Engine/Transmission (1994 - 1998) Whats my problem?

[WillHarris]

I just bought a 95 2500 auto 175,000 miles 4x4. The check engine light comes on sometimes and then just goes off. but when it is on the rpm gauge doesnt work!! Can you help me??

 

[BigPapa]

Sounds like a crankshaft sensor or possibly the PCM. Check all the connections for both and make sure they're clean and not corroded. If everythings OK there I'd suggest finding someone with the same or similar truck and swap some parts to find out which is bad.



Scott

 

[Vaughn MacKenzie]

Will I would make sure the tachometer pickup is the correct distance from the crank damper. There are 2 nuts holding it. . . loosen those, stick a piece of cereal box cardboard in there to work as a feeler gauge, and tighten the nuts. See if that solves your problem. Don't use a regular metal feeler gauge like used for valve lash.

 

[Joe G.]

Just about the only thing that can cause a CEL on a '95 is the alternator.

 

[bdcraig]

Does the alternator quit charging? If is it an auto does the TC unlock when it happens? Mine did all of this and it was the PCM.



Brian

 

[WillHarris]

The alternator works just fine!! But the TC does unlock!! How do I go about getting the pcm checked and where is it?

 

[Joe G.]

On the fire wall behind the air cleaner.

 

[WillHarris]

Ok today i checked the tach gap with the cereal box and it still didnt work!! So Im thinking it might be the PCM!!! Does anybody know how to check it so that I know its bad? and a price range I should expect to get one for and where?

 

[bdcraig]

While everything is working take it and have it scanned by a local repair shop or maybe a autozone. It has to be working. Tried mine with everything acting up and would not scan. I bough one from a dealer because I needed it pronto and didn't have time to look around and it was around $400.



Good luck,

Brian



Scan plug is in engine compartment next to cowl.

 

[Howard Durand]

Before spending money on a new PCM, unplug the large connector at the PCM and hose it down with some electronic cleaner.

The TPS uses 5 volts and the crankshaft position sensor uses 8 volts but they both use the same ground return back to the PCM. You may have an intermittent connection there and cleaning the pins would be a good place to start.

Following that, check all of the grounding points you can find tlhroughout the vehicle.

 

[WillHarris]

Howard: I cleaned the connection today and it seemed to work for about 20 minutes then the CEL came back on and the altenator voltage went down to around 12v. I have a brand new altenator!! Is there a voltage regulator or something in the PCM?? O and the grounds seem to be making good contact!!

 

[Stmpplr]

Just last week had a buddy with the same simptoms. It was bad crank sensor. His mechanic said he had gotten a TSB on the problem.

 

[Howard Durand]

Will, voltage regulation is provided by the PCM. If you have a dealer that you can believe, have them do a diagnostic and possibly a reflash on it. It does look to be a PCM problem but, as noted above, it may be the crank sensor.

 

[WillHarris]

I know this is a dumb ? but can you point me to the right direction to where the crank sensor is?? thanks

 

[Joe G.]

Look just above the vibrations damper on the nose of the crank. The sensor is the gadget with two wires to it.

 

[Howard Durand]

There is no such thing as a dumb question. Sometimes you will get a dumb answer but not from these folks.

When you do find it, follow the wires up to the connector and make sure it is in good condition.

 

[WillHarris]

Thanks, the truck is at the dealer right now and the head mechanic cant find anything wrong with it! but he cant get the CEL to come on!! so more troubleshooting tomorrow!! I love your timer on my 24v truck!!! Its awesome!!!