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Well, thought i had it running good...


rusty ol ranger

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87 ranger 2.9.

Been having issues with it being doggy, think i more less got that settled...but...

Last night sittin in a drive thru the idle kept dropping slowly, then it ran rough as piss, then quit. It started right back up immeditaly.

Did it twice. Run good once under throttle.

Im thinking IAC....but ive never had one fail and idle low...
 


RonD

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Yes, IAC Valve would be first stop

Computer gets RPM data from the TFI Module
Computer has "Target idles" based on engine coolant temperature(ECT sensor)
Cold target is about 1,100rpm
warmed up, manual trans, 650rpm, automatic 750-800rpm

Computer opens IAC Valve all the way with Key On, for starting engine
That's why any fuel injected engine should REV up when you start it, without touching the gas pedal.
Computer then starts to close IAC Valve to set Target Idle based on ECT sensor temp

After cold start computer continues to close IAC Valve as engine temp gets warmer, so the 1,100rpms will drop down to warm engine target idle over then next 5 minutes or so.

There is a minimum idle RPM so its not solely temp based, i.e. RPMs don't drop lower than minimum if engine overheats :)
 

rusty ol ranger

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Yes, IAC Valve would be first stop

Computer gets RPM data from the TFI Module
Computer has "Target idles" based on engine coolant temperature(ECT sensor)
Cold target is about 1,100rpm
warmed up, manual trans, 650rpm, automatic 750-800rpm

Computer opens IAC Valve all the way with Key On, for starting engine
That's why any fuel injected engine should REV up when you start it, without touching the gas pedal.
Computer then starts to close IAC Valve to set Target Idle based on ECT sensor temp

After cold start computer continues to close IAC Valve as engine temp gets warmer, so the 1,100rpms will drop down to warm engine target idle over then next 5 minutes or so.

There is a minimum idle RPM so its not solely temp based, i.e. RPMs don't drop lower than minimum if engine overheats :)

Ok let me ask you this...

Engine seems to be loading up whenever its under load (giving it throttle) then letting off back to idle. It does NOT do this if you keep just a little pressure on the throttle.

Case in point, driving up to get my check today. Rollin along 55 like normal, downshifted (throttle closed), slowed to 40 or so, then popped it into neutral to stop, engine stalled dead. But fired right back up.

Is it possible the IAC is not responding fast enough, choking off all air and causeing it to flood when you close the throttle plate?

However at idle if i unplug the IAC it stalls/drops to a super low idle untill i plug it back in then it pops back.

No codes besides 18, but the truck actually is running pretty damn good till this shit happens, then it gets boggy again, im guessing from excess fuel. It also smells gassy.
 

RonD

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Fuel injection system should turn OFF fuel injectors when coasting in gear, engine RPMs above 1,500 and throttle Closed(TPS under 1 volt), this is one of the benefits of EFI, high vacuum 0 fuel use, with carbs the high vacuum sucked in extra fuel from idler jets when doing this, so coasting in Neutral saved fuel, but wore out brakes, lol.

Computer should restart injector pulses when RPMs drop under 1,500 or if TPS goes above 1volt, foot on the gas pedal.
Computer doesn't use IAC Valve until TPS is under 1volt
Might be worth while to use volt meter to test TPS voltage, center wire, and make sure it is going below .99volts each time its closed
I use a sewing needle to pierce wires to test voltage

The IAC valve movement is not all that much, about 3/8", so almost instant response from engine for even a little movement.
Does IAC Valve seem to work other wise, i.e. cold engine high idle RPM then lower and lower as engine/coolant warms up?
 
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rusty ol ranger

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Yes, the IAC seeems to work fine otherwise.

I did test OHMS on the TPS and that all seemed to be fine, i didnt test the TPS for voltage.

I also have a rough idle at times, like when things settle down to normal idle RPM (cold or hot), rusty #1 always idled like shit to so i didnt think anything of it. But is it possible i got some bad fuel injectors?

This truck sat for 12 years, and when i first startef driving it it had a miss but eventually worked itself out one day when i hammered it. But now it doesnt seem to miss at all under throttle, only under the conditions i described above.

Also, i know this is weird, but the truck still feels doggy untill i get it to temp, shut it off for 10-15 minutes, then restart it, then it runs like a raped ape. That coupled with the factnmy EGR was totally carbon blocked leads me to believe something is making it pig rich. But i have no codes to point to a sensor.

No fuel in the FPR line either.

Edit...

Hold on, if Efi kills the injectors above 1500, and code 18 is a tach signal lost, then its not a stretch to think that may be whsts causing this.

I was really hoping not to have to dig into that one....

Guess ill have to crack open that book...

Im really regretting going to EFI for a daily driver
 
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bobbywalter

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is there signal at pin 4 or not?
 

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bobbywalter

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i dont see them as problems...i would just drive it.
 

rusty ol ranger

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is there signal at pin 4 or not?
Havent checked that yet.

I would assume so seeing as how unplugging the spout makes things worse.

Ill unplug the ECM and see what i can get. But id like to check the resistance between that pin and the corrosponding TFI wire, but my test leads on my meter arnt long enough.

Can i just tape wire to the leads to extend them? Or will this throw the meter off? Forgive me if thats a dumb ass question, but 3/4 of my dragging feet here is the fact i know very little about using a voltmeter
 
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fastpakr

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Measure the resistance of what you're adding, then add it to extend.
 

rusty ol ranger

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Measure the resistance of what you're adding, then add it to extend.
Im making this way harder then it needs to be aint i?

Either way ill get some needles from china mart and test the TPS for shits, then ill pull the cpu plug and see if this old dog can learn new tricks.

Im guessing its a good idea to yank the battery cable before i get anywhere near the ECM?

Also just doing some reading, found a pinout document that says "Do not probe pins with DVOM or permanet damage will result to pins, use breakout box" i dont have a breakout box...is this one of those idiot warnings like "Set your parking brake before opening hood" or should i take that seriously?
 
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rusty ol ranger

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Alright did some digging today...

Tested the TPS, I had 1.04 volt at closed, 4.96 at WOT, but my meter shows like .4V even when its not hooked to anything...so im assuming it was pretty close to spec.

Pulled the ECM out of the truck. Other then dried dieelectric grease, all the pins looked good and clean and straight, as did the ECM connector.

I got froggy and even pulled apart the ECM, everything looked good inside of that, no water intrusion, leaking capacitors, no funny shit.

So, according to the manual i got, following flow charts, it said 1 of 4 things can be causing this...(code 18)

1- Open Harness.
2- Grounded harness.
3- Failed TFI (rule that out, its brand new)
4- Failed ECA (thinking that means ECM, but not sure)

Now, after what i described about the computer, is there any chances it could be bad still without any obvious signs?

Also, i know Pin 4 is the one to probe for ohms, but what else? Do i go pin 4 to spout? Pin 4 to the corrosponding wire on the TFI?

This is where im getting lost now.
 

fastpakr

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Can you post the section of the book for code 18?

Sent from my SM-G960U using Tapatalk
 

rusty ol ranger

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Can you post the section of the book for code 18?

Sent from my SM-G960U using Tapatalk

I can tomorrow its out at the old house, in the truck, in the pole barn lol.

Which part you want? I followed it to the section it listed for that code, and those were what was there as probable causes. I did not see anything really for specificly testing those circuits without a break out box.
 

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Usually when it refers to a breakout box you can figure out a way to do the same tests without the dealership tools.
 

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