1987 mustang gt 5.0 flooding itself when it’s in gear

Willyc

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Aug 31, 2022
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Thanks in advance for your help. I have a 1987 mustang GT 5.0 HO. I’ve only had it for a year. The car went to the mechanic to get a theft deterrent switch installed, a switch that shuts off the fuel pump. It also went in because the signals were not working, he didn’t fix the signals but said repaired some wiring in the steering column. Went to pick up the car, it idled ok but when you let the clutch out it would immediately die. And to be clear, you only have to let the clutch out about 1 inch, just enough to engage the clutch safety switch. You can keep the car going by giving it a lot of gas. We drove it home because the mechanic couldn’t figure it out. While driving behind it you could smell the raw fuel coming out the exhaust, that’s how much fuel is coming out. So as soon as you let the clutch out, the clutch safety switch is sending a signal that it is under load and the engine is dumping fuel and changing the timing like it’s at full speed. Checked it over when I got home, found one O2 sensor not plugged in and the other wiring harness was melted on the exhaust so replaced them. The EGR valve had been plugged on purpose so fixed that. Repaired any vacuum leaks in the system so the vacuum is where it should be. I replaced the map sensor because that is what controls the fuel and timing but nothing happened. The question I have, with the map sensor unplugged, there is a ground wire, a 5v constant wire and a signal wire. I’m getting 5v from the constant wire and the signal wire, does that sound right? With the map sensor being plugged in and the car running, the signal wire is sending a 2.5v signal almost all the time, even when the engine is revved up.
These are the codes I dumped. Key on engine off, 81 and 85.
Key on engine running, 4 came up first, then 1, then 94 and 44
Sorry for the winded post, wanted to try and give you the best information
 
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Mustang5L5

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Mod Dude
Feb 18, 2001
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Being excessively rich does in fact make it very easy to stall out the engine. You would need to give it more throttle than typical to keep the engine from stalling out. This, plus the fact that you state it seems raw gas is pouring out the exhaust point to an overly rich condition. When it stalls, it probably stumbles a bit on restart I assume? You can help that by depressing the accelerator to put the ECU in flood clear, and crank. Should make it easier to restart

Speed Density cars are VERY sensitive to vacuum leaks. I would perform a smoke test on the car to look for leaks. This probably more critical on 86-88 cars than the 89+ cars due to the MAP reading manifold vac to adjust fuel/timing. Video that shows how to build a simple home machine below.

Code 81 is one of the smog solenoids failing (usually paired with code 82)
Code 84 is an EGR vac regulator failure
Code 41 is RH O2 sensor indicates lean (could be due to vac leak)
Code 94 and 44 are referring to the air injector system for the air pump. Typically if the pump is deleted.


I would troubleshoot for a bad vac leak related to the code 41




View: https://www.youtube.com/watch?v=crc6CJ_ni2w
 
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Willyc

Member
Aug 31, 2022
8
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Being excessively rich does in fact make it very easy to stall out the engine. You would need to give it more throttle than typical to keep the engine from stalling out. This, plus the fact that you state it seems raw gas is pouring out the exhaust point to an overly rich condition. When it stalls, it probably stumbles a bit on restart I assume? You can help that by depressing the accelerator to put the ECU in flood clear, and crank. Should make it easier to restart

Speed Density cars are VERY sensitive to vacuum leaks. I would perform a smoke test on the car to look for leaks. This probably more critical on 86-88 cars than the 89+ cars due to the MAP reading manifold vac to adjust fuel/timing. Video that shows how to build a simple home machine below.

Code 81 is one of the smog solenoids failing (usually paired with code 82)
Code 84 is an EGR vac regulator failure
Code 41 is RH O2 sensor indicates lean (could be due to vac leak)
Code 94 and 44 are referring to the air injector system for the air pump. Typically if the pump is deleted.


I would troubleshoot for a bad vac leak related to the code 41




View: https://www.youtube.com/watch?v=crc6CJ_ni2w

I did the smoke test and didn’t find any leaks. I’ve been trying to test the map sensor and I believe that is where all my problems are. Either it’s a bad map sensor, which I replaced already, or there is a problem with the wires between the map sensor and the computer, or I have a computer problem. Everything I’ve read about dumping the computer codes with key on engine running has told me that the computer should give you code 11, and that will tell you the computer is ok. Then it gives you 4, which tells you it’s ready to do a self diagnoses, then it gives you the codes. When I did it, it gave me 4, then after a long pause it gave me 1, after another long pause it gave me 94 and44. So I’m wondering if there is a computer issue. Does anyone have a 1987 or 88 that they could test the map sensor plug. Test it with key on engine off, and the plug unplugged from the map sensor. I need to know if the signal wire should be sending 5v. I’m worried it’s not supposed to be sending 5v and it fried my new sensor
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
39,465
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4 is not the proper separation code between KOEO and CM codes. It should be 10, which is a single blink.

You should get an 11, then a 10 (which is one blink) and then an 11 if everything is all clear. Sometimes a 4 blinks to indicate number of cylinders (4= 8 cyl)

What method are you using to pull codes?
 

Willyc

Member
Aug 31, 2022
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4 is not the proper separation code between KOEO and CM codes. It should be 10, which is a single blink.

You should get an 11, then a 10 (which is one blink) and then an 11 if everything is all clear. Sometimes a 4 blinks to indicate number of cylinders (4= 8 cyl)

What method are you using to pull codes?
I’m using a multimeter with this wiring diagram
 

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Mustang5L5

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Mod Dude
Feb 18, 2001
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That method works fine, but interpreting the sweeps can be a little confusing. That’s why I usually recommend the innova 3145 reader as it gives you hard numbers.

I don’t think you have an ECU issue at all. Unfortunately those codes that did come up don’t really cause some of the issues that you are seeing.


The sensor wire for the MAP should send 5v on the orange/white wire from pin 26 off the ECU
 

Willyc

Member
Aug 31, 2022
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1
13
That method works fine, but interpreting the sweeps can be a little confusing. That’s why I usually recommend the innova 3145 reader as it gives you hard numbers.

I don’t think you have an ECU issue at all. Unfortunately those codes that did come up don’t really cause some of the issues that you are seeing.


The sensor wire for the MAP should send 5v on the orange/white wire from pin 26 off the ECU
Thanks, I’ll look into the reader.
I’ve tested the map sensor with a vacuum pump to see if the signal wire is sending different voltage while at different pressures, but it will only read 2.5 volts. Do you think it’s just a bad map sensor even though it is a new one? At this point I’m running out of ideas, so if anyone has any, please let me know
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
39,465
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224
Thanks, I’ll look into the reader.
I’ve tested the map sensor with a vacuum pump to see if the signal wire is sending different voltage while at different pressures, but it will only read 2.5 volts. Do you think it’s just a bad map sensor even though it is a new one? At this point I’m running out of ideas, so if anyone has any, please let me know


The MAP sensor does not output a signal in volts. It outputs a frequency. So that’s why the voltage stays the same.

Give this a read. Sorry for the ads.

 

Willyc

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Aug 31, 2022
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The MAP sensor does not output a signal in volts. It outputs a frequency. So that’s why the voltage stays the same.

Give this a read. Sorry for the ads.

Thanks for everyone’s help but we found the problem. We took the computer out and opened it up. There was a lead that was broken, we soldered it back together and that fixed the problem. Thanks again for your help. I hope this feed may help someone else in the future
 

Willyc

Member
Aug 31, 2022
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Pin 46 trace I assume?

Glad you found it
We found it on the computer board, we took it apart just to see if anything was going on with it. Next would have been checking the wiring between the computer and the sensors
 

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