ajm55

At my wit’s end here and would appreciate some input.

I have a Weistec E55 with loads of supporting mods. The car is really strong but I have a lingering Fuel Pressure issue that for a very long time now has been hampering my enjoyment of the car. Hope some of the experts here have some useful ideas and will chime in.

On the fuelling side, I’m running 2 AEM 320 lph pumps with the stock (brand spanking new) fuel sender unit, stock fuel lines, Weistec’s fuel rails (larger diameter than the stock rails) and Weistec’s 650cc injectors. I have new fuel relays, a new CPS and a new cam positioning sensor fitted.

I’m measuring fuel pressure via the DashDAQ. Although it’s not properly calibrated, I can gauge with enough certainty from the fluctuations in FP readings what’s happens to FP in different situations. So at idle, the DashDAQ will read at around 6.2 which equates to about 5.3 bar. On a WOT run, when the FP issue is not present, the DashDAQ reading will fall to a low of around 5 which equates to about 4 bar.

The issue: The issue is more likely to arise in hot weather than cold, when the tank is closer to empty than full and when I’ve been driving for longer periods than shortly after start-up.

When the issue arises, FP will drop off dramatically under hard acceleration, For e.g. on a short WOT burst, FP will quickly fall to low 3s and I’ll immediately come off the gas. I’m sure that if I stayed on the gas, FP would fall away altogether (and my rebuilt motor would go boom in the process).

If, after the issue has arisen, I cruise at moderate speeds, FP will usually hold-up but the moment I get on the throttle, it falls quickly to dangerously low levels. The issue will resolve itself if I park the car and allow it to cool for a period. The cool-off period required varies. Leaving the car overnight will always resolve the issue. Sometimes leaving it parked for an hour or two will suffice.

Heat is clearly a factor. The fuel rails are extremely hot to the touch, even after a short (5km) drive first thing in the morning. I’ve tried heat-wrapping the fuel lines but no improvement. My mate who’s trying to help with this thinks that when the issue arises, either the pumps begin to cavitate or the fuel starts percolating in the fuel rails. We have no idea why either of these scenarios would occur.

Any suggestions/input welcome, thx

AgSilver

Try some temperature sensitive tape on the rail and see what the indication is.

The SLR's have fuel coolers.

http://www.wahltempplates.com/

It may also be possible that the fuel line diameter from the tank to the engine is not sufficient for the Weistec setup.

ajm55

Thanks for the suggestions. I'll look into them

I was considering a Fuel Cooler but canned the idea on the basis that none of the other Weistec 55s are having the issue (as far as I know) and installing a Fuel Cooler may simply mask some other underlying defect that needs to be addressed.

There are no insulators used by Weistec at the points where the fuel rail is bolted on. Is it possible that excessive heat is being transferred from the motor to the fuel rail as a result? We'd need to modify the fuel rail to accommodate
insulators and I'd rather not do so unless that is likely to solve the problem

uraberg

Tank vent bad? Try driving a bit without the gascap on.

Hulk

He would have thrown a code if it wasn't venting

jcjmw

[QUOTE=ajm55;6214160]Thanks for the suggestions. I'll look into them

I was considering a Fuel Cooler but canned the idea on the basis that none of the other Weistec 55s are having the issue (as far as I know)[\QUOTE]

If no other Weistec 55s are having the same problem, then you could go back to the OEM fuel pump set up and see if you have the same problem.

jcjmw

In my situation, my gas tank vent and purge valve broke, there was no code just unable to fill the tank more then 6 gallons at a time. But does a bad fuel tank valve cause the fuel problems of OP....that I don't know.

uraberg

That depends on how the system works. The problem is not an inability to create vacuum, but rather the presence of excessive vacuum.
Granted, my experience with his comes from carbureted motorcycles, but the symptoms are identical.

Hulk

When the venting on my car wasn't working, it threw a code

Hulk

Iirc its code P0455

Chomanche

It sounds like you either have a volume or resistance issue. Im thinking that once the vehicle is hot theres a electrical contact that has too much resistance in it cuz heat = resistance and two pumps at full bore is quite a lot of amprage. It may be that the wires just arnt capable of carrying the load of those two pumps. Maybe a relay and some heavier duty cables are in order to carry that load.

ajm55

Thanks to all of you for the feedback.

We've wired the system so that the 2nd fuel pump relay is now triggered by the 1st rather than by the ECU. We have also installed an LED light on the dash which illuminates when current is going through to the 2nd relay. The LED will therefore illuminate from start-up and stay on at all times. Does the fact that the LED does not switch off when the FP issue arises negate your theory or would the LED remain on even if the issue is due to an amperage inadequacy?




[QUOTE=jcjmw;6214235]Thanks, this is possibly my next move. We haven't done this yet as there are a number of modified E55s around these parts that are running high flow pumps with stock fuel lines and the stock sender unit without any issue.

If Hulk is correct, I'm not seeing any codes. It does, however, sometimes happen when I fill up that the auto filler will disengage every 5 liters or so. Once, after the FP issue had manifested, I did remove the petrol cap and resume driving but doing so didn't resolve the issue. Are you suggesting that vacuum build up would cause the fuel to heat up in the tank? If so, then clearly I'd have to remove the cap from outset and not only once the FP issue arises in order to test the theory

Chomanche

I dont know cuz the led really just needs a certian voltage to turn on. Just like lines need to be bigger to flow a greater amount of fuel, wires have to be a smaller gauge to move more electrons. If you need to increase the volume of your rails to make more power your going to need to fill those rails.

ajm55

Understood, thanks

Sir-Boost-a-Lot

iTrader: (1)

Ajm55- I experience none of the aforementioned problems at all. Since our setups are nearly identical , I could only assume that if your twin AEM pumps were replaced with a new MB pump/filter setup like I run, that yours would run the same.

I think those pumps are just making too much internal pressure prior to being recirculated internally and heating the fuel.

ajm55

Yeah, thanks Chris - I think my set-up is virtually the same as yours barring the fuel pumps. We're probably going to end up having to re-instal my OEM pumps just to test. If it is the AEM pumps causing the fuel to heat up, would one not expect to see the same result on all E55s running high flow pumps? I know of two E55s here that are doing so without any issue. The only difference of note is that they are not running the Weistec charger.

Sir-Boost-a-Lot

iTrader: (1)

The problem I'm almost certain is the pumps heating the fuel, then cavitating at WOT as your friend suggested. Wrapping the lines was probably counterproductive as the heat is coming from inside the tank.

Are you sure both AEM pumps are functioning properly? Aftermarket stuff does fail at a much higher rate than OEM. Assuming that both pumps are wired, plumbed correctly and both functioning properly, that would leave the variable of input voltage. Your ECU programming is from Weistec while the other E55s running AEM pumps are running other software.

Have you compared the input voltages at the pump plug? I know that's a pain to check but I'm just tossing ideas. Perhaps Weistec increases pump voltage to a point that is beneficial on OEM pumps but problematic on larger AEM pumps.

ajm55

I'm confident the pumps are working as they should. I previously had the Aeromotive pumps installed and replaced them with the AEM pumps to eliminate the possibilty that the Aeromotives were at fault. The FP issue is identical with both the Aeromotives and the AEMs installed. The AEM pumps are wired and plumbed correctly.

I don't think we've checked the input voltage - I'll look into that. I'm actually running a Eurocharged tune - although I had the same issue previously when running the Weistec tune. I'll enquire from Jerry whether this could be tune-related. Thanks for the input

Roverron

Im sure I read the OEM pump vary pressure as needed.
It might be done by voltage which the aftermarket pumps might not like.
Like pressure on demand I would switch back to OEM and see what goes.
Also the pumps filters might be clogged or something restricting flow and causing them to heat up.

ajm55

Thanks for the feedback. I've not heard of the OEM pumps varying pressure as needed but worth looking into. All filters are new so no blockage there. Nevertheless, reinstalling the stock pumps may be the most sensible next step

jcjmw

Good luck to you! Keep us posted! If the problem is solved via reinstalling OEM pumps, then you at least know its something oem voltage related. Again, good luck!!!

ajm55

Thank you sir! Got a set of OEM pumps from Chawkins - helpful as always - and installed them last week. Did some testing on the weekend and I'm stoked to report that so far all is good. Need to do some more testing in hotter weather but I'm hopeful. It's worth noting that the fuel pressure drop under WOT is significantly less on the OEM pumps than on the AEM pumps (when functioning the way they should).

chawkins2001

Good deal homey

Gadget

Back before I switched to the Weistec tuning I was having all kinds of trouble. I looked and searched and so on looking for a way to read fuel pressure and the best I could tell is that the E55 does not have a fuel pressure sensor and you cannot read fuel pressure from the OBD.

So, how are you able to read fuel pressure with a DashHawk??

G

ajm55

Thanks again for all your help and advice brotha

Not sure how it is hooked up. All I know is that I had to get a particular sensor installed. Apparently there are some other guys on the forum who are also reading fuel pressure off the DashDAQ. Perhaps one of them can chime in with the details