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Discussion Starter #1
Im still in the process of installing an 03 Explorer engine into my 95 Tbird.

The car starts, then dies. It will run if I hold the gas, but it wont idle on its own.

I was checking the IAC valve circuit, it has power 12 volts in the run position .. but when I am monitoring the + and - on the pigtail with the engine running or off .. the voltage is very low, maybe .023 volts and doesnt change when I try to idle it at a low speed.

TPS voltage is .98, using the Explorer Throttle body, tried 2 different EGR valves, IAC valves, and looking for vacuum leaks.

Maybe a bad EEC ? What else would make the IAC not work ? Anything from the EGR, DPFE, O2's ??
 

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have you tried resetting the EEC? i once had a glitch show up that sent full power to the IAC valve which in turn made the car idle ridiculously high in neutral and drive.....reset the EEC with the fuse trick and its been fine since then

have you modified anything else on the Tbird?

ideally, its best to have an IAC for your model year car, since it has a transfer function of its own, just like MAFs, that dictate what duty cycle will produce a certain amount of airflow......im not sure to what extent a non-stock IAC would have on your stock EEC, but just throwing it out there
 

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Hows the idle screw on the Tbody?


My first thought would be major Vac leak for one of the main lines.But that would be really noticable.
 

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Discussion Starter #4
I havent messed with any idle screw, tried 2 different Throttle bodies, one from a 96 Tbird and the 03 explorer one.
I have 3 different IAC's, one from a 94, 96, and the 03. Doesnt change anything.

My concern is that the negative trigger for the EEC isnt making the IAC open op, it has power at the pigtail harness, but when I use my multimeter, it doesnt show very much power at all.

Right now the engine has just headers and about 2 feet of exhaust on each side, with the o2's hooked up. It should run with the exhaust wide open .. but it wont idle on its own.

I suppose I could always adjust the idle set screw on the TB .. but that doesnt fix the IAC. I am not getting any CEL or codes.
 

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Discussion Starter #6
Used another chassis ground to test the + side of the IAC harness, and the + and - to see if the negative is working.
 

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so you do get 12V but only with the ignition on, and the engine off....but if you start the car, and artificially make it hold idle by giving it throttle, there is no voltage at the wires in the IAC connector?
 

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Discussion Starter #9
Voltage is about .1 volt at the IAC, and .3 volts at the EEC .. shouldnt it be on a 0-12 volt scale ? I am thinking it cycles the power, so it should be a constant on/off ??? Either way it looks like there is a small voltage difference .. sometimes it goes up to .5 at the EEC .. then I test it at the IAC again and its 12 volts, I dont understand why I am getting so many differences.

I can get it to idle on its own by adjusting the set screw for the throttle body blade. But when I first start it, it wont start running unless I open the throttle up a little bit more.

I think I am using the IAC for a 96 Tbird .. should the 03 explorer one be calibrated differently for this engine setup ?
 

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try this....get the thing started by opening up the TB manually.....once you get it to idle while holding the TB openend manually, disconnect the IAC connector, and slowly close the TB so that the car idles at just a tad below 750 RPMs (like 700ish).....once the RPMs slightly dip below 750, set the throttle stop screw so that it holds the TB at that precise angle that allows the car to idle just slightly below 750 w/o any IAC influence......now plug in the IAC, and note any changes in idle speed....it shouldnt vary all that much, maybe even go up like 20-30 RPMs tops (neutral idle RPM is set at 768 in 94/95 4.6L MN12s)

if all looks well, turn off the car....then turn the ignition ON.....you'll have to readjust the TPS sensor because it is probably reading over 1V now that the TB blade has been adjusted.....so loosen it up if necessary and get it 0.97-0.99.....now attempt to start the car.....dont forget to plug in the TPS and IAC if you took them off again....let me know how that goes
 

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Discussion Starter #11
Well okay .. I took a look at the set screw on the throttle body and it looks like it was cut a little bit shorter. Weird. I picked it up from somewhere, its a 70mm unit from a 5.4 I think. Anyways, I Got it started, set the idle to about 750 rpm like you said, then turned it off and set the TPS to .99 volts. So it will start now, the RPM's go up and them dip down like its going to die, then it starts to idle about 750. Dont notice any fluctuation, didnt test the IAC circuit.

When I rev it up a little bit, and let off the gas, the RPMs will dip down, and it dies. Any thoughts ?
 

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then you either have a whole bunch of IACs that dont work or the EEC is fried.....normally when you rev it up a little, the IAC is supposed to add a bit of air on its own (called dashpot), so it can slowly reduce the airflow to softly drop down to idle RPM after you suddenly close the throttle

i have my stock IAC and another one that I believe came from a Cobra that you can have if you'd like to rule out the IACs you have

also, i believe the power wire to the IAC should be fused somewhere instead of it being a direct line to the EEC....i'm not totally sure, but if I were you, i'd check each and every single fuse in the cabin fusebox, and in the power distribution box under the hood just in case it is fused along with some other circuit
 

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Discussion Starter #13
Yeah thats why I was doing some voltage tests for the IAC circuit on the EEC.

I have 3 IAC's here, at least one was pulled from a good running engine, thanks for the offer anyways.

The primary power wire that the IAC uses is shared by the fuel injectors .. so its a known good power source. So I am checking for voltage with my multimeter using that positive wire and the white / light blue wire that goes to the EEC as the ground - and it is running at about .23 volts. Way too low if you ask me. Then I was checking it directly at the EEC - with the + lead directly to the car battery, and the - lead into the EEC harness .. it still only shows maybe .3 or .5 volts, nothing over 1 volt. So I need to find out what kind of voltage it is supposed to be running at, borrow an EEC from a working car, or figure out why the EEC wouldnt be sending a signal to the IAC. At least I got it to idle on its own and start up without pressing the gas. Thanks for the help so far.
 

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i'll go outside and hook up my DMM to see what kind of voltage the IAC sees while idling

edit: i'm gettin right around 5V with a duty cycle of 0.51 (this is not typical because of the custom tune i'm running).....your's should have a duty cycle of around 0.30-0.35%, so you should be seeing just a tad bit less voltage, i'd say in the 3.0-4.0VDC range
 

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Discussion Starter #15
Cool, thanks for checking. So it must operate on a 0-5 volt scale like some of the other electronics.
I am seeing 0.2 to 0.5 volts .. not very much power at all.

This weekend I will be borrowing an EEC from a buddy and see how that works out. The EEC I am using now came out of a wrecked car, never tested it until I started to actually run my engine. I dont have the EEC that came with my car originally ..
 

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Discussion Starter #17
Okay, just to update things ... the EEC is one of the problems right now.
I swapped it out with another EEC, same code .. and the IAC had 9 volts at idle .. engine ran alot smoother, and it doesnt die when I rev it up and let off the gas. When I put my original EEC back in, it ran just like it did before and died out easily.

Now the passenger side cat is starting to glow red and shoot spark out .. was shooting out a little fire after that so I turned it off.

So Ill be looking to replace the cats and exhaust, and the EEC soon ..
 
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