S4 Spider (Motronic 4.1) Cold Start Circuit - Page 3 - Alfa Romeo Bulletin Board & Forums
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post #31 of 40 (permalink) Old 08-11-2015, 01:46 PM Thread Starter
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After a weekend away, got a chance to replace the fuel pressure regulator. I ended up getting a Bosch (same part number as the one I removed), turns out this parts is also used on many VW's of the same era. There seems to be some issues with the regular part suppliers about the right part number (exactly as Dom pointed out, threaded vs. nipple connections). I didn't want to go down that foxhole, so just got the right Bosch part number (0 280 160 235) which is a 3bar regulator by the way.
Put it in and the car runs (dare I say...) as it should. I fiddled around with the idle stop, and it doesn't seem to be too sensitive, I guess the IAC is simply compensating to get the right amount of air in there. Here is what I ended up doing : Found the point where the set screw comes in contact with the throttle (using a very thin feeler gauge is good for this), marked the point, then turned the screw CW (in) to see where TPS sensor trips open (bottom two pins, normally closed), found this point then turned the set screw back (CCW) to see when the TPS closes again. There is, of course some hysteresis in the switch. This is shown in the picture below.
The idle seems pretty insensitive to the position of the set screw, as long as it is between the first contact point and the point where the TPS opens. The idle does increase as soon as the TPS opens, and the idle does go down when the throttle is fully closed, but in between these two positions, i did not notice much difference, so I left it at the halfway point.
Can anyone confirm that the TPS open and close positions are more or less right?
The last thing I need to address is the evap solenoid not getting a good ground switch to come on, I think what I will do is just ground the neg side of the coil so that the solenoid comes on when the ignition is on since the 12V is supplied by the switched relay. I believe that the solenoid is always on with ignition unless it is cold, in which case it either waits for the coolant temp to get to a min value or uses some other trigger. Does anyone know the switching logic for the evap solenoid?
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post #32 of 40 (permalink) Old 08-11-2015, 01:58 PM Thread Starter
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I just read the link about setting the throttle stop on a TS, I beleive that this should be identical to the S4, will give that a try to dial it in a bit more

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post #33 of 40 (permalink) Old 08-11-2015, 02:03 PM
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The TPS position is adjustable. So using where it's at now may or may not be a decent guide.

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The last thing I need to address is the evap solenoid not getting a good ground switch to come on, I think what I will do is just ground the neg side of the coil so that the solenoid comes on when the ignition is on since the 12V is supplied by the switched relay. I believe that the solenoid is always on with ignition unless it is cold, in which case it either waits for the coolant temp to get to a min value or uses some other trigger. Does anyone know the switching logic for the evap solenoid?
Not a great idea, since IIRC the Motronic actually adjusts the mixture slightly when it opens the solenoid to account for the additional air. Are you sure it's not ever opening the solenoid? You may just be checking for ground during times when the solenoid is supposed to be closed: it's not open all the time.

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1963 Giulia Spider (1750 engine)
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post #34 of 40 (permalink) Old 08-11-2015, 02:07 PM Thread Starter
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Quote:
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Not a great idea, since IIRC the Motronic actually adjusts the mixture slightly when it opens the solenoid to account for the additional air. Are you sure it's not ever opening the solenoid? You may just be checking for ground during times when the solenoid is supposed to be closed: it's not open all the time.
You could be right, I've been assuming that it is open when the engine is warm, but I know what happens when one assumes...

I'll check it in a few more operating conditions to see whether or not it is turning on or not. Thanks for the tip.

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post #35 of 40 (permalink) Old 08-11-2015, 02:08 PM
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Also, if the solenoid is malfunctioning you will get a check engine light and code. This happened to me so I know the self-test works. So I'm thinking you may not actually have a problem.

Tom

1963 Giulia Spider (1750 engine)
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post #36 of 40 (permalink) Old 08-11-2015, 03:23 PM Thread Starter
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Thanks Gubi, that is good to know. I've never had a check engine code for anything other than O2 sensor out of range (1223).

Gubi or Dom (or anyone with a 91 spider) would any of you be able to do a quick voltage check at the evap solenoid to see if your is on when the car is running and at operating temp?

I am going to drive the car around for a day or two, and if there are no more symptoms (or check engine lights!), I will go in for my smog re-test. finger crossed!

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post #37 of 40 (permalink) Old 08-11-2015, 06:52 PM Thread Starter
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Believe it or not, I just glanced through the owner's manual (what one does once the problem is more or less solved...)and found the following paragraph about the evap solenoid :

"When the engine is operating under load conditions, with a considerable flow of air into the engine, the injection and ignition ECU provides for the opening of the "evaporative" solenoid (14)"

So it would seem it is NOT on all the time, just under load. I am going to assume that mine is functioning correctly since I've tested the solenoid itself, checked that the lines aren't plugged, and don't get a check engine light concerning it. Thanks for prompting me to investigate this further Gubi.

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post #38 of 40 (permalink) Old 08-12-2015, 02:17 AM
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so just to sum up....the root cause was in fact a bad fuel pressure regulator, that correct?

Glad it's fixed and good luck with the Smog test!

Dom - Alfa Spider 1990 S4 - formerly: Alfa 101 Sprint, 2600 Sprint, Montreal - family classics: Jensen Interceptor II, '58 Hooper RR Silver Cloud I, Shadow II, '60 Corvette.
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post #39 of 40 (permalink) Old 08-12-2015, 02:28 PM Thread Starter
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Yes, it seems that the fuel pressure regulator was the cause of the idle problems. Thanks very much Dom and Gubi for getting me through this one!!

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post #40 of 40 (permalink) Old 08-17-2015, 09:25 AM Thread Starter
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Passed the smog test with flying colours :
previous / limit / new
HC (ppm) 199 / 121 / 3
CO(%) .16 / .76 / 0
NO (ppm) 2842 / 807 / 0

no oddities at all driving the car, I think it is safe to say that the problem is solved!

Thanks again, vielen danke for all the help Dom and Gubi!

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