Engine start problems after service & CHT sensor upgrade

philikon · 10:35 AM

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!

Tippy · 04-16-2012, 04:09 AM

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

Poor-sche Lover · Poor-sche Lover's Garage

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!

philikon · 04-16-2012, 08:28 AM

Quote:

Originally Posted by Tippy

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

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).

philikon · 04-16-2012, 08:30 AM

Quote:

Originally Posted by Poor-sche Lover

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.

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

SilberUrS6 · 04-16-2012, 08:36 AM

Quote:

Originally Posted by philikon

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).

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.

philikon · 04-16-2012, 08:46 AM

Quote:

Originally Posted by SilberUrS6

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.

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.)

JJ 911SC · JJ 911SC's Garage

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?

philikon · 04-16-2012, 08:55 AM

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?

philikon · 04-16-2012, 09:10 AM

Quote:

Originally Posted by philikon

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.

steely · 04-16-2012, 09:32 AM

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

philikon · 04-16-2012, 09:35 AM

Quote:

Originally Posted by steely

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.

philikon · 04-16-2012, 10:20 AM

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?!?

SilberUrS6 · 04-16-2012, 10:29 AM

Quote:

Originally Posted by philikon

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".

philikon · 04-16-2012, 10:33 AM

Quote:

Originally Posted by SilberUrS6

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?

SilberUrS6 · 04-16-2012, 10:39 AM

Quote:

Originally Posted by philikon

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.

philikon · 04-16-2012, 10:57 AM

Quote:

Originally Posted by SilberUrS6

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!

philikon · 04-16-2012, 11:37 AM

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

Tippy · 04-16-2012, 12:30 PM

Quote:

Originally Posted by philikon

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.

This is why I asked if you checked while running.

Elombard · 04-16-2012, 12:38 PM

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?