1998 Chevy Truck V8 Four Wheel Drive Automatic 56.000 miles
I seem to have a dead spot on my Throttle Position Sensor (TPS). The big V-8 runs rough at the 75% almost full throttle position. If I floor it, the engine goes smooth. Back off to the 75% postion and it's rough. Only happys after the engine is warm. I just cleaned the MAF with CRC MAF Cleaner - the stuttering at 75% throttle is still there unless I pull over - put it in park- turn the vehicle off - re-start. This re-start is sort of a ' re-boot'. Once restarted the struttering goes away but will eventually return. So before I change the MAF - I'm thinking I have a dead spot of the TPS and rather replace a $39 possible issue before I go for a $150 new MAF. The obvious like plugs/wires/dist cap/rotor are new. How do I replace and re-calibrate an new Throttle Position Sensor on this ' 98 Chevy Truck with a 5.7 liter?
If this TPS does not work I will go for a new MAF. I and also wodering if a new MAF needs to be calibrated of is it just a simple replacement with no need of calibration?
So I'm down to 1. How to calibrate a TPS % 2. Does a new MAF need to be calibrated?
Do not jump to the conclusion that it is the tps sensor or the maf sensor. Blindly changing parts is not good. Test the tps sensor first. The tps sensor is a variable potentiometer, meaning it varys voltage. The ecm reads this varied voltage and adjusts fuel delivery accordingly. A 'dead spot' in this sensor is not likely. To test the tps--with the sensor plugged in--back probe the dark blue wire terminal with the positive lead of a DC voltage meter. Connect the negitive probe to a good engine ground. Turn the key on but do not start the engine. The voltage should be 0.6 volts at closed throttle. Open the throttle slowly and smoothley. The voltage should increase smoothley to 4.5 volts at wide open throttle.
Your maf sensor needs to be hooked up to a scan tool to test. At operating temperature the maf sensor should read 4.0 to 9.0 grams per second.
Testing sensors first will save you time and money. You say you replaced the plugs-wires and distributer cap. Why? These wires are good for 100000 miles. If you used after market wires you'll only be replacing them again in about 25000 miles or so. Were the plugs bad? With these engines always use A/C Delco or GM replacement parts. I know these are more expensive, but they seem to be the only parts that work, for any amount of time, in these high voltage ignition systems.
Test your map sensor. This sounds like it may be the problem. Back probe the light green wire with the positive lead of a volt meter and the negitive lead to a good ground. Turn key on but do not start. The voltage should be 4.0 to 5.0 volts. Start the engine and allow it to idle--the voltage should drop to 0.5 to 2.0 volts. If these tests turn out to be good check back here--let me know how you make out.
Is your check engine light on?
BTW there is no calibration on either the tps or the maf sensors.
January, 18, 2008 AT 11:08 AM
Thank you for the response concerning 5.7 liter chevy V8 1998 K 1500 and it's miss firing at a particular pedal position.
In your response you said " BTW there is no calibration on either the TPS or the MAF sensors" I thought when replacig the TPS, one had to loosen the two screws and move the TPS up or down at idle ( engine running) until a certain Voltage reads out. I did not know it was simply remove the old TPS - Replace with new and plug in the wire? Do I have this right or did I miss read something? The TPS was only $35. Since the truck is close to 9 years old, I figured it replacing since I do seem to have a dead spot on a particular pedal position, but your point of testing before buying is sound.
As to the MAP sensor being a possible issue, thanks, never considered that and I appreciate the test proceedure.
As to your question of Cell going off. Yes I get a ' check engine light" when I let the truck stumble holding the pedal at that same 75% full throttle position that always starts the miss firing once the engine warms up. If I avoid that pedal position the cell light eventually goes off by itself after so many trips = as long as I avoild the bad pedal position.
January, 18, 2008 AT 9:37 PM
I have never had to calibrate a TPS like that, but your way does make sense. I always use GM parts so the part always exactly fits.
If your engine light comes on then there is a trouble code stored in your computer. Autozone or a place like will scan your truck, as long as the light is on, for free. The next time it comes on have the engine scanned. You can take it to a dealer and have the memory scanned but that will not be for free. Get the code and let me know what it is. If the light comes on for a failing sensor, the computer will not reset the light. The light will stay on until it is manually cleared. An engine light that comes on and off usually means--in this case--a cylinder is randomly misfiring--then it clears up. This problem is most likely mechanical. These engines are notorious for this!
Here are some of the causes--worn out distributer gear--sticking or clogged fuel injectors--failing fuel injector--bad fuel pressure regulator--leaking lower intake manifold gasket--and the hardest to diagnois, sticking exhaust valve. Keep me posted