Yet another CIS cold start issue....but different
07-18-2007, 10:14 PM
#1
Burning Brakes
Thread Starter
Yet another CIS cold start issue....but different
Hi guys, thought I would ask about my current problem with CIS.
Engine is a 3.2, based on a Euro 930/03 engine, stock CIS (Euro), SSI's, 29,000 km without a hitch....until now.
Characteristic is that on cold start, idle starts at about 1100 rpm (fairly normal), then keeps on climbing until fully warmed up (usually 10 minutes of driving) up to about 2000 rpm. Usual bucking and surging occurs here (never happened before). Once warmed it runs perfectly, no issues whatsoever, so I am convinced it is the cold start system....
First thought is the auxiliary air regulator, but it checks out. Continuity is there (33 ohms), closes in the freezer and warms up with battery connected (to pretty well fully opened).
Next logical step is either the auxiliary air valve (unlikely as it is a dumb device and it only really operates very early in the start sequence) or that there is no power getting to the regulator. Haven't checked yet, but since that circuit powers the fuel pump as well, and that is obviously fine....seems unlikely....
What do you guys all think?
Dennis Kalma
'75 911S with Kremer 3.2
'89 911 Carrera project car
Engine is a 3.2, based on a Euro 930/03 engine, stock CIS (Euro), SSI's, 29,000 km without a hitch....until now.
Characteristic is that on cold start, idle starts at about 1100 rpm (fairly normal), then keeps on climbing until fully warmed up (usually 10 minutes of driving) up to about 2000 rpm. Usual bucking and surging occurs here (never happened before). Once warmed it runs perfectly, no issues whatsoever, so I am convinced it is the cold start system....
First thought is the auxiliary air regulator, but it checks out. Continuity is there (33 ohms), closes in the freezer and warms up with battery connected (to pretty well fully opened).
Next logical step is either the auxiliary air valve (unlikely as it is a dumb device and it only really operates very early in the start sequence) or that there is no power getting to the regulator. Haven't checked yet, but since that circuit powers the fuel pump as well, and that is obviously fine....seems unlikely....
What do you guys all think?
Dennis Kalma
'75 911S with Kremer 3.2
'89 911 Carrera project car
07-19-2007, 01:49 PM
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cold control pressure could affect it. so, i would suggest finding out what it should be for your engine and check it with CIS gauges. Check the current WUR thread too for info on that, if you need help.
David
David
07-24-2007, 03:03 PM
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Hi Dennis,
I thought someone else would have caught this by now, but your AAR should be open when in the freezer, and pretty well closed when warm.
Maybe that is what you intended to say.
I thought someone else would have caught this by now, but your AAR should be open when in the freezer, and pretty well closed when warm.
Maybe that is what you intended to say.
08-15-2007, 11:56 PM
#4
Burning Brakes
Thread Starter
Just thought I would close the loop for posterity.
I happen to have a spare AAR and AAV around, I replaced both of those, with no effect. Thought I would check to see if the WUR was unhappy, so again, I have a spare, replaced it...no effect.
This is getting annoying.
Checked the voltage on the AAR, seemed to be OK. Now what.
Talked to my friendly dealer, his top mechanic reinforced what I had been reading, namely the WUR and other pressure issues will mainly affect how it runs...if the pressures are off, then you get the popping and spitting kind of effect. Idle speed is really only a matter of the air bypass screw (unchanged in my case) and the AAR.
I finally plugged my AAR, let the car sit over night, and sure enough, it did not idle at all well for quite a while until the car was entirely warm. No sign of high idle or any of the previous problems....ergo, the problem lies in the AAR.
Checked the voltage, this time it was zero. Oops, not right. Go check the voltage at the WUR (the WUR, AAV and Thermovalve are all on the same circuit).
Since I have a '79 engine in a '75 chassis, it took a while to trace wiring down. Finally got to the WUR relay, which on a '75 is in the rear electrical panel. There is a relay on the '75 dedicated to the WUR, and gets power directly from the voltage regulator so that circuit operates any time the alternator is providing power, and in my case it powers all three devices....decided it was a bad relay, replaced it . Voila....problem gone.
Only one worry, I figured I would test the relay for operation on the bench. Well, it worked perfectly.
Only hope is that it was somehow stuck open, taking it out or perhaps getting stronger voltage to it on the bench allowed it to operate....I hope so.
Any comments on failure modes of the round black relays is appreciated. If my repair failed, I will update this document...
Dennis
I happen to have a spare AAR and AAV around, I replaced both of those, with no effect. Thought I would check to see if the WUR was unhappy, so again, I have a spare, replaced it...no effect.
This is getting annoying.
Checked the voltage on the AAR, seemed to be OK. Now what.
Talked to my friendly dealer, his top mechanic reinforced what I had been reading, namely the WUR and other pressure issues will mainly affect how it runs...if the pressures are off, then you get the popping and spitting kind of effect. Idle speed is really only a matter of the air bypass screw (unchanged in my case) and the AAR.
I finally plugged my AAR, let the car sit over night, and sure enough, it did not idle at all well for quite a while until the car was entirely warm. No sign of high idle or any of the previous problems....ergo, the problem lies in the AAR.
Checked the voltage, this time it was zero. Oops, not right. Go check the voltage at the WUR (the WUR, AAV and Thermovalve are all on the same circuit).
Since I have a '79 engine in a '75 chassis, it took a while to trace wiring down. Finally got to the WUR relay, which on a '75 is in the rear electrical panel. There is a relay on the '75 dedicated to the WUR, and gets power directly from the voltage regulator so that circuit operates any time the alternator is providing power, and in my case it powers all three devices....decided it was a bad relay, replaced it . Voila....problem gone.
Only one worry, I figured I would test the relay for operation on the bench. Well, it worked perfectly.
Only hope is that it was somehow stuck open, taking it out or perhaps getting stronger voltage to it on the bench allowed it to operate....I hope so.
Any comments on failure modes of the round black relays is appreciated. If my repair failed, I will update this document...
Dennis
08-16-2007, 01:12 AM
#5
Three Wheelin'
A lot of times relays only fail hot. This is the case with the earlier round Porsche relays and the later dual DME/fuel pump relays like in the Carrera 3.2/944/968/964/993 (or any relay for that matter). The problem is either a broken solder joint or the contacts get burnt up. You can pop the top off and see for yourself. Either way, replacement will fix it of course.
As an interesting aside on the round relays, they now all say "made in China" on them an not surprisingly the quality has gone way down. We have tried several different sources, can't seem to get German made ones, either red (higher current rating) or black. I had a hell of a time with a no-start on a 914 a few months back, would crank but not start. Cleaned all the contacts on the relay board as they love to corrode and stuck the relay back in, and it fired, but died a few minutes later. Swapped in a new red "made in China" relay, nothing. But, jumping 30 and 87 ran the pump. Spent much time making sure I had good power signals and grounds (86 and 85 to both relays), from the ECU and the power relay, everything was there! It was getting full 12V too, which can be an issue on these old cars w/ old wiring . . . . I was scratching my head. Tried another new relay out of the box, no dice. For fun, tried the original relay, and it worked! Tried another red relay from a 911 we had in the shop, also worked! So in the end I ordered a new batch of red relays and those ones were fine.
2 in a row bad out of the box, now you just don't expect that!
---Chris A.
As an interesting aside on the round relays, they now all say "made in China" on them an not surprisingly the quality has gone way down. We have tried several different sources, can't seem to get German made ones, either red (higher current rating) or black. I had a hell of a time with a no-start on a 914 a few months back, would crank but not start. Cleaned all the contacts on the relay board as they love to corrode and stuck the relay back in, and it fired, but died a few minutes later. Swapped in a new red "made in China" relay, nothing. But, jumping 30 and 87 ran the pump. Spent much time making sure I had good power signals and grounds (86 and 85 to both relays), from the ECU and the power relay, everything was there! It was getting full 12V too, which can be an issue on these old cars w/ old wiring . . . . I was scratching my head. Tried another new relay out of the box, no dice. For fun, tried the original relay, and it worked! Tried another red relay from a 911 we had in the shop, also worked! So in the end I ordered a new batch of red relays and those ones were fine.
2 in a row bad out of the box, now you just don't expect that!
---Chris A.
