Help Way Down On Power!

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by jchav02, May 3, 2014.

  1. My car seems to be way down on power and I can't figure out why. Here is my set up 95 k stock short block, tmoss ported cobra intake, 70mm throttle body, 90mm lightning mass air, trick flow 170s with lsx springs, custom cam(degreed), correct push rods, 1.6 roller rockers, new lifters, 24 lb injectors, 3.73 gears, tko 600, bbk shorty headers, high flow h pipe, flowmaster cat back, tuned with a quarterhorse and binary editor. The car put 250hp and 292 trq(SAE) and has run a best of [email protected](7600 ft density altitude). Ive gone over everything I can think of compression test 140-150 psi btw all cylinders, perfect intake head alignment, messed with timing and fuel, changed cap and rotor, new wires, nothing seems to help. Am I missing something? Any ideas?
    #1 jchav02, May 3, 2014
    Last edited: May 3, 2014
  2. Specs on the valve springs?
    What parts are new?
    What was already installed when the car felt good?
    An HCI car should make more, BUT the GT40 intakes aren't that great and custom cam can mean a lot of things.
    More details would help. Who did the tune?
  3. How about some basic stuff. Clean MAF (affects fuel load) and solid grounds (affects every sensor).
  4. These are the springs
    The heads, valve springs, cam, roller rockers , lifters, push rods, injectors, mass air, and headers are new.
    The car had the exhaust, cobra intake, throttle body, and C&L mass air previously. It now has more power then before but I dont have any before times or dyno numbers so its hard to say much improvement there was. The cam is an FTI with around .570 lift designed for my combo I don't have the cam card with me. It drives and runs perfect. I did the tune with the help of decipha from efi dyno tuning, the car will run fine on the stock tune with C&L no difference in felt power either way.
  5. I've tried two different mass air meters that were both cleaned. My grounds are the there and connected in tact look good visually is there a way to check them?
  6. Disconnect them and ensure everything is clean and tight. Strip back the cable sheathing about 1" and look for signs of corrosion. The copper should be bright and shiny not dark and green. Two grounds are critical. These are the battery to engine and engine to chassis and should be at least a #4 cable.
  7. Thanks I'll do that!
  8. Codes? Did you get an 11 when you dumped them?

    Cylinder balance test: use this to find dead or weak cylinders:

    Revised 25 March 2012 to add necessity allowing the KOEO tests to finish before starting the engine and the need for a properly functioning IAB/IAC to run the cylinder balance test.

    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 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.



    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.


    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.


    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 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.

    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 1400-1600 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. Use a jumper wire or paper clip to put the computer into test mode. Let it finish the Key On Engine Off (KOEO) code dump. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. Remember to keep the clutch pedal (5 speed) depressed to the floor during the test. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. 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

    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.

    See the link to my site for details on how to build your own blow down type compression tester.


    Revised 28-Oct-2012 to add signal ground description & possible problems if it is bad

    Grounds are important to any electrical system, and especially to computer controlled engines. In an automobile, the ground is the return path for power to get back to the alternator and battery.

    Make sure that all the ground places are clean and shiny bare metal: no paint, no corrosion.

    1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.

    2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. The clue to a bad ground here is that the temp gauge goes up as you add electrical load such as heater, lights and A/C.

    Any car that has a 3G or high output current alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects. The 3G has a 130 amp capacity, so you wire the power side with 4 gauge wire. It stands to reason that the ground side handles just as much current, so it needs to be 4 gauge too.

    The picture shows the common ground point for the battery , computer, & extra 3G alternator ground wire as described above in paragraph 2. A screwdriver points to the bolt that is the common ground point.

    The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
    Picture courtesy timewarped1972

    Correct negative battery ground cable.

    3.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally: it comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
    In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
    In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
    You'll find it up next to the starter solenoid where the wire goes into the wiring harness.

    All the grounds listed in items 1,2 & 3 need to bolt to clean, shiny bare metal. A wire brush or some fine sandpaper is the best thing to use to clean the ground connections.

    4.) All the sensors have a common separate signal ground. This includes the TPS, ACT, EGR, BAP, & VSS sensors. This ground is inside the computer and connects pin 46 to pins 40 & 60, which are the main computer grounds. If this internal computer ground gets damaged, you won't be able to dump codes and the car will have idle/stall/ performance problems

    5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is an orange wire with a ring terminal on it. It is located in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or bolt on back of the cylinder head.

    6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself. The TFI module ground terminates inside the computer.

    7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

    See for help for help troubleshooting voltage drops across connections and components. Be sure to have the maximum load on a circuit when testing voltage drops across connections. As current across a defective or weak connection, increases so does the voltage drop. A circuit or connection may check out good with no load or minimal load, but show up bad under maximum load conditions. .

    Voltage drops should not exceed the following:
    200 mV Wire or cable
    300 mV Switch
    100 mV Ground
    0 mV to <50 mV Sensor Connections
    0.0V bolt together connections


    Extra grounds are like the reserve parachute for a sky diver. If the main one fails, there is always your reserve.

    The best plan is to have all the grounds meet at one central spot and connect together there. That eliminates any voltage drops from grounds connected at different places. A voltage drop between the computer ground and the alternator power ground will effectively reduce the voltage available to the computer by the amount of the drop.
  9. Grounds checked out good.
    Codes key on engine off 11, 15
    Key on engine on 11
  10. something else to look for, vacuum leaks.
  11. Did you load the electrical system by turning on the lights,fan and other accessories when you did the ground voltage drop checks?

    Cylinder balance test results?

    code 11- system passed its' internal diagnostics.

    Code 15 - No Keep Alive Memory power to PCM pin 1 or bad PCM (Memory Test
    Failure). The voltage to the Keep Alive Memory (KAM) is missing (wiring problem)
    or the KAM is bad. The KAM holds all of the settings that the computer "learns" as
    it operates and all the stored error codes that are generated as a result of
    something malfunctioning while the engine is running. Use a voltmeter to check
    the voltage to the pin 1 on the computer - you should always have 12 volts. No
    constant 12 volts = bad wiring. If you do always have the 12 volts, then the KAM is
    bad and the computer is faulty.

    If the computer has to "relearn" all the optimum settings every time it powers up,
    the initial 5-30 minutes of operation may exhibit surges, poor low speed performance,
    and rough idle.

    Note that some aftermarket chips will cause code 15 to set. Remove the chip,
    clear the codes and retest. If you have a custom tune chip, ignore code 15 after you have checked the voltages for the computer.

    Before replacing the computer, remove the battery ground cable for about 20
    minutes. This will clear all the codes. Retest after several days of running. If the 15
    code is gone, then don't worry about it. If it is still there, then you get to do some

    See the following website for some help from Tmoss (diagram designer) & Stang&2
    Birds (website host) for help on 88-95 wiring

    Diagram courtesy of Tmoss & Stang&2birds
    #11 jrichker, May 6, 2014
    Last edited: May 6, 2014
  12. Yes the electrical system was loaded.
    Cylinder balence test passed
    Compression test is 140-150 psi on all cylinders.
    Code 15 does disappear when I disconnect the quarterhorse.
  13. If he put it on the rollers would that give any insight into what's going on?
  14. I'm going to check my harmonic balancer it may have slipped. Hoping its that. Otherwise the only other thing I can think of is I degreed the cam wrong.:bang:
  15. If hour balancer slipped, you'd know it right away due to the vibrations
  16. I retested the car tonight all the same except now its shows code 96. Following @jrichker testing procedure I got 11.83v at the green/yellow wire at fuel pump rely, voltage at both sides of inertia switch, and 11.83v at pink/black wire back at the fuel pump relay. @jrichker Is 11.83v at fuel relay close enough to 12v? If so then my fuel pump is bad.
  17. Since the car is running, you need to test the fuel pressure and flow if you suspect fuel pump problems.

    If you were to check the battery voltage against the readings at your test points and the difference is +/- .25, then the electrical part of the fuel pump system is OK.
  18. Ok battery voltage was 12.44 so electrical should be good. I'll test for fuel pressure and flow.