Your truck has a lot of the same symptoms my 89 Dakota has. I have an entry under runs terrible in cold weather. Yesterday was in the low 60's and the truck ran like crap. It also seems to backfire through the throttle body. I have problems with the truck having no power on takeoff and then the truck would surge then bog down again. I get no codes on the computer. Today however was in the mid to upper 70's and the truck ran great. I think I have a sensor that is temperature sensitive. This is driving me batty, You have done a lot more to your truck than I have, but I thought I would let you know I have a similar problem. I wish you luck because I know I am getting frustrated with this. Not sure if yours is a sensor problem like I think mine is. That would be the easiest fix. Read my entries runs terrible in cold weather, maybe you will see some similarities.

 

thanks for the reply.
i have been following your posts as well. Your issue seems odd as well since the problem is when cold, while this seems to always show after the engine is run on highway for a bit.

 

when you checked your harness over did you check for spread pins? i would also take a spin with my vac gauge on it personally so i can see it as it breaks. what kind of dis pickup and crank sensor did you use? i've seen some low qaulity ones that pick up the signal intermittantly. the codes clear in 10 drive cycles. have tried your other pcm on it since you got it home? i wouldn't suspect it though. the belly pan leaks on these probbly wouldn't cause this issue. do you see blue smoke on accel? if you haven't had your dis loose yet then don't. if it was good before (timing) it's good now. that and to set it back right you have to use the drblll to set the cam synch signall. you don't have to pull it to do the intake either. also have you pulled your dust cover off at the bell houseing and checked your flywheel? that could cause this issue aswell. i suspect a short somewhere where the 5 volt ref is shorting to groung or 12v+.

 

Thanks for the input 9652.

Good thought., i have not checked for spread pins, but i will check all connectors.

The Vac was decent when we tested, but it was running good then. i want to catch it when running crappy and recheck. i was thinking of duct taping the gauge to the windshield and extending the hose through to the engine so we can watch while we drive.
( i thought about doing the same with the fuel pressure, but got nervous thinking about a hose coming off and spewing fuel all over) could become a bad day then.

the cam and crank sensors are factory.
which have you seen as failing most frequently?

i have another PCM that was off a runner and have validated it's operation prior to this round of issues. Same issues regardless of PCM.

no reports of blue smoke on this. i take it that is a sign of the plenum plate leak?

i have only had witness reports of black smoke which lead me to think mixture control or restricted air flow. As you read, we opened the exhaust and still got the same issue.
Wasn't planning on moving the dist. Thanks for the heads up.

had not checked the crank pos'n wheel. Thats another good check.

i have opened the harness right to the sensor connectors to check for bum splices and pinch points etc, but i didn't pull the pins from each connector. i'll probly do that in case nothing else shows up.

 

checked the crank position pulse wheel today. can't find any flex or movement in the wheel. All looks solid. no debris stuck in the holes, no signs of contact with anything. So that is one possibility off the list.

checked the Vac today while driving. (we extended the gauge hose into the cab). when it was running good, the vac was solid, but when it misfired the vac went near to zero and all over the map.
Rechecked the TPS. 0.65V at idle, and continuous signal up to 3.7V at WOT.
Rechecked the coolant temp sensor against the charts in the FSM, and it was right in the window.
Going to recheck the sensors after the engine cools overnite, and recheck the vac during startup.

 

i wouldn't actually pull the pins out of the connectors just use some sort of pin to gauge if it's spread. i use a set of back probing pins that are 0.048 inches thick. all you want to do is see that you have comparable resistance in the connector pins when you pull it out. so with your vac going to almost zero and having black smoke i wouldn't think air restriction outside the intake (would still have vac) i would wonder what it's doing to the timeing and mixture. as for the fuel gauge i do that regularly at work to verify running pressure. i just tape it to the windshield. as long as your hoses and fittings aren't qeustionable. if you are still concerned just take an extinguisher with you. maybe leave the hood off :P the vac dropping and fluctuating like that is odd though.
and blue smoke is a sign of oil consumption. i had it pretty bad when my intake blew. had some in the morn for a day after to. just had to burn it out. been about a thousand miles since and all is well so far.

 

so today we did a few rechecks.
Since it cooled overnite, we checked the CTS right at the sensor (~14.5k) and then rechecked through the harness at the PCM connector (within 100 ohms)

So then we decided to check the plugs and verify gap (~0.35") all good. The secondary wires are all new.
Then we rechecked the cap/rotor for carbon tracking and the cam sensor. And noted a bit of oil in the dist body. Since i had wiped this clean a month ago, finding oil seemed odd.
When rechecking the rotor shaft i found that in one direction the rotor shaft had about 1/8" movement side to side. The thinking here is that the rotor shaft bushing is worn and allows rotor to change position a tiny bit in the cap which could lead to cross firing???. Ever seen anything like this?
We went to pickapart this pm and pulled a dist base that was dry and had shaft endplay but no side to side. So now we get to swap the dist body without the scan tool to check the injector timing.

We put it together and started to check the MAP sensor against the FSM values, but the truck wouldn't idle long enough to check the voltage at idle. We then started rechecking the IAC circuit, and went shopping for a replacement valve.

 

Sounds like an EGR valve issue. Mine was bad tested good, took it to Mr. Redneck for backup tested good but all symptons were EGR. Replaced valve, Presto problem went away.

 

So latest update in this saga, is>>> it runs.

As mentioned previously we found some movment in the distributor shaft during rechecks of the various sensors. there is the usual gear lash in the drive gear, but this is side to side movement of the shaft in one axis.

we pulled the distributor and installed a used part that was tight. We pulled all the plugs and followed the procedure in the FSM to rotate to TDC and marked the old distributor.
Then followed the procedure in the Dodge tips to set the correct distributor body position using a DVM, since we don't have access to the DRB scan tool. We were really careful in doing this, and found the procedure put the ideal location for the cam sensor to switch was about 1/32 rotation advanced from where the original distributor body was located. However the engine wasn't happy and would not quite start with that trigger point, so we backed the settings off a tiny bit and after a couple tries found a point where the cam trigger and the crank position were happy and it runs.
we think that the different distributor position is likely due to drive gear wear, plus assembly tolerances from one distributor body to the other shifting the trigger point for the cam sensor, and possibly the original setpoint was not perfect either.



Question for those with more knowledge of the PCM routines, does anyone know if the PCM will "learn" the ignition / injector timing and optimize itself over time? OR is the procedure using the DRB scan tool the only way to properly set this point and it will never change?

(to my old ears the engine could use a touch more advance, but it does rev out to redline during WOT acceleration runs, where it previously would break up by 3800rpm.

At present, startability is good. (maybe two turns and it fires and idles)

Cold start is good, we are seeing 45 - 50F at nite at present.

i will post updates after we get a week or two of run time to advise if anything changes.

Thanks for all the help and ideas from the various members.

 

the pcm uses the pickup in the dist to tell where the cam is and the crank to identify cyl 1. it compares the two and come up with a varience (messured in degrees of rotation) and it needs to be within +- 5 to be right but myne was at 15 advanced (had to do it at home then set it at work) and ran ok till redline when it set a code for loss of cmp. you can play with it a bit and maybe get close. if it's running then you should be in the neghborhood of 15 or closer. it won't learn it over time though. i don't know why they didn't make it able to but they didn't. as long as your close though you should be fine. and setting the cam synch when you have it figured out most dealers would do for about $100. and the reason it hurt so bad may not have only been the firing issues (did you get a new cap btw?) but also difficulty in seeing the gate on the bottom of the dis top (just under the botton i know there is a name but i can't remember it. this would explain why it appeared you had a timing issue.


edit
forgot to mention pull your connectors at the ect and pcm check the individual ckt resistance. you should only have 5 ohms or less risitance in the harness. that may be a part of your issues.