| Author |
Message |
    
Todd
| | Posted on Tuesday, May 21, 2002 - 06:25 pm: | 
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A new problem came up this past weekend while I was driving on the interestate. I was crusing between 70-75 and it felt like the transmission slipped or something. It didn't matter how much gas I gave it, it wouldn't speed up. It gave out for about 2 seconds and then did fine, then it happened again 30 sec. after that. This process went on all the way home. Anyone have any ideas of what might have happened?
Thanks,
Todd |
Jay
| | Posted on Tuesday, May 21, 2002 - 11:50 pm: |
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Mine did the same thing once, I narrowed it down to 3 things.
1. I figured it could be fuel delivery so I ran a bottle of fuel system cleaner.
2. I removed and cleaned my stepper motor (there is a good tech write up in the archives. Go and search for it here.
3. Im soon to install a new Vehicle speed sensor.
I havent had any problems since I cleaned the stepper motor so I think it was that.
You can do everything yourself very easy and fairly cheap. |
Scott Tschantz (Scott)
| | Posted on Wednesday, May 22, 2002 - 01:04 am: |
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Mine did the same thing at 75000 miles it was the vss |
Milan
| | Posted on Wednesday, May 22, 2002 - 12:14 pm: |
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Isn't the "stepper motor" really IAC (Idle Air Controlller), i.e. it only controlls the idle speed? |
todd
| | Posted on Wednesday, May 22, 2002 - 03:26 pm: |
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thanks for the info.
I will run a bottle of fuel system cleaner and see what that will do for it. Is there anyway to tell if it is the vehicle speed sensor. The check engine light did come on, but went off right after.
Todd |
Kyle
| | Posted on Wednesday, May 22, 2002 - 03:26 pm: |
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VSS
Kyle |
Paul T. Schram (Paulschram)
| | Posted on Wednesday, May 22, 2002 - 03:51 pm: |
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Todd:
The Vehicle Speed Sensor is little more than a variable resistor. What most likely happens is that at the point where the throttle would be at 55 mph wears out from the continuous pressure right there. As a result, the circuit becomes disco-ntinuous at that point. One can test the operation of the VSS by disco-nnecting it from its wiring harness and attaching an ohmmeter to the leads. As you move the throttle through its range of motion (with engine off), watch the meter, looking for a point where the resistance precipitously increases. This indicates the break in the carbon trace and that you will need to replce your vehicle speed sensor. You would expect to see a linear change of resistance with throttle position if the VSS were good.
Paul |
Kyle
| | Posted on Wednesday, May 22, 2002 - 03:53 pm: |
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Hmm
Wrong Paul.... 
Kyle |
M. K. Watson (Lrover94)
| | Posted on Wednesday, May 22, 2002 - 04:28 pm: |
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ok, i will bite where is the VSS? i believe reading once that this wigget could cause the engine to overwork to maintain given speed whenit is worn beyond specs thus effecting the fuel economy.???????
mike w |
Kyle
| | Posted on Wednesday, May 22, 2002 - 04:42 pm: |
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The VSS is on the transfer case and its a pulse generator , not a resistor..
Kyle |
M. K. Watson (Lrover94)
| | Posted on Wednesday, May 22, 2002 - 04:51 pm: |
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oh! that is no where near what i was thinking thanks Kyle.
mike w |
David Dryden (David914)
| | Posted on Wednesday, May 22, 2002 - 04:53 pm: |
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I think Paul was thinking of the TPS (throttle position sensor), not the VSS. Be careful you don't get your TPS and VSS mixed up, or you'll wind up on your ASS... 
David |
Kyle
| | Posted on Wednesday, May 22, 2002 - 04:55 pm: |
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And he is a rocket scientist,,,,damn , no wonder they grounded that bird he works with...
Kyle |
Paul T. Schram (Paulschram)
| | Posted on Wednesday, May 22, 2002 - 05:20 pm: |
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Kyle:
Thank you for pointing out my mixing up the TPS and the VSS, but YOU ARE WRONG (in one respect)!!! Apologies to Brian Bonner.
Wrong Paul. I quit working on airplanes in the mid-80s. I'm an EH&S Engineer.
How does one go about checking the VSS, I'll check the ETM this evening. I suspect that it may be very similar to the TPS, although, it could be either a 4-20 ma. signal or a digital output (PWM?) maybe a voltage to frequency conversion. Might require an oscilloscope or frequency counter.
Now that I think about it, how do we know it is not the TPS and the VSS? seems as though they could both exhibit the same response-stumbling at certain points in either engine RPM, or vehicle speed.
At this point, we might suggest to Todd that he take steps to determine if the vehicle exhibits the same problem dependent upon engine speed or vehicle speed.
Peace,
Paul |
Kyle
| | Posted on Wednesday, May 22, 2002 - 05:30 pm: |
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VSS needs to go on a scope. The VSS typically displays the symptoms desribed. TPS issues are rarely (Thats right folks said rarely) to blame for such serious driveability issues..
Kyle |
todd
| | Posted on Wednesday, May 22, 2002 - 08:34 pm: |
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wheww...
ok, first off..now that I know the VSS is located on the transfer case, how do I go about checking it and replacing it if necessary.
second..the problem seems to be vehicle speed dependant not engine speed dependent. The truck does great until I hit 55 or 60.
One question, if the problem was as paul described earlier(where the VSS wore out at a point where the throttle would be at 55 mph from the continuous pressure right there) wouldn't me pushing on or letting off the throttle at that point solve that problem. Well, me pushing on or letting off the gas doesn't solve the problem. The speed decreases until around 65 and then will pick back up to 70. Then it will decrease again.
Thanks again for the help.
Todd |
Ron
| | Posted on Thursday, May 23, 2002 - 01:13 am: |
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Just replace the VSS
Ron |
jp
| | Posted on Thursday, May 23, 2002 - 04:04 am: |
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It could also be a fuel pressure/delivery problem couldnt it? Check you fuel filter. I think the schedule only calls for changing at LONG intervals, but I think it should be changed depending on fuel quality/cleanliness - here in Saudi with dust everywhere I change it around once a year whatever mileage I do. On my previous disco I changed it as soon as I got it, and it made a marked difference in power. Check the rail pressure - 37 psi max should be available with vacuum disconnected from regulator.
jp |
Kyle
| | Posted on Thursday, May 23, 2002 - 10:07 am: |
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Thank you ROn.....
Kyle |
Paul T. Schram (Paulschram)
| | Posted on Thursday, May 23, 2002 - 10:38 am: |
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I agree with Kyle. Although it could be other things, the preponderance of the evidence is such that it is likely to be the VSS. Otherwise, letting off of the throttle would result in a quick change in engine performance-would it not Kyle?
Kyle-thanx for taking my comments in the manner they were intended. I was trying to make light of the whole situation.
Peace,
Paul |
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