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mustangporsche · Joined: 08 Oct 2003 Posts: 283 Location: California Lodi

Well I discovered that someone had my filter on backwards, i think, the flow goes towards back right? I finally got a new one and was putting it on when I discovered it was backwards. I thought I should replace it because I thought it might be plugged up some because my fuel pressure was only at about 60psi., after i but the new one on it went up to 75 80. I am just going through and checking everything because it won’t pass emotions test? So my question is sense the old filter has been backwards ever sense I have owned the car would this screw everything up? Like my new pump, new frequency valve or fuel dist.? Because the car won’t really run at all, it will fire up for a few seconds that die out; I think maybe it’s just running on cold start? But the only thing I changed was the fuel filter? So I don’t know whats going on what do you think?

924RACR · Posted: Sat Aug 13, 2005 11:24 pm Post subject:

Correct, flow is towards the back of the car. Yes, this would screw up trying to get the car running well - mainly when you go for higher fuel flow situations (higher revs and throttle openings).

Since your fuel pressure is now higher (as in, where it should be), I would expect your running settings such as mixture, if they were previously tuned for the incorrect filter installation, would need to be reset.

Does sound like it is dying after burning off the cold-start charge. Try richening it up till it'll run, and fiddle around with it till it'll idle steady.

Once idling steady, I've found the following works surprisingly well for setting mixture. Lean out carefully until engine speed starts to drop; quickly make a note of the wrench angle and richen it up before it stalls. Do the same to the rich side, noting where it starts to stumble. Turn it back to the very middle between the two, then go maybe 5 degrees to the rich side of the center.

This was the technique I used to set mine last; when run on the dyno with no further tuning I posted good stock numbers.

HTH...
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mustangporsche · Joined: 08 Oct 2003 Posts: 283 Location: California Lodi

Ok yeah I think you are right about needing to richen it up till it will run because I richened it up a bit and it would run a few seconds longer. But the strange thing it that when I first started it up with new correctly installed filter it was running fine, than I changed to the plugs and that’s when it started to have the problem? I even tried putting the old plugs back it to see but no difference? Also I don’t know how it was running as good as it was before with only 60 psi even at high revs, I never had a problem?? Weird

924RACR · Posted: Mon Aug 15, 2005 6:36 am Post subject:

Obviously you weren't driving it hard enough...

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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

mustangporsche · Joined: 08 Oct 2003 Posts: 283 Location: California Lodi

Ha-ha well I did bring it up to red line a few times, but most of the time it was driven pretty easy. Well I got it running pretty good now. Wow what I difference it runs really good now, no more intermittent miss at idle that was really annoying. I think the mixture is pretty good; I used the method you suggested and seemed to work well. Now I need to get another cat. Because I think from it running so rich before it cooked mine,

it was brand new last year. Than it’s off to smog test, hope it passes this time.

Paul · Posted: Tue Aug 16, 2005 1:22 pm Post subject:

Make sure you put regular gas in it before going for the smog test.

mustangporsche · Joined: 08 Oct 2003 Posts: 283 Location: California Lodi

ok yeah i got a haft tank of regular in it now, so it should be good.

mustangporsche · Joined: 08 Oct 2003 Posts: 283 Location: California Lodi

I failed smog again, even with a different cat. And the fuels filter on right way. So I just ordered a CO analyzer to get the mixture and idle dialed in prefect. I tried to take it to many shops put as soon as I say Porsche they run. ha-ha, well one place was willing to give it a try, I showed them everything and drove the car on the dino but it didn’t work, not sure why, I think it was because the filter was on backwards and everything was messed up? the guy said my computer was not working?? So now I am back to doing it myself, I found a CO analyzer that was reasonable so I think I will get it now.

Smoothie · Posted: Sat Aug 20, 2005 3:01 pm Post subject:

Which emissions gas did it fail on? With a cat, you need to be just slightly rich to hit the "sweet spot" where all 3 gasses are lowest. Look at #2 here - http://pg.photos.yahoo.com/ph/smoothies931pics/detail?.dir=341f&.dnm=dc16.jpg&.src=ph -Notice that if just a bit too lean, NOx shoots way up.
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mustangporsche · Joined: 08 Oct 2003 Posts: 283 Location: California Lodi

well it is hi in CO and HC here is what the first test looked like 15mph HC Meas @-254 max is 138 25mph HC Meas@-180 max is 110 CO@ 15mph Meas@6.30 max is .98 25mph@ 6.07 max is .78 the NO was really low 66 and 46 max is 1136 and 966, so I figured ok I can lean it out and have a lot of room for the NO to go up. Ha-ha the guy didn’t like this, way rich is over 3 times the limit.
2nd try CO 15mph meas. 3.28 aw went about half down
25mph meas. 3.87
HC 15mph meas.183
25mph meas. 140 also went down a little

3rd try CO 15mph meas 4.46 aw what went up?
25mph meas 4.02
HC 15mph meas 207
25mph meas207 also went up
NO went up some 15mph meas@411 25mph meas@533 Max 1136 and 966 so still have room to play with.
Now what I did that was different on this last test that put a different cat. On and correct my backwards fuel filter, also I was leaned out as far as I could go and be able to start the car. It should have been safe it was at 16.0 AFR at idle and went up as rpm increased @ 3000 it was at mid 12s. I was just going to lean it down and go in, but the guy turns the car off, to check the fuel cap, so it has to be able to start. I would have thought it would have got better not worse? beats me, now this is starting to piss me off I think I might have weakened or slightly blown my head gasket from running a bit lean, because I noticed today a little coolant leaking, aw man well I am hoping it will go away, bet it still runs good, I have been watching it real close? I need a leak down tester to see if it has a crack or what’s up, I hope it’s the heater valve or something else? Well what next

JamesWilson · Joined: 10 Jun 2005 Posts: 132 Location: San Diego, CA

When I had my 931 on a gas analyser, CO and HC went down as we richened it up.....seems counterintuitive, but the car had been running waaaay lean and was putting out some really high emissions numbers. The guys at this Porsche shop said traditionally on the CIS cars that they have seen, though their machine doesn't test NOx, if the cat is functioning (all numbers would be up with a bad cat, not just NOx) and the HC and CO numbers are good, then NOx should be too unless you are just getting way too much cylinder temperature.

I'm off to smog my car here in CA in the next two weeks, once the new suspension is on it....and that damn wastegate!!

-JamesW
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mustangporsche · Joined: 08 Oct 2003 Posts: 283 Location: California Lodi

huh that’s interesting mine seems to do the opposite, but I will see once I get my analyzer, should be here tomorrow I hope, than I can get things hailed down good, I hope. Thanks for the Cat. James, i was hoping that would do it, put i didnt get so lucky, but my old one didnt look to good anyway, from running so long way rich.
Yeah that wastgate is fun huh, i had to do mine not too long ago. Did you upgrade to a 930 spring in yours?
So you are running with no Cat. now, or did you get a new one? will it pass without a cat.

Lizard · Posted: Tue Aug 23, 2005 3:26 pm Post subject:

1 thing I would like to mention is that whenever you adjust the air fuel mix, it is VERY sensitive,
as well you should never tune from rich to lean, you always need to tune from lean to rich when on the gas analizer.
1 other thing you can do it to get a wideband or regular O2 sensor, if you have a voltmeter measure the voltage coming off it, it will range from .1 of a volt to 1 volt, the higher the reading the richer it is, obviously you want about .5 volts. you can also use a dwell meter on the frequency valve.

good luck with it.
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JamesWilson · Joined: 10 Jun 2005 Posts: 132 Location: San Diego, CA

I ended up welding a high-flow 3" cat, a 24" x 3" resonator, and 3" sewer piping all the way back....no muffler, still very quiet and tons more responsive. It should pass smog, I am having a shop install the wastegate (I don't have a lift here) this week, as well as redoing the front coilover suspension. Car goes to paint next week (I'm supposed to have it looking "like a Porsche" for when my in-laws arrive, proving I am not a complete f-up hehe).

I have pics from the recent PCA autocross, as well as some video that's on the pcasdr.org web site of the car flying by (shifting and lifting to avoid overboost!).

-JamesW
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