Steve,

I think Ian is just saying that if the WOT switch currently makes contact at say 75% open throttle would you get any improvement by rotating the WOT switch to make contact sooner, say we change it so it contacts at 65% open throttle? This would cause WOT maps to come in at an earlier throttle position.

I have already played with this and I must warn no to rotate the WOT switch to much counter-clockwise because (in my car) if rotated fully counter clockwise it causes the Throttle plate not to fully open. So if you do try this be sure to re-position it while the throttle plate is being hand held fully opened.

Steve,

Thanks a bunch for the graph, it's logging the same exact parms that I am and my chart looks very similar, other than my AFR is not as flat.

I also read, in a book titled "How to Understand Service and Modify Boch Fuel Injection & Engine Management", that the AFM bottoms out at 4000RPMs but the book is a general purpose Motronic book and maybe in other cars it bottoms at 4000RPM and this is why I was concerned. It's nice to see my AFM also bottoms at about 5500RPMs as you can see from an earlier post. I think this clears up where the Carrera AFM bottoms.

Once again thanks for your deep understanding and most importantly for sharing the graph.

Steve,

I really liked your graph format so I created my data in the same format, here's my graph:

http://forums.pelicanparts.com/uploa...1189177436.jpg

I had to use 0-10000 scale for RPM WOT and AirFlow so it looks nice. I will use this style graph for all results for now on.

OK, I found something interesting: I ran a WOT 2nd gear 2000-6000RPM run yesterday. Then today I just losend the AFM spring about 4 notches, this allows the AFM to drive further open at WOT than in the first run. You can see in the runs that the second run drives the AFM door to about 87% open and in the first run it goes about 84% open. So losening the spring did allow the door to go more open.

The other interesting thing is that my AFR curve remained about the same but the entire AFR curve was driven down by about 1.0AFR and now in the second run my AFR curve is where it should be.

Very interesting that I could move the entire curve down just by adjusting the AFM spring. I do not recommend folks to mess with there AFM as it has 2 adjustments: one is the spring and losining this widens the window but it also has a pointer adjustment to get the idle air spot on. In my opinion you MUST have an WideBando2 meter to even attempt to mess with this.

I will go back to the tighter spring as yesterday and try the run again to be sure I get the same results.

Here is yesterdays graph (tight spring):

http://forums.pelicanparts.com/uploa...1189188625.jpg

Here is todays run (Lose Spring):

http://forums.pelicanparts.com/uploa...1189188663.jpg

Steve, if you ever have the oppertunity to try this, could you? I plan to repeat the testing to be sure of my results.

Bottom line: I can't fix the low and high spots in the curve but I could move the entire curve down by losening the spring.

The graphs I have posted so far are from Microsoft Excel but here is what the actual data logger software (TEWBLog.exe) program looks like. The log is of a 1000RPM to 6000RPM run starting in 2nd gear then shifting into 3rd:

http://forums.pelicanparts.com/uploa...1189192500.jpg

As you can see the software lets you anylize your runs as well. I just also like to put them all into Excel for future refrence.

I did a bit more testing this weekend with my new WideBandO2 logger and am now questioning my fuel pump. I have reason to suspect the pump may be getting old and may be affecting my WOT AFRs. I think the pump may not be delivering the fuel needed at WOT above 3000RPMs. I did some runs of WOT and the AFRs did not look good, they where all over the place at this time time I was at about 1/4 tank of gas and decided to fill up. After the fill up the WOT runs leveled out. Also the pump hums and it hums even more when tank is low.

Any suggestions on howto best test fuel pressure under load (WOT) at 3000-6000RPMs? I have tested pressure at idle parked and all is well. But how do folks test for max flow in these cars?

Also, any folks have luck with aftermarket High Flow Pumps like the MSD-2225?

here is a graph of one of my ugly runs 2gear and 3rd gear shift, the White line is RPM the Purple is AFR:

http://forums.pelicanparts.com/uploa...1189452345.jpg

Thanks.

Hi Sal,

I would suspect (although I'm not sure), that the fuel pump delivery is not based on throttle setting, but is constant. The fuel pressure regulator regulates the pressure based on manifold pressure and returns excess to the tank.

If you suspect the pump, you can flow test it to ensure it delivers the required quantity in the specified amount of time, but that's about it I think...

ianc

I'm no expert but to me it would appear that an in-dash or in-cockpit fuel pressure guage which you could monitor simultanously as your laptop, would provide you with the needed info on fuel pressure at WOT.

Since I don't have much experience with it, I'm not sure if they make some kind of sensor/sender that can send the info electronically via wires, so you don't have to run fuel lines into the gauge in the car, but it would seem something like that would be ideal.

I was thinking of something like this, but what a pain to put a fuel pressure gauge near the dash! I may just have to do this to see what the pressure is doing at WOT under heavy load.

Thanks

I just checked, apparently they do have "electronic gauges", in particular I saw one from Greddy for $165 or so. The cheaper mechanical ones are under $20 but seems like it would be harder to install in an older porsche 911...

The supplier of your logger doesn't sell a fuel pressure logging accessory? I suppose that would be ideal...

Actually, the fuel pressure is regulated by a pressure regulator in the fuel circuit. Pressure is raised as manifold pressure raises (to help providing the required fuel under load). The pulse modulation alone on the injectors does not have enough dynamic range to cover everything from idle to WOT at max. RPM.

I think you should check whether that pressure regulator is working properly. The specifications are:

engine off, fuel pump running: 2.5 bar (36 psi)
engine running: 2.0 bar (29 psi)
engine running, vacuum hose disconnected (simulate full load): 2.3 - 2.7 bar (33-39 psi)

The fuel pump should deliver 0.85 liter/30 sec. (0.9 qt.)
The fuel pump should draw between 4-6 Ampere when running

That is a lot to check before jumping to conclusions. Seems like a mechanical gauge would be a good start....

I think Sal understands the above point as do I. I think what he seems to be saying is that under max load the pressure seems like it might not be high enough so perhaps he is suspecting that the pump and not the regulator is the source of the problem. Also he hears the humming noises.

I myself am not jumping to any conclusions, just attempting to answer the question he asked about how to check fuel pressure at WOT.

Because the FPR releases excess pressure away from the rail back to the tank, if SAL thinks he's not getting enough fuel because the fuel pump isn't working, I think it's a reasonable assumption. But with anything else, it is only a place to start. I think it's plausible sounding guess though.

But if one is connecting the gauge to the rail and it is not showing the right pressure, I would think one couldn't rule out a faulty FPR either??

Another thing you can do is hook the fuel gauge up to the rail and manually increase the throttle from the engine bay. However, I suppose this is not the same thing as having the car in gear and the engine under load.

Better yet, for $125 or so do some dyno runs, but before you do the dyno run hook up the fuel pressure gauge to the rail and watch the gauge as someone else does the run. That would give you pretty conclusive results.

There's an aftermarket fuel pressure regulator in there of unknown origin and specification right? First thing to do is remove it and reinstall the OEM regulator. If you need a new fuel pump, the OEM Bosch is more than sufficient. It's not worth all the grief you're putting yourself through.

Steve,

You are right on the FPR not being stock. Actualy it really is a stock regulator but apparently someone (PO) altered the pressure in the requlator to 3.5bar rather than the stock 2.5bar. Not sure how they did this, but I suspect they squezed the top of the regulator by using a vise.

The real problem now is that, as you know, the custom chip was created with this requlator and if I just put a stock one in I'm back to square one. I think the chip you created would run extremly lean with the stock requlator, correct?

However, I agree with you that it seems best to put the stock regulator back into the car and start from square one. I also think the fuel pump may be getting old as it does hum loud when the tank is low.

Steve, I may speak to you privately to see how I should proceed if I put the stock regulator in. Here are a few questions:
Should I also put back the stock chip to start?
Or could you more or less calculate a new chip from the current chip you created?
The only thing changing would be the fuel pressure from 3.5bar (current) to 2.5bar (stock).

Thanks folks.

Subscribed...

Well first thing is to to fix what is obviously bad, which is your fuel pump, it needs to be done. The FPR is up to you, but when I mapped this chip, it was done from the full throttle dyno AFR long the previous owner provided. I was never told about the FPR and the 3.5 bar fuel pressure, so with the exception of full throttle, now part throttle mapping is much richer than what I intended. That's probably why your seeing 13-13.5 AFRs in part throttle, which may be great for throttle response, but is not exactly fuel efficient or where you need to be in a cruising type situation. If you're happy with the way it runs, then just leave it alone. But if you revert back to the stock FPR, a whole new chip needs to be created and should go back to the stock chip for a baseline. I can't recalculate a new one from the old one - too many variables going on here.

Steve,
Thanks a million for all your advice.
First, I'm not 100% certain the pump is bad but I would guess it may be. It hums loud when tank is near empty and I'm sure it should not do this. Also, the WOT AFRs are all over the place after 3000RPMs if the tank is near empty, I see AFR approaching 15.0 which is way to lean! But if I fill the tank to 3/4 or more the WOT AFRs are much better and nice flat line between 12.8 and 13.2.

I was trying to find out if I could somehow test the fuel pressure at WOT and I think the best I can do is mount the FP gauge with maybe a long hose up to the back window and have someone watch it for me as I drive in WOT mode, I may actually do this because I hate to just change parts.

As for the Part Throttle maps I have this under control now, I was able to dial them in by just simply adjusting the AFM via the Sping Tension and the other pointer adjustment and now my part throttle AFR is right at 14.5 with NO O2 sensor signal to the DME. I'm happy with my part Throttle AFRs at this time.

I think I'll start with just the Fuel Pump and not replace the FPR just yet as this will open up other issues with the chip and will require it to be re-chipped, maybe sometime down the road when I have the cash.

The good news is I did see very nice AFR curve at WOT with the tank near full, this is why I suspect the pump is border line. I also plan to take a look at the in tank fuel filter as well.

Once again thanks.

Sal -- Sounds like you have a good plan...

Not to throw this thread on a tangent -- but I was not aware there was an in-tank filter. Does anyone have any specs on how often this needs to be replaced and how much this part costs? I've changed the other cannister filter before, but I was just curious on getting more info on this....

Hopefully you can provide some more detailed info on this, and the thread can resume right back to the main discussion at hand...

See part #25 here:
http://www.pelicanparts.com/PartsLookup/Output_Images/Size3/911_USA_84_86_KATALOG-084.jpg

The part number is 911-201-141-00 look it up on our host.

I have never seen this filter, but I assume it may just be a screen that can be cleaned and reused. But there it is right in the parts diagram

Hm, without trying to sound like a broken record I would try and do the flow test and the pressure tests as described in the Porsche WSM (a:engine running, b: engine runinng, vacuum disconnected). This should give you a basic idea about the fuel pump and its ability to deliver enough fuel and enough pressure.

Next, I fully agree with Steve in that you should probably revert back to stock (pressure regulator, mapping) and then consider a tuning from there. Steve does excellent work in this field.

84porsche9113.2, sorry if I offended you. This wasn't my intention. I simply wanted to point out that there are a number of tests that should be performed to check whether fuel pressure and delivery rates are in spec. Next, to isolate transient problems one has to get more inventive and monitor fuel pressure under varying load and load spikes.

Cheers,
Ingo