Puffs black smoke right after sartup, help!

[T86951]

My na '86 starts great and no flooding on start up, hits and starts right up fine. Then in a couple seconds it gets really rich and chugs and puffs black smoke for about 20-30 seconds and clears up and runs fine. I Thought a leaking injector but pulled my plugs after startup and they were all 4 totally black. The colder it is the worse it is. I have checked and an '86 doesn't have a cold start injector. Would the engine temp sensor be causing this or the auxilary air valve? All 4 injectors wouldn't go bad at once. The computer has to be saying ricken up and then quits after 30 sec or the aux air valve not working. If the injectors were leaking off all 4 plugs would not be black, just the one or ones with the bad injector and startup would be hard because the cylinders would be flooded, starts perfect and then gets rich. Anyone had this?

[Magnus_944]

If I understood the system right the auxiliary air valve can't affect the mixture, it can only let some "extra" air pass the throttle to raise the idle then the engine is cold. Am I right? I hope this is of some help..

/Magnus

[drew1]

I would say the auxillary air valve sunds more like it than the injectors. It seems like it would be worser in warmer weather with leaking injectors. I think what you all are calling the auxillary air valve is that thing up under the intake. What about the idle motor (don't think this is really the right term)? Maybe it's not getting a signal or not opening.

drew1

[monteness]

Is it the Idle Air Mixing Valve? I'm still waiting on my manuals but a friend of mine had something similar on his 944S; the mixing valve(I think) was going bad and the DME was giving it more fuel until the voltage signal staightened out. Just a thought..
Bret

[T86951]

Thanks Guys for the input.
Sounds right, the auxiliary air valve (under the intake) wouldn't appear to affect the mixture but just to let "extra" air in to raise the idle then the engine is cold. My idle doesn't raise when I start it though, the idle is lower til it warms up. Does that indicate the valve is bad and the DME getting a bad signal?

Bret, where is what you are calling the Idle Air Mixing Valve on your friends 944S located? Is that maybe the the auxiliary air valve (small shinny cannister you can see under the intake runners)? Did your friend replace that and it fixed it?

thanks

[T86951]

Ok I checked the parts section on this site and 83-85's have an auxiliary air valve and '86 and later have a idle control valve that pelican says is similar to the auxiliary air valve, the control valve adjusts and maintains the proper idle for the car whether it's cold or hot acording to the ad.

Anybody know if that is my problem? They cost $151 so I don't jut want to try on and hope. You have to pull the intake to change it. Would hate to do all that and have the same problem!

Thanks

[Magnus_944]

One wild guess, O2-sensor? Can it do something like this problem? My car don't have one so I don't know much about it.

/Magnus

[lm6y]

I'm not for sure, but don't the later cars use a heated o2 sensor? If it does, it could be the heating element in the sensor not warming up quick enough, and sending a "lean" signal to the DME. It could be the idle control valve sticking closed when the DME tells it to lean out, causing a rich condition, if this happens, The DME will cut back the injector pulse width, leaning out the mixture. I've never had one off of a Porsche, but on GM cars with TPI, you remove it, and clean it out with carburetor cleaner, and it works as good as new. GM's part hardly ever goes bad, don't know about the P-cars though. It's worth a try.

[T86951]

Does anyone know the specs using a meter to check an idle control valve on an '86na? I have the spec's for a 2 wire one but I think mine has 3 . Thanks

[Jim Franks]

Originally posted by T86951:
Does anyone know the specs using a meter to check an idle control valve on an '86na? I have the spec's for a 2 wire one but I think mine has 3 . Thanks

I'd try unplugging your O2 sensor on a cold start to see if it changes anything. I got my O2 sensor for about 50 bucks. It's a Bosch 3 wire for a Ford or something. I just had to splice in to the long harness that ran up to the back of the engine compartment. Good Luck! Jim 86 951

[scottewid]

From the Bosch fuel injection manual:
First check that the auxiliary air valve is closed. After the car warms up, check the idle speed. Then disconnect and plug the hose that runs from the aux air valve to intake manifold. Restart, if no change in idle speed, it's closing properly after warmup. If it's slower, the aux is not closing.

Assuming it's working, reconnect aux air hose and close the idle air bypass screw (not sure on 86, but should be on top of throttle body or close by on manifold) Then loosen the lock nut on the throttle stop screw and adjust for lowest possible rpm without engine dying (around 600rpm). This is minimum idle speed. Then back out the idle air bypass screw to adjust idle speed between 900 rpm for manual Porsche 944 1983-1986.

The smoke condition on startup could be caused by an overly rich condition due to the coolant temp sensor, incorrect carbon monoxide, aka air-fuel ratio (AFR), adjustment, bad fuel pressure regulator, or bad oxygen sensor, or a combination of all four.

After you adjust idle as above, you'll need to check the CO level. This is controlled by the the large AFR screw on the side of the airflow meter. It may be covered with a plug, which you'll have to drill with 1/8" and pull out. Turning it clockwise enrichens and counterclockwise leans mix over entire rpm band. To do it right, you really should take it to a shop and hook it up to an emissions analyzer. A quick and dirty method is to connect a voltmeter to the oxygen sensor wire (after car is warm). You can check O2 sensor operation first.
Disconnect the O2 sensor connector wire and connect a voltmeter between the O2 sensor and ground. Start the car and let it run at least 2 minutes. Touch the other O2 sensor lead that goes to the ECU with one hand and touch the positive battery terminal with the other hand. This will send a small voltage to ECU telling it the car's running rich. The rpm and O2 sensor voltage should drop. If nothing happens, connect the ECU wire that goes to O2 sensor to ground. This tells ECU a lean condition and rpm and O2 voltage should rise. If it passes either test, then the O2 sensor is good. If not, replace.

Next reconnect the sensor to ECU and put a voltmeter in line. To roughly adjust the AFR, run the engine and watch the O2 sensor voltage: it should be constantly fluctuating between 0 and 1 volt (if not, it's suspect even if it passed the above test). If it's stuck above 0.5 volt, the mix is too rich (turn AFR screw counterclockwise), if it's constantly below 0.5 volt, it's too lean (turn AFR screw clockwise). If you can't get it to constantly fluctuate between 0 and 1 volt by adjusting the AFR screw, replace the O2 sensor.

Once the idle and AFR is set, check the coolant temp sensor. I've never done it on the 944 so don't know where it is, but it should be in the water jacket of the cylinder head, and or near the thermostat. It will have two wires. You'll need an ohmeter to check it. Disconnect the wires and check resistance between the two terminals. At 68 degrees F, it should be 2,000-3,000 ohms, at engine operating temp. it should be less than 200 ohms. If the resistance doesn't drop significantly when it gets hot, it's telling the ECU to increase the injector pulse width, which will create an overly rich condition once warm.

If this checks out, try the FPR next. At idle, high vacuum is generated creating about 35-40 psi in the fuel rail (hook up a fuel pressure tester). As rpm and engine load increase, the pressure in the manifold increases due to the increased air flow and open throttle. This causes FPR to increase pressure acting as an accelerator pump at injectors. If FPR is bad or you have a vacuum leak, it will be too rich at idle, but will be OK when then engine is under load and higher rpm.

If none of this pans out, check the injectors themselves to make sure they're not leaking or stuck open. Then check the air temp sensor in the air flow meter. This richens mixture the denser i.e., colder the air is. It's influence isn't as dramatic as all the rest and I doubt it could cause such a rich condition that it would smoke, just hard cold start problems.

Hope this helps.

[T86951]

thanks for your input, it all helps in trying to figure out the cure to the problem.

Does anyone know if the OS sensor works when the engine is cold? I thought I read somewhere it only works after the engine gets to normal operating temp but am not sure of this.
It starts great so I am sure the injectors are not bleeding off. Also I pulled the fuse and ran the injector pressure off and let it sit overnight and it still did it when it started up. Its not flooded on startup and all plugs are black, but starts loading up about 5 seconds after I start it and quits in about 30 seconds. The colder it is the worse it is. In the summer when its 90 no problem. When its 40 does it just a bit and when 20, really bad.

[This message has been edited by T86951 (edited 01-02-2001).]