Ignition Timing (?) Problems

Discussion in 'Fox 5.0 Mustang Tech' started by fast9050, Aug 26, 2012.

  1. I searched google for related problems, but haven't found any posted solutions. Lots of suggestions but none seemed to fix the problem.

    I have a '90 GT, with the laundry list of bolt-ons like most of us power hungry Mustang owners. I bit the bullet and bought a Kenne Bell Blowzilla with the standard inlet, and installed it this past April. I had some minor fitment issues, but it seemed to work out. With my 190lph fuel pump, 30lb injectors I had no detonation when flooring the accelerator. I bought an XCT chip and planned to dynotune when I had a chance, but there seemed to be no hurry (haha). I drove her maybe three times with the 3" pulley (8lbs boost) before changing to the 2 7/8" (10lbs). I took her out maybe twice with zero problems. The third time with the new pulley, she starts backfiring like a machine gun when around 1800 rpms...the rpm needle dipped to zero as she wanted to stall, but recovered several times before stalling altogether.

    The car restarted...but a few miles later, the same thing with with the backfiring, then she quit outright. Also, I noticed the brake pedal became increasingly harder and harder to depress. The booster is a new/rebuilt unit I put in when converting to a set of '98 Cobra brakes last year, using the '93 cobra booster and master cylinder.

    Towed her home, and replaced the distributor and all spark plug/coil wires. She started, and I set the timing to 0 degrees, since KB says to retard the timing 1 degree per pound of boost. Car started, but same thing...backfiring, no power until she dies again with no starting. Replaced the ignition module and hall effect sensor, and she started again, but again stalled around 1800 rpms, and won't start again.

    Brakes are still hard as a rock. I checked all the vacuum lines and they are intact. I suppose the booster not working could be coincidence, but it sure is strange.

    I checked and the #1 piston is at TDC when the distributor rotor says it should be, along with the crankshaft damper timing marks...

    As I said, I found several threads on several sites with similar issues, but no "Holy Crap That Fixed It!!" moments.
  2. For the record, KB has been less than helpful with their install support during and after.

    Their recommendation was to have my car towed to a garage to be fixed. This must be a first, I guess.
  3. Also, I have ordered a "high performance" coil to see if that may keep the ICM from frying, although that seems like putting the horse behind the cart. :shrug:
  4. Backfiring out the intake is either a valve stuck open or a lean mixture or spark plug wire(s) connected to the wrong cylinder(s). Check compression on all cylinders and then look for vacuum hoses loose, cracked, or misconnected. Check the line for the vapor recirculation system – it is easy to knock loose and not see it when you connect the air pump plumbing. If the vacuum line for the EGR valve and the air pump are cross connected, some very strange things can happen. Check the mass air flow electrical connection and see that it is tight, the same goes for the fuel injection wiring harness connectors up on top of the manifold near the firewall.

    Sticking valves: If a intake valve is bent, has a bad spring or is misadjusted, the engine will sometimes backfire through the intake. Use a vacuum gauge connected to any convenient spot on the intake manifold. Run the engine at 1000 RPM & look for 18-21 inches of vacuum with a steady needle. A problem intake valve will make the vacuum gauge needle sweep 5-10 inches.

    Lean fuel mixture breaks out into several sub categories:
    A.). Vacuum leaks
    B.) Air entering the intake without passing through the MAF on Mass Air cars (89-95 models).
    C.) Failure of the MAF, BAP/MAP (Baro or Manifold Air Pressure, same sensor, different name), ACT (air charge temp), or ECT (engine coolant temp). These should set a code in the computer.
    D.) O2 sensor problems: one or both O2 sensors with low output or bad O2 sensor heater ground. This should set codes 41/91. The O2 sensor heater ground is an Orange wire in the engine mounted fuel injector harness. Ground it to the back of the head or intake manifold.
    E.) Leaking exhaust gases from EGR valve at WOT or EGR opening when it should not be open.
    F.) Poor fuel delivery due to bad fuel pump, clogged filter or bad fuel pump wiring. Look for low pressure or fluctuating pressure. Standard injector pressure is 39 PSI at idle, with the vacuum line disconnected from the regulator and capped.
    G.) Clogged fuel injectors.- see the cylinder balance test below
    H.) Fuel injector wiring problems causing injector not to deliver rated flow (dirty or stuck shut injectors).
    I.) Computer problems: (computer problems are not common like sensor problems)
    J.). ROM has bad data in fuel or timing table. This should also set a code in the computer.
    K.) Failure of one or more of the computer's driver transistors for the fuel injectors. No code set on this one. Use a noid test light to test the injector wiring & injector drivers,
    L.) MAF calibration off or mismatched to injectors.
    M.) ACT or ECT bad. Sometimes the sensors will be off calibration, but not bad enough to set a code. If they falsely read too high a temp, the engine will back off fuel delivery.

    The HO firing order is 1-3-7-2-6-5-4-8.
    Non HO firing order is 1-5-4-2-6-3-7-8


    Cylinder balance test:
    See the procedure below to dump the codes and place the computer into diagnostic mode.

    Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. 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

    Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

    Dumping the computer diagnostic codes on 86-95 Mustangs

    Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

    Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

    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.

    Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

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



    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 driveablity 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, and clutch (if present) is pressed 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.

    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 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 $30.
  5. It's not backfiring out the intake.

    After replacing the TFI and pick up almost half a dozen times, the problems were related to several bad pick ups, including brand new ones, and a bad EGR valve and/or sensor. Maybe.
  6. #1 pull any diagnostic codes
    2 you should have a boost gauge, you should be showing vacuum @ 14-18lbs at idle if not
    3 Do a compression check. should show @ 140psi per cylinder
    4 what is you air/fuel ratio. @ idle/cruising 14.5:1 and 10.5 - 12.0:1 WOT