Help me create the "Surging Idle Checklist"

Discussion in 'Fox 5.0 Mustang Tech' started by jrichker, Apr 10, 2005.

  1. No engine shake due to too much ignition timing advance,

    Do a cylinder balance test to find dead or weak cylinders.

    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.
  2. Thanks. I have already done a compression check and all cylinders came up between 160-170. Guess I need to check the balance as well.
  3. I feel like it can only be 1 of 5 things (pretty sure I've checked everything else.

    Bad wires, 'bad coil/tfi/dizzy', vacuum, cylinder balance, or not getting enough air at idle. Out of those 5 areas which do you guys think is most likely to cause erratic engine shudders?

    Cant wait to get off work so I can check the resistance of all my wires and put on this iac bypass.
  4. Code 158 = MAF Sensor Fault - High Voltage

    Only explanation bad MAF? Or coukd high voltage be caused by something else.
  5. Guys I really need some help here I feel like I'm out of options.

    Two days ago I pulled the codes and got a 158 which is MAF SensorFault - High Voltage. So last night, I bought a remanned Cardone maf sensor and put it on, same erratic shuddering engine idle. Measure between pins c and d and got 1.1 at idle. Wtf? So okay, Cardone is know for their :poo:ty remanned parts so I return it today and swap it out for another one and then clear the codes. Start it up, it immediately seems better. No shuddering. Until idle settles, same :poo:. So I measure between pins c and d, 1.1 at idle AGAIN! WTF?! Could it be that I got two defunct Cardone sensors? I take it for a drive. Still, no power, no throttle response. Go back and dump the koeo and koer codes again. 172 - o2 lean, but its a brand new o2 sensor so I assume its because the converter is currently cut off (I thought MAYBE my cat had melted down was partially blocked). No more code 158 but still, both Cardone sensors AND the original one, ALL MEASURE 1.1v at idle. I also got a 538 code, which is "bad cylinder balance test due to throttle movement" and "insufficient rpm change during dynamic response test."

    So I said okay, maybe I dropped a :poo: ton of timing or something. Pull the spout, still at 17* where I set it immediately after the build. Lower it to 10*, TERRIBLE shuddering. Advance the timing WAY past 17, like 20-25*, smooths out. I'm so freakin fried with this bull:poo: I'm about to cry.

    Please please, any ideas? Help!!! lol
  6. 3 digit computer codes? What year car/engine are we dealing with? 86-93 cars are all 2 digit, and 94-95 are 3 digit, as well as 96- present.
  7. 1995 F-150 5.0 2wd auto
  8. Have you considered that you may have spun the harmonic balancer? That would account for the engine shuddering and shaking, as well as the odd timing problems.

    Here's some help. First find TDC, the compare to TDC determined by the test method to the alignment of the TDC marks already on the harmonic balancer.

    TDC location process courtesy of Michael Yount
    If you're trying to find ACTUAL tdc for cam installation/degreeing, follow the steps below:

    Positive stop – obtain an old spark plug for the Ford engine – most of us have at least one laying around. Put it in your vice, and with a tool of destruction you deem appropriate – cut off the ground tip and bust up the ceramic around the center electrode. Keep pounding to get the ceramic and center electrode removed so you’ve got a good ¾” or so of hollow space inside what used to be the ‘business’ end of the spark plug. If you happen to break the ceramic on the other end of the spark plug, don’t worry about it. Once you’ve got a nice hollow space in the tip of the plug, take a 5/16” tap, and cut threads inside that end of the plug. I found that diameter to go right in without any drilling required. Once you’ve cut threads, screw in a 5/16" bolt about 1.5” to 2” long. Then take your hack saw and cut the head off the bolt. Wouldn’t hurt to take your file/grinder and dress up the freshly cut surface so no sharp edges or shrapnel enter the combustion chamber. Also clean up the threads on the plug so that it easily screws into and out of the plug hole.

    Determining TDC – remove the passenger side valve cover. Rotate the engine (socket on crank bolt) until the #1 piston is down the cylinder on the intake stroke. Unscrew the spark plug in that cylinder, and replace it with the positive stop you just made. Only screw the positive stop in hand tight. Install your cam degree wheel and pointer (no easy task in some cases as harmonic balancer and other accessories will have to be removed). You may want to remove all spark plugs at this point because it will make it easier to smoothly turn the engine over in small increments. GENTLY rotate the engine clockwise until the piston comes to rest against the stop. Note the degree wheel reading. GENTLY rotate the engine in the opposite direction until the piston comes to rest against the stop. Note the degree wheel reading. TDC is exactly half way between these readings. Calculate where that position is on the degree wheel, remove the piston stop from the cylinder, and rotate the engine to TDC as you calculated it.

    Compare the TDC measurement found by the above method to the alignment of TDC and the timing pointer. They should be exactly the same within a very small margin.
  9. I had not considered that. What would cause that to happen?
  10. age and use, the balancer is basically two chunks of metal held together with rubber/urethane/some other kind of soft bonding agent, and it wears out after a while letting the outer shell spin free of the hub.
  11. Update... kinda. Dampener felt tight, no wiggle. I used a different scan tool and got a 225 - Knock not sensed during dynamic response test KOER. So, this is a very real possibility I think, could account for all my trouble symptoms (bad knock sensor). However, apparently you can no longer buy this part... So what do I do? Could I clear codes and start the truck and essentially bypass it by just leaving it unplugged or would this cause just as many problems?
  12. #412 jrichker, Mar 9, 2014
    Last edited: Mar 9, 2014
  13. Okay, am I right in thinking its not a base engine concern because it runs smooth as silk on a cold start up, until the idle drops down to where it stays at operating temp?

    Had the dampener moved, wouldn't that have moved it off the initial 16* I had set it to as well? It was exactly where I had set it right after the build. I will go ahead with the TDC check anyway.

    The bad knock sensor could be causing my timing to retard a whole bunch (remember when I'd advance it way up it would smooth out), a physically shuddering engine, weird engine noises, fuel economy drop, and poor performance in general (according to the internet).

    As far as the part number, here are all the interchangeable parts:

    And no online parts site that I have found in the last 2 hours carry any of them.
  14. Knock sensor - Check out and see if that helps.

    Just for reference to make sure we are viewing this correctly...

    Setting the timing:
    Paint the mark on the harmonic balancer with paint -choose 10 degrees BTC or 14 degrees BTC or something else if you have NO2 or other power adder. I try to paint TDC red, 10 degrees BTC white and 14 degrees BTC blue.

    10 degrees BTC is towards the drivers side marks.

    Note: setting the timing beyond the 10 degree mark will give you a little more low speed acceleration. BUT you will need to run 93 octane to avoid pinging and engine damage. Pinging is very hard to hear at full throttle, so it could be present and you would not hear it.

    Simplified diagram of what it looks like. Not all the marks are shown for ease of viewing.

    ATC ' ' ' ' ' ' ' ' ' '!' ' ' ' ' ' ' ' ' ' BTC
    ---------------- > Direction of Rotation as viewed standing in front of the engine.

    The ' is 2 degrees.
    The ! is TDC
    The ' is 10 degrees BTC
    Set the timing 5 marks BTC. Or if you prefer, 5 marks towards the driver's side to get 10 degrees.

    To get 14 degrees, set it 7 marks BTC. Or if you prefer, 7 marks towards the driver's side to get 14 degrees.

    The paint marks you make are your friends if you do it correctly. They are much easier to see that the marks machined into the harmonic balancer hub.

    Make sure that you set he timing when the engine is up to operating temperature.

    At this point hook up all the wires, get out the timing light. Connect timing light up to battery & #1 spark plug.

    Remove the SPOUT connector (do a search if you want a picture of the SPOUT connector) It is the 2 pin rectangular plug on the distributor wiring harness. Only the EFI Mustang engines have a SPOUT. If yours is not EFI, check for a SPOUT: if you don’t find one, skip any instructions regarding the SPOUT
    Warning: there are only two places the SPOUT should be when you time the engine. The first place is in your pocket while you are setting the timing and the second is back in the harness when you finish. The little bugger is too easy to lose and too hard to find a replacement.

    Start engine, loosen distributor hold down with a 1/2" universal socket. Shine the timing light on the marks and turn the distributor until the mark lines up with the edge of the timing pointer. Tighten down the distributor hold down bolt, Replace the SPOUT connector and you are done.

    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

    #414 jrichker, Mar 9, 2014
    Last edited: Mar 9, 2014
  15. Yep, I had the timing at 16. After problems started I rechecked and it was still at 16. I have a red line on 10 and a silver on 14. After the problem started I went to retard it back down to 10* and the shudder was way worse than if advanced up high.
  16. I'm going to clear the codes and run the truck without the knock sensor in it. If the problem is still there am I correct in thinking its not a faulty knock sensor retarding the timing too much? My theory is a faulty knock sensor can send erroneous signals causing the timing to retard, but if it isn't plugged in the sensor cant send signals to retard the timing, lol
  17. Any ideas why my original maf and both Cardone remanned maf's are measuring 1.1v at idle between pins c & d? I have a hard time believing both Cardone maf's I got are defective from the parts store (although I suppose stranger things have happened).
  18. I'm driving myself insane trying to ditch the random sticking surge spike, i've cleaned out the throttle body, installed new gaskets, replaced the EGR and IAC with a brand new one, cleaned out the MAF and connections, Adjusted the idle with the IAC unplugged and set the TPS to .8 volts with throttle closed, tested the TPS for smooth increase and decrease along with a mild tap test for distortion. I have no check engine light and on top of that my car won't communicate with a code reader. I test drove it and it seemed alright for about 30 miles without a surge then it came out of nowhere and started doing it over and over. Its completely unpredictable and i don't know what i should even shoot for next; Any ideas?

    It doesn't seem to do it all the time just sort of when it wants to then it really acts up.
  19. First thing that comes to mind after reading that tidbit is a faulty ecm.
  20. Computer will not go into diagnostic mode on 91-93 model 5.0 Mustangs

    How it is supposed to work:
    The grey/red wire (pin 46) is signal ground for the computer. It provides a dedicated ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the computer into self test mode. If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. Since it is a dedicated ground, it passes through the computer on its way to the computer main power ground that terminates at the battery pigtail ground. It should read less than 1.5 ohms when measured from anyplace on the engine harness with the battery pigtail ground as the other reference point for the ohmmeter probe.

    What sometimes happens is that the test connector grey/red wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60. Only an experienced electronics technician can open the computer up & repair the trace if it burns up and creates an open circuit.

    The STI (Self Test Input ) is jumpered to ground to put the computer into test mode. Jumpering it to power can produce unknown results, including damage to the computer. The ohm test simply verifies that there are no breaks in the wiring between the test connector and the computer input.

    How to test the wiring :
    With the power off, measure the resistance between the computer test ground (grey/red wire) on the self test connector and battery ground. You should see less than 1.5 ohms.


    If that check fails, remove the passenger side kick panel and disconnect the computer connector. There is a 10 MM bolt that holds it in place. Measure the resistance between the grey/red wire and pin 46 on the computer wiring connector : it should be less than 1.5 ohms. More that 1.5 ohms is a wiring problem. If it reads 1.5 ohms or less, then the computer is suspect. On the computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than 1.5 ohms. More that that and the computer’s internal ground has failed, and the computer needs to be replaced.

    See for Joel5.0’s fix for the computer internal signal ground.

    If the first ground check was good, there are other wires to check. Measure the resistance between the STI computer self test connector (red/white wire) and pin 48 on the computer main connector: it should be less than 1.5 ohms. More that 1.5 ohms is a wiring problem

    The following is a view from the computer side of the computer wiring connector: it is for an A9L, A9P computer.


    Diagram courtesy of Tmoss & Stang&2birds

    Check out the diagram and notice all the places the grey/red wire goes. Almost every sensor on the engine except the MAF is connected to it.

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

    See the graphic for the 10 pin connector circuit layout.