Cold pressure, Residual pressure & cold start?

groovydude · 07-18-2016, 10:33 AM

I'm trying to trouble shoot a nagging cold start issue ('82 SC).

History: Bought the car about a year ago, after having the worst PPI in history. One of the unmentioned problems was poor cold starting. I bought a pressure guage, followed the instructions in Bently, and ran the tests. System pressure was fine, cold pressure was low, warm pressure was fine. So I sent my 090 WUR to CIS Flowtech and bought a rebuilt unit.

I don't remember exactly what the cold starting symptoms were prior to this, and there was also an air leak at the time, and idle mixture was way off to compensate for the leak. I removed the CIS and checked all the components (except the csv), and replaced all the rubber and the air box. When it was all put back together, the leaking was all fixed, and the cold start was better, but not perfect. And the problem was intermittent, some times it would work just like new. I did a pressure test at the time and everything was within spec, so I decided to just live with it.

But lately it seems that the problem is getting much more permanent and less intermittent. Maybe it's just the warmer weather, or maybe whatever is wrong is settling in.

So I did another pressure test yesterday. System pressure is spot on. Warm pressure is spot on. Cold pressure is 1.75 bar at 66.5 degrees. This looks to be in spec, but at the bottom edge of the graph in the Bentley manual, and just barely. Also, in watching the gauge while testing the cold pressure, it took about 5 seconds to reach 1.75, and there was a hitch in the needle movement ( a little bounce down and up) at about 2 seconds. Is 5 seconds too slow? Is the hitch revealing a WUR problem? I've got an email in to Larry at CIS to see what he thinks.

Also, I noticed that, when installing the pressure gauge, in disconnecting the fuel line from the fuel distributor there was no latent system pressure - no fuel leaked out. So I checked the residual pressure as well. It looks fine after 10 and 30 minutes, well above spec according to Bentley, but it drops to 0 after several hours (perhaps 4 or 5). I understand that the pressure needs to stay high to prevent vapor lock on a hot start, but isn't some residual pressure needed on a cold start too, or does the fuel pump provide start up pressure quickly enough?

gazzerr · 07-18-2016, 10:57 AM

Hey groovy, I think the drop in pressure over a number of hours is normal. Mine does the same. If your CSV is leaking (drip drip) after it runs that could explain your symptoms. The WUR drives the pressure changes you see has it heats up when the 12V is applied. Are you seeing at least 12V at the WUR plug? If you aren't getting 12V then it won't drive the WUR properly.

I have the same issue. The warm/hot weather has made it worse for me too. Once it's warm it runs great. I really want to solve this too so very interested to see where you get with it.

I have noticed that when it's really hot (let's say 90 or so) the AAR closes too quickly before the engine has a chance to warm and it runs pretty awful (not enough air) until the engine warms sufficiently and the WUR leans out.

groovydude · 07-18-2016, 11:20 AM

Hey Gazzer, lol, it doesn't get to 90 around here very often! I don't think it's been over 80 all summer yet. One of the joys of the PNW. It's why I shelved my AC! (Targa of course).

I hadn't thought about a leaking CSV. I do think it's either that or the WUR, maybe the cold pressure us just a tad too low. Btw, I'm certain I'm getting voltage at the WUR. And the heating element inside the thing is working too. What's your cold pressure reading? How long does it take to get there?

Joe Bob · Joe Bob's Garage

Hot and cold start issues can be a bad check valve in the neck of the fuel pump. Cheap fix, easy replacement.

groovydude · 07-18-2016, 12:52 PM

Sounds like if I had a bad check valve I would be seeing hot start problems too. Not the case.

dhanl82 · dhanl82's Garage

I also have a 1982 sc with the same problem. I live in Tampa Florida and it has been very hot this summer. I am interested to see the opinions of some of the very knowledgeable forum members so hopefully I can get mine sorted out as well.

Joe Bob · Joe Bob's Garage

Maybe the cold start injector.....

gazzerr · 07-18-2016, 04:34 PM

Some days here it's 100. The don't call it Hotlanta for nothing

. dhanl82 have you done any fuel pressure tests?

Good question groovy I do need to do another pressure test. Could be the CSV like JB says. I didn't test mine ... I replaced all the other injectors. The car fires up fine when cold it just never gets its 1300 rpm. Always 1000 or lower and grumpy until warm.

groovydude · 07-18-2016, 07:12 PM

Gazzer, that sounds like a failed WUR to me. Mine will work up to around 1400 after about 15 - 20 seconds of being "grumpy" as you put it, then it settles down to 950 as the car warms up. Since the AAR starts open, I'm sure that's not the problem. The WUR is supposed to enrich the mixture until the car warms up, as I understand it. Pressure readings should tell you if it's working. I would like to hear from someone else how quickly the pressure is supposed to max out when cold. As I said, mine takes about 5 seconds (at this summer temperature) and it's not perfectly smooth.

gazzerr · 07-18-2016, 07:39 PM

Hey Groovy, I'll do a pressure test on the weekend and report back. I've got a bunch of stitches in one hand after an accident so I'm a bit disabled at the moment. Hopefully will be able to do it on the weekend!

I seem to remember after about 3- 5 mins it should max out. Is yours faster? If so then then you need to check the resistance of the heater coil in the WUR. It should measure in the 22 (4?) Ohms range I believe.

Maybe my WUR does need a tweak.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by groovydude

Gazzer, that sounds like a failed WUR to me. Mine will work up to around 1400 after about 15 - 20 seconds of being "grumpy" as you put it, then it settles down to 950 as the car warms up. Since the AAR starts open, I'm sure that's not the problem. The WUR is supposed to enrich the mixture until the car warms up, as I understand it. Pressure readings should tell you if it's working. I would like to hear from someone else how quickly the pressure is supposed to max out when cold. As I said, mine takes about 5 seconds (at this summer temperature) and it's not perfectly smooth.

groovy,

Could you check the heater resistance of your WUR-090 in the morning (cooler) and later in the PM (warmer)? I might be able to tell you something about your problem(?). Include the ambient temp. when you take the measurement.

Could you elaborate more about this (highlighted above)? What was the cold control fuel pressure and WCP in 5 seconds? Thanks.

Tony

groovydude · 07-19-2016, 05:20 AM

Hey Tony,

I got different results this morning. At 64 degrees (17.8), cold pressure jumped up to 1.55 in about 2 seconds, then it started climbing slowly and kept slowly going after 30 seconds it was up over 3. I shut it down then, but it was still climbing. Heater resistance across the contacts was 10.1 ohms - that seems low from the other threads I've read.

As I mentioned earlier, my problem has been intermittent. The readings I got this morning seem to fit my usual grumpy start, so that along with the fact that results today are different, and that the resistance is low suggests to me that the WUR may be funky.

Warm running has never been a problem. My fan belt is off at the moment, I'll run a warm test when the new one is installed.

groovydude · 07-19-2016, 06:18 AM

Hey Gazzer, I think you'll find this interesting. I just spoke with Larry at CIS Flowtech (sold me my WUR). He tells me that he calibrates his WURs to be at the low end of the curve, so my numbers are within spec. Also, it is supposed to jump up to start up pressure very quickly (might be my problem). This morning it jumped right up, but not so the other day - 5 seconds is too long, so I'll run another few tests over the next few days and see what I get. Also, the system is supposed to climb up to 3.6 bar over the next 30 seconds as the strip heater in the WUR warms up. I took my resistance reading AFTER the test (oops), so I was measuring a warm heater and the reading for that is supposed to be around 9 ohms, so it also is within spec.

It's interesting to get the nitty gritty on how these systems are supposed to work. It sounds like the high rpm that you're not seeing is function of your AAR and not your WUR, since the heater in the WUR is fully warmed up in 30 - 40 seconds.

Larry suggested that the thermotime switch might be the culprit, and the test is to measure resistance for that. I'll report back...

T77911S · 07-19-2016, 07:09 AM

the CP on my 930 was slow to hit CCP when I first got it. it went back to normal but I don't know why. I know I changed my fuel filter at one time but I also had a fuel damper on my line to the WUR.
you can do a flow test out of the fuel dist to the WUR.

low CCP is good. little extra fuel for cold starting is OK.

2 secs is probably ok.

groovydude · 07-19-2016, 12:10 PM

My thermotime switch seems to be within spec, 24 ohms on one side, 0 on the other, and 24 across both.

Two readings today of my CP are 1.55 @ 17.2 degrees, and 1.65 @ 18.9 degrees. What do you think Tony?

These look low to my reading of the chart. I think the only other culprit could be the csv, I'll try and check that tomorrow.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by groovydude

My thermotime switch seems to be within spec, 24 ohms on one side, 0 on the other, and 24 across both.

Two readings today of my CP are 1.55 @ 17.2 degrees, and 1.65 @ 18.9 degrees. What do you think Tony?

These look low to my reading of the chart. I think the only other culprit could be the csv, I'll try and check that tomorrow.

Groovy,

Since you asked, test the operation of the cold start valve and TTS. Test and confirmed. Your system fuel pressure should register within a second or two after closing the valve for the pressure gauge. The WUR has nothing to do with the system fuel pressure. It is the primary valve in the FD that determines the SP. It is not acceptable nor normal to take 30 sec. for the SP to register. Next, your WUR-090 is out of spec. Your cold idle would be always erratic until the WUR is re-calibrated or the engine gets warmed. Send it back to your rebuilder for recalibration. Larry is very experience and should know your problem. If this was not serviced by a professional shop, I would offer to help you. But I would refrain from doing it. You paid for it and should expect to get a calibrated WUR. The WUR is working OK when it gets hot or heated but out of spec when cold. Discuss this problem to him. Don't totally blame the WUR for the problem because there are other CIS components that could contribute to the anomaly. And keep us posted.

Tony

gazzerr · 07-19-2016, 04:47 PM

Cool thanks Groovy that's very interesting. I'll let you know what results I get.

Yes the higher RPM is supposed to come from the AAR. I think maybe I have too much fuel. I'll test my TTS too.

groovydude · 07-20-2016, 06:14 AM

Tony, just to clarify, on my car when the valve is closed the system pressure reaches its peak almost immediately, it's when the valve is open that it takes 30 seconds or so. My understanding is that this is normal, the strip heater in the WUR takes that time to warm up. So I agree that the WUR seems to be out of order. Thanks for your input!

Gazzer, does your car ever rev up to where it's obvious that the AAR is open? Mine does every cold start, it just takes 20 seconds or so. Too much fuel sounds like my problem too. I've always felt it was acting too rich at startup (which is why I was fiddling with my idle mixture the other day). If I understand the WUR correctly, a cold pressure that's too low will create an environment that's too rich. So it does seem like that could be our problems, and it seems the WUR is the likely culprit.

gazzerr · 07-20-2016, 04:46 PM

Hey Groovy,

When cold it just takes a few cranks to fire so I think the CSV works pretty well. Mine revs up just a little bit - let's say 1000 to 1050 rpm. Sometimes it will hunt between 900 and 1000 depending on the ambient temp. It's really obvious when the AAR closes though. You can watch the rpms drop in sync with the AAR closing. Once it warms up and the WUR leans out it settles at 950 rpm and purrs. The car really boogies in 3rd going flat out so there's not too much wrong with it I think.

One thing I did notice was I could hear air rushing past the sensor plate when it was idling and the air cleaner was off. Does yours do that? I was wondering perhaps that meant my sensor plate was set too low.

I agree it's *probably* too rich cold. I can certainly smell it from the tailpipe. Once I get these stitches out of my hand on Monday I'll test everything again.

T77911S · 07-21-2016, 03:03 AM

the way to test control pressure is to remove the electrical plug from the WUR. when you run the pump, the pressure should jump up fairly quickly. this is your CCP.
then plug in the power to the WUR. NOW the pressure should climb slowly. this could take anywhere from 30sec to a minute or 2.
once the WUR is warm and pumps turned on, the pressure should reach WCP fairly quickly.

it was my understanding that when you turned on the pump, it took a long time just to reach the CCP. if this was the case I might look into the fuel filter, the system pressure reg or the fuel dist.
I would see how fast system pressure comes up
I would do a flow test out of the dist to the WUR.