Fuel System Issue Diagnosis and the value of gages

[JFairman]

I think the Chinese ones are URO brand. If the Porsche dealer relays are from the same supplier and it's possible more than one place is making them there and some are better than others, the lowest bidder.. etc.

The ones you buy from Porsche will hopefully have gone through their own final inspections and put in a cool little box.

[RarlyL8]

I bought both types and they appear identical. Both embossed Made in China. The only difference is the "OEM Supplier" brand cost $19 and the "Porsche" brand cost $34. The one that failed in my car was the Porsche brand unit. I believe this is where the term "Porsche Tax" comes from. I can understand higher prices for low volume products, I experience that with my line of exhaust systems, but to charge double just because it's put in a fancy box and sold to wealthier folks is deceptive and complete BS.

[911nut]

Originally Posted by Rawknees'Turbo

And what is really bizzare about the suckage is that 944s/951s of the same years, do not suck. My brother has a 1986 951 and its electronic componentry is totally "modern" for its time (unlike my 1987 930, which is very 1950s-1960s) - blade fuses, standard style relays still used on today's cars, much better fusing practices, etc. That just doesn't make any sense.

The 911 didn't get modernized electrically (or otherwise) until the 996(?). It was the company cash cow and building it was like printing deutsche marks until 1989, when high labor costs collided with the archaic design.

[Rawknees'Turbo]

Originally Posted by 911nut

The 911 didn't get modernized electrically (or otherwise) until the 996(?). It was the company cash cow and building it was like printing deutsche marks until 1989, when high labor costs collided with the archaic design.

That is very interesting, thanks.

I think one of the things that most floored me when I first bought my 1987 back in 2006 or so (had never even ridden in any kind of 911 prior, or even looked one over very closely) was how similar many parts of the car were to the two 1971 914s that I owned in the past - plywood floor boards , ancient style fuses and relays and sloppy/dangerous wiring practices , a/c that was a joke for anything above about 80 outside (especially if humid) I thought "holy shart, and this car is 16 years newer?!?!?!

And then I started to learn about the pre-Jurassic fuel system still being used, when much better options had existed for years, and was like a triple !

[RarlyL8]

I had a similar experience, my first 911 was a '73T MFI. Next was a '78SC. I compared that '78SC to my brothers '78 Pontiac Trans AM and was just puzzled at how primitive the 911 seemed. It was simple though and easy to work on. Forward to the '85 930 and nothing much changed. The 928 was a space shuttle compared to the 930. Then they kept the basic CIS 930 air cooled engine until 1994??? WOW, talk about a cash cow! Still there is no excuse for these relay and fuse issues to not be addressed for over 20 years of production. Now that there are no quality parts available this becomes a real issue.

[Rich76_911s]

Brian,

I recall you doing a little write-up on installing the fuel pressure gauge. I searched but couldn't find it, any chance you remember where you wrote that?

Thanks
Rich

[flightlead404]

Originally Posted by Rawknees'Turbo

That is very interesting, thanks.

I think one of the things that most floored me when I first bought my 1987 back in 2006 or so (had never even ridden in any kind of 911 prior, or even looked one over very closely) was how similar many parts of the car were to the two 1971 914s that I owned in the past - plywood floor boards , ancient style fuses and relays and sloppy/dangerous wiring practices , a/c that was a joke for anything above about 80 outside (especially if humid) I thought "holy shart, and this car is 16 years newer?!?!?!

And then I started to learn about the pre-Jurassic fuel system still being used, when much better options had existed for years, and was like a triple !

Ease of home wrenching is inversely proportional to the level of complexity in the design. I constantly tell people the 911/930 is the easiest to work on car I've ever owned, including a '77 Rabbit and an '82 Chevette. Perhaps comparable to the '73 Ventura and almost as easy to work on as an airplane. On the other hand, complexity doesn't necessary gain you much (of the things *we* care about). My '86 was the highest horsepower and fastest car available on the American market the year it came out. Not sure about the specific power numbers, but I'd guess that ~300bhp out of 3.3L is reasonably good for the time.

[RarlyL8]

Follow up to the story, the car has been sitting sense the relay was changed out as I haven't had a chance to take 'er out for a romp. Took some time today to do that and verify everything is OK.
Well it's not exactly OK and again the gages tell the tale. Car fired right up and the AFR's and fuel pressure rose as they should over time as the engine warmed. Typically I just get it and go but this time I wanted to observe the entire warm-up cycle. Once the fuel pressure reached 53psi the AFR is usually 13.0:1, this time it was 12.5:1. That's odd. So I got out the little allen wrench and cranked the idle mixture screw until the AFR raised to 13.0:1. At that point I heard a slight miss and random pop out the tailpipe. It sounded like a lean pop. After thinking about this for a second I realized it was a lean pop and lowered it back to 12.5:1. I'm pretty sure what has happened is the plugs have fouled causing a slight miss and rich reading due to incomplete burn.
I went ahead and took 'er out for a drive, sounded really good off idle but I could hear a slight miss at even cruise. AFR had dropped from typical 14.3 to 13.7. Got to a good spot and stomped it to blow all that leftover carbon and fuel out and WOW, what huge plume of smoke blew out when the boost hit! Repeated again and the smoke was gone. Took 'er home and at idle there was a distinct miss. Looks like new spark plugs are in 'er future. Not really unexpected, could have been worse.
So one more thing the AFR gage can tell you, fouled plugs!

[flightlead404]

Originally Posted by RarlyL8

Once the fuel pressure reached 53psi the AFR is usually 13.0:1, this time it was 12.5:1. ...cruise. AFR had dropped from typical 14.3 to 13.7.

You run significantly richer than my. My warmed up idle AFR is around 14.2 and cruise is leaner too.

I don't really have much of a clue about this, I let Tuner Studio calculate it. Am I so far off base?

[RarlyL8]

CIS does not offer infinitely adjustable tuning of idle vs cruise. Idle runs nicely at 13.0-13.5 AFR and cruise 14.2-14.7 AFR. The adjustments are not independent, you can plan on about a 1.0 point increase from idle to cruise.

[boosted79]

'87 slant conversion I bought last year has no relays, red covered aircraft toggle next to the key. Flip it on, pumps start, turn the key. Flip it off, engine shuts off. No air meter switch, don't get in a wreck.

[flightlead404]

Originally Posted by boosted79

'87 slant conversion I bought last year has no relays, red covered aircraft toggle next to the key. Flip it on, pumps start, turn the key. Flip it off, engine shuts off. No air meter switch, don't get in a wreck.

I suppose you could put in one of those mercury switches you used to find in old thermostats. At least you can have it cut off if the car was more than, say, 45 from the horizontal :-)

On a more practical note, Summit and various other places have inertia switches, I'd put a relay in and use the manual switch to power the relays and put the inertia switch in line with it to interrupt the power to the fuel pump relay in the event of a bump.

I put one in the plane after Kyle and Amanda Franklin's accident a few years ago (survivable crash, she died because the smoke oil pump kept on pumping). Easy to install, place it in the the circuit between the power supply and pin 86 (I think, power supply to the coil). Hard to trip accidentally (rough road won't do it for example) but any crash would certainly do it.

[boosted79]

That's a great idea with the inertia switch. I don't like driving it with this setup and am going to re-engineer the whole circuit with good relays, not these Porsche ones. But that is in the future along with EFI. Worst case scenario with this setup is you get in a wreck, engines stalls and you can't flip off the pumps, fuel line is broken, pumps keep pumping and it's crispy critter time.

[flightlead404]

Originally Posted by boosted79

That's a great idea with the inertia switch. I don't like driving it with this setup and am going to re-engineer the whole circuit with good relays, not these Porsche ones. But that is in the future along with EFI. Worst case scenario with this setup is you get in a wreck, engines stalls and you can't flip off the pumps, fuel line is broken, pumps keep pumping and it's crispy critter time.

Exactly. I think it would be an easy think to do, an afternoon's work. You could easily convert the current circuit so the manual switch controls a relay that provides power to the pumps instead of directly, and then add the inertia switch inline with the manual switch. The only think you need to make sure is the inertia switch is firmly fixed to the frame of the vehicle.

This is actually the one I use.

When you say "aircraft switch" is if the Carling G series? Or the Potter Brumfield switches with the built in circuit breaker? The right switch spec should handle 30A without problem, but the PB switch breakers have gotten a bit of a rep for failing in the field due to internal mechanical issues with the woven copper "wire" that flexes when you actuate the switch. I like the Carling G series personally, have switched everything to that.

[Bucketlist]

Originally Posted by flightlead404

Exactly. I think it would be an easy think to do, an afternoon's work. You could easily convert the current circuit so the manual switch controls a relay that provides power to the pumps instead of directly, and then add the inertia switch inline with the manual switch. The only think you need to make sure is the inertia switch is firmly fixed to the frame of the vehicle.

This is actually the one I use.

When you say "aircraft switch" is if the Carling G series? Or the Potter Brumfield switches with the built in circuit breaker? The right switch spec should handle 30A without problem, but the PB switch breakers have gotten a bit of a rep for failing in the field due to internal mechanical issues with the woven copper "wire" that flexes when you actuate the switch. I like the Carling G series personally, have switched everything to that.

Wow, thanks for posting this, something l've been thinking of doing for a while since someone wired this one without the air meter switch circuit. Looks like a good solution.

[boosted79]

I'm not sure what make it is, I haven't taken it out. It's just a metal toggle with the red flip up safety cover. The guy who sold it to me is a pilot and he restores vintage biplanes. He does beautiful work, he used the factory slant fenders and headlight mechanism when he did the conversion on this car. But he also trades natural gas futures and I suspect he may have got in over his head, thus my purchase of the car. Good info on the Carling switches. If it's good enough for an aircraft, it's more than good enough for a car.