IAC Operation dodge caravan

Ask our auto mechanics for help to all your Dodge and Chrysler questions.
dw85745
Posts: 8
Joined: Fri Feb 12, 2016 12:34 pm

IAC Operation dodge caravan

Unread post by dw85745 » Fri Feb 12, 2016 12:48 pm

1994 Dodge Caravan 3.3L
Understand IAC is a stepper motor and PCM controls steps in and out. Believe steps range from 0 To 200.
What I don't understand is this:

1) Does the PCM keep a "permanent" IAC count (last step count at shut-down)
OR
2) Does the PCM reset the step count (say back to zero) at Start-Up or Shut Down and retract the Pintel to that base position ?
3) At "Initial" Start (KEY-ON) where should IAC pintel be located?

User avatar
carriedi
Posts: 2445
Joined: Wed Apr 10, 2013 12:42 pm

Re: IAC Operation dodge caravan

Unread post by carriedi » Sat Feb 13, 2016 2:02 pm

the iac position is relative to where the computer wants your idle to be at. The iac is just an opening between the front of the throttle plate and the back of the throttle plate. The pcm want your idle to be at a certain rpm and adjusts the iac so that the engine achieves that rpm. If there are loads on the engine, like from park to drive, the ac turns on, you turn the headlights on, the defroster on, all those things will pull the idle down so the iac will bring the idle back up to keep it at what the computer is programmed to see from manufacturer.

As time goes by you can develop coking on the throttle body that will reduce the amount of air that gets by the throttle plate. The Iac will compensate for that loss of air flow. So the iac counts will go up higher. If your iac count is zero you should still have an idle of 575 t0 875rpm. (minimum airflow) Depending on how cold your engine is and the loads on your engine the actual iac count will vary. Even a very dirty air filter can affect your iac count.

are you having a problem with your vehicle? It would be helpful for me if you would tell me why you are looking for this type of information.

dw85745
Posts: 8
Joined: Fri Feb 12, 2016 12:34 pm

Re: IAC Operation dodge caravan

Unread post by dw85745 » Sun Feb 14, 2016 1:16 pm

Thanks for responding. Pic looks like (around) 1966 charger. Friend had one back then. Had a 1974 myself.

Yes. Been working on an intermittent No-Start / Stalling Issue for almost a year.
See this link: http://forum.chryslerminivan.net/showth ... 0085aad3b7
Last post today (#55).

FWIW: Not much of a part changer. Only have 98600 (deceased father orignal owner) on vehicle but because of age and year long issue redid fuel system
(Tank, Fuel Module, Filter, Regulator, Hoses) about two weeks ago. Didn't solve the intermittent and raised some new questions such as:
What is an acceptable leak down rate?. For example, No leakage at injectors IMO -- but a pressure drop
from spec (48 psi) to 5 psi in a five hour period.

Is this normal (acceptable) and if NOT, what is normal?
Chrysler shop also says two check valves inside module (supply and return). Why on the return side?

User avatar
carriedi
Posts: 2445
Joined: Wed Apr 10, 2013 12:42 pm

Re: IAC Operation dodge caravan

Unread post by carriedi » Sun Feb 14, 2016 4:04 pm

Read your 6 pages. you need to start with the basics. forget everything and keep some equipment in your vehicle so you can check it when it dies and won't restart. You need to check for spark, injector pulse and fuel pressure, when cranking. Find out if one of those things are not working. If you have a code reader or scanner, check your coolant temp and your fuel trims.

If the IAC was the problem you would be able to start the vehicle by opening the throttle by the gas pedal and bypass the iac so I don't think that would be your problem. The Iac could be a problem if it stalls when you come to a stop because of throttle body coking but it should still start up afterward. (do a minimum idle test to check for coking)

It could be possible that you have more than just one problem.

dw85745
Posts: 8
Joined: Fri Feb 12, 2016 12:34 pm

Re: IAC Operation dodge caravan

Unread post by dw85745 » Sun Feb 14, 2016 4:46 pm

start with the basics. forget everything
Agree (Aiir, Fuel, Spark, Compression).
Fuel is easy, can run around again with a Fuel / Pressure guage taped to window..
Spark another issue. Have thought of getting some extra long plug wires and inline spark tester and also taping to window.
Once it dies, no better than where I'm at.
Use a stethoscope and in-line LED for injector pulse.
Scan tool worthless, no codes.

Right NOW, see post #56, few minutes ago, this car is dead in the garage.
If the IAC was the problem you would be able to start the vehicle by opening the throttle by the gas pedal and bypass the iac so I don't think that would be your problem. The Iac could be a problem if it stalls when you come to a stop because of throttle body coking but it should still start up afterward. (do a minimum idle test to check for coking)
Did try you pedal to the metal to try and start. Got a pop -- not sure what.
After than checked TB inlet. Interestingly the "back side" of the flapper and an oily residue.
Cleaned it an TB area I could reach with gas, so clean now.
It could be possible that you have more than just one problem.
Agree

BTW have been using the forum link I gave you to try and keep things in one place for record purposes.

User avatar
carriedi
Posts: 2445
Joined: Wed Apr 10, 2013 12:42 pm

Re: IAC Operation dodge caravan

Unread post by carriedi » Mon Feb 15, 2016 11:15 am

Scanner is not usless. but a code reader would be. A scanner will be able to see the data stream while you are driving. you can see the fuel trims, you could see if the O2 sensor goes lean just before it dies. You can see if the computer raises the injector pulse to try and give it more fuel as it goes lean. You can look at the voltage and see if voltage jumps or drops. There are a lot of things a scanner can tell you if you can graph the data stream and then freeze it when the it acts up to see what changed all of a sudden when it died. You can zoom in and see what happened just before the rpm dropped off.

dw85745
Posts: 8
Joined: Fri Feb 12, 2016 12:34 pm

Re: IAC Operation dodge caravan

Unread post by dw85745 » Mon Feb 15, 2016 9:34 pm

A scanner will work on an OBD-1?

User avatar
carriedi
Posts: 2445
Joined: Wed Apr 10, 2013 12:42 pm

Re: IAC Operation dodge caravan

Unread post by carriedi » Tue Feb 16, 2016 3:33 am

Yes, it will

dw85745
Posts: 8
Joined: Fri Feb 12, 2016 12:34 pm

Re: IAC Operation dodge caravan

Unread post by dw85745 » Fri Feb 19, 2016 11:06 pm

HAPPY DAYS ARE HERE AGAIN !!!!!!!!!!!!!!!
Started over from scratch and found the problem.
The moral of the story is:
1) Just because you get spark, does NOT mean the coil will keep the engine running.
2) It appears the test for Crank / CAM through the coil is accurate even though the coil may be bad (at least in my case).
What I found was the primary was high by ".01" over specifications on the 2/5.
Just enough out of spec to cause intermittent stalling and finally a no-start.

During the course of solving this, I still have a few questions which I never have found an answer to(any takers):
1) What is an acceptable minimum bleed down time for the fuel pump?
2) Will the strainer resting on the bottom of the tank possibley cause early failure (dodge original pumps are elevated slightly off the bottom) ?
3) Best way -- without removal and without a scanner -- to evaluate for flex-plate cracking?

==========================================

I want to THANK everyone who posted for their input. It was greatly appeciated.
BTW, never had to install a Crank or CAM Pos.

User avatar
carriedi
Posts: 2445
Joined: Wed Apr 10, 2013 12:42 pm

Re: IAC Operation dodge caravan

Unread post by carriedi » Fri Feb 19, 2016 11:35 pm

congrats on finding the fix for your vehicle.

the length of time that the fuel pressure stays in the fuel rail is not all that important. Anything more than few minutes would be fine for most vehicles. Most of the cars today that use electric fuel pumps build up fuel pressure fast enough that you don't need residual pressure to start the engine. Some vehicles say an hour some say longer. I have had many vehicles that will bleed down in seconds after the engine is turned off with no bad effects on running or restarts. Where leakdown becomes a problem is where the pressure leak to. If the check valve in the pump section is weak then the pressure will leak back into the tank through the pump. Most American cars has a pump prime when you cycle the key and that will usually bring up the pressure quick enough to start the engine right away. If it get pretty bad then you may have a slightly extended crank time. If the leakdown is through the fuel pressure regulator then you could have a problem with either low fuel pressure or fuel leaking through the diaphragm and put unmetered fuel into the intake. And if the leakdown is from a leaking injector you could have rough idle, High emissions, possibly hydrostatic lock if a cylinder fills with fuel.

the strainer doesn't usually sit on the bottom of the tank. That's where the dirt, scum and water goes. The strainer is just barely off the bottom. If the strainer does touch the bottom then usually there is a lower spot in the tank that is not by the strainer.

checking the flex plate for cracking is different from vehicle to vehicle. If there is a cover you can take off to see the flex plate, that would be the easiest. Some you could pull the starter and look through the hole the starter was in. Other vehicles you may have to remove the trans to see what's happening. But, you don't usually look for a cracked flex plate until you have a problem where you suspect that your flex plate could be the problem. It's not something you inspect for maintenance or something.

are you having a problem that you think might be from your flex plate?

dw85745
Posts: 8
Joined: Fri Feb 12, 2016 12:34 pm

Re: IAC Operation dodge caravan

Unread post by dw85745 » Sat Feb 20, 2016 8:44 am

Thanks for the excellent response. Re:
are you having a problem that you think might be from your flex plate?
No. Just question for future reference.
Supposedly the Caravan (not sure my year) has had some flexplate issues.
A number of post re: this issue state only way to tell is transaxle removal (PITA).
The starter can be removed but only a small portion of flexplate is visible.
Whether one can get a borescope up to take a look see ???
The strainer is just barely off the bottom
Original OEM fuel pump had a rubber pad on the bottom of the pump module.
The pad for the most part was gone -- either from rubbing bottom of tank or gas eatng it.
When the new fuel pump (module) was installed, examined its position through the fill tube hole.
Hard to tell , but looked like strainer was sitting on bottom (or very close to it).
Since strainer was dry, when wet, may be different story.
New and old tanks do not have wells -- this vehicle.
Don't know what if anything I could do other than buy dealer pump.

  • Similar Topics
    Replies
    Views
    Last post