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Cold Start Issue

I've searched for cold start issues but none seem to help much. Plus I don't have much experience with the fuel distribution system on the 930.

The car is running well overall but it has a cold start issue. It fires right up every time but then idles really low or stalls. fires right back up again and idles very slow or stalls. Takes about 5-10 times before the engine will at least remain running.

If I press on the throttle during this slow cold start it just dies or hiccups. Once it is running if I try to rev the engine it backfires.

If the engine runs long enough for me to run to the back of the car and press on the flap on the fuel distributor it idles really nicely. Once I hold the flap down, the engine remains running and runs ok or backfires for a mile or 2.

After warming, the car runs fine. Warm restarts are ok. One crank and it fires and idles fine.

I don't know much about the WUR or how it operates. Looking for guidance on what to investigate.

Also, once warmed, sometimes it will idle above 1k and sometimes idle below 800. What could be causing this?

Thanks in advance.

Old 10-28-2014, 07:15 AM
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you need to check fuel pressures and check for air leaks.
the aux air regulator could also be part ofthe problem.

what year is it

did you just buy the car? how long has this been going on?
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 10-28-2014, 08:43 AM
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Its a 1986. I've had the car for 5 years now. Has about 125k miles.

The hard starting began about a month ago. Otherwise it runs great. Just put in new plugs, wires, rotor, cap, and adjusted the valves.


Old 10-28-2014, 08:55 AM
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What you are describing are classic lazy WUR symptoms. Do the easy free stuff first and check for vac leaks and AAR function. Once those are confirmed OK check the cold control pressure against the graph for your P/N. It needs to be at the middle to low end of spec to eliminate as the issue. If at the top end of spec check system pressure. If that is OK then press in the cold plug to low end of spec or send it to me for a rebuild.
Old 10-28-2014, 09:48 AM
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Rarely L8 is spot on, there is one guy you need to talk to first before you pull that AAR. the routing of the vacume lines is what determines if the cold start works correctly. i fought this for a while and even PORSCHE could not get it right. helio is his name. do a search for him. really nice guy and knows the vacume system pretty well. i think i have his phone number if you email me your number i will call you

John
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Old 10-28-2014, 01:09 PM
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Quote:
Originally Posted by RarlyL8 View Post
Do the easy free stuff first and check for vac leaks and AAR function.
I've checked for vacuum leaks already using carb cleaner. Haven't found anything yet. I checked intakes to heads; fuel distributor; throttle body; intercooler to throttle body; intercooler to up pipe; AAR and hoses. Any place else to check for vacuum?

About the AAR, is there an easy way to test this? Does it fail open or closed? If I open the throttle a bit, isn't that the same as the AAR being open?

A question about fuel distributor mounting: The fuel distributor is held on with several hex head screws surrounded by springs although not all the screws have springs. How are these to be set? Several of these were loose; I tightened them but this didn't help the cold start.
Old 10-29-2014, 09:22 AM
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Don't mess with the spring loaded screws, they are designed to protect the housing.
AAR will open the gate when cold. Put it in the freezer and see if it opens.
I'm going to assume that cold start low rpm will not respond well to throttle input. If the AAR is malfunctioning you can simply throttle up the idle speed for a few seconds and the engine will run on its own. If the WUR is lazy this action will not work. You'll have to hit the key several times until the fuel pressure catches up with the AFR needed to keep the engine running. Temporarily unplugging the WUR may speed up that process.
Old 10-29-2014, 09:40 AM
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Quote:
Originally Posted by RarlyL8 View Post
Don't mess with the spring loaded screws, they are designed to protect the housing.
I thought I had a vacuum leak under the housing so I checked the spring loaded screws. Several of them spun a couple of turns until they seated. Some did not have springs and were firmly screwed in.

Quote:
AAR will open the gate when cold. Put it in the freezer and see if it opens.
I'm going to assume that cold start low rpm will not respond well to throttle input. If the AAR is malfunctioning you can simply throttle up the idle speed for a few seconds and the engine will run on its own.
Correct. Modulating the throttle doesn't do anything to increase the RPM. Pressing on the distributor flap can bring the idle to a nice constant RPM.

Quote:
If the WUR is lazy this action will not work. You'll have to hit the key several times until the fuel pressure catches up with the AFR needed to keep the engine running. Temporarily unplugging the WUR may speed up that process.
What exactly does the WUR do and how do I test it? I saw some videos (on a Mercedes) with a fuel pressure gauge with 2 connections and a valve.
Old 10-29-2014, 10:15 AM
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usually a bad WUR will start fine when cold then run bad when warm unless someone has tweeked the WUR or mixture to make it run good hot, then it has bad cold starts.

since this started while you owned it and i assume you have not done anything to it, i would look for air leaks. even with a bad AAR you should be able to idle the engine up with your foot.
if you are having to add fuel by pushing down on the senor plate that really sounds like an air leak.
check the IC seals. look for cracked or broken vacuum hoses. check control pressures. if your return side of the WUR is clogged it can raise the cold CP and make it lean.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 10-29-2014, 10:56 AM
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Quote:
Originally Posted by RarlyL8 View Post
AAR will open the gate when cold. Put it in the freezer and see if it opens.
There is an easier way to test this.
Start the car and immediately clamp the hose from the AAR to the manifold shut with a pair of needle nose vice grips. If the rpm's drop the AAR is working correctly.
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Old 10-30-2014, 05:37 AM
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Quote:
Originally Posted by T77911S View Post
check the IC seals. look for cracked or broken vacuum hoses. check control pressures. if your return side of the WUR is clogged it can raise the cold CP and make it lean.
The IC seals look good. Just had the intercooler off to change plugs/wires. Also checked when running with carb cleaner. Checked all the vacuum lines as well with carb cleaner. No change in engine speed/sound when sprayed. I'll check again.

Looks like I need to inspect the WUR.

One thing I don't understand with the WUR is how at cold temps with the fuel pressure lower the engine runs richer. I would think that higher pressure would mean more fuel.
Old 10-30-2014, 08:07 AM
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More than you probably care to know about CIS here:
CIS911Primer.com

I assume that if the cold start idle is so low the engine struggles to run that clamping the AAR hose will have no effect.
I'd say the majority of the WURs we rebuild have punch marks on the cold pressure pin. It is a very common problem as they age.
Old 10-30-2014, 08:13 AM
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Quote:
Originally Posted by spoke View Post
The IC seals look good. Just had the intercooler off to change plugs/wires. Also checked when running with carb cleaner. Checked all the vacuum lines as well with carb cleaner. No change in engine speed/sound when sprayed. I'll check again.

Looks like I need to inspect the WUR.

One thing I don't understand with the WUR is how at cold temps with the fuel pressure lower the engine runs richer. I would think that higher pressure would mean more fuel.
did you do this before or after it started running bad?
did you do any work before it started running bad?
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 10-30-2014, 09:00 AM
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Quote:
Originally Posted by spoke View Post
One thing I don't understand with the WUR is how at cold temps with the fuel pressure lower the engine runs richer. I would think that higher pressure would mean more fuel.
Remember that we are talking about control pressure, not fuel pressure being supplied to the injectors.
Control pressure is in fact using fuel flow to apply a force to the top of the metering piston in the fuel distributor. This force acts as a counterforce to the air metering plate that's being pushed on by the air that's rushing into the intake tract (the air metering plate is connected to the metering piston in a pivot arrangement). The two opposing forces dictate the position of the metering piston in it's chamber in the fuel distributor. The piston has a tiny slit in it that allows fuel to flow to the six chambers in the fuel distributor. Less counterforce allows the air metering plate to move lower in it's housing for a given air flow, lifting the piston at the other end and exposing more of the slit in the piston to the chambers, increasing fuel flow to the injectors.
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Old 10-30-2014, 01:37 PM
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You should invest in CIS Gauges and an Adjustable WUR - - along with Pen and Paper. It wouldn't hurt to get Wideband AFR, too.

I've said this hundreds of times, but it bears repeating: "If I didn't have CIS Gauges, BL WUR and Wideband AFR, I wouldn't know how to do anything to impact my car's running..."
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Old 10-30-2014, 03:26 PM
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Originally Posted by spoke..
"One thing I don't understand with the WUR is how at cold temps with the fuel pressure lower the engine runs richer. I would think that higher pressure would mean more fuel."

It's been mentioned many times so searches will help you understand how CIS works.
The fuel pressure you mentioned above never goes to the injectors, it's called control pressure. You chould look up the generic definition of control pressure to understand what it means.
In the CIS fuel head it's gasoline under pressure frrom the fuel pumps that's gone through a tiny orifice so returning some of it to the fuel tank in changing varaible amounts changes this seperate fuel pressure that is used as hydraulic fluid pushing down on the top of the metering piston. There are no slits in the piston as mentioned above. There are 6 vertical narrow slits in the cylinder wall the piston is inside of and fuel flow through those slits is metered by the position the piston is in inside the cylinder. There's so much more to it though you should read a PDF on the K-Jetronic fuel injection and study the cross section diagrams to understand whats going on.
The '86-'89 930 Lambda fuel heads get even more complicated with another completely seperate control pressure circuit that fine tunes the AFR to meet emission testing and it has nothing to do with the control pressure regulator or WUR.
Old 10-30-2014, 04:18 PM
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Quote:
Originally Posted by T77911S View Post
did you do this before or after it started running bad?
did you do any work before it started running bad?
I changed plugs/wires/adjusted valves before the cold start issue. Did not have the cold start issue until about a month after the work was done. It was starting and running well after the service.
Old 10-30-2014, 06:32 PM
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Quote:
Originally Posted by mooney265 View Post
You should invest in CIS Gauges and an Adjustable WUR - - along with Pen and Paper. It wouldn't hurt to get Wideband AFR, too.

I've said this hundreds of times, but it bears repeating: "If I didn't have CIS Gauges, BL WUR and Wideband AFR, I wouldn't know how to do anything to impact my car's running..."
I've been reading the 911 CIS Primer - Index the last few days.

I have a wideband AFR and it's on my list to mount the sensor on the car. Seems like CIS gauges and perhaps BL WUR will be on my shopping list.
Old 10-30-2014, 06:36 PM
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Took the car out for some errands tonight.

First crank, fired right up, idle dropped to 200RPM, then died.
Second crank, fired right up, idle dropped to 200RPM, then died.
Now I sprayed carb cleaner around the base of the fuel distributor.

Third crank, fired right up, idled low, about 400RPM. sprayed some more carb cleaner around the base of the FD and the idle came up to 1k. Only caveat here is I didn't have the air cleaner securely bolted to the FD so some of the fumes may have been ingested helping the engine to run.

Drove the car 6 miles to my first stop; ran beautifully but idled at about 1100RPM after warmed up.

After 30 minutes, drove about 5 miles to my second stop; One crank, started right up; ran good again.

After 10 minutes, drove 1 mile; one crank, started right up but idled at about 500RPM. Tried some carb cleaner on the base of the FD before driving, didn't seem to make a difference in RPM.

After 20 minutes, drove 10 miles home; one crank, started right up but idled at about 400RPM and seemed to be slightly hunting a bit. Got on the freeway and ran good up to 80MPH. Upon exiting, now in 2nd gear, it backfired once, then ran well, very well. Idle back up to 1k.

In the garage still idling, I clamped off the AAR hose and the RPM went down significantly. The AAR is still open! OK there's one issue to be resolved.

Back a month ago I noticed the idle a bit high (>1k) so I adjusted the idle with the idle screw to about 800RPM, but the screw is all the way in.

Can the AAR be serviced? Or just replaced?

Thanks for all the help.
Old 10-30-2014, 06:50 PM
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One often overlooked source of vac leaks the intake manifold bolts. They become loose with time and slowly start causing odd running issues. Easy to check, just put a small wrench on and see if the bolt can be hand tightened a few pounds. Go around to all of them as the one you miss is the one that is loose.

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Old 10-30-2014, 07:31 PM
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