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+1 for allmine comment, it does seem like the ECU is losing one vital piece of input and goes into "leap home" mode. If you ever experienced this mode, it sounds exactly like what you described. Now this doesn't help I know. Reading the thread I didn't find any follow up on the knock sensors, disconnecting one would probably get you into this mode, at least you could compare. The ECU won't let you desintegrate your engine, just don't push it.
it may be time to dig alittle deeper.....i had a broken valve spring cause a similar problem or even a valve seat falling out and then going back into place....just an idea.....vinnie
@techman : since my car had the braided ground wire and I read they can be troublesome I have replaced it with the updated one about a year ago.
@mesprit87 : you're right about the knock sensors, haven't tried this yet. Can I just disconnect one while the engine is running? The problem happens also when I start and just let it idle so I can easily disconnect one while it's idling. About the "leap home" mode, wouldn't that store a fault in the ECU memory? When I connect Tore's OBD cable to the car it reports no errors, that' s the strange thing of this problem. According to the car there's absolutely no problem.
@Vincent : that crossed my mind also but wouldn't it happen more often then? It's always when warming up, never stone cold or fully warmed up.
Don't know if your aware, but on start up for the first couple of minutes the dme chucks far more fuel in to the engine than it actually needs to run, the purpose is to get the cat up to operating temperature as fast as possible so it can do what it's ment too do as quickly as possible
Probably not relevant, but thought I'd mention it as you said you issue happens in the first minute or so when starting the car
I think my car is definitly female!!
When she HAS to misbehave she behaves perfectly.
This weekend I have acces to a Durametric.
Made 3 runs with the Durametric plugged in to trend the live values. Perfect behaviour of engine.
Will try again when she cooled down enough.
Finally hooked up the fuel pressure gauge.
When engine runs smooth I've got 3.6bar (52psi) on idle.
When running rough the pressure goes up a bit 3.65bar (54psi) on idle.
Very weird, I hope you guys have some sort of explanation of this.
Also made small movie with iPhone so you can hear the weird engine sound.
Not the best quality and some wind noise on the background but the best I have right now.
Try to isolate the problem to one side or the other.
It looks like your video is the left side. Is that the side
that is sounding rough or do both sides sound rough?
Then try to isolate the problem to one cylinder.
When the engine is running smooth disconnect one
injector. Does the fuel pressure rise? By the same
amount you noted earlier of 2 psi? (I have not done this
test so not sure if the pressure will rise or not.) If so then maybe
an injector is not working properly. Could be the electrical
signal to the injector or the injector is clogged, dirty,
sticking or dripping.
When the engine is running rough, disconnect one
injector at a time and check if the engine note changes
or stays the same. If it stays the same that could be the
problem cylinder.
Haven't read the entire post but have you ever removed and cleaned
the injectors?
There is another set of tests you can do on the injectors but will require
an oscilloscope and low amp probe and appropriate test leads.
Check each injector voltage waveform and the current waveforms.
The injector contains a coil and pintle and these waveforms will tell
you if the injector is functioning properly.
I had my injectors checked and cleaned and they were tested before cleaning and after. Not much improvement there, they were pretty good before cleaning and marginally better after. Also all six had a normal spray pattern.
As suspected, car behaved the same after installing the injectors.
As suggested before, maybe the car goes in "limp home" mode. Could it be that the reference impulse sender on the flywheel sometimes loses the signal because it is on the outer edge of its limits, more then 0,2mm as indicated in the workshop manual.
Does anybody knows what happens when the signal is lost on an already running engine? If the sensor doesn't pickup the signal when cranking, the engine doesn't start, but when it's already running?? Does it go in "limp home" mode then?
Is it safe to disconnect the plug from the sensor on a running engine?
I know it can be tested with an oscilloscope but that's something I don't own.
I would want to put a timing light on it just to see if that changes when the tone changes. I do not know if limp mode will fix timing at a specific value or not..
Curt
Don't know if fuel pressure regulators on these cars are vacuum referenced... If so then a reduction in engine vacuum will result in an increase in pressure...
hello, there are two major culprits who make this phenomena on your ROW 993.
the problem is to know which one of the two, to spend less $
1- engine temperature sensor
2- ignition switch part number 993.602.706.00 or bosch equiv. 0227100200 below driver seat. there are fake bosch switches in the market, so buy from reputable source
If you say when hot, the problem goes away 100%, then it is more the temperature sensor
try checking the temperature of this sensor by OBD on cold car. If it shows above 100* celcius, it is dead and it does not show as error on PST2 unless it is erratic or volatile reading.
my best regards
@Geolab : Ignition switch has indeed been replaced with a Bosch part purchased in a Bosch centre. It was one of my first suspects after reading a reply from you about this. Temp sensor behaves normal, see below pics.
So today I tried 2 things :
First unplugging the flywheel sensor to see what happens : the engine just stalls the moment I unplug it so I don't think the sensor loses signal.
Next I hooked up the OBD cable with the scantool hoping the engine misbehaves so I can see some live values, well it did!
I noticed that when it runs rough the base inj LOAD and base inj time changes. I'm not sure why it changes but my guess is that the DME does this for some reason, now the question is why?
Below are some pics I took.
First pic engine running rough at idle, second rough running holding 2000rpm, 3rd pic engine running normal.
Did you check the temperature of the spark plugs? It sounds to me like someone has put in too cold a plug since it operates normal after it warms up. We used to have that kind of problem when we were using the leaded gas and it was cold.
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