dhc905

tl;dr

Every 25 seconds when the car is in idle or below 2,500 RPM my check engine light flashes 1,2,3...pause...half flash. Rinse and Repeat. No error codes are ever stored. Car drives and idles normally. Light never flashes at higher RPM's or highway speeds. See video below.

If you know the answer and it works, I'll happily send you either two bottles of wine (you won't be disappointed) or $50.


Hi all,

Since my bracket is thoroghly busted and both schools I had any interest in following are out, I wanted to come back and address a long standing issue.

As you may have read in my other thread about my typically trouble-free, unmodded 1991 C2 964, I've been having an issue with the Check Engine Light ("CEL") flashing at me. Normally, a CEL comes on, an error code is stored, you fix whatever is the issue and go along your merry way.

This is unique for a couple reasons:

1. No error codes are stored. I bought ToreB's diagnostic tool specifically to address this issue, and have also had RicardoD's tool scan the car. No errors.

2. There is a distinct pattern to the flashing part of the CEL - it flashes 1,2,3 times, pauses then has a half 4th flash. Almost* exactly 25 seconds later, the pattern repeats.

* See video below

3. Car drives perfectly fine; have not noticed any adverse effects on driving, idle, fuel consumption, oil consumption, oil dripping, etc.



Backing up briefly, this issue seems to have originated at the same time I swapped my CupII's for MY02's. I had to do the front two and rear two wheels separately; everything went smoothly and honestly nothing in that process would suggest anything during that process went wrong. I'm thinking this is simply a coincidence, but want to put all the facts out here.

So what have I done to rectify this:

- Changed O2 sensor
- Changed oil/filter
- Replaced Idle Speed Control Valve
- Removed and cleaned the Air Flow Sensor (very little oil/dirt)
- Changed air filter and cleaned airbox (clean)
- Replace DME with solid state DME
- Unplug battery overnight, after replacing 02 sensor
- Car is always kept on a battery tender

Engine work that has been done in the past year:

- Valve Adjustment
- Distributor belt
- Replace Alternator
- All new belts

So, if you can give me the answer, I'll send you either two bottles of wine or $50, your choice. Let me know if there are any follow up tests or information you need to help you in any way. I have ToreB's diagnostic tool if that helps.

For full disclosure, I called a local indie and he suggested that my diagnostic tool may be "insufficient or incorrect" to identify the problem, and that he would attempt to diagnose with a 2 hour minimum. He also had some pretty derogatory things to say about 964's when I spoke with him, hence my appeal to this board before making that plunge.

And a glamour shot:

Spyerx

Hmmm. Shooting in the dark. If you were down here we could use my durametric.

http://members.rennlist.com/billwagner/checkengine.html

Battery? Alternator? Have you checked your battery running and not running voltage?
Hard to say. 3 with 1.
Knock sensor?

See if you can get it in self diag mode.

Try this. Very clear steps

http://forums.pelicanparts.com/porsc...tml#post668387

Silvertarga

As you know these cars are prone to weird things ...electrically speaking

I would start with coils, connections at spark plugs and mist the plug wires with water from a spray bottle while motor is running and see if there is any arcing

Flashing CEL in most cars indicates a misfire

wallra

looks like It's flashing code 31 knock sensor 1. this is how you do the self check with no scan tool. Ignition on depress accelerator pedal completely down for 3-5 seconds. Then count the flashes. the first one's together like 123 than 1 would be code 31.

Rocket Rob

+1 - Check for ignition leaks. How old are your spark plug wires and coils?

wallra

here is a code chart.

dhc905

Thanks guys.

Wallra - So in addition to the Bergvill diagnostic tool from ToreB, I be also used the self-diagnosis WOT when the car is on, engine is off method and get the same result - 1 flash followed by 5 quick flashes, which I believe indicates no codes. As far as I understand, the car won't flash codes at you while just driving; maybe I'm wrong and that's the solution, but haven't heard that before?


Sypder - I got a new alternator in the past year and battery was tested to be strong. I keep it on a tender, and have never had any other electrical issues or difficulty starting.

Rob - I know my plugs haven't been changed since I've owned the car (3 years and 4K miles) and I'd hazard to guess the plug wires haven't ever been changed. Is there some magic with the 25 second interval and it only happening under little load that would indicate and ignition leak?

Rocket Rob

About 5 years ago, my cab started getting weird Check Engine light flashes. I have a Scantool and it wasn't recording any faults. I lived with it until it got to be nearly constant. I then changed my coils and spark plug wires. All of the weirdness went away. My theory is that one or more spark plug wires was leaking and the sparks were surprising the DME computer and it was giving odd faults. If your spark plug wires have never been changed, they are probably due for it (over 25 years old). I would change the coils too just to be safe.

dhc905

Thanks Rob - I've reached out to my mechanic to see if I can get new plugs/wires/coils some time in the near future. If that works out, I'll connect with you for the prize.

If anyone has any other ideas for me to consider, please let me know.

Steve Weiner-Rennsport Systems

JMHO,.....

Unfortunately, we see a lot of cars with plug wires that have been in service for 50K or more. I'm guessing that people just don't want to replace worn/old parts unless its an utter dire emergency, even though they may be critical for proper operation of the engine or safety.

I counsel my clients is that proactive maintenance is always FAR cheaper than reactive maintenance. This means changing oil & replacing parts when they need it and not simply kicking that can down the road until something goes wrong. In many cases, the consequences can rapidly get very expensive.

Plug wires are just like tires, brake pads/rotors, spark plugs, oil & oil filters, perishable. None of these components last the life of the car and in some cases, not 50K. You would likely be quite surprised by what I've seen over 40+ years at this such as corded tires, brake pads worn to the backing plates without any friction material, 25K oil changes, engines running on 3-4 cylinders simply needing a tuneup.

Most of what you need to know about maintenance is in the Owner's Manual, the rest can be found by asking people such as myself. If you don't trust the people who maintain your car and believe they are simply trying to sell parts & services, its time to find the ones you trust and hold your best interests at heart.

Take good care of your car and it will take good care of you!!!

jimq

I didnt think a 1991 US car came with a check engine bulb in the light

dhc905

Steve - if only you were closer!

I've ordered a new set of coils which I will probably tackle myself; following that I will most likely take the car to someone to do a new set of spark plugs and cables. Any idea what (approximately) that should cost? I know the cables can be very pricey if Porsche (vs. Beru); any other tips as I go down this path?

Steve Weiner-Rennsport Systems

I'm not that far away and there are no sales taxes in Oregon.

I RARELY replace coils unless there is solid evidence they are the source of a problem. Same goes for the Ignitors.

Plug wires are always a big issue because people seem reluctant to replace them when required. I suppose its rooted in economics and thats a story for another day.

I cannot tell you what things will cost in CA since labor rates vary widely.

Porsche plug wire sets are made by Beru so this is one case where you should not pay the "Porsche" Tax. We use & sell the aftermarket Beru sets all the time and they work very well. None of them last beyond 35K miles due to heat issues.

klokwerk

I agree with Steve. Coils and ignition Control Units rarely go out, but when they do, what a pain. Just make sure if you replace your igniters DO NOT buy the cheep HUCO units. They're junk. Buy Bosch or Porsche, I'd have $3k in my bank still had I not made that mistake!

dhc905

Only 669 miles and 11.5 hours of driving. Easy when the CEL doesn't flash on the highway

I bought new cables (Beru - I could not even find them on Sonnen, which is where I typically buy my parts) and will hopefully find a guy who can replace them in the near future. The coils seem easy enough that I'll probably do that first, followed by replacing the rotors in the distributor (I have two new OEM extras), and finally the cables.

Also, the cables were quite cheap given the first local mechanic I called said he wouldn't even look at my car without a $400 minimum; so by those standards I'm doing just fine so far!