302 IAC Signal??

[97Beast]

A mechanic down the road told me told me that my IAC was bad when I took it to their shop. But I'm pretty sure of myself that were just giving me a BS generic answer, so I took the IAC off (i had cleaned it before i took it to the mech.) and I hooked up to my battery and it clicked up and down.
So it looks like it works under the proper voltage, which I hear is .98-.99, but I'm not sure what kind of voltage it actually gets, and if it gets the proper signal.
So what kind of signal does the IAC receive??

[Thadoggma]

well it gets a signal from the pcm (computer) and depending on the voltage the computer sends it, it controls the amount of air that the engine receives at an idle, as the intake butterflys are closed at an idle, and the iac is the engines way of getting air around that... supposedly there is a specific voltage it should be receiving when idling at its specified rpm, but im not sure what it is... let me look that up real quick...

The voltage on the IAC control circuit should read B+ -30-35% or 9 to 10 v. If the % is higher, the PCM is raising the idle. If lower, look for a short to ground between the IAC solenoid and the PCM

Read more: http://www.justanswer.com/questions/...#ixzz0Pb7vOZ7j

[97Beast]

Ok. thanks Thadoggma. I wonder what type of signal the PCM sends off, and if I'm getting a signal.
But I have a feeling the IAC is not a problem, that the shop was BSing me.
It starts up normal, but it doesnt want to go down to an idle when cold, instead it just dies.

The prev. owner replaced:
TPS
MAP
EGR----But not the EVP
IAC
02 sensor
New Cat
TAB & TAD-- I replaced these

Basically all I can think of is somehow vacuum is leaking somewhere, (but I havent found it), the Coolant Temp Sensor, and the EVP.
OR.. I could have a bad PCM possibly.

[Thadoggma]

the pcm is doubtful, if it was bad you would most likely have a host of other problems with your truck. does your truck have A/C ?

[97Beast]

Originally Posted by Thadoggma

the pcm is doubtful, if it was bad you would most likely have a host of other problems with your truck. does your truck have A/C ?

Nope. the A/C doesnt work. It was converted to R134, and he says that it just needs to be charged up, but who knows what the deal really is.

Is the EEC the samething as the PCM, or is it a separate module that works with the PCM??

[Thadoggma]

well is your heater on when the truck decides to die? i ask because my truck did what you are describing, and it was because of the ac compressor clutch engaging, when the system wasn't charged. might or might not be your problem.

in my case i disconnected the plug on the top of the clutch and it has solved my problem since i dont use a/c anyway...


and no i dont thnk they are the same, if i remember right, the eec works with the pcm, but they are two separate controls.

edit: the eec and pcm are the same thing, just different terms for it.

[97Beast]

Ok so I unplugged it and I drove it around and let it idle, it seems to do alot better now, but it still feels quirky.
I did notice that the compressor was fidgetting and trying to egage,
My fan works but the system isnt charged, so it may just need a recharge or a new compressor.

Thanks for your help!

[Thadoggma]

your welcome!

as long as the system isnt charged, i would leave the clutch unplugged, as running the compressor without coolant will burn it up, which sounds like what was starting to happen.

[97Beast]

Yea, I'm just going to leave it unplugged. I think it helped but I'm not sure what else could be wrong with the truck.

[miesk5]

John,
Did the "mechanic" do a Code Test?
Do a Self Test anyway;
SELF TEST & DTCs, COMPREHENSIVE by Steve83
Remember to have engine @ Normal Operating Temperature before doing the KOER portion
You may need to clean the throttle body and intake manifold (upper & may as well do lower) someday (could cause sim. symptoms as a bad IAC); TB Cleaning by 86beast

Post Codes here; and read; Overview & Testing; "First let me say this little thing has many names. But they all talk about the same item under the hood. Here all the names I’ve had the torture of learning throughout the years: Idle Air Bypass •Idle Air Control •Idle Speed Control •Throttle Bypass Air •Idle Bypass •Inlet Air Controller •Inlet Air Bypass •Intake Air Bypass •Intake Air Control..."
Source: by Ryan M (Fireguy50) at fordfuelinjection.com Do his simple test at end of the article

A scope is a good tool to have access to when testing; but I Won't bug ya w/these details; esc for this;
Waveform, Good, Scroll down; "...This is a typically good ford idle air control (IAC) motor waveform. The Ford IAC waveform has its own unique "sawtooth" signature. The IAC valve is being pulsed and the duty cycle determines the volume of air through the valve. A 100% duty cycle is fully open and a 0% duty cycle is fully closed. When checking this solenoid look for dropouts or spikes in the waveform that could indicate a problem..."
Source: by omitec.com

[JKossarides]

Usually a Code: 67 ~ would indicate either A/C or NSS issue......

Good Luck ~

[97Beast]

The "mecahnic" didnt pull any codes at least from what he told me, but I think I'm just going to do the self-test, or I might just go up to that shop and hound them till they let me pull my codes, with their reader.
Thanks for all the info on the self tests.

[97Beast]

I looked through all the links, my chilton and hayne's books about the self test and I was wondering maybe it cant be much to get ahold of the scan tool for my truck.
So I found this for $26 bucks. Is it legit?? Will it work??
http://www.sjdiscounttools.com/epi3145.html

[JKossarides]

Just make sure the Code Reader matches the TEST plug connectors over on the right side, near the battery area.....

It looks like my Ford Code Reader which is very easy to use, does this product have the Code Book as well for that price............if not go to www.fordfuelinjection.com and you can copy the fault code explanations for FREE, it's owned by FSB Member Ryan McCormick aka Fireguy50......

Good Luck ~

[97Beast]

Originally Posted by JKossarides

Just make sure the Code Reader matches the TEST plug connectors over on the right side, near the battery area.....

It looks like my Ford Code Reader which is very easy to use, does this product have the Code Book as well for that price............if not go to www.fordfuelinjection.com and you can copy the fault code explanations for FREE, it's owned by FSB Member Ryan McCormick aka Fireguy50......

Good Luck ~

It looks like it would match up with my test connector, since my 89 is EEC IV.
Is your battery on the passenger side or drivers side? Mine has an "EEC Test" connector on the drivers side behind the intake.
Is that the right connector or am I missing something, it looks like the one described in my Chiltons book.

[JKossarides]

My Test Connectors and Battery are on the "right side" (passenger) behind a black EGR Vacuum Reservoir .....my BKO is an 86 but as long as the Code Reader and Test Connector Plugs are the same it should be fine......

EEC-IV - Electronic Engine Control - 4th generation...

I like the Code Reader because it's fast, fun and readable, but make sure it's "battery" is good so it triggers the PCM ....the # 10 is usually a "separator" code not a "fault" code.......make sure you read the code book thoroughly and you're good to go....

Good Luck ~

[97Beast]

Ok, cool, if it says its for EEC IV i should be good to go.
I read up about the procedure for testing, I have all the codes saved to favorites, in addition the the codes the Chiltons and Haynes books gave me.
For $26 bucks the reader is well worth it.
I paid $84 for them to tell me a bunch of bs, and I'm sure they didnt pull codes.
I'm done with mechanics, because being only 16 I dont have much money to waste, and I need to get the bronco fixed for as cheap as possible.

I'm not looking to pay $450 to fix a $50 problem, plus doing this myself is teaching me all kind of stuff.

[miesk5]

ok, but we're trying to save you even that for that $26.00 code reader; you can do the self-test for zip & then use the $ for any part you may need to buy.
BTW, I try to get only Ford Motorcraft parts or the orig eqiupt manufacturer (OEM) that Ford used when building the Broncos (& F Series/and many cars that used the exact same part).
For example, 3 dealers in area wanted $150.00 for the DPFE Sensor and would not discount; so I got the MOTORCRAFT DPFE15 thru Amazon w/free S&H for $60.00.
We've all been in the same boat as you (I still am because of the changes to the Federal CS system) and want to repair our Broncos instead of paying big $ for labor & parts.
GL!

[Thadoggma]

if your a/c compressor is still trying to engage after you have unplugged the clutch, that means that somethings going out. it shouldnt do anything wih it unplugged.

[JKossarides]

97Beast: You got the right attitude Brother, DIY is really what this site is all about and helping each other keep these rigs rolling.......

I've learned a great deal about EFI from being an FSB member and making a lot of friends too........AND you can 'search" FREE for any information you might need when there's a problem.......try that with the local mechanic...NOT!

I refuse to go to a mechanic any longer because it's all about the labor rate $$$$$$ for them and most of the time they don't know/care what they're doing and you get ripped off.....so unless it's something I can't do because of the lack of proper tools, professional equipment or knowledge like rebuilding an automatic transmission or cylinder head work etc......I can can do most it myself and that's a great feeling, not to mention the money you save as well........

This past Sept...I swapped in a new 302 EFI long block entirely myself, I had a little help from some of the FSB guys here ........lol lol

Good Luck ~