I have a 2.8 that's been giving me grief for a while now. While I have fixed many issues, more keep popping up. I am currently battling a random misfire/bucking and excessively rich fuel condition.
The TPS and it's pigtail were replaced not long ago and the voltage was verified to be in the correct range. Now all of a sudden I have a code 22 for low TPS voltage. I checked the voltage and now it is only 0.05 volts at wide open throttle, and 0 volts when closed. The power supply also only shows 0.05 volts. I swapped out the TPS for another one and got the same readings. Unless I am missing something here, it appears the TPS itself is fine and there is a power supply issue.
I've cleaned and checked all the grounds I can find. I even swapped ECM's and cleaned it's ground. I also added more grounds to chassis and engine, and cleaned the connections below the C500. Anyone out there have any suggestions or thoughts on what I might want to check next? This low voltage might be what's giving me all the headaches.
The TPS shares the same wire for the reference 5V signal with the MAP sensor. If the MAP sensor is buggered up, it may be drawing the reference signal down. Try unplugging the MAP and re-measuring the reference voltage at the TPS. If it's a solid 5V, then you know the MAP sensor is the problem.
If that doesn't do the trick, it could also be that the splice where the 5V wire branches off between the MAP and TPS is corroded or has gone bad. Trace the wire until you find the splice and check it out.
The TPS shares the same wire for the reference 5V signal with the MAP sensor. If the MAP sensor is buggered up, it may be drawing the reference signal down. Try unplugging the MAP and re-measuring the reference voltage at the TPS. If it's a solid 5V, then you know the MAP sensor is the problem.
If that doesn't do the trick, it could also be that the splice where the 5V wire branches off between the MAP and TPS is corroded or has gone bad. Trace the wire until you find the splice and check it out.
I disconnected the MAP, but no change in the voltage. I will have to dig into the harness some more to find that splice, but not tonight as I'm out of time. Hopefully I can get it checked out tomorrow. Thanks for the input.
I double checked the TPS wires and pigtail, they all appear to be sound. All splices were soldered and covered with heat shrink tubing.
[This message has been edited by ITALGT (edited 02-15-2015).]
Sounds like you are going to need to get to the ECM and check the 5v reference there. I not good there check you ECM grounds before condemning it. If good there check where the reference signal splits in the harness.
Also... can anyone verify the correct order of the TPS wires? I am finding conflicting information. I thought that the top is grey, middle is blue, and bottom is black. Some diagrams I am finding show the top one as black and the bottom as grey.
Some of you may have noticed that this topic is a spin-off from my "2.8 erratic/high idle issue" thread. Since that thread is getting rather long and cluttered with info, I thought it would be best to start a new topic specifically on the low voltage issue. I'll get back to that thread after this problem is solved, or whenever necessary.
Here's some more insight into what's happening:
Last weekend while the car was up on jack stands for a new fuel pump, I took the time to clean and inspect the starter/solenoid connections as best as I could. They were dirty and not very tight, but unfortunately there wasn't any change after they were cleaned. Here's the kicker though. Over the past couple months now, the starter has been acting up. Most of the time it turns the engine over just fine, but every now and then it struggles terribly. It's been progressively getting worse, just like the bucking/misfire. It kinda' acts as if it's turning over an engine which has it's timing is too far advanced (it's not), or as if it's just not getting enough juice to crank.
I am beginning to wonder if the low voltage at the TPS is directly related to the problem I am having with the starter. Maybe a random short or bad ground in the solenoid or starter could cause this erratic bucking/misfire/rich condition with low TPS voltage? That would certainly explain why I still have the current symptoms.
Anyone have any thoughts about this? Low TPS voltage... erratic bucking and misfire... excessively rich condition... starter occasionally struggling...
[This message has been edited by ITALGT (edited 02-16-2015).]
...If that doesn't do the trick, it could also be that the splice where the 5V wire branches off between the MAP and TPS is corroded or has gone bad. Trace the wire until you find the splice and check it out.
I traced the wires to that splice and it is good; no corrosion, bright and shiny.
It turned out to be one (or both) grounds for the ECM on the engine block. Not only were they both a little loose, but they were so caked in oil that they were hardly visible.
I cleaned them up and scuffed up the mounting points for a good connection. TPS voltage is now back to normal. The code 22 is now gone, however the engine's bucking/missing/running rich hasn't changed. Bummer, because for a minute there I thought I might have discovered what the misfire/bucking problem was.
Give the ECM some re-learn time...you may have fixed more stuff.
I will be driving it to work tomorrow to see if there are any changes.
quote
Originally posted by Bloozberry:
Great find. You do know that there's two pairs of ECM grounds in that area right? Did you check both sets?
Two pairs? Well let's put it this way. The two grounds I cleaned today are both bolted on the rear of the front cylinder head. Where are the other two located? There were a couple missing when I bought the car, so maybe I'm missing something. I've added one ground going from the cylinder head to the firewall, and the ground wire attached to the transmission was relocated to a better spot on the chassis.
[This message has been edited by ITALGT (edited 02-16-2015).]
Yup, those are the ones I cleaned up. I think I just misunderstood what you meant by pairs, now I get it; there are two grounds per connector.
At this point I think I've had my hands on about every ground there is, except for inside the interior. I am fairly confident that the engine and chassis grounds are all in excellent shape now.
Next on my list is to make sure the O2 sensor is grounded properly. Hopefully I can do that tonight.
[This message has been edited by ITALGT (edited 02-17-2015).]
Sorry to bring back, having same issue with code 22 and 35. Tested voltage at TPS, have 4.97 reference, .97 throttle closed, 2.63 at wot. Tried to find required voltage on AllData but could only find reference to .27 and throttle closed, nothing to what it should be at wot. What lead me to this was car requires just a little bit of throttle to start and keep running, once warmed up 3-4 minutes it will remain running but will stumble.
