Misfiring engine?

SpeedracerIndy · 08-27-2002, 07:28 AM

I have a 1988 Carerra 3.2 all original. I bought it in December from a very reputable dealer, and it had all of the records. It came with 75000 miles, and all of the maintenance was up to date. Since then, it now has 83000 miles and all that has been done is an oil change. Yesterday while I was leaving from work, I started up the car and it was normal for about 10 seconds, then all of the sudden it started ideling very rough. When I reved up the engine it felt as if it was unbalanced, and out of sync. I assume that it is misfiring. Well I drove it home on the back roads to try to figure out what was going on. I also noticed that the exhaust system was very hot. I assume that this is the cat burning off the unburned fuel from the misfiring cylinder. It had significantly less power than normal and hesitated and learched when under a small load. It felt like it was "trying" to get into sync and catch up. When I floored it, while there was still not as much power as normal, it seemed a little smoother and didn't hesitate. The exhaust sounds really weird at idle, and it has a pronounced "puf" about every revolution or two revolutions. I didn't hear any pings, bangs, or other horrible noises. The valves seemed to chatter louder than usual, but that could be me just being paranoid. Oil, and oil pressure were all fine. So is this something as simple as a plug or wire, or am I into something as serious as valves? Where should I start?

Tim Polzin · 08-27-2002, 07:33 AM

If you have a Bentleys manual handy, you might want to check the head temp sensor. When I had problems with mine, it ran (when it ran at all) very very rich.

Tim

MotoSook · 08-27-2002, 08:07 AM

Check your plug wires, dist cap fitment and then plugs! Sounds like an ignition problem. But then I don't own a smart fuel/igniotion equiped motor.

As you indicated, the unburned fuel may be causing your cat to heat up. This happened to me before on a V-6. I could smell the cat and it would glow read hot, yikes! Stupid me.

Good luck.

SpeedracerIndy · 08-27-2002, 09:24 AM

Thanks for the help. That's kind of what I figured but needed a second opinion. I kind of thought of the temp sensor a while ago. The car always ran very rich and didn't idle well at all when cold. When hot it always ran fine though. I'll probably start there along with some plug wires. While tinkering around in the garage this morning, I pulled one of the wires apart trying to get it off of the distributor! (DAMN!!, another $230 down the drain). On the other hand I guess the wire shouldn't have pulled apart if it was in good condition.

MotoSook · 08-27-2002, 10:47 AM

Buy the Magnecor 8.5KV wire set for about $150, you will like them.

sms1305 · 08-27-2002, 10:57 AM

Check the connector to the O2 sensor.

BGCarrera32 · 08-27-2002, 11:10 AM

As for the wire pulling apart and replacing them with Magnecores...I will chime in my 2 cents worth...

1) It may be possible from the dealer to purchase just 1 wire...

2) I would be careful about jumping to the Magnecore wires for a street application. I have no doubt whatsoever that it is probably a fantastic wire. However, after just receiving a set, the distrubutor cap ends of the wires do not latch onto the serrated Bosch cap terminals anywhere near as good as the original Beru connectors (the designs are different)---in fact even after an audible click I could gently shake the wire and get it to pop off. Also, the ignition coil wire I received had an incompatible connector end with my '84 (did they box the wrong wire by accident? perhaps...), and the lengths are not exactly the same. I also question the spark plug ends, as the boot design is different which seems to not grab ahold of the plug quite as well as the Beru. Magnecore can tell you all day long about how good their connectors are, but remember, they probably use the same connector ends for their wires that go on Hondas and Fords and all sorts of stuff....

If you can 't find your problem in a sensor, check your spark plugs. You may find one that has a bunch of unburned fuel (black sooty carbon), and this may indicate a fouled injector at one of the cylinders. I am going through the same thing to a lesser degree right now...

Good luck-
BG

Early_S_Man · 01:03 PM

CD,

If it was just the crimped brass 'screw terminal' that pulled loose ... it can be replaced! The part is 911.609.310.00 and is available at Mercedes or Porsche dealers, and the dealer can crimp the new one back on the wire!

The 'puff' you hear once every two revolutions is a very serious concern ... and, may be due to one or more broken Dilivar head studs! I suggest that you check all 24 head studs for tightness ... ASAP!!! You will need a 10 mm hex bit for the barrel nuts, and a 4.5" - 6" extension, and a 3/8" drive torque wrench.

SpeedracerIndy · 08-27-2002, 03:52 PM

Thanks for the replys and sorry for the double post, got confused, the second post was acctually meant to be an email to a tech support person instead of an additional post. I didn't think a head stud pulling loose was a problem for the 3.0 and 3.2s, jsut 2.7s. I'll check anyway. I haven't been driving it, so it's in no danger of getting worse, but I still have to figure out what went wrong. I've got a busy night ahead.

Early_S_Man · 08-27-2002, 04:16 PM

CD,

In the SC and 3.2 engines it is an entirely different problem than the 'pulling out' of magnesium case threads ...

Because of corrosion, the Dilivar head studs fracture rather suddenly, without warning! As the factory made changes to the Dilivar studs' coatings ... some people thought the last of the SC's and all 3.2 engines were immune from breakages of the studs, but now, 3.2's of varying age seem to be showing up with the problem. I suspect it is an environmental humidty/rainfall exposure effect.

ps ... you can delete the other thread by 'editing' the first post and checking the box.

SpeedracerIndy · 07:57 PM

Ok, didn't know you could delete an entire thread. I'll do that right away.

So would a broken head stud also contribute to the cat heating up from burning the extra fuel?

EDIT: Tried deleting the second post, said I didn't have permission...