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  1. #76

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    Quote Originally Posted by Jack Hidley View Post
    Clamp on O2 bung?
    For the wideband. I thought the EEC might get confused if it wasn't still seeing both regular O2 sensors. And I wasn't sure if I could run the wideband straight to the EEC either.

    Sent from my SM-G960U using Tapatalk
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  2. #77

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    Brad,

    I've never seen a clamp on O2 sensor bung before. The thing that scares me about it is this. If there is ANY air leakage, then the readings will be junk.

    You can do this. Most wide band O2 controllers also have a narrow band out. You install the wide band sensor into the existing bung on one side of the car. Then wire the narrow band output from the wide band controller to the EEC O2 sensor plug. This solves all of the problems and you don't have to drill any holes in the exhaust.
    Jack Hidley
    Maximum Motorsports Tech Support

  3. #78

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    Okay, cool. I guess I should've asked first. I tried canceling my order, but that function on Summit's page wasn't working, of course. If i receive it and have to send it back, not the end of the world, I guess. Anyway, here's the item.

    https://www.summitracing.com/parts/AVM-30-2355-250

    It does come with a gasket to help seal, so that's something. I'm glad to not need to add another bung. Here's the wideband I ordered.

    https://lmr.com/item/INV-MTXL3844/mu...mtx-l-innovate

    Moates mentions it specifically on their page as compatible with their stuff.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  4. #79

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    Brad,

    Surprisingly, that particular wideband O2 sensor, does not have a nonlinear output. Only a linear output for a data logger. You will still then need to install the bolt on O2 sensor bung.
    Jack Hidley
    Maximum Motorsports Tech Support

  5. #80

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    Aw, shoot. I guess I'll email Summit again.

    Sent from my SM-G960U using Tapatalk
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  6. #81
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    .....
    Last edited by qikgts; 04-11-2020 at 06:37 PM.
    '85 GT

  7. #82

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    Got the wideband all installed. Calibration is very easy.

    Started the car with 2 gallons of fresh 91 octane non-oxy in the tank, although I'm sure some sludge from the old gas remains too. The idle is rolling like crazy and the afr is lean. I tried advancing the timing a few points past 13 and that really made no difference. Didn't have the chance to fiddle with it further. It's ready to take down the road, but I'm single parenting this weekend, so I can't leave the house anyway.

    Sent from my SM-G960U using Tapatalk
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  8. #83
    FEP Super Member xctasy's Avatar
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    Lean is common. Ive found that all of those slightly more advanced computers are designed to keep on the lean side. The KAM codes will be relearned only when you have a free 80 mile drive with a hot and cold cylce. Had the same issue with my Nissan Stagea and Toymoters. All that later 90s computer stuff is designed to have a working base of points. When Mama is back.

    Good work on the Transnational Speed League ....Clutch!

  9. #84

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    Thanks!

    I'm just hoping when I get back on it (hopefully tomorrow) I find something like a vacuum leak or a nearly plugged fuel filter or something. This isn't a little bit of rolling it's doing. It's going up and down like 1000 rpm. It's crazy.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  10. #85

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    Well, I gave it a once over under the hood and found... nothing. I have NO clue why the motherf***er won't idle. Maybe the distributor is still a tooth off... maybe this... maybe that. It's hot as f*** today so I couldn't find the motivation to fight a losing battle with this damn thing anymore. The clutch thing may not be solved either.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  11. #86
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    Have you messed with the idle screw on the throttle body? If so, that's a no-no with all "stock" components. Below will get you going if needed...

    From Joel 5.0...

    Summarized/Corrected Base Idle Reset version


    1. Clean TB with carb cleaner and nylon brush (toothbrush size). Engine off, fully open TB blade and spray/brush TB until all gunk and oil residue is cleaned.

    2. Allow to dry, or close TB blade and start engine until it clears all carb cleaner fumes/liquid.

    3. Let engine idle...if it doesn't, increase idle speed via TB stop screw until engine stays idling on its own.

    4. Disconnect IAC valve, if engine dies repeat 3 with IAC disconnected.

    5. Set idle speed to the lowest setting possible between 600-800 rpms with IAC disconnected. It is key to use the lowest possible to prevent idle surge, rolling, etc once the IAC is connected as follows.

    6. Turn engine off, and reconnect IAC

    7. With Ign On Eng Off, check TPS voltage output....if it's between .7vdc - 1.0vdc, it's OK. This voltage check should be done between the Green and Black wires at the TPS side connector as shown in the pic below....(-) terminal of the DVOM on the Black wire and (+) terminal on the Green wire.

    8. Disconnect battery (-) for 3-5 minutes.

    9. Reconnect battery, start engine, allow it to idle for 2-4 minutes to confirm setup,

    10. If idle speed falls too low or stalls, increase idle speed via the TB set screw a little at a time.

    11. Turn engine off for 20 seconds, re-start engine and repeat 9 - 11 if required.

    12. Reconfirm TPS output is within the .7vdc - 1.0vdc range.......you're done! (almost)...

    FYI..no need to reset ECM KAM (reset computer) b/c the TPS minimum value used for idle control, is automatically reset by the EEC-IV every time the ign is cycled on-off for 20 seconds-on, and as explained in the next post

    13. Allow a 10-20 minute "relearning" period under normal driving conditions (drive cycle).....now you're done.
    Last edited by qikgts; 06-02-2020 at 12:28 AM.
    '85 GT

  12. #87

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    Thanks! No, I have not touched the idle screw.

    What really has me discombobulated is the fact that before I took stuff apart to install a few things this spring, it was idling fine. It just doesn't make sense. One of the things I did is wire up pin 30 correctly so the computer now knows when the car is in neutral. You'd think that would be a good thing. Apparently not!
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  13. #88
    FEP Super Member erratic50's Avatar
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    I have to wonder if increasing the idle screw then re-setting the tps would help .....

    Some drill larger holes in the blades on the throttlebody and adjust the throttlebody until it’s closing to the point it would stick shut if it weren’t for the idle screw

  14. #89

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    Base idle reset would be worth a try. Double check the tps voltage too. I'll fiddle with it and see if we can get anywhere.

    Sent from my SM-G960U using Tapatalk
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  15. #90

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    An observation: when I turn the distributor well into where it's showing the part number on the balancer, it seems happier. It still rolls like crazy, but it doesn't go down so far it nearly dies.

    Does that mean the distributor is off a tooth? The only other thing I really notice is that it's quite lean at idle. 16-19 usually. This is before I pulled the spout and started messing with the timing.

    Oh, and in regard to the idle speed, right now, it's rolling between like 800 and 1500. It seems wrong to me to turn it up when it's already so high. The tps voltage is good at present with the throttle closed.

    Sent from my SM-G960U using Tapatalk
    Last edited by ZephyrEFI; 06-10-2020 at 03:49 PM.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  16. #91

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    Alright, so I did a smoke test and didn't find any vacuum leaks. I'm pretty surprised by that, but nonetheless. Also, I fooled with the distributor timing, and I'm pretty sure I've got it right, so we can eliminate those things. Also, the injector plugs are all snug in place.

    I'm fairly certain now I have the wrong MAF. I have the right housing, and a sensor for a 70mm housing, but still not the right application. It is an F2VF. I shopped for reman MAFs, and the stupid application data on Rockauto and O'Reilly for the Cardone Cobra unit claims it's the same one for '90-91 GT/LX cars too. Well, you and I know that can't be the case. So I emailed them to ask WTF. I really hope this is what fixes the idle problem.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  17. #92
    FEP Power Member Broncojunkie's Avatar
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    They are the same for cobra. The cobra ecm was programmed to run 24lb injectors. The aftermarket industry came up with the idea of "tricking" the stock ecm into running different sized injectors by messing with the maf settings.
    79 Pace Car - 331, t5
    79 Pace Car- 302, 4 spd
    79 Cobra - working on 351w, t5
    82 Capri- working on 302, t5
    82gt - working on 408w, c4

  18. #93

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    The tps tells the computer where the throttle is, the iac adjust air bypass to keep it running.

    All I ever do is get the car warmed up a bit then I unplug the iac and I turn the thrittle screw down until the car is barely running and plug it back in. Its a 30 second procedure.

    Ive never really trusted mass air. I feel like it just needlessly complicates and already fine system by adding another finicky sensor.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  19. #94

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    Quote Originally Posted by Broncojunkie View Post
    They are the same for cobra. The cobra ecm was programmed to run 24lb injectors. The aftermarket industry came up with the idea of "tricking" the stock ecm into running different sized injectors by messing with the maf settings.
    Really? I guess that would explain the F1 part number. I wonder if the larger housing is just larger enough in proportion to accommodate the larger injectors. Maybe that's where the aftermarket got the idea.

    Part of the confusion though is the fact that the Cardone units come with the housings. I think you can agree the earlier cars never came with 70mm housings though!
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  20. #95

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    Quote Originally Posted by Haystack View Post
    The tps tells the computer where the throttle is, the iac adjust air bypass to keep it running.

    All I ever do is get the car warmed up a bit then I unplug the iac and I turn the thrittle screw down until the car is barely running and plug it back in. Its a 30 second procedure.

    Ive never really trusted mass air. I feel like it just needlessly complicates and already fine system by adding another finicky sensor.
    I get that! I'm so sick of having problems like this, I'm almost considering a carb!

    My stupid idle is rolling so badly right now, if i did your procedure, the thing would just die.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  21. #96

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    Brad,

    Is every part of the air inlet tract in front of the MAF stock?

    Have you tried clocking the MAF to get the idle to stabilize?

    The rolling idle is usually a symptom of the mixture being off.

    Do you have the ability yet to datalog a wideband O2 sensor, timing and IAC duty cycle?
    Jack Hidley
    Maximum Motorsports Tech Support

  22. #97

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    Quote Originally Posted by Jack Hidley View Post
    Brad,

    Is every part of the air inlet tract in front of the MAF stock?

    Have you tried clocking the MAF to get the idle to stabilize?

    The rolling idle is usually a symptom of the mixture being off.

    Do you have the ability yet to datalog a wideband O2 sensor, timing and IAC duty cycle?
    Yes, all stock, including the paper filter. But excluding the silencer.

    I have not tried reclocking the MAF sensor yet. I'll look at doing that after I get the correct sensor in there and I still have a problem.

    I do have the ability to datalog in theory, but I haven't hooked things up and done it yet. The idle thing is taking a back seat to the clutch problem for the next week or so, but we'll see after that.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  23. #98

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    Brad,

    Without datalogging what the engine is actually doing, you are guessing as to the problem and solution. There is zero reason to do that. EFI gives you the massive advantage of actually knowing what is going on in the engine. It is pointless to waste that.
    Jack Hidley
    Maximum Motorsports Tech Support

  24. #99

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    Quote Originally Posted by Jack Hidley View Post
    Brad,

    Without datalogging what the engine is actually doing, you are guessing as to the problem and solution. There is zero reason to do that. EFI gives you the massive advantage of actually knowing what is going on in the engine. It is pointless to waste that.
    I won't. I'll set it up soon.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  25. #100
    FEP Super Member xctasy's Avatar
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    http://vb.foureyedpride.com/showthre...fuel+injection


    Quote Originally Posted by ek1 View Post
    the surging idle checklist:

    1.) Dirty or defective IAB (or IAC) - clean or replace IAB. Some TB's are coated and are marked "Do not clean". If they have no markings, spray them down & use a toothbrush to do the tough places that refuse to come clean. Spray some more and wipe up the mess with a paper towel. The rest will go through the engine with no problems. The stalling when an engine is first cranked up or cold is a clue to a non-functional IAB.

    First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. Then the current through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

    The IAC depends on the computer to provide a ground to make the IAC work. Bad wiring, dirty connections or a failed IAC circuit inside the computer can keep the IAC from adjusting the idle like it should.

    IAC doesn't work: look for +12 volts at the IAC red wire. Then check for continuity between the white/lt blue wire and pin 21 on the computer. The IAC connector contacts will sometimes corrode and make the IAC not work. The red wire on the IAC is always hot with the engine in run mode. The computer provides a ground for the current for the IAC. It switches the ground on and off, making a square wave with a varying duty cycle. A normal square wave would be on for 50% of the time and off for 50% of the time. When the idle speed is low, the duty cycle increases more than 50% to open the IAC more. When the engine speed is high, it decreases the duty cycle to less than 50% to close the IAC. An old-fashioned dwell meter can be used to check the change: I haven’t tried it personally, but it should work. In theory, it should read ½ scale of whatever range you set it on with a 50% duty cycle. An oscilloscope is even better if you can find someone who has one and will help.
    2.) Defective TPS - replace TPS. An idle that sticks high and won't come down unless you turn the key off & restart the engine is a sign of a bad TPS.

    Try this... Currently there is some dispute about the effectiveness of setting it at .99 volts, but anything less is probably OK. All you need is less than 1.0 volt at idle and more than 4.25 at Wide Open Throttle (WOT). You'll need a good Digital Voltmeter (DVM) to do the job.

    The Orange/White wire is the VREF 5 volts from the computer. You use the Dark Green/Lt green wire (TPS signal) and the Black/White wire (TPS ground) to set the TPS

    Here’s a TPS tip I got from NoGo50

    When you installed the sensor make sure you place it on the peg right and then tighten it down properly. Loosen the back screw a tiny bit so the sensor can pivot and loosen the front screw enough so you can move it just a little in very small increments. I wouldn’t try to adjust it using marks. Set it at .97v-.99v, the closer to .99v the better.

    (copied from MustangMax, Glendale AZ)

    1.) Always adjust the TPS and Idle with the engine at operating temp. Dive it around for a bit if you can and get it nice and warm.

    2. When you probe the leads of the TPS, do not use an engine ground, put the ground probe into the lead of the TPS. You should be connecting both meter probes to the TPS and not one to the TPS and the other to ground.

    3. Always reset the computer whenever you adjust the TPS or clean/change any sensors. I just pull the battery lead for 10 minutes.

    4. Check the procedure for your year, on my 90 I have to turn the idle screw until it just touches the tab, then insert a .010 feeler gauge and give it about one more turn. Then you adjust the TPS voltage to .98v, reset the computer. Start it up, if the idle is to low then turn the screw in until it is just right, then readjust the TPS voltage to .98v and reset the computer and start it up. The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed.
    3.) Vacuum leaks - locate & replace leaky gaskets & hoses. Spend $8 or so at the auto parts store for enough various sizes and lengths of vacuum hose to replace all the vacuum lines. The hard plastic lines get brittle over time and will crack and leak. See http://www.veryuseful.com/mustang/te...uumDiagram.jpg and http://www.veryuseful.com/mustang/te...g5.0Vacuum.gif for vacuum diagrams. The carbon canister plumbing is often damaged or missing, causing vacuum leaks. The big hose coming from the bottom of the upper manifold and going to the front of the engine is for the carbon canister.

    To find vacuum leaks around bolted joints, use motor oil in a squirt can. When you find a leak, the oil will be sucked and the engine speed will change. The oil is messy, but works great and will not pose a flash fire hazard. Avoid using flammable fluids like carb cleaner or propane gas – flash fires are not pretty and are very hazardous to your health.
    4.) Bad O2 sensors or bad or missing O2 sensor ground - replace o2 sensors and check the ground wire. The ground comes out of the fuel injection wiring harness & is a orange wire with a ring terminal on it. After 60 K miles of usage, the O2 sensors are generally on the downhill side of things.

    Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

    Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. You can expect to see the voltage switch from .2 volt to .6 volt on the average O2 sensor. More voltage swing is good, less voltage swing is bad.
    5.) Insufficient voltage at idle - reduce electrical load, replace or upgrade alternator. Use a good Digital Voltmeter (DVM) to measure the voltage. At 1000 RPM you should see 13.8 – 14.2 volts on a warm engine. Keep in mind that at 650-725 RPM, the output will be less, and may be below the 13.2 volts required to keep the battery charged. This is not good and can cause problems: underdrive pulleys may aggravate the situation.

    6.) Dirty 10 pin wiring connectors or damaged wiring going to/from the 10 pin salt & pepper shaker wiring connectors. See http://www.veryuseful.com/mustang/te...PS_IAB_Pic.jpg for the 10 pin connector locations. See http://fordfuelinjection.com/images/harness02.gif / for the wiring inside the 10 pin connectors. Clean the 10 pin connectors with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

    7.) Dirty or defective MAF element: Clean or replace the MAF element. Disconnect the MAF and start the car. If the idle smooths out, then proceed from here. Keep in mind that this does not work on every car.

    The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

    The MAF output varies with RPM which causes the airflow to increase or decease. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow. Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer.

    At idle = approximately .6 volt
    20 MPH = approximately 1.10 volt
    40 MPH = approximately 1.70 volt
    60 MPH = approximately 2.10 volt

    Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

    There should be a minimum of 10K ohms between either pin C or D on the MAF and ground.

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

    http://www.veryuseful.com/mustang/te...nks-ign-ac.gif

    http://www.veryuseful.com/mustang/te...1eecPinout.gif

    http://www.autozone.com/servlet/UiBr...3d8019595a.jsp
    8.) MAF meter on CAI system that needs clocking or protection from engine compartment air turbulence. A cone type filter located inside the engine compartment is almost sure to have surge problems due to the turbulent airflow around it. Try cleaning the MAF element & then "clock" the MAF by rotating the entire MAF housing to see if changing its position helps any.

    9.) Clogged fuel filter, damaged fuel lines or dirty fuel pump sock. Poor fuel delivery will cause severe problems.

    10.) Bad grounds in a computer controlled engine will make all sorts of strange problems.

    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. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

    The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.

    All the sensors have a common separate ground. This includes the TPS, ACT, EGE, BAP, & VSS. This ground terminates inside the computer, but still uses the computer power ground as its source.
    See http://www.fluke.com/application_not...1&SID=103#volt for help troubleshooting voltage drops across grounds

    11.) Dirty or defective ECT and ACT sensors. Look for codes 21, 24, 51, and 54 when you dump the codes. The ACT sensor will get coated with gunk over time and may need to be cleaned.
    ACT & ECT test data:

    The ACT & ECT have the same thermistor, so the table values are the same

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

    Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer. Here's the table :

    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

    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
    12.) Defective PCV. The PCV is almost impossible to see unless you have the engine out of the car, have the intake manifold off, or you are a snail & have an eyeball on a stalk.

    The PCV fits in a rubber grommet that plugs in the block at the rear of the lower intake manifold. The rubber grommet is notorious for not fitting tight or sealing like it should. It connects to the upper manifold by a 3/8" vacuum hose coming from the rear of the upper intake manifold. The easiest way to find it is to follow the hose with your hand and pull it out of the rubber grommet. Check the screen below the PCV while you have it & the grommet out if you can get to it.
    13.) Mismatched MAF and injector size. The MAF must have a matching flow rating for the injectors. If you have 24 lb in injectors, you need a 24 LB MAF. The Cobra computer is the exception to this rule, since it uses a 19 LB MAF & internal tables to modify the fuel curve. Some aftermarket devices can modify the mismatch, but they are not very common.

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