Turbo 3.6, hot start issue

BoxxerSix · 03-22-2009, 08:03 AM

1994 Turbo 3.6, has a hot start issue after ~15 minutes of driving. This car had an issue awhile back where fuel was pouring out of the vent tube into the airbox and it was diagnosed that the internal WUR diaphram had a crack in it. I repaired the WUR and the car ran great there after. Now the car has a hot start issue, usually after about 15 minutes of driving. At first I thought it might have been a residual pressure issue but that seems to be in order.

Anyone else have some thoughts on this one? Things I should look at or into? I have the Bently manual on this car to reference to.

I should add this car is completely bone stock.....air injection and all.

930gt-40r · 930gt-40r's Garage

Another WUR problem? Is it adding too much fuel when it is hot? Im wondering if that could be caused by a bad thermal switch.
My ultimate correction for that problem: EFI

911nut · 911nut's Garage

Usually hot start issues are related to vapor lock, which is related to vapor present in the fuel lines instead of fuel.
Check the residual fuel pressure in the system after a 15 minute soak. Range is 2 bar at 32 - 45 deg. F to 4.5 bar at 95 - 104 deg. F. If the pressure falls outside these values replace the fuel accumulator.

Speedy Squirrel · Speedy Squirrel's Garage

What 911nut said for sure. Also, air leaks between the fuel distributor and throttle. The cold start injector doesn't squirt when the car has been warmed up, making it susceptible to the air leaks, which lean out the mixture and prevent starting.

911st · 03-22-2009, 10:48 AM

The C2 Turbos is supposed to have a different head that should keep that from being an issue.

Do you have a modified or substitute head. If not I would look at the WUR as that seems to have some history.

964 T #304 · 03-22-2009, 11:29 AM

Install yourself a digital wur and be done with it.

BoxxerSix · 03-22-2009, 12:08 PM

Quote:

Originally Posted by 930gt-40r

Another WUR problem? Is it adding too much fuel when it is hot? Im wondering if that could be caused by a bad thermal switch.
My ultimate correction for that problem: EFI

HAHA! Yeah that's my end all solution as well. This car is staying bone stock though, and only because it's a '94 Turbo 3.6. If it was any other turbo I'd already have gone EFI and 35R on it but I'd like to keep this one as bone stock as possible for it to hold it's value. At least for now

Quote:

Originally Posted by 911nut

Usually hot start issues are related to vapor lock, which is related to vapor present in the fuel lines instead of fuel. Check the residual fuel pressure in the system after a 15 minute soak. Range is 2 bar at 32 - 45 deg. F to 4.5 bar at 95 - 104 deg. F. If the pressure falls outside these values replace the fuel accumulator.

This is what I was thinking myself. I did have to break open the fuel system to repair the WUR, although the residual #'s came back within spec according to the Bently manual. I repaired the original WUR by replacing the diaphram(stainless spring disk) inside it.

Before I repaired the WUR the car ran 100% great, just leaked fuel into the airbox through the WUR vent tube. The car runs/drives fine now..... AFR's are right on spec for .7 Bar boost, idles fine. Just will not start after a hot shutdown without sitting for a good hour.

x98boardwell · x98boardwell's Garage

Not sure how much the C2 is different from the 930's with fuel systems (I know they are CIS, but anyways), but check out this thread below and my original post was yesterday (#14) and some interesting info from there.

Fuel Accumulator Symptoms?

May just be a bad accumulator.

Best of luck,
Bryan

BoxxerSix · 03-22-2009, 09:00 PM

C2 systems are pretty similar to the 930 setups, just have a slightly higher flowing head and lambda control.

Read through that thread you posted up there. I'll have to go and check the control pressure and see what that's set at while the engine is hot, it's been referenced too a few times here as a possible culprit.

I'd like to think the accumulator is fine, just due to the fact that this issue was not a problem at all until I cracked open the WUR to replace the fuel diaphram disk(not the boost reference diaphram at the base of the WUR case).

I will report back if/when I figure it out

BoxxerSix · 04-11-2009, 07:22 PM

Here's a little update on this car and some fuel system numbers I'd like for you CIS gurus to give me your input to.

-Cold System Pressure is 98psi
-Cold Control Pressure STARTS at about 40psi at 68 degree F ambient temp, but climbs at a steady pace to about 60psi in a matter of about a 45 second period. this is while the engine is running(idle). The 68 degree temp is tested at the body of the WUR via a laser thermometer.
-Warm Control Pressure remains at that 60psi once the car is fully heated and running(idle)
-Warm Rest Pressure drops and holds at 40psi as soon as you shut the car off
-Residual Pressure Holds that 40psi for well over 30 minutes. If I tap the fuel tester bleeder the pressure drops to ~23psi and continues to hold that for at least 30 minutes.

This car still has a weird hot start issue. If I start and drive the car smoothly, warm it up fully, and then come to a complete stop I can shut the car down and it will start up fairly easily.

However if I warm the car up fully and drive the car HARD into full boost, then come to a rest at say a stop sign the car idles rough and wants to stall unless I feather the throttle for a few seconds. If I shut it down at that point, the car will not start at all and will continue to do so for at least 10-15 minutes minimum, sometime longer.

The Cold control pressure doesn't really fit the specification, nor does the 40psi rest and residual pressure tests. My books and experience have always said around 21-23 psi after 20 minutes or so for the residual tests. MY experience also suggests that cold control pressure should be about 32psi at that temp and SLOWLY rise with temperature to about 61-65 psi.

Can any of you gurus discuss this a bit more with me? elaborate on the control pressure and residula pressures which seem to be quite high??? I've been very sick the past few weeks here and this has just got me even more bugged (bad pun I know

)

at this point I think it's time for an adjustable WUR, but I still want to know why this is happeneing(hot start issue) and whether these pressures ARE the culprit or not.....

thanks!!!

Ag02M5 · 04-11-2009, 07:42 PM

Fuel filter and accumulator replacement cured my hot start issues.

BoxxerSix · 04-11-2009, 08:03 PM

Quote:

Originally Posted by Ag02M5

Fuel filter and accumulator replacement cured my hot start issues.

Filter is brand new, litterally just installed it last friday after the entire fuel system/tank/lines were removed from the car and cleaned so I could rule out contamination or clogging. Others had suggested Accumulator as well awhile back but checking records shows it was replaced not even 5K miles ago(long before car was purchased here).

Fuel pump output volume was also checked and good.

This issue started after fixing/replacing a leaking fuel diaphram inside the WUR, which was dumping fuel into the WUR body and up through the vent tube into the airbox.

I'm thinking the WUr is goofed up but I still just wanted CIS guru opinions or insight on this problem.

BoxxerSix · 04-11-2009, 08:04 PM

Also, can someone here confirm a WUR number from a 930 that matches this WUr possibly???

Number on the top of the WUR was 0 438 100

going through my stock piles of parts here I found another WUR from an '89 AUI 200 quattro NON turbo with the exact same part numbers and fuel port dimensions, just didn't have the boost referenceing diaphram chamber in the middle.

BoxxerSix · 04-13-2009, 07:03 PM

Anyone have any other insight to the fuel pressure numbers I posted just above(post #10)?????

I'm at a loss on this one.

I'll buy an adjustable WUR IF that's what the problem is revolving around

fredmeister · fredmeister's Garage

This is a WAG but did you look at the fuel pump relays?
It may be worth replacing them as they sometimes cause funky problems when they get hot and start failing or the connections get corrosion where they plug into the fuse box. I have driven my car hard and shut it down and it would not start. Drove me crazy until I checked and they had worked themselves loose from the fuse box...pushed them in tight and that fixed it. Bumpy roads perhaps caused them to loosen....I thought that was strange.
I cannot comment on your pressure readings, but you are on the right track by being methodical in testing everything to specification.
I don't think the fuel accumalator has a history of failing on these cars.....I have read it is pretty robust.
Are you sure it is not a spark issue with the CIS box. They fail too and act sporadic when they get hot and don;t always fail all at once.

JBL930 · 04-14-2009, 08:44 AM

Quote:

Originally Posted by BoxxerSix

I'll buy an adjustable WUR IF that's what the problem is revolving around

You don't have to buy one, you send Brian Leask yours and he makes that adjustable. Plus he'll set it exactly to stock specs for you.

It sounds like your WUR is ok though from what you've observed. It could be something else heating up, expanding and causing the problem? I'm not sure what though? Dizzy maybe? Some air leak somewhere which only rears it's head when it heats up? It's certainly weird.... Good luck with it

BoxxerSix · 04-14-2009, 02:17 PM

Quote:

Originally Posted by JBL930

You don't have to buy one, you send Brian Leask yours and he makes that adjustable. Plus he'll set it exactly to stock specs for you.

It sounds like your WUR is ok though from what you've observed. It could be something else heating up, expanding and causing the problem? I'm not sure what though? Dizzy maybe? Some air leak somewhere which only rears it's head when it heats up? It's certainly weird.... Good luck with it

I've been checking a host of other things on this car and trying to sort out what may be the problem.

My only issue is that this hot start issue didn't start until immediately after I repaird the WUR diaphram that was leaking. Prior to that the car ran 100% top notch.

The fuel relay issue I thought of as well and replaced them. I also tested the pumps for fluid output and they're both well within spec.

I tried to get ahold of Brian L today to talk about his WUR upgrades and ask him about these fuel pressure numbers. At this point I'm not against adding the adjustable WUR to the system, as long as that corrects the problem at hand. Be a shame to spend ~$400 on a part that isn't going to be used to it's fullest extent and still not have it solve the problem.

How long does it typically take for the WUR to go from the COLD control pressure(dead cold sitting overnight) to the full WARM control pressure??? On this WUR it happened within literally 40-45 second at most. That just doesn't seem right to me at all.

JBL930 · 04-14-2009, 02:39 PM

It's a bimetalic strip that moves as current passes through it, raisng control pressure. I've watched this using an LM1 from cold to warm and it took about 5 minutes. That was my experience anyway, i have no idea how long it actually should take.
I guess what is important is whether it is getting the warm control pressure right once the ignition has been on long enough. Have you tried turning the ignition on and leaving it for a good 5 minutes or so and seeing whether it raises control pressure further? Or disconnecting the power to the WUR and letting the car run for a while to get warm, then reconnecting the wire after 5 minutes or so and seeing whether it runs better?
I'm "guessing" that if the bimetalic strip warms up too quickly, the car is cutting out as it's too lean for it being still cold? Worth a try...

BoxxerSix · 04-14-2009, 06:50 PM

Well I just got off the phone with the owner and it's a 99% chance that this car will be up for sale very shortly. He's been looking for a GT3 and found one well in his price range.

I'm going to go put the WUR back in on Friday and bring it to Daniel Jacobs to get back in top running order again. That man is a Porsche guru to say the least and will take care of this beauty no doubt. Likely, the car will be bought back by Weissach Auto where he initially purchased it from, and sold through there although I cannot be exactly certain about that.

If there is an interested party in the car I can put you in direct contact with the deal. 1994 Turbo 3.6, black on black, all original(even the air injection is still attached and working), original factory Speedline's, mileage in the 80K range. Xenon lowbeams in factory headlamps. Engine recently reworked by Dan Jacobs(Dan will have more info on that work). Aside from this recent and annoying issue the car has no problems whatsoever.

Price unknown, I'll post more when I know more from the owner.