Cold start FI problem

[shawn71]

Now it's getting colder I really should get around to sorting the cold start out on my 411 fitted with a 1700 and 'd' jet injection.
The problem seems related to air temp and a cold engine. When its cold it will start but is very smokey, not blue oil smoke but darker, like its over rich. It also runs like a bag of nails.
I have cleaned and made sure all connections in the engine are tight and this made no difference. All air pipes appear in good order and tight as well.
Once the engine has warmed up it runs very well and all the time the engine is warm will restart with no issues.
This leads me to suspect a temp sensor which I assume is fitted somewhere? Any ideas?

Thanks in advance for any help or ideas

[937carrera]

Do you have acces to a multimeter to test components.

IIRC the auxilliary air valve used to fail . The test value is 12.5 ohm +/- 1ohm at 20 C

Get yourself the D-Jetronic manual from here http://pcbunn.cacr.caltech.edu/jjb/Pors ... tronic.pdf

[Editor]

There is a cold start injector which is controlled by a temp sensor (thermo switch), and from '70 models only operates when the starter solenoid is eenergised and conditions are cold enough. I believe earlier Type 4s had a relay to power the valve. If the thermo switch is faulty I guess it may be staying on too long, or possibly the 5th injector is leaking some fuel until things warm up enough. The sensor is on a bracket bolted to the crankcase near the air-intake distributor.
The cold start injector works if the engine is really cold - maybe below 5deg C. It's the equivalent of a choke flap in a carb.

The auxiliary air regulator (AAR) is really a fast idle control - i.e. it allows more air in to the manifold, which the manifold pressure sensor interprets as an increased throttle opening. It doesn't richen the mixture at all. I think the Type 4 has an electrically heated AAR, though Type 3s only had that on automatic transmission engines.

Maybe Jim Bourne has a clue on this - he's your nearest Guru on Type 4s. He may have spare parts to compare or try, too.

[937carrera]

.

The auxiliary air regulator (AAR) is really a fast idle control - i.e. it allows more air in to the manifold, which the manifold pressure sensor interprets as an increased throttle opening. It doesn't richen the mixture at all.

Agreed, but if the 5th injector is working, and the AAR isn't allowing additional air in then the mixture is too rich and there is insufficient air for fast idle running when cold. (see the last para on the page numbered 225 in the link above for more info)

That would seem to fit the symptoms, but I could well be wrong and will bow to those with greater experience.

[Editor]

According to page 225, the starting enrichment is only present when the starter is being operated, and only then if the engine temp is pretty cold.
The warm-up enrichment is done based on the cylinder head temp sensor. It would be worth checking the cold value of the resistance to see if it is within acceptable limits - around 300 Ohms downwards, depending on head temp. The resistance should fall as it warms up. A higher resistance will richen the mixture, so bad connections or fraying wire will tend to make it run richer. Another major problem that makes for rich running is low charging voltage. Check the voltage regulator is giving out 14V at medium rpm.

The AAR simply causes extra air and fuel in by reducing the vacuum in the intake manifold - the extra air causes extra fuel to be injected. That ratio is not controlled separately by the temperature sensors. The manifold pressure sensor, throttle opening and engine rpm are all measured to allow the ECU to determine how long to open the injectors for.

Something else that can cause stumbling is when the injector plug connectors are not a good fit on the injector pins, which could be temp dependent. Also of course, many non-FI engines are a bit pig-like when cold. It's easy to blame the fuel injection system, when it's a problem in the ignition system, which could easily be aggravated by low temps!

[shawn71]

I have finally found time to check all that you have suggested and the only thing that I can find is the thermo switch seems to have a permanent open circuit, so looks like this is at fault. I will double check the timing when I get my timing light back from brother...

[richtbiscuits]

Sorry to revive an old thread but did changing the thermo switch solve the problem? My 412 LE is doing pretty much exactly what was initially described in this thread. It starts, runs fine for 30 secs then the revs fall and it runs like a dog before cutting out. There’s white smoke with a petrol odour and heavy sooting in the exhaust. It’s fine once warm although it does stumble at constant speed and needs a dip on the accelerator to clear it. It’s recently had a new alternator and voltage regulator so I don’t think it is a charging problem.

[shawn71]

Haven't used it much this winter but changing the temp sensor/thermo switch did make a difference

[richtbiscuits]

I'll give it a go then - I'm sure I've a thermos switch tucked away amongst the spares somewhere. Thanks.

[richtbiscuits]

I changed the thermo switch but no joy. Found the cylinder head temp sensor cable was loose so fitted it properly and the engine runs worse. Its back-firing now. If I allow more air into the air distributor box by partially disconnecting the hose from the case breather the engine picks up and the smokey exhaust clears. Seems I'm just not getting the air in. Anyone ever had problems with air supply through the air filter or with the throttle body. On the outside chance I'll change the plugs and condenser just in case its a sparking thing, it does feel underpowered and lumpy when driving. If anyone has any suggestions I'd be most happy to hear them. Thanks.

[Editor]

Sounds like an over-rich problem, due to too much fuel. Try removing the 12V connector to the cold start injector and tape it up. If that continues to inject (or even dribble) while running, it will mess up the mixture big time. It shouldn't even try to inject fuel unless the temp is very low, but the fuel line is still pressurised, so if the injector doesn't close fully, it can leak.
Main injectors leaking into cylinders can also produce the same symptoms.
Problems with a leaking manifold pressure sensor diaphragm makes the injection system think the throttle is more open than it is, so more fuel is injected.
Some Type 4 control boxes had a click knob on the end that could adjust the richness. It might be worth seeing if yours has, and trying to adjust it to see if that improves. Make sure to note where it is to start with, so you can put it back to the original point again if there's no change.

[richtbiscuits]

Thanks for the advice, much appreciated. I disconnected the wiring to the cold start injector with the engine idling while cold and it made not a jot of difference. I haven't yet pulled the injector to see if it injects due leakage. I'll take it out, tape up the hole and see if it does leak. I swapped the pressure sensor for a spare I had and again there was no difference. The control box, is that the 'computer' under the arm rest? If so I'll have a look at that. Could poor adjustment on the throttle body cause over-rich mixture due to lack of air? I used the car to commute to work today and there's so little power in the engine, it just doesn't accelerate, as if its always running rich.

On a completely separate note, should the fan in the engine bay supplying air through the heat exchangers to the cabin be running when the engine is on or is it connected with the eberspacher switch? I ask because when I open the control leavers between the seats nothing really happens. A bit of hot air comes through but there's no draft as such so it feels like nothing more than a sniff of heat through convection. The ducting is largely intact as are the control cables and I can see them working the flaps under the car. When I pull the ducting off the heat exchanger there's no draft there either.

As always any advice is most welcome. Thanks.

[richtbiscuits]

So I removed the cold start injector but no change. I changed the carbonized plugs but no change. I twiddled the knob on the control box and ... it's like a completely different car. After adjusting all the way clockwise and letting the engine cough itself clear of all the excess fuel in clouds of smoke it now idles sweetly and pulls well through all gears. What a joy it is to drive now, I'm absolutely loving it!

I can't thank you enough for the gem of advice as I would surely never have got there as a cause of all the trouble. My car and I will be enjoying a trip out to Dubfreeze tomorrow to celebrate!

Thanks again from one very happy 412 owner

[Editor]

Glad it is running OK now. That was just a bit of memory raking!

I don't recall which way weakens the mixture. It was never generally fitted on the Type 3s, but it's possible there was a dodgy bit on the potentiometer that got cleaned up by turning it. I wouldn't expect fully one way to be the exact correct adjustment, but you really need a CO meter to check. FI is a really low CO value when properly adjusted.

Keep an eye on things and take a look at the plugs to make sure it's not running too hot - their colour may give a clue as to whether the mixture is now OK or perhaps a bit too lean. which could do damage to the engine through overheating.