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Old 08-24-2007, 05:16 AM   #1
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Default OBD Says TPS Low Voltage -

EDIT:

Subject vehicle is a 95 Bonneville SE 3.8 (3800) Non-Supercharged.

Here'* the VIN: 1G2HX52K6S4264365

ISSUE RESOLVED Results posted at end of this thread.

Purchased the car with 73,000 miles in it in 2004 and up until the the past 30 days had no problems at all. I've got just over 204K miles now and a huge problem. About a month ago I developed this oddball symptom. If the fuel was less than a quarter tank AND I turned Right the car would stall momentarily. Regardless of the amount of accelerator pressing this stallout persisted until the car was righted into the traffic lane. Once done it ran fine. I assumed that the fuel filter was in need of change. Replacing it did not correct the symptom. The symptom continued. I parked the car at work, about 8 blocks from its last Rt. hand turn. This time it sputtered, missed and generally ran rough. When I parked for work was the last time the car has run. I replaced the fuel pump, thinking the strainer or pick-up tube might be having trouble when the gas shifted to one side of the tank on the turns. Turning Left, inclines, downhill, rapid acceleration, nor idle caused the stall, only Rt. Hand turns.

In the beginning I felt this was a fuel delivery issue. A couple of guys from work said the car sounded like it was out of time. Skipping the bloody details here'* what I've replaced in addition to the air, oil, fuel filters. The timing chain and gears (yes it was in time and there was no evidence of wear on the sprokets or chain), the cam sprocket inturrupter magnet (that little booger shot across the room and hid...FYI Use great caution when pressing on this little gizmo. Its small, hard to find, and cost $42 at O'Reilly) I also changed the Cam Position Sensor, Crank Position Sensor and fuel pressure regulator. The check engine light hasn't ever come on but I did rent an OBD scanner and the only thing that it showed was "Throtle Position Sensor-Low Voltage" Not knowing exactly what this meant I also purchased and installed a new TPS. Should have read here first and saved a lot of effort on needless parts. Oh well they are installed and have a life expectancy/peace of mind factor.

Initially the car would turn over but would not start. It would "hit" now and then but not start. This I thik is why the advice from my arm chair quarterbacks was the timing being off. I also replaced the Ignition Control Module beneath the coils. Since I had the car on jack stands and the rear plugs were unusually accessable, I changed the plugs and wires. After doing this the car would crank and run by using a steady supply of carb cleaner/starter fluid down the gullett. Still seems a fuel supply problem.

Now this is where it gets strange. Yes, I did read about the ground busses. As a matter of fact, I checked on them today having read up on them last night. I pulled up the carpet on the driver side along the door and did not find the ground bus. I discovered it forward of the door almost under the kick panel. The bus was taped to the outside of flexable protective tubing and was wrapped with about a half a mile of electrical tape. Checking inside, I found the metal strip to be clean, shiney and free of any corrosion. Checking the passenger side yeilded the same. I brushed both with a brass brush and applied dielectric grease, and put them back as i found them, only with less tape wrap.

I have checked for grounds under the hood. Found one behind the battery with three or 4 wires. Two on the drivers side fender one with a single connection containing two wires and one just aft of that with 3 wires. I cleaned all the connections and greased them. I did not find an engine to chassis ground, or a chasis to frame ground. I believe there is another ground at or near the tranny. I'll look for it tomorrow.

I did manage to find and ultimately destroy a few deterrorating vaccuum connections. The "T" that comes off the throtle and supplies the TPS was crumbling. When I moved it to install the TPS it broke. As did the 90 degree fitting on the Fuel Pressue Regulator.

So many parts of this sound like posts from others, its scarey. Have I put in enough information for anyone to take a stab at where things are wrong? If the voltage at the TPS is low, do you know where the ground is for it? What should the voltage be and can it be checked with a voltmeter?

One other semi unrelated queston. Should there be residual pressure on the fuel pressure regulator? When I depress the valve core there seems to be none if the car isn't being cranked. I think the vaccuum bleed off from the bad connections is the culpret there. Just putting out another grass fire in the forrest fire.

Thank you in advance for any help, advice, comments.[/b]
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Old 08-24-2007, 06:40 AM   #2
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Looks like you've read up and covered a lot of the basics.

A couple questions ... What year and model space ship do you hope to drive again one day?

It 100% sounds like a fuel issue. If the engine will stay running with a supply of anything flammable..then it would almost have to be fuel. Toss a fuel pressure gauge on it and if you have anything less than 37psi after turning the key on and off a bunch of times to get the fuel pump priming..then it'* fuel.

One other quick question.. Have you added any additional fuel to the tank? Your first symptom of right hand turns is typically the baffles being bad in a 92-93 model year.
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Old 08-24-2007, 04:10 PM   #3
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Default I'm sorry...Forgot this little bit ov vital information

I apologize for the oversight, omitting the yr mk and model. I have posed this same question on other BBS sites and in the cutting and pasting I missed getting the following in this one:

1995 Bonneville 3.8 (3800) SE (Non-Supercharged)

8th Character in the Vin: K

Quick answer / follow-up question: Yes I added additional fuel to the tank following the fuel pump installation. Naturally, a great deal of fuel was lost in the removal of the tank. The tank is approximately 1/2 full now.

What baffles?

Thanks for looking over my questioin.
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Old 08-24-2007, 04:52 PM   #4
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Check that Vin again.
& the coil/spark plug wire routing.

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Old 08-24-2007, 04:56 PM   #5
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Quote:
Originally Posted by Technical Ted
Check that Vin again.
It must be that rare vin B model, Pat must know the rpo code for it.
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Old 08-24-2007, 05:15 PM   #6
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Default Checking

Let me verify the VIN again. I may be grossly in error.

I have discovered some vaccuum issues as well. The "T" on the throtle body that feeds the fuel pressure regulator and the "L" that connects the regulator to the hard vaccuum line are both rotted. Also, the splices from the hard line to the vaccuum resoviour were in bad shape. I'm on the way to the dealership to locate the fittings. I'll check back. Thank you all for helping me. I need to get this thing running or I need a rag and a bottle of volitile liquid. More within the next couple of hours.
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Old 08-24-2007, 09:11 PM   #7
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Default UPDATE

Sorry about not getting this right to start with.

Here'* the VIN: 1G2HX52K6S4264365

I believe I've gotten the vacuum leaks all sealed up. The connectors are hard to find, some are no longer serviced by OEM parts. I still am getting no residual pressure on the fuel pressure regulator after initial "key to on position" fuel pump priming. I don't have access to a guage so I can't say that there isn't any pressure on start-up. Perhaps since I can't get the engine to run at the moment I can't generate a vacuum.

I still would like to know the location of the TPS ground. Further, what might cause the code to be TPS - Voltage Low. This is not an adjustable TPS, so I'm guessing that there isn't enough current going to it. Are there known issues?

Again, all help is appreciated.
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Old 08-24-2007, 10:03 PM   #8
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I'll check a wiring diagram & see if it shows the TPS ground but you might need someone with a factory service manual.

Have you check all the fuses under the dash on both the driver & passenger sides?
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Old 08-25-2007, 12:42 AM   #9
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Default Thanks Ted

I haven't checked for a passenger side fuse block. The driver'* side fuses are all good as are all the maxi fuses uner the hood. I am not aware of any relays or switches in the power distribution area which would be involved. Because this issue began as an intermittent problem I would not have thought a fuse would be indicated.
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Old 08-25-2007, 01:05 PM   #10
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Here'* the three things we like to check first for a no-start condition.

Spark at each of the 3 front cylinders.
Fuel pressure at the schrader valve on the fuel rail/regulator.
Fuel injector pulse.

It appears the ground (black) wire for the TPS goes to the PCM. I don't believe low voltage from the TPS will prevent the engine from starting.
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