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It's been a while - I thought I would post an update although the problem remains: My mechanic is a friend so he's done many things so far without charging much: replaced the complete wiring harness with another used one, checked and fixed vacuum leaks, tested throttle body, pedal potentiometer, cleaned fuel tank, lines, & filter, etc. We believe it has to be the ECU! Incredibly, the alternative we had tried may also be faulty so we were misled. My DME is being checked by a local specialist - cannot say if they have the expertise which I see on ECU Doctor's website but hopefully they will come up with something. The only other thing that would be left at this point is the wiring in the front part of the car - though my mechanic says he's had that checked for continuity (including checking behind the fuse box, etc).
Hello, thank you very much for the suggestion. It was one of things I tried: I plugged in the DME of another car and, although the engine would not start with the "foreign" DME of course, this DME also came up in Durametric with the exact same errors and live values. Currently the car is at my mechanic's who has found a severed wired somewhere between the gas pedal and the ECU - I will ask for the details when I get the car back and will update here. Thanks again.
Thanks Ahsai, I managed to unplug the TPS, as a test, and it made no difference. Can we draw any conclusions from this? i.e., if the wiring to the DME were OK and I unplugged a bad TPS would I see anything different? Are these values (30.7% etc) what you get when there is no connection whatsoever to the TPS? I am thinking that, normally, with the TPS unplugged Durametric shouldn't show 5V for it. This suggests a short somewhere in the wiring from the TPS to the DME?
Thanks guys. I just tried wiggling that particular MAF ground. Also disconnected the MAF completely and the plug to the throttle body. No change. I will try Ahsai's suggestions tomorrow (it's nighttime here). Might need some help locating the pedal position sensor - as far as I can tell, there is a metal wire leaving my throttle pedal, which probably ends up to the potentiometers, somewhere behind the dashboard(?). Many thanks again!
Agreed on the wiggling being suggestive (very). That is why I looked there first. However, I think I probably have a good connection near the DME now. Interestingly, the values in an old thread match my own: (pedal value 30.07% exactly and similarly for the voltages)! Update: the guy had also posted the same question elsewhere and there he updated saying the issue was resolved by re-establishing the ground to the MAF! I will have a look - it is pin 9 on connector III for the 7.8 DME.
Thanks JFP, I have updated the original post. So it is likely a connection issue, not much chance of, e.g., the throttle potentiometer(s?) going bad? I have the attached pinout for the 7.8 Motronic. In theory, should I be able to check with a voltage meter if the gas pedal is sending any values? Then again, if the connection is lost, why are the live values 4.54 and 5.00 Volts? If I unplug that section of the DME, durametric shows no values at all. Also, why would there be a lost connection on the throttle plate values as well (and at the same time)? Those are on a separate connector I think (connector III in the pdf). Thanks again! Porsche_DME_7.8_Pinout.pdf
What could be causing the attached faults simultaneously? I parked the car last night - this morning it would not start. I checked and cleaned (contact spray) the DME connectors to no avail. In the past, I had a few occasions when the throttle would "stick" causing the car to idle at around 2500 rpm. Moving the DME connectors around would solve it (I assumed a bad contact on one of the signal cables). I have also checked all the fuses and the plug to the throttle body. The live values on Durametric do not change, no matter how I press the gas pedal. Normally, they will vary - e.g., "Pedal Value" going from around 0%, to 100%. Now, Pedal Value is stuck at 30%. Of note, but I don't believe it is relevant: The engine is an M97.21, the car has been running fine with it since 2010 (I reprogrammed the original DME myself). Any suggestions on how to approach this would be greatly appreciated. I am at a loss since the faults suggest a problem on both ends (pedal and throttle plate). I tried my best to ensure good contact for the wires plugging into the DME - I even removed each of the two "sections" that slide into the safety clip and checked that each wire is pushed all the way forward and locked. I am assuming it is extremely unlikely that the DME itself can go bad only in the circuitry involving the e-gas? EDIT (per the suggestion of JFP below): The car is a 2003 986 s. No modifications to the wiring harness, with the exception of an extension to control the M97.21 engine's two-stage valve lift.
It could have been a bad batch of Pirellis. I have since replaced them with Goodyear Eagle F1 Asymmetrics and there is no shimmy at any speed. I gave the last set of Pirellis to a friend (who also has a Boxster S) and they shake on his car, too. BTW, for a street tire, the F1 Asymmetric's grip is impressive.
Just a quick thanks for Renntech V3. I searched for a thread on this - it is hard to believe that I am the first to comment! :-) The new design is the best I have seen anywhere, period. Fantastic! It is pleasant to read and navigate and it is also stylish. Thank you Loren.
My car is a 2003 986 boxster S with a manual gearbox. There is a M97.21 motor, from a 987 Boxster S with around 14000 miles, which I am thinking of swapping in place of my M96.24 (which is now past 65000 miles). I would have to use my original exhaust system (including headers), my original clutch/gearbox (flywheel is on the new engine), and my original ECU. The shop that proposes to do the work assures me the swap will work without any problems but, since there must be differences at least in the exhaust system and the ECU, I am doubtful. What do you think: Can a competent shop do the swap? Will the engine work properly with the old ECU and exhaust? What could be the greatest difficulties? Thanks very much!
Steve, I agree, but I had paid full price for the first set of tires :-) Only the replacements (due to this problem) were free. I am going for another brand, for sure, but I am curious as to what is going on with the Pirellis. I mean, just the fact that the distributor replaced them three times is odd.
There are quite a few threads already on vibration, or shimmy, but my problem is specific to a tire model and I believe it involves "Radial Force Variation" - an issue that is not discussed so often. This is why I am starting a thread to focus specifically on the N3 Pirelli P-Zero Rosso's. I am currently on my fourth(!) set of these tires (225/40/18 fronts and 265/35/18 rears). Under normal street driving, always with the manufacturer's recommended pressures, the tires eventually develop what feels like flat spots but is more properly described as "radial force variation". The shake can be very intense and disconcerting - enough to make you worry about tire integrity and overall safety. Severity is not constant - it depends on tire temperature (I believe) and it is much worse after having decelerated from high speed, e.g. from 120mph (I am in Europe). The shimmy is present when braking, rolling, or accelerating but it is felt only past 70 mph or so. It does not go away at higher speeds but it becomes less intense due to the higher frequency. It does not feel like coming always from the front wheels. Hard cornering or repeated hard braking have, intermittently and to a varying degree, succeeded in alleviating the problem, only temporarily: It returns with a vengeance either the next day or after a bit of driving. Testing (over months) with combinations of different rims and tires has excluded every other possible cause. Brake rotors were replaced, wheel bearings too, anything rubber in the suspension is good. Balancing also seems perfect. (Unfortunately no shop here has a balancer that exerts a force on the tire - like the Hunter in the USA). In short, putting different tires on my rims (even if they are used), without changing anything else, solves the problem immediately. I have not moved to a different brand/model because the local Pirelli distributor have already replaced the tires thrice(!) for me - free of charge (do they know something is up?). This last set was fine for a couple of months and, for no apparent reason, it now developed the problem. I would appreciate any suggestions on how to escalate this issue with Pirelli or any insight into what might be up with the p-zero rosso (where there any "bad" batches that have found their way into the market?). I should say that grip and response are very good in general so, if not for this problem, the tire would be excellent.
Right, which is why I added the spacers. So now the offset is 47 (42 + 5). If adding a 5mm spacer brings the offset to +47 then the wheel's original offset must be +52 (52-5=47). Offset is the distance between the rim's center-line and the surface which mounts flush on the hub. The spacer "brings" this surface closer to the center-line and pushes the wheels out. So, with spacers, you can only reduce positive offset. Bringing the wheels out changes suspension parameters such as the roll center or the scrub radius. It also reduces the effective spring rate because the wheel acts on the springs through a "longer arm". It could also put more load on bearings etc. So, generally, it pays to be conservative with offset changes. At 5mm, however, there should not be much of a concern, especially if your final offset is 47 - which corresponds to Porsche's post-2002 986 IXRC option: "Sport Techno wheels" (8Jx18 ET50, 10Jx18 ET47). Now, if you do have a rim that is ET42 - and I apologize for doubting you again - and by adding a 5mm spacer it rubs less that before on the outside lip, I must have my definitions wrong.
I usually disconnect the positive. I don't mean to sound like I have more experience than Loren working with cars (I don't :-), and I realize the question is about disconnecting one terminal, not both, but I thought I should point out that if you are disconnecting the battery completely, it is safer to do the negative first.