Let's Play Guess What CEL 5-8 Issue I have!

I've been getting the occasional CEL 5-8 on the 348, but only on sustained RPMS over 5-6k. In other words, the quick jaunt up to 7k in first or second will never light the bulb, but 3rd or 4th (yeah, I'm moving pretty good by the time I hit that in 4th) will cause the CEL to light, then go out as soon as I up shift.

There may be a slight reduction in HP, but not much. No issues at all driving around town.

Yes, I'll pull the codes this weekend. I just thought it would be fun to see who could guess correctly.

I'm predicting a battery or alternator issue, simply due to the strange correlation to high RPM. Maybe a slipping belt...

 

This only an uneducated guess....but I'm guessing a crankshaft speed sensor...

But, what do I know? I'm only guessing.

Mike in Kuwait

 

...where is the brotherhood on this??

 

Good guess, but unlikely.

Replaced that about 4 months back after the connector disintegrated (thanks Ricambi!). Unless of course that pesky thing has come loose or shattered again, which is possible.

Italy seemed to have a poor grasp on the plastic manufacturing process in the 80's, as did several other countries.

(Jeopardy music playing in background)

 

They're still writing their answers down on that little screen thing.

Remember, whoever guesses the correct code (when I pull it) wins fabulous prizes*!














(*an empty box from a twleve pack of miller lite)

 

Well, I may be, and probably am, wrong.... but at least I guessed...!!!!

Mike "NOT Alex Trebek" in Kuwait

 

I finally got around to pulling the codes. Today the usual CEL 5/8 poppped on shortly after full throttle. The car also stalled when I pulled in the drive way, which is a new issue, but it did start right back up and idled fine.

Anyhoo, looks like I have a 1113 and a 1211.

In my limited experience with these cards, the 1211 seems like a pretty general error that can be caused by a slew of things.

The 1113 is the pot on the throttle. I suspect that the engine could be running horrendously rich or lean if the ECU can't tell where the throttle is, or thinks it is in the wrong spot.

Any of you encounter the throttle pot warning? I'm going to dig on the site, but on the off chance I don't find any info I'd love some "brotherly" advice.

I'll be pulling the pot and cleaning it / contacts tomorrow.

 

Hey John,

I had those light up on me about 8 months ago but on the 1/4 side... same thing as you stated mostly with high RPM but also with lower rpm sometimes. After changing O2 sensor (which turned out to be a waste of money) and trying to resolve the issue for months, it turns out that the solution was the most simple thing... cleaning the connectors of the TPS sensor and Phase sensor!!

I hope this helps.

 

Thanks Dean. I changed the phase sensor about 6 months ago, but I'll check that also.

I'm encouraged that it may be a simple fix. I'll likely swing by Radio Shack and pick up some pot cleaner and then check out the contacts tomorrow.

Will post results.

 

Stopped by Radio Shack and picked up some Potentiometer Cleaner (aka tuner cleaner and lubricant). I also found some nifty contact cleaner/de-oxidizer and stabilizing coating spray so I picked that up as well.

Back at the bat-cave, I removed both throttle position sensors. Immediately I could see one problem. By sticking my finger in the plastic actuator inside the pot and rotating the unit back and forth I could feel the oxidation; it skipped and felt like sand was inside it. I blasted both with some tuner cleaner and moved them back and forth until smooth. What a difference.

Next I disconnected all of the quick remove clips from the ECU, TPS, Coil, etc. and cleaned the contacts on both sides, then used the protectant.

Finally, I hooked the battery back up (don't forget to disconnect if you plan on spraying stuff on your wires) and performed the sacred idle re-learn ceremony.

The first thing I noticed was the sound-- the change in timbre of the engine at high RPM is night and day now. The roar is now more of a scream, and throttle response is dramatically improved. The car jumps from 4-7.5k RPM now so fast I almost mis-shifted. A test run with more than a few taps of the rev limiter received ZERO check engine lights, and even a couple chirps shifting from 2nd to third. I hadn't realized how much power this silly problem was costing me.

Assuming the improvement holds, I suspect that the pots become inaccurate, or in extreme cases, probably are grounding out and sending the ECU and erroneous reading. I really should have hooked the pot up to an oscilloscope for some before and after graphs, but in any case, I think this will become bi-annual maintenance for my car.

Anyway, 2008 is off to a good start!

 

Nice fix!

 

Great news John! Was the difference in sound and response you mentioned a result of cleaning the TPS? If yes, I would like to do that too. Can you provide some detail on how you did the above (how to remove them and did you disassemble them)? Any pics?

Did your 5/8 light go away?
Thanks,
Dean

 

Yes. CEL is gone. Only drove about 10 minutes, but I normally would have seen it by then. I was also already at operating temperature due to the idle re-learn, so I am fairly confident it is resolved.

The procedure was pretty simple. I removed the cables on the two TPS, then removed both screws on the TPS. After the screws are off, they pull right out. The pot only rotates about 100 degrees or so, so I think it will only go back on one way. Might want to take pictures or mark the unit just in case.

Once the unit is off, flip it over and you will see the innards: a white ring, a rubber seal, and the keyed plastic slot that the throttle arm fits inside. I jammed my pinky finger up into the pot and "felt" the movement for scratchiness and debris, and to establish a baseline. I then aimed my pot cleaner up into the innards, around the ring, and into whatever crevice I could find and gave a few short blasts. After that, I checked the movement again and actuated the pot back and forth about thirty times to loosen up any oxidation. It felt like sand was in the pot at first, but then smoothed out.

After that, I just reassembled and reset the ECU. I'd imagine that the corrosion made the TPS read out of sync with my actual throttle position, making both sides not "jive" with each other and almost certainly screwing up my air/fuel mixture. Perhaps No Doubt can comment on how critical the accuracy of this sensor is? Does the ECU only care about 20 degree increments? 45? Or is it a fully analog sensor-- in which case I imagine any "scratchiness" in the signal would rob us of our precious, precious horsepower.

Thinking about it, this hypothesis also explains why my car stalled after the most recent CEL; the pot was likely seding data saying my throttle was wide open/shut and it was flooding/starving my 5/8 side.

For the record, almost all of the contacts on my car looked VERY clean compared to pictures I've seen on these boards. In this regard, I suspect others may benefit from this procedure as well.

BONUS: I pulled all my window switches out and my door connector and cleaned those as well. Fixed my intermitent window problem also.

 

Yes they will, and great work!

Another valuable thread for fixing your 348 on the cheap............Brotherhood style!

 

Nice writeup!


Cool way to start out the New Year.





*on M2.5's, the TPS isn't very precise (idle, mid-range, and WOT)
*on M2.7's, the TPS measures in 1% increments from 0 to 100

 

So the most important part of this procedure is that after I remove the cables and then remove both screws, before removing the TPS I should mark the unit because it has to be put back exactly at the same angle it was? If not this will mess up its setting?

 

It's the shaft under the TPS that matters. When you lift up each TPS you'll see a metal shaft that is semi-circular. Just note the position of the flat side. The plastic on the underside of the TPS will have a flat side on its inner cylinder that lines up with the flat side of the metal shaft (so after you've WD-40'd that inner cylinder, be sure to return it so that it will once again line up with the metal shaft's flat side).

But, keep in mind that each TPS is inverted from the other, so the shaft won't be in the same position for both TPS's. Speaking broadly, the shaft will be where the TPS is all of the way turned to one side for one TPS, and all of the way turned to the other side for the second TPS.

 

My experience suggests there is only one way you will be able to put the pots back on the shaft, so long as your keep the 5/8 and the 1/4 on their respective sides (if they are different).

 

Thanks guys! Will do it this weekend.

 

Same TPS. They just go in different directions based on being mounted on left or right side.

 

Thanks for sharing this with us John. Dean, here are a couple of pics from when I serviced mine:

1. Removal of the 5/8 bank TPS. (Disconnect wires, remove screws and pull TPS straight up.)
2. Note the flat surface on the spindle that comes from the TB and how it mates with the pot on the TPS.
3. Cleaning my pot, LOL.
4. Taking a resistance measurement (throttle closed, hook up your multimeter to the 1 and 3 pins on the TPS).
5. Resistance measurement pulling the throttle cable to roughly half open.

Note that your measurements will be reversed between banks; i.e. the 5/8 bank TPS shows low resistance when closed, and increasing resistance as the throttle is opened. On the 1/4 bank, resistance starts high with throttle closed and drops as the throttle is opened.
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Eric, thanks so much for the pictures! What did you use from Radio Shack to spray the inside?

 

I don't know if it is the same stuff John found: Radio Shack SKU #: 640-4345 "Precision Electronics Cleaner" claims to clean away dust, dirt and oxidation inside electronic devices. Had similar results to John in that my pot was a little rough rotating and smoothed out after applying this spray. "Safe on most plastics" - I'll report back in the morning if it turned my TPS into a pile of goo!

 

My stuff actually refernced tuners as I recall, but I'll check when I get back home and post the exact name.

I think that many different solutions would work, but I stuck with a poteniometer (aka tuner, volume knob) cleaner since it was specifically designed for this use. An oil based lubricant may actually work better due to the humidity- ND?

For the record, motor is still running MUCH better (faster start, smooth idle and much more power), and my TPS are still not a pile of goo. Anxious to hear other results.

 

Hey, you're the new expert on tps's! I used your tutorial and just sprayed in WD-40. Took my wife to a nice Italian lunch at Cafe Ciao today to try out this 348 cleaning, and it worked just fine.