Engine New problem, hesitating on acceleration and hard starting

JohnG

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Mar 21, 2020
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San Antonio, Texas
My car is a 1991 GT, with roughly 270K miles on it. She is a daily driver, as has been since I bought her new in 1991. I have been experiencing hesitation and backfiring/popping back into the intake for a while. I have been attempting to clean the injectors with Lucas cleaner. Seems to help somewhat, but not totally. Could be my imagination.

Now, she is exhibiting hard starting, getting slowly worse.

I ran the codes today and have 44. I think this is wrong because (long story here) I had 94 and 44 a while ago. So I pulled the cross over tube and it was plugged. Cleared it out and reinstalled it. Still had 94 and 44. Then checked the air injection ports on the back of the heads. Plugged, as you can imagine. I pulled off all the accessories on the front of the engine, including the screw in plugs. Then used a drill and wire coat hanger to "rod" out the passages. After replacing all the stuff on the front, I fired up the engine and had pulsing exhaust out of both sides of the rear of the cylinder heads. The TAD and TAB tested good, so this is why I don't believe the 44 code. Unless some of the ports from the common rail to the exhaust port are plugged. Maybe one side is not getting the same flow as the other because of this.

I also have 85 code, which is the evap vacuum solenoid missing, which it is.

So, I am thinking coil or wires, since I have recently went through the distributor and new spark plugs.

Any thoughts? She runs good when warm and does not exhibit as much hesitation/backfiring when warm.

Also note, the engine is completely stock. Only mod is 3-chamber quite FlowMaster mufflers which replaced the originals 10 to 15 years ago.
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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Have you checked for timing chain slop? That's a lot of miles.
Wires are always an over looked wear item but most times cause a miss not a back fire, run a compression test and/or put a vacuum gauge to it. A bad valve will make a vacuum gauge needle flutter.
 

JohnG

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Mar 21, 2020
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Thanks. Sounds good. I look into getting a compression tester and vacuum gauge. I have a lot of other cars which can use these also.
Wires are easy to get and change. Wires and coil may be next on the list.

I had the timing chain cover gasket blow out many years ago, and the slop did not seem excessive when I changed it. This car is not raced or driven hard (any more). I drove her with some gusto when she was new, but I take it easy, based on her age and mileage, however it is hard to keep my foot out of it all the time.
More info: the injectors are original and never have been removed. The coil was replaced many years ago, so not new anymore. Plug wires are not original, but (I think) 8 or 9mm blue Motorcraft replacements. They barely fit in the holders.
 

Dan02gt

10 Year Member
Mar 2, 2003
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Wow it’s crazy you bought that car new and are still daily driving it!!

Sounds like it is running a little lean before it goes into closed loop. I would check the engine coolant temp (ECT) and intake charge temp (ICT) sensors. Also check and make sure you don’t have any vacuum leaks. Even though you’re ECU doesn’t monitor the O2 sensors in open loop it would be a good thing to swap them if they are old.

If you haven’t opened up the ECU and checked the capacitors, I would have a look at them too. They start leaking and cause lots of issues.

There is a surging idle check list sticked her that has tons of troubleshooting advice that I would recommend you go through.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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If it's stock or close to just get some quality wires, don't need no high dollar race wires, keep it simple.
The 'surging idle checklist ' is a good way to get to know how things work and proper diagnostic procedures.
It's in here with a lot of good stuff.
 

JohnG

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Mar 21, 2020
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Thanks guys. I appreciate the advice. She is truly one in a million (or one of a million???) You don't see one-owner cars this old. I get a lot of offers for her, but when they learn I bought her new, right out of college, they back off because they know I just won't sell. I also get a lot of interest in my other Mustang, a 1965 Coupe which was my high school car, and my first car. Also, she is NOT for sale. Causes much heart ache locally.
 
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jrichker

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What do you get for engine running codes?
Cylinder balance test: use this to find dead or weak cylinders:

Revised 09-Sep-2017 Added reminder to write down the stored codes and engine running codes.

The computer has a cylinder balance test that helps locate cylinders with low power output. You’ll need to dump the codes out of the computer and make sure that you have the A/C off, clutch depressed to the floor and the transmission in neutral. Fail to do this and you can’t do the engine running dump codes test that allows you to do the cylinder balance test.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Be sure to turn off the A/C, have the clutch depressed to the floor, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.


Here's how to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

583775.jpg


583776.jpg


If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

583777.gif


The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

583778.gif


The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.
This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and drivability problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you dump the codes and then you start the engine with the test jumper in place. Be sure the A/C is off, clutch depressed to the floor and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10
583779.jpg




Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see www.midwayautosupply.com/Equus-Digital-Ford-Code-Reader/dp/B000EW0KHW Equus - Digital Ford Code Reader 3145.
It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.
Order it at Walmart for a better price and free shipping
583780.jpg


Write down the codes that the computer outputs since they will give you information on problems that are stored in the computer's memory


Cylinder balance test


If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1300-1500 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.

Warm the car's engine up to normal operating temperature. With the test jumper in test position, start the engine and let it stabilize. It should flash a 10 and then a 4 and maybe an 11. If no 11, then there are other codes that will be dumped.

Write down the codes that the computer outputs since they will give you information that the computer found when it is running. These are often different from the stored codes.

One of the first tests it does is to open the EGR all the way, this will cause the engine to stumble and almost die. If the engine dies here then you have EGR problems.
To start the cylinder balance test, briefly floor the accelerator past 2500 RPM and let off the accelerator. The engine will stabilize at about 1300-1450 RPM and the cut off the fuel injectors one at a time. The engine speed will drop briefly and the computer will turn the fuel injector for the cylinder under test back on. Then it starts the process for the next cylinder. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure

See View: https://www.youtube.com/watch?v=HDXrkKS4jTE
for a visual tour through the process. There is no voice narration so you have to listen carefully for the engine sounds. I posted the link for the benefit of Stangnet members who had questions about how to do a cylinder balance test. I do not own that video and I am not the creator.

Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder balance test. Low compression on one of these cylinders rules out the injectors as being the most likely cause of the problem. Look at cylinders that fail the cylinder balance test but have good compression. These cylinders either have a bad injector, bad spark plug or spark plug wire. Move the wire and then the spark plug to another cylinder and run the cylinder balance test again. If it follows the moved wire or spark plug, you have found the problem. If the same cylinder fails the test again, the injector is bad. If different cylinders fail the cylinder balance test, you have ignition problems or wiring problems in the 10 pin black & white electrical connectors located by the EGR.

How to do a compression test:
Only use a compression tester with a screw in adapter for the spark plug hole. The other type leaks too much to get an accurate reading. Your local auto parts store may have a compression tester to rent/loan. If you do mechanic work on your own car on a regular basis, it would be a good tool to add to your collection.

With the engine warmed up, remove all spark plugs and prop the throttle wide open with a plastic screwdriver handle between the throttle butterfly and the throttle housing. Crank the engine until it the gage reading stops increasing. On a cold engine, it will be hard to tell what's good & what's not. Some of the recent posts have numbers ranging from 140-170 PSI. If the compression is low, squirt some oil in the cylinder and do it again – if it comes up, the rings are worn. There should be no more than 10% difference between cylinders. Use a blow down leak test (puts compressed air inside cylinders) on cylinders that have more than 10% difference.

I generally use a big screwdriver handle stuck in the TB between the butterfly and the TB to prop the throttle open. The plastic is soft enough that it won't damage anything and won't get sucked down the intake either.

A battery charger (not the trickle type) is a good thing to have if you haven't driven the car lately or if you have any doubts about the battery's health. Connect it up while you are cranking the engine and it will help keep the starter cranking at a consistent speed from the first cylinder tested to the last cylinder.




Beg, buy, or borrow a vacuum gauge... backfiring out the intake is due to a lean fuel mixture in most cases.
Vacuum gauge indications:
vacuum-gauge-readings-jpg.jpg
 

JohnG

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Mar 21, 2020
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I did an injector test and it showed a code of 19, then 9. The book did not explain fully what this could mean.

New wires and coil have been ordered from Rock Auto. Should be here Tuesday. Good thing because I have to drive her out of town on Saturday for a 300 mile trip.
 

jrichker

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I did an injector test and it showed a code of 19, then 9. The book did not explain fully what this could mean.

New wires and coil have been ordered from Rock Auto. Should be here Tuesday. Good thing because I have to drive her out of town on Saturday for a 300 mile trip.
Injector test?
Are you sure that you didn't mean Cylinder Balance test as described in my previous post?
 

Willybill32

Active Member
Jul 16, 2019
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Lexington, KY
Thanks guys. I appreciate the advice. She is truly one in a million (or one of a million???) You don't see one-owner cars this old. I get a lot of offers for her, but when they learn I bought her new, right out of college, they back off because they know I just won't sell. I also get a lot of interest in my other Mustang, a 1965 Coupe which was my high school car, and my first car. Also, she is NOT for sale. Causes much heart ache locally.
I bought my ‘86 GT new and feel much the same way you do, although mine hasn’t been a daily driver for 20 years.
 

JohnG

Member
Mar 21, 2020
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San Antonio, Texas
Congrats on keeping your 86 GT. Maybe we should create an Original Owners Society. I am guessing it would be a small group.

Sometimes I question the sanity of driving a 30-year old car with over a quarter million miles as a daily driver, but then I realize I can fix anything on it cheaply. Not so with more modern cars. But, she has been very good to me.

Also, just to brag here, she has her original clutch still. It has seen ALL the miles put on her. When it finally gives out, I will probably have it framed.
 

JohnG

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Mar 21, 2020
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San Antonio, Texas
Changed the plug wires and coil last night. When I fired her up, I noticed a ticking sound right around 1800RPM. It was not present below or above that. I am kinda thinking a sticky lifter. Maybe varnished up with 30 years of use. I have been using Mobil 1 full synthetic since the car was new, after breaking, so I can't imagine much gunk inside the engine. When i changed the valve cover gaskets, the tops of the heads were very clean.

Hopefully it is not the lower end getting sloppy.

How many miles can you get out of a stock daily driver anyway?
 

kilgorq

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Jul 19, 2006
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Did the Plug Wires fix the backfire and hard start issues?

Did you do a compression test? Make sure all of the plugs are out when you do. That way if you have a head gasket failure between 2 cylinders it will be easier to detect.

Common Things to check...
Head Gasket.
Fuel Filter
Fuel Pump. ( This is the sneaky one that gets past a lot of mechanics. )
Valve Train.
Temp Sensor for ECU.
ECU.


Computer control systems rarely cause a backfire with the exception of The Temp Sensor for the ECU. Or the ECU Being Bad. Rough Idle and backfire are usually cause by Valve train issues (Worn Valves, Sticking Valves, Worn valve Springs, Worn Timing Chain), Head gasket blown between 2 cylinders, Or incorrect fuel air mixture.

I have seen 500K miles on a couple of stock daily drivers but they were not a Mustang. One was an Acura and the other was a Chevy Pickup.

Original Clutch with that many miles is impressive. Sounds like you take really good care of it.

Lower end is probably getting a little sloppy with that many miles. But if it was to the point of being an issue you would know it. It would be making a lot of noise when it was cold and kinda clear up once it warmed up. Or you would be knocking and ticking a lot.
 

Willybill32

Active Member
Jul 16, 2019
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Lexington, KY
Congrats on keeping your 86 GT. Maybe we should create an Original Owners Society. I am guessing it would be a small group.

Sometimes I question the sanity of driving a 30-year old car with over a quarter million miles as a daily driver, but then I realize I can fix anything on it cheaply. Not so with more modern cars. But, she has been very good to me.

Also, just to brag here, she has her original clutch still. It has seen ALL the miles put on her. When it finally gives out, I will probably have it framed.
Mine was a daily driver for 13 years in all kinds of weather, including snow and ice. It had the fabulous Ford factory paint job that peeled off over time. Still, even with a number of offers to buy it, I just couldn't let it go. Engine, suspension and braking system have all been updated, now waiting for a paint job, and no plans to let it go.
 

Wayne Waldrep

Before I post a pic, do you have one of yours?
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Apr 14, 2003
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I think @Wayne Waldrep has almost 300k on his and still DDs it
Hey! You shorted me 100k...lol. I'm a couple hundred miles away now. 400k. My factory engine was fine when I pulled it at 248k. Young and stupid had to have a fancy engine. Finally built me a factory type engine with all major parts OEM. I'm just over 150k on that one now.