Ahsai

It's normal if it's just a slight suction. Healthy crankcase vacuum reading is around 5" of H2O.

Frank, sounds good. I can only do local ~20 min drives next wk. Can only do more controlled highway runs a couple of wks later. Will report back.

Any CEL and error codes? Have you tried disconnecting the MAF and drive around? Do you have Durametric or any OBDII scanners? I think the key is to find a shop that is willing to actaully diagnose it for you as opposed to just throwing parts at it. Also, any mods on the intake? Cleaned the idle stabilizer?

I agree that tires can get hot depends on how you drive (e.g., sudden accelaration and deceleration) but the OP is talking about the rims and he seems to imply steady speed, light brakes kind of cruising. I doubt the tires can heat up the metal rims to 170F under that condition.

OEM 997 shifter is still shorter (and much tighter) than stock 996 by 15-20%, just not as short as an SSK.

Definitly something is wrong and I really doubt it's from the radiator. Fresh air goes through the radiators and exits at the sides of the front bumper bottom, right ahead of the front wheels. The front wheels are seperated from the radiators by the plastic wheel liners, completely isolated from the radiators. In fact, there are brake ducts diverting fresh air from the bottom of the front bumper to the wheel/brake/rotor to keep them cool!

According to the Bentley manual, each battery cable has a 35mm^2 cross sectional area of copper, which is just a hair fatter than AWG 2, which has a 33.6mm^2 cross sectional area http://en.wikipedia.org/wiki/American_wire_gauge

C2 or C4? Under similar condition, my rear wheels are warm to the touch and front wheels are just a little above room temp....nothing near 170F. I heard sometimes you have to remove the rotor and rotate the wheel hub by hand to feel a marginal bearing. The wheel hub is a lot lighter than the rotor + wheel so any grittiness of the bearing will be easily felt.

Also curious to see more details. That's quite a story. "I once again decided against the new IMS bearing" <- So you took the whole engine apart but decided to reuse the original IMSB or put a new OE IMSB?

Glad things work out for you James and good call on fatter cables :clapping:

Hi James, I do not know the length but my guess is it's <0.4m so the resistance will be at least 10 times less if you only use one 4 gauge cable (resistance directly proportional to length). With THREE in parallel, the resistance will be 30 times less than a single 4m 4 gauge cable. Power = I^2 x R so for the same current I, the power produced by the cable (as heat) will be 30 times less.

Btw, have you considered adding the cable you plan to make at a different location (somewhere on the engine case and the chassis) as a temporary extra ground strap while waiting for the OE ground strap?

Your test C reveals that the ground strap is bad because the airfilter bolt and the engine are separated by the ground strap. Similarly, the engine case and chassis are separated by the ground strap (obviously) hence you saw 1.x volt in both cases. The Toyota tests were just to illustrate the principles in general. On Toyotas, the battery and the alternators are both in the engine bay so the cables are much shorter than ours so it's not surprising our cars have a little bit higher drop but now I think 0.35v sounds pretty good (especially after I measured mine :eek: ~0.7V all lost on the insulated side). So I think you can probably ignore #28 for now, which is actually good news since I can only imagine the labor for that... I do agree with Loren and JFP that using the stock ground cable will be the best considering the labor to replace it. However, if you need a stop gap solution, as long as the "aggregated" thickness is comparable to the original ground strap, you should be fine. Heck, anything will be better than your current situation! :thumbup:

James, I just did Test A on my car and what do you know, I got 0.46V with a/c and headlights on (total ~57A load). Test B I got 0.037V (i.e., very good ground strap). My alt +ve is 13.84V (a little low), eng +ve term is 13.34V, and battery terminals are at 13.18v. Therefore between the alt and the battery, I lost total of ~0.7v (~0.5V on what's equivalent to your #28 + ~0.2V for the rest of the cables in between). Hope that gives you a reference. Even though I don't have any symptoms, based on the measurements above, I would want to change that #28 to the updated version some time.

All right! Glad you confirmed the culprit. Just realized I meant to ask you to use the jumper directly on the engine and not the airfilter bolt. Thats why you didn't see improvement. Anyway, I think 0.22v vdrop on #28 is still excessive and should be addressed eventually as well. Regarding ground strap, I think you can replace with equivalent but keep in mind that the cable is exposes to the elements so you need to make sure it is weather proof. As long as it's as fat and as short as the factory cable with equivalent crimps and heavy connectors at its ends, I think you would be fine.

You're welcome James and I really hope you can confirm it's the ground strap before replacing it due to the labor. Sorry I forgot you have a TT. I can see both ends of my ground strap ('03 C2). "can I simply use the engine shell as a replacement?" <- YES "on the battery or the lead?" <- clamp it directly on the battery end of #1 without disconnecting #1 from the battery. Just make sure #1 is tightly on the -ve battery terminal. Yes, test with ac and headlight ON just like other tests. Good luck!

Btw, I don't think reving the engine will have much effect on the voltage drop because the alt output voltage is regulated by the solid state regulator at the back of the alternator at all engine speed. I.e., your battey gauge reading does not change based on the rev either. The exception is if your alternator is marginal and doesn't regulate the output effectively, then the ouput voltage may rise a bit when you rev up the engine.

All right! I think you're zooming in. Test A result is too high at 0.22v for such a short cable (#28). Your total vdrop on the insulated side is 0.33-0.4v and that's over the whole length of the car between the alt +ve to the battery +ve term and you lost 2/3 of that on cable #28, which is only a foot long. So I think you have to address that sometime. Let's fix the ground side first since that's the biggest drop. Can you do the following Test C? Vdrop between airfilter bolt and engine side of ground strap (#36) Vdrop between engine side of ground strap and chassis side of ground strap Vdrop between chassis side of ground strap to chassis side of #1 (battery -ve cable) Vdrop between chassis side of #1 and -ve battery terminal If you see any big drop, you found your problem. Then try to add a jumper cable to short out that problematic section. If you want to see another confirmation of ground problem, you can use a jumper cable to short out the -ve battery terminal and the airfilter bolt and you should see immediate improvement. Try to use gauge 8 or fatter jumper cable. Good luck!!

Exactly, you got the idea now :) basically hunting where you lost that 1.8v between the alt and the battery.

It does look like the ground strap is the culprit but I still want you to verify with test B above, where you should see 1.8-1.9v shown on the meter. Actually the quickest way is to do the two toyota tests in the link I sent above. Then you immediately isolate whether you lost the voltage (~1.8v) on the +ve branch of the circuit or the ground branch or a little bit on both. Lets see what you get first before thinking about test C...so far everthing points to the ground branch. The only thing I cannot reconcile is why your jumper cable connecting the engine and the chasis did not help. If the problem is trully in the ground branch, i dont see why you need to gain access or touch anything on the +ve branch (i.e., starter and transmission).

James, what I was saying is turn on the cold engine, a/c and headlight and let it idle. Then set your multimeter to DC 2V range. Test A for #28: Put the red probe on the "+ve alt terminal" and the black probe on the "engine +ve terminal (#29)". The meter should read very close to 0v if #28 is in good condition. If you see +0.3v or higher, you know #28 and/or its contacts are questionable. Test B for #36: Put the black probe on the "alt casing" and the red probe on the "airfilter bolt". Again, it should read very close to 0v if #36 is in good condition. If you see +0.3v or higher, it means #36 and/or its contacts are questionable. You can repeat tests A and B when the car has warmed up. Also, you can do another 2 tests described on page 14 here http://www.autoshop101.com/forms/h8.pdf Same principles.

Ok, looked at your tests more carefully seeing how methodical you are, I would guess you are an engineer :) A few comments first. Forget about measuring the resistance since the problem may be (and most likely) are at the connection points so even if the cable itself is perfect, you lost voltage across those bad connections. If you remove the cable, you lose the chance to detect those bad connections. Besides, a regular digital voltmeter (200ohm range) will not be able to measure the low resistance accurately. The resistance of the measuring probes themselves may be in the same order of magnitude. So focus on the principle of applying a high current on the segment you want to measure and then measure the voltage drop between the ends of the segment in question. I suggest you turn on the a/c and headlight (like you did) then measure the following. You should see close to 0v and not even 0.1v - voltage drop between alt +ve terminal and engine +ve terminal (#29) - this will verify #28 - voltage drop between alt casing and the airfilter bolt - this will verify #36 Use the same principle to trace upstream all the way to the battery for different +ve segments from the engine to the battery. None of the segments should have a significant voltage drop. I would say 0.3v max.... Hang in there and I'm sure you're getting pretty close already. Again, try to focus on measuring voltage drop and not the resistance. For reference, when a/c and headlights are on for my car, the alternator puts out ~40A and I measured almost 0v for those two set of test points I suggested above.

Since you have Durametric already, why not read the real-time O2 reading for all 4 sensors to confirm? Will also help after you replace the faulty one to confirm the repair. A working pre-cat sensor should flip between 0.2v to 0.8v around once per second during idle. Many threads on this topic. One here http://www.renntech.org/forums/topic/43522-p2096-porsche-fault-code-16-oxygen-sensor-ageing-delay-bank-1/#entry234254

Can you use a jumper cable to make a "parrallel connection" with the ground strap to see if you get improvements? To test the ground strap, you could just let the engine run and turn on some heavy accessories. Then measure the voltage drop between the engine and the chasis close to where the ground strap is bolted on. If your previous measurements were correct (quoted below), you should see about 1.2v to 1.8v (which is WAY too high). "Voltage +ve directly from alternator (I fitted an independent lead from the alternator) -ve Hydraulicoil oil body / engine / gearbox / alternator case =14.0v (hot/cold) +ve directly from alternator -ve airfilter bolt / chassis / door lock =12.2v (hot) or 12.8v (cold) "

Some posts I saw before with similar symptoms traced to a faulty evap valve. The intake is pulling vacuum on the gas tank via the valve then it stals the engine.