What's IAC?

 

Idle Air Control

 

Ok, I went out this morning and it started just fine. I pulled the codes and got a crank position sensor and PCM internal fault.

I reset the codes and PCM using he key method and -bat disconnect.

With the new PCM the internal error came back and engine runs fine (at idle).

With the old PCM there is no code at all, even with shutting down the engine and starting several times.

I called the PCM rebuilders and they said it was common for this fault to show after something has tripped it and they'll send me a new one. They said that its common for new pcm's to be tripped like this with a crank pos fault.

So I'm going to replace the crank pos sensor again to make sure I didn't get a bad part.

What I don't understand is why the injectors pulse after the engine dies. I'm sure I haven't gotten the engine hot enough just yet to trip the crank pos sensor error, but its going to happen.

 

I suggested this in your other thread, but I'll go ahead and say it again. You really, really need to track down where that burning smell was coming from. It sounds to me like it's probably burned through the insulation and the wire is shorting out.

When you have a wire making connection to things that it's not supposed to be connected to you'll get all kinds of different, bizarre behavior. Including symptoms and codes that point you in the wrong direction.

Until you track that down and fix it, you're basically just beating your head against a wall if you keep trying to fix other things.

 

Well I've taken that seriously after all. I thought I had mentioned it but not sure- it seems as though the burning smell may not be related at all. The heads were taken off and valves gone through. After all the looking that I've done and not finding any wires burnt, I'm thinking it may be the new gaskets and rtv I've been smelling.

Today I learned how to reset the pcm and pull codes with the key. I've also replaced the crank sensor with another new one just in case.

When the engine gets nice and arm after driving she starts the stuttering and dying all over. The longer I let it sit to cool the longer she'll run the next time.

The only codes I'm getting now are 320 "no crank ref signal at pcm" and 1299 "iac closed" but the last one only shows when the engine stumbles a lot before shut down. I think its residual to the way the engine dies and not the cause.

Here's what's stumping me- why do I get a 320 code only after the engine is hot?

 

I'd start ripping apart those wiring harnesses and visually inspect all the wires inside and replace any that are burnt for sure. When the engine warms up the heat expands something or some sensor shoots a voltage back to the PCM which may be shorting out other things too if there's crossed wires.

I'd start with the crank sensor harness and then just move to the PCM connectors. If you have time to pull heads and check the vavles, then cutting open wiring harnesses will be no problem, just eletrical tape them back up when you're done.

 

I didn't do the heads. I bought the d from a bank that repo'd it and when they took it to get serviced shop told them the valves needed work.

I'm thinking they may have pinched something. Afterall, the crank sensor runs to the main harness behind the engine at the firewall and thn separates to the sensor with heat sleeving. I'm going to have a lot of trouble getting in there. I'd just test from the pcm connectors to the sensor connector but it may not be indicative since the possible short is intermittent with heat. I may just break down and take it to a shop and have them go through the whole harness.

 

Would anyone here be so kind as to look at their 2002 4wd 4.7 diagram and see if the crank sensor is tied to the IAC?

I've gotten the IAC code a couple of times with my PCM problem (I've got another thread on it)

I also need to know that if the crank sensor isn't tied to the IAC do all 3 wires from the sensor go directly to the PCM? What are thé crank sensor wire colors (I can't make them out at the bottom) I'm going to run an ohm and short test and have to know if another system will interfere.

Thanks guys.

 

You could do us a favor and keep as much of this in one thread as possible. You are really hurting yourself by making multiple threads as you get answers from people who have read half of your problem.

 

Well I'm sorry about that. All I have is my phone here in the mountains. I can't navigate except through the links I get from email notifications. On those threads with more than one page I have to try quite a few times to get to the second page, and the mobile version isn't showing me my own threads to select and read. I'd kill for a laptop and air card right now. I've found the links from the stickies for diagram downloads but I can't do that either.