Chaoticmass Posted August 15, 2006 Share Posted August 15, 2006 I've got my car, with turbo and megasquirt 'n spark extra, running nice. When tuning it I had to set the REQ_FUEL variable on the constants page a bit higher than the base map I downloaded. The base map I used had the setting at 6.0 or 6.5 if I remember right, but my engine would barely run at that setting and I have it now set at 9.5 and it runs good. I was always a little uneasy as to why I had to set it so much higher, but figured every engine is different... The other day after driving home I popped the hood and was looking at things and happened to look at the Fuel Pressure Guage on my fuel rail. It was showing 20 PSI! I revved the motor and the fuel pressure did not seem to rise very much. I remember my on my old NA motor I would have 30-40 PSI. So that got me thinking.... if the Fuel Pressure has always been low, that would explain why I had to increase the injector pulse width so much so it would still get enough fuel. But on the other hand, maybe the fuel pressure is low BECAUSE I have the pulse width so long. I dont THINK that the fuel pump or fuel filter is causing this because those parts were working fine on the old NA motor before the Turbo motor was swapped in. Same goes for the FPR, too. I bought a new FPR about a year ago and used it on the old NA motor, and am still using it on this motor. Any Thoughts? It's early in the morning-- before I go to work I'm going to take the vacuum line off the FPR and see what that does to the fuel pressure. Quote Link to comment Share on other sites More sharing options...
Chaoticmass Posted August 15, 2006 Author Share Posted August 15, 2006 Also would like to clarify that the injectors are set for alternating and not simultanious, so the value entered in the box for REQ_FUEL is not halved (where 12 entered would be halved to make 6). Quote Link to comment Share on other sites More sharing options...
mobythevan Posted August 15, 2006 Share Posted August 15, 2006 maybe the fuel pressure is low BECAUSE I have the pulse width so long. Check over your fuel system and fix the pressure problem so that it is up to spec according the engine manual(30-40psi, i don't remember exactly off hand). Just because you bought new parts does not mean they are good parts. Check the voltage at the fuel pump, make sure it is not low voltage because of small wires or bad grounds/connections. If you still have the old FPR swap it back in and see if the pressure changes. If the FPR is working correctly the pressure will rise in the rail when you give it throttle. The longer pulse width will not lower the fuel pressure in the fuel rail. Quote Link to comment Share on other sites More sharing options...
Chaoticmass Posted August 15, 2006 Author Share Posted August 15, 2006 Okay, good to know. FYI, I took the vacuum line off the FPR and the PSI at idle went to 40 PSI. Does this suggest the pump is working right? Quote Link to comment Share on other sites More sharing options...
mobythevan Posted August 15, 2006 Share Posted August 15, 2006 You will have to look up the spec, but that sounds correct. Then when you put the vacuum back on the manual should also tell you approximately what pressure to expect(20psi sounds low, but look it up??). When you rev the engine it should fluctuate between the two. Quote Link to comment Share on other sites More sharing options...
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