new o2 sensors, new harness, high idle??

[OonDeanisS]

i just replaces my o2 sensors with ford racing parts from 50resto, and i replaced the harness they connect to with a unit from ebay (hold your applause), and now when i start the car, it goes up to 3100 RPMs and holds there. i can give it throttle, but it just comes back down to 3100.

IF i disconnect the MAF, the engine dies. If i disconnect BOTH (the 02 harness and the MAF) the car will start, rev to 1500 RPMs, then die, with NO throttle response at all.

IF i connect the MAF but NOT the o2 sensors, the car starts and idles fine but misfires under load.

any thoughts?

 

[HISSIN50]

is the 02 harness from the donor vehicle exactly the same as the one that was in your vehicle?

 

[OonDeanisS]

its brand new, says it is for an 87-93 5.0 mustang with manual trans. the new one has wire loom over it, so im not sure, but i am sure that the one on my car WAS wrong, so i cant really compare.

 

[HISSIN50]

That's a lot of variables and unexpected results. Can you put the old O2 harness and old O2's in to see if the car behaves as it did before the new/ebay parts were installed? If it does not, that might suggest that something else happened coincidentally. Otherwise, I'd clear the KAM, start it up (assuming you can do so safely) and then I'd try to pull codes to see if the EEC will give a clue as to what's occurring.

 

[OonDeanisS]

thanks, how do i clear the KAM?

 

[HISSIN50]

Abort a code pulling session or disconnect the battery and turn on the headlights for a minute. You'll lose any saved adaptive strategies that last way.

 

[OonDeanisS]

well i disconnected the battery and left the headlights on for about 15 minutes then plugged in both the MAF and the o2 harness, and started her up... high idle. then, i pulled the harness off the IAC motor, and the idle dropped down to normal, car runs great. Dare i say, better than ever. I think the problem is fixed, and i drove it quite a bit, with no problems. Thanks so much. i will still run the codes and try to figure out why the IAC makes it idle so high at normal temp, but i do believe my MAF and O2 problems are a thing of the past! yeessssssss.

 

[HISSIN50]

You can try to clean the IAC but be prepared to buy a new one - sometimes cleaning them makes them worse.
In case your current IAC is not OEM, some aftermarket IAC's require being mounted upside down - if that's not done, things can act a little funny.

 

[OonDeanisS]

i just got a new IAC, so this one being no good seems improbable, but who knows. Which way is "upside down"?

 

[HISSIN50]

I don't have that much faith in parts store parts (if this is a Motorcraft IAC, disregard that).

If the IAC needs to be upside down, the instructions would indicate that (there's generally a scrap of paper in the box).

 

[jrichker]

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.

Recommended procedure for cleaning the IAC/IAB:
Conventional cleaning methods like throttle body cleaner aren’t very effective. The best method is a soak type cleaner used for carburetors. If you are into fixing motorcycles, jet skis, snowmobiles or anything else with a small carburetor, you probably have used the one gallon soak cleaners like Gunk or Berryman. One of the two should be available at your local auto parts store for $22-$29. Take the solenoid off the body and set it aside: the carb cleaner will damages some types of plastic parts. Soak the metal body in the carb cleaner overnight. There is a basket to set the parts in while they are soaking. When you finish soaking overnight, twist the stem of the IAB/IAC that sticks out while the blocker valve is seated. This removes any leftover deposits from the blocker valve seat. Rinse the part off with water and blow it dry with compressed air. The IAC/IAB should seal up nicely now. Once it has dried, try blowing through the bottom hole and it should block the air flow. If you can still blow air through it, it is defective. Reassemble and reinstall to check it out.

Gunk Dip type carb & parts soaker:

Setting the base idle speed:
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 electrical signal 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. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPM’s to 650-725 RPM’s

Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

This isn't the method Ford uses, but it does work. Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks.

Disconnect the battery negative terminal and turn the headlights on. Leave the battery negative terminal disconnected for 5 minutes or so. Then turn the headlights off and reconnect the battery. This erases the computer settings that may affect idle performance.

Warm the engine up to operating temperature, place the transmission in neutral, and set the parking brake. Turn off lights, A/C, all unnecessary electrical loads. Disconnect the IAC electrical connector. Remove the SPOUT plug. This will lock the ignition timing so that the computer won't change the spark advance, which changes the idle speed. Note the engine RPM: use the mechanical adjustment screw under the throttle body to raise or lower the RPM until you get the 600 RPM mark +/- 25 RPM. Changing the mechanical adjustment changes the TPS, so you will need to set it.

When you are satisfied with the results, turn off the engine, and re-install the SPOUT and reconnect the IAC. The engine should idle with the range of 650-750 RPM without the A/C on or extra electrical loads.

 

[OonDeanisS]

i g the IAC from 50resto, i believe it is a Ford part. it could not be cleaner, but thanks.

 

[MaRu_GT]

Hi man, I guess that you are facing the same issue I had before:
http://www.stangnet.com/mustang-for...installing-new-o2-sensors-please-help.835200/
it might be different harness and you might need to re-pin it. If your fox is 1990 then I am sure it's the same issue because some of 1990's foxes got that different harness from factory. That harness may toast your ECM if you keep using.

 

[OonDeanisS]

crap, ive put like 160 miles on it already... runs fine but the IAC is unplugged. I read that post, and im going to check the loop wire monday to make sure that it connects the purple yellow to the blue/yellow. (first on left top and bottom)... any tips on how to re-pin it if need be? im not sure how to get the wires and pins out of the harness.

 

[jrichker]

Back to basics -see the "Surging Idle Checklist” for help with all your idle/stall problems. You can guess at the problem and throw parts at it, or you can use the checklist to help you find the problem quickly and inexpensively. It’s free and doesn’t cost anything: at last count there were more than 103,000 visits and still climbing

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. 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.

 

[OonDeanisS]

well, i opened up the harness, and sure enough, the loop wire is incorrect. going to attempt to re-pin it, then update again. thanks. i printed out the entire surging idle thread, and i am going to also run the codes when im done. thanks so much.

 

[OonDeanisS]

got it re-pinned (correctly this time) and re-connected my IAC. Car runs GREAT! except i was dragging one of my new o2 sensors... so i need a new bung and sensor, but hey, its FIXED!! thanks to YOU GUYS! i cant thank you enough. didnt have time to run the codes, but i will once i get the new o2 sensor installed.

 

[OonDeanisS]

aaaaannndd the car doesnt dump codes. crapzilla. im wondering if "the wiring that puts the computer into diagnostic mode" includes both o2 sensors, because i only had one plugged in when i tried to dump the codes. i thought it would just drop a code for the hego.

 

[jrichker]

Computer will not go into diagnostic mode on 86-90 model 5.0 Mustangs

Disconnect the battery positive terminal before making any resistance checks.
The voltage drop in the ground cable will cause incorrect resistance readings.

How it is supposed to work:
The black/white 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 black/white 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.

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 (black/white 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 black/white 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 repaired or replaced.

See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 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.

Diagram courtesy of Tmoss & Stang&2birds

Check out the diagram and notice all the places the black/white 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 http://www.veryuseful.com/mustang/tech/engine

See the graphic for the 10 pin connector circuit layout.

 

[OonDeanisS]

when i turn my dvm to 200 ohms range, it comes up with a 1, reading the resistance of the air between the leads. when i touch them together, i get a .3 so i know it works, but when i test the resistance between pin 46 and ground, it doesnt change from the 1. i guess 1 is good wiring and the computer is suspect? i can NOT get myself into that corner with the leads and a light to test the pins on the computer while also reading the DVM, so my question is this: can i take the computer out to test the resistance or do i need to test it bolted down?