speeder Posted December 4, 2009 Share Posted December 4, 2009 Scottie/GNZ and I are working on a Megasquirted Turbo LS2 which is posessed. Tuning was progressing well until we started to see lean conditions starting under low boost conditions, and continueing to lean out under increasing boost until the car would backfire and stall. Rigging a fuel pressure gauge showed fuel pressure dropping from base pressure (~43psi) as boost increased. We were running twin Wabro 255s in the tank, and quickly found one of them bad, actually bleeding pressure from the good one when both were running. Long story short, getting the pump hanger with 2 Walbros back into the small tank opening (2nd Gen RX7) proved almost impossible, so we installed a single Bosch 044. Same fuel pressure problem. Troubleshooting to date: 1.Connecting compressed air to the the regulator (Aeromotive A1000) reference port while running the pump makes fuel pressure track properly ( fuel pressure increases from base setting at 1:1 ratio to reference). Reference air pressure was injected at the vacuum distribution block's feed point from the manifold to make sure a vacuum operated accessory on the block was not dropping manifold pressure. Same problem under boost load. 2.Just for grins, replaced the regulator. same problem. 3. Checked for no restrictions in the fuel lines or clogged filters. 4. Checked for full voltage at the pump relay (rear mounted battery, < 3 feet of 10 guage wire to the pump ) under load, looked good. (Can't get on the intank connections but pulled the pump and gave a good visual inspection - no way they are bad. 5. Installed a 255L Walbro inline downstream from the intank pump, with its own relay for power. Interesting result was the fuel pressure decrease under boost was WORSE! This has to be telling us something. Some sort of blockage? Bad (new) intank pump restricting flow? 6. I will once again verify no blockages in the fuel line - The pump hanger has been removed and tested to have no internal leaks or clogged filter sock. 7. Next is checking the injector drive signals for anything weird - I'll take a storage scope onboard and see what they look like. Grasping at straws, I did a quick calculation and found that 100% duty cycle with the 8 -65 lb injectors *could * have more flow than the Bosch could provide (depending on what the real specs of the pump are) , but certainly not with a booster pump inline. Also, at the problem area, 3600 rpm and 7 psi boost, datalogs report 75% duty cycle and 17MS pulse width. These numbers make no sense except for tuning adjustments made to compensate for low fuel pressure, not any kind of ECU-caused problem. I just want to verify these numbers with the scope. I'll post a datalog later. I would welcome any observatons/ suggestions here. Quote Link to comment Share on other sites More sharing options...
speeder Posted December 4, 2009 Author Share Posted December 4, 2009 Datalog of the problem: Any insights are welcome! Quote Link to comment Share on other sites More sharing options...
woldson Posted December 6, 2009 Share Posted December 6, 2009 I'm going to pee into the wind here and take a stab at it. Too small of lines and your cavitating the pumps. Quote Link to comment Share on other sites More sharing options...
speeder Posted December 11, 2009 Author Share Posted December 11, 2009 Well, We are building a dual Walbro pump setup to replace the single Bosch. Everything else checks out. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted December 11, 2009 Share Posted December 11, 2009 Both the RPM and MAP signals are very noisy. What are the Lag values for them? I'd suggest taking them lower to smooth things out. Also perhaps you can take the MAP signal from a different port on the manifold where there's less fluctuation? On my L6 just moving the MAP port from the end (near the power brake vacuum port) to the middle made a significant difference in smoothing the signal above 6k rpm. I can't help but wonder if you had a smooth RPM and MAP signal what the PW and AFR traces would look like. My sense is that the PW would smooth out and put a more even load on the fuel pump. But I really can't guess if that would solve the backfire/stall issue. Still, I think you will want to get these cleaned up anyway so couldn't hurt to do it now in case it helps. Quote Link to comment Share on other sites More sharing options...
speeder Posted December 12, 2009 Author Share Posted December 12, 2009 Both the RPM and MAP signals are very noisy. Yeah, that is puzzling - but I can see no reason for fuel pressure to decrease as a result. Also before this fuel pressure problem everything was good(smooth) on the datalogs. I think the major thing to look at is the wbafr trace - a classic signature of lean misfires, backed up with simultaneous decreasing fuel pressure. We're attacking the fuel pressure as a primary cause. Still don't understand the difficulty with making a pump and regulator work... But then I have had a horrible recent history with bad new parts. Quote Link to comment Share on other sites More sharing options...
rags Posted December 12, 2009 Share Posted December 12, 2009 Rick, Where are you taking FPR reference signal from? Have you tried taking the signal from a different port? Changed the hose you are using? Are you actually seeing the fuel pressure drop at the FPR while under boost? How is the fuel system run, looped or dead ended like stock? Joe Quote Link to comment Share on other sites More sharing options...
speeder Posted December 12, 2009 Author Share Posted December 12, 2009 Rick, Where are you taking FPR reference signal from? A port just behind the throttle body - LSx motor with stiock TB. Have you tried taking the signal from a different port? No, It was working fine with this same source when the first Walbro failed. Changed the hose you are using? Hose is good - I removed the hose at the vacuum port to connect my compressed air for testing, including the whole vacuum distribution block and all hose we are using. Are you actually seeing the fuel pressure drop at the FPR while under boost? Yes. How is the fuel system run, looped or dead ended like stock? Full return system using the Aeromotive regulator at the inlet of the fuel rail. Joe Like Scottie said, "I am frustrated and angry at this whole situation." Bout sums up my mood too. I'm sure when we find the solution it will be a forehead slapper. We're back on it today with pump hanger rev 3. Quote Link to comment Share on other sites More sharing options...
rags Posted December 12, 2009 Share Posted December 12, 2009 One other thing you can try is removing the gas cap. If not for nothing it will remove the chance of a vacuum situation being created by boost. I don't know how this could be but the troubleshooting step won't cost anything. Good luck. Joe Quote Link to comment Share on other sites More sharing options...
softopz Posted December 13, 2009 Share Posted December 13, 2009 Its funny before reading this, Last night I was looking at the buick build looks hefty I guess it was a coinky dink. Anyways from what I saw you had twin fuel rails on the build. Just a couple of questions.. How are you driving the injectors all through ms? How are they configured through ms and wired? which ms are you running? with that said Im more concerned with fuel setup and twin rails. Especially after reading your fuel pressure is decreasing as you try to get into boost. Quote Link to comment Share on other sites More sharing options...
speeder Posted December 14, 2009 Author Share Posted December 14, 2009 Turns out the problem was a clogged fuel filter. Why people use those little 1-1/4" diameter tubes with the disc elements (like this: http://www.summitracing.com/parts/SUM-230101/ )inside for fuel injection is beyond me. The filter element had no visible debris captured (I visually checked it about 3 times during this embarassing episode) , but was restricting flow to the point where I could hardly blow through the assembly. Took the element out and the problem is gone! softop, PM me for the info you requested - It's not relevent to this thread. The fuel rail used on this engine is the stock LSx one, and yes, we had that one off to check. Quote Link to comment Share on other sites More sharing options...
woldson Posted December 16, 2009 Share Posted December 16, 2009 Good job! Glad to see you fixed it. Quote Link to comment Share on other sites More sharing options...
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