Alfa Romeo Forums banner

1 - 20 of 40 Posts

·
Registered
Joined
·
273 Posts
Discussion Starter #1
Hi,
Does someone know how the cold start circuit works on a Motronic engine?
My car is starting a bit rough when cold, then hesitates for about a minute, and then snaps to life (rather abruptly) and runs fine afterwards. It is like clockwork, and very repeatable, so I am guessing there is something that is timed or dependant on coolant temp.
Wondering what to look for to resolve the problem.

Thanks
 

·
But Mad North-Northwest
Joined
·
10,078 Posts
It doesn't really have a cold start circuit like L-jet. The computer richens the mixture during cranking via injector duration, IIRC. So my guess is to look for a bad sensor or actuator.

Stuff that comes to mind is bad coolant temp sensor, sticky idle air controller, or maybe a bad O2 sensor heater. You getting any check engine codes?
 

·
Registered
Joined
·
7,659 Posts
Like Tom says sounds like a sender/sensor

I'd check the plug connection and wires under the rubber boot on the Motronic CTS (Coolant temp. sensor), that is the blue one on intake.

if you pull the plug connector you can also check the resistance of the sensor itself (never ohms test the plug!)
CTS Ohms test:
@ –10°C the resistance should be 8.3 to 10.5 K.ohm
@ +20°C should be 2.2 to 2.7 K.ohm
@ +80°C should be 0.28 to 0.36 K.ohm

if you confirm sensor is bad, p/n is Bosch 0 280 130 026
 

·
Registered
Joined
·
2,297 Posts

·
Registered
Joined
·
273 Posts
Discussion Starter #6
Thanks very much for the feedback.

I was getting a fault code a while ago, for the O2 sensor, so I replaced it. I did curiously get the fault one more time AFTER replacing the sensor, but that happened only once, and hasen't repeated lately.
@Gubi : I am going to check the heater circuit of the O2 sensor, that seems like a good avenue.

I checked the coolant sensor yesterday as the car was cooling down, and got a reading of 640 Ohms at 60 degC (according to the dash temp gauge). Seems to be in the ball park. Will test also when it is cold.

I picked up some carb cleaner and will pull off the idle control valve and give it a good cleaning.

For additional info, I did consume an entire can of carb cleaner a few days ago, spraying on anything I could see related to the intake looking for vacuum leaks an could not get a change in idle, so would appear that there are no vacuum leaks

Will keep you posted

Thanks again for chiming in with your feedback.
 

·
Registered
Joined
·
7,659 Posts
I picked up some carb cleaner and will pull off the idle control valve and give it a good cleaning.
after you clean it, then give it a very brief squirt of WD40 to slightly lubricate.
Also make sure the rubber seal it sits into (on the plenum) still seals.....they get loose over time and can be a cause of false air, so I always smear some silicone grease around it to make sure.

whilst there, you could also check the resistance of this valve....somewhere between 7-11 ohms between the 2 pins is good.
(I get 7.7 ohms on my S4)
 

·
Registered
Joined
·
273 Posts
Discussion Starter #8
Quick question : on the Oxygen sensor, there are 3 wires coming off, two white ones that go to a 2 pin connector, and one black one going to a signle pin connector. I've assumed the single wire is 12V for the heater and two pin connector is for the signal, is this correct?
thanks
 

·
But Mad North-Northwest
Joined
·
10,078 Posts
Backwards. Two wire Bosch connector is 12v to the heater. Single wire is signal output.
 

·
Registered
Joined
·
273 Posts
Discussion Starter #11
Oddly enough I got a check engine light this morning when I started it to go to work, it was idling like a race car until it warmed up. I did pop the hood to confirm that the VVT solenoid was working, which it is. The fault code was 1223, O2 sensor out of range. will check to see that the O2 sensor heater is getting 12V, then carry on to cleaning out (and lubricating) the idle control valve.

Will keep you posted.
 

·
Registered
Joined
·
273 Posts
Discussion Starter #12
So I've confirmed that the O2 sensor heater is getting 12V. I ended up changing out the idle control valve with a new one, and this did indeed fix the race car idle when cold. Curiously it took about 3 or 4 ignition cycles to kick in, almost like the ECU took a few cycles to release the fault. The car now idles much better, BUT the check engine light is still coming on when the car idles! It is still the 1223 fault, and to be honest it does smell a bit rich.
What else could it be? I am thinking maybe the air flow meter is out a bit, could have been tampered with (very likely in fact, since the cover has visibly been removed at some point), or maybe the injectors are leaking a bit of extra fuel?
I will check the continuity of the wires back to the ECU, I am a bit doubtful this is the problem and am reluctant to disconnect/connect the big connector, for fear of damaging or upsetting any one of the fragile terminals there, so trying to exhaust other possibilities first.
How does one check that the Air flow meter is calibrated, when the flap is closed, what should the voltage on the output pins be? What about at idle, what voltage should I see?

Thanks again in advance for your input, it is much appreciated
 

·
Registered
Joined
·
7,659 Posts
if it helps, these were the values I got on my euro S4 AFM when I tested it a few months ago.
Hopefully the wire colours are the same on the US models.

Pins are numbered 1 to 5 counting from right to left:
Pin#5 – Grey/Red
Pin#4 – Green (Ground)
Pin#3 – Light Blue/White
Pin#2 – White/Black
Pin#1 – Blue

Resistance Test (on AFM itself...NOT the plug going back to the ecu!):
2+4: 38 Ohm (Reference value about 100) - Note: my result here seems low compared to reference value, but it works fine so I am leaving it be!
2+5: 2400 Ohms (ambient temp, about 20C) - ok
3+4: 352 Ohms (Reference value about 400) - ok

Volt Test (Rubber Boot pulled back; Connector back probed; DVM set to 20VDC and connected; and only then turn Ignition ON for each individual test):
1+4 [CO pot output]: 2.48V (Reference value 2.5V) - ok
3+4 [Reference voltage from ECU]: 4.97V (Reference value 5.0V) - ok

Flap Movement/AFM removed from air cleaner (Pull back the rubber boot and back probe the Plug, then open/close the flap with your fingers):
2+4 [Airflow output]: closed flap 0.25V >>> 4.50V with flap fully open - ok (Note: voltage should rise and fall absolutely smoothly as flap is opened and closed, otherwise the track needs cleaning (ONLY clean with isopropyl alcohol – NOT contact spray!) If cleaning does not help then the arm will require bending to sweep a new part of the track)
 

·
Registered
Joined
·
273 Posts
Discussion Starter #14 (Edited)
Thanks again Dom for the generous help
I made the check on the air flow meter, and it seems like it is behaving properly

Resistance checks:
Pin 2-4 : 47 Ω
Pin 2-5 : 1034 Ω
Pin 3-4 : 360 Ω
The temperature was probably around 50C as the AFM was still hot from running, nearly too hot to touch, so that might explain the difference for the pin 2-5 measurement. Looking at the wiring diagram that measurement should perhaps be pin 4-5 instead to isolate the thermistor, 2-5 seems to me to be measuring both the pot and the thermistor in series

Voltage checks:
Pin 1-4 : 2.49V
Pin 3-4 : 5.00V
Pin 2-4 : 0.25V (fully closed) 4.78V (fully open) the voltage increased smoothly as I opened the flap.
Seems that the AFM is working fine.

The temp sensor also seems to be ok :
60C (approx.) = 636 Ω
25C (approx.) = 2050 Ω

I also removed the idle control valve from the plenum (it is a new one by the way, genuine Bosch), then started the car and watched it to make sure it was moving. Of course the engine was hunting on the idle since valve was removed, but I could see clearly the valve operating trying to control the idle (opening and closing as the idle went up and down). It appears that this is working also.

I also swapped out the brake booster hose as it looked really poor and was quite brittle (without a doubt the original that is now 25 years old!). I swapped it this morning before starting the car, and upon removal there was a “whoosh’ of air, indicating that it was not leaking as it held vacuum overnight. Nevertheless, I have a new booster hose on it now.

After all this intervention, the car now seems to be running better (but not perfect). I am back to the situation where I don’t have a check engine light at idle (or any other condition), but the idle is still a bit rough when cold, and if I try take off within 1 minute of startup, it hesitates, but almost like clockwork after a minute it snaps to life and runs fine. The idle does still “hunt” ever so slightly, but I probably wouldn’t even notice it if I were not troubleshooting this problem.

So all I can think of is more small vacuum leaks. The main spot I suspect would be the seal between the inlet plenum and the idle control valve, in fact I was surprised not to get this seal with the valve itself. Is this a Bosch part or an Alfa part?
Is there anywhere else that a vacuum leak could be that is not near the intake plenum? Also, what about the air conditioning, mine does not work really and seems to be disconnected, does the ECU do anything to the idle if the AC is on?

Thanks again for the really great help, it is very much appreciated.

Andrew
 

·
Registered
Joined
·
7,659 Posts
Your AFM tests as good as mine at least, and my car runs/idles fine!
Yes that IAV rubber seal on the plenum can harden or slightly shrink, but nothing that a little silicone grease smeared around it won't cure. I have never seen that actual seal for sale.

Have you cleaned out your OVS (Oil Vapour seperator, next to the coil) and checked all the hoses there? that gets very clogged with horrible crud and can affect the idle. (I do it every year now)

If you still suspect a minor air leak somewhere, have you tried this method that Vin posted?
http://www.alfabb.com/bb/forums/spider-1966-up/417834-vacuum-hose-leak-test.html
 

·
Registered
Joined
·
273 Posts
Discussion Starter #16 (Edited)
Good suggestion about the OVS, I will check and clean this as well. I am sure it must be filthy, based on the amount of maintenance that the car appears to have had in it's previous life.
One other thought that comes to mind is the throttle position sensor, I would like to make sure during idle that it is both a) telling the ECU that it is closed , and b) is in fact really closed. Do you happen to know what the resistance should be at the closed position (or the voltage signal)?

Will try also the pressurized leak test (from Vin), just need to go get the air nozzle with the rubber tip.

Thanks again for the help Dom, if I were near Koln I would buy you a Kolsch beer! (I have family in and around the Bonn/Koln area, nice part of the world!)
 

·
Registered
Joined
·
7,659 Posts
Andrew, a few more thoughts:
make sure that your throttle returns correctly to the throttle stop.
you could check that the butterfly/throttle body is clean inside (need to remove the big air pipe and the hard plastic pipe) as even when throttle is fully back on its stop, the butterfly is very slightly open (so it idles!) so dirt here will affect smooth idle too.

the TPS is really just a on-off sensor
Easy test is (engine off) just move throttle off the idle stop with your finger and as soon as it moves you should hear a slight click (the trip point) from the TPS.

If it doesn't click, unscrew the 2 screws and rotate just enough so that it does click when coming off idle.

An ohmmeter between pin #18 & #2 (the top two pins) should move from no resistance to infinity, that is the trip point.
 

·
Registered
Joined
·
273 Posts
Discussion Starter #18
A few more updates to this saga, I thought that the idle was “good enough” to go for the smog test, and it may have been, but I failed miserably on NOx, so getting a new catalytic converter installed this morning. In any case, I don’t think this is related to the idel problem (smog test is on the dyno for 15 and 25mph)
I did a few more tests last night : OVS not plugged, and the hoses are not plugged either. The hose going from the OVS to the manifold is not it great shape, but does not appear to be leaking. I’ll replace this, but I don’t think that is the culprit.
I checked the TPS and it does click just as it comes off “closed”. The switch behavior seems a bit inconsistent with you had Dom:
I didn’t see the pin numbers on the connector, so just referring to them as top, middle and bottom as oriented on the car

PIN-PIN : Throttle Open / Throttle Closed
Top-middle : Open / Open
Middle to bottom : Closed / Open
Top to middle : Open / Open

So it would seem that pin 18 and 2 are the bottom two pins on mine, yet for you it was the top two? The other strange thing is that the pin 18 to 3, which would be the normally open contact, does not close when the throttle is opened. Do you know if the Motronic is looking at this pin also? There is a wire in the connector, so I guess it is there for something (redundancy perhaps).
What about the closed position of the throttle, is there a way to make sure it is set at the right position?
I also checked evaporation solenoid valve, this is strange. It gets the 12V from the Motronic relay, and then the ECU switches ground to activate it. It seems to turn on when the ignition is on (at least on a warm car), but measuring the voltage I got only 3.2V across the terminals. The terminal closest to the fender is getting full battery voltage when measured to ground (13.7V when the car was running), but the other terminal (closest to the engine) was at 10.5V relative to ground (?). I was wondering if it was a PWM perhaps, but the DMM couldn’t pick up a frequency. Is this definitely an on/off 12V solenoid? If so, I guess I will go hunting a bad wire back to the ECU. With the ignition off, the valve is closed (i.e no air gets through). I didn’t test when running, but really suspect the valve is not opening.

Thanks again for the input!! Getting close-ish!!
 

·
Registered
Joined
·
7,659 Posts
Well I wouldn't be so sure a new Cat wont solve your idle problem.....it might have come apart inside and causing a slight blockage!

yes, the Evap solenoid is just on/off. It allows gasses from the tank to pass out from the charcol canister (under the rhs fender) and get recycled thru the intake.
just take off the wires on the evap solenoid and connect 12V....you will hear/feel a slight click. If it clicks the solenoid is basically working.
The 2 wires of the Evap solenoid connect to a) pin 34 of the ECU and b) pin #87 of the 'auxiliary' motronic relay under the rear shelf.....But yours sounds as if it is working anyways.

TPS: operation sounds fine: the middle pin (#18) is ground (G66)

Throttle: does it sit on the stop? There is a stop adjuster, but is factory set so I wouldn't touch that (yet!)...........if it sits on the stop and the tiny gap I mentioned between butterfly and throttle body is there (did you clean that...pain I know to take all the hoses off again, but worth checking!), then it sounds good. If it is not sitting back on the stop, try disconnecting one of the throttle rod balls on the throttle, now it should.
 

·
But Mad North-Northwest
Joined
·
10,078 Posts
I'm not so sure your TPS is working right.

Yes, middle pin is common IIRC.
One of the other pins is the idle signal. This should have continuity to common with throttle closed and open once you slightly open the throttle plate.
The other is the full throttle signal. This should be open with throttle closed and have continuity to common when you fully open the throttle.

You can test the solenoid by disconnecting the wires to it and touching the solenoid terminals with a 9V battery. You should be able to blow through it when voltage is applied.

You really really shouldn't ever touch your voltmeter probes to any wires in the harness. This is very bad form and can damage the ECU. Always disconnect the harness connector and test the sensor or solenoid, not the wires.
 
1 - 20 of 40 Posts
Top