Not a problem. I have been working on mine full time making some mounts for a set of custom rails so, take your time!

 

Damn all of this Michigan rain

 

Okay I changed out my t-stat and the coolant temp sensor, when I first started it it did the same thing, the battery has been out for a few days so i expected it to run a little off, after a couple hours of driving the mixture seems to be better when warm( I did use premium gas though) so I will try in the morning and see what it does, I'm not very optimistic though.

 

have you checked vacume lines? sometimes there can be a small crack that's hard to find.

 

If you go back a couple pages I've already checked the vacuum lines, and checked the vac pull for the whole system.

 

What should have been done would have been to clear / flash the PCM 100% after those were changed out. If not, I would connect an OBD III scan tool and monitor what is going on in open loop mode.

The main two components affected by thermal change is the CTS and the O2 sensor and, in your truck, that little sensor (CTS) is the MASTER sensor and everything else is based off it's output.

During Open Loop modes, the PCM receives input signals and responds only according to preset PCM programming. Input from the oxygen (O2S) sensors is not monitored during Open Loop mode.

When you hit the key, the fuel system is activated. Then, the PCM pre-positions the IAC stepper motor. It then determines atmospheric air pressure from the MAP sensor input to determine the fuel amount. The PCM then monitors the ECT sensor input. It now MODIFIES the fuel amount based on it's output voltage. The IAT sensor is monitored and the TPS is monitored.

The ASD relay is energized for 3 seconds and the fuel pump is energized through the fuel pump relay through the PCM and lastly, the O2 sensor heater element is energized via the ASD relay. However, as was stated before, the O2 sensor input is NOT used by the PCM to calibrate the A/F during this mode.

Now we go into Engine Startup Mode / Open Loop Mode. When the starter motor is engaged, the PCM receives input from the the following:

- Bat voltage
- ECT sensor voltage
- CKPS sensor
- IAT sensor
- MAP sensor
- TPS sensor
- Starter motor relay
- CPS

The PCM monitors the CPS for a brief period of time for output. After that, the pump is activated by the PCM through it's relay.

Voltage is then applied to the FIs via the PCM through the ASD relay. The PCM then controls the injector pulse width by turning the ground circuit to each injector on / off.

Last, the PCM determines the proper ignition timing based on the input it receives from the CKPS. Here's another factor that may be the root cause for your issue. It may be that your TIMING is off at this stage and, only until it goes into closed loop mode can it be corrected. If those last changes do not remedy the issue, that's most likely the cause and I will explain later why in the section called: Closed Loop Mode

Now we go into warm up mode which is Open Loop Mode.

During Engine Warm Up / Open Loop Mode, the following three inputs are used:

-Battery voltage
- CKPS
- ECT
- IAT

The next phase is Closed Loop Mode where, the PCM now adjusts the ignition timing by first using the O2S input and adjusts the A/F ratio. It also adjusts the engine idle speed through the IAC. Last thing to happen is the PCM turns the ground path on / off to the coil so it can correct the out of balance condition.

This is where I believe your trouble is rooted. It's in the open loop mode and, most likely a timing issue. That will also explain why when it gets colder out the worse it gets- it runs it richer making the timing worse or happen more frequently.

 

so if you were to check the timing on a cold start immediately after starting the truck (before the o2 sensor gets to temp and controls the a/f ratio) then it would tell you if the timing was off, correct?
and what about the map sensor, how long does the pcm use its signals in open loop. or to rephrase, how big of an impact will the map sensor have on the idle while in open loop mode.

i've always had a bit of a rough idle on start up (open loop) and so does my dads 98 ram.
after starting, the idle will hang around 900 rpms for about 45 seconds to a minute and a half. and it will bobble down to 800 or so, then you can hear the IAC open up and you hear the rush of air into the intake and it comes back up to 900.
i never thought too much of this happening, but whenever dr donut gets his figured out then it will be nice to get mine and my dads fixed as well.

as far as the map goes, i've got another one that i'm going to throw on my truck just to see if it changes anything. when i got a used throttle body it had all three sensors on it. and the truck ran good when it was wrecked.

 

ok well I started the truck this morning and same ****, I'm pretty sure the pcm is clear the battery was out for 4 days and i also touched the connectors and turned the key on like everyone says to so that was done. CM: I'm not really sure what your talking about with the timing, If my timing was off wouldn't it run horrible all the time. Which leads me to believe your talking about something the computer controls versus the acutual timing of the motor. And yes I will deffinatley let you know how to fix this if i ever can sheriff.


I do have an obd2 scanner I plugged it in even though there were no codes and tried scanning(got nothing) cleared it a few times makes no difference. If you are talking about one that will show your sensors readouts well.... I don't have one they're to much money.

 

To answer your first question- no, it would NOT run like junk ALL the time. Re-read that section and become familiar with how it functions. It's not that your timing is OFF ALL the time but, there's two phases of timing listed there.

One is static. If you read the first section on engine warm up, you will see where I mention the PCM uses a set of preset parameters. These are static parameters meaning, they do not change / they are fixed and, part of this set of parameters uses the CKPS for the timing.

Do you understand this so far?

Moving on:

The next stage is closed loop / post warm up. Now, the PCM uses non- fixed parameter based programming to compensate and self-adjust the timing.

Do you understand this? Is this starting to become clearer now?

So, your timing can be off on stage one (OLM) but be fine in stage two (CLM). This is why it may smooth out when it reaches temp.


Which OBD scan tool you have makes a HUGE difference in being able to read, record, and see real time changes in open and closed loop modes, engine temps, rpms etc. Most are just glorified code readers that are useless as **** on a bull.

Now, as you are aware, if the engine runs like junk, the timing is off no matter what the mode of failure is. Almost everything in some way affects the timing of the vehicle. Heat, air flow, injector pulse width, CKPS voltage, O2 sensor input etc all play a part on the timing.

From a simple bad ground wire to low voltage to a vacuum leak to cracked heads affects the timing of the engine thus causing it to run poorly.

Since everything works and functions as a system, all work together. When one part or component is operating out of spec, the end result affects the timing as the timing is controlled by the feed back of those components at the PCM level. It's not a set parameter like it was on old carb setups that used points and condensers. That was based on distributor reference and, it was set. Nothing affected that spark time other than advancing or retarding the dizzy.

EFI systems are entirely different and, this is why you can move the dizzy around (small amount) and it does not change the timing at all. The only thing it does is change the reference of the rotor to the cam. It has zero affect on the timing. All one is doing is delaying the spark or advancing the spark which is really creating an out of sync spark in relationship to the timing set at the PCM.

 

Wow, some good questions. Yes, if the timing is off, and it's running rough, it should show with a timing light. But, if it's just a slight bounce- it may read fine.

The best way to monitor this is with a software scan tool. It's of greater accuracy than using a T-light in my opinion. It shows the CAM to CRANK relationship and at higher resolution. NOTE: it's not uncommon by the way for the PCM to show corruption of this relationship.

When this occurs, a software tool can be used to reset this. It will then clear all the previous data for that parameter only and start fresh while keeping all else in tact. This allows for a more accurate way of trouble-shooting vs. clearing everything out. When you clear all out, now you have no idea of which one was at fault.

As simple as it sounds, this entire system is actually complex and, in my opinion, a b-i-t-c-h to troubleshoot Dodge vehicles.

The MAP sensor is always on 100% as this is what monitors the amount of vacuum. Without it in circuit, the vehicle will not run. In part, it helps control the amount of fuel that is needed under current load.

Does that answer your questions?