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I would like some help with electrical. It may be simple and I may be overlooking something, and it's concerning the IAC valve. To make all this short, could someone test their IAC for voltage on each terminal, and then on each terminal to ground, and post the results? I'm chasing down an occasional RPM hang and varying degree of wavering idle.
1987 F150 4.9. T18 manual
From what I gather, the IAC receives constant 12V from the battery POSITIVE. The ECM pulses GROUND on and off. But I am getting 14V on the upper RED wire, and 9V on the lower BLACK wire on the IAC. There is apparently a diode in the IAC I am unsure how to test.
IAC tests fine by resistance between terminals and terminal to IAC body. So given the above and the fact that I was not reading a GROUND, I replaced the ECM with a spare unused one. Same issue with IAC and the occasional rev-hang. At the same time, I replaced the TPS and let it do the idle relearn procedure. Still same issue. When it does this rev-hang and occasionally climbs a couple hundred between shifts, flooring it and then letting go remedies the rev-hang.
To make the long short, I used starting fluid and propane to test for vacuum leaks and did not find any. TPS tested good out of the box but the sitting voltage is around 0.8V, is that too high? When it rev-hangs/climbs, flooring it and then letting go will remedy that for the duration of the drive. Idle on startup will be around 600, and after driving, will be around 800-900. See video
Attached is a video of the slight wavering idle. Of note is that my EGR feed tubes are cracked, so my idle has a usual amount of waver
I know it's a lot, but any help is appreciated. Thanks in advance
87 was the first year for fuel injection for the 4.9
They ran better than the previous carbureted ones but did do exactly as you say
They basically idled like sheet
I would clean the injectors and clean the throttle plate and see if it improves
Your testing is not in any Ford book
If you do the pinpoint tests for a IAC in The PCED you will see things like this below (basic voltage tests are not part of it)
[img alt="This is a 1989 PCED.
You get yourself the same info for your 1987 and verify it is the same or better yet, use a 1987 book."]https://cimg5.ibsrv.net/gimg/www.ford-trucks.com-vbulletin/2000x1124/iac_testing_89_pced_11a3dffed32d20adfde487ef333911 24e000f7ff.jpg[/img] This is a 1989 PCED. You get yourself the same info for your 1987 and verify it is the same or better yet, use a 1987 book.
I would like some help with electrical. It may be simple and I may be overlooking something, and it's concerning the IAC valve. To make all this short, could someone test their IAC for voltage on each terminal, and then on each terminal to ground, and post the results? I'm chasing down an occasional RPM hang and varying degree of wavering idle.
1987 F150 4.9. T18 manual
From what I gather, the IAC receives constant 12V from the battery POSITIVE. The ECM pulses GROUND on and off. But I am getting 14V on the upper RED wire, and 9V on the lower BLACK wire on the IAC. There is apparently a diode in the IAC I am unsure how to test.
IAC tests fine by resistance between terminals and terminal to IAC body. So given the above and the fact that I was not reading a GROUND, I replaced the ECM with a spare unused one. Same issue with IAC and the occasional rev-hang. At the same time, I replaced the TPS and let it do the idle relearn procedure. Still same issue. When it does this rev-hang and occasionally climbs a couple hundred between shifts, flooring it and then letting go remedies the rev-hang.
To make the long short, I used starting fluid and propane to test for vacuum leaks and did not find any. TPS tested good out of the box but the sitting voltage is around 0.8V, is that too high? When it rev-hangs/climbs, flooring it and then letting go will remedy that for the duration of the drive. Idle on startup will be around 600, and after driving, will be around 800-900. See video
Attached is a video of the slight wavering idle. Of note is that my EGR feed tubes are cracked, so my idle has a usual amount of waver
I know it's a lot, but any help is appreciated. Thanks in advance
Specifically how are you testing you're IAC valve wiring?
It should be tested with the key on, engine off, by back probing the connectors two wires, rather than testing each wire to ground. (I use wire piercing probes rather than back probing).
Test it that way and see what voltage you get.
Check out posts 3,4 and 5 at this thread for information about the diode 88 IAC wiring harness | Bronco Forum - Full Size Ford Bronco Forum https://share.google/YOOXPhUZ5KvoGKo7l
The two wires at this connector should be connected to your battery negative terminal. They're the power grounds at pins 40 and 60, and the ground for the ECM relay coil. If you have this style of battery terminals, they're known to cause issues with loose connections and corrosion.
This connector is configured the same as the O2 sensor harness connector. Make sure your O2 sensor wiring is connected properly. The wiring for it comes out of the harness at the firewall near the heater blower motor, travels around to the passenger's side fender behind the battery, then follows the starter cable down to the O2 sensor.
On my '88, someone had connected the O2 sensor wiring to the power grounds connector.
If your idle is hanging, it's just as likely an issue with the throttle body linkage or shaft hanging up.
With the throttle cable disconnected from the throttle body, do the throttle body blades spring closed properly if you open them by hand then let go of them?
If you're going to check for engine codes, you're going to need a code reader, or you can use the method described at this link Lincolns OnLine | Tech Tips and Articles https://share.google/6go1O2H9904PHrVEm
There isn't a check engine light on a 1987 F150 to flash out diagnostic codes.
Make sure the engine is at operating temperature before checking for codes.
Run codes first. That'll take your far. It may not even be your IAC valve. Are you running a new one or the old one?
On this truck I've never been able to run codes. It has a red ENGINE light. My 1991 F250 has an orange ENGINE light and I can get codes off of that one.
I am running a newer IAC valve, maybe 6 months or so old? I can't quite recall. It tested good according to my HAYNE'S manual
If you're going to check for engine codes, you're going to need a code reader, or you can use the method described at this link Lincolns OnLine | Tech Tips and Articles https://share.google/6go1O2H9904PHrVEm
There isn't a check engine light on a 1987 F150 to flash out diagnostic codes.
Make sure the engine is at operating temperature before checking for codes.
SWEET! I've never been able to get codes off of this one like I can on my 1991. I think I have a working analog multimeter somewhere. I've got an OBD1 code reader that needs some work done to it. When I get a chance I will pull codes. Thanks for that
Specifically how are you testing you're IAC valve wiring?
It should be tested with the key on, engine off, by back probing the connectors two wires, rather than testing each wire to ground. (I use wire piercing probes rather than back probing).
Test it that way and see what voltage you get.
Check out posts 3,4 and 5 at this thread for information about the diode 88 IAC wiring harness | Bronco Forum - Full Size Ford Bronco Forum https://share.google/YOOXPhUZ5KvoGKo7l
The two wires at this connector should be connected to your battery negative terminal. They're the power grounds at pins 40 and 60, and the ground for the ECM relay coil. If you have this style of battery terminals, they're known to cause issues with loose connections and corrosion.
This connector is configured the same as the O2 sensor harness connector. Make sure your O2 sensor wiring is connected properly. The wiring for it comes out of the harness at the firewall near the heater blower motor, travels around to the passenger's side fender behind the battery, then follows the starter cable down to the O2 sensor.
On my '88, someone had connected the O2 sensor wiring to the power grounds connector.
If your idle is hanging, it's just as likely an issue with the throttle body linkage or shaft hanging up.
With the throttle cable disconnected from the throttle body, do the throttle body blades spring closed properly if you open them by hand then let go of them?
I can't exactly recall when I tested and replaced my O2 sensor but it was more than a year ago in hopes to increase my MPGs. It still reads funny but it's within spec so I let it be. I can assume O2 wiring is good
I will check for binding.They've always appeared to spring closed BUT I've always had the throttle cable connected. I like the idea of removing it. I can check for side-to-side play at the same time. Thanks for that
87 was the first year for fuel injection for the 4.9
They ran better than the previous carbureted ones but did do exactly as you say
They basically idled like sheet
I would clean the injectors and clean the throttle plate and see if it improves
Your testing is not in any Ford book
If you do the pinpoint tests for a IAC in The PCED you will see things like this below (basic voltage tests are not part of it)
[img alt="This is a 1989 PCED.
You get yourself the same info for your 1987 and verify it is the same or better yet, use a 1987 book."]https://cimg5.ibsrv.net/gimg/www.ford-trucks.com-vbulletin/2000x1124/iac_testing_89_pced_11a3dffed32d20adfde487ef333911 24e000f7ff.jpg[/img] This is a 1989 PCED. You get yourself the same info for your 1987 and verify it is the same or better yet, use a 1987 book.
Huge huge help.
I don't want to remove injectors simply because of the intake sitting right on top, but I've always been curious if mine are single or multi-hole. I've heard mixed reviews about "upgrading" to multi-hole injectors. Occasionally I'll run MMO in my gas tank. Videos I've seen show it to be better at removing gunk than Seafoam. I can only hope it actually works.
Someone else suggested removing the throttle cable from the throttle body and check for correct closure, and I'll check for side to side movement at the same time
Your book simply suggests resistance testing between pins and from either pin to IAC housing, both tests I have done and passed I believe. My IAC pin to housing was OL. The voltage and resistance tests are outlined in my HAYNES manual. The other information I get from forums or facebook or old websites.
I will definitely take a look at this book for my model year. The more information the better. My co-worker said he had the CHILTON and HAYNES and would cross reference when one book left something out or didn't make sense.
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