Hey all! I've got a recurring problem with my truck, and I was hoping someone could shed some light for me.

I have a 97 2500, 4x4 with a NV4500 tranny, a NP242 transfer case, and the stock 360 under the hood.

Back in February, coming back from Cadillac, at around 60 MPH she started bucking and ******* out.... did that 2 or 3 times before it finally corrected itself, displaying a "Check Engine" light. Made it home, no problems. Eventually the Check Engine light went away, so I didn't think nothing about it.

About a month or two ago, the problems began to surface. She started ******* BAD BAD BAD. I couldn't even get it upto 15 MPH without having it in 4th gear (yes, 4th gear). It took me over 30 minutes to get home, a half mile away. Got home, parked it, and began to work on it.

I went down and got an ODB2 code reader from Auto Zone, which diagnosed the problem as a "Vehicle Speed Sensor Failure". Great! Wonderful! That's so much easier than I thought it was going to be. Went down to AutoZone and got a new sensor ($50) and popped her in. And everything was fine and drove great....

....until the next day. Next day, same problems. Since this was nearing the end of my semster, in the parking lot she sat until today.


Today, I began to tackle the problem again. Pulled the vent hose and breather, all checked out fine, no cloggage or obstruction (I began to think there was an obstruction that was causing ATF to come out through the VSS, perhaps). Took her for a drive with the 4 vacuum hoses on the transfer case disconnected, still the same trouble. I'm nearing the end of my troubleshooting capabilities, and have no idea what is causing this problem.

She starts and idles ok, then as soon as I give it some gas, RPM's drop drastically, almost to the point of stalling. The more gas I give her, the more the RPMs drop. And what's worse, is the sound. It sounds like I tried swapping out my 360 for a Geo Metro 3 cylinder. A very very high pitched whinny sort of sound.

Some miscellaneous info for ya: when I replaced the VSS< I checked the voltages. The signal voltage was in line with what my Haynes reported it should be, however, my ECM voltage was 5v when it was reported in the Haynes that it should be 8v.

Is it possible that I just got a crap sensor? Or could there be an underying problem with the ECM? Maybe the ECM is damaging the sensors, or perhaps my ECM is just malfunctioning altogether?

Has anybody else had any similar problems? I really really love my truck, but if the ECM is failing, I think it may be time to trade her in for one of the new Power Wagons....

Whatcha all think?

 

Did you check your throttle position sensor? It sometimes causes the computer to think the VSS is bad. They're a common issue with the 2nd gen Rams......come to think of it, they seem to be a common problem for a lot of vehicles [>:]

Anyway, that's something I would check first.

 

Thx for the reply, TBM. I'll check the TPS tomorrow after I ship the kids off to school! =) Will let ya'll know what happens!

 

Checked the TPS and no dice, the TPS works fine so that's not the problem. I went ahead and checked the voltages to the VSS again, since I was hoping one of my wire spices broke or something, and I get steady voltages. About 5.6v signal and a 5.1v reference instead of 8v which my manual said it should be.

I might go get a new sensor, take AUto Zone up on their warranty, and see if maybe I've got a faulty sensor.... other than that, I'm not sure...

Any other ideas, anyone? :-\

 

which sensor are you talking about? the one on the tranny or the rear diff?

actually, now that I think of it, check for a vacuum leak. I had an old carb truck do this exact same thing on me and the base gasket on the carb blew causing a leak.

 

The VSS, on the output of the transfer case (or the tranny on 2wd models). It could also be on the rear diff on older models, rotations are the same at the transfer case or rear axle, so it's just a matter of placement preference..


Cool, I'll keep that in mind as I begin my rigors again tomorrow. I wanna get my truck running before I'm forced to drag it into the dealership *gasp* Hey, I'm getting despereate here! =)

 

UPDATE:: Replaced the VSS (AGAIN) and this time there is absolutely no change in the symptoms. So, I'm looking into alternate problems, specifically, Steve's recommendation about the vacuum/gaskets.

Here's the thing. I was checking the PCV valve to see if I had vacuum there, and while I had the hood up and the engine running, I can swear that I can hear a "hiss" that wasn't there previously. Actually, it's more than a his, sounds more like an air compressor. I wasn't able to locate the source of the sound yet, but it did sound like it was coming from the upper rear of the engine (throttle body location) although, I wasn't able to tell any difference in left/right, so I'm thinking it's the back. If I pull the air cleaner off, I should be able to see/feel air or gasket, correct?

I'll be working at this over the course of the weekend. Come Monday, if I still can't take her muddin', then I'll be singin' "Hi ho, hi ho, off to the dealership I go..... parts at 200%, labor for $63 an hour, hi ho, hi ho hi ho hi ho..."


;-)

 

pop off your TB and have a look, it's only 4 bolts, 2~3 cables, 3 connectors and 1 vacuum line... takes 10 minutes tops. then have a look at the base gasket to see if it looks ok, hell, get a new one, there only a few bux. also check your IAC valve, it may be stuck and no longer working... if it's stuck open in such a way that it may cause your motor to lean out really bad when you hit the throttle and die.

I believe IIRC that if you disconnect the battery to reset the pcm, then have someone turn the key on while you have the IAC in your hand, you should see it go thru the entire range of motion that the motor has. if it doesnt move, chances are it may be dead. I can check on mine sometime over the weekend since i'm gonna be working on it a bit but I have no idea when during the weekend...

I had a similar problem like what you describe at your 1st post and it turned out that my o2 sensor wires shorted to gnd (burnt) and blew the o2 heater fuse (2000 ram 4x4). It did not have the hissing sound that you describe but it did buck and complain when it was warm and in closed loop mode. (open loop ignores the o2's IIRC)

 

check that... start with your IAC 1st, then go to the TB... i'll bet the IAC is dead.

 

Thanks, I'll check the IAC pronto!


I found the source of the incessant "hissing", it's a major vacuum on the throttle body. I'm not sure if it's a normal thing, cause I've honestly never noticed it before. I've got the picture highlighted where it's sucking air. I put my hand over it, and it felt like it could damn near suck my skin off.



Is it normal to be sucking a lot of air through there??