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FPR is a Bosch # 0 280 160 262 ('87 S4 FPR)
Front Damper is Bosch # 0 280 161 008
Rear Damper is Bosch # 0 280 161 021
So that's not it. Next hypothesis, please.
I initially suspected that too and even posted a picture to confirm. Ken confirmed they were 24#, and the evidence confirms it's not an injector issue. It has to be a pressure/flow issue.
The fuel rail gauge clearly shows that the pressure is less that the spec'd 45-50psi. and the WBO2 also shows it to be lean. So there are 2 forms of evidence to support that the fuel is not being delivered - one at the input, and one at the output. If the evidence was only at the end, then I would still suspect the injectors, but it has to be upstream of the FPR, or the FPR itself.
I'm quite certain if I were making the fuel pressure that I should be, it would not be running lean with Ken's chips.
The dampers are the correct part numbers and the FPR is brand new. I suppose it could be a bad FPR. Interestingly, when I swapped the new pump in, I pressurized things to check for leaks and to see if I got better pressure. Static pressure (car off, pump running) was ~55psi. Does that sound right?
So it's got to be either a filter issue or some other restriction in the line. The new filter did not show up today, so maybe tomorrow.
Yes, 55 is correct, with the fuel pump jumpered and the engine off. That is how the fuel pressure is supposed to be checked.
Running, with vacuum hooked up to the FPR, you should have a lower number. If you pull the vacuum line off the regulator with it running, it should be close to 55 psi. Note that he only difference between static testing and engine running testing with the vacuum line off is the fact that the injectors are spraying.
So, that could certainly be a volume problem, but I'd think that the pressure would drop as the fuel demand increased, if it had a volume problem.
However, you have some really strange fuel pressure readings!
Definitely time for that fuel filter, next. Fuel filters hate to dry out, once they have had fuel through them.....and if the fuel turns sour, at all, they really plug up. I used to routinely have fuel filter issues on 911s that had the engine removed for a few months (the filter sits above the fuel level.) Certainly 928s, with the filter below the tank, would be very resistant to the filter drying out....but who knows?
And.....Ken's idea of a wonky front damper also makes sense, with the strange pressures you are getting.
55 is correct, warm-not-super-hot engine, engine off, relay jumpered.
OK! OK! 55 PSI!
Front damper could still be fubared? Got-a-spare?
I do not have a spare front damper. Will consider it after the filter.
Originally Posted by PorKen
Left field, but...how about a blocked or restricted vent (carbon cannister) hose?
Wasn't the car smooshed on the front right corner?
On a race car the vent system should look like below or even better just a 'U' at the firewall to connect the to and from lines. Chuck/cap everything else.
(The vent line dumps/breathes behind the center of the rear aluminum bumper.)
Haven't looked at it. But if it was restrictied, then I would have seen issues when the tank drained when changing the pump, and it flowed freely (and really fast!). I'll poke my head up there and take a peek.
Originally Posted by Dave928S
On that theme ... have you checked every inch of the line from the tank/pump for damage?
I have, visually. I noticed a very slight bend (kink is too strong of a word) by the pump near the banjo fitting on the "S" pipe to the filter. I doubt it would have any significant impact. Other than that, I didn't notice anything anywhere else. But I think I will run my fingers along the entire length to see if there is something non-obvious.
Originally Posted by GregBBRD
Yes, 55 is correct, with the fuel pump jumpered and the engine off. That is how the fuel pressure is supposed to be checked.
Running, with vacuum hooked up to the FPR, you should have a lower number. If you pull the vacuum line off the regulator with it running, it should be close to 55 psi. Note that he only difference between static testing and engine running testing with the vacuum line off is the fact that the injectors are spraying.
So, that could certainly be a volume problem, but I'd think that the pressure would drop as the fuel demand increased, if it had a volume problem.
However, you have some really strange fuel pressure readings!
Definitely time for that fuel filter, next. Fuel filters hate to dry out, once they have had fuel through them.....and if the fuel turns sour, at all, they really plug up. I used to routinely have fuel filter issues on 911s that had the engine removed for a few months (the filter sits above the fuel level.) Certainly 928s, with the filter below the tank, would be very resistant to the filter drying out....but who knows?
And.....Ken's idea of a wonky front damper also makes sense, with the strange pressures you are getting.
The car sat for at least a year between when I bought it and when it fired up. The tank had some fuel in it the entire time, but it could have gummed things up. The filter seems most obvious at this point.
The LH has no air pressure or temperature compensation maps so stock WOT AFRs will be too rich in summer and tending to lean in the winter.
MAFs are do a decent job reading airmass but after many years of non-stop chip tuning I can tell you they are not perfect.
Air pressure makes a big difference in fueling at WOT. Low pressure = lean, high = rich.
The MAF outputs different voltages depending on whether it is hot = lean or cold = rich.
(I don't know if it is because it reads the relative temperature of the sensor wire to the air flowing through it, or if it is the relative temperature of the MAF electronics, or both, or something else. Basically, it sucks to be a tuner guy. )
As well, there is no gear or speedometer input so AFRs are variable according to the gear ratio.
(Fueling tables are based on RPM vs. MAF. Change one of the variables and you are in the wrong part of the map.)
I dont think that is true Ken... the MAF , doesnt know the difference between a high temp, and low pressure day.... those are strictly fine funing elements. Ive always done dyno runs, at a minimum one on a really cold day and one on a really hot summer day.... the mixtures are almost identical as measured by the wbo2 sensor. actual power varies, but thats expected and corrected HP is near the same. ive been on the dyno countless times..... 370 to 375 is the range ive seen power wise and the AFRs are always 12:1.... NEVER any leaner....I wish, right? remember, im too fat because the injector size is just too large for the power im making (30lbers) ... so i always long for the cold days... it seems to run better on those race days (leaner), but the mixtures and dyno runs dont show a difference.
so, thats no correct that the pressure of the day can make a major difference in mixture. the range of air pressure for a standard day vs a odd day, is just not that much to be a "major difference". in other words, even if you have a 3% difference in air density, that would only be a .3 change in AFR. (e.g. 12:1 going to 12.3:1) this is if the mass flow sensor didnt measure a change in mass flow. (which it does) .. we are only talking sensor accuracy and the temp and pressure sensors compensate as well. all in all the MAF is accurate alone, and the sensors make it very accurate. this is proven by countless dyno runs on hot vs cold days and the mixture not changing any more than is normally seen by just the fact that its a different dyno occasion.
Left field, but...how about a blocked or restricted vent (carbon cannister) hose?
Wasn't the car smooshed on the front right corner?
On a race car the vent system should look like below or even better just a 'U' at the firewall to connect the to and from lines. Chuck/cap everything else.
(The vent line dumps/breathes behind the center of the rear aluminum bumper.)
those vent lines mean very little, but could provide a vaccum in the pump if the gas cap was totally sealed..... dont think that could be a problem. ive capped off those lines and removed them.
Originally Posted by AO
OK... I hate to disappoint, but:
FPR is a Bosch # 0 280 160 262 ('87 S4 FPR)
Front Damper is Bosch # 0 280 161 008
Rear Damper is Bosch # 0 280 161 021
So that's not it. Next hypothesis, please.
I initially suspected that too and even posted a picture to confirm. Ken confirmed they were 24#, and the evidence confirms it's not an injector issue. It has to be a pressure/flow issue.
The fuel rail gauge clearly shows that the pressure is less that the spec'd 45-50psi. and the WBO2 also shows it to be lean. So there are 2 forms of evidence to support that the fuel is not being delivered - one at the input, and one at the output. If the evidence was only at the end, then I would still suspect the injectors, but it has to be upstream of the FPR, or the FPR itself.
I'm quite certain if I were making the fuel pressure that I should be, it would not be running lean with Ken's chips.
The dampers are the correct part numbers and the FPR is brand new. I suppose it could be a bad FPR. Interestingly, when I swapped the new pump in, I pressurized things to check for leaks and to see if I got better pressure. Static pressure (car off, pump running) was ~55psi. Does that sound right?
So it's got to be either a filter issue or some other restriction in the line. The new filter did not show up today, so maybe tomorrow.
that was i was wondering... so, you got 55lbs with engine off and fuel pressure jumped. i thought you said when you turn off the car, it went to 45lbs or something and normally idling at 40lbs? anyway, if thats the case, certainly there is a flow issue, because usually the "engine off , fuel jumped" pressure is the same as when the car engine is turned off, or vacuum line removed. and just because the engine is running, shouldnt degrade the pressure unless there is a flow issue. thats what the fuel regulator is for.
i have video of the stock system going WOT, to redline at 335rwhp with the stock fuel system and the fuel pressure doesnt move at all from set pressure. (and that was near 75psi) . I dont think the stock fuel pressure regulator would be any different at 55psi . so, i think we are narrowing it down to a flow issue. gas does weird things when sitting for a year. can turn like peanut butter. not good... in the wrong spots can certainly cause havoc . however, you would think the fuel pressure reg, might be clogged and that would raise pressure ... or if the lines are just restricted or maybe that damper, then that could be it too. the plot thickens!!
I don't have a definitive proof, but I think the filter was the culprit. I swapped out the filter with a new one and now Idle pressure seems to be higher at about 45 PSI. I had to disconnect my wideband O2, but will reinstall tomorrow and take it for a spin to see if I have, indeed, fixed it. It's also too late to do the "driveway dyno."
This black crud came poring out of the inlet of the old filter! Pretty sketchy. The tub was super clean too!
I don't have a definitive proof, but I think the filter was the culprit. I swapped out the filter with a new one and now Idle pressure seems to be higher at about 45 PSI. I had to disconnect my wideband O2, but will reinstall tomorrow and take it for a spin to see if I have, indeed, fixed it. It's also too late to do the "driveway dyno."
This black crud came poring out of the inlet of the old filter! Pretty sketchy. The tub was super clean too!
hmmmmm , that's kind of what all old filters look like... but i dont think that can cause the issue. I hope im wrong!
hmmmmm , that's kind of what all old filters look like... but i dont think that can cause the issue. I hope im wrong!
does the fuel come out the clean side freely?
Couldn't really tell. I wasn't about to run the pump with it disconnected. But I guess on reflection, the fuel did NOT seem to come out the filtered side, but came out the inlet side much more freely.
Cut it open, the filter paper is more or less identical to that in our oil filters. The case is really thick but hacksaws easily.
That would be the mindset of a pathologist. As a marketing and business guy, I tossed it in the garbage last night, and the truck already came by this morning.
That would be the mindset of a pathologist. As a marketing and business guy, I tossed it in the garbage last night, and the truck already came by this morning.
it really doesnt matter. a clogged filter at low flow rates will not change the line pressure... that is the fuel pressure regulator job. if you have 45psi at idle now, and it drops to 40psi with vacuum attached, its not the fuel pump or filter. If it is, ill eat my hat!
think about it, you get a small pin hole leak in your garden hose, the pressure is still 100psi, there is little flow, but the pressure is 100psi. at the higher flow rates, the pressure will drop. if you have static prssure on your fuel system of 55psi with pump jumpered, the pump is fine and you did the flow test into a bucket, that proves its got the flow too. the only way the pressure can drop, is if you had a real bad leak in a few injectors. (pooring gas into the cylinders) even that would be doubtful.
idling wont change the pressure to dop, especially if youre running lean. you even ran to high RPM at WOT, and that pressure is the same as it is idling... if you had a clogged fuel filter.... that pressure drop radically.
you checked the maf and injector size and Temp II... the only thing left is your ecu..... can you check another stock box or put the stock chips back in?
Mark you misunderstood. It's now 45PSI with vacuum attached, running at idle. I'll know more tonight.
so more like 48psi when you pull the vaccum?? then you shut it down and it goes to near 55psi after you turn the car off?
what was it before under the same circumstances? 40psi? very hard to believe that the filter could do that at low flow rates and then not kill the car at WOT flow rates. but heck, if it did.... i have a hat to eat!
lets hear the tests tonight.. AFR at WOT..
you can also pull the 02 sensor and you should get 13:1 idling if all is working well on the low RPM mixture side of things.
09-21-2015, 11:13 PM
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