Guest powerman Posted September 18, 2007 Share Posted September 18, 2007 Vehicle info: Mainly stock 77 280 with a 78 L28 in it. Cold air intake, MSA large throttle body, headers and exhaust. Problem: It has been sometime since I did the engine swap and I have remembered that the donor car that I got my engine out of had a lot of fuel pressure gauges on it. (after fuel filter and a sender to read it from the dash) This led me to believe that it may of been having a problem.(duh) I put a pressure gauge in after the fuel filter to check my pressure. It reads 30 psi a idle. I checked the factory manual and its should be 36 psi I believe. I have replaced the fuel filter and the pressure regulator to narrow it down. Now I'm thinking it could be clogged lines, fuel damper, or a failing pump. What do you guys think? Quote Link to comment Share on other sites More sharing options...
Clifton Posted September 18, 2007 Share Posted September 18, 2007 If you have a restriction, clog, or failing fuel pump, that 30 psi at idle will drop a huge amount when the revs come up with some load. Disconnect the vac line to it and see if it steady as the revs increase or better if you can see it while driving at WOT. If it stays pretty much at what it is at idle( assuming the vac line is off), it's the regulator. Quote Link to comment Share on other sites More sharing options...
Pyro Posted September 18, 2007 Share Posted September 18, 2007 The pressure depends on the amount of vacuum. High vacuum causes low pressure due to a vacuum sensitive FPR My car idles at 26 psi and drops to 22 during deceleration. 36 to 38 psi at WOT (zero vacuum). You can unplug the vacuum hose from the fuel pressure regulator to simulate WOT. Quote Link to comment Share on other sites More sharing options...
Guest powerman Posted September 18, 2007 Share Posted September 18, 2007 Ok I looked at the gauge while it was under a load and the pressure went up. This should happen since it stays "36" psi over the manifold pressure (I think). I took the vac hose off and it went to 36-38 psi. My car idles at 26 psi and drops to 22 during deceleration. 36 to 38 psi at WOT (zero vacuum). You can unplug the vacuum hose from the fuel pressure regulator to simulate WOT. When it was unplugged (zero vacuum) it went to 36-38. So this is normal then? As long as it is correct when under a load is important? Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted September 19, 2007 Administrators Share Posted September 19, 2007 When it was unplugged (zero vacuum) it went to 36-38. So this is normal then? Yes. As long as it is correct when under a load is important? Yes... sort of... based on your description, your fuel pressure is pretty high with the vacuum line attached. This *implies* that your engine is not making much vacuum. At this point, I'd recommend buying a cheap vacuum gauge and letting us know what your idle vacuum reads. Quote Link to comment Share on other sites More sharing options...
Guest powerman Posted September 19, 2007 Share Posted September 19, 2007 Vacuum pressure is 60 kpa or 8.70 psi at idle Quote Link to comment Share on other sites More sharing options...
rossman Posted December 7, 2007 Share Posted December 7, 2007 That sounds low. Mine is ~15 psi and I know I have at least two small vacuum leaks. Quote Link to comment Share on other sites More sharing options...
ktm Posted December 8, 2007 Share Posted December 8, 2007 Rossman, vacuum is measured typically in inches of mercury or in. Hg. A good, tight engine with a stock cam usually pulls around 17 in. Hg which is around 8.3 psi. Your 15 psi is most likely 15 in. Hg. Quote Link to comment Share on other sites More sharing options...
rossman Posted December 8, 2007 Share Posted December 8, 2007 Ya know, I knew that didn't sound right when I typed it. Thanks for the correction. Oh and this is a fairly old thread. Hopefully powerman has figured it out by now Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted December 8, 2007 Share Posted December 8, 2007 Oh and this is a fairly old thread. Actually it's not that old. What is amusing are threads from 2002 being answered... What would really help us if the OP would respond to suggestions given to their questions. If they worked or not or what they did that fixed a problem. LARRY Quote Link to comment Share on other sites More sharing options...
Guest powerman Posted January 2, 2008 Share Posted January 2, 2008 What would really help us if the OP would respond to suggestions given to their questions. If they worked or not or what they did that fixed a problem. Sorry about that, I just got out of Navy boot camp and was sorting through my email (a huge pain may I add) and I saw that the thread had a reply. I didn't end up fixing anything. It runs and runs well, no missing or dramatic loss of power. The fuel pressure is normal when it is being driven. I robbed the pressure guage off of the old on and drove the car with it. I don't have time to mess around on it anymore so it will stay as it is untill something actually goes wrong. You know what they say; "If it ain't broke, don't fix it." then my personal favorite for the Z "If it ain't broke, fix it until it is." Quote Link to comment Share on other sites More sharing options...
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