Help...dropping fuel pressure under boost!!
02-09-2003, 02:47 AM
#16
Burning Brakes
Thread Starter
The fuel pump is the same as the upgrade pump sold by Lindsey Racing, Bosch part no. 0.580.254.942. It's quite a bit larger than the stock 951 pump. It's original equipment for a 1978 Mercedes 450SLC.
tecart - under boost, 12.5:1 a/f ratio (as measured on wideband) corresponds to the first blue light on my arm1. I did some more full-boost runs, and no, the arm1 doesn't seem to drop down when the fuel pressure is dropping. I'm not sure why, you'd think it would start getting leaner. Maybe it's that I didn't keep revving too far after the fp started to drop. While I'm all for carrying out this test to help you know what the arm1 reads, I'm certainly not willing to run my car at full boost with dropping fuel pressure for too long.
I installed a fixed 3-bar fuel pressure regulator today, and did some more runs. The problem is still occuring, and now I'm a bit stumped. I've now replaced the DME relay, fuel pump, and fuel pressure regulator. I've checked for vacuum leaks as well. What else could be the problem? It doesn't happen all the time, but seems to happen more regularly when the car is warm. I notice it when doing full boost runs in 3rd gear, and the fuel pressure only starts dropping above 5500rpm. A couple times now when I've been doing full throttle 4th gear runs, my car has suddenly lost power at high rpm. Does anyone have any ideas?
tecart - under boost, 12.5:1 a/f ratio (as measured on wideband) corresponds to the first blue light on my arm1. I did some more full-boost runs, and no, the arm1 doesn't seem to drop down when the fuel pressure is dropping. I'm not sure why, you'd think it would start getting leaner. Maybe it's that I didn't keep revving too far after the fp started to drop. While I'm all for carrying out this test to help you know what the arm1 reads, I'm certainly not willing to run my car at full boost with dropping fuel pressure for too long.
I installed a fixed 3-bar fuel pressure regulator today, and did some more runs. The problem is still occuring, and now I'm a bit stumped. I've now replaced the DME relay, fuel pump, and fuel pressure regulator. I've checked for vacuum leaks as well. What else could be the problem? It doesn't happen all the time, but seems to happen more regularly when the car is warm. I notice it when doing full boost runs in 3rd gear, and the fuel pressure only starts dropping above 5500rpm. A couple times now when I've been doing full throttle 4th gear runs, my car has suddenly lost power at high rpm. Does anyone have any ideas?
02-09-2003, 03:42 AM
#17
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ian i do believe your arm1 shows 12.5 to 1 not just because you got off the throttle before it would drop off with the fuel pressure gage reading but also i think that at only 16 psi your not boosting high enough to cause a lean issue, you wont really have your arm1 go full lean unless your into 18-19+ psi at full boost, that may be why the arm1 stays ok (12.5-1) while you tested the car, so lets assume the arm1 will go full lean at 19 psi with the fuel pressure falling off, now we need to know how much is the fall off at 16 psi, what amount of pressure? A new pump and bigger pump should keep pressure loss down to zero or 2psi-5 psi max, could the voltage to the fuelpump be the culprit here or its voltage regulator?
It appears ian their is an acceptable amount of drop off but not that much under full boost here is an example i found: "Willie's comments: Not many mods since last time, but one important one. I discovered that with the stock fuel pump, my fuel pressure was dropping from 48 psig (with vacuum line disconnected) to 41 psig. TPIS told me that maximum acceptable drop-off at WOT should be no more than 2 psig. Well, what a surprise!! I'm dropping 7 psig -- not good at all. This means my engine is leaning out on the upper end, causing a loss of power and potential of blowing her up!! With the new Bosch fuel pump, my pressure not only holds at 53 psig, but rises under boost to 60 psig (7 psi boost). Removing the front sway bar allows more weight transfer at launch to the rear. The front end definitely lifts much more without the sway bar. I like it. Gained 0.14 seconds. Obviously, fuel pressure was a problem. Now, I'm getting enough fuel, but the car still does not have any upper end guts. I've got to replace Mr. Peanut. This cam was meant to be installed in my grandmother's car, not mine." that shows ian their is a problem either with your sensor/gage or the pump, lets see what danno says
It appears ian their is an acceptable amount of drop off but not that much under full boost here is an example i found: "Willie's comments: Not many mods since last time, but one important one. I discovered that with the stock fuel pump, my fuel pressure was dropping from 48 psig (with vacuum line disconnected) to 41 psig. TPIS told me that maximum acceptable drop-off at WOT should be no more than 2 psig. Well, what a surprise!! I'm dropping 7 psig -- not good at all. This means my engine is leaning out on the upper end, causing a loss of power and potential of blowing her up!! With the new Bosch fuel pump, my pressure not only holds at 53 psig, but rises under boost to 60 psig (7 psi boost). Removing the front sway bar allows more weight transfer at launch to the rear. The front end definitely lifts much more without the sway bar. I like it. Gained 0.14 seconds. Obviously, fuel pressure was a problem. Now, I'm getting enough fuel, but the car still does not have any upper end guts. I've got to replace Mr. Peanut. This cam was meant to be installed in my grandmother's car, not mine." that shows ian their is a problem either with your sensor/gage or the pump, lets see what danno says
02-09-2003, 07:11 AM
#18
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My guess here is that there's a vacuum leak somewhere in the system that's draining boost-pressure from the FPR. Why only at high-RPMs I have no idea.
One good test to verify the fuel-pressure gauge is to hook up a second boost-gauge but taking pressure right at the FPR instead of from the intercooler pipe.
One good test to verify the fuel-pressure gauge is to hook up a second boost-gauge but taking pressure right at the FPR instead of from the intercooler pipe.
02-09-2003, 09:03 PM
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Ian,
Something else to check out. Remember that the fuel pressure regulator increases pressure from the boost signal it sees via the control line. Have you considered checking to make sure there are no leaks on that line. If the regulator is not seeing the full boost, it would not make full fuel pressure. It might be something that simple. Good luck,
Mike Lindsey
LindseyRacing.com
Something else to check out. Remember that the fuel pressure regulator increases pressure from the boost signal it sees via the control line. Have you considered checking to make sure there are no leaks on that line. If the regulator is not seeing the full boost, it would not make full fuel pressure. It might be something that simple. Good luck,
Mike Lindsey
LindseyRacing.com
02-09-2003, 09:35 PM
#21
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If you are trying to maintain 60 psi at wot high boost with your stock fuel lines forget it. go to 52 lb injectors less psi more flow. Also note that your pressure gauge is reading from the end of the fuel rail. To get an accurate reading it should be before the injectors.Once your injectors open you get a fuel pressure drop across the rail
02-09-2003, 10:41 PM
#22
Burning Brakes
Thread Starter
fuel pressure drop across the rail? So maybe this "problem" has always been occuring, but I've never noticed it before? Yes I do have 52# injectors, big fuel pump, but stock fuel lines. There seems to be lots of guys making as much and more hp than me, still using stock fuel lines. I'm not running 60psi static, I'm running 3 bar or 43.5psi. But at 16psi of boost, the fpr ramps fp up to 43.5+16 = 59.5psi.
Mike - I'll take another careful look at the vacuum line leading from the intake manifold into the fpr. Perhaps I missed a pinhole when I was inspecting it. Pretty much everything engine related in my car is less than 20,000km old, so there are no old crusty lines or anything obvious under the hood. I very much appreciate the input, and I'll keep you all informed as to what I find out. BTW, the fuel filter was also recently replaced, so I've ruled that out.
Could it somehow be related to a weak alternator? Once my car is warm, the voltage needle in my dash sits just barely above the 12 volt mark. One other thing, this couldn't have anything to do with the air temp sensor I just mounted in my intake system could it? I disconnected the Huntley fixed voltage input from my wiring harness, and reconnected the stock air temp sensor into pins 1 and 4 of my AFM plug (took sensor out of AFM, and tapped into MAF sensor).
Mike - I'll take another careful look at the vacuum line leading from the intake manifold into the fpr. Perhaps I missed a pinhole when I was inspecting it. Pretty much everything engine related in my car is less than 20,000km old, so there are no old crusty lines or anything obvious under the hood. I very much appreciate the input, and I'll keep you all informed as to what I find out. BTW, the fuel filter was also recently replaced, so I've ruled that out.
Could it somehow be related to a weak alternator? Once my car is warm, the voltage needle in my dash sits just barely above the 12 volt mark. One other thing, this couldn't have anything to do with the air temp sensor I just mounted in my intake system could it? I disconnected the Huntley fixed voltage input from my wiring harness, and reconnected the stock air temp sensor into pins 1 and 4 of my AFM plug (took sensor out of AFM, and tapped into MAF sensor).
02-09-2003, 11:54 PM
#23
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I run 60psi fuel pressure (at idle), and up to 24psi boost. No fuel drop! I have 55# injectors, large fuel pump, and adjustable fuel regulator. The stock lines are not a problem!
Check the voltage at the fuel pump under boost. Also make sure your FPR is fine. Install a mechanical Fuel Pressure at the end of the rail and have someone monitor it under load on a dyno.
Check the voltage at the fuel pump under boost. Also make sure your FPR is fine. Install a mechanical Fuel Pressure at the end of the rail and have someone monitor it under load on a dyno.
02-10-2003, 01:51 AM
#24
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Ian,
I'm having a similiar problem... When the car warms up during a hard run, my fuel mixture isn't where it needs to be... It's at the last green dot instead of the first blue dot. When I turn the 'high' **** on the arc1 over a few clicks to richen it up: I get nothing. Like I hit a wall on fuel mixture.
I'm running 20 to 22 psi with 55lb injectors with the adjustable fpr.
I think the adjustable fpr will only rise to a certain amount of pressure before it maxs out.
Before I went to 43.5psi(3.0bar) on the adjustable fpr, i ran 34 psi. When I ran 34 psi, I didn't have this problem. Thats a difference of about 10psi, which would be enough headroom for the additional pressure needed.
I'm really interested to see how the new(stock) fpr works for you.
Good Luck,
-Sean
I'm having a similiar problem... When the car warms up during a hard run, my fuel mixture isn't where it needs to be... It's at the last green dot instead of the first blue dot. When I turn the 'high' **** on the arc1 over a few clicks to richen it up: I get nothing. Like I hit a wall on fuel mixture.
I'm running 20 to 22 psi with 55lb injectors with the adjustable fpr.
I think the adjustable fpr will only rise to a certain amount of pressure before it maxs out.
Before I went to 43.5psi(3.0bar) on the adjustable fpr, i ran 34 psi. When I ran 34 psi, I didn't have this problem. Thats a difference of about 10psi, which would be enough headroom for the additional pressure needed.
I'm really interested to see how the new(stock) fpr works for you.
Good Luck,
-Sean
02-10-2003, 05:32 PM
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sean: you should have zero porblems with that fuel pressure and the 55 pounders handleing the ability to allow your arc2 to richen up the mixture 1 or 2 dots on the arm1, your 22 psi isnt that big of a deal either, but if your running a big 2.8 or a big k29 turbo then you need bigger then 55 pounders and that extra fuel on the afpr your doing now, the arc2 will only enrich 20% over the stock chips map in total, thats it nothing more, so if your running stock chips or weak chips that may be the problem, the other may be your fuel pump is too small the other may be you need bigger injectors, let us know sean what it was that didnt let you run the arc2 into the blue area??? post back here
also to ian, if you want i can send you my end rail VDO fuel pressure gage that you slip onto the end of your fuel rail to test out you fuel pressure at idle and on load at a dyno, you just have to send it back to me when done, i to wonder about your problem, maybe mine does it too? did you take the little ball bering out when you did your fuel gage setup because it should be taken out unless the stock end cap is on, also the part about fuel pressure dropping once all 4 injectors are being fed as WOT does mean that the readings at the end of a long fuel gage would be weaker and drop, and the drop would be worse the more fuel that the injectors use up/ WOT... but since you say that it only started to happen has me second guessing all my thoughts, are you sure you did WOT runs and never saw the fuel pressure dropping ever before and that the drop is very signifigant?
also to ian, if you want i can send you my end rail VDO fuel pressure gage that you slip onto the end of your fuel rail to test out you fuel pressure at idle and on load at a dyno, you just have to send it back to me when done, i to wonder about your problem, maybe mine does it too? did you take the little ball bering out when you did your fuel gage setup because it should be taken out unless the stock end cap is on, also the part about fuel pressure dropping once all 4 injectors are being fed as WOT does mean that the readings at the end of a long fuel gage would be weaker and drop, and the drop would be worse the more fuel that the injectors use up/ WOT... but since you say that it only started to happen has me second guessing all my thoughts, are you sure you did WOT runs and never saw the fuel pressure dropping ever before and that the drop is very signifigant?
02-10-2003, 06:30 PM
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Sean,
I have an upgraded fuel pump, Bosch 55# injectors and an adjustable Fuel Regulator.
Few additional items to check:
* hard & soft fuel lines from the tank to the engine bay.
* Fuel filter.
Also, to rule out the FPR as a problem. Block off the fuel return line. Extreme caution when messing with fuel lines!!!
Also, unless you are using a good WideBand O2 sensor, the stock units can and will give inacurate readings if they are old.
I have an upgraded fuel pump, Bosch 55# injectors and an adjustable Fuel Regulator.
Few additional items to check:
* hard & soft fuel lines from the tank to the engine bay.
* Fuel filter.
Also, to rule out the FPR as a problem. Block off the fuel return line. Extreme caution when messing with fuel lines!!!
Also, unless you are using a good WideBand O2 sensor, the stock units can and will give inacurate readings if they are old.
02-10-2003, 08:12 PM
#28
Burning Brakes
Thread Starter
tecart - thanks for the offer. I'm sure my fuel pressure gauge is not the problem, but I appreciate your offer. I had one of those mini VDO gauges prior to using the electronic gauge inside the car.
I'm now going to follow fast951's advice and start searching for potential electrical problems. I'm going to tap into the fuel pump power wire, and see if voltage is dropping at higher rpm. I've already noticed my voltage gauge drop once the car warms up, sits only slightly above 12 volts.
fast951 - as discussed above, I'm pretty sure it's not the fpr. I thought it might be my Huntley afpr, but just a couple days ago replaced it with a fixed 3-bar fpr. That would have to be pretty bad luck for me to have gotten a dud brand new fpr, that has the exact same problem as the afpr that I removed. Fuel filter is quite new, replaced within the last 6 months. So to review - I have a brand new upgrade high-flow Bosch fuel pump, new fuel filter, new 3-bar fpr, 6 month old 52# injectors, and a new DME/fuel pump relay.
If anyone has a good set of electrical diagrams for a 1989 944 Turbo, could you tell me what colours are the fuel pump power wires going both into and out of the fuse box, as well as the corresponding fuse box plug and pin numbers?
I'm now going to follow fast951's advice and start searching for potential electrical problems. I'm going to tap into the fuel pump power wire, and see if voltage is dropping at higher rpm. I've already noticed my voltage gauge drop once the car warms up, sits only slightly above 12 volts.
fast951 - as discussed above, I'm pretty sure it's not the fpr. I thought it might be my Huntley afpr, but just a couple days ago replaced it with a fixed 3-bar fpr. That would have to be pretty bad luck for me to have gotten a dud brand new fpr, that has the exact same problem as the afpr that I removed. Fuel filter is quite new, replaced within the last 6 months. So to review - I have a brand new upgrade high-flow Bosch fuel pump, new fuel filter, new 3-bar fpr, 6 month old 52# injectors, and a new DME/fuel pump relay.
If anyone has a good set of electrical diagrams for a 1989 944 Turbo, could you tell me what colours are the fuel pump power wires going both into and out of the fuse box, as well as the corresponding fuse box plug and pin numbers?
02-10-2003, 11:32 PM
#29
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A problem with some of the fuel pressure issues may be the wire to the pump. If you upgraded the pump the stock wires may not be big enough to avoid a voltage drop, Danno? I helped a friend re-wire his Tec3 install. The installer used the existing wires in a very strange way. How'd you like to have a new Tec3 no DME and still have the DME relay controlling your fuel pump? At any rate he had the big Bosch pump and the stock wire. I was amazed at how small that wire was.
On my Weldon 2025 pump installation I ran #10 wire straight to the pump and used a Bosch relay to trigger it.
The Weldon pump at 43 psi flows about 160 GPH at 14 amps. Get the boost to 22 psi and the pump now runs at almost 17 amps. If I drop the voltage to the pump I can hear the change.
If I had that little stock wire on the Weldon I'm sure I'd have some issues with wire size.
Alan
On my Weldon 2025 pump installation I ran #10 wire straight to the pump and used a Bosch relay to trigger it.
The Weldon pump at 43 psi flows about 160 GPH at 14 amps. Get the boost to 22 psi and the pump now runs at almost 17 amps. If I drop the voltage to the pump I can hear the change.
If I had that little stock wire on the Weldon I'm sure I'd have some issues with wire size.
Alan
02-10-2003, 11:59 PM
#30
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</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Alan C.:
If you upgraded the pump the stock wires may not be big enough to avoid a voltage drop, Danno? </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Well, I'm not Danno, but this certainly could be a problem. If the wire gauge isn't big enough, it won't be able to flow enough current to maintain the voltage hence a drop in voltage to the pump and a resulting slower pump speed. Are the wires to the pump easily accessible?? After a high throttle run, feel them and see if they're really hot. Also any of the associated circuitry that supplies power to the pump could be a problem.
At high throttle, the with the alternator cranking away, there should more than enough juice for all the electronics in the car (including the big pump) so you should see a permenant 13+ Volts on the stock gauge. The only time it would drop significantly is at startup or when the engine isn't running andd you've got some accessories going.
I like the idea of finding another method of measuring fuel pressure as this seems to be the area of question - loosing pressure at WOT.
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
If you upgraded the pump the stock wires may not be big enough to avoid a voltage drop, Danno? </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Well, I'm not Danno, but this certainly could be a problem. If the wire gauge isn't big enough, it won't be able to flow enough current to maintain the voltage hence a drop in voltage to the pump and a resulting slower pump speed. Are the wires to the pump easily accessible?? After a high throttle run, feel them and see if they're really hot. Also any of the associated circuitry that supplies power to the pump could be a problem.
At high throttle, the with the alternator cranking away, there should more than enough juice for all the electronics in the car (including the big pump) so you should see a permenant 13+ Volts on the stock gauge. The only time it would drop significantly is at startup or when the engine isn't running andd you've got some accessories going.
I like the idea of finding another method of measuring fuel pressure as this seems to be the area of question - loosing pressure at WOT.
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />