1987 Mustang Issue

Why can't you pull codes? It doesn't work, you don't know how or what?

Ethan smith said:

Also the tach keeps dropping and coming back up real quick when the issue happens.

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You are not likely to get any useful answers until you tell us why you can't pull codes.
Without having the codes, diagnosing a problem that we are not standing next to when it happens is very difficult.

Throwing parts, labor and time at a problem without having accurate diagnostic information results in a very low success rate.

I think you two gents scared young grasshopper away

51 coolant temp sensor out of range
31 canister or egr valve
85 excessive fuel, constant flow or canister purge circuit.

Sounds like you've removed the charcoal canister and are tripping codes for that. Your coolant temp will cause bugs, but typically those are at idle.
I would start by cleaning all your connections and grounds, then cleaning the egr if you have one equipped.

Your car bucking in cruise is also a sign of poor ignition timing. Verify TDC with the spout removed and adjust your timing.

Not the gauge sensor. The coolant sensor the ecu uses to determine engine temps.

You need to hook that back up asap. If your mustang guy did that he needs to be fired.

CODE: 31 (KOEO) - EVP circuit below minimum voltage. Vref (5 volt reference voltage supplied by the computer) missing or broken wire or bad connection in circuit. Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or MAP sensor located on the firewall near the center of the car. Use the black/white wire for the ground for the DVM.
With the sensor removed from the EGR and still connected, press the plunger and watch the voltage change on the brown/lt green wire. Pull the passenger side kick panel and measure the voltage at the computer. You will need to remove the plastic cover over the wires and probe them from the backside. A safety pin may prove very useful for this task. Use pin 27, EVR input (brown/lt green wire) and pin 46, signal ground (black/white wire) to measure the voltage. The orange/white wire is Vref and should always be 5 volts -/+ .25 volt. Be sure to measure Vref at the EGR sensor to rule out any broken wires or bad connections.
Measuring the voltage at the computer helps you spot broken wiring and intermittent connections.
See the graphic for the 10 pin connector circuit layout.








Code 51 Engine Coolant Temperature (ECT) sensor signal is/was too high -
Possible bad ECT sensor, or wiring. Possible missing signal ground – black/wire 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 ECT sensor is not the same as the temp sender for the temp gauge. It is located in the front part of the tubing that feeds coolant to the heater. It has two wires connected to it.

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

Voltages may be measured across the ECT by probing the connector from the rear.
Use care in doing it so that you don't damage the wiring or connector.

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



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

Code 85 CANP solenoid - The Carbon Canister solenoid is inoperative or missing.

Revised 11 –Jan_2015 to add warning about vacuum leaks due to deteriorated hose or missing caps on vacuum lines when the solenoid is removed.

Check vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.

If you disconnected the carbon canister and failed to properly cap the vacuum line coming from under the upper intake manifold, you will have problems. You will also have problems if the remaining hose coming from under the upper intake manifold or caps for the vacuum line are sucking air.

Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.



It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook it up & use it?


The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.

The purge valve solenoid should be available at your local auto parts store.

Purge valve solenoid:



The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
Carbon Canister:





Alternate placement for a temp gauge sender:

Revised 24 July 2011 to add better temp sender location description and the necessity to loop the fluid flow through the heater circuit.

How it works:
If you want any kind of operation similar to stock, the ECT/heater feed line is the best place for a temp sender or fan thermo sensor. After all, the computer uses the ECT to pick up data on how warm the engine is. Putting the temp sender in the same line as the ECT is a simple way to get the best possible accuracy at minimum cost and complication.

Some things to keep in mind:
Just be sure that you haven’t blocked the coolant return because of a leaky heater core. For this to work correctly, the coolant needs to flow from the ECT sensor tubing back to the water pump. That means a leaky heater circuit gets looped rather than just plugged up. Join the rubber hoses together with a hose splice from Home Depot rather than plug them up.

Where to put it:
Use the heater feed that comes off the intake manifold that has the ECT sensor in it. Cut the rubber hose that connects the manifold water feed to the heater and splice in a tee adapter for the temp gauge sender. That way you will get the most accurate temp readings since the coolant is always flowing through the heater circuit in a stock car. Remember to include a ground wire if you use an electrical sender.

Tee adapter info:
Make a pilgrimage to your local hardware or home supply center and get some copper pipe and a tee that fits the temp gauge sender. Solder two pieces of copper pipe onto a copper pipe tee with threads in the tee part. Find the correct brass fitting to match the temp sender threads to the tee fitting.

Ethan smith said:

yes, thats the only place the aftermarket gauge would fit.

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You either replace the factory temp sending unit in the driver front lower intake by the distributor with the aftermarket sending unit, or get a new thermosat housing with a threaded bung to install the aftermarket temp sending unit. As mentioned, you need to replace the ECT sending unit asap That tells the computer the coolant temperature and without it, your car will run poorly.

Replace your cannister

Why did you block off your EGR?

You need to learn how to set the timing and base idle.

People need to research before they start hacking up cars and then wonder why it runs poorly afterwards.