Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 911 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: Jan 2018
Location: The CLT
Posts: 110
Garage
3.2 running like it has a hair ball stuck in throat

So, my 76K mile 87 Carrera all of a sudden started "coughing" like it has a hairball in its throat. Let me explain - starts fine, idles above 1K rpm and then settles at like 900. Once it is a bit warm - idle will drop out - almost to cutting off and then "catches" itself back to normal. Shift from 1->2nd usually has this same deal - kind of like a "bump start" ie. jerks and then drives. Doesn't seem to happen after that while driving in 2nd, 3rd and 4th.

A couple of times at stop sign/light - RPM has just randomly run up to 2K - hit the go pedal and it comes back down.

What have I done:

- replaced the 76K mile DME relay - didn't help
- replaced Dist Cap a few thousand miles back - drove fine.
- Pulled ICV plug - made it worse
- Pulled ICV and cleaned / tested - all good
- Replaced fuel filter - have not driven since

Any obvious things to check - I'm no mechanic - but can do some easy stuff. Electricity is sorcery to me as well.

thanks - RLK

thanks

__________________


1987 3.2 Carrera Coupe - Venetian Blue
Old 09-13-2019, 07:38 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Get off my lawn!
 
GH85Carrera's Avatar
 
Join Date: Nov 2007
Location: Oklahoma
Posts: 57,202
Garage
Likely your two reference sensors are going bad. Just replace both of them. Mine stared acting like it was possessed by an evil spirit. It too would die, and run very erratic. I just barely made it back home, and changed the two sensors. Runs like a Porsche now.

And be very careful driving it much until the problem is fixed. The sensors can just die, and you are only moving on the back of a tow truck.
__________________
Glen
43 Year member of the Porsche Club of America
1985 911 Carrera; 2017 Macan
1986 El Camino with Fuel Injected 350 Crate Engine
My Motto: I will never be too old to have a happy childhood!
Old 09-13-2019, 07:49 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Chain fence eating turbo
 
Join Date: Dec 2008
Location: Austin, TX
Posts: 8,844
Another phantom 3.2 jerking issue.

Never figured out mine. Good luck. Shotgun parts approach has been the norm for some of us.
__________________
Cory - turbo'd '87 C3.2 Guards/Blk, 3.4, 7.5:1 CR P & C's, soon to be 993SS cams and GSXR 750 ITB's fed by 964 intake, Borg-Warner S366 turbo @ 1.4 bar, Treadstone full bay IC, TiAL F46 WG, HKS 1 1/2" BOV, twin 044 pumps, MegaSquirt 2 (v3.57 board) w/EDIS, Tramont wheels (285's rr, 225's frt), Big Reds frt, 993 rr., tower brace, MOMO wheel
Old 09-13-2019, 08:06 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: Jan 2018
Location: The CLT
Posts: 110
Garage
Quote:
Originally Posted by GH85Carrera View Post
Likely your two reference sensors are going bad. Just replace both of them. Mine stared acting like it was possessed by an evil spirit. It too would die, and run very erratic. I just barely made it back home, and changed the two sensors. Runs like a Porsche now.

And be very careful driving it much until the problem is fixed. The sensors can just die, and you are only moving on the back of a tow truck.
I guess that is what the AAA and Hagerty flatbed tow insurance is for (fingers crossed I wont need it). Unfortunately, around here - its a drive to anyone that could do that work, unless its pretty straightforward. Any part #'s? I see this one:

Part #: 911-606-215-01-M14
__________________


1987 3.2 Carrera Coupe - Venetian Blue
Old 09-13-2019, 08:19 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
Join Date: Dec 2018
Location: Leuven, Belgium
Posts: 134
Garage
Since it only occurs when it has warmed up, it could be the O2 sensor gone bad (is a replaceble item every 60K miles). Mine used to idle fine until 2 minutes in, apparently that is when the O2 sensor is heated up enough so the ECU (Motronic) starts using the O2 sensor data to adjust the fuel trim.

I also used to have the oscillating behaviour that could be killed with a blip of power. Gone now after changing out the O2sensor on the cat and readjusting the idle postion screw.
Old 09-13-2019, 09:15 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
Join Date: Oct 2008
Location: Denver, CO
Posts: 2,212
couldn't your confirm/rule out the O2 sensor by unplugging it (letting the engine run in open loop) and seeing if the "hairball" goes away? (if yes, replace 02 sensor next)
Old 09-13-2019, 09:31 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: Jan 2018
Location: The CLT
Posts: 110
Garage
Quote:
Originally Posted by darrin View Post
couldn't your confirm/rule out the O2 sensor by unplugging it (letting the engine run in open loop) and seeing if the "hairball" goes away? (if yes, replace 02 sensor next)
Roger that - can try. Although the O2 sensor installed new when I replaced the CAT with by-pass pipe. Can easily unplug and try though I guess.
__________________


1987 3.2 Carrera Coupe - Venetian Blue
Old 09-13-2019, 09:37 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
BE911SC's Avatar
 
Join Date: Aug 2009
Location: ULC (Upper Left Corner)
Posts: 2,932
John Walker disconnected my O2 sensor several years ago, adjusted the air/fuel mixture with the tailpipe sniffer and it's run like a Swiss watch ever since. FWIW.
__________________
'84 Carrera Cabriolet

Last edited by BE911SC; 09-13-2019 at 10:03 AM..
Old 09-13-2019, 10:00 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Amateur
 
pmax's Avatar
 
Join Date: May 2014
Location: SF Bay Area
Posts: 4,993
Garage
Quote:
Originally Posted by Pigeye View Post
Roger that - can try. Although the O2 sensor installed new when I replaced the CAT with by-pass pipe. Can easily unplug and try though I guess.
Was it ever running fine with the bypass ?
__________________
I don't need that.
Old 09-13-2019, 11:11 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
NutmegCarrera's Avatar
 
Join Date: Oct 2009
Location: Plymouth Wi. - Spitting distance from Road America
Posts: 707
Garage
Don’t forget to take a look at the “wiper” on the rheostat in the “barn door” air flow sensor.
Requires that you disassemble the unit and check to see if the contact area has worn through. I was able to overcome a problem like the one you describe by doing this.
Night and day difference.
Not discounting the reference sensors - but this one is essentially a free fix.

My experience is that you need to change the “height” of the wiper on the shaft so that you get the feedback on a fresh area of the stationary contact.

This is very much like the way the old R/C car speed controls work (only reference I can think of - and I’m not an electrical guru by any means.).

Good luck!
Old 09-13-2019, 11:48 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
Join Date: Dec 1999
Location: Novato, CA
Posts: 4,630
Quote:
Originally Posted by Pigeye View Post

Any obvious things to check - I'm no mechanic - but can do some easy stuff. Electricity is sorcery to me as well.

thanks - RLK

thanks
You mean to tell me there are no reputable Porsche shops where you live?
Old 09-13-2019, 12:27 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Registered User
 
Join Date: Jan 2018
Location: The CLT
Posts: 110
Garage
Quote:
Originally Posted by stlrj View Post
You mean to tell me there are no reputable Porsche shops where you live?
There are few and hugely outstripped by the number of air-cooled cars in need of attention. They have gobs of work. Unfortunately, this isn't SoCal.
__________________


1987 3.2 Carrera Coupe - Venetian Blue
Old 09-13-2019, 01:00 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
 
Registered User
 
Join Date: Jan 2018
Location: The CLT
Posts: 110
Garage
Quote:
Originally Posted by pmax View Post
Was it ever running fine with the bypass ?
Like a fine swiss watch. No issues
__________________


1987 3.2 Carrera Coupe - Venetian Blue
Old 09-13-2019, 01:01 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Banned
 
Join Date: Aug 2015
Posts: 1,574
CHT going bad?
Old 09-14-2019, 08:24 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
Registered User
 
Join Date: Jan 2018
Location: The CLT
Posts: 110
Garage
So, figured I would update this - took a look at both reference sensors via the left rear wheel well. The insulation was pretty well cracked and falling off - so while I had it on jack stands - I pulled them both and will replace the CHT sensor as well. At least doing this will narrow down the field of potential gremlins (fingers crossed).

What I will say is that top allen head is pretty hard to get to, esp it you don't have the smallest of hands. I have not even started on trying to pull the grommet through the firewall - I was pretty wrecked from just removing the sensors. Live to play another day.

Anyone have tips on getting that grommet out and getting the sensor leads back to the panel on the left side of motor? I have a "fish tape", so hopefully it won't be too brutal. Famous last words, right?
__________________


1987 3.2 Carrera Coupe - Venetian Blue
Old 09-15-2019, 10:20 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)
Banned
 
Join Date: Aug 2015
Posts: 1,574
Partial engine drop.
Old 09-15-2019, 12:21 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #16 (permalink)
That's fond- just deglaze
 
Join Date: Mar 2015
Location: Minneapolis, MN
Posts: 186
Garage
Hi Pigeye- I still think this is one of the best references on how to replace/adjust the sensors (including removing the grommet and fishing the leads) without an engine drop:
no-spark problem finally resolved
__________________
Missed Approach
Petra- 1986 Coupe

Last edited by Missed Approach; 09-15-2019 at 02:48 PM..
Old 09-15-2019, 02:45 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #17 (permalink)
Diss Member
 
Quicksilver's Avatar
 
Join Date: Jul 2002
Location: SC - (Aiken in the 'other' SC)
Posts: 4,740
A few things listed here can be dismissed from causing your issues.
- The AFM's barn door "wiper" has nothing to do with idle. The AFM is ignored until you get off of the idle position switch.
- The O2 sensor wouldn't cause an issue with the RPM running up and down. Anyway the O2 sensor only comes into play with the engine running in "closed loop" mode.
- I'm pretty doubtful about the flywheel reference sensors causing an issue as your symptoms don't sound like anything even a reference sensor could cause.

The 4 big obvious things related to idle I can think of are:
- ICV which you say you have checked. (How was it checked?)
- Idle position switch. (and that should be an easy check with an ohm meter.)
- Make sure the throttle is returning completely to idle reliably. (Is it triggering the switch consistently?)
- A BIG and highly variable vacuum leak. (Not sure what could make this happen.)

The idle speed is controlled by the DME's programming when the idle position switch is triggered. The earlier Carreras have chips that tell it to idle at 800 RPM and the later Carreras have ROMs that set the idle at 880 RPM.
If the DME isn't consistently getting the signal that the engine is at idle it will be all over the map. To be thorough you will want to check both the switch and also check the harness by checking continuity at the plug at the DME.

Another item that could be causing "all over the map" issues is the DME (not the relay). If it has solder connections that are starting to crack it can act completely crazy. The only "user" way to make any type of check would be to take your DME and plug it into a car that is running good and see if the problem follows the DME. The only other "testing method" is to send it to Systems Consulting or Steve Wong on the West Coast, or Sal "scarceller" on the East Coast.

While you're at it it would be good to check all the grounds back in the engine compartment. (The one on the driver's side intake manifold and the ground strap at the front of the transmission are prime candidates.)

About the reference sensors...
- One of them is detects top dead center. If that one fails to "sense" just once the engine won't fire for a complete rotation. If it fails completely the engine won't start.
- The other one detects how far the engine has rotated so if it is marginal it will retard each spark by how many teeth it has missed. If it completely fails the engine won't fire.
As you can see from all that it is pretty inconceivable that could cause your symptoms.

I'm wondering if you have a couple different things going on. "Symptom stacking" is hell to figure out. Important checks would be fuel pressure at the injector rail test port on the drivers side and seriously checking all the rubber hoses for cracks and leaks. If you have never replaced the fuel lines to the injector rails now would be a good time to take care of that as that is a "burn it to the ground" issue. (New fuel lines should be teflon lined hoses so they never wear out.)
__________________
- "Speed kills! How fast do you want to go?" - anon.
- "If More is better then Too Much is just right!!!" - Mad Mac Durgeloh

--
Wayne - 87 Carrera coupe -> The pooch.
Old 09-15-2019, 05:19 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #18 (permalink)
Get off my lawn!
 
GH85Carrera's Avatar
 
Join Date: Nov 2007
Location: Oklahoma
Posts: 57,202
Garage
When my sensors were going bad the engine felt like it was possessed. The idle would run up and down, all by itself, and then die even while driving along at 50 MPH. It would be a real challenge to restart, and start the process all over. I had a heck of time getting back home without a tow truck.

Replace the sensors with the BMW part (lots cheaper) and the problem was instantly fixed.
__________________
Glen
43 Year member of the Porsche Club of America
1985 911 Carrera; 2017 Macan
1986 El Camino with Fuel Injected 350 Crate Engine
My Motto: I will never be too old to have a happy childhood!
Old 09-16-2019, 06:11 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #19 (permalink)
Registered User
 
Join Date: Jan 2018
Location: The CLT
Posts: 110
Garage
Quote:
Originally Posted by Quicksilver View Post
A few things listed here can be dismissed from causing your issues.
- The AFM's barn door "wiper" has nothing to do with idle. The AFM is ignored until you get off of the idle position switch.
- The O2 sensor wouldn't cause an issue with the RPM running up and down. Anyway the O2 sensor only comes into play with the engine running in "closed loop" mode.
- I'm pretty doubtful about the flywheel reference sensors causing an issue as your symptoms don't sound like anything even a reference sensor could cause.

The 4 big obvious things related to idle I can think of are:
- ICV which you say you have checked. (How was it checked?)
- Idle position switch. (and that should be an easy check with an ohm meter.)
- Make sure the throttle is returning completely to idle reliably. (Is it triggering the switch consistently?)
- A BIG and highly variable vacuum leak. (Not sure what could make this happen.)

The idle speed is controlled by the DME's programming when the idle position switch is triggered. The earlier Carreras have chips that tell it to idle at 800 RPM and the later Carreras have ROMs that set the idle at 880 RPM.
If the DME isn't consistently getting the signal that the engine is at idle it will be all over the map. To be thorough you will want to check both the switch and also check the harness by checking continuity at the plug at the DME.

Another item that could be causing "all over the map" issues is the DME (not the relay). If it has solder connections that are starting to crack it can act completely crazy. The only "user" way to make any type of check would be to take your DME and plug it into a car that is running good and see if the problem follows the DME. The only other "testing method" is to send it to Systems Consulting or Steve Wong on the West Coast, or Sal "scarceller" on the East Coast.

While you're at it it would be good to check all the grounds back in the engine compartment. (The one on the driver's side intake manifold and the ground strap at the front of the transmission are prime candidates.)

About the reference sensors...
- One of them is detects top dead center. If that one fails to "sense" just once the engine won't fire for a complete rotation. If it fails completely the engine won't start.
- The other one detects how far the engine has rotated so if it is marginal it will retard each spark by how many teeth it has missed. If it completely fails the engine won't fire.
As you can see from all that it is pretty inconceivable that could cause your symptoms.

I'm wondering if you have a couple different things going on. "Symptom stacking" is hell to figure out. Important checks would be fuel pressure at the injector rail test port on the drivers side and seriously checking all the rubber hoses for cracks and leaks. If you have never replaced the fuel lines to the injector rails now would be a good time to take care of that as that is a "burn it to the ground" issue. (New fuel lines should be teflon lined hoses so they never wear out.)
Thanks - I tested the ICV - by feeling it "hum" when key turned, but actually removed it, hit it with carb cleaner - then tested it with 12volt source (think it was ground to middle pin and then hot to either side) to make the valve move - which it did.

Thanks for other tips - on the speed and reference sensors - lots of others had same symptoms and "magically" fixed by replacing them - car isn't going anywhere, insulation was cracked and falling off so, ill replace them anyway. Fuel lines are on the list too.

__________________


1987 3.2 Carrera Coupe - Venetian Blue
Old 09-16-2019, 07:40 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #20 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 03:23 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2020 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.