Feudal Serf

Hey, more parts for the duplicates box. I have 2 new ignition modules i didn't bother installing myself.
Are you using a scan tool? I use the durametric, it does help when you go into actual values and see that the timing is retarded by 6*. Which is what happened to me when I had the rough idle, also threw the hall sensor code.

One other thing, did you try looking for wire arc ing by misting a running engine in the dark? Simple enough to do.
If you go to the trouble of doing wires, you prob should do plugs with it. The Porsche tool kit is helpful for plugs.

I went through your thought processes re running on single distributer. Prob ok for a little while but the combustion chamber is designed for 2 plugs and from what I read you are losing 10pc of combustion by running on one plug. Fuel and carbon deposits on valves?

Did you try running the engine on the rough idle coil and serially unplug each cylinder from the dizzy cap? Each time I did it, really lumpy idle except one wire that turned out to be the problem. I suppose if you are getting arcing or shorting this May not help, but it will isolate say a bad plug.

Good luck and keep the updates coming.

FS

Tmistry

Thanks FS! I fear I may have f'ed something in chasing this down. I test drove the car yesterday after replacing the ignition modules and it wasn't good. I was getting all the warning lights at once along with a loud beep that seemed to vary in tempo. The car was also stuttering a bit as I drove. Clearly, something I did caused the problem since this has never happened to me before. I assume it's icm related. Regardless, I'm leaning toward taking it to my friends at Automotive Techniques here in MI to get everything sorted out. Any advice, thoughts are appreciated! Have a good Sunday all.

Feudal Serf

Hi Tmistry,
Been busy installing a new garage door opener, though I'd rather be working on the 964.
More of a sense of accomplishment. I've only owned mine for less than a year and had a tranny rebuild with the dreaded broken carrier for planetary gears. I fretted for a while, called the pro's who helped me with the car and lightened my wallet.

I think your problem is fixable yourself if you have the time and inclination.

I kept a log as I was working through my recent problem, I'll post it here:
All of my check listed items were obtained by searching here and reading about similar problems.
Its a great forum.

porsche 964 March 20th 2014

Re: repeated Bucking under load post trans rebuild (2 engine drops)

No Backfire, erratic but worsening, first noticed when engine warm on highway. First 5 Km of driving OK. 20Km total since

no problem revving in neutral except hesitation

?Suggests Lean condition or ignition problem

recent valve adjustment and replacement of lower left valve cover.

Previous owner recently replaced ignition Coils, wires, plugs, distributor caps in 2013, 3000Km ago

New ide control valve

no recent Air Flow Meter work done

had low fuel level in gas tank for 6 months while in Halifax


To Do 1

964 distributer belt test, car has the distributor vent modification already.

http://p-car.com/diy/dualbelt/

There are a couple ways to verify operation of the belt. First, remove the secondary distributor cap and see if the rotor spins freely. If it spins – at all – the belt doesn’t have a hold of it. The other way is to remove the input plug from the top of the primary distributor cap, forcing the car to run on only the secondary distributor. If it starts and runs – no problem. No start, no belt.


Done: Belt Test OK starts on secondary

pulled wire from front coil to primary dizzy idles smooth cold, some hunting when warm.

Pulled wire from rear coil to secondary dizzy and idles rough, tough to start and stalls, hard to hold steady 1400rpms with light throttle

Confirmed with pulling wiring harness from each coil

Inspected the top of primary Dizzy, looks new, no corrosion. wire on top seated well.

Pulled cover off primary dizzy, belt OK, looks new





To Do 2

Durametric Scan read codes

Done: Hall Signal 34 unable to clear with both coils connected

However cleared when primary ignition coil wiring harness disconnected !

Timing -6 !

To Do 3

Reseat each spark plug, look for arcing in wires. make sure wires are not damaged

Partly Done: Upper plugs all reseated (secondary dizzy)

Inspected wires in engine bay-OK

Light water mist in dark with engine running-no arc

To Do 4

DME relay replacement, ordered and shipped

Removed and reseated DME relay.

Felt warm

To Do 5

Remove and Service Air Flow Meter, check for wiring harness modification as per TSB, look for interference between oil breather hoses and AFM harness, have hoses been secured in clips

Partly Done: AFM harness TSB already done, breather hoses well away (spec 15mm)

Haven’t pulled the AFM and cracked the plastic plate for cleaning the board.

Engine - Erratic Idle, Loss of Power, or Stalling

May 15, 1990
Subject: Engine, Inconsistent Performance
Model Group

911 C2/911 C4 2

Part Identifier Number

9750 9005
ATTENTION: Service Manager/Service Technician

This bulletin replaces Technical Bulletin Group 2, Number 9005, dated April 6, 1990.

Models Affected: 911 Carrera 2 and 911 Carrera 4, Model Years 1989 (K) and 1990 (L)

Concern: Inconsistent acceleration, erratic idle, loss of power or engine dies.




Possible Cause: The air flow meter wiring harness protective cover (Figure 1) contacts the engine ventilation hoses (Figure 2) causing current flow interruptions on the plug terminals.

Vehicle Information: The protective cover on the air flow meter wiring harness plug was discontinued from production date February 13, 1990.

VIN's 96 - LS 45 1659 Coupe 96 - LS 46 0409 Targa 96 - LS 47 1072 Cabriolet

Repair Information: 911 Carrera 2 model year 1990 and 911 Carrera 4 model years 1989 and 1990 prior to the above VIN's should be modified when the engine is removed or when working on the air flow meter, even if no engine performance problems are present.

Work Procedure: 1. Remove air filter housing cover and filter.



2. Push down locking spring on air flow meter wiring plug and disconnect plug (arrow in Figure 6).

3. To gain access to plug, pull wiring harness with plug between air flow meter and idle stabilizer towards rear of vehicle.



4. Pull back rubber boot and cut protective wire covering using side cutter or similar tool (arrow in Figure 3).



5. Heat protective wire covering with hot air blower to maximum 110~ C (230~ F). Pull off and discard protective wire covering (Figure 4).



6. Reinstall rubber boot on plug housing. Loop wiring harness along side of plug and tie wrap as shown in Figure 5.



7. Reconnect wiring plug. Make sure spring lock is engaged. Figure 6 shows wiring plug connected (engine removed).

Important: Do not use contact spray.



Work Procedure: 8. Check clearance between wiring harness and vent hoses. Distance should be at least 15 mm. If necessary, bend bracket on right shock absorber mounting slightly forward (arrow in Figure 7). Make sure vent hoses are properly installed on bracket at shock absorber mounting and on bracket in front of air flow meter. The small diameter hose must be routed below the large diameter hose, 9. Reinstall air filter and filter housing cover.



10. Mark air flow meter with a black paint dot as shown in Figure 8.
Parts Information: Tie wrap: PN 999 513 021 40

Labor Information:
Labor Operation: 97 50 19 OA
Damage Code: 97 50 40 000 1
Time Units: Engine installed - 80 Engine removed - 20

To Do 6

Clean all electrical contacts from engine harness, distributor

Done: Pulled connectors in engine bay and inspected, all look clean

To Do 7

O2 sensor check, order replacement. Old sensor. Test drive with sensor wiring harness disconnected.

Partly: O2 sensor wire through grommet looks frayed and has dielectric grease on it. No exposed wire. Durametric reading with warm engine 1.0

?OK, but should be on to do list to replace

To do 8

Even though ignition coils are new, consider replacement.

This appears to be the problem, primary Ignition coil failure

Cannot rule out out of sync distributors, haven’t pulled both caps.

to do 9

Fuel filter replacement

Partly: looks new

to do 10

check battery connections and ground wire at body

Done: terminals cleaned as well as body ground cleaned with wire brush and contact cleaner

check battery voltage engine off and at idle (?durametric)

Idle running 13.1V



March 23

Resolution: Order 2 new ignition coils

Lift car to inspect lower ignition wires and reseat lower spark plugs

DME relay replacement, need spare in glove box anyway

Currently: Harness from primary Ignition coil disconnected.

Hall Signal 34 successfully cleared.

Test Drive running on secondary Dizzy only

No bucking some idle hunting but no stall

Also Timing on durametric hovering -0.8 to 0.8 !

Suggests that Hall sensor is functioning

DME related timing retarding due to poor ignition

Cant rule out a distributor problem such as poor bearing or primary/secondary out of sync, belt in tact though.

Test drive with both Coils hooked up

Bucking severely now, pinging, stalling

Hall signal 34 reappears and cannot be cleared until primary coil harness pulled





March 24

thinking its time to check the lower spark plug connection

Fixed !!!!!


Make a list, check em off as you go through them and read through the posts here on rennlist.

FS

Tmistry

Whoa! Thanks FS!

I have my work cut out for me on this. I'll give it a go, but I might just slap the easy button on it as I don't ah too much time to chase this. Free time has been consumed lately and I fear if I don't hire it out, my 964 will gather dust during the prime driving season, which after this winter in MI, feels all of about 7 days long!

Will update. Thanks again/

Tmistry

Hi all,

This is getting really frustrating. My car was running well, until I decided to replace the ignition coils due to one incident if a long start.

Now, I just replaced my distributor caps and rotors as well as the coil wires. All new parts. The car starts, but idles like total **** and stalls out. I've come to believe i simply shouldn't work on my car. For example, the wires are all numbered. The distributor caps have numbers, corresponding to said wires. There is a diagram illustrating the caps, with I and II labeling. Is this diagram to insure the caps aren't mounted backward? It seems it would be difficult to mix up this, due to the mounting of the caps and the numbering. Can anyone advise what I've possibly done wrong?

Does something need to be redone after replacement like this?

Are these in wrong? Needless to say, I feel like a total dumbass.

Thanks

Silvertarga

I just had the same fun, turned out to be a bad plug wire combined with a bad bosch silver coil

Once I put back the original coils the car would start, still waiting to do the wire..

Yes as mentioned above these cars are very sensitive to spark problems

Vandit

So now it's running bad on either distributor?

Steve Weiner-Rennsport Systems

JMHO, but these silver Bosch coils are a POS, compared to the original black German-made ones. Unfortunately, there are no other viable alternatives.

I have my clients carry a spare (just like the DME relay) just to keep from getting stranded since a local Pep Boys/Autozone may not have them in stock.

Tmistry

I haven't done the single coil test. Will tonight.

Also, I'll swap back to the black coils to determine if I got a bad coil. The new ones feel light in comparison to the old coils.

I swapped since i thought it might be an upgrade after 24 years!

Tmistry

Ok, I did the separate coil test and the same result. So, the interesting thing is with the two new coils, both attached, it runs bad. With the primary distributor coil detached, runs great. With the old coils, with both attached, it ran great.

So, I'm on to thinking its a plug or wire issue, somewhere downstream of the distributors.

I have a new set of wires, but fear the work!

Feudal Serf

Hey Tim,
Your problem appears to be with the lower plugs/wires.
Start with them, take off the cat converter. a few bolts, rest it on a paint can so you don't have to deal with the crusted O2 sensor. Lower engine shield and you are there.
I would change all six lower spark plugs and replace the lower wires.
That should fix your problem.
good luck
FS

Silvertarga

I am about to try the Standard Motors UF 37 coil...they are about 15 bucks shipped..AC Delco also lists the E587A for the 964 but cant seem to find one or two

UPDATE

I just got the Standard UF 37 coil, cost $33.99 for the poair with shipping, open the box and there is Bosch Brazilian Silver Coils (..ok for the price they are ok..)

Tmistry

Finally solved the problem! Thanks Feudal Serf for the assistance. It really helped.

I pulled the Cat and inspected the plugs and sure enough, one wasn't properly seated. Such a simple issue and I ended up replacing coils, ICMs, distributor caps and rotors. The great news is that the car runs smooth as silk. Solid and even idle on either coil. I took a nice 60 mile drive that ranged from backroad curves to motor way at high* speeds and the car just sang.

Thanks to all that helped with this! I'm really a total amateur mechanic and it's great to have the help of other members.

Best,
Tim

Vandit

I'm glad you got this sorted, and now you're that much more familiar w/ the car's ignition system. Had you previously messed w/ those lower wires? Strange for one to just pop out of place.

Tmistry

Thanks Vandit! Appreciate your input as well and the help getting this sorted.

Embarrassingly, yes, I am the root cause of the problem. You see, I replaced my catalytic converter with the fabspeed bypass, almost purely for cosmetic reasons, since I had a hollow cat to begin with. The old worn cat just looked bad and I thought, why not? Well, I did the cat bypass and at the same time replaced my engine carrier and engine mounts. This all took place over the winter and I had multiple projects going.

I seem to recall pulling one of the plugs off to inspect and I'm sure it was I that didn't reseat it properly. I feel like a moron, as I should.

What's odd is that with the old coils, the problem was present, but it didn't affect the performance enough to know there was a problem. But for the single incident of a long start, which caused me to do the individual coil test, I'd never have known.

Replacing the coils made the issue more pronounced, since with the two new coils in, I was getting engine misses and stalling and the Christmas tree thing. It reasons that the new coils are less tolerant of one another's downstream components, which may be a good thing.

As you say, I come out of this with a much better understanding of my cars ignition system and I feel better aware of potential issues, should they arise. Like, say some dumb *** pulls a plug wire off and doesn't reseat it....I'll know just what to check!