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1994 3.9L V6 Dakota- I’m thinking the PCM is not right and I am wondering if PCM upgrades on these trucks are worth it or should I just go for a replacement OEM PCM? Here’s the story.
I posted complaining about the low RM’s and poor performance after a lot of work. I did the Hughes Engines Intake Plenum and the timing chain with TSB tensioner. I added all new sensors to the intake and TB. All the tune up stuff & coil, oil sensor, EGR, and had the tranny adjusted.
It has improved responsiveness over time but its not yet right. I increased mileage from 170 miles on the 22 gal tank when I bought it to 365 miles last full tank which I ran dry because the fuel gauge don’t work yet. (its got a new pump)
I took it on a 200 mile trip last week and that seems to have helped it some but the RPM’s are still way low and responsiveness is not yet reliable. I always have to wonder if its gonna decide to delay when I hit it and that makes for frustrating driving as I have to stay behind idiots I would sooner pass.
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For the low idle the IAC would be suspect. Have you cleaned the
passages? For the performance issue Can you rev the motor in park
and does it feel strong or break up?The IAC and all sensors in the intake or TB are new. It sounds great and feels strong its just that it never wants to rev up and make power when I’m driving. Even when it responds quick and takes off the RPM’s are low. ??? One time I punched it and it went up over 4K for a moment is but usually it never goes much above 2500.
I’d suggest your torque converter clutch is locked. The torque converter clutch has to unlock for the engine to rev and make power. It should do this when you punch the accelerator.
[quote=”barneyb” post=111475]I’d suggest your torque converter clutch is locked. The torque converter clutch has to unlock for the engine to rev and make power. It should do this when you punch the accelerator.[/quote]
How would I diagnose that?
I looked at the tc video and read the diagnosing transmission. It seems like the gears are fine it is probably some part in the tranny that is the problem with the tranny. It tends to jump from a start when it is warm especially on an uphill start.
Here is video made by a gentleman who has installed a manual switch for the torque converter clutch. What’s nice is you get to see what happens to rpm when he uses the switch.
That is interesting. Mine idles at 2-400rpms which is low but it seems to be fine. Right after I bought it it was way high and I discovered someoene had manually adjusted it so I turned it down by ear which had it at about 700 and the PCM seems to have taken it down from there starting the next time I drove it. When I did all the work and tanked the Intake and TB I adjusted the screw so that the butterfly was closed as previously it was a bit open at the TV cable fully closed position. It has idled that low with no problems for months. This video may be showing me a reason why.
His problem seems worse than mine but it did almost the same thing which is pretty much not change much no matter what input I was giving the pedal. If it is not clear mine has improved since I did the work I mentioned. It is still not right and I’d like to get it right so I can spread the word on how to make these things work right in stock condition. Well close to stock I did add the new intake plenum, Dodge’s TSB was to just put in a new gasket which is a setup for it to start happening again as it does not remove the main problem, dissimilar metal expansion rates. One thing is good mine went from 9 MPG’s or 170 miles on 22gals to 16 mpg’s or 365 miles on 22gals in town.EDIT
I am not going to leave it totally stock since I discovered Dodge went from a 3″ exhaust on the 3.9L in 93 to 1 1/2″ in 94. I think I will eventually go up to the 3″ exhaust manifold and on out as they changed the port size but not the bolt pattern.A plugged exhaust is another possibility. But I wanted to show you how a vehicle acts when the torque converter clutch doesn’t unlock when it should. I hope this was some help.
Thanks Barney. Wgat would it cost to change a TC? I wonder how hard changing a TC is? Then there is how do I find a good quality one? I saw a page on one search that showed quite a few for the same 42RH transmission that were all different according to how they labeled them. I imagine that has something to do with the fins on the stator Eric mentions in his video.
If the problem is the TC locking the TC is working. The problem would lie in the controls in the transmission. Since transmissions are complicated I think it would be worth it to at least get a diagnosis from a mechanic who knows transmissions. Then you’d be a position to make better decisions.
Well that’s the thing. I am doing this work because the local market is full of pirates in all fields. The aamco I took it into for a band adjustment and TV cable adjustment tried to get me to go for a new TC based on the sediment in the pan. They had it on a two part lift for ten minutes with the front end down low to get the sediment to run forward. I should have checked to make sure they dumped it instead of leaving it in the pan. There was nothing about any other issue but it felt like an “oh we found this now” kind of situation. BTW there was no change in function the TV cable was not touched and I suspect they never adjusted the bands.
Another example; That other rig I’m on here about when I firsat bought it I took it to a shop that was supposed to be so great to look over the heater. They removed it and took out a mouse nest (It had been parked for years) then put it back in and called me to come get it. After I paid they informed me of holes in the housing that made it necessary to change the housing to have proper air flow. I asked if they taped it and they acted as if I asked if they had put a bomb in the car. SO I have already paid for removal and installation and they wanted me to pay again to install the new core instead of calling me when they had it out to tell me! That’s the kind of people I live among.
By the sound of it I think you may be dealing with a transmission issue. I wouldn’t rule out a restricted exhaust either, that’s easy enough to check for though.
You really shouldn’t just go in and start making transmission adjustments hoping to fix something. I’m surprised that the transmission shop went in that direction.
It’s not a good idea to wire up torque converter clutches in that way. There’s a reason they’re automatic. Putting band aids on problems like that really doesn’t fix anything.
More information on solving performance issues and transmission issues can be found here.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
http://www.ericthecarguy.com/faq/solving-transmission-problems
Keep us posted on your progress.
Did the vacuum test with that mighty vac thing guys use for the brake bleeding. It had 10 inches and that seemed low so I clamped both ends of the hose and it went up to 15. When it revved up it dropped for a second to 5ish then went up to 18 and stayed there the first time. The second time it went up to 18 then up to 20 the back to 18. I was revving by hand inside the engine bay so I may have caused that. Except for seeming low it did what your YT video said it should for a clear exhaust.
Any other ideas? I already looked at the solving transmission issues page and TC video. I am unsure what else I might look at.
ThanksI did the power brake test as it is recommended by ETCG & the 95 Dakota FSM I have downloaded from another site. Apparently it is almost identical to the 94 anyway its the same 42RH transmission. This is in the preliminary diagnosis instructions if vehicle is drivable.
“(4) Perform stall test if complaint is based on sluggish
acceleration or if abnormal throttle opening is
needed to maintain normal speeds with a properly
tuned engine.”Result: I used reverse as its in the driveway (blocked both wheels and the E brake set). It went up to 1600 then started to drop off it went down below 1400 when I stopped. I only did it for about 5 seconds. The motor seemed ok.
I’m going to keep reading it but if anyone knows what this means a post would be appreciated.
It’s always implied but Thank You for any help.EDIT
Just read this in the FSM (I did not do it warmed up I think I’ll go for a drive and do this warm.
“STALL TEST PROCEDURE
(1) Connect tachometer to engine. Position tachometer
so it can be viewed from driver seat. (this veh comes with in dash tach)
(2) Check transmission fluid level. Add fluid if necessary.
(3) Drive vehicle to bring transmission fluid up to
normal operating temperature. Vehicle can be driven
on road, or on chassis dyno if shop is so equipped.
(4) Block front wheels.
(5) Fully apply service and parking brakes.
(6) Open throttle completely and record maximum
engine rpm registered on tachometer. It takes 4-10
seconds to reach max rpm. However, once max
rpm has been achieved, do not hold wide open
throttle for more than 4-5 seconds.
CAUTION: Stalling the converter causes a rapid increase
in fluid temperature. To avoid fluid overheating,
hold the engine at maximum rpm for no more
than 5 seconds. In addition, if engine exceeds 2100
rpm during the test, release the accelerator pedal
immediately; transmission clutch slippage is occurring.
(7) Stall speeds should be in 1750-2150 rpm range.
(8) If a second stall test is required, cool fluid
down before proceeding. Shift into Neutral and run
engine at 1000 rpm for 20-30 seconds to cool fluid.
(9) Refer to Stall Test Analysis”If it turns out the same there is this reading which actually describes the issue. Be back in a bit to let you know.
STALL SPEED TOO LOW
“Low stall speeds with a properly tuned engine indicate
a torque converter overrunning clutch problem.
The condition should be confirmed by road
testing prior to converter replacement.
The converter overrunning clutch is slipping when:
Stall speeds are 250 to 350 rpm below specified minimum
and the vehicle operates properly at highway
speeds but has poor low speed acceleration.” The stall speed should be 1750 to 2150Warmed it up and did the test.
This time it went up to 1400 then dropped to 600 and the tranny was not happy.
I’m thinking the suggestion by barneyb was dead on.
Thank YouIs there anything else I should do?
EDIT
The FSM says to replace the TC if it fails the stall test so that is what I will do.I’ve been thrown for a loop sort of. I contacted a recommended transmission guy. I asked if he would do the torque converter. he started asking me questions mainly stating that if I did not test the pressure that FSM Stall Test according to the manual is not reliable enough to diagnose the torque converter. by the time he was done he was talking about a rebuild with upgrades and $1700! I get that his work would be good but that’s is way out of line.
The thing he mentioned was the governor could be locking up the converter and it may be just fine. I cannot find any way to test that governor does anyone have any ideas to diagnose a bad governor in a 42RH transmission?
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