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A question about the construction of the flywheel. Are the timing teeth, starter gear ring, and the center flange (shown in this photo) welded together as a single piece and bolted onto the crankshaft? https://rennlist.com/forums/11360135-post3.html
Then the second mass is on the other side of the flywheel coupled to the first mass via springs?
From the workshop manual I've attached an image below of the sensor and starter rings and my annotations are a guess as to which is which. This would mean the sensor ring is closer to the engine than the starter ring. The Bentley manual shows a few assembly photos that show that the sensor ring is closer to the engine than the starter ring. If that is true then both starter and sensor rings are on the primary mass attached to the crankshaft.
So a plausible scenario for an errant misfire detection is as follows. Engine running is roughest at idle so the springs need to do lots of damping work and the primary and secondary masses of the DMF are frequently moving significantly against each other. If I happen to engage the clutch to accelerate at a time when the secondary mass is ahead of the primary mass, i.e. at a compression phase, the DMF will try to absorb the maximum rotation. If the spring is weak or broken it won't do so gently but will kick the engine side of the DMF backwards. The sensor ring is on the engine side, and it may detect this kick and sudden rotational slowdown as a misfire.
There are probably several ways to test this hypothesis. One is that when the car is acting up, can I reduce the problem by clutching very very gently? I already know part of this: the problem sometimes occurs at idle (when it's really bad) but far more often when transitioning out of idle into gear, and when transitioning from deceleration to acceleration in gear. It seems not to happen at all when cruising.
From the workshop manual this is the best image of the sensor and starter rings and my annotations are a guess as to which is which. This would mean the sensor ring is closer to the engine than the starter ring. The Bentley manual shows a few assembly photos that show that the sensor ring is closer to the engine than the starter ring. If that is true then both starter and sensor rings are on the primary mass attached to the crankshaft.
So a plausible scenario for an errant misfire detection is as follows. Engine running is roughest at idle so the springs need to do lots of damping work and the primary and secondary masses of the DMF are frequently moving significantly against each other. If I happen to engage the clutch to accelerate at a time when the secondary mass is ahead of the primary mass, i.e. at a compression phase, the DMF will try to absorb the maximum rotation. If the spring is weak or broken it won't do so gently but will kick the engine side of the DMF backwards. The sensor ring is on the engine side, and it may detect this kick and sudden rotational slowdown as a misfire.
There are probably several ways to test this hypothesis. One is that when the car is acting up, can I reduce the problem by clutching very very gently? I already know part of this: the problem sometimes occurs at idle (when it's really bad) but far more often when transitioning out of idle into gear, and when transitioning from deceleration to acceleration in gear. It seems not to happen at all when cruising.
Yes, your explanation of the starter ring and sensor ring is also what I understood. I'm just curious how the flywheel got damaged and what tripped that P0336 code. My understanding is the code is tripped because the DME cannot detect the correct number of teeth and expected reference teeth pattern after a number of revolutions of the flywheel. Obviously if one or more of the teeth are damaged, this code will be tripped but that doesn't explain why it works fine at other times and also can't imagine how towing can damage the sensor ring as it's not touching anything.
So let's say the springs got damaged by towing (car was in 1st gear and handbrake was NOT engaged), your explanation of the second mass kicking back the primary mass which messes up the teeth counting is plausible. However, I think during idle (neutral) the engine is acting up too? It's hard to imagine the second mass itself (plus the clutch and transmission idle shaft) will kick back the sensor ring enough to cause it to miscount but I guess that's possible too. Also, how the temp/time trigger the symptoms?
There are only 4 things: DME, wiring, CPS, flywheel so I'm pretty sure is one of the 4
BTW, I forgot now but did you ever measure the new CPS signal at the DME to confirm the signal's amplitude looks normal when the engine is normal and when it's acting up? Or it's like what you observed with the old CPS that the CPS signal was heavily attenuated when the engine is acting up?
BTW, I forgot now but did you ever measure the new CPS signal at the DME to confirm the signal's amplitude looks normal when the engine is normal and when it's acting up? Or it's like what you observed with the old CPS that the CPS signal was heavily attenuated when the engine is acting up?
No I didn't and now I am kicking myself. I still have the probe wires attached to the DME connector so I can still do this. Will see if I get some time.
I am cross posting this to the couple of threads I started while chasing this issue. It appears to be FINALLY resolved. To recap, after receiving the car back from Flat6 after an IMSB-caused repair, the car violently misfired after some time. It was perfect when put on the truck at Flat6, and really bad right off the truck. It has taken 4 months to get to the bottom of it. I am indebted to Jake at Flat6 and Tony Callas of Callas Rennsport for providing a huge amount of initial help, and especially to Clint Pfeifer at Euro Trends in Ceres, CA who finally diagnosed and chased this down. In the end it had nothing to do with the rebuild, but may be a typical problem for cars with more than a few years on them, possibly especially from northern or other climates where corrosion can occur.
The bottom line was multiple layers of electrical issues: wiring harness and connector corrosion, slowly deteriorating electrical components, resulting in lack of spark when hot and intermittent CPS sensor. P0336 (CPS) fault code always thrown; P030x fault codes (misfires) thrown when severe misfiring occurred. Also learned: the ECU's fault codes are excellent starting points. If it throws a code, that is probably the problem, or very close to it. Don't start looking at other things until the entire diagnosis for the fault code has really been done, all the way down to the wires.
Specifics:
1. 3 key pins of the X59 connector pair in the engine compartment were corroded: two CPS sensor wires and the main V+ wire from the ignition relay supplying power to the hot sides of the coils and injectors. As the engine compartment heated up, the resistance of these connectors increased to the point where spark failed, causing violent misfires progressively getting worse as engine compartment temperature increased (usually while idling or after stopping for gas or an errand).
2. Numerous electrical components were slowly deteriorating and not supplying as much power as new parts: alternator, alternator/starter cable, corroded pins on X59 connector, engine/chassis ground strap. Ignition coils looked fine, but replacing them improved the issues. An additional ground strap was added from transmission to chassis.
3. The sum total of voltage issues eventually crossed a threshold where coils did not supply enough voltage to spark. The dominant problem was the V+ supply to the coils losing voltage at the X59 connector, but it was not the only one. As each component above was replaced, the issues improved but never completely went away until the last link in the chain was replaced.
4. CPS cable in engine harness is compromised somewhere along the line. Replacing the X59 connector pins for the CPS wires reduced the P0336 codes, but did not completely eliminate them. The final fix was to install a completely separate cable from CPS into the DME. This nailed the P0336 codes.
The car has about 150 miles on it since the final fix, under hot operating conditions, and has been running perfectly. Why the transportation from Flat6 to home tipped the scale, we don't know and probably never will. The problems were there all along.
Great thread! I'm working through some misfiring and a new code of P0355 after installing a set of supercup mufflers. My first thought was to immediately replace the mufflers, which I'm planning to do with Fisters.
I recently replaced the starter & y-cable to address slow/no start when hot. The issue is *mostly* resolved in that no start isn't occurring and slow start is occurring pretty infrequently and with less severity. But, the issue is not gone 100%.
Last night after installing the new exhaust I took the car on a spirited highway drive. A-ok, running very well & started up quickly in 85-90F outside temps. High speed shifting & acceleration was smooth on the highway. Once I got back into town I felt what seemed like a clutch slip, but soon realized it was some type of firing interruption - fuel, voltage, I'm not sure. As I drove towards home the problem became worse & threw P0335-Crankshaft Position Sensor A Circuit Malfunction. I stopped to read the code & experienced slow start followed by misfires when trying to accelerate in anything but a smooth, gradual pace.
One data point that's different than the OP is voltage. I've consistently observed 14v after starting and while running with negligible variation.
So next steps... I'm not sure that I have the degree of electrical issues that OP has given my car's history in the southwest (New Mexico 2 years, SoCal 11 years, Utah now 1.5 years). I did observe notable corrosion in the old y-cable (dark and variable coloration vs. new copper unit), and realized there's a similar cable that runs from the front of bank 2 back through the engine bay (this cable is likely corroded as well and could contribute to the lingering hot start).
That's where I am. Worst case scenario I'll take it to my indy. Even with that approach I'd like to give them a good overview to improve the chances of success & reduce exploratory research & parts replacement. The car is sitting until I can get a clear idea on next steps. First order is to investigate CPS replacement as the misfires haven't thrown any codes but I have observed a rare ignition interruption or two in the past few months. My thinking before today was fuel pressure regulator & potentially a fuel pump, but after reading this and combining it with my recent slow start work, I'm less confident the fuel system is to blame.
OP here. It has been nearly 30k miles since the thread and the engine has been flawless after the fixes I described. Well except I found some minor throttle positioner issues a little after posting my last thread (bad throttle position readings, and poor idle) but I forget the codes right now. Given my experience, I focused right away on the throttle electrical connector, and knowing that I had disconnected and reconnected that connector a couple of times during my previous diagnosis efforts, I sprayed some DeoxIT DN5 in both sides of the connector and bingo, problem has been gone ever since.
So I would recommend as a first step taking apart any connectors that have recently been touched, spray DeoxIT DN5 in them, let them sit a while and put back together.
Did a little work today & got some reasonably close shots of the CPS. The code P0335 comes on during moderate to heavy throttle when the car is at the upper end of operating temps, say when coolant is >210F. The impact is sputter in power and the CEL stays solid, no blinking.
Here are some shots of the CPS & incoming wiring. My next step is to buy a new CPS and I'd like to replace the up/downstream wiring to try and remedy the issue. An oscilliscope seems to cost around $100 minimum, so I'm comfortable taking some clearly aged parts & throwing money at it while the costs are relatively low.
Any idea if the Bentley Manual includes a diagram of this data, or if anyon has one handy? I'll keep searching in parallel with inputs this thread.
endpoint of the CPS
a bit closer shot of the input into the housing
looking up at the first connection to the CPS wire
a different angle of the first connector
Last edited by TonyTwoBags; 07-15-2017 at 05:55 PM.
Finally have a new CPS installed. The awkward angle plus me being a dolt complicated the removal & install, so I delegated an hour of labor. After the first drive it seems P0335 is gone. It hasn't come on the last several drives, and pushing it this morning was met with no stumbling and consistent acceleration through the range. If the condition recurs I'll look into replacing the downstream wiring that looks to be nearly due for replacement.
I used a matching Bosch part # for what it's worth.
Replaced the CPS and just recently replaced the starter and battery cables to it. That fixed my slow hot start issue. Before I replaced the CPS, I had to wait a bit before even trying to start it once it was hot. When the car was back on the road, I saw the bucking and no hot start issues were gone, but I could tell the starter was slow when hot.
Interesting. I'm on the fence right now on replacing more battery/starter cables. The y-cable is new, along with the starter (done last month). If the issue persists with slow start when heat soaked, I'll have to scope out a more thorough wiring update. If only it was easier to get to those parts, the work itself isn't very bad!
07-23-2014, 01:44 PM
