Intermittent No Start, how to test?

[acorad]

Question: Adjacent to the burned area on the WUR power cord in my photo is the rubber/plastic section of the fuel line that goes from the WUR to the fuel distributor. That rubber/plastic section is very old/hard and seems to be slightly damaged next to the burned section of the power cord.

Can I replace the rubber/plastic section of that fuel line, or should I just buy a whole new one?

And are there better designed options than our host's OEM?

Andy

[acorad]

Also, for those who were interested, the bottom wire of the jumpered 25A #16 fuse that blew the other day (caused by the WUR power cord short) was not "loose."

That bottom wire is directly connected very firmly into the mess of wires that go to the back side of the fuel pump relay.

Andy

[PeteKz]

The rubber sleeve over that plastic fuel line is just a protective sleeve. Unfortunately, no way to replace it without cutting the plastic (nylon) line and then splicing it back together afterwards. If it bothers you, buy new ones, or buy something fancier like the stainless steel braided lines. I have used a spiral wrap that is common on wiring harnesses to provide protection for fuel lines and hoses, like this:

https://www.amazon.com/Spiral-Cable-Wrap-10ft-Electrical/dp/B0918XNP8J/ref=asc_df_B0918XNP8J?tag=bingshoppinga-20&linkCode=df0&hvadid=80195744240747&hvnetw=o&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4583795273156158&psc=1

[acorad]

Thanks Pete, I didn't know that's how the lines were constructed. Very helpful.

Andy

[acorad]

I also did an air leak test the other day.

I injected the oil mist through the brake booster line and found leaks around the pop off flapper in the airbox, some small cracks at the rear driver side corner of the airbox above the #1 intake runner, and at all 6 injector seals.

I'd say the pop off flapper leak was at least as much or more than all the other leaks combined.

Is there any good info on fixing or replacing the leaking flapper?

I've been looking but haven't found much good info.

Andy

[acorad]

The leaky flapper:

[PeteKz]

Press down on it when doing the test. Remember, the flapper is getting sucked down by intake manifold vacuum when the engine is running. If it still leaks, then look at the O-ring in the lid.

[acorad]

Thanks Pete.

Andy

[acorad]

Hi all, as you saw from the photo above, the subharness to my WUR shorted out and burned through, and I'm now trying to determine what repairs are necessary.

Please understand that while I've done a fair amount of wrenching over the years, I've done almost no electrical, and zero CIS, previously.

My initial hopes of quickly splicing in new wires seems unrealistic as the wires in the subharness look damaged from the WUR's (broken) plug to past the spot where it enters the wrapping of the main engine harness.

There are 4 (now damaged) wires in the WUR's subharness, 2 black, 2 red/white.

If I'm reading the wiring diagram correctly, one black & red/white pair goes to the WUR, and the other pair goes from the WUR to the AAR.

Question 1) I believe the WUR's red/white power wire originates at the #10 terminal on the 14 pin connector, but where, physically, does the black (ground) wire to the WUR originate? Where does it physically connect to ground?

Question 2) Should I just abandon those 4 original subharness wires and replace them with new wiring?

Question 3) And where can I get new (hopefully) plugs/connectors for the WUR and the AAR?

[edit] I think I found the plugs/connectors: https://www.ebay.com/itm/285580033413?_skw=bosch+connector&itmmeta=01JARGPR08RW3M550VBXZPPA63&hash=item427de57d85:g:u7kAAOSweIplXPpi&itmprp=enc%3AAQAJAAAA8Mxmj%2BiGvOveHXEBClPb29hO7Mt VjoXqNjEV1Cp0p5o0nO1Rrj4a7C0nKR3NrcMTqdtmHzqX0Qgj2 U%2FbXMf2I1g2RHxRnoHACzFaY5Nbx8wLi9wMMguKmthezPtIF XmHpRI7NTJCmFXYivKktA7siyWWbqq1NJKP3FPPqSQhkd%2BcD 3FfXjHNNccWlzSiFI7GxYewY2xJP27cgRRjjuAa0q8ZxovQu3x 0OJ%2FsECIeLTUtCa%2FH296%2BP6duQTxcsguq5j2UN25YHoM 2%2BrnYVRn500KrrexpRA%2BP%2BvscesL5qJCALLBOrOfTpW7 yZnrC2XDb0Q%3D%3D%7Ctkp%3ABk9SR5qA25DWZA

Andy

[PeteKz]

That looks like the right terminal (no guarantees!). I'd order several of them, because there are a handful of them in the engine bay, and you might need to replace others some day.

Re the burnt wires: Those tend to get hotter at their connector ends because that's where the highest resistance is. I've seen many wiring harnesses where the insulation was melted at and near the connector, but still ok inside the harness. Open the 14 pin connector on the engine wiring harness and see if the red/white wire is melted there. If not, put it back together, put on a new connector and run it. You could also do a continuity check between the other wires in the harness at the 14 pin connector, and if you don't have any shorts from that wire to others, make a note of what happened, but leave it alone. You are likely to cause more problems by pulling the harness apart.

Yes, you can bypass the red/white wire and the brown wire--that wire should be brown for ground, not black. the brown wires are grounded at several points, including on the engine. If you feel that you must bypass the melted wires, then the red/white wire carries power when the ignition switch is on to all the CIS component on the engine, and the brown wire carries the current to ground. Any ground point on the engine or chassis will do.
As far as soldering and crimping technique, there are plenty of YouTube videos on how to do it. Look at those.

[acorad]

Thank you Pete, super helpful.

Andy

[boyt911sc]

Andy,

You might not be lucky next time. Your engine wire harness is more than 40 years old and about time to retire it. I would contact Dennis P. (Timmy2) for a replacement engine wire harness or how to fix it.

For peace of mind, I will bite the bullet and spend for a new engine wire harness. It is your car and you make the final decision.

Tony

[acorad]

Originally Posted by boyt911sc

I would contact Dennis P. (Timmy2) for a replacement engine wire harness or how to fix it.

Tony

Thanks Tony, I just sent him an email.

Andy

[acorad]

Hi all. As you can see in the above posts, the 25A fuel pump circuit fuse and the subharness to my WUR (which also powers the AAR) shorted/burned through.

I'm trying to make sure that neither the WUR nor the AAR caused the problem.

The engine has not been run in several days so it's at about 70*F, and the 090 WUR resistance is 10.1 ohms, and the 218 AAR resistance is 33.6 ohms.

I've read here on Pelican that the 090 WUR should have about 3X more resistance (around 31 ohms), and that the 218 AAR resistance looks pretty much exactly in spec (33 - 34 ohms).

V=IR says I (Amps/current) would only increase very little, like 0.1A, due to the lower-than-designed resistance of the WUR, so I think I can rule it out as causing the short. Right?

Also, does the cold WUR's 10.1 ohms conclude that there's a WUR problem that needs to be fixed, or do I need to run the engine until it gets hot and remeasure the resistance to make that conclusion?

I'm pretty sure the engine will run without the WUR and AAR connected.

Andy

[PeteKz]

Andy, the resistances through the heating elements in WURs depends on the particular part number, but is somewhere between about 10 ohms and about 30 ohms. I checked my specs book, but it doesn't list the resistances for each part number. The way they are made, I would not expect the element to change resistance over its life, except to break and go open circuit. If you are measuring 10 ohm on the 090, that's probably what it should be, unless it was rebuilt and someone substituted a different element.

In any case, that will not cause you warm running problems. It might cause some stumbling during warmup, because it will warm up the WUR faster, and lean out the mixture sooner. Otherwise, no difference.

Yes, you can run the engine without the wires connected to the WUR and AAR. That will make starting the engine harder and you may have to keep your foot slightly on the gas for a minute or so until it warms up sufficiently. However, keep the TTS and CSV connected, or it will be really hard to start cold. After the engine has reached operating temperature, the heat elements have no further role. 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".

V=IR, or V/R=I. Examples: 13v/10 ohms=1.3 A, 13v/30 ohms = .43 A

[acorad]

Thanks Pete, I should have shown my math.

I mostly was trying to make sure that neither the WUR nor AAR will short any new harness wiring.

The "expected" values of 31 ohms for a 090 WUR and 33 ohms for a 218 AAR are both from old Tony (boyt911sc) posts here on Pelican.

From the wiring diagram I believe the WUR and AAR are in series and so I believe their resistances are additive.

So the "expected" total resistance is around 31+33= 64 ohms for both the WUR + AAR, so 13/64 = 0.2A is their expected power draw.

But my "actual" resistance is around 11 + 33 = 44 ohms, so 13/44 = 0.3A is their actual power draw.

So my thinking was the additional amperage draw due to the low resistance in the WUR is about 0.1A (0.3 - 0.2) which I would think should not be the cause of my subharness and 25A fuse burning. i wouldn't think even the 1.3A that you calculated would cause an overdraw like that.

Does that thinking make sense or am I off in the noobie weeds somewhere?

In another old post by Tony, he mentioned that he could tell if a WUR was ok by simply measuring the cold and warm resistances, so I suppose I should drive the car and measure the warm resistance too.

Andy

[boyt911sc]

Originally Posted by acorad

Thanks Pete, I should have shown my math.

I mostly was trying to make sure that neither the WUR nor AAR will short any new harness wiring.

The "expected" values of 31 ohms for a 090 WUR and 33 ohms for a 218 AAR are both from old Tony (boyt911sc) posts here on Pelican.

From the wiring diagram I believe the WUR and AAR are in series and so I believe their resistances are additive.

So the "expected" total resistance is around 31+33= 64 ohms for both the WUR + AAR, so 13/64 = 0.2A is their expected power draw.

But my "actual" resistance is around 11 + 33 = 44 ohms, so 13/44 = 0.3A is their actual power draw.

So my thinking was the additional amperage draw due to the low resistance in the WUR is about 0.1A (0.3 - 0.2) which I would think should not be the cause of my subharness and 25A fuse burning. i wouldn't think even the 1.3A that you calculated would cause an overdraw like that.

Does that thinking make sense or am I off in the noobie weeds somewhere?

In another old post by Tony, he mentioned that he could tell if a WUR was ok by simply measuring the cold and warm resistances, so I suppose I should drive the car and measure the warm resistance too.

Andy

Andy,

Go back and review the wiring diagram for the fuel pump circuit specially terminal #30. The FP, AAR, WUR, TTV, etc. are connected in PARALLEL NOT in SERIES. If they are connected in series, a failure of any of the load would disable everything connected.

Tony

[PeteKz]

What Tony said. Just like circuits in your house.

[acorad]

So I am off in the newbie weeds somewhere. Dang. Ok guys. I know I'm a noobie regarding all this wiring stuff, but it's frustrating because it seems like the more hours I spend I trying to learn and figure it out the more I find out from you guys that I figured it out wrong.

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.

From looking at a wiring diagram (which it is now clear that I don't know how to read correctly) I thought that one pair of those wires (1 brown & 1 red/white) was going from the 14 pin to the WUR, and the second pair (also 1 brown, 1 red/white) was going from the WUR to the AAR.

But I now know that is wrong because as you say the WUR and AAR are not in series, they're in parallel. So can you tell me where that second pair of wires is going?

I think there is something fundamental in wiring that I am missing.

Andy

[boyt911sc]

Originally Posted by acorad

So I am off in the newbie weeds somewhere. Dang. Ok guys. I know I'm a noobie regarding all this wiring stuff, but it's frustrating because it seems like the more hours I spend I trying to learn and figure it out the more I find out from you guys that I figured it out wrong.

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.

From looking at a wiring diagram (which it is now clear that I don't know how to read correctly) I thought that one pair of those wires (1 brown & 1 red/white) was going from the 14 pin to the WUR, and the second pair (also 1 brown, 1 red/white) was going from the WUR to the AAR.

But I now know that is wrong because as you say the WUR and AAR are not in series, they're in parallel. So can you tell me where that second pair of wires is going?

I think there is something fundamental in wiring that I am missing.

Andy

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