Engine start problems after service & CHT sensor upgrade
 

Bought an '84 Carrera a few months ago and had it checked and serviced back then. Now with a few thousand miles more on the clock I decided to do a bit of maintenance the engine today: oil, oil filter, fuel filter, air filter, ignition rotor, distributor cap, spark plugs. I also swapped in a new cylinder head temperature sensor. My mechanic had suggested the upgrade to the two-wire one (as does the related Pelican Technical Article).

After I was done, I was ready to fire up the engine again. At first I cranked the engine a couple of times using the starter motor with the ignition coil disconnected, to build up oil pressure. After reconnecting the coil, it fired up pretty quickly. However, a lot of white and then black smoke was coming out of the exhaust pipe. It went away after half a minute or so, but I'm curious whether that's normal or not.

The other thing I noticed is that instead of idling normally, it would constantly alternate between ~1000 and ~2000 rpm. While changing the air filter, I had noticed that the vacuum line connected to the fuel pressure regulator had come loose. And even though I had reconnected it, I wondered whether it had come loose again and was causing the erratic idle. So I turned the car off and went to check. Sure enough, it had come loose again. So I reconnected it and tried again. No luck, same behaviour. Turns out, the rubber hose would always slide off the plastic line and I couldn't get them to stay connected reliably. So now I wonder whether they were even connected before.

The next suspect was the CHT sensor I had just installed. So I took the multimeter and measured the resistance at the connector. It was 0.8 kOhms which less than the 1-2 kOhm range that the article was talking about, but then again the engine was slightly warm from running for a few minutes. So I decided to see what would happen if I warmed up the engine all the way and went to start the car again.

Except it wouldn't start! The engine would turn over and there was a smell of fuel coming from the exhaust pipe. But no spark. Even though I hadn't touched anything related to the ignition, I rechecked everything but couldn't find a fault. I even continued to measure the CHT sensor reading as the engine cooled down, and it went up to ca. 1.5 kOhms after half an hour or so.

I'm at a loss. I had started the engine several times while troubleshooting the erratic idle and all of a sudden it just went dead like this. I will double check all fuses, connections, and grounds tomorrow, but I was wondering whether anybody had any idea what the heck is going on... Thanks!

Did you check oil level while engine running? Sure you didn't overfill? How many quarts of oil?

I have/had an intermittent starting issue that I "may" have solved. I will have to wait until it gets warmer outside to confirm it, but I think the experience might help you.

As you know, the male end of the CHT sensor mounts into the metal bracket, and is secured in by that piece of metal that slides/screws in. The female connector then snaps into place via the small wire clamp that is so easy to lose.

Anyway, as I was fiddling with the brand-new CHT sensor, I discovered that the male end of the connector was not completely pushed into the metal bracket. This allowed the female end to "connect", but not fully seat. I took all three sensors out of the bracket, and plugged them in completely. It has started every time since I have done that.

Like I said, it might not be your problem, and it may not even be mine.....but I'm starting to gain confidence that it will start every time I turn the key again. Good luck!

I filled 10.5 quarts which is what the Bentley manual said the capacity was. With the engine running but not warmed up it ended up being around the low mark (a little below IIRC).

I suspected the same thing so I took the connectors out of the bracket and connected them directly. No change.

My understanding was that you never get all the old oil out - there's some still in the oil cooler and lines. So adding system capacity means a 2-quart overfill, IIRC.

Please someone correct me - I've never gotten any more than about 9 quarts out on a change.

I see. Well, that would explain the smoke then...

Speaking of smoke, I just got the car to start. Some smoke still coming out and the weird idle persists.

(CHT sensor was reading 2.4 kOhms, btw, so it seems just fine.)

If you kept the ignition rotor and distributor cap put them back.

It would not be the first instance of premature failure...

Did you use the same type of spark plugs?

So, seeing how the car started this morning, my guess is that I overfilled it on oil. What must've happened last night is that the oil got warm and soaked into the intake, blocking it... Might also explain the weird idle?

I'm gonna say yes to that theory after opening one of the tubes leading to the idle control motor and finding it coated with oil on the inside. Ooops. Guess I'm going to have to clean that out.

Glad you found that. Try siphoning some oil out of the oil tank (turkey baster) - I think I read that here. And do take care of that vacuum line connected to the fuel pressure regulator. goodluck

I drained a bit from the tank's drain plug. Now taking apart the intake and cleaning it. I see now that there's a ventilation hose from the oil tank to the intake... I bet that acted as overflow. *facepalm*

Yeah, that vacuum line, I'm going to have to take care of that somehow. The plastic tube keeps sliding out of the rubber hose no matter what I do.

So I removed the AFM and idle control valve and related hoses, cleaned all of them on the inside and tried to start it. No dice. It started less than 2 hours ago! WTF?!?

Plugs are now fouled, and you're getting no spark. Smell the exhaust - smell like raw gas?

If so, "bingo".

Bingo! And yeah, that came to my mind right after posting, too. What do I do? Just let it sit and dry out?

Gotta change out (or clean up) the plugs.

Yeah, I removed one to check and it looked pretty bad. Removing all the other ones now and cleaning them.

Thanks everybody for the help! Maybe I'll make it home today! :)

Well, I cleaned all the plugs, but it still won't spark. Hrm.

This is why I asked if you checked while running.

I think the computer 'learns' and it is standard for a 3.2 to 'hunt' while it learns - maybe the vacuum line connect is causing it to re-learn? I dont know much about the 3.2 fuel injection - just bought one and learning. ASny way first is to get it started.

I noticed that getting the dizzy cap on is a bit of an excercise, did it get set down on their tight? maybe one side is loose and not getting good contact?

Yeah, distributor cap is on there nice and tight. I mean, the car *has* run after sitting for periods of time.

The only way you had an overfill of oil with a 9 quart add is to not have removed all oil from the 2 drain points. I'm a bit lost on how he could have overfilled it. Did I miss something?

Doyle

I definitely drained both the crankcase and the tank. Thoroughly. I then filled 10.5 quarts because that's what the Bentley said. I wasn't even sure whether it would take all of it at once, so I searched the interwebs and some forum post said "oh yeah, it'll take the whole 10 quarts in one gulp". So I was like, ok, let's do this.

I guess the overfill is because some of the oil remains in the front oil cooler which is included in the capacity? (I'm a bit annoyed by the Bentley for skipping details like this. It does this all the time... What do y'all use for instructions?)

Going to pick up new plugs after work since my cleaning obviously didn't work and then we'll see.

I'm not quite sure I agree as to oil cooler/lines amounts as related to oil changes.

Of course, for me, it's a '89 so some things may be different. But, she will take 10.5 quarts on EVERY changeout,..resulting in level-ground, running temp, at idle,..MID MARK levels on the stick. Regardless, I still load 10 quarts on the changeout then run the sheeit out of her for a while,..then slowly add what's needed to make the stick happy. My MAIN rule of thumb is to NOT add oil until I have nice toasty send/return lines AT the front cooler. Only THEN do I worship the stick.

True that the system oil capacity is "larger" than what one can extract (as you mentioned: the front running lines/cooler content),...but, after extracting all oil from the 2 points, it's amazing that one would experience an "overfill" at 9 quarts !!!!!!!!!! (and that's including any "oil remnants elsewhere in the system")...

What am I missing here? Is there that much difference on a '84?

Anyone else here experienced an overfill condition at ONLY 9 quarts, on a Carrera?

BEST!

Doyle

Of course, the above process would include installing a NEW oil filter (just saying)..

Doyle

New plugs installed, the car runs! The white/blue smoke disappeared after a few seconds, so that's good.

It did, however, show the same bouncy idle that I was seeing yesterday: alternating between 1k and 2k during warm up and then as it warmed up, it zeroed in on 2k. Guess I either didn't clean the AFM and ICV thoroughly enough or I ****ed them up with the overfill.

When I step on the throttle, it chokes as if it's missing and black smoke comes out the tail pipe. So something's definitely messed up. :(

He didn't add 9 quarts. He added 10.5 quarts.

I only get out about 9 quarts when I drain mine. I put in 9 (sometimes more, but not more than 9.5 quarts) to get it to halfway between the marks. I drain both the tank and the sump, but not the oil cooler or the oil cooler lines.

On my car, 10.5 quarts would be a very serious overfill.

Edit: Adding 10.5 (in addition to what's already still in the system) would be a serious overfill.

As to documents (instructions),..I was able to find a Porsche Service manual for a 1989 Carrera on Fleabay (CD),..very affordable,..and the real deal...

Now I get to research elements, side by side, as related to the Bentley Manual.

I would add (from some time ago) that the Bentley Website does provide corrections to errors that were previously published,..it may bode well to check which Bentley Rev you (and all else) are running......... I would guess that they correct the errors in subsequent runs, but am not sure. Nor am I sure that that they've ID'd "ALL" errors that DO exist !!!!!!!!!

Best!

Doyle

If I were guessing, I'd guess "really rich mixture". Clean the AFM and ICV again, and see what happens. I'm shooting in the dark now, because I don't know how your overfill might have affected all the components.

Nobody is immune to errors as they are human by-product... 101 Projects for your Porsche 911: Corrections & Updates

I'm sorry,..I see my error in post #6.

I guess the question would now go to Eric as to the "9 quart overfill" issue,..as well as philicon's "10.5 quart overfill", as well.

10.5 quarts is no where near an overfill on a 1989 (much LESS a "serious" overfill),..I can say that for sure, being someone who owns a daily driver that sees new oil (and filter) every 3K miles.,..measuring oil levels correctly (again: front lines nice and toasty), I can assure you (in my case) I'd probably NOT even see the frikin oil line (barely, at best) on the stick with a 9 quart load. I think I remember seeing a VERY low oil level (in the early days, that is) when I DID drop 9 quarts in her then added as necc'y. Sometimes, she would take ~ 10.3 quarts,.....

I've never measured the oil amount extracted on an oil change, but surely that would answer the (soecific) question, eh?

Otherwise, I trust my oil stick, exclusively.

Thanks for the correction, Eric.

Best,

Doyle

Precisely! Certainly: no one.

Good catch, BTW. Any other sources should be verified, as well.

Yes: human (or, homosapiens [better said]);)

THANKS!

Doyle

This is the absolute best advice.

So, on my first change, I purchased a new oil pan that could hold 3 gallons. Since it was made of plastic, it was very easy to mark the level of used oil. I poured the old oil down the storm drain and wiped out the pan with young kittens.

I then filled the pan with water to the mark, and poured it into a 3-gallon bucket marked off in quarts. I did this on the first change to know how much oil came out, so I knew approx. how much to put in. It came out just shy of 9 quarts used oil. So, I refilled with 8.5 quarts, and ran the car to get it up to temp, and found I needed just a little over 0.5 quart to bring it to the mid-point between the lines.

Subsequent changes (without the measuring) have been the same.















(No I do not pour oil down storm drains. I save the oil in a container to be sent for recycling. And no kittens were used as shop rags. Only shop rags were used for shop rags.) :)

Well, I consider this to be a lesson learned, for sure. Going to clean the AFM and ICV again, more thoroughly.

Oh, btw, it won't start anymore AGAIN. Sigh...

Any other 85's out there that use (only) 9 quarts on the changeout?

So far the lessoned (assumedly) learned is that there's a huge difference between 1985 and 1989. (for me)

Best,

Doyle

Sound like you got an intermittent electrical problem that is not related to your oil overfill...

How right you are!

Thinking the same thing I retraced my steps. Since I had changed the CHT sensor as part of this service, I went to check what the ECU was "seeing" of the CHT signal. Turns out: it wasn't! The connection was wide open. Judging from reports on the interwebs, this is a likely culprit for the engine not wanting to start up when it's anything other than stone cold. Also, running like ****.

I then did a simple test on the connectors in the engine compartment and it turns out the ground prong wasn't making a connection. My guess is corrosion since it had never been used until now. I hot-wired the connectors and gave it a separate ground, and voila, the car started right up and it's running JUST FINE. Purrs like a kitten.

Now I just gotta fix it for realz. Fortunately Bosch systems from the 80s are all the same and we've got an couple of old BMW E30 wiring harnesses lying around in the shop... :)

Thanks everybody for the support! The continuous input was very helpful in verifying (or sometimes refute) my assumptions.

In case anybody's interested, here's the thing I cobbled together from the old sensor's cable and a connector stolen off an E30's wiring harness:

http://i.imgur.com/SmszJl.jpg

And this is what it looks like installed in the car:

http://i.imgur.com/dR6tnl.jpg

In case you can't see, I stole the ground off the cable-holding bracket on the bottom right.

Excellent work.