NewBie-Car misses then runs fine after warm-up

[whiz05403]

Hey Guys, my 1987 Targa seems to be missing for about the first ten minutes of driving then runs great. It's cold here I'm not sure if that matters.

I have had the car for about three weeks and it has been sitting for two. The PO said he just put in new plugs, points and cap. Maybe I should re-do that myself.

Any ideas or suggestions? Thanks.

On another note, I was very excited to get my package from Pelican with my new and exciting 101 Projects for your 911 book, only to open it and have 101 Projects for your Boxter book instead.

[kodioneill]

There are no points in a 87 it's Motronic controlled. The injection and ignition systems are tied together under a engine management system. If the plug wires haven't been replaced I would do that first. There could be vacuum leaks. Possibly the CHT (cylinder head temp sensor). If I had to guess this would be the most likely culprit.
Spend some time using the search function there are many posts about poor running conditions. Also I would familiarize myself on the Motronic system so you can better understand how everything works.

So, welcome to the board, you will find this to be a valuable resource. The members always request photos of a new member vehicle.

You may want to search CHT first.

[KTL]

Congrats on the new '87. Nice year for these cars.

I agree on the CHT. They are known to present intermittant driveability issues. Not a bad place to start. Also consider the O2 sensor and it's age. The O2 is a critical part of the engine managment in terms of startup, as cold starts are the worst for emissions.

[whiz05403]

Thanks, I'll start with the spark plug wires. The CHT might be too bold for my beginer level, we'll see.

I did install new gas hood struts today, pretty easy, even the drivers side. Tomorrow I'm resoldering the new capacitors to the back of my quartz clock as per the clock threads. I hope it brings my clock back to life!!

This forum is great. Thanks again

[kidrock]

if you can solder quartz clock capacitors, testing and replacing your CHT sensor will be a snap.

[KTL]

I agree with kidrock. The CHT is a simple sensor plugged into the #3 cylinder head. If you get under the car, you can see it on the drivers side of the front of the engine, somewhat nearby the other two sensors connected to the transmission bellhousing. I believe I removed the CHT sensor quite easily with a 17mm flare wrench (the kind usually used for brake line nuts).

All you have to do for the initial diagnosis is take a look in the engine compartment, near the left & forward side of the engine (under the rear window). There are three connectors in a metal frame that are stacked vertically on top of each other. Two of them are the sensors I mentioned before- the ones at the engine-transmission interface under the car. The third sensor is the CHT. The CHT is clearly different by its smaller wire going into the plug end. I believe the CHT is also typically a white plug end. If your CHT is only one wire, you should replace it anyway since the one wire sensors are prone to fail and the current sensor is a two wire. If it's already a two wire sensor, then it should be diagnosed for resistance/continuity to see if it's still in spec.

Also while you're under there, it's not a bad idea to look at (but don't tug at) those aforementioned two transmission sensors. These are the reference sensors that tell the engine computer the rpm/speed reference. The covering on these wires is known to go bad- it splits and then moisture gets in there and messes up the wiring. I'm not saying the bad wire covering is potentially you're problem. Just saying that this is something to look at for preventative maintenance purposes.

When these wires get contaminated and corrode, you have intermittant operation problems. Car will run just fine one day, then the next time you go to start it, it won't start. Or it might just decide to stall on you. Come back later and try again, it can start right up and run fine again. Not always easy to diagnose something like that! My understanding of one of the sensor's use is to simply detect a pin in the flywheel on startup. After that you could disconnect the sensor and the car would keep running. But shut it off and start it again w/out sensor connected, and it won't run.

[whiz05403]

I have been looking for the Cylinder Head Temperature Sensor in Pelican new parts with no luck. Only found later models. Any links for an 87? Thanks

[fritzgator]

thats because a 78 doesn't have one

Originally Posted by whiz05403

I have been looking for the Cylinder Head Temperature Sensor in Pelican new parts with no luck. Only found later models. Any links for an 78? Thanks

[whiz05403]

My car is an 1987, sorry about the 78 goof.

[ossiblue]

Originally Posted by whiz05403

My car is an 1987, sorry about the 78 goof.

Okay then. Everybody...I'm about to delete my former post! We'll let the late comers try to figure out what this is all about
(At least stuff like this boosts my post count!)

[whiz05403]

Well, she ran fine for a couple of weeks. Today I had a nice hour long drive in my 87 Targa, she ran great. Then I got stuck in some traffic, temp stayed normal, and she started missing again.

I have read all the "missing" posts.

Tonight after Little League I will try to figure out what cylinder is missing. Tomorrow all new plugs and go from there.

Sounds like Magnacore 8.5's are next order along with cap and rotor from Pelican.

Or maybe Clewetts?

Any other suggestions?

Sucks when she's not happily running

[kidrock]

clewett's or magnacores. both are great

[whiz05403]

Well, tonight I pulled a plug wire for each cylinder, cranked her up six different times and pretty much determined the missing cylinder to be number 3.

The cap looks brand new, the little metel tips on the cap that the rotor hits about half looked like they had little scratches in them??

I then put them all back together and tried the dark spray water on the ignition wires looking for arcing or something. I sprayed like crazy in the pitch dark with the motor running and saw nothing, just more dark.

So does that mean my wires are ok?

Better study up now on changing the plugs.

Any suggestions? Thanks.

Mike

[fritzgator]

the bushings in your distributor might be worn, causing the scratches in the cap. That's what it was in my case. Distributors routinely need oiling, and are routinely overlooked. Mine was so bad, the shims were friction welded to the springplate, and had to be milled off.

[KTL]

Originally Posted by whiz05403

So does that mean my wires are ok?

Not necessarily. The check you did in the dark is good to check for arcing, but you should also check them for resistance. The connectors on the factory wires actually screw into the wires (both the cap end and the plug end). The Beru plug connectors have resistors in them that can go bad. So you can check the resistance of the wire, independent of the plug connector to see if it's the wire or the connector. Do some resistance check on #3 wire vs. the others to see what you find.

Plug change is not that hard. Just have to be patient. The spark plug tool in the factory toolkit is VERY good for changing plugs. Works quite a bit better than a standard spark plug socket.

[whiz05403]

OK gents,

I changed all the plugs today. I used the Porsche tool and without sounding arrogant but it was very easy!! Each plug came out real easy and each new one went in in a snap. Took about 30 minutes. The Porsche tool rocks!!

Started her back up and no miss!! Ran her real good and still no miss!!

So why would a spark plug stop working or get fowled? Is this going to happen again?

Here is a pic of the plugs I pulled.




The plugs all looked pretty good except the number 2 plug. Very black compared to the others and dry.

Well at least the miss is gone, however, I suspect it will be back.

Just poured BG44K into the tank, maybe that will clean some stuff out.

[whiz05403]

#6 was pretty black as well.

[KTL]

No arrogance, good fortune is nothing to be shy about sharing! Glad to hear the plugs came out easy. Sometimes people overtighten them and they can be a bit of a struggle to get out. Factory plug socket is the hot setup, isn't it?

Spark plugs are pretty durable parts, but they do fail on occasion. Sometimes the ceramic insulator can crack, causing a miss. Maybe that's what happened.

The fouled plugs could likely be attributed to worn valve guides on those cylinders. If you have the opportunity to have the exhaust system off the engine (Very easy to do if it has been removed recently. If not, don't go there because broken exhaust studs await you if you aren't prepared to remove the nuts with oxy-acetylene level of heat) you can look at the exhaust valves for carbon buildup. A bad valve guide situation often shows itself by the plug oil/foul and also a substantial amount of carbon buildup in the exhaust port.

However good fuel injection cleaner like BG, Techron or Berryman B12 can clean out that carbon stuff really fast. I used Berryman on my car and in one tank of gas the carbon was pretty much completely gone.

[Daytona]

Originally Posted by KTL

Not necessarily. The check you did in the dark is good to check for arcing, but you should also check them for resistance. The connectors on the factory wires actually screw into the wires (both the cap end and the plug end). The Beru plug connectors have resistors in them that can go bad. So you can check the resistance of the wire, independent of the plug connector to see if it's the wire or the connector. Do some resistance check on #3 wire vs. the others to see what you find.

Plug change is not that hard. Just have to be patient. The spark plug tool in the factory toolkit is VERY good for changing plugs. Works quite a bit better than a standard spark plug socket.

Kevin,
Your knowledge base is right on. My question and I think I know the answer is corrosion at wire ends that screw into the plug connector. I cleaned the corrosion by sanding and electric spray and reinstalled, however two would not screw back in tight. I also replaced dizzy cap and rotor, cleaned plugs which were showing good firing signs.
So I had recently been getting an electric misfire which is why I performed the above service.The misfire became less but still there. I can also cleaned up misfire by grabbing hold of the plug wire in question, I even felt some voltage when touching the wire at the connector.
This leads me to the conclusion that the wires are bad on the car which is a 1988 Carerra. My question is what wires would you suggest, Clewett, Fyrebraid, or orig equipment Beru?
Thanks Larry

[KTL]

The Clewett wires seem to be quite popular, along with the Magnecor wires. I have the Magnecor wires on one of my cars and have had good results with them for about 7-8 yrs. However my car sees limited use, so take that recommendation with a grain of salt.

As far as the OEM wires go, there's better options. The wire material itself is good, however the plug-end connectors have been known to be problematic. Given today's outsourcing to lesser high quality standards, i'd be leary with getting new replacement connectors. They are not necessarily cheap @ $26.50 ea. here at Pelican, so six new plug end connectors are nearly the cost of a new, more modern, complete wire sets. For reference a set of Magnecor wires is just over $200 and the Clewetts are a bit less at $150.

I’ve been happy with my Magnecor, aside from the dist. cap boots being stubborn to push on. They seal so tightly that the air pressure wants to pop them off. So you have to pull back the edge of the boot to let the air escape.