Idle surge trial and errors

Discussion in 'Fox 5.0 Mustang Tech' started by dangrego, Jul 4, 2008.

  1. Howdy, my '88 mustang has a bad idle surge and runs very rich at idle, exhaust gasses burn my eyes in the garage...can't figure it out and tuned over and over again, etc. I read all the idle surge posts and so I am trying to attack this problem with as much info as possible, however, maybe some of my mods have something to do with it? are a few details (BBK Cold Air Induction and Full Length Headers, FLO-17113, Flowmaster American Thunder Exhaust (Diameter: 2.5"), MSD Blaster TFI Coil PN 8227, MSD-8456 MSD Distributor, Stock Heads Reworked ( 1.9 Intake & 1.6 Exhaust Valves), Scorpion studmount rockers (1.6 ratio), Roller Lifters HT-2205, Mass Air Conversion Kit, A9L computer, 24 lb injectors, 255 LPH Fuel Pump, 70mm Throttle Body, 70mm EGR Plate, Edelbrock Performer RPM II upper and lower intake, Ford Racing B-303 Cam) and I also gutted out all the smog **** and even both the heating and a/c systems entirely! Anyone want to read through my setup and possibly have helpful input? thanks, v/r
  2. See the "Surging Idle Checklist for help with all your idle/stall problems. The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes] for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.
  3. Any codes? the strong exhaust smell sounds like something with the 02 sensors because thats what mine does when I was only running 1.....

    Pull the codes and reset the idle and tps like the thread says and it should do something
  4. working it

    still working O2 sensors are only a year old but maybe i should spend some cash to rule that out...just pulled the codes today, ouch, here they are:

    51 O, C (ECT sensor out of range/circuit open)
    67 O (Neutral pxs switch circuit failure, circuit open)
    85 O (Canister purge solenoid circuit failure and/or Shift solenoid 3/4 - 4/3) what's that?
    95 O,C (Fuel pump secondary circuit fault)
    29 C (Insufficient input from vehicle speed sensor)

    When I tried to pull R codes (engine running), the meter wouldn't give me anything- not even let me know if it was running in safe mode or not.

    Am determined to figure it out eventually!
  5. Code 29 - Vehicle Speed Sensor (VSS) is an electronic sender mounted on the speedo pickup gear
    on the trans. It works the cruse control for both 5 speed and auto trans cars. The VSS is used to tell the
    computer to speed up the idle as you slow to a stop. This helps keep the engine from stalling when you
    slow down for a stop sign or stop light.
    Check to see if the electrical connector is plugged into it. Clean the connector & contacts with non
    flammable brake parts cleaner prior to replacing the sensor, as that may fix the problem. The sensor cost is
    under $30 and it is easy to replace.

    Code 51 Engine Coolant Temperature (ECT) sensor signal is/was too high -
    Possible bad ECT sensor, or wiring. Possible missing signal ground –
    black/wire wire broken or bad connection. With the power off, measure the
    resistance between the black/white wire and battery ground. You should see
    less than 1 ohm. Check the same black /white wire on the TPS and MAP
    sensor. More than 1 ohm there and the wire is probably broken in the harness
    between the engine and the computer. The 10 pin connectors pass the
    black/white wire back to the computer, and can cause problems.

    Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

    Voltages may be measured across the ECT by probing the connector from the rear.
    Use care in doing it so that you don't damage the wiring or connector.

    50 degrees F = 3.52 v
    68 degrees F = 3.02 v
    86 degrees F = 2.62 v
    104 degrees F = 2.16 v
    122 degrees F = 1.72 v
    140 degrees F = 1.35 v
    158 degrees F = 1.04 v
    176 degrees F = .80 v
    194 degrees F = .61
    212 degrees F = .47 v
    230 degrees F = .36 v
    248 degrees F = .28 v

    Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.

    50 degrees F = 58.75 K ohms
    68 degrees F = 37.30 K ohms
    86 degrees F = 27.27 K ohms
    104 degrees F = 16.15 K ohms
    122 degrees F = 10.97 K ohms
    140 degrees F = 7.60 K ohms
    158 degrees F = 5.37 K ohms
    176 degrees F = 3.84 K ohms
    194 degrees F = 2.80 K ohms
    212 degrees F = 2.07 K ohms
    230 degrees F = 1.55 K ohms
    248 degrees F = 1.18 k ohms

    Diagram courtesy of Tmoss & Stang&2birds


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

    Code 67 - clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position
    when codes where dumped. Possible neutral safety switch or wiring problem. This code may prevent you
    from running the Key On Engine On tests. You can generally ignore this code, since it has no effect on
    engine performance.

    The computer wants to make sure the A/C is off due to the added load on the engine for the engine
    running tests. It also checks to see that the transmission is in Neutral and the clutch depressed (T5, T56,
    Tremec 3550 & TKO)). This prevents the diagnostics from being run when the car is driven. Key On Engine
    Running test mode takes the throttle control away from the driver for several tests. This could prove
    hazardous if the computer was jumpered into test mode and then driven.

    The NSS code 67 can be bypassed for testing. You will need to temporarily ground computer pin 30 to the
    chassis. Computer pin 30 uses a Lt blue/yellow wire. Remove the passenger side kick panel and then
    remove the plastic cover from the computer wiring connector. Use a safety pin to probe the connector
    from the rear. Jumper the safety pin to the ground near the computer.
    Be sure to remove the jumper BEFORE attempting to drive the car!!!

    Code 85 - CANP solenoid - The Carbon Canister solenoid is inoperative or missing. Check vacuum
    lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation.
    Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.

    The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any
    time the ignition switch is in the run position.

    Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose.
    Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects
    to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line
    that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side
    injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas
    tank. The solenoid valve opens at cruse to provide some extra fuel.

    It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car
    from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook
    it up & use it?

    Code 95 Key O, Engine not Running - the following test path is for 86-90 model Mustangs.

    The 95 code is because at one time or another, the fuel pump relay hiccupped and didn't provide power the
    pump when the computer told it to run. Sometimes this is a one time thing, other times it is a no run or
    runs poorly condition.

    To help troubleshoot the 95 code, follow this link for a wiring diagram

    Using the diagram, check the red/black wire from the fuel pump relay: you should see 12 volts or so.
    If not, check the inertia switch: on a hatch it is on the driver’s side by the taillight. Look for a black rubber
    plug that pops out: if you don't find it, then loosen up the plastic trim. Check for voltage on both sides of
    the switch. If there is voltage on both sides, then check the Pink/black wire on the fuel pump relay: it is the
    power feed to the fuel pump. No voltage there, check the Orange/Lt blue wire, it is the power feed to the
    fuel pump relay & has a fuse link in it. If there is good voltage there & at the Pink/black wire, swap the relay.

    Some Mass Air conversions neglect to run the extra fuel pump wire, and they always have a 95 code.
    See for more information on the
    Mass Air wiring conversion.

    Fix the code 67 and the engine running codes will dump. Usually you just have to push in on the clutch and
    make sure the A/C is off when you dump the codes.
  6. MAF

    ALCON: my MAF sensor is a 75mm and my throttle body is a 70mm...that is a non-issue, though right? v/r
  7. None of The codes you posted pointed to a MAF related problem.

    If you have a Cold Air Intake or aftermarket MAF not matched to the injector size, you could have a MAF related problem and not get a MAF code (code 66).
  8. too rich of an idle will cause surging, seeing how you are running 24s on a stock tune i would check in that area... perhaps putting stock injectors and MAF back on to see if it clears it up... that will let you know whats wrong.
  9. no worries there, thanks, i am working the checklist...really want to get a dino tune on it, but pointless to do with all these problms right now! back to the garage i go and by garage i mean outside in the 95 degree Louisiana sun :)
  10. Well, i was finally able to get a key on engine running test and guess what, she's been running in "Failure Mode"....a code 98 accompanied by a code 51 (ECT sensor out of range/circuit open), so that is what i need to fix first. Do I need to put the ECT sensor back in (remember, i gutted the heating system in which the ECT sensor was mounted) or can i burn a chip to fix that? Got to get the car out of Failure Mode, maybe that is why it is running rich. v/r
  11. The ECT is necessary to help the computer set the proper air/fuel ratio.

    A trip to Home Depot can help you find some brass fittings to mount the ECT directly in the intake manifold if you don't want to use the heater supply tubing.