAP sensor measures the barometric air pressure. The ACT sensor measures the inlet air temperature. Using the input from these two other sensors helps the computer actually calculate the air density, The air/fuel ratio is calculated on the basis of air density, so the MAF, MAP ECT & ACT work together to make it happen. The O2 sensors provide a feedback mechanism to help keep the calculations in the right range.

Code 26 - Mass Air Flow out of range – MAF Voltage output too high or too low

Revised Oct 31, 2019 to update wiring and measurement directions

Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF. This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

Computer wiring harness connector, wire side.
71316.gif


Computer wiring harness connector, computer side.
88243.gif




Diagrams courtesy of Tmoss and Stang&2Birds

ECC Diagram for 88-90 5.0 Mustangs
88-91_5.0_EEC_Wiring_Diagram.gif


ECC Diagram for 91-93 5.0 Mustangs
91-93_5.0_EEC_Wiring_Diagram.gif


94-95 Diagram for 94-95 5.0 Mustangs[/b]
94-95_5.0_EEC_Wiring_Diagram.gif



How the MAF works

There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables. Changes in RPM causes the airflow to increase or decrease, changing the voltage output. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow.

Actually, MAF pins C & D float with reference to ground. The signal output of the MAF is a differential amplifier setup. Pins C & D both carry the output signal, but one pin's output is inverted from the other. The difference in signal between C & D is what the computer's input circuit is looking for. The difference in the two outputs helps cancel out electrical noise generated by the ignition system and other components. Since the noise will be of the same polarity, wave shape and magnitude, the differential input of the computer electronically subtracts it from the signal. Then it passes the signal on to an Analog to Digital converter section inside the computer's CPU chip.

The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

Do not use body, engine or chassis ground when making resistance or voltage measurements unless specifically instructed to do so.

89-90 Model cars: Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

91-95 Model cars: Measure the MAF output at pins C & D on the MAF connector light blue/red and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

MAF output readings: Use the computer connector diagram to help choose the proper pin connection on the computer when measuring the MAF output voltage. Since the car is most likely parked for simplicity’s sake, the idling voltage check can the done with the voltmeter directly stuck in the backside of the MAF connector.

At idle = approximately .6 volt
20 MPH = approximately 1.10 volt
40 MPH = approximately 1.70 volt
60 MPH = approximately 2.10 volt

If the output of the MAF C&D pins exceeds the specs above, there are two possible problems:

1.) The MAF sensor is defective and needs to be replaced.
2.) The MAF sensor is installed in a a different housing than the one it was designed for. The sensor is designed to work with a specific MAF part number or model MAF housing.

Check the resistance of the MAF signal wiring
For the next 2 checks make your measurement with the MAF disconnected from the wiring harness.

Pin D on the MAF wiring harness and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF wiring harness and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 10K ohms between either pin C or D on the MAF wiring connector and pins A or B.

Reconnect the MAF to the wiring harness and proceed to the next section.

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/

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

Fuel pump, alternator, ignition & A/C wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Computer, actuator & sensor wiring
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Fuse panel layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Vacuum routing
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg
 
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