97 Dalota idling problem (stalls)

SLADE25

MEMBER
1997 DODGE DAKOTA
6 CYL
2WD
AUTOMATIC
130 MILES

97 Dakota 3.9L 2wd auto

rough idling issue: I cleaned the IAC carefully and replaced the temp sensor, wires and ignition coil. When truck is cold it stalls immediately when put into Drive unless the accelerator is depressed. When warmed up (90-100), it will stall out eventually while idling in Drive. Never stalls out in Neutral or Park. If I shift to Reverse it will sometimes stall out as well.

issue #2 : no comms with ECM, cannot run scanner to get any codes. Today I removed all 3 connectors at the ECM, checked continuity and voltages (all good) with connector port inside truck, replaced the connectors and the check engine light disappeared. That might be a good sign, however still cannot run a scan.

Drove 25 miles afterwards, check engine light did not return, vehicle performing a little better but will still stall out in Drive while idling.

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Saturday, January 29th, 2011 AT 2:11 AM

12 Replies

CARADIODOC

MECHANIC
33,916 POSTS

When the battery is disconnected or run dead, or in your case, the Engine Computer is disconnected, it loses its memory. It must relearn "minimum throttle" before it will know when it must be in charge of idle speed. Usually you also won't get the nice idle flare-up at engine start-up.

To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals.

Caradiodoc

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Saturday, January 29th, 2011 AT 6:56 AM

SLADE25

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Strangely enough, my scan is now working/talking to the ECM. I did 2 or 3 scans and I have no codes.

When I run the I/M checks, I am getting:
Misfire - Ready
Fuel - Ready
CCM - Ready
EGR - Ready
O2S - Ready
CAT - NOT Ready
H2OS - NOT Ready
2AIR - n/a
A/C - n/a

can anyone advise on the 2 Not Ready findings?

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Saturday, January 29th, 2011 AT 5:27 PM

CARADIODOC

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That just means the conditions haven't been met to run the self tests. Sorry I can't tell you what those conditions are but they will involve such things as driving at a steady speed for a certain number of miles without totally letting off the gas or touching the brake, possibly a brief burst of wide-open-throttle, or a specific period of coasting.

In some emissions testing areas, all that is required to pass is all those self tests must be passed. In some places, the vehicle can still pass if the tests are run manually like they do on older vehicles.

Caradiodoc

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Saturday, January 29th, 2011 AT 10:07 PM

SLADE25

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I am experiencing increasingly worse stalling out problems with my 1997 Dakota Sport 3.9L 2wd, automatic.

Recently I got my diagnostic scanning capability back and I now have the following codes PO138, PO141, PO783 (the O2 faults seem to come and go)

I think I could also possibly have a vacuum related problem. Can't visually locate a problem but engine sounds "funny" when cold, almost like I can hear it trying to suck for air.

Fault: especially when cold, engine will stall out in Drive. Even after it's warmed up, if traffic slows to a crawl or I stop at a light, the truck will stall out unless I keep the rpm's up. Lately i've had to put the transmission into neutral in order to stop it from stalling out.

What had I done maintenance wise lately:
replaced plugs, wires, ignition coil, temp sensor. Removed and cleaned IAC. Cleaned throttle body and used recommended liquid cleaners (fuel injectors were cleaned last year). Had exhaust work done a few months back --> duel leads of cross over pipe into the engine had to be re-clamped. No other apparent exhaust trouble

I am wondering about three things now:
1. EGR valve related issue? Btw, does anyone know for certain if the 97 3.9L engines use an EGR?
2. Transmission problem - do I have a potential torque converter problem? (Code indicates a 3/4 shift malfunction)
3. Finally, how would I know if my catalytic converter is plugged or no good?

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Thursday, February 10th, 2011 AT 11:34 PM

CARADIODOC

MECHANIC
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If you have an EGR valve it will be way at the back of the engine to the right side. You can unbolt it and reinstall it with a thin piece of sheet metal to block the ports. If the stalling problem clears up, check for the valve stuck open due to carbon buildup.

The transmission code is not related to a stalling problem.

A plugged catalytic converter will cause the engine to idle especially smoothly and you'll hear a steady hiss from the tail pipe instead of the normal "putt-putt". You'll also have a hard time reaching highway speed.

Caradiodoc

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Friday, February 11th, 2011 AT 2:19 AM

SLADE25

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Before I went to the transmission shop today, I checked and I had codes PO783 and PO141 come up on my cheapo obd ii. When I got there, the tech put his $10k machine on it and was coming up with nothing on the transmission diagnostic side. On the Engine side of the diagnostic he came up with both the PO783 & PO141. Kind of surprising but I`m hoping that means the tranny side is okay.

Now here`s where it got very weird. We did a test drive and he left his $10k scanner hooked up as we drove around. The truck started to perform really badly (way worse than when I drove over I might add) stalling out and seemingly slipping gear and performing like crap. Then something i`d never seen before started happening. The Air bag light came on and an audible alarm started to beep (same sound as when the gas guage is low). And then the RPM and Speedometer guage started to fluctuate and proceed to go to zero. This was all while we were test driving. When we got to the parking to the told me he thinks I need a new ECM before I do anything else. He did another scan and was getting communication error. I thought oh noooo

We popped the hood and he checked the trans fluid, it looked and smelled okay he said. I pushed the 3 connectors from the bus harnass onto the PCM and put my cheapo obd ii on the scanner port and it read the damn codes ! PO783 and PO141 again. I went and got him again, he got his machine out and he got the same. And nothing showing on the transmission side. He still thinks I have a PCM related issue. Intermittent or whatever (worst kind actually).

So I drive it home and the damn truck performs like a dream all the way. No stall outs, smooth shifting of the transmission, no coughs, burps, etc.
Talk about a system that is all over the place. I don`t know what to think now, but I`m sure it will act up again tomorrow morning after sitting all night.

Anyone have any suggestions on this conundrum?

Also, I noticed this the other day - my odometer milegae (178,000KM) disappeared for a moment and the number 12 came up. It did this a few times, swapping back and forth. I found that weird. Anyway, might be worth a mention. Wondering if I have an intermittent wiring or harnass type fault with respect to the bus?

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Friday, February 18th, 2011 AT 12:42 AM

CARADIODOC

MECHANIC
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There's too many things going on here to be related to the Engine Computer. Once you mentioned the air bag light, that means there's much more involved. What I would rather have you do the next time this acts up is to try the power windows and wipers. If either of them makes the problem worse or those items run real slow, there might be a poor connection related to the ignition switch. In the meantime, you might wrap a wire around a fuse terminal and connect it to a voltmeter so you can monitor the voltage on that line when the problem acts up. Use fuse 9, 11, 17, or 19. There are three different circuits coming off the ignition switch. Start with this one for now. If the windows or wipers are affected we'll have to check the other circuits.

Caradiodoc

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Friday, February 18th, 2011 AT 1:43 AM

SLADE25

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Here's where I am at today.

The truck has settled out and improved since the having the Transmission techs use their Solus Pro scanner the other day (something was way wrong with them or their scanner). In fact during the drive home, oddly enough it worked quite well. Different story the next morning :-(

In this order it's throwing codes PO141, PO138, PO783

Main problem is that I am having serious stalling out/poor idling in Drive issues. I know I need to take care of the codes first and perhaps that will help my overall stalling issue. Would the downstream O2 sensor create this much havoc? Also experiencing poor gas mileage performance. I have replaced plugs, wires, ignition coil, temp sensor, checked all fuses and relays, cleaned IAC and TB.

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Saturday, February 19th, 2011 AT 7:06 PM

CARADIODOC

MECHANIC
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Not the sensor itself, but the wiring to it. The front O2 sensors switch rapidly between "rich" and "lean" when the fuel system is working properly. All the rear sensors do is watch what has happened to the exhaust gas after it has left the catalytic converters. Normally they will switch between rich and lean too but very slowly. As the efficiency of the converter goes down, no change in the composition of the exhaust gas takes place so the rear sensor begins switching at a faster rate. When its switching rate nears that of the front sensor, the computer knows the converter isn't doing anything and it sets the appropriate fault code. The engine will still run fine but tail pipe emissions will increase.

The O2 sensors don't detect unburned oxygen until they reach about 600 degrees. That may not happen during prolonged idling and it won't happen for the first few miles of a drive cycle. To get them up to operating temperature faster they have heaters built in. Your first two codes are related to that heater. The sensor's output voltage is typically between 0.2 and 0.8 volts. Code 138 says the sensor voltage is much too high. Since the sensor can't develop that much voltage, the wire has to be shorted to some other wire that DOES have that much voltage. That would be the heater wire. Here's where it gets interesting. The voltage for the O2 sensor heaters comes from the automatic shutdown (ASD) relay. That is the same relay that turns on the ignition coil, injectors, and alternator field. If a shorted wire is drawing the voltage down on that line, the coil and injectors won't fire properly. I would start by looking at the wiring near the rear O2 sensor. If no problem is found, try driving with that sensor unplugged. It will set codes but the engine should run fine.

Caradiodoc

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Saturday, February 19th, 2011 AT 7:47 PM

SLADE25

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Discovered a bad wire on the O2 sensor, replaced that and gone are the 138 & 141 fault. Truck seems to drive soother and the transmissions cycles thru gears better (as best I can tell).

However, after taking it on the highway for the ECM to relearn, it threw back the following to me:
PO740 P
PO783 P

I guess we're into the damn transmission now. Any ideas, as it seems the tranny is working fairly good at the moment. I did have a filter change/flush approx 20 months ago.

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Sunday, February 20th, 2011 AT 11:35 PM

CARADIODOC

MECHANIC
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I'm not really a transmission expert but the first code states the computer didn't see engine speed drop about 200 rpm when the torque converter was commanded to lock up. I did a huge pile of work on a '97 Dakota that Chrysler donated to my school so I'm pretty familiar with it. I'm pretty sure the transmission is not computer-controlled like the front-wheel-drive vehicles, but the torque converter IS controlled by the Engine Computer.

What you can watch, if you have a tach, is once the engine is warmed up and you're driving over 45 mph in third gear or overdrive, hold the gas pedal perfectly steady while maintaining a steady speed, then lightly tap the brake pedal. The torque converter will unlock, then relock about two or three seconds later. You should see engine speed go up 200 rpm then drop back down. If that doesn't happen you can try pulling the brake pedal up with your foot. If that makes the torque converter lock up, the switch may be out of adjustment.

If you do not see any rpm change you will probably also notice that when you try to slowly speed up, say from 50 to 55 mph, the engine speed will go up as soon as you move the gas pedal. If the converter is locking up properly, engine speed will not increase until road speed increases, similar to driving a vehicle with a manual transmission and clutch.

The second code relates to engine speed not going down when it shifts into fourth gear. You should feel three nice solid upshifts plus, the locking torque converter will feel like a shift too. There will be a way to lock out the overdrive, either with the shift lever, a button on the dash, or a button on the end of the shift lever. If you press that you should feel the shift to third gear. Press the button again and you will feel the shift to overdrive. If you can feel the transmission going into every gear, I don't have an answer on why it is setting those codes. It could be detecting slippage in one of the clutch packs but you should feel that too.

Caradiodoc

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Monday, February 21st, 2011 AT 8:55 AM

SLADE25

MEMBER
18 POSTS

Hello

After some extensive troubleshotting with pro help, i'm advised to get another ECM and go from there. My question is this:
I have a part # 56040378AE ECM. With these being rather expensive i've found that I can get another, but it's a 56040378AA. Will this work for my purposes?
Does it need to be flashed?

Steve

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Tuesday, February 22nd, 2011 AT 6:59 PM