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4.3 Vortec rough running and/or rich running
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Dale_3rd
New User
Dec 28, 2014, 8:23 AM
Post #1 of 9
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4.3 Vortec rough running and/or rich running
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Hello all,
1994
Oldsmobile
Bravada
4.3 Vortec
125,000+ miles haven't looked at it in a while
As noted, I have an Olds Bravada, 94', that is running very rich. I've replaced the fuel pressure regulator, which was leaking but it still didn't fix the issue. I also replaced the plugs, wires, distributor cap and rotor button. Still runs rough and is hard to start when hot, seems to start okay when cold. I bought a OBD scanner, it returned 22, throttle position sensor signal voltage low and 34 MAP sensor low voltage during ignition on. I replaced the TPS as it was the first in the list, but that didn't fix it either. I then checked the TPS voltages, good ground (read 12.28V and about 35 ohms), also had 5.02V for the 5V reference. I cleared the computer and the error codes still exist and it still runs poorly. I also now have the issue of high RPM and late shifting. Any ideas where to look now? I don't want to throw another $50 at a MAP sensor and it not be the problem.
Thanks everyone.
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Discretesignals
Ultimate Carjunky
/ Moderator
Dec 29, 2014, 6:02 AM
Post #2 of 9
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Re: 4.3 Vortec rough running and/or rich running
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When you did the regulator, did you also do the nylon fuel lines that connect to the injector? Those where known for cracking and leaking under the intake causing the engine to run really rich, fouling out plugs, and possibly fouling out the O2 sensor. If the sensor is fouled, you'll have to replace it.
fuel line kit:
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Dale_3rd
New User
Dec 29, 2014, 8:18 AM
Post #3 of 9
(4121 views)
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Re: 4.3 Vortec rough running and/or rich running
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I replaced the "spider" I think it was called several years ago and the "nut kit" I think they called it. When I replaced the fuel pressure regulator the fuel line side was dirty, not showing any signs of leaks, nor did I see drips when I turned the key on to bring the fuel system up to pressure. The vehicle has been running rich for quite some time as I wasn't able to get the truck into my parents garage to attempt repairs. The truck only gets weekend use, to and from my parents house, so it also wasn't a priority to repair. :(
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Discretesignals
Ultimate Carjunky
/ Moderator
Dec 29, 2014, 11:27 AM
Post #4 of 9
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Re: 4.3 Vortec rough running and/or rich running
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Need to measure the voltages on the three wires for the TPS first. You have to back probe the TPS sensor connector with your meter's black lead connected to battery negative. Don't unplug the TPS connector to take your voltage measurements.
Measure these voltages on these wires for the TPS with key on:
Grey: 5 volts
Blue: between .5-1.0 volt. Voltage goes up steady as you slowly open the throttle to around 4.5 volts at wide open throttle
Black: should be less than 0.3 volts
Take the measurements and let us know what you find out.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 29, 2014, 11:30 AM)
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Dale_3rd
New User
Jan 1, 2015, 9:07 AM
Post #5 of 9
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Re: 4.3 Vortec rough running and/or rich running
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Grey - 5.02V
Blue - .3V but goes to <0.01V when I move the throttle
Black - essentially 0V (Fluke 189 measures 0.0002V)
The plugs measures all voltages correctly when unhooked from the sensor, from the research I've done. But plugged in I don't get the varying 0.5 to 4.5V indicating that the TPS is working as it should.
Got a bad TPS sensor from the parts store???
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Hammer Time
Ultimate Carjunky
/ Moderator
Jan 1, 2015, 9:24 AM
Post #6 of 9
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Re: 4.3 Vortec rough running and/or rich running
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To measure that properly you really should be using the black wire for a ground when measuring the blue wire.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
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Jan 1, 2015, 11:30 AM
Post #7 of 9
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Re: 4.3 Vortec rough running and/or rich running
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Not necessary to use sensor ground as a reference. I personally always use battery ground unless you are wanting to get a cleaner signal measurement from something like a digital MAF sensor.
If you have no voltage on the signal wire, you either have a bad connection with your back probe, the signal circuit is shorted to ground, or your TPS sensor is defective.
To test the signal circuit to see if it grounded due to a wiring issue, you could unplug the ECM connectors and then use a 12 volt test light connected to battery positive. Probe the blue wire at the TPS connector. If it lights up, the signal circuit is shorted to ground.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jan 1, 2015, 11:34 AM)
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Dale_3rd
New User
Jan 3, 2015, 9:13 AM
Post #9 of 9
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Re: 4.3 Vortec rough running and/or rich running
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I retested the connections, verifying that I did indeed have good connections.
Grey - 5.01V
Blue - this time I had .61V to 4.5V smoothly through the range of the throttle
Black - I used this sensor ground for the testing, 0V for this wire to the battery ground and 11.99V for this wire to battery positive.
With the new TPS installed, I get high rpm before shifting out of 1st, but seems to shift smoothly under normal driving conditions, with the old sensor in I get a very rough idle with stalls, but the shifting issue seems to go away.
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