Rough idle during warm-up, 78mod
05-17-2015, 03:05 PM
#1
Instructor
Thread Starter
Rough idle during warm-up, 78mod
Hi
My car starts up fine when cold but idles really rough and at a very low rpms, almost so low it does not show on the tachometer. After some minutes of warming it rises to the normal 750rpm and no other issues at all.
Any ideas? My thought has been issues with the warm up regulator, but I do not have any gauges to measure fuel pressure.
My car starts up fine when cold but idles really rough and at a very low rpms, almost so low it does not show on the tachometer. After some minutes of warming it rises to the normal 750rpm and no other issues at all.
Any ideas? My thought has been issues with the warm up regulator, but I do not have any gauges to measure fuel pressure.
05-17-2015, 09:05 PM
#2
Rennlist Member
I would look first at the aux air valve. If the performance hot is OK, its unlikely to be mixture. The WUR is the last place I would go unless you have other symptoms. My CIS car had a low poor idle some time ago,with occasional stalls. Checked the hole through the AAV when cold and it wasnt as open as it should have been. To check this remove the hoses connected at front and rear of AAV, and shine a light through - you should be able to at least poke a pencil through. If not, you can drill out the rivets and dismantle. I bent the arm holding the spring until it was fully open after a time in the freezer. Also check that when warmed up the hole closes fully. Reassemble with M6 bolts. My cold idle came up to ~ 1100rpm, had to adjust the hot idle a little.
jp 83 Euro S AT 56k
jp 83 Euro S AT 56k
05-18-2015, 05:18 PM
#3
Instructor
Thread Starter
I would look first at the aux air valve. If the performance hot is OK, its unlikely to be mixture. The WUR is the last place I would go unless you have other symptoms. My CIS car had a low poor idle some time ago,with occasional stalls. Checked the hole through the AAV when cold and it wasnt as open as it should have been. To check this remove the hoses connected at front and rear of AAV, and shine a light through - you should be able to at least poke a pencil through. If not, you can drill out the rivets and dismantle. I bent the arm holding the spring until it was fully open after a time in the freezer. Also check that when warmed up the hole closes fully. Reassemble with M6 bolts. My cold idle came up to ~ 1100rpm, had to adjust the hot idle a little.
jp 83 Euro S AT 56k
jp 83 Euro S AT 56k
05-18-2015, 07:55 PM
#4
Rennlist Member
How and when did this low idle issue arise? Had you made ANY changes recently before it arose? Can you assess if the mixture is bad while its running badly at start up? eg, try sniffing exhaust for fuel smell, indicating its too rich. Lean is more difficult to assess without instruments. WUR is very sensitive as changing cold mixture id a matter of tapping the pressure regulator part (iron) in or out, difficult to regulate; or tapping the post in/out, also difficult to regulate.
Try lifting the idle when cold with the big screw at the front of the spider body, and if that smoothes the idle well, but gives you a high idle when hot, then sounds like problem is AAV. If lifting idle when cold doesnt smooth out running, then it might be mixture. You can check WUR in situ some - jump the fuel pump relay, remove the wire connector to WUR (so it doesnt warm up); with an extinguisher handy, and rag, crack open the WUR return line - fuel should come out steadily, showing that control pressure is being lowered - if not , the mixture will be lean, the WUR is blocking flow. If this fuel flow is OK, move to the next connection (distributor), crack that open, check for flow - if little to no fuel comes out, the pipe is blocked between here and the WUR.
If WUR is blocking flow when cold, remove WUR from car, remove adaptor at inlet, check brass gauze filter for debris, and try blowing a solvent like brake cleaner through the fuel passage in both directions. Reassemble to car and try again.
There is a guy in Holland who knows a lot about CIS at www.ferrari400parts.com . Try to get a copy of Watson's book on Bosch injection systems, very good on CIS.
jp 83 Euro S AT 56k.
Try lifting the idle when cold with the big screw at the front of the spider body, and if that smoothes the idle well, but gives you a high idle when hot, then sounds like problem is AAV. If lifting idle when cold doesnt smooth out running, then it might be mixture. You can check WUR in situ some - jump the fuel pump relay, remove the wire connector to WUR (so it doesnt warm up); with an extinguisher handy, and rag, crack open the WUR return line - fuel should come out steadily, showing that control pressure is being lowered - if not , the mixture will be lean, the WUR is blocking flow. If this fuel flow is OK, move to the next connection (distributor), crack that open, check for flow - if little to no fuel comes out, the pipe is blocked between here and the WUR.
If WUR is blocking flow when cold, remove WUR from car, remove adaptor at inlet, check brass gauze filter for debris, and try blowing a solvent like brake cleaner through the fuel passage in both directions. Reassemble to car and try again.
There is a guy in Holland who knows a lot about CIS at www.ferrari400parts.com . Try to get a copy of Watson's book on Bosch injection systems, very good on CIS.
jp 83 Euro S AT 56k.
05-19-2015, 05:44 PM
#5
Instructor
Thread Starter
How and when did this low idle issue arise? Had you made ANY changes recently before it arose? Can you assess if the mixture is bad while its running badly at start up? eg, try sniffing exhaust for fuel smell, indicating its too rich. Lean is more difficult to assess without instruments. WUR is very sensitive as changing cold mixture id a matter of tapping the pressure regulator part (iron) in or out, difficult to regulate; or tapping the post in/out, also difficult to regulate.
Try lifting the idle when cold with the big screw at the front of the spider body, and if that smoothes the idle well, but gives you a high idle when hot, then sounds like problem is AAV. If lifting idle when cold doesnt smooth out running, then it might be mixture. You can check WUR in situ some - jump the fuel pump relay, remove the wire connector to WUR (so it doesnt warm up); with an extinguisher handy, and rag, crack open the WUR return line - fuel should come out steadily, showing that control pressure is being lowered - if not , the mixture will be lean, the WUR is blocking flow. If this fuel flow is OK, move to the next connection (distributor), crack that open, check for flow - if little to no fuel comes out, the pipe is blocked between here and the WUR.
If WUR is blocking flow when cold, remove WUR from car, remove adaptor at inlet, check brass gauze filter for debris, and try blowing a solvent like brake cleaner through the fuel passage in both directions. Reassemble to car and try again.
There is a guy in Holland who knows a lot about CIS at www.ferrari400parts.com . Try to get a copy of Watson's book on Bosch injection systems, very good on CIS.
jp 83 Euro S AT 56k.
Try lifting the idle when cold with the big screw at the front of the spider body, and if that smoothes the idle well, but gives you a high idle when hot, then sounds like problem is AAV. If lifting idle when cold doesnt smooth out running, then it might be mixture. You can check WUR in situ some - jump the fuel pump relay, remove the wire connector to WUR (so it doesnt warm up); with an extinguisher handy, and rag, crack open the WUR return line - fuel should come out steadily, showing that control pressure is being lowered - if not , the mixture will be lean, the WUR is blocking flow. If this fuel flow is OK, move to the next connection (distributor), crack that open, check for flow - if little to no fuel comes out, the pipe is blocked between here and the WUR.
If WUR is blocking flow when cold, remove WUR from car, remove adaptor at inlet, check brass gauze filter for debris, and try blowing a solvent like brake cleaner through the fuel passage in both directions. Reassemble to car and try again.
There is a guy in Holland who knows a lot about CIS at www.ferrari400parts.com . Try to get a copy of Watson's book on Bosch injection systems, very good on CIS.
jp 83 Euro S AT 56k.
The low idle issue has been there as long as I have owned the car.
I will check the AAV, to get the pencil trough is that at "summer temps"?
I guess I have to write it in quotes as I live in Norway
I have not smelled the exhaust directly but I think the car smells of unburned fuel when cold.
I will check some of this next time I get the chance to go to my native place where I store the car.
05-19-2015, 07:29 PM
#6
Rennlist Member
Try adjusting the idle up at the big front screw first as above, see what happens to hot idle.
The pencil test to see if the air hole is open is done stone cold.
There is a video at this post https://rennlist.com/forums/928-foru...-question.html
Starts at 26C, at lower temps should be open more.
jp 83 Euro S AT 56k
The pencil test to see if the air hole is open is done stone cold.
There is a video at this post https://rennlist.com/forums/928-foru...-question.html
Starts at 26C, at lower temps should be open more.
jp 83 Euro S AT 56k
05-19-2015, 07:43 PM
#7
Rennlist Member
I suggest getting a gauge. IMO, this is no way to tune properly without. Also helps to have a Colortune to adjust A/F mixture (one of my fav tools).
I just can't imagine trying to do this properly w/o a pressure gauge.
PS. I just rebuilt 2 sets of FD's and WUR's for 928 guys from Norway. Small world.
I just can't imagine trying to do this properly w/o a pressure gauge.
PS. I just rebuilt 2 sets of FD's and WUR's for 928 guys from Norway. Small world.
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05-21-2015, 04:12 PM
#8
Instructor
Thread Starter
I suggest getting a gauge. IMO, this is no way to tune properly without. Also helps to have a Colortune to adjust A/F mixture (one of my fav tools).
I just can't imagine trying to do this properly w/o a pressure gauge.
PS. I just rebuilt 2 sets of FD's and WUR's for 928 guys from Norway. Small world.
I just can't imagine trying to do this properly w/o a pressure gauge.
PS. I just rebuilt 2 sets of FD's and WUR's for 928 guys from Norway. Small world.
I follow your site on Facebook with great interest as well as some of your threads on the early cars, congrats on the shop by the way
I have been looking at your services and might order a rebuild, if I find out that the WUR is at fault. To bad I do not live in the US, then I would definitely let my #398 get some tune up at your shop.
What kind of turnaround do you see for something like this (WUR service), do you know from the other 2 Norwegian guys? Just afraid I will be without a WUR in my car for months, due to posting first to US then back.