2nd Gen Non-Engine/Transmission Possible PCM problem...

[KCloward]

Hey guys both me and my dad are new to the forum, and want to say it's a really cool place with a lot of information. I'm 17 and just sold my 2000 Jetta to buy a CTD and low and behold I got one two weeks ago. The truck is a 1995 2500 Auto with a DIY #0 plate and AFC hasn't been touched yet. I've been reading and searching all the posts about bad PCMs and tachs not working due to the fact that this is the problem I am having. My tach hasn't worked since the day I bought the truck but I figured it was just a bad fuse and an easy fix. I've replaced fuse 9 and even the ESS (cranshaft pos. sensor) and neither has helped. I get a charge of 13 instead of the regular 14, not sure if this matters but throwing it out anyways. Could the bad tach possibly cause weird shifting patterns also? After I get done writing this I am going out to clean the connectors on my PCM with some dielectric grease and hopefully it will fix it and get a good connection... if not then I'll update but any other leads as to what the problem may be will be good and appreciated.



Thanks a lot,

Bryce

 

[JFaughn]

Testing before parts , but this means the right tools , for test movement sensors , a scope [ hand held just for auto repair in modern shops ] , in this case I would start at the tach. , to see if a good signal [ tool above ] is getting to tach. , if not then same test right at sensor , to see if its putting out a good signal , get a shop manual [ factory , everything els is a waste of $$$ ] there is a air gape measurement between sensor & crank pulley , sometimes some dirt / iron filings can get in & around the sensor & crank , to give bad signal , then if & when all that looks & test good , a continuity of the wiring to PCM to make sure the wire is OK , the PCM also controls the alternator charging .

 

[DPapworth]

If the engine speed sensor is not working, the PCM cannot tell how fast the engine is running. One consequence is that the tach will not work (because the PCM drives the output to the tach). Another consequence is that the PCM may reduce/eliminate field current to the alternator, and thus your charge voltage is low. Finally, the PCM uses engine speed info, among other things, to decide when to shift the transmission into overdrive and when to lock the torque converter clutch. (The shifts from 1st to 2nd to 3rd on a 1995 will not be affected by the PCM or the ESS).

So your symptoms seem consistent with a lack of engine speed info to the PCM. You can confirm this by pulling codes from the computer with the on-off-on-off-on sequence, and counting flashes of the MIL light. A problem with the ESS should set code 11.

Attempting to get codes is a good diagnostic thing as well, because you can tell that the computer is alive. You should at least get the "55" code.
(Another way to tell is that if your speedometer works, the computer is alive).

 

[KCloward]

Well I cleaned the PCM and was hoping it would fix it but to my dismay it had no effect. Thanks for the info on checking the codes DPapworth, I've watched my friend check his but that was on a 2000 so it showed the actual code. I will check the codes in the morning and tell you guys what I find. Thanks for all of the help.



Bryce

 

[KCloward]

I checked the codes yesterday and it flashes 1 time waited for a few moments then flashed 2 right after each other then waited and flashed five and then waited and flashed five again. Would this be a "12" code and the "55" code?

 

[JFaughn]

That means its cleared / no codes , I forget [ not doing auto repair anymore ] 12 meant system working , 55 end of check , the manual would use different terms , but thats the jist of it .

 

[JFaughn]

I'm not against learning / self taught , but when it comes to computer controlled cars & trucks , if you have a limit on $$$ , find a independent shop with a good reputation , the training & tools required , its just not eifficant for the individual , but with so many shops , not doing a good job [ getting the job done right the 1st time ] its a tough choice .

 

[Dave M]

I see you replaced the Engine Speed Sensor. Did you check the gap? Mine was specified . 049 - . 051 between sensor and damper. I used a brass (no-magnetic) feeler gauage from Napa and set it to . 050 (inches).



Dave

 

[DPapworth]

Code 12 means you disconnected the battery within the last 50 key-on, key-off cycles. No big deal. Code 55 means end-of-codes. It is always output, and indicates (mostly) that the computer works and the guy running the test can count.

A non functioning ESS SHOULD set code 11, in my opinion. I am perplexed why it is not there.

Try the following test:
Deliberately disconnect the ESS, and leave it disconnected
Start the engine.
Let it run for 30 seconds
Shut the endine off
Re-check codes.
Does it get code 11? If yes, then your ESS is good and the problem lies elsewhere.

If not, continue with the following test:
Disconnect the fuel shut-off solenoid connector (at the back of the injector pump)
Crank the engine for about 30 seconds (it should not start)
Shut the key off
Re-check codes
Does it post code 11? If yes, your ESS and PCM are good.

If you can't make it post code 11 with this set of tests,
then I am mistaken about the behavior of code 11.

(The second test is to provide a nice long time for the PCM to think about the lack of an engine speed signal during crank, and give it every chance to post code 11).

It is possible that you have more than one problem, and that none of them relate to the ESS.

1) The tach itself is bad
2) The system voltage is not really low, or is low because of the grid heaters.
(I suggest you make measurements, at 800 and 1500 RPM, with a hand-held voltmeter)
3) The TPS is dirty, resulting in the overdrive and TCC "hunting" in and out at 45MPH

 

[JoeBioDiesel]

Hi KC and welcome to the forums!

I'm not sure you have a problem with your truck, except maybe a broken Tach. Is it an auto or 5 speed? If it's an auto, does it shift into 4th? and does the converter lock up? If the crank sensor was bad, or if the PCM was not operating the alternator would not charge at all, not charge incorrectly, and if it's an auto it won't give you 4th gear or converter lockup. Have someone put a scanner on it. Dodge is nice about reporting desired charge voltage, and actual charge voltage in the datastream. Don't drive yourself nut when you don't have to.

Joe

 

[Flinty]

FYI... my truck didn't tell me didly when the ESS hung up it's spurs. No tach, no charge, no WTS light, no A/C. I double checked with my scan tool, it gave me the all clear. Highly irritating.

 

[KCloward]

The gap on the ESS is correct. I took it to Smith Diesel in Cedar City, Utah and we could not figure out the problem. I do have the "hunting" problem. My truck is an automatic. The owner before me said he had a 4-5K transmission installed and I believe this because it shifts hard and fast and when my TC does lock-up it's very hard same with the OD however when I turn OD off then back on around 45 it's like my truck doesn't catch up with itself... it's very hard to describe without experiencing it. I will try again tomorrow after I take her out and see what she is doing exactly.