theastronaut Posted January 26, 2015 Report Share Posted January 26, 2015 Car is an '87 TSi, all stock except for a drop-in K&N, gutted downpipe cat, and full 2.5" exhaust. It ran great for the first ~5000 miles of ownership, but it's fought me ever since. Changed a bunch of parts and had it running great for a while but it's started acting up again recently. Symptoms: It idles fine but has low power/hesitation starting off from red lights, then surges back to normal for a second, then hesitates again. It's definitely noticeable but not so bad that it's undriveable. It never bucks or loses power, just doesn't pull smoothly like it should at low rpm and low throttle. From about 2500 up at part throttle it runs normally, plenty of power. Over 5 pounds of boost it stutters and won't pull, and will knock/ping if I stay in the throttle for more than a couple seconds. It hesitates when its both cold and warmed up. It's getting 18.3 mpg, mixed highway/city. I have checked the fuel pressure and it's high, gauge starts at 50 and climbs with boost as it should. I've had three different fuel pressure regulators and they're all the same; starts at 50 and climbs w/boost. I've blown out the return line with compressed air and have verified that the line was moving air through (bubbling in the tank). No error lights except for O2 sensor, but I have a gutted downpipe cat and full 2.5" exhaust. I've read that having a less restrictive exhaust won't let the stock unheated O2 sensor warm up so the code might be normal? Not sure if thats correct information though. The O2 code goes away after 10-12 miles of driving at 45-55 mph. I'm thinking it's a fuel issue? The back bumper is getting covered in a black film like its running rich and 18 mpg seems low, it used to get 20 when it was running better. I don't know why running rich would make it knock over 5 pounds of boost though. So maybe timing and fuel? Parts and work done since last April. Injectors replaces with used OEM pieces. Both passed ohm test.New injector clips (soldered, not crimped).Throttle body cleaned/resealed.TPS upgraded to Mazda unit.Plugs/wires/cap/rotor.Advance mechanism cleaned and lubricated.Vac advance replaced.Coolant temp sensor replaced.Vacuum hoses replaced as needed.Coil replaced/upgraded.New underhood fuel filter.Inspected in-tank sock filter (sock and inside of tank are spotless).Cone filter removed. Blew out fuel return line.Timing verified to be correct. Link to comment Share on other sites More sharing options...
scott87star Posted January 26, 2015 Report Share Posted January 26, 2015 50 psi fuel pressure is WAY over the factory spec of 35-38 psi at idle. I think you've answered the question. Link to comment Share on other sites More sharing options...
theastronaut Posted January 26, 2015 Author Report Share Posted January 26, 2015 So how do I lower it? I've tried three different fpr's, all are high. The return line doesn't seem to be clogged. Link to comment Share on other sites More sharing options...
scott87star Posted January 26, 2015 Report Share Posted January 26, 2015 Where do you have the reference hose connected on the throttle body? Link to comment Share on other sites More sharing options...
mikec Posted January 27, 2015 Report Share Posted January 27, 2015 Any chance you are mis-reading the fuel pressure gauge - wrong units for example (i.e. it reads in something other than PSI), absolute versus relative pressure, etc? Factory fuel pump or aftermarket? An incorrect aftermarket fuel pump could be stuffing too much fuel to the throttle body - more than the FPR and fuel return hose can bleed off resulting in high fuel pressure. A blockage in the t-body where the FPR attaches can also lead to high pressure - a blockage between the FPR itself and the fuel return hose... though I'd expect your fuel pressure to be constant in this case - independent of boost pressure. If the fuel return piping is 100% blocked then the FPR is rendered totally useless so you'd always measure raw fuel pump output pressure. Follow the fuel return hose from the throttle body down... does it plug into anything in the engine bay? It should not - it should just turn into a hardline going to the fuel tank. Any chance a previous owner installed a second fuel pressure regulator like a BCFPR or RRFPR? Got a gas-safe bottle or something you can hold near the throttle body for a test? A two-gallon gas can for lawnmowers works great. Disconnect the fuel return line from the t-body and run a new hose from the t-body to your catch bottle. Wrap a rag around the hose where it enters the catch bottle to prevent fuel splashing out. Use the fuel pump test connector to run the fuel pump and see if your fuel pressure is closer to stock levels... if so, the fuel return hose is partially blocked. If no fuel pours out into the catch bottle... you've confirmed a blockage in the t-body or FPR. mike c. Link to comment Share on other sites More sharing options...
theastronaut Posted January 28, 2015 Author Report Share Posted January 28, 2015 Here is where the fpr is connected to the throttle body. http://i557.photobucket.com/albums/ss14/theastronaut/Random/Starquest/B9EF9D2D-3441-46C3-8762-112D09269AAC.jpg It has an Airtex fuel pump, has been in the car since I bought it last April. No problems with it in 13-14k miles so far. I did check the fuel pressure gauge against the air pressure gauge on our air compressor but I can try another gauge too. I will bypass the original return line and see of the pressure drops any, I did get air to go through the line and into the tank but it could still be restricted somewhat. I haven't seen another aftermarket for added in anywhere. Just sucks that I finally had it running really strong with no issues and then started this, it's been slowly getting worse. Link to comment Share on other sites More sharing options...
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