Intermittent No Start, how to test?

[boyt911sc]

Originally Posted by accord

The shorted out subharness to my WUR had 4 wires in it. 1 brown and 1 red/white going to one of the WUR's terminals, and 1 brown and 1 red/white going to the other WUR terminal.

Andy,

Are you sure you read it correctly? You can not have a (+) charge and a (-) ground on the same terminal. That’s the reason electrical plugs are used to avoid this problem. Please double check your PLUGS. Keep us posted.

Tony

[acorad]

Originally Posted by boyt911sc

Andy,

You will know the answer to your question by simply inspecting and looking at your wire harness. That is how you learn things. Have an inquisitive mind and accumulate experience. What wiring diagram are you using for your references? Get a copy of the PSM (Porsche Shop Manual) printed in color for easy reading if you don’t have one yet.

Don’t feel bad. We all started some where with little or no experience in the subject. Educate your self by starting to READ and understand the schematics or diagrams. It would be difficult at first, but as you get familiar reading them, it will be like reading the alphabet.

Tony

Tony, I am spending hours inspecting and looking at my wire harness, however almost all of it is wrapped inside a black covering. I don't understand, how do I inspect it to answer my question about where the second pair of wires from my WUR is going?

The wiring diagram I'm using is a pdf copy of "911 72-83 Porsche Workshop Manual." The cover says "Workshop manual 911 DR. ING h. c. F. Porsche KG STUGGART-ZUFFENHAUSEN." Is this correct manual to use?

[edit] I do see a different manual on Amazon, is this this the one you suggest?

https://www.amazon.com/Porsche-Service-Manual-1978-1979/dp/0837617057/ref=asc_df_0837617057/?tag=hyprod-20&linkCode=df0&hvadid=693463915385&hvpos=&hvnetw=g&hvrand=3187419101083420494&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9031146&hvtargid=pla-492574888231&psc=1&mcid=bd2bce44bb3c36078275fcfe15b13b8c

Andy

[acorad]

Originally Posted by boyt911sc

Andy,

Are you sure you read it correctly? You can not have a (+) charge and a (-) ground on the same terminal. That’s the reason electrical plugs are used to avoid this problem. Please double check your PLUGS. Keep us posted.

Tony

Thanks Tony, yes, you are correct, I wrote that wrong. There are two browns to one WUR terminal, and two red/whites to the other.

The "Current Flow Diagram 911 SC USA, Model 81, Part I" in the pdf manual that I have, has something called a "Supplementary Air Valve" wired directly to the "Warm-Up Regulator." (I now realize that Supplementary Air Valve is an alternate name for the AAR.)

Anyway, [edit] in the image below the SAV is wired parallel with the WUR? Please confirm so that I know that I'm reading the diagram correctly. If I am reading it correctly, the SAV is where the second pair of wires from the WUR is going? [edit] Just found out that the SAV is aka AAR. Also edited to clean up some of my inaccuracies.

[boyt911sc]

Andy,

AAR (auxiliary air regulator) is commonly referred as SAV (supplementary air valve) in many CIS reference manuals even in Porsche Technical Bulletins due to translation from German to English. SAV is not the same as AAV (auxiliary air valve). AAV does NOT have heater as AAR OR SAV.

Tony

(Edited)

[acorad]

Originally Posted by boyt911sc

Andy,

AAR (auxiliary air regulator) is commonly referred as SAV (supplementary air valve) in many CIS reference manuals even in Porsche Technical Bulletins due to translation from German to English. SAV is not the same as AAV (auxiliary air valve). AAV does (not) have heater as AAR OR SAV.

Tony

Thanks Tony, that helps a lot. And that explains why I could not find the AAV in the wiring diagrams, because it does not have an electrical connection because it does not have a heater.

[acorad]

Originally Posted by PeteKz

Since I have a hand throttle in my 1973 car, I eliminated the AAR, AAV, decel valve, and all the plumbing in the "triangle of death".

The urban legend of the dangerous and mysterious "Bermuda Triangle" was part of my childhood in the 60's and 70's as I grew up on the east coast of the US, and was what immediately came to mind with the term "triangle of death." :-)

Anyway, I just googled ToD as it relates to our 911s, and although I don't have the bandwidth to tackle that particular project right now, I do see the advantages!

Andy

[acorad]

Well, the shorted WUR/AAR harness has been replaced. The car idles fine and the FP, WUR, and AAR are drawing 7.5 to 8.5A.

I probably won't have a chance to actually drive the car for a few days.

Andy

[PeteKz]

Good to hear. Please post a followup after you have verified everything is working.

[acorad]

I drove the car home today and did some errands, the current draw through the fuel pump fuse was between 8.5 and 9.0A when I checked it. So, that looks good.

The intermittent no-start remains, however.

I did a smoke test a couple weeks ago, and there are some seemingly minor leaks that I will try to seal up.

I did get a fuel pressure gauge, so the cold and hot pressures will be my next tests.

Andy

[acorad]

Just a quick update.

As you remember, my original problem was an intermittent no-start every 4 o4 5 or so starts.

Then, my WUR/AAR subharness shorted out, and I replaced it.

The next day, after replacing it, I had another no-start.

Since then, during the past week or so and dozens of starts, I've had zero no-starts.

The only difference I can think of is the temperature here in SoCal has dropped by a lot. From the 100s to the 50s-60s.

Also, now, on cold morning startup, the engine idles at like 1800-2000 rpm, then when it warms up it idles at around 900. I don't remember that higher cold startup idle rpm happening before.

Anyway, I probably won't have time to work on it any more until next week.

Andy

[acorad]

...and I had a couple no starts yesterday and today. Both were when restarting about a half hour or so after drives of 20-30 miles on coldish days ~ 60F.

Not sure if that means my issue is actually a hot start issue, or if it really doesn't mean much of anything at all.

Anyway, I'll get back to working on it next week.

Andy

[acorad]

Hi all, I'm getting ready to test my CIS fuel pressures for the first time.

"Joe Engineer" has a youtube video on how to do it: https://www.youtube.com/watch?v=Q7qjmfJHoLI&t=188s

It looks pretty simple.

Question: Is this the full process? Is there any other info I should know before I dive into this for the first time?

Andy

[acorad]

Hi all, I just did the fuel pressure test and these are the results:

1. Year of engine: 1981
2. US or RoW (Rest of World): US
3. WUR model number: 090
4. Ambient temperature at time of test (in degrees C): 62F/16.6C
5. Cold WUR Resistance (in Ohms): [edit] ?
6. System Pressure (in bars): 4.5 (supposed to be 4.5 - 5.2)
7. Cold Control Pressure (in bars): 0.5 (supposed to be 1.7 - 2.2)
8. Warm Control Pressure (in bars): 3.4 (supposed to be 3.4 - 3.8)
9. Time delta for Cold -> Warm Control Pressure (in minutes & seconds): 2 mins
10. Warm WUR Resistance [edit] 10 Ohms
11. Residual Pressure @ 1 min (in bars): 0
12. Residual Pressure @ 10 min (in bars): 0 (supposed to be 1.3)
13. Residual Pressure @ 20 min (in bars): 0 (supposed to be 1.1)

notes:

1. I tested this AM after car was not run for 16 hours or so.
2. When I removed the Fuel Distributor line from the WUR no fuel dripped out of the line.

I guess the WUR needs some attention?



Andy

[PeteKz]

Andy, it seems we are recovering the same ground in this thread. Maybe I didn't read back far enough. TLDR.

However, with the numbers you posted, you need to double-check several things.

First, make sure the return line from the WUR to the tank is not plugged. You should be able to blow through it (loosen the gas cap before you try). Make sure the line from the FD to the WUR is not plugged. Then re-run your CCP and WCP tests. If those are still out of spec, send it to Tony or adjust it yourself.

SP: On the low side but within spec, so it should not be the reason for your no-start problem. Do not adjust the SP until you find the source of the no-start problem first.

WUR resistance: The fact that the CCP increases up to the WCP indicates your WUR internal resistance heater is working (you did this test without the engine running, right?), so I don't see why you would measure a resistance of 0 ohms, which would indicate it is internally shorted. Are you sure you set your meter on the right resistance range? Are you using a digital or analog meter? Have you tried a different meter, or checked your meter against a known low resistance? On the other hand, if it really does have an internal short, that might explain why your wiring got melted in the first place.

RP: I mentioned the possible loss of RP in my post #14. Have you tested or replaced your FA? If not, test it by unscrewing the drain line (and plug the line), running the pump, and seeing if fuel leaks out the bottom fitting. If your FA is known/tested good, then you are losing RP through the FP check valve, or WUR, or FD. Try pressurizng the system and pinching off the rubber fuel line from the pump to the FA. If it holds RP, then the FP check valve is bad. If it doesn't, then pressurize the system and turn the CIS test valve off, to cut off fuel to the WUR. If it holds pressure, then the WUR is leaking down. Otherwise, it's the FD.

Report your results.

[acorad]

Are you sure you set your meter on the right resistance range?

Well, that's embarrassing. Yes, in the correct range it reads 10 ohms, digital meter.

Andy

[PeteKz]

[acorad]

(you did this test without the engine running, right?)

Yes, not running. For CCP I disconnected the WUR harness connector, for WCP I connected the WUR's harness.

Andy

[acorad]

Originally Posted by PeteKz

lol I deserve that!

Andy

[acorad]

First, make sure the return line from the WUR to the tank is not plugged. You should be able to blow through it (loosen the gas cap before you try). Make sure the line from the FD to the WUR is not plugged. Then re-run your CCP and WCP tests.

Will do.

Andy

[acorad]

Have you tested or replaced your FA? If not, test it by unscrewing the drain line (and plug the line), running the pump, and seeing if fuel leaks out the bottom fitting. If your FA is known/tested good, then you are losing RP through the FP check valve, or WUR, or FD. Try pressurizng the system and pinching off the rubber fuel line from the pump to the FA. If it holds RP, then the FP check valve is bad. If it doesn't, then pressurize the system and turn the CIS test valve off, to cut off fuel to the WUR. If it holds pressure, then the WUR is leaking down. Otherwise, it's the FD.

Will do if the fuel lines check out ok.

Andy