billy610

Hi, I have a '89,944S2. Recently, when it has been lying for a couple
of days and I start her up there is a cloud of black smoke coming
from the exhaust. There is also a missfire 'til it clears.
I am sure it is burning too much fuel, it smells like it's too rich
(you know the smell I mean). Has anyone had the same problem? and
what was the fix?
I think it could be an injector leaking, and dripping fuel into the
inlet manifold, til the fuel pressure drops. Then it is burnt off on
startup, giving me the too rich smoke effect. Any ideas where to
start?
Other than that she runs fine,and there is no noticable difference to
the fuel consumption. I have checked the air filter, and pipes for
blockages etc and they are all ok too.
Thanks in advance, Billy

M758

Probably an Injector leaking down.

There is rich condition I am chasing in my 84 944 street car. I have thread in the main 924/944/951/968 forum "Running Rich" where I am trying to solve it. If you are rich only on cold start and only right away it probably is an injector. Check the plug to see if one or all are black. If it just one then i'd bet it would be that injector leaking.

Jaxon

If it is injectors, what would a set of injectors run for these cars, and how much labor is involved?

Mike Buck

Jaxon,
sent you a PM

smkn951

i recently pulled all my plugs and found that there's a build up of black soot on each and every one, the fuel preassure gauge located at the end of the fuel rail indicates that it's holding preassure at least overnight. what else can it be? could it be a weak ignition system?

billy610

Still can't get to the bottom of this. I pulled the 4 plugs after a cold start up and running for about 30 seconds, they were all black soot, none was worse than the rest. This makes me think that the injectors are either all leaking, or there is something else, I don't think all the injectors would leak at once, so what do i do? The car has a K&N panel filter fitted, which was supposed to have been cleaned and oiled at the last service (1000 Miles ago) it was not! it was filthy, (Thanks Sportstune!) I used the K&N cleaning/oiling kit and refitted it. No improvement. I suppose the next step is to pull the injectors and have them cleaned,flow and leakdown checked, or fit new injectors. Any thoughts? any other ideas? anybody, please help!
Regards Billy.

peanut

If you are getting a over rich mixture at startup then you need to look at the whole process of fuel/air metering at coldstart. This involves a whole heap of sensors influencing the DME such as the IAC idle air control which regulates the gas/air mixture at startup
The fuel pressure regulator ETC

there is a heap of excellent faq files over on Parragon
http://64.226.197.185/

peanut

Hey billy did you find the cause of your problem yet ?
Is the smoke a recent thing or has it been coming on a while ?
It might help to put some hotter running plugs in until you find and cure the cause. A compression test is easy to do and if you know how to read the results it might indicate a problem with valve guides or rings maybe

billy610

No, (or should that be DOH!!!) I've not got to the bottom of it yet. Seems to be something that has crept up over the past 6 months.
Don't think it is anything to do with engine wear, it's not oil burning, it's fuel. I will probably pull the injectors this week, and get them checked/cleaned, at 14 years old, and 120k miles I think they deserve it!
I have a compression test guage, last time I checked the compression was Feb this year, all 4 were within about 5psi of each other at around 190psi, IIRC, only done it out of interest!
The reason I posted this, was incase there was a common problem (read easy fix!) that other listers had come across and I had not.
Looks like I will be the one to get to the bottom of it,.
Thanks for your input, it is appreciated, and I'll let you know how I get on.

Regards Billy.

vwghia-guy

Did you ever get this problem solved?

peanut

this thread is over 8 years old now.
You'd be better off starting a new thread really.
If you have a similar problem let us have all the facts and we'll see if we can help.

A quick test to see if you have an over-fuelling situation on cold startup is to disconnect the electrical connector to one of your injectors.

Sure Its gonna run a bit lumpy on 3x cylinders but If the engine runs better without the smoke then chances are that either you have a leaking injector or the fuel pressure is too high (FPR valve stuck).

Either way you should do a fuel pressure and fue pressure leakdown test

Legoland951

Rich condition is rarely ever the injectors. The AFM adjustment being out of spec is the most likely problem. If you don't know what you are doing, take it to someone with a exhaust gas analyzer like a smog station and they will adjust it for you. I can explain to you how to do it without any machinery but it will take me too long.

peanut

on the contrary on a 944 its quite common for the injectors to be the reason for an over-rich fuel delivery but not just from leaky injectors.

On cold starting the ECU enriches the mixture by either pulsing the cold start injector or increasing the injector pulsing depending on model.

if the coolant temperature switch is faulty the ECU will enrich the mixture for too long thinking the engine is cold

Anyhow this thread is over 8 years old

Legoland951

I know the thread is 8 years old so I am addressing the question of the guy who revived this necrothread. To be literal, all over rich fuel delivery is accomplished by the injectors, but very few are "caused" by it as it can only be the cause if IT is the malfunctioning part by leaking. The coolant temp at the head does not fail nearly as often as AFM being out of adjustment. I had to change only 2 of those out as I had to adjust the AFM on over 100 different 944s in the past.

90 percent of the time, the AFM is adjusted improperly when the car is running rich. In California we have the wheel dyno smog check and rich condition will render a vehicle illegal to operate.