DME? engine died @idle, rough at ~3K in gear when accelerating
04-05-2008, 02:43 PM
#16
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update for anyone still following: I just tested the engine at idle with primary, then secondary, distros unplugged from coils. Each one offered similarly crappy throttle response, so i can't conclude that just one of them is bad. Possibilities:
- Both are on their last legs. I suppose it's possible they both have gone to pot simultaneously, but that seems…unlikely
- It's one of the aforementioned idle/throttle microswitches. I still really don't know what to look for here, nothing looks physically broken or disconnected in the vicinity of the idle control valve
- It's R41, which I still haven't replaced/tested with a homemade jumper. An actual R41 replacement shows up Monday.
- It's bad fuel. I still can't see how this could be the case because I wouldn't expect the engine to run well when spun up at idle, let alone under load. It still sorta runs pretty well between 3-5K RPM out of gear.
Argh. Such a nice spring day here for futzing with this problem, and I can't yet rule out every possible cause.
- Both are on their last legs. I suppose it's possible they both have gone to pot simultaneously, but that seems…unlikely
- It's one of the aforementioned idle/throttle microswitches. I still really don't know what to look for here, nothing looks physically broken or disconnected in the vicinity of the idle control valve
- It's R41, which I still haven't replaced/tested with a homemade jumper. An actual R41 replacement shows up Monday.
- It's bad fuel. I still can't see how this could be the case because I wouldn't expect the engine to run well when spun up at idle, let alone under load. It still sorta runs pretty well between 3-5K RPM out of gear.
Argh. Such a nice spring day here for futzing with this problem, and I can't yet rule out every possible cause.
04-06-2008, 04:45 AM
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You haven't said whether you've checked the battery connections as suggested earlier. I had similar, if not entirely the same, symptoms some time ago. Improved no end by soaking the earth cable from the from the battery to the car with WD40. Then had the cable replaced (there was an updated part and my car still had the old one). Problem gone, no returned yet.
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04-06-2008, 09:11 PM
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Cleaned off battery ground cable; WD-40'd it, scrubbed batt. post and clamps/tabs. No dice; still runs as crappy as ever under load. I'm going with R41 until that's proven wrong, maybe tomorrow evening when it arrives, at which time fuel pump, idle microswitches, and who knows what else are to blame. I can't tell if the current performance is indicative of stuck open loop mode, limp-home mode, or anything else, but it sure seems the DME is literally in the middle of this.
Attached a photo of the ground cable as proof it looks pretty good.
Attached a photo of the ground cable as proof it looks pretty good.
04-07-2008, 04:43 AM
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you're right, the cable looks pretty good, mine did look a bit green. The updated cable fitted to my car has a plastic sheath, but it does sound like the problem lies elsewhere.
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04-07-2008, 01:49 PM
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In my '90 C2 I had the exact same issues last year/summer. Took the car in to a Porsche only shop that I trust unconditionally. We went through, as I recall, just about everything. Wound up replacing cyl head temp sensor, and swapping in/out Motronic with a known good box - all to no avail. Same intermittent terrible idle, terrible hesitation under load, seemingly misfiring and/or running on less than 6 cylinders. All up; we wound up cleaning the ISV and car ran flawlessly for the season.
Return of symptoms just this past weekend as car was brought back to life after storage. Checked all, referrring to Adrian's book, et al. No change to the very itermittent coming and going of the full cast of symptoms as above. Reseated the ISV electrical connection, checked the battery connections, car is running normally again - jeez WTF ?
The thing that bothers is that neither the shop, this thread or others I've read have seemed to have gotten the root cause. I sure would like to know as/if you
get this solved. Good luck.
Return of symptoms just this past weekend as car was brought back to life after storage. Checked all, referrring to Adrian's book, et al. No change to the very itermittent coming and going of the full cast of symptoms as above. Reseated the ISV electrical connection, checked the battery connections, car is running normally again - jeez WTF ?
The thing that bothers is that neither the shop, this thread or others I've read have seemed to have gotten the root cause. I sure would like to know as/if you
get this solved. Good luck.
04-07-2008, 08:40 PM
#23
Instructor
Are you sure the TSB as describe din this thread has been done?
https://rennlist.com/forums/showthre...ng+Harness+Mod
With the engine cool you can just about reach behind there to feel the wires on the sensor, but is easier with the airbox side off. An easy thing to check and eliminate from the mystery...
https://rennlist.com/forums/showthre...ng+Harness+Mod
With the engine cool you can just about reach behind there to feel the wires on the sensor, but is easier with the airbox side off. An easy thing to check and eliminate from the mystery...
04-08-2008, 12:18 AM
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Shoot, missed everyone's latest posts. Must've missed email alert.
Replaced R41 tonight with the new 993. part Adrian specifies, performance not even slightly changed. (Still sucko.)
@mike_99l: I'd like to think so since that'd be easy, but fuel filter was replaced 2/07 and visually looks clean. They should last several years, yes?
@mpeters951: Cleaning the ISV seems pretty doable because it's easy to access in the compartment and, hey, it worked for you! Is this 993 approach similar enough to the procedure you went through? http://p-car.com/diy/isv/
@AB_oz: That TSB looked a bit tedious to get into properly, but I'm officially ready to try anything! Certainly worth a look next.
So, I think I'll try the TSB check first, the clean up the ISV. One thing to revisit: this literally started happening while accelerating in second gear, about 2 miles after filling the tank at a gas station I haven't visited before. I suppose it's still possible I've got bad gasoline in there, or maybe I absent-mindedly chose 89 octane instead of the usual 93. But the car would run rough rough at idel or under load if the fuel was bad, right?
Thanks for all the posts! The fact that anyone's still out there listening is encouragement enough to keep trying to resolve this myself! If the next two checks fail, it's off to Eurosport. Sigh.
Replaced R41 tonight with the new 993. part Adrian specifies, performance not even slightly changed. (Still sucko.)
@mike_99l: I'd like to think so since that'd be easy, but fuel filter was replaced 2/07 and visually looks clean. They should last several years, yes?
@mpeters951: Cleaning the ISV seems pretty doable because it's easy to access in the compartment and, hey, it worked for you! Is this 993 approach similar enough to the procedure you went through? http://p-car.com/diy/isv/
@AB_oz: That TSB looked a bit tedious to get into properly, but I'm officially ready to try anything! Certainly worth a look next.
So, I think I'll try the TSB check first, the clean up the ISV. One thing to revisit: this literally started happening while accelerating in second gear, about 2 miles after filling the tank at a gas station I haven't visited before. I suppose it's still possible I've got bad gasoline in there, or maybe I absent-mindedly chose 89 octane instead of the usual 93. But the car would run rough rough at idel or under load if the fuel was bad, right?
Thanks for all the posts! The fact that anyone's still out there listening is encouragement enough to keep trying to resolve this myself! If the next two checks fail, it's off to Eurosport. Sigh.
04-08-2008, 08:12 AM
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Yes/10-4 to the Q on 964 ISV cleaning procedure vs. same for the 993 ISV. Rennstatt of Ann Arbor, the shop in which I've complete confidence, is a bit mystified by my situation last year that sounds exactly the same as yours now.
They went through all the fault codes, replaced everything even remotely related and anything they honestly thought could/would help in order to narrow the gremlin search, put a lot of diligence into reading all the related matters/TSB's/Rennlist posts and still the "solution" devolved to cleaning the ISV. They had also looked very closely at and cleaned/re-sealed the AFM to cross that off the list. The throttle position sensor and Motronic were swapped with known good units and subsequently proven to be good. They still scratch their heads on this problem as do I.
As previously indicated, a return of all the symptoms you describe visited me last weekend upon putting the beast back on the road after winter storage. Drove it a half dozen times with increasing stress level. Cleaned up all throttle related bits and unseated/re-seated electrical connection to ISV and the bloody thing runs as new - now for the last 3 days - fingers still securely crossed.
I wish I understood the root cause. Best of luck.
They went through all the fault codes, replaced everything even remotely related and anything they honestly thought could/would help in order to narrow the gremlin search, put a lot of diligence into reading all the related matters/TSB's/Rennlist posts and still the "solution" devolved to cleaning the ISV. They had also looked very closely at and cleaned/re-sealed the AFM to cross that off the list. The throttle position sensor and Motronic were swapped with known good units and subsequently proven to be good. They still scratch their heads on this problem as do I.
As previously indicated, a return of all the symptoms you describe visited me last weekend upon putting the beast back on the road after winter storage. Drove it a half dozen times with increasing stress level. Cleaned up all throttle related bits and unseated/re-seated electrical connection to ISV and the bloody thing runs as new - now for the last 3 days - fingers still securely crossed.
I wish I understood the root cause. Best of luck.
04-08-2008, 08:33 AM
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mshobe
"fuel filter was replaced 2/07 and visually looks clean. They should last several years, yes?" - yes provided they don't get clogged - in which case they can last as little as a few seconds.To check - disconnect the fuel line after the filter - turn the fuel pump "on" and see if there's a significant amount of fuel flowing.
Dual distributor system, while independent from one another, both are required to be functioning for proper engine performance.
Hope this helps
Bill
fuel filters should last 7 years provided they
"fuel filter was replaced 2/07 and visually looks clean. They should last several years, yes?" - yes provided they don't get clogged - in which case they can last as little as a few seconds.To check - disconnect the fuel line after the filter - turn the fuel pump "on" and see if there's a significant amount of fuel flowing.
Dual distributor system, while independent from one another, both are required to be functioning for proper engine performance.
Hope this helps
Bill
fuel filters should last 7 years provided they
04-12-2008, 06:43 PM
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Update: thoroughly cleaned ISV, re-seated electrical harness, exact same problem persists. Listening to the car "breathe" on this latest test, I noticed the hesitation is actually occurring in neutral as well, not just under load (but hesitation/"burping" is similar). My dad took a listen and after a quick look in Streather's book has concluded it's most likely in the airflow sensor/intake temp meter. So, off to this TSB next. If THAT doesn't suss it, then I hand the whole mess over to Eurosport because then it's time to start experimenting with high-dollar part replacement.
04-12-2008, 09:38 PM
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Yep, just checked. The "upper" closed throttle switch seems to be making proper contact with the plate at idle, and the lower switch's cam turns, but doesn't make premature contact and for WOT (wide open throttle), at least not in my finger press-tests. I've attached two photos with the switches highlighted to help verify that I'm checking what you're talking about. Do I have it right?
At this point it remains a mystery that *seems* to say, bad DME, bad connection to DME, or something about the airflow/intake temp sensor. I really do think it's tied to the intake/mixture activity. Might try one more cheap solution and throw some fuel detergent into the tank and see if it really is —*gasp —*a bad tank of gas.
At this point it remains a mystery that *seems* to say, bad DME, bad connection to DME, or something about the airflow/intake temp sensor. I really do think it's tied to the intake/mixture activity. Might try one more cheap solution and throw some fuel detergent into the tank and see if it really is —*gasp —*a bad tank of gas.