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I have a 2005 C2S that developed a rough running misfire upon first start up this spring. I got codes for misfires in each individual cylinder as well as multiple/random misfire code. In realtime monitoring I'm getting misfires in all cyls as well. I get no other codes pending or hard set. I have replaced the coils and plugs, drained the fuel and replaced but no improvement. I have unplugged maf with same result. I had no maf codes until I disconnected it so I do not suspect that. I cleared the maf code and it does not come back. It runs as normal during high idle and then sputters and boggs once it changes to low idle, to the point that it wants to stall. I should also mention that the interior lights dim with rpm as it is struggling to run after it comes off high idle. Is it possible that a poor ground or failing starter /alternator harness would be causing the misfires? I suspect the starter/alternator harness is probably failing as they do even though it has previously been replaced years ago. Perhaps the alternator? I will be removing it and taking it in to be bench tested just in case. Could it be the variocam solenoids? I will be taking them out to test them myself and replace as required. Also one weird thing . With the battery connected as normal and no key in ignition, all doors closed and locked until the engine compartment light goes out by itself (car should be somewhat asleep) I was replacing my serp belt and when leaning on the rear bumper my arms were in contact with the steel fasteners which gave me a tingly shock like a slight bee sting. I was in bare feet on cement floor. Car was completely off ground on quick jacks. It seems I was becoming a path to ground. This can't be normal. Does this confirm that I have a grounding and /or positive lead issue? Could all of this be related to a random misfire in all cyls?
So I am going to replace my alt/starter harness.....clean up the ground straps and see if that illiminates the bee stings and perhaps the misfiring. Here's a pic of the junction where the intermediate positive lead and the starter/alt harness get married. There is another small lead that is also connected there that comes from under the rear cabin and some connector on top of the manual trans. It is visibly corroded and weak to the touch. I can't find it in any of the parts diagrams and have not seen it in any pics I have seen posted of this juction. Anyone know what it is? I imagine it might go into the rear relay box. Ideas?
Wow! It sounds like you've already spent a lot of time and money replacing the coils and plugs, and I would say that the chances of all the coils or plugs going bad after a few months in the garage, is highly unlikely. Certainly it might be fuels system related. and you were right to change the gasoline. Use a fuel stabilizer in the future; Jay Leno has featured a couple of products, here's one:
Addressing your stray voltage question, while this is possible with household 120 VAC, I have never heard of anyone experiencing a shock from 12VDC, and certainly not because they were "grounded" via the ground they were standing on, since this doesn't complete a circuit with regard to the cars electrical system and your tires are insulators as well, your jack-stands have a better chance of being a good path to ground; and I presume you didn't have a battery tender hooked up at the time, which if bad, could have caused that sensation, and worse, could certainly damage the electronics of the car. So if you had a battery tender on the car over the winter, check the output of it and make sure there is no AC present. I would check the continuity of the metal parts on the engine and make sure they have 0 ohm resistance to the chassis/ground. (Remember that on a vehicle, grounding is simply any metal car part that has an unfettered path to the negative side of the battery, there are good grounds, ie, those intended, and bad grounds, i.e. those that are incidental, by virtue of say a screw-head that goes through a something else that's grounded. Anyway, I would start with the basics, and get a full understanding about what the ECU codes can tell you, and what they may not tell you. With my own experience, it takes a lot to get these cars to throw a code so egregious, that it makes the check engine light come on, or maybe before it even logs the code...I don't know. But that aside, because you describe tingling, that type of voltage in a car can only be created by a coil, that could be a coil in a relay, ignition pack, or electric motor; so I would check the fuel pump for a good connection and path to ground. Check ALL of your fuses, who knows, while the fuses should be on the 12V+ side, some circuits could be interdependent, and if there is a failure in a particular circuit, there may not be a reliable path back to ground for another circuit. Find out where any fuseable links are on the car, the tie point you took a picture of looks a bit like a fuseable link, although you would have two studs, not one, unless it's underneath where I can't see it in the picture. Electrical problems can be fairly tricky, especially if you don't have a schematic, and nearly impossible if you're a novice, unless it's obvious, like a lose wire, blown fuse or what-not. Just think, you could have a failing fuel pump relay that's chattering, and you can't hear it, and it doesn't produce a steady fuel pressure to run the engine reliably, but maybe it reaches operating pressure just long enough to prevent a code from being set...who knows!
Have you checked to see if mice built a nest in your exhaust system? Back pressure would definitely cause misfires.
I should clarify. The sensation I got and get in the most sensitive part of ones forearms...the tender underbelly...lol, I wouldn't characterize as a shock. More like what you might have got when touching your tongue to a 9v alkaline battery, even less. If you use the palm of your hand or a finger, you won't feel it. I thought at first I was just leaning on a sharp edge of the fastener and repositioned my arm to find it reoccured the same on all of the exposed fasteners on the rear aprons upper mounts (where the rear lid covers when closed).
I also do not normally work bare footed but when I get an idea to fiddle the car is 5 feet away and stably lifted in a clean, heated clutter free garage so no biggie. I can confirm that when I put shoes on, the tingle goes away......slip one foot out and touch the floor...tingle is back. Battery connected, no tenders, all doors closed except rear lid, and doors locked with no key in ignition. I get the short horn beep indicating the rear lid is open and then a few minutes later the rear engine comp light goes out. Should be sleeping somewhat, even though these cars seem to never sleep.
Car is jacked on a quickjack and insulated from the quickjack by 6" of dense rubber pads at the jacking points and then the quickjack unplugged. esentially the same as if it were sitting on all its tires and insulated from the floor.
I know my fuel pump is working properly from when I used it to drain my fuel tank.
The Junction box I am referring to will be well known by anyone who has replaced their starter/alternator harness. The harness is an infamous cause of poor charging/starting due to a manufacturing defect. Mine was done a few years ago but they do fail again over time depending on many factors such as climate or just plain manufacturing quality in the crimps. Those who have done this have not made mention of the third "mystery" lead coming from the top of the manual trans and the cabin floor as shown in my picture. Nor have I seen it in any pictures of others posts. It looks to be coming from where the rear relay box would be located however I have never had need to access the rear relay box and don't know exactly where it is. I don't see this lead on any parts diagrams. This is a 3.8l C2S so maybe I have something the other posters didn't. Someone must know what this is.
There is zero chance of mice being a problem.
During high idle the exhaust pressure is even and constant from both sides and normal so no nests in the exhaust.
I appreciate that some feel taking it in to get it looked at by experts is a better choice, but I am an expert of sorts...on commercial Jet aircraft though.....and I know that this will be a target to toss parts and labour at. We do the same with the jets but not on our dime. So I want to save a few thousand dollars worth of labour and a toss a few hundred dollars worth of parts at it before I resort to the dealer.
I've got a couple weeks off starting next week so I will be pulling the alternator for bench testing by a alternator shop. When I do this it will reveal the starter harness connection that is usually the point of failure and burned/melted up. I will replace the harness anyway.
I'll cut the mystery lead open where it is corroded and likely cut back to good wire and splice some new wire in for reconnection. It is visibly green and corroded at the crimp even though the tab is polished clean.
I'll clean up all the grounds.
I'll check all the vac lines while I have more exposed.
Start and do realtime recording of all parameters.
If I get weird variocam values on either bank I will remove and clean/test the four of them on the bench or replace if they are faulty.
Gonna be a fun couple weeks . I do actually enjoy doing the work...as long as there is a positive outcome of course.
You could verify/measure the voltage/current from the point on the car where you get the tingle to a real earth ground (Your garage's electrical wiring ground is probably good enough; be careful you don't inadvertently get the hot side).
Then do it with the battery disconnected. Then reconnect the battery.
Then do it while pulling each fuse.
It could be a pinched/chafed wire.
Do you have a way to test the fuel system pressure to see if it's influencing the misfires?
I cant imagine the starter cable is leading to the misfire. The simplest way to diagnose a bad cable is to check the voltage at the alternator and at the battery. If you see more than a ~.5 drop its the cable. You can also shine a flashlight on the rubber boot that covers the cable connection to the starter. You might see heat damage. Mine was melted.
Maybe I missed it in the original post, but how was the car stored for the winter - battery on a tender? How old is the battery?
Without any of the additional information and just the various fault codes, my first thought would have been a weak or failed battery. Is the battery a sealed type or the type with caps where you can check the water level. I think the battery may be internally failed and one or more of the plates shorting which might also explain why you would have voltage bleeding to the ground side resulting in the tingle and why you initially got misfire codes on all cylinders. These cars do very strange things when the font get enough juice from the battery.
Petza914 reminds me of something; many of the ECUs are very voltage & current sensitive, it could be a weak battery that causes problems like weak firing, I remember I had this problem in a BMW 750 years ago, and this was with the engine running! So just because the engine is running and you would think your alternator is then making the voltage and current the car needs, does not mean all the components are getting what they need to run correctly. As far as shorted plates, that would just lower the voltage output.
Remember with voltage, you must complete a circuit, this is why birds can sit on the bare primary wires and not get electrocuted...you might check to see if the breaker box for your house is grounded!
If you have a DMM/voltmeter, try disconnecting one of the ignition coil connectors and putting a probe on the ground pin and checking continuity to the vehicle ground, to make sure it reads close to 0 ohms or is a short. Might want to check all of 6 of them. Could be a bad connection/corrosion in a harness or wire.
Sounds like next step is to swap the battery. That’s an easy one to test.
@Petza914 question: if it was a vacuum leak would you tend to see the engine stumble at higher rpm, vs the low rpm the OP reported?
That's a good thought. Vacuum leaks are usually worst at idle and will result in a wandering and hunting idle. They tend to be less noticeable underway since there's so much more air moving through the engine.
With misfiring on all cylinders, the vacuum leak would be upstream of the split off for the left and right banks, so throttle body, plenum input, airbox, MAF, etc
I keep reading this without wanting to say it ... But ... Rodent damage. The little beasts get into the unseen crannies and chew wires creating all kinds of havoc.
Squirrels built a nest in my Supra Twin Turbo requiring quite a bit of wiring repair when the motor started stumbling. Look for signs and hope there are none. I found acorns where there should not have been acorns.
The tingling is an interesting symptom, 12V is not enough to feel the current- to compare touch both terminals on the battery.
Electricity wants to take the path of least resistance. You “connecting” the rear of the body (bumper hardware?) to the concrete(poorly in electrical conductivity scale), only to go back up the jack stands and back into the body is NOT a good circuit. Any voltage potential at the rear of the body would dissipate through the LARGE crosssection of the unibody to the ground strap at the battery. If it can’t, your car has been cut in half and glued back together with insulating glue. Does that seam silly? It is. If you can’t feel the current when touching both terminals of the battery, adding a couple poor human connections to the concrete and back is only going to reduce the current.
Now if you told me it tickled when you touched the motor, while running, then I would believe a poor engine to chassis ground because you could be feeling the higher voltages of the coils firing into a poorly grounded block, using your body to get back to the chassis.
All this said, you are on the right track with that “mystery lead”. IIRC this is the source of power for the rear relay support- including the feed for the DME and relays. If it truly is a bad connection (easily tested with a voltage drop measurement when loaded) then yes your engine will run poorly if at all.
05-04-2019, 05:52 AM
Chasing my tail...an update....need a clue!
