930 WUR - Pressure Test Complete (Pix), Perplexing Results
 

To any who have been following my CIS issues. Background:

- Hard start cold. Cranks for 30+ seconds then chuggs to life.
- Lean mixture readings cold and warm. A/F ~ 16:1 CO ~ 0.0%
- Runs perfect and has the proper mixture on boost, A/F 12.5:1

This condition came on gradually over a few months. Symptoms were a slow start of several seconds accompanied by steady increase of cruezing A/F ratio from 14:1 to 15:1. All crashed to present condition in one weekend.

Here are the Pressure Readings:

COLD - 1.5 bar (20psi)
WARM - 3.2 bar
SYSTEM - 5.7 bar
BLEED - 1.6 bar held for 20+ minutes

These readings are within spec. WHAT THE HECK IS GOING ON?

My mechanic swears it is the WUR. How can this be when all seems to be working as it should? Are the readings close enough to being off-spec that they would cause this condition?

(Jim, expect a call Thursday. HA!)




http://forums.pelicanparts.com/uploa...1114656651.jpg

How about vacuum leaks around the intake or the intercooler?

Sorry, I didn't follow your other thread, but...

CSV and AAV working properly? Those are the two biggest culprits for hard cold starts...

ianc

I had a similar problem (hard start, but irratic idle) and went through the WUR testing and was confused by the results. I checked the prices for a WUR for a Euro 3.0L 930 ($$$$!) and decided to check the vacuum hoses for problems. I replaced the cracked distributor vac line and discovered another vac line was pinched under the left lower intercooler mount. Fixed that and all was fine. Just a thought.

I have eyeballed the vacuum lines and all apear sound. They will all be replaced soon if this issue persists.

My CIS is extremely minimalistic. Only the fuel head, WUR, and cold start valve remain. All other components were removed when the engine was rebuilt 2 years ago.
You'd think only 3 components would be easy to diagnose.

How old are the ignition wires and plugs?

This might be a silly question, but why were the other components removed? They're there for a reason...

The lack of an AAR, AAV will decrease starting\cold running performance...

ianc

No, those parts aren't needed. When I left Illinois they left the car.
You only need the AAV and AAR if you live in a cold region or don't like to hold the throttle for a few moments after start up. Remember those 2 items do not function until AFTER the engine starts. That is the beauty of CIS, being a component system.

This engine has run PERFECTLY in its minimalistic form sense the rebuild.

Good idea on the wires, I don't know how old they are. They are braided steel sleaved like OEM. The plugs are also 2 years old. The CIS components are all original. I took the entire system apart during the rebuild, cleaned and inspected everything. Fuel head was interesting.....

I'm sending a used WUR that I bought from a fellow PelicanHead off to be rebuilt. We will see how that turns out. In the mean time I'll do as all of you have suggested and look into other possible reasons for the problem. I'll look into each area one at a time using the existing WUR so as not to change the baseline.

Not true. The AAV is there solely to provide extra air at startup. It closes and does not reopen as long as the engine is running. The AAR also supplies extra air at startup and during warmup until the bimetal in it closes the valve.

ianc

I know what they do, you don't need extra air until AFTER you start the engine. You get the same result if you crack the throttle with your foot. Early CIS cars had a hand throttle for this function.

Trust me, I've been driving this car in all types of temperatures for 10 years. You don't need all that crap. Most of it was emmision related.

Rarly,

I want to clean up my engine and get rid of all that stuff and go minimalist. Are there some step-bystep instructions available somewhere to accomplish this?

Jim

Why not do a propane or acetylene vacuum leak test?

JW has said that the mixture screw has a lot more impact @ idle than @ higher revs. Since your WUR function seems fine and your A/F is fine @ WOT, but your CO is 0.0% @ idle, why not try richening your mixture @ idle and see what happens? Maybe you will be as rich as reqd for start and warmup, yet still be OK for boost.

Now the right guy is on the job...

sounds like either the hot idle mix needs to be richened, which also makes the cold running richer by adding to what the WUR is supposed to do when it's cold, or the WUR needs to be richened to run the engine nicely when cold. is the 930 engine lambda equipped, or not? either way, i tend to leave the oxy sensor unplugged and set the hot idle mix to as much as 4% on 930s. there also was a thermo-valve originally, that kept the vacuum retard from operating for a minute or so, which kept the idle up.

Paul - one of the original symptoms was a slight occillation at idle when warm, about 300rpm. Because I adjust the mixture seasonally and it is spring I tweeked it lean. When I put it back the occillations went wild, a typical response to a rich condition. The CO reading at that point was off scale 0%. You cannot richen the mixture warm.

John - the mixture, both cold and warm, needs to be more rich. The engine is a 930/63 modded and does not have a Lambda system, K-jetronic only. When the engine was rebuilt a little over 2 years ago I set it at 3% CO. It remained rock steady until a couple of months ago.

To me, it appears that the WUR is fighting itself and the Fuel Distributor with the result being an occillation at idle.

Another unusual symptom, now that the mixture has been set an 1/8 turn lean to releave the occillation, is that the idle is higher. It was 1000rpm before, now it is 1300rpm.

Jim - I don't know of any step-by-step instructions. You need to evaluate the real-world use of your car, the weather in your region, and your love/hate for gadgets that do things like raise the idle for you. In Northern Michigan you may not wish to eliminate much if any of the system.

John - Do you know/use anyone who rebuilds WURs? I have contacted an outfit called Fuel Injection Corporation in Livermore CA. Know anything about them?

Why not just modify the WUR yourself to make it adjustable? Being able to set it to a variety of settings might help to compensate some for the missing bits, or whatever else is freaky.

ianc

My WUR is adjustable. I have tried to compensate and have achieved a little improvement. Right now it looks like I'll wait for the rebuilt unit to arrive (next week). That should tell me something.

RarlyL8,

Just a few more thoughts.

Are you sure your CO gauge is correct? 0.0% sounds very odd.
1/8 turn is about 1%, maybe even 1.5%. Can you just nudge that screw in smaller increments? That's what I typically do.

Haxe you checked your sensor plate to make sure it is moving freely and not hanging up or weighted down by grease, etc? I think you mentioned you have already checked for air leaks. I see you still have a decel valve. Did you check that? I assume you have already checked distributor, timing, plugs, wires and all 7 injectors.

I find that is not unusual at all for the idle speed to change w/ the mixture setting. When the mix is leaned I always have to lower the revs.

Why do you say the mixture cannot be adjusted when warm? I don't understand that.

My Bentley manual says the AAV adds bypass air while starting only. The AAR adds bypass air during warmup only.

Your CCP was just a little low. if you were @ 10C. At what temp did you measure it?

I am wondering if your bimetal strip is shot in the WUR or maybe the relationship between the cold and warm settings is off. This can be changed by adjusting a screw on the bottom of some WURs.

What color is the inside of your tailpipe? I find on my car, the richness of the mix definitely changes the shade of it...leaner=brownish; richer=blackish. This is w/ Sunoco 94. I have noticed over the years, however, that tailpipes of turbos are quite often quite a bit lighter than NA cars.

Yes, the AAV is only open during startup, and is meant to add extra air. As soon as the engine develops any appreciable vacuum, it closes. The AAR (which is what I think you meant in the second part of your statement) will also add extra air at start because it's open at that point. It doesn't shut until it warms up.

In my experience, the thing that really kills the startup is the cold start valve not working for some reason, so I'd investigate that first. Is the thermotime switch working (measure resistance cold and warm)? Are the wires connected to it hooked up the right way? It DOES make a difference if the connections are on backwards. Is the CSV acually shooting gas? Hook up your pressure gauge and look for a press drop when you jump the CSV.

Even on a mild CA summer day, if the CSV is not working, you can crank the thing forever from cold and it won't start...

ianc