81 SC dying at speed
 

Sorry in advance for a longish question, however I'm working on a head scratcher of an issue on this one, and would appreciate any thoughts/help you all could lend while I try to chase this one down:

What it is doing (approx 3 times so far):
At highway speed, vehicle shuts off completely, with no warning. Meaning: cruising at 60-80 mph under power, then...nothing. No hesitation, no sputtering, no shuttering, no surging idle, not a thing...just off. Completely off. The only initial indicator is the sudden lack of engine noise, and slowing of vehicle. Note: the 3-4 cases of this doing it are days a part with NO driving on the days between.

What didn't work:
2 times popping the clutch while coasting restarted the vehicle and I continued on...not the 3rd time. Vehicle came to a rest, and turning the key resulted in starter turning over engine, no audible indication of engine trying to fire.

Roadside repair attempts and then started again:
After 5+ minutes and a few failed attempts to start it, I replaced the red relay and one random fuse for the blower motor that looked a bit worn. (doubt the blower was part of the issue, just addressing while in there) The car fired up on the first try and got me to work/home that evening with no further issues. Somewhat makes me think of vapor lock symptoms, but would that happen before it is at temp on a CIS vehicle?

Other thoughts:
This is now the 3rd red relay I've had in the car since fall. Replaced the first one after the vehicle wouldn't start after warm. Second one was replaced the other day when I started having these issues, now on the 3rd relay.

Conclusions/questions:
Seems to be either fuel or electrical, but where do I start with that wide range of variables. Concerned that it isnt likely that 3 relays all going bad...that there is an underlying issue that manifests (coincidentally) with the relay replacement.

Long story short: what do you all think I should start by further investigating/replacing/etc. Thanks so much for your help on this one!

Faulty ignition coil maybe. Checking the primary and secondary winding resistance may not help as you may have an intermittent short. If it's silver and made in Brazil just replace it but I don't think these were installed on SC's.

Thats a good point, I can check the coil, however I replaced it about 3 years ago with a Flamethrower. (Doesnt mean its not faulty, of course...)

Perma-Tune CDI box?

http://forums.pelicanparts.com/porsche-911-technical-forum/209506-how-test-rev-limiter-sc-cis.html

Mark

This is interesting...I hadnt considered, and of course I probably dont recall what RPM I would have been at.

Ignorant question. Suppose the limiter DID cut off ignition...would it have trouble restarting for some reason? Logic tells me that it should restart without issue, but you know what they say about logic and reason...

The airflow safety switch at the back of the CIS metering assembly also cuts off the fuel pump by grounding the circuit (See pic in Mark's thread above http://forums.pelicanparts.com/porsche-911-technical-forum/209506-how-test-rev-limiter-sc-cis.html#post10465364).
Try disconnecting it temporarily to see if it is the culprit.

Have you checked fuse contacts? .. Maybe a critical fuse has poor contact. Happened to me, although I was not at speed; was about to park my car at a restaurant when engine just shut down. Nothing got it started. A few people helped me push it into a spot. I went inside, enjoyed a nice steak and a cab ... went out to the car and fiddled with the fuses, rotating some of them. Started up, no subsequent issues.

Verify the plug is secure into the CDI unit. Verify the green coax cable coming out of the distributor is not the culprit. With engine running, gently manipulate that little cable to see if the engine stutters or dies. Finally, what you describe could be the CDI unit itself. A common symptom of near failure is that it dies with some driving, but can restart immediately or after a short rest. Substitute with a known good CDI box to at least eliminate that as a potential problem. I have a loaner that I routinely provide to people for the cost of shipping to try/troubleshoot. --Bob

It doesn't matter what RPM you were at. When the module fails, it stops the fuel pump, regardless of the RPM you were running. It could happen at idle.

When mine failed, sometimes the car would immediately restart, but most of the time I had to wait a bit for things to cool for some reason.

Just unplug the white connector and see if the problem goes away. If it does, then you got off easy. If the problem continues, then you have more work to do.

Mark

And it will sputter and die. OP is not experiencing this. Instantaneous engine cut out.

Mark is right. It's been a while but as I recall on restoration of a 78' SC, my rev limiter was defective. I disconnected it from the harness and the car ran like a top. My issue as a little different than mzavada; once you plugged the rev limiter back on, the fuel pump got no ground, hence no electric charge and the car would not even start.

Sure, at idle. But at speed, it's pretty abrupt.

Mark

Thanks everyone! You've given me a great list to start combing through!

I got myself organized tonight, and will start figuring these out tomorrow night! http://forums.pelicanparts.com/uploa...1561427978.jpg

I have experienced it under acceleration. It's brutal.

Assuming just cruising and fuel pump cuts out it would be similar to the red relay breaking connection.

I maybe experiencing the same issue with my 82 engine. I don't believe I have a rev limiter since my car is a 77, but not sure about airflow safety switch. I am leaning towards the coil/CDI. Car starts up and runs great, idles smooth. I haven't driven it yet since the engine swap. About 20 mins when temp is up around 180-190, sputters, backfire, stalls.

Run it in your driveway for about 20 mins to see if it happens then. I have a feeling it will.

You got it backward.........
 

Brian,

The presence of a ground contact (terminal #85) in the FP circuit shuts off a running FP. Installing back the Rev limiter with an open ground to the car will have no effect to the pump (normal). The three (3) sources of ground for terminal #85 are:
1). AFS switch.
2). Rev limiter.
3). Car alarm/immobilizer.

You got it backward. Putting back a defective Rev limiter (grounded) will energize the NC (normally closed) 87a~30 to 87~30 (normally open) with the ignition switch @ RUN. The problem with your Rev limiter was it was grounded causing the coil inside the FD relay to switch off the FP.

Tony

@mzavada - that "to do" list is over the top!

Timed it today. Idle in the garage. Everything smooth with warm up and settled around ~950. 21 mins in sputter, loss of idle, backfire, dies.

So I would say very similar to your issue. temp was up around 180 - 190

Cracked solder........
 

Mzavada,

Nditiz1’s CDI was sent to Bob Ashlock for evaluation. And Bob found a cracked solder @31/1 terminal. As the CDI warms up from the engine heat, the cracked solder opens up and lose ignition signal causing the motor to stop running. When the motor is allowed to cool, the cracked solder regains its contact back and allowing the CDI to operate again until the next cycle to shut off. Have your CDI tested.

Tony

Agreeing with Tony. Also, I bet those 2 other relays you replaced will work fine. It just so happened that you replaced them and the car cooled so the next time you fired it up the CDI was working again making you think it was the relay all along.

Hell, send out your CDI anyway to Bob and get it upgraded and purdy.

I stepped away for a few days, however I've tried out a couple things, and potentially uncovered more issues.

Order of steps and outcomes:
1. Battery: confirmed battery voltage of 12.XX, consistent with every other battery check on this battery.

2. Checked Fuses: visually evaluated all fuses, replaced a few: fuel pump (fuse, not relay), blinker fuse and parking lamp fuse. (Did not attempt to drive/start)

3. Coil: confirmed 1.2 ohms across terminals, 0 ohm reading from positive to center (!?). Reconnected battery, turned ignition on (not started) and received quite a scare...

4. Fuel Pump: when ignition was turned on to try to test coil, a loud hum/buzz was emitting from frunk and under hood, near fuel accumulator. Turned off ignition, then turned on again to confirm noise. Swapped out fuel pump relay, noise went back to quiet fuel pump hum like normal. (For fun, swapped back the initial fuel pump relay, and noise was back to quiet normal sound)

5. Starting: turned key to start, nothing...no starter solenoid noise/cycle, nothing. Turned key to off, tried again, nothing. Instinctively reached under key and pushed on wires while turning key to start, it fired right up. (could be coincidence?) While running, I pushed on wires, and did not have any issues with running. When it started, the starter was just as strong as always, and vehicle fired immediately, just as it always does.

6. Coil: back to checking the coil while vehicle is running, positive on positive terminal, negative grounded...received an 0v reading somehow?

I didnt go for a long drive, nor did the vehicle get up to operating temperature.

In addition to checking things like rev limiter/CDI...I guess I'm adding checking for ground faults to the list? Wire integrity between battery/key/starter? Anything else I'm missing? It sure feels like I've taken the first step in the rabbit hole and am quickly gaining speed into the abyss....

mzavada

So the car starts and runs good and then after some time when it is fully warmed it dies. As someone mentioned with my similar issue hook a timing light up and check to see if it starts missing. This will tell you if you are facing an ignition issue or not.

You should be able to drive around for 10 mins and then let it idle for another 5 to get up to temp. My issue would not show itself unless the temp reached ~180. A connection inside my CDI would break due to heat and cause a no ground fault killing the engine. Let it cool for 5 mins it would start back up, then die within a minute or so.

If it is fuel related you can hook a CIS fuel pressure gauge to your CIS and go through the steps of checking for correct fuel pressures.

I have a feeling that if it starts and runs good and then dies it is CDI related.

Haha...yeah, I've been known to overdo it with my organization. Doesnt always yield great results though!

Just another data point ... you mentioned you tried to measure voltage at the coil. With a CDI ignition, you will not be able to measure anything at the coil with a common voltmeter. The discharge pulse on the positive lead is very fast and only can be seen with an oscilloscope. It is only about 20 usec. wide. I responded to your private message earlier ... get back to me via email (bob@ashlocktech.com) and I will arrange to loan you a spare test 6-pin CDI unit. The test unit works great, but is so ugly nobody would ever want to keep it on their car any longer than necessary for troubleshooting purposes ... ha ha ha.

Fuel issue, tach will slowly drop to zero. Ignition tach will immediately drop to zero.

Yes, sounds electrical.

I would check the ground strap from the tranny to the body. Remove the strap/clean/replace if necessary. While you are there, check the starter connections.

Disconnect the battery first :rolleyes:

Not a ton of progress to report from tonight, but checked out/maybe ruled out a few things:

1. Trans/Body Ground: Removed and cleaned both ends and the surfaces they mate to. Looks to be in good condition overall

2. Starter: while in that vicinity checked to ensure that the starter was getting adequate power. Tested 12.12 v at top of solenoid.

3. Battery: tested at 12.12 v

4. Idle/operating temp: started vehicle and let run in driveway for 15 minutes . Ensured to replicate all accessories that were running at time of last stall. Vehicle ran fine the entire time, no stalls. Took the throttle high into RPMs a few times, with no ill effects. (Again, without load on the car)

Emailed Bob about borrowing CDI box and because I'm slow to process things sometimes, I concluded that borrowing it would tell me:

1. Stalls with his loaner CDI: its something else
2. It doesnt stall with his loaner CDI: its probably my CDI

Either way, now that I've evaluated a few things, replaced or adjusted a few things, I think I need to take it for a drive to see if symptoms replicate. (As another baseline)

Wish me luck tomorrow! Also, huge thanks for keeping all the comments coming. Dealing with CDI/Ignition isnt something I've done much so I'm learning from you all!

Check for tights connections under the dash of all the round wire harness plug-ins.

I hit a bump at 65 and the car completely quit like yours. The solution was pushing in one of the wire harness plugs for the ignition switch.

My vote is fuel pump. It backfired and died. Sounds to me like fuel pump.
Tony

So did it stall at the 15 minute mark?

When I did my warm stall tests, I timed it two separate times. The first was 21 minutes and the outside temp was ~85. The second time took 28 minutes and the outside temp was 77. Good luck on the next run. Pay attention to the temp gauge. That was what helped my zero in on a component failing to function due to heat, the CDI.

You've checked the battery voltage but have you checked the alternator output when the car is running? It should be in the. 13.5-14.2V range with all accessories and lights off.

I've been keeping an eye on that area too. I've triple checked the connections and as stated, pushed on the wires both before starting/while running. I'll continue to keep an eye on that area while I sort through this! Thanks!

It did not stall at the 15 minute mark last night. I turned the car off at that time, mostly because it was getting close to 10pm, and my neighbors live pretty close to my idling car noise. (thankfully they are cool)

My commute is consistently 10 minutes each way, and the times the car has stalled it has been around the 5-8 minute mark of my commute. (guestimating)

Temp during last stall during commute was in the low 70's, last night with no stall was in the low 80's. Will be continuing to pay attention to ambient and engine temp during this. In an attempt to determine if its the CDI doing the hot stall, I'm planning on bringing a bottle of compressed air to blow on the CDI to see if it speeds up the restart.

Great reminder, I checked it during the first drive of the year in early April and it was in the high 13v...did not check last night/since. Will do when I restart. Thanks for the reminder!

Actually...now that I think of it, that would cause the car to stall, but it wouldnt explain how when it came to a stop, I turned the key and the starter turned just fine, would it?

In other words, after the car stalled and came to a stop, the starter engaged, but engine would not fire.

Update from my first decent drive since the last stall:

Drive time: put in over 30 minutes total drive time, and about 5 minutes of idling time before heading out for a drive. Similar speeds/variables to when the car stalled last time, except I wasnt on the highway. (But still got to about 60-65 MPH) NO STALLING! Air temp was around 85 degrees and humidity was about 4,000 percent. (kidding)

Aside from a bit of protest when it first started, all seemed OK. The fuel pump did seem a bit louder than usual, however I am wondering if I just am hyper focused on anything being out of the ordinary and 'hearing' things. (Will obviously keep an eye on it) I have another couple of 'confidence' drives planned over the next two days and will update when I have something more.

You are absolutely right. There is more going on.

Not in my experience. At idle, it might sputter and die but at speed it'll be a different matter.

The fuel pump in my 86 (yes,I realize it's not CIS) died at speed and it just shut down immediately exactly like the OP said. In this case, it absolutely was the fuel pump and again, behavior was the same.

I am experiencing a problem somewhat similar to mzavada and I eliminated the possiblity of the fuel pump by removing the FP relay and using a jumper wire to keep it energized.
When the vehicle quit at speed I just coasted to a stop and did not touch the key.
I checked and the FP was still operating which would leave me to believe my problem is electrical (ignition).
But I've yet to find the solution.