Engine problems/issues '84 911 3.2
 

Hi everyone,

I have a couple of questions regarding my '84 3.2 911 coupe. I bought it 3 months ago and can consider it in good shape. I did get sort of PPI and it was also considered as a pretty neat car by the guy who did the inspection.

The problems l want to ask about were present while I was having my test drive but of course the more you spend time with the car, the more they seem obvious and I just want to check with the experienced ones here if you really consider these as problems which I have to take care of immediately or as usual early 911 issues that are not "that" important.

1. After a cold start (which the engine starts quickly and smoothly) it more or less everytime stops when I take my foot off from the gas (usually in the first trafic lights). I restart the engine and sometimes experince this another time and then it runs just fine. So is this a common cold start issue or else?

2. Maybe connected with the first and third issue (I'm not sure anyway...), both when the engine is cold and at ideal working temp, while cruising at constant low rpms (2000-3000) the engine vibrates, well actually shakes. It feels like there is something wrong with the gas (or air) it takes at these rpms. When I go above 3500 I don't really feel it but while runing at the lows, it feels like it lacks the power and that vibration starts to annoy me more and more.

3. This issue, I face from time to time. Especially in 2nd, 3rd and 4th gear when I just open the throttle completely and accelerate from 2000 rpms to 5000-5500s, it backfires as soon as I take my foot off the gas. As I said I don't really experince it everytime, but it looks like when I have the backfire it doesn't do that even I accelerate quickly again for some time (which I think a bit weird a well).

I'll really appreciate if you share your thoughts or experiences on those above issues.

Thanks very much in advance...

Demir

Demir,

the 84 engine is controlled by a DME. The DME is a computer that evaluates sensor inputs and delivers outputs for fuel quantity and spark timing. In your case I would look into the following:

From what you describe under load and decel it sounds like the mixture is off. The O2-sensor determines the amount of fuel that is injected to achieve a target Air/Fuel ratio. If that sensor is bad you would see issues like you describe.

The cold start issues could be caused by the cylinder head temperature sensor being bad. This sensor reading adjusts the fuel mixture and timing when the engine is below operating temperature.

Search the board, there are tons of threads talking about both. The CHT, especially the one-wire type is known to go bad. Some owners disconnect the O2 sensor for lack of better knowledge. Check if yours is present and connected. And measure its output with a DVM to make sure it is alive.

Hope that helps,
Ingo

I would agree with Ingo and add, having had one of these engines, that you need to also make sure you don't have any element of the input system to the DME faulty. There are several sensors that connect back to the DME. Make sure each is functioning as it should. If one, such as the O2 sensor mentioned above, is not working fully, you can experience issues such as this and others. Normally previous owners don't spend the money to change the sensors.

Good luck.

Before you start making any adjustments to the air/fuel ratio you really need to make sure you have a good baseline to start from. How old are the spark plugs, rotor, distributor cap, plug wires and air filter? If you don't know, change them out. Same with the fuel filter.

Get a replacement DME relay. More than likely the one you have is the original. Change it out and keep the old one as a spare.

Once those items have been changed out, now is the time to see if the intake manifold gaskets have shrunk and you are sucking in air past the gaskets. This is a common problem on the 3.2 engine.

Only after you have done the above should you start looking at other problems.

Who did the PPI for you? I would think a clean bill of health includes being able to pull away from a light. Engine shakes? Come on -

These are smooth running cars when they are dialed in.

Working sensors (reference, cht, 02) are a must for the DME to do their job.

BTW - drop down a gear and go from 3000+ rpms when you put your foot in it - 2000 rpms is lugging the engine.

Thanks very much for all the very useful contributions guys. I'll go thru with a detailed search in the forum as well. I hope this is not gonna cost me much at the end :)

As far as I understand these for sure are problems, but not "urgent" issues to take care of, am I rite? Because also the guy who did the PPI told me that there are certain things I need to look at after I buy the car (not detailing these spesifically) but not any urgent stuff...

Btw I live in Holland, so sometimes the service you get here really sucks :) -hope the guy was right thou-

If it hasn't been done yet, it might be a good idea to begin with a basic ignition tune up.

It would be sad to find out later after spending so much time and money on parts you did not need only to find out that it was something so simple.

Don't rule out fuel injectors... How many miles on the motor?