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Author Topic: 1986 Cougar 3.8L V6 won't Idle  (Read 1009 times)

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Offline Foxbody Cougar

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1986 Cougar 3.8L V6 won't Idle
« on: May 31, 2018, 12:01:44 AM »
First some background info. My 1986 Mercury Cougar 3.8L won't idle on its own. The problem started showing itself when the car would be idling normally and the idle would idle up and idle back down for unknown reasons. This idle surging became more pronounced over time and eventually the car would no longer start on its own. However, if I spray starter fluid (or carb. cleaner or raw gasoline) down into the TBI it starts right up and runs great until it burns off the fuel. The only way to keep it running after priming it with fuel is to keep goosing the gas pedal over and over again. When you take your foot off the gas pedal it stalls out. The following are what has been done to attempt to solve this problem:
1. replaced the fuel pressure regulator
2. throttle position sensor (TPS)
3. replaced the fuel injectors
4. replaced the control module
5. replaced the pick up coil
6. replaced the fuel filter
7. replaced the computer
8. replaced the battery cables
9. fuel pump is ok and fuel pressure is good
10. Bought a tune up kit for the throttle body (TBI) and rebuilt that
11. Replaced the idle speed control motor
12. I have found no vacuum leaks.
The car is currently at a auto repair shop that specializes in fox body mustangs. I had it towed there because they have the diagnostic equipment (that I don't have) which should have shown a code or codes telling us what the problem is. But the car shows NO codes. They said they can't figure out what the problem is. For some reason the injectors aren't getting fuel. I bought the car new in 1986, it has 135,000 miles on it and its never been wrecked. I don't want to give up on the car for sentimental reasons. There must be a way to fix this. Any advice would be greatly appreciated!!!


Offline pinto_one

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Re: 1986 Cougar 3.8L V6 won't Idle
« Reply #1 on: May 31, 2018, 08:24:38 AM »
well you could have a map sensor problem , to check remove the vacum line and plug ,should go full rich , or the shop might have one on the sheff to test , other things it could be shorted O2 sensor , temp sensor sometime give a code but not always , last it could be a jumped (bad) timing chain , put a vaccum gauge to check for low vaccum to check if it will run long enough after you prime it with fuel , fould a few of those over the years , they seam to wear out quicker running around town than on the highway , but keep us posted if they find it ,
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0

Offline Foxbody Cougar

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Re: 1986 Cougar 3.8L V6 won't Idle
« Reply #2 on: May 31, 2018, 10:57:26 AM »
Thanks! I'll pass your ideas on to the mechanic.

Offline Lonny Candel

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Re: 1986 Cougar 3.8L V6 won't Idle
« Reply #3 on: June 01, 2018, 10:25:19 PM »
I am curious as to how many miles your Cougar has on it. I wonder how good that 3.4L engine is? Thanks.
90 Mustang LX w/ 84 TC 2.3 / 88 TC injectors, VAM, & computer
84 Mercury Cougar LS 3.8
81 Ford Durango 3.3
81 Chevy El Camino 350 Crate

Offline Foxbody Cougar

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Re: 1986 Cougar 3.8L V6 won't Idle
« Reply #4 on: June 02, 2018, 12:11:32 AM »
The Cougar has 135,000 miles on it and the 3.8L V6 it has is the original engine. When its running the engine sounds good.   

Offline Lonny Candel

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Re: 1986 Cougar 3.8L V6 won't Idle
« Reply #5 on: June 03, 2018, 02:26:16 PM »
Not too many miles, but enough for it to have issues. Have you ever had the tranmission rebuilt? And I take it the engine hasn't had a rebuilt. Can you post some pictures of your senitmental Cougar?
90 Mustang LX w/ 84 TC 2.3 / 88 TC injectors, VAM, & computer
84 Mercury Cougar LS 3.8
81 Ford Durango 3.3
81 Chevy El Camino 350 Crate

Offline Foxbody Cougar

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Re: 1986 Cougar 3.8L V6 won't Idle
« Reply #6 on: June 04, 2018, 12:21:50 AM »
The tranny, is the original C5 and was rebuilt in 2001. The engine has never been redone. Why do you ask?   

Offline Lonny Candel

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Re: 1986 Cougar 3.8L V6 won't Idle
« Reply #7 on: June 05, 2018, 10:33:29 AM »
Just for potential things to think of if I ever get one.
90 Mustang LX w/ 84 TC 2.3 / 88 TC injectors, VAM, & computer
84 Mercury Cougar LS 3.8
81 Ford Durango 3.3
81 Chevy El Camino 350 Crate

Offline 65ShelbyClone

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Re: 1986 Cougar 3.8L V6 won't Idle
« Reply #8 on: June 05, 2018, 12:43:22 PM »
It looks like many parts have been replaced without any troubleshootin g. Not to rub salt in it, but that's the "shotgun approach" and always costs lots of money with a low probability of fixing the problem. Unfortunately with how many things you replaced, it has also introduced the possibility of defective new parts causing problems or new parts not being adjusted properly.

You've described a fuel delivery problem. Among other things, you said the injectors are new, the regulator is new, the ECU is new, and the pressure is "good." That suggests that the injectors are not being commanded to inject enough fuel, leaving wiring and sensors as the next areas to check.
The Ford MAP sensor of that era outputs a digital frequency signal rather than voltage. It will require a multimeter that can read frequency (Hz).

As an FYI, the O2 sensor(s) is out of the picture until the engine reaches operating temperature. The ones most responsible for mixture control on cold startup are the air temp sensor, coolant temp sensor, and manifold pressure sensor.
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Offline Lonny Candel

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Re: 1986 Cougar 3.8L V6 won't Idle
« Reply #9 on: June 10, 2018, 09:56:27 AM »
Hey Foxbody Cougar, I just traded my Jeep for a 84 Cougar 3.8L. It seems like it is a good running, with ice cold ac, updated pioneer stereo, car. It looks like it has 105K miles on it according to the OD. I am not sure if I will be keeping it though. I am not really into the body style. However, it does have some rust in a couple of places, and a small dent. Otherwise, the gold paint and body are in really nice condition. Interior is good, but the center console is roughed up. If you are interested, lmw while I ponder on what to do with it.
90 Mustang LX w/ 84 TC 2.3 / 88 TC injectors, VAM, & computer
84 Mercury Cougar LS 3.8
81 Ford Durango 3.3
81 Chevy El Camino 350 Crate