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I think replacing all coils and plugs is a good idea especially when those were not replaced before. Just think of them as maintenance items. That may cure your problem or at least eliminate themselves as the culprits.
Re the MAF, just unplug it and see if the idle smooths out. If it does, it points strongly to a bad MAF. You can also monitor the MAF values (g/s) and voltage at warm idle. Should read ~1.3v and 14~15kg/hr when no accessories are on.
Those are good tests, BUT there are times when a MAF will test perfectly, but still have an issue during certain ranges of operation can give an issue. It takes very little enrichment differential to create a misfire.
The operation voltage is also a good test, but I have had them test perfectly and still be the culprit.
I have hundreds of good cool packs.. I should give some to you guys so you can ship them to one another for evaluation purposes. That keeps people from having to buy new stuff just to test a theory.
Re the MAF, just unplug it and see if the idle smooths out. If it does, it points strongly to a bad MAF.
I tried this two months ago, the first time it ran rough and the check engine light turned on. Unplugging the MAF did not cure it. I'll try this again soon.
Those are good tests, BUT there are times when a MAF will test perfectly, but still have an issue during certain ranges of operation can give an issue. It takes very little enrichment differential to create a misfire.
The operation voltage is also a good test, but I have had them test perfectly and still be the culprit.
I have hundreds of good cool packs.. I should give some to you guys so you can ship them to one another for evaluation purposes. That keeps people from having to buy new stuff just to test a theory.
Agreed, especially the OP said the fault is intermittent. I was hoping the OP could catch the bad MAF in the act.
BTW, the Bosch MAFs are quite reasonably priced these days. OP, I think this is the correct one but please verify on your own
That matches the Porsche part number (986-626-125-01) at Pelican Parts. I like getting my parts from a local (California) company, but they're selling the Bosch MAF sensor for a lot more. And they have Bremi brand for less.
This morning the engine is running smoothly (intermittent problem), so unplugging the MAF sensor won't tell us anything at this time.
Whatever you do, please only use the Bosch or genuine MAF. Amazon is great. Got my Bosch O2 sensor from them for $100 or so and it's made in Germany.
Originally Posted by DrMEMS
That matches the Porsche part number (986-626-125-01) at Pelican Parts. I like getting my parts from a local (California) company, but they're selling the Bosch MAF sensor for a lot more. And they have Bremi brand for less.
This morning the engine is running smoothly (intermittent problem), so unplugging the MAF sensor won't tell us anything at this time.
Here are three graphs over 28 minutes of running starting with a cool engine. There were zero misfires, so there is no misfire graph. Graphs and comments:
* Engine speed
* MAF, coolant temperature, oil temperature
* Rough running. This is on the same Y scale as my earlier post. Note how the vast majority of the accelerations here running smooth are in a tight window of -5 to +5 rev/s^2, compared to -10 to +30 when running rough.
You can look up the part number on the Bosch part finder (boschautoparts.com/VehiclePartFinder/Pages/VehiclePartFinder.aspx) and search for the part number on Amazon. When I last bought a MAF (early 2013), going this route saved $350 over buying from the Porsche parts counter...
I got some Deoxit from Radio Shack today. I'll try it soon.
Back on the X59 connectors, I tried the following:
* Unplugged them and plugged them back in. The problem with the coolant temperature sensor not being connected recurred.
* I sprayed on the Deoxit as instructed, made the connection, and wiggled the connector to try to scrub off any oxidation, then sprayed a little more on. The Deoxit goes on as a liquid. I waited 30 minutes for it to dry, but it didn't. I wiped off as much as possible, then remade the connection. The temperature sensor was still not connected.
After 15 minutes of driving, the connection to the temperature sensor was remade. The engine is still intermittently running rough.
The residue is a protectant and it's not supposed to dry up so no worries there. Not sure what's the deal with your temp sensor though.
Originally Posted by DrMEMS
Back on the X59 connectors, I tried the following:
* Unplugged them and plugged them back in. The problem with the coolant temperature sensor not being connected recurred.
* I sprayed on the Deoxit as instructed, made the connection, and wiggled the connector to try to scrub off any oxidation, then sprayed a little more on. The Deoxit goes on as a liquid. I waited 30 minutes for it to dry, but it didn't. I wiped off as much as possible, then remade the connection. The temperature sensor was still not connected.
After 15 minutes of driving, the connection to the temperature sensor was remade. The engine is still intermittently running rough.
Hi Flat6 or Ahsai Mine is a little different too, the only misfire I get is cyl #2 NO other cyls. If I baby the car the code P0302 will not come on for weeks, but the moment I spin the tires or punch it hard from a dead stop the code P0302 will come on instantly. I have done a leak test, smoke test, changed coil and spark plug, new injector. Im running out of options so with that being said would this BDMEM 7.8 would that fix the problem and if it does where can I purchase it ? also lately ive been getting P0430 code but it only does it once in a blue moon when I fill up the tank. when I get the codes I erase them with the scan-tool. and then it never comes on again until the next fill up.
Hi Flat6 or Ahsai Mine is a little different too, the only misfire I get is cyl #2 NO other cyls. If I baby the car the code P0302 will not come on for weeks, but the moment I spin the tires or punch it hard from a dead stop the code P0302 will come on instantly. I have done a leak test, smoke test, changed coil and spark plug, new injector. Im running out of options so with that being said would this BDMEM 7.8 would that fix the problem and if it does where can I purchase it ? also lately ive been getting P0430 code but it only does it once in a blue moon when I fill up the tank. when I get the codes I erase them with the scan-tool. and then it never comes on again until the next fill up.
Medevack, I was chasing a odd misfire and it turned out to be a leaking seal for the variocam adjuster solenoid. They are cheap, so replace them to eliminate the possibility.
Yes, I remember your case. It sounds like lifters to me but I'm not sure. I think only the variocam test per the service manaul can confirm. I'm not familiar with the BDMEM 7.8. Is it an aftermarket flash? I can't imagine how it could fix a single cylinder misfire.
I also rememeber Peter's case of leaking variocam solenoid seals. I still have to understand how air leak into the engine head/crankcase can cause a single cylinder misfire but maybe like Jake said, it's possible when the a/f ratio is not optimal, it could make just one cylinder misfires, or at least affecting one cylinder much more prominently.
P0430 is bank2 catalytic efficiency below limit so it's likely your bank 2 cat going bad/element loose. You can monitor the four O2 sensor voltage in real-time when driving to troubleshoot it.
Originally Posted by Medevack1
Hi Flat6 or Ahsai Mine is a little different too, the only misfire I get is cyl #2 NO other cyls. If I baby the car the code P0302 will not come on for weeks, but the moment I spin the tires or punch it hard from a dead stop the code P0302 will come on instantly. I have done a leak test, smoke test, changed coil and spark plug, new injector. Im running out of options so with that being said would this BDMEM 7.8 would that fix the problem and if it does where can I purchase it ? also lately ive been getting P0430 code but it only does it once in a blue moon when I fill up the tank. when I get the codes I erase them with the scan-tool. and then it never comes on again until the next fill up.
Until you get the X59 issue worked out, you can have all sorts of phantom issues. This is especially true with the coolant temp sensor, as the engine looks to CLT for most everything of significance. With a bad connection there, leading to no gauge signal, you could have all sorts of issues.
Those are good tests, BUT there are times when a MAF will test perfectly, but still have an issue during certain ranges of operation can give an issue. It takes very little enrichment differential to create a misfire.
Following up on Jake's suggestion that the MAF sensor could be a off a little, I got a new Bosch MAF sensor (thanks to Ahsai for pointing out the cheapest one on Amazon).
I ran a warm-up cycle from cold with the old sensor, then a few days later with the new sensor. At the cold start, both times the engine speed was 1100 rpm (see graphs below; I reved it a few times to see if anything unusual would happen). Both times there were a small number of misfires recorded by the Durametric (but no CEL) and the engine felt rough for the first minute or so. The roughness was confirmed by the Durmatric's "rough running" rotational acceleration measurement of up to +/- 8 rev/s^2 (see bottom graphs). During this time, the engine speed remained constant, but the measured mass air flow rate slowly dropped. This is expected because the volume flow rate is constant (0.5 X engine speed X displacement) and the air temperature is slowly rising, making the air less dense, so the mass flow rate falls.
Both times, when the coolant warmed to about 26 C, the engine suddenly smoothed out. I could feel it and the rough running measurement showed it, dropping to +/- 2 rev/s^2.
Later, when the coolant reached about 33 C, the engine speed dropped to 700 rpm.
The old and new MAF sensors give about the same flow reading at the cold start (39 kg/hr), and also when the engine speed dropped to 700 rpm (19-20 kg/hr). I can't see that the new MAF sensor changed anything.
02-12-2016, 01:37 PM
