Typical 94-95 Gt Power Loss? Where To Start Looking?

bennylava

Member
Oct 18, 2017
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Hi all. I wanted to stop by and ask about the well known decline in power issues, in the 94-95 Mustangs. I have a 94 GT and I know the power is not what it should be. It was the same way in another car I used to have, and a buddy of mine had the issue before he sold his car. Its not terrible, but you can tell the car doesn't have the power that it should. I've talked to a lot of people, and I'm sure many of you here have had this issue or experienced this.

I have done a full tune up. New air filter, fuel filter, plugs, wires, cap, rotor, and even new O2 sensors. I also cleaned the MAF sensor with MAF sensor cleaner from a spray can. Didn't even put a dent in the problem, the car still runs the same as before. It has 168k miles on it, but it is in great condition other than this engine issue. I've worked hard to keep the car tip top condition, but now I've finally got to tackle this power loss issue. There is also the occasional engine jiggle that you can feel, even with the AC off. There is no check engine light. That occasional jiggle makes me think it has a random misfire. Could be where I should start looking for some of the power loss. I also replaced the coil about a year ago, when the old coil finally died. So it looks like the usual suspects are going to be good. Seems like I'm going to have to delve deeper. I'm looking for a list of things to check, even if that list is really long. I'll check them all.

I was hoping that someone here was familiar enough with these cars to know what to check, to find this seemingly common issue.
 
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Is it an auto or 5 speed car? If auto, could the trans be slipping a bit and make the car feel slower?

Also, I read where an old ACT sensor once made a person's car run like crap. They replaced that along with the coolant temp sensors, and said it fixed their issue. May be worth a try since they dont sound to be swapped out yet and are cheap.
 
I just had my MAF go bad, the car ran but it felt sluggish. However, mine threw codes first. Also, I replaced the fuel pressure regulator and got some good power back. Your coil could also be a culprit. I just went through this myself, and I had to replace all three before the engine would purr again.

The sensors on our cars rarely fail completely. They get quirky, and start lying to the computer. The lies start small, and the computer can adapt to them. But when they get too big, the engine starts running a bit rough. So you might have several sensors that are reporting wrong values and are causing your engine to run poorly.
 
Sounds like its going to be a long hunt to find what is actually causing this. I'm trying firing the "parts cannon" at the car. That's why I am looking for things I can check first. I have a high good scanner with an OBD-1 connector for Ford. Some have told me to scan the car even if there are no codes. I will do that first.

Where exactly is the fuel pressure regulator?
 
Sounds like its going to be a long hunt to find what is actually causing this. I'm trying firing the "parts cannon" at the car. That's why I am looking for things I can check first. I have a high good scanner with an OBD-1 connector for Ford. Some have told me to scan the car even if there are no codes. I will do that first.

Where exactly is the fuel pressure regulator?


If you want to save a TON of time and BUNCH of money, you might want to try running jrichker's Surging Idle Checklist.

I think it even includes a sections specific to 94/95:

https://www.stangnet.com/mustang-forums/threads/help-me-create-the-surging-idle-checklist.698148/

@jrichker may be able to help point out differences.
 
Yes I actually took a look at that thread when I was searching, before I created this thread. But I do not have a surging idle, just seems like the car has 20 hp less than it should. That combined with the occasional jiggle at idle makes me think that there is some power loss going on.
 
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.

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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.

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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.

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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
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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
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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.