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1989 Ford Thunderbird SC
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Discussion Starter · #1 ·
Hello there,
My name is Brandon, I am having a drivability issue with my 1989 Super Coupe.
Short version, if I unplug my battery for a few hours the car runs great. Idles good, throttle is good, and WOT is good. As I drive the car the engine progressively runs rougher. It starts with a bad idle that shakes the car, to low RPMs around town, to eventually almost feels like a miss at throttle going up hills. This can happen in as little as a 30 minute drive home from work or a few hours. Occasionally, out of no where, the car will run smooth as silk while on a 2 hour drive, but as soon as I turn it off, it gets rough again. No check engine light, however, I do know that the light works as the light will come on if I unplug the MAF sensor or the EGR Feadback, ect.
I want to apologize in advance for the length of this first post, I want to lay all my information out for viewing.
Car in Question:
1989 Ford Thunderbird Super Coupe.
161k miles, Automatic, mostly original.
I bought the Super Coupe two years ago with 155k miles on it, diagnosed a possible head gasket issue, then stored it in a enclosed bin for a year.
When I did pull it out of storage, it ran like crap and did not want to idle. I got rid of all the old gas and replaced it with 93 octane, car ran well after that. Two months later the head gasket gave out, nearly hydro-locking the motor within seconds. Car was at 159k miles.
As of July 2022, the cylinder walls looked good, no signs of scratches or excessive wear. Heads were straight and cleaned. I replaced both head gaskets with Fel-Pro, new ARP Head Studs, new gaskets throughout the motor, new O2 sensors, new Motorcraft spark plugs, new idler pulleys, and did a A/C Delete.
.
Things I have checked or cleaned since head gasket blew:
I cleaned the IAC, MAF, Fuel Injectors, multiple wire connections under the hood, I also got the coil pack tested which was in spec.
Engine mounts appear to be in good shape.
.
I daily drove the SC from early July to late September, resulting in over 2k miles, at which point I bought a 96 Cougar as my winter car. I had noticed a exhaust leak was developing around where the exhaust manifolds bolt up to the cats.
.
Since I have put the engine back together it has not run right. At first it was intermittent, as in as once a week. I would appreciate any thoughts, opinions, feedback, and some insight as to what I should consider replacing or diagnosing next. Thank you for your time.
 

· The Parts Guy
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9,466 Posts
What is the fuel pressure doing when it acts up? How about manifold vacuum? Have the O2's been replaced since the headgasket failure?
 

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1989 Ford Thunderbird SC
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12 Posts
Discussion Starter · #3 ·
Thank you for your reply,
I am unsure about fuel pressure, currently I do not have a way of testing it. I will see if we have a tester at work.
I do not know how accurate the Vacuum/Boost guage is on the dash, but if I go by that, I would say the car stays consistent around 12-14 Vacuum at idle.
O2 sensors were indeed replaced. It was not right away, I did a soft reset by leaving the battery unplugged for 6 hours that day, at which point I learned that disconnecting the battery resulted in the car running better, although temporarily.
 

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Vacuum should be about 20 in neutral or park and about 15 in drive idle if an automatic.

Could be exhaust leak messing with the fuel trims. If it runs better after the batt is disconnected.
 

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If you got your O2 sensors from Ebay, or other online seller, that could be your problem. The sensors short to power, and the fuel trims go lean from the false O2 signals. You need to monitor the O2 voltage to see what it is doing.
 

· The Parts Guy
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9,466 Posts
Agreed that it sounds like you have a vacuum leak. A smoke test, and connecting a fuel pressure gauge to verify your fuel pump isn't failing as it warms up, would be the first two diagnostics that I'd run.
 

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1989 Ford Thunderbird SC
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12 Posts
Discussion Starter · #9 ·
I bought the O2 sensors off Rock Auto. NTK 22013, which claimed they were "Actual OE". The car did not improve, nor did it get worst after I swapped the sensors.
I will post my results from the fuel pressure test and smoke test in the next day or two I hope.
 

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Those are good sensors. When you disconnect the battery, you reset the fuel trims to 0%. As you drive the O2 sensors report to the PCM to adjust fuel trims to get idle, and cruise fuel to 14.7 A/F. You could disconnect the O2 sensors, after clearing the PCM memory, and see what happens, as a test. Also, is the breather hose plugged into the air intake hose that runs between the MAF, and throttle body? Fuel pressure, and bleed off tests would be good.
 

· The Parts Guy
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If you're going to run the engine with the O2's unplugged, stick a junk/old set of O2's in. Running them without the heater circuit enabled doesn't do them any favors.
 

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If you're going to run the engine with the O2's unplugged, stick a junk/old set of O2's in. Running them without the heater circuit enabled doesn't do them any favors.
That applies to wide band O2 sensors, that run very hot, high current heaters. A 40 minute of so test, should not not harm the stock narrow band ones. If it is running real rich, it might foul them. If careful, you could spray starting fluid around intercooler pipes, and upper intake, etc. Also, a volt meter tapped into the O2 sensors, (with them plugged in), is a good way to monitor a rich, lean condition. Monitor the O2 signal, while spraying for leaks works very well, also.
 

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1989 Ford Thunderbird SC
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Discussion Starter · #13 ·
Thank you for the replies, I brought the SC with me to work today so I can do the diagnostic work.
Plan of attack so far:
Car is currently running rough as I have not pulled the battery in over two weeks.
Start with the smoke test.
Check fuel pressure at start up, while idling, and under load while cold.
If I do not find a issue at this point, I will use my multi-meter on the O2 Sensors to get a benchmark of what they are reading.
Then I will pull the battery and disconnect the O2 Sensors for a few hours.
Test drive vehicle with O2 Sensors disconnected for about 20 ish minutes.
From there I will post results by the end of today.
 

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97 Thunderbird 4.6, 98 Mark VIII LSC
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· The Parts Guy
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That applies to wide band O2 sensors, that run very hot, high current heaters.
It applies to both, it just sucks to kill the more expensive wideband sensors even more.

OP, if you're able to pull fuel trims (not sure what you have available to you at your work), that would tell us alot.
 

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1989 Ford Thunderbird SC
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Discussion Starter · #16 · (Edited)
I got home late tonight, but I said I would message an update.
.
First, I did the smoke test. Resulted in finding two leaks. One was through the return spring for the throttle body/valve. Second was a hole that had formed in the line that controls the butterfly between the Supercharger and vacuum. There was enough vacuum still to open that valve but it was easy to move by hand. I sealed that leak up temporarily and will see about a replacement in the near future.
.
From there, I started the car, which was rough but soon smoothed out as I let it idle. I took the car for a test drive. While the idle was much smoother, as soon as it goes in to gear the rpms drop way low. The lower the rpm, the lower the vacuum, the more it tries to stall. It does not idle up to compensate.
.
Later in the day I pulled the battery and unplugged the O2 sensors. During this time I did my front brakes and tie rods, inner and outer. Unfortunately two hours was not long enough, when I started the car with the sensors unplugged, the car almost did not idle. There was no CEL on, but the idle was very bad. I am impressed that it did not stall, seriously that was low. I gave it about a minute with no improvement, idled it up by hand a couple times. The car smelled very strong, can not say it was gas per say, more like very strong emissions? Lot of CO2. It has done that since the head gaskets were changed, but this was worst than lately. I turned the car off, did not attempt to drive it.
.
I drove home tonight with the sensors plugged in, vacuum temporarily sealed, and some unrelated repairs. At idle, in neutral or park, the car is much smoother. However, the vibration and studded the car had at 2200 rpm now happens as low as 1600 now while under load. When I keep my foot off the pedal, it smoothes out. I noticed my head lights were dim tonight too.
When I got home, I realized I was supposed to go out again, so I started the car back up. This was within a minute of shutting it down, lights and heater were all off, and the car almost did not want to start. Sounded like a dead battery, yet I was just on the road home for about 30 minutes. So... wild idea here... alternator?
.
Tomorrow I will plan to check fuel pressure, do the self diagnostic (thank you for the link), examine my exhaust leaks, and test my alternator.
Thank you everyone for your time and suggestions, I will keep you all posted as I go here. Hopefully the solution helps someone else out in the future too.
 

· Registered
1989 Thunderbird Super Coupe
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10 Posts
Hello there,
My name is Brandon, I am having a drivability issue with my 1989 Super Coupe.
Short version, if I unplug my battery for a few hours the car runs great. Idles good, throttle is good, and WOT is good. As I drive the car the engine progressively runs rougher. It starts with a bad idle that shakes the car, to low RPMs around town, to eventually almost feels like a miss at throttle going up hills. This can happen in as little as a 30 minute drive home from work or a few hours. Occasionally, out of no where, the car will run smooth as silk while on a 2 hour drive, but as soon as I turn it off, it gets rough again. No check engine light, however, I do know that the light works as the light will come on if I unplug the MAF sensor or the EGR Feadback, ect.
I want to apologize in advance for the length of this first post, I want to lay all my information out for viewing.
Car in Question:
1989 Ford Thunderbird Super Coupe.
161k miles, Automatic, mostly original.
I bought the Super Coupe two years ago with 155k miles on it, diagnosed a possible head gasket issue, then stored it in a enclosed bin for a year.
When I did pull it out of storage, it ran like crap and did not want to idle. I got rid of all the old gas and replaced it with 93 octane, car ran well after that. Two months later the head gasket gave out, nearly hydro-locking the motor within seconds. Car was at 159k miles.
As of July 2022, the cylinder walls looked good, no signs of scratches or excessive wear. Heads were straight and cleaned. I replaced both head gaskets with Fel-Pro, new ARP Head Studs, new gaskets throughout the motor, new O2 sensors, new Motorcraft spark plugs, new idler pulleys, and did a A/C Delete.
.
Things I have checked or cleaned since head gasket blew:
I cleaned the IAC, MAF, Fuel Injectors, multiple wire connections under the hood, I also got the coil pack tested which was in spec.
Engine mounts appear to be in good shape.
.
I daily drove the SC from early July to late September, resulting in over 2k miles, at which point I bought a 96 Cougar as my winter car. I had noticed a exhaust leak was developing around where the exhaust manifolds bolt up to the cats.
.
Since I have put the engine back together it has not run right. At first it was intermittent, as in as once a week. I would appreciate any thoughts, opinions, feedback, and some insight as to what I should consider replacing or diagnosing next. Thank you for your time.
I had a similar very intermittent problem with my 1989 SC and it ended up being the cam position sensor. Intermittently the voltage would drop coming from the sensor causing the engine to run extremely rough for several minutes then disappear. Only hint was the tachometer would not work while this was happening. After replacement the car has been running fine.
 

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1989 Ford Thunderbird SC
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Discussion Starter · #19 · (Edited)
I had a similar very intermittent problem with my 1989 SC and it ended up being the cam position sensor. Intermittently the voltage would drop coming from the sensor causing the engine to run extremely rough for several minutes then disappear. Only hint was the tachometer would not work while this was happening. After replacement the car has been running fine.
My speedometer bounces around sometimes when in gear coasting around parking lots.
.
Got my codes from the Self Test. 85 and 32. From AllData it appears to be, "EGR Valve Not Seated" and "Canister Purge Circuit Failure", which I believe is in the passenger side fender well?
.
Edited: ment to say "speedometer".
 

· The Parts Guy
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9,466 Posts
Either of those could explain the inconsistent nature of this issue.

Here's what to check regarding the EGR position: EEC-iv code 32 - Ford Truck Enthusiasts Forums

Run down this diagnostic path for the CANP, and be sure to check that system for leaks as well (smoke test it): Code 85!

The speedometer bouncing points to a VSS issue, it shouldn't cause the engine issues you're having.
 
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