94 C1500 Silverado stalls when put in drive/wont start
March 22nd, 2020, 12:14 AM
#21
CF Beginner
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it is your throttle position sensor. You have to calibrate it with a multi meter. There Is a 5 V constant, a signal wire, and your ground. Find your 5 volt constant, Then you know the other 2 wires are your ground and signal. Splice into the signal wire without cutting through it and check that you have voltage when the key is forward with the engine off. It has to read around 0.48v Closed throttle ... Once you get it close to 0.5 v closed, use your hand and open the throttle...the multi meter should read close to 5.0 volts wide open throttle. You adjust the voltage by loosening the screws that hold it to the tbi while checking the voltage with a multi meter. Once you are in range, screw it down tight being careful not to move it or you will change the calibration again. Even a cheap $5 multi meter from Harbor freight will get you back on the road again. I suggest checking the calibration on your throttle position sensor before just replacing it.. I spent a bunch of money buying a new one and after I learned how to calibrate it, I realize I didn't need a new TPS at all
on first starting engine idles well in neutral cold about 1000 rpm drops to 800 after a few minutes.
In drive idle drops to 650 no throttle foot on brake.
Start diving driving sluggish throttle response on light throttle up to 1200rpm get over 1500rpm throttle response is good engine not fully warmed up.
Engine up to temperature on the highway steady 50-55mph occasional stutter throttle response a little slow.
Back in town 25-30mph stop start driving at traffic lights idle drops to 300-400rpm engine sounds ok but labouring (obviously tickover is to low) but not feeling like its going to stall still sluggish up to about 1300rpm.
I am sure the new plugs leads rotor arm and distributer cap have helped and needed doing but not a cure.
No check engine lights i did run as scan test and only got a 12 which is normal.
I think a full scan with a pro scanner would certanly help will try to get one done during the week if I can.
Tomorrow morning I am going to test the TBS and try recalibration as you suggest it sounds pretty easy I have a few multimeters (some Harbor freight freebies) and have researched what each wire does. Hope it all goes well and calibration works I did read that when they go bad it is usually at the lower part of there operating range 20-30% throttle which makes sense and also fits my symptoms.
I think I will also give the ignition control module a check over as well it cant hurt.
Once again thank you for the information.
March 22nd, 2020, 11:34 AM
#22
Now that it’s running better without codes. Good practice is to go thru and clean all your grounds. Marginal grounds can cause problems with ECM, sensors. There are something like 4 grounds. I think, but not sure - One firewall junction block area, engine to firewall or frame at back, battery to frame, and one on CTS housing. Maybe someone knows for sure and will comment. Regardless, since ECM makes all its decisions on timing and fuel based on sensor inputs and if the signals are noisy or voltages are degraded then it can get bad data and be erratic.
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terrydo
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October 17th, 2019 3:47 AM