View Full Version : Q4 won?t go over 1,5krpm
I will need a bit of help from you guys...
Unfortunatelly, I have had engine coolant leakage on my Q4 and because of that, I have overheated the engine once a bit. The cylinder head looked fine so we just had it straightened just a bit on the bottom, replaced all the gaskets and while everything was off, we also replaced timing belt and countershaft belt, as well as the water pump and engine cooler.
What happened now, when everything was put back together, is that the engine won?t go over 1,500 rpm, badly backfiring and smoking black smoke from the exhaust doing so. The spark plugs are completely dry. If I apply more pressure on the accelerator, the engine dies immediatly. The fuel pressure is OK.
Another thing: the injectors are on voltage full-time. Is that OK? Shouldn?t there be intervals of voltage?
Any ideas?
Thank you in advance for all your help...
Welcome to the forum, is your car in the register? Where are you from?
Sounds like my car did when the map sensor pipe was not connected after some work, check this. Mine could rev over 1500rpm but it took some time.
The injectors having voltage the whole time, not sure about this but with the engine running they would be pulsing so fast I dont know if a volt reader could keep up with the changes. Just guessing here..
Thank you for your welcome, my car isn?t in the register yet. I come from Ljubljana, Slovenia.
MAP pipe is connected, have checked that. And the injectors have the voltage even before the engine is running, as soon as I apply contact on the key.
I come from Ljubljana, Slovenia.
One of a few then :cool:
Send details and photos of it to: webadmin@berlinasportivo.com and it will get put on the register.
Sorry cant help much on the problem. I suspect an air leak somewhere causing a big mixture problem.....or, thinking back to when I could not get my Q4 to run for the first time it did give very similar symptoms, I gave it to an Integrale garage and they changed the cam phase sensor - never did know if it was really broken but worth a check - not sure what the testing procedure is though...
Check the blue coolant sensor is plugged in and working, maybe you have some wires plugged in the wrong way around.
Send details and photos of it to: webadmin@berlinasportivo.com and it will get put on the register.
Will do as soon as the lady decides to run again :rolleyes: so I can make a photo or two...
Check the blue coolant sensor is plugged in and working, maybe you have some wires plugged in the wrong way around.
Coolant sensor is working, when I disconnected it, the car didn?t start at all.
How does the engine feel at idle? Smooth?
Will it stay at 900rpm? Is the timing 100% correct?
How does the engine feel at idle? Smooth?
Will it stay at 900rpm? Is the timing 100% correct?
Timing was triple-checked and is OK. At idle it feels a little bit rough and very sensitive on throttle position sensor. If you catch the TPS the car should stay around 900 rpm, but running a bit "roughly".
Is this correct: one ignition coil ignites cylinders 1-4, the other ignites 2-3. OK?
I think that is correct - it uses the wasted spark system..will confirm later as mine is in pieces..
Juan AR155Q4
26-08-08, 15:36
Ignition coils are OK.
As for the injectors, the ECU switches ground, so it?s normal if you are having +12V all the time.
For some reason more fuel is being feed.
If diaphragm of FPR has a hole, fuel could be going to cylinders, check this by disconnecting compensation hose.
Compensation hose is the one going from the regulator back to the gasoline tank, is that correct?
Is it possible that I would have problems like this due to faulty ignition modules?
Compensation hose is that the vacuum right!
Yep, I'm still thinking blue coolant sensor though, I would check the values at the ECU end to check.
Do you maybe know which pins are to check on ECU? Although I have checked the sensor itself and it has just the right Ohm value (cold engine, around 25?C air, value around 2kOhm). On the ECU, which values should be read?
Some days ago, mine made the same thing (first day after engine rebuild ) , wont go over 1500 / 1600rpm, i cleaned injectors and the tps was not correctly set.
Once with the injectors clean the car started smoothly and runs great.
Do you maybe know which pins are to check on ECU? Although I have checked the sensor itself and it has just the right Ohm value (cold engine, around 25?C air, value around 2kOhm). On the ECU, which values should be read?
I think if you search the site you will find a table of values (or a link to it), It wasn't all that long ago it was discussed.
Is there a possibility of the wrong plugs on the wrong sensors? There are two blue sensors, one for guage, one for ECU. Checking values at the ECU plug is always preferable as it rules out many possibilities.
The reason I am thinking this way is that you have just put everything back together, so may have knocked something or put it back in the wrong place. If it worked before, it should work now...
Plug leads the wrong way round?
Plug leads the wrong way round?
Sorry, plug leads? You mean the ignition cables? :redface:
Yes, cables to the spark plugs :)
No, if it is 1-4, 2-3 then it is OK. I have tried 1-4,2-3 on one ignition coil variant, and then I have changed the igniton module-to coils plugs between them (2-3,1-4). All the same, no good...
OK, it seems like we have located the problem. It looks like the RPM sensor on the crankshaft is faulty. We tried to start the car and then move it a bit and suddenly the car gained rpm and sounded very healthy indeed!
I read that the distance the sensor is from the phonic wheel is quite crucial. Hope its the fault your looking for :)
The problem was that the distance was in the correct range(0.85 from phonic wheel) and the car barely worked.Then we adjusted it to 0.55 the car would not even start anymore, as soon as we pulled the sensor away(probably further then 1mm) the car started normaly and the throttle response was normal.
Look like the sensor is losing signal somewhere and somehow(probaby the years of use made their tool).One way or another....the sensor is going to be changed. :)
Unfortunatelly, it is back to the drawing board for us. The RPM was replaced and the situation is not even slightly better.
You better check the crankshaft position sensor too. I had hard times with it, lot's of unpredictable behavior ...
it was changed to a new unit...
What could be the cause of ECU giving an uninterrupted GND signal to injectors? Two ECU units were tried and both do the same. As you all probably know, the injectors on the Q4 have a static positive pole connection through relay and the ECU interrupts GND signal in order to open/close the injectors. Well, mine have uninterrupted positive and GND signals all the time...
cuore_sportivo_155
02-09-08, 10:36
do you have an oscilooscope? try scoping the injectors and the primary side of the coils, to see if either injections or ignitions are missing. if both, it'll be an RPM sensor issue, if none, something is messing up the ignition timing or injection quantity.
try to remove the vacuum reference for the FPR and see if that makes a difference...
Will try to convince a guy working in an electrical workshop to give me a hand with an oscilooscope reading, I am unfortunatelly not very handy with those.
As far as the FPR is concerned, I have tried to remove it and the engine runs the same.
I have tried to read the ignitions with a stroboscope and it seems that two cylinders have poor and uneven ignition, but I cannot figure out why. I have changed the cables, the coils, the ignition modules, spark plugs, TPS, MAP, RPM sensor...Nothing. And then, for the cherry on the top of this Q4-cake, the engine goes mad for a second and revs to 6,5k rpm on the press of the pedal. Once, and no more.
cuore_sportivo_155
02-09-08, 17:57
carefully check the wire for the RPM sensor, and make sure it's running far away from the ignition wires. if the wire is shielded, make sure the shield is grounded on the ECU end only.
Missing ignitions randomly tell me there's a problem with the RPM sensor or wiring...
If you're not handy with an oscilloscope, you could put a diode (not a lamp) in series with the injectors
Looks like the problem is solved. The guilty part was one of the connectors on ignition coils, which was found pretty much by accident. Well, the car runs fine now, goes into rpm and accelerates as it should.
Thank you all for your help!
Well, the car runs fine now, goes into rpm and accelerates as it should.
That's great news :smile:
Greetings,
Marc
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