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[Joe G.]

Joe G: Haven't replaced the sensor yet. Sensor and wires appear to be in good shape. Nothing externally has damaged them anyway. If it's not getting the 8 volts, how would it work?



I made a sharp probe so I can check the pin outs for sensor grounds and the 8 volts for the crank and transmission speed sensors. That's tomorrows project.



If the PCM is not putting out the 8 volts, wouldn't that mean it's bad?

You can look at the sensor all day and not tell if it is working or not. If it has an internal problem like a broken circuit or short it may it may look fine and not work. The only way to tell without a scope is to replace it with one you know is working. If you don't have someone you can borrow one from you have to buy one.

 

[LandShark]

Joe G: Shouldn't the check engine light (MIL) come on when the key is turned to the on position (prior to engine start)? Also shouldn't I get 8v going to the crank sensor with the key on? I can't get any replacement parts til at least Monday. I also live out in the sticks Would you mind putting a voltmeter on the plug for the crank sensor and seeing if you get 8v from the PCM with the key on?

Missouri Mule: My truck is a 95. 5 volts is for the TPS. 8 volts for engine speed sensor (crankshaft) and transmission speed sensor. Alternator was intermittently going from dead to full power but was giving no charge prior to adding the regulator.

 

[Joe G.]

I checked mine. The CEL comes on during the bulb test. Other inicator lights do as well. I have 8. 3 or 8. 4 volts at pin 1 (middle pin) of connector to the engine speed sensor. I hate to say it, but you may have a bad PCM. You may want to check pin 7 of the PCM to make sure that it is reading the same thing as pin 1 on the engine speed sensor connector.

 

[LandShark]

OK... I think we're getting close. Checked the middle pin with engine running and I get about 1v; same at Pin 7 of PCM (should be 8v). Pin 6 on PCM which should be 5v was only 0. 5v. Pin 3 which should be 'battery' for the PCM was 10. 4 with key on, and about 0. 2 with engine running. Not sure what to make of that except it's bad. I'm now going through the manual to track down where the 'battery' to Pin 3 of PCM comes from.

Joe G: Thanks a bunch for checking that for me!

 

[Missouri Mule]

The 95's must of had the PCM supply more volts(8) or the 96 service manual has the incorrect info in it.



You should check out your Battery temp sensor also I believe if it not working correctly or supplying the temp to the EVR mite cause a no-charge condition.

Of course it will not cause any other conditions. (At 75 to 80 degress F ohms reading should be at 9 t0 11 k. )



I still think your main problem is PCM. Hopefully it is the ground or engine speed sensor.



In most cases if something is wrong with the Engine speed sensor being not enough volts,bad sensor or bad ground it will not set a code.

 

[LandShark]

I found out why the PCM wasn't getting 12v to Pin 3: The moron at Cruise America in Everett, WA, where I bought my camper in 1995 used the pin prick method to find the wire he was looking for to activate the camper charging circuit he was installing. As I tracked the Pin 3 wire I found where he had pricked several wires on the firewall (drivers side) near where finally picked a wire to splice into. The pin 3 wire had a tell tale blue/green corosion on it. I replaced the wire and now have battery voltage at Pin3, 5v at Pin 6, and 11. 5 at Pin 7. Don't know why Pin 7 is so high (should be 8v).

Now that the computer has power, nothing has changed... no charge, no CEL/MIL lamp prior to start, no speedo, no trans lockup. I really thought I was getting somewhere!#@$%!

I did at least do the Pin 54 trick to give me trans lockup so I can go pick up a trailer tomorrow. Oo. I won't be able to get back to troubleshooting til tomorrow afternoon.

 

[Rams-n-Hogs]

Don't know if it will help, or not, but a while back, a friend of mine had multiple issues with his truck, some of them the same as yours. Turned out, there are two relays on the cowl, just above the firewall, right behind the injection pump. It was the one on the left causing all the problems. Replaced the relay, and all was well.

 

[LandShark]

Rams-n-Hogs: Thanks for the input. Never really noticed those before. I have no idea what they are. The larger one one the drivers side has 'HI-RAM' printed on it. Guess I'll dig into the manual and see.

 

[Missouri Mule]

Landshark, the relays on cowl are the fuel heater relay(left side looking at engine), and the fuell shut off solenoid relay (right side looking at engine, also larger).

 

[6BT-Dakota]

I discovered the the transmission won't lock up in third and will not go into 4th at all.

That is because they are controled by a solenoid that is controled by the CPS and the ECM

 

[LandShark]

Computer is now running enough to throw codes. It still has about 10 volts where it should have 8, no tach, no charge and no speedo. The 5 volt supply is perfect. The OD light will now come on but still no OD or lockup. The trans temp comes on and stays on. The wait to start comes on and cycles the grid heaters even though it's 65 degrees here and then starts to flash continously.
Codes are:
23 - intake air temp sensor voltage too high or low
24 - TPS voltage too high or low
36 - torque converter clutch solenoid CKT or trans temp sensor voltage too high or low

Common thread here is high voltage. I can't think of any way the PCM would be putting out too high a voltage unless it's fried.

Is there any way to clear these codes? I don't have a scanner.

 

[LandShark]

I went by Bremerton Dodge (WA) last Thursday and ordered a PCM. While there I spoke with a tech (Dave) and described what was going on and he agreed that it's likely the PCM. The key, he said, was the flashing 'wait to start' light.

I should have it by Tuesday and will report back.

Anyone know if it's possible to clear the codes without a scanner?

 

[Missouri Mule]

What I have read you need a scanner to clear codes. But when you put the new PCM in there won't be any codes stored on it.

 

[PBrauer]

Hope I don't come across wrong here but crank/cam speed sensors are notoriously hard to prove good or bad. The output amplitude of the pulses can degrade/decrease, especially at low rpm, to a point where the PCM/ECM considers the "signal" valid but may start using the other (cam vs. crank) sensor for timing, etc. It's a redundant feature that is present in the firmware of at least some ECM's/PCM's.



The problem is that this condition (from experience), which is actually a fault, may or may not set a code... worse yet, any codes set may or may not be "instantly" cleared when the condition, as seen by the computer, "goes away". In other words, a weak crank or cam speed sensor can seem intermittent when it's actually just plain "weak". You can "see" a MIL then not get any codes.



The cam sensor has all the information but half the resolution of the crank sensor. The symptoms can be as "small" as poor economy from less than ideal timing to more obvious things like loosing the tachometer or longer crank times to start (even if it runs normally once it starts). Since several of your symptoms also appear to be ASD related (things that don't operate until the engine is "turning") they only increase my suspicions.



FWIW, any time I see these "type" of symptoms, I just want to SCREAM out "replace that stinkin sensor". Don't probe, measure, or even think about anything else until you're 99. 999% sure the sensor isn't the culprit... and because of its nature, replacement is about the only way to be "that" sure.



I'll be honest... I switched from "reading" to "scanning" this thread as soon as I saw two things: intermittent tach "operation" and a temp. MIL with no codes... I am also concerned that those codes you posted a few days ago are simply the result of your troubleshooting efforts vs. the root problem. All three of those "can" be set by simply unplugging the pigtail with the key on. It is very nice to have a way to clear your own codes.



My 1st direct experience was on a 4. 7HO gas engine but that one will live with me forever... I now carry spare crank and cam sensors every where I go. I've already replaced them both on my '06 Cummins and keep the old ones in the truck, since they were apparently OK. No regrets, once they're ruled out you can move on. I would not replace that PCM w/o replacing both sensors first. Dealership techs, even with a scanner, can't see much more than you have already described in this thread. Many new PCM's have failed to fix many old problems... Worse yet the problem can go away then come back later since the weak signal can get just a little bit stronger with a brand new connector. The amplitude of those pulses are probably in the low millivolt range or less... regardless of the rms or dc levels you are seeing with a meter on the harness.



Enough said by me... for now anyway. This is one of my all time "over thought about", "over preached about" issues. Sorry to go so long. Good luck.

 

[LandShark]

PBrauer: No cam sensor in a 1995.

I did try a new engine speed (crank) sensor this last week with no change. I spent the $100 on this because it was mentioned so many times here. I suspect that the sensor doesn't normally fail except from physical damage like from a frayed belt. That said, I'm sure that they can fail from moisture, ect... Tach was not intermittent except for the first day of problems, then totally dead. Also that day there were voltage spikes that reached 18+ volts, likely caused in part by failing diodes in the alternator. I suspect these voltage spikes caused the failure ot the 12 volt computer supply wire which had been damaged years ago. My guess is that these combined failures fried the computer. We'll see in a couple of days when the new PCM comes in.

The Dodge tech I spoke with said the the flashing 'wait to start' light is a good indication that the PCM is messed up. He works on this stuff every day.

There are a few checks that can be done on the engine speed sensor. One of the 3 pins is sensor ground, one pin is 8 volts (on a 1995), and the other pin is sensor output. Putting a digital ohm meter across the power pin and sensor pin will give a brief 270 ohm reading, then back to 0 ohms. This made not prove that it is good, but it's a start.

 

[LandShark]

New PCM arrived this afternoon and it fixed all outstanding problems. $610 including tax - $120 core, from Dodge dealer. Yikes! But nice to have the truck back running.

Thanks to everyone for their input. I'll post a rundown on what happened in the 2nd gen forum.