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Discussion Starter #1
My 1966 with a 1988 5.0 has this problem where the a/c works good but will eventually cause the car to sputter and die only at idle. Have been taking my time going through it, have cleaned the throttle body and iac (were pretty dirty) but it did not fix the problem. My friend hooked up his ac manifold tester and the blue gauge dropped down to 10 when it was cutting off, he said that is not good and that i need to put more freon in it. The red gauge was unable to be hooked up because the nipple on the ac compressor line is too small. When i first turn on the car it seems to do alright at idle with the ac on, surges a little sometimes but does alright-seems to only make the motor die when it is up to temp. Timing also seems a little high at the moment but i havent gotten my hands on a timing gun just yet. Spark plugs have alot of gas on them so i will need a new set. (Not sure if that could be related to ac problem) but i still need new ones or at least to clean them. Also have misplaced my obd 1 scanner because i have been busy with other things up until recently.
Wanted to get your guys thoughts as me and my buddy work through the motor.
Thanks -Mike
 

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Is your IAC getting the "ac on" signal to kick the idle speed up when you air is on? There is a wire that gets a signal from the ac to do that...
 

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Maybe check PIN 54 wired to the AC relay. Wide-Open Throttle A/C Shutoff relay (WAC) not only shuts off A/C at wide open throttle but also under prolonged idle.
 

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Maybe check PIN 54 wired to the AC relay. Wide-Open Throttle A/C Shutoff relay (WAC) not only shuts off A/C at wide open throttle but also under prolonged idle.
will have to take a look at that tomorrow. should there be a particular voltage on it or should i just check if there is a signal? and is the signal only present when the a/c is on?

Today i brought the idle down because even with the a/c off the base idle seems to get high when the car warms up. I put a timing light on it and messed with the idle and it sounded good.. but after the car warmed up it would just choke, sputter, and die like it did when i put the ac on before i messed with the idle/timing. Now it happens without the a/c on. any idea about that? The injectors are the ones that came with the motor.. maybe dirty or going out? Should check fuel filter? The fuel pump is a new msd one.

Thanks Don
 

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Check the plug/vacuum hose to your MAP sensor(assuming your 88 is a non California speed density setup). If it's not getting a good vacuum signal, the car will run like crap.The low side A/C pressure can read low as long as it's not at 0. The only way to know the correct charge is to evacuate and recharge the system. If you have converted to r134a, the charge should be a little lower than the r12 charge due to higher pressures. As @DonP said, The 5.0 has a relay that sends voltage to the ECM that raises the idle when A/C is engaged.
 

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Discussion Starter #6
Check the plug/vacuum hose to your MAP sensor(assuming your 88 is a non California speed density setup). If it's not getting a good vacuum signal, the car will run like crap.The low side A/C pressure can read low as long as it's not at 0. The only way to know the correct charge is to evacuate and recharge the system. If you have converted to r134a, the charge should be a little lower than the r12 charge due to higher pressures. As @DonP said, The 5.0 has a relay that sends voltage to the ECM that raises the idle when A/C is engaged.
Will do thanks, i assume i need a special tool to check the vacuum level? I will make sure that the hose is present for the map sensor. i did blow smoke into the vacuum line and nothing appeared to leak, but im not sure if i blew hard enough to make it through the system since i used a cigarette ?
 

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I don't have A/C yet and honestly don't know much about how it works. I simply saw the WSD relay in the 88-91 diagram which is actually MAF so I don't know how/if it applies to SD if that is what you have. http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Schematic, in color, of the Fuel & Alternator & Ignition & AC, for a 5.0, by TMoss:

That site is a great resource btw: Mustang FAQ - Wiring & Engine Info

As for how it works , I will simply quote verbatim from the book How to Understand, Service and Modify Ford Fuel Injection and Electronic Engine Control by Charles O. Pobst, SAE. (p.138 7.3)

Wide-Open Throttle A/C Shutoff Relay
The Wide-Open Throttle Air Conditioner (WAC) Shutoff Relay receives sings to briefly cut off the air-conditioner under full throttle conditions , or under prolonged idle.


To me, that sound like it cuts off AC not raise the idle. But again, I don't actually have A/C or any first hand experience with it in this application, so take that as you will.
 

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Discussion Starter #8
Maybe check PIN 54 wired to the AC relay. Wide-Open Throttle A/C Shutoff relay (WAC) not only shuts off A/C at wide open throttle but also under prolonged idle.
i messed with it a bit today and the idle does not go up when i turn on the a/c. after speaking to my dad (he had some of his company guys swap the 5.0 a year ago they usually do big dump isuzu trucks and arent very familiar with old 5.0s) it seems like the wire to the ecu to raise the idle was never installed... they were in a hurry and the ac was not even hooked up when the motor was first swapped... i think that may be my problem. do you know if pin 54 is what increases idle? and i assume i would need to wire whatever wire powers the a/c to the ecu... at them moment my a/c can be turned on even if the car is off.. i dont really like that and will have to fix it.
 

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Discussion Starter #9
Is your IAC getting the "ac on" signal to kick the idle speed up when you air is on? There is a wire that gets a signal from the ac to do that...
thanks i think that is the problem.. the car does not go to higher rpms, it immediatly drops a bit when the ac is turned on.
 

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I don't remember the details of color or location, but there is a wire in the harness that sends the ac signal to the ecu. Either a wiring diagram or a Google search will find it. Should be simple as connecting the wire.
 

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Discussion Starter #12
Maybe check PIN 54 wired to the AC relay. Wide-Open Throttle A/C Shutoff relay (WAC) not only shuts off A/C at wide open throttle but also under prolonged idle.
Any idea what kind of relay this is? Im not very familiar with relays.. it goes to pin 54...still learning haha i think the only ac is wired into the radiator fan relay atm lol.. or any idea of the volts that come from the relay
744496
 

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Any idea what kind of relay this is? Im not very familiar with relays.. it goes to pin 54...still learning haha i think the only ac is wired into the radiator fan relay atm lol.. or any idea of the volts that come from the relay View attachment 744496
Not sure but I just searched for 1988 Ford Mustang WAC relay and did get results.
RockAuto seems to call it a HVAC relay. They seem be priced around $28.
You would need source a socket for the relay as well.
It is wired to PIN 10, 37/57, and 54

All this is doing is cutting off AC at Wide Open Throttle and/or extended idle. You could just as well just turn the AC on/off manually under the same conditions, LOL.
 

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Here is a little info I gleaned from a Google search, it refers to a '91 harness so there could be color changes possible depending on what year yours is but the general idea is the same.




  • . 9. For air conditioning, you have several options. If you do not have any plans of using air conditioning, you can remove the A/C connections from the harness. If you are using air conditioning and don’t want to connect it to the EFI harness, you can remove the A/C connections from the harness. The engine will run fine, but you will be removing what is known as a “feed-forward” signal to the EEC. When the EEC senses the +12V going to the compressor clutch, it anticipates the load on the engine and increases the idle slightly. Without this input, your engine might stall when the compressor engages with the engine at idle. In all reality, the engine probably will stay running, but may stumble for a second at idle when the A/C compressor engages. Above idle, this signal does not matter. The other EEC control function is WOT (Wide Open Throttle) cutoff. If the EEC senses WOT from the throttle position sensor, it will deenergize the A/C WOT relay and cut power to the compressor. This function is solely to cut the parasitic drag from the compressor at WOT so the engine can put maximum power to the transmission. The A/C compressor and engine will work just fine without this function connected. If you want to use these functions with your air conditioning, it’s easy enough to do. The following steps refer to the A/C WOT relay, pressure safety switch, compressor clutch connector, and the gray round 8 pin connector. They look like this (the WOT relay in my harness was messed with at one time – the crimp connectors should not be there):   a. If you have no plans of using air conditioning or don’t wish to use the EEC control functions for A/C, do the following: i. Remove the light green/purple wire from the round 8 pin connector. This wire runs directly to the pressure safety switch. ii. Remove the pink/light blue wire at pin 10 of the 60 pin EEC connector & the orange/light blue wire at pin 64 of the 60 pin EEC connector. These wires go to the WOT relay. An additional pink/light blue wire runs between the pressure safety switch and the WOT relay. iii. Follow the red wire from the WOT to the splice in the harness. Clip this wire from the splice. iv. Remove the A/C clutch connector from the harness. It has 2 wires – a black/yellow and black/light green. The black/yellow goes to the WOT relay. Follow the black/light green wire to the splice in the harness and clip this wire from the splice. v. The A/C WOT relay, pressure safety switch, clutch connector, and associated wiring should now be free from the harness. b. If you are using A/C and want to use the control functions, it’s very easy to do. Do the following: i. Remove the light green/purple wire from the round 8 pin connector. Disconnect the power wire going to you A/C compressor clutch and connect this wire to the light green/purple wire. ii. If your system has a pressure safety switch, clip the existing pressure safety switch connector from the EFI harness. Connect the light green/purple wire to one terminal of your pressure switch (it does not matter which terminal). Connect the pair of pink/light blue wires to the other terminal of the pressure switch. iii. Connect the black/yellow wire in the clutch connector to your compressor clutch power feed. The black/light green wire is not needed if your compressor clutch is grounded through the compressor case. If your compressor clutch is not grounded through the case, you can use the black/light green wire for your ground.



 
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