I have a 2003 Blazer LS 4-door, 4WD, 4.3L V6



If you check out my threads, I've had a lot of work done to the vehicle. However, even though I've been told my transmission is OK, I still get hesitation on acceleration and very low gas mileage (like 10mpg where I used to get 15-20mpg).

I could use some help - I think it's now either the Throttle Position Sensor (TPS) or the Vehicle Speed Sensor (VSS). Here are my symptoms:

- An unexplainable bucking and jerking in the vehicle
- Sudden engine stalling without any apparent reason
- Extreme Hesitation while accelerating
- Difficulties in changing gears
- The transmission will not smoothly change gears
- A drastic drop in fuel economy
- To change gears when going from say 25mph to 45/50 mph I have to floor it (and I almost redlines to 6K rpm) -- transmission revs higher before it changes gears
- Brakes are sometimes harder than normal when coasting

Again, I've been told my transmission is fine.

 

normally with a faulty VSS you just lose your shifting and your speedometer but should not effect the way the engine runs. my 1993 has the same transmission as yours and havent had the VSS hooked up in years as its just a offroad truck and runs fine, just doesnt shift.

might be a computer issue or multiple problems hard to tell without seeing it

 

I agree with abig84. A couple smaller problems working together multiply trouble they cause. If it's not the computer itself, I'm sure the computer can give a direction to start. Take someone with a live data scanner for a ride before buying parts.

 

I have an OBD-II reader and I'm not getting any error codes. I've had the transmission looked at and there aren't any issues there either. Yesterday, I replaced the TPS and the acceleration was helped by ~20%. I have the VSS part to install, I'm going to try that out. If I'm still having issues, I'm going to stop chasing down parts and go in for another inspection. I'm frustrated, though, that there aren't any error codes.

 

After re-reading all your posts I'm wondering if a section of the wiring harness was damaged from the overheating. My wiring harness was shorted, burnt, melted and corroded under the bracket that holds the ABS motor.

Visually inspect all the wiring under the hood. Look in the tighter areas and around the engine and exhaust manifolds where it got the hottest.

 

<-- How I feel!

Where is that harness located? I'll take a look for sure this evening - I'm still having issues with acceleration. I tried changing the VSS on my Blazer, but the bolt seems to have seized (and it was close to 100 degrees outside when I was under my car) - so I gave up that attempt. The Throttle Position Sensor was changed over the weekend and that seems to have helped a little.

Do you have a diagram or could point me to one?

 

Under the hood coming out of the fuse box. The black plastic tubes full of wire. Follow them from the box looking for places where its rubbed against something or got too close to something hot and melted. A flashlight and a small mirror help.

 

You mentioned: overheating.

What was that overheating? Engine? Trans? Electrical?

What was the reason for the short in the ABS wiring? Melted connectors?

Pictures?


The following is for information and should in no means be a discouragement, but a help to make better, more informed decisions.

Concerning OBD II and some misinterpretations:

OBDII has been implemented as an advanced protocol over OBDI (obviously) and has two main reasons to be there:

1st the emissions laws mandated a means of on board self diagnostic to tell if something is wrong with the emissions controls.
https://en.wikipedia.org/wiki/OBD-II_PIDs

2nd the U.S. legislation mandated an access to all vehicles via a standardized connection. (IMHO something related to the anti trust laws). All foreign manufacturers have adopted the OBDII connection in some countries as well due to anti trust laws in some just out of convenience.
https://en.wikipedia.org/wiki/On-board_diagnostics

Despite it having the name of "ON BOARD DIAGNOSTICS" What can OBDII really do?
It will give you the required standard output codes defined in the OBDII standard. This means that the computer is passing along the information required by the OBDII - that is what you can read with your scanner.
It will, apart from the sensor data which can be read while running, not give you any additional troubleshooting or analytical data.
That is: The computer may have a much better idea of what went wrong with let's say the reason for the stalling but is not telling you! Instead it may or may not trigger a "CYL #4 MISFIRE".
You think: Gee - my spark must be bad for the misfire. But what the computer is not telling you is that it is the injector itself which is out of spec in resistance. Instead it gives you the generic "MISFIRE" code.

When you hook up a factory computer (most of the time on the same OBDII connector) and the guy/girl using it is competent it can tell you a lot more than that. The factory equipment can send a code to the control units on the car which identifies it as factory computer and they start be a lot more talkative then with a generic OBD scanner.

Take your ABS harness. The computer will throw a generic OBDII code for the ABS - let's assume it throws "C0040 - Right Front Wheel Speed Circuit Malfunction".

Does this identify the problem?
No it is not the correct identification of the problem - there is more to it.
Modern (and your 2003 should be considered more or less modern) computers will tell the factory diagnostic computer a lot more than that but will just pass the above DTC to the OBDII connection.

The factory diagnostics can tell if the wiring is broken. It can tell if the ABS control module has an internal fault. It can tell if you have a signal but it is weak (e.g. a bent sensor support on the wheel). It can tell if you have an intermittent signal (e.g. same as before or a short or bad connector). Depending on the wiring and the diagnostic capabilities you can run active tests with the factory testing equipment. The computer may also be able to tell if the sensor is out of spec (e.g. reads too high or too low resistance/current/voltage).

Not sure but I guess that a 2003 factory diagnostic should also have troubleshooting guide built in. This will tell you what steps to take one by one to come up with the correct diagnostic. Assuming the above ABS code it may tell you to disconnect the connector in the wheel well and measure for resistance. It will also tell you what the resistance should be. Then it will tell you to disconnect the connector at the ABS control module and reconnect the wheel sensor and measure the lines from the module to the sensor, again with the expected values.
Within 5 minutes or so an expert may be able to tell what is wrong.

With multiple problems such as you encounter it may be a solution to check with some GM dealerships which have the correct diagnostic and have them make a preventive on the diagnosis itself and after that for the repair and parts needed.
Sometimes you pay 50$ for the diagnostics and printout and it's worth it's money.

Good luck

 

To me, the all the symptoms taken as a whole, sounds like the cam timing is off by a tooth, maybe 2? Have you verified that? I don't think that would set the CEL light.

 

?????????????????????????????? Yes it would