z-ya Posted August 19, 2002 Share Posted August 19, 2002 I have a weird problem. When it's hot out, and the engine compartment get's really hot from idling, or from a 20 minute session on the track, my idle fuel pressure can drop as much as 25psi. It has only happened a couple times. I'm running an adjustable Malpassi regulator. Typically what happens is I'll stop somewhere and shut off the engine. When I start it back up after it has been sitting, it will run like crap because the fuel pressure has dropped. If I adjust it it's fine until the engine cools off. Then I need to re adjust it because it is too high the next time I start it. Anyone have this happen? Pete Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted August 19, 2002 Share Posted August 19, 2002 This sounds like a similar problem with manual boost controllers. The fuel pressure is regulated with a spring on a diaphragm, and when the spring gets hot it loses tension, dropping pressure (or in my case, boost rose!). Sounds like a different pressure regulator may be needed - I've never noticed this problem with a factory regulator... Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 19, 2002 Share Posted August 19, 2002 I don't have it either with the Bosch asjustable one I got from JWT. Of course I got to plumb it over by the return line, so that is in its favor. Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted August 19, 2002 Share Posted August 19, 2002 You could also be getting fuel with a lower boiling point. Are you running racing fuel or avgas? I have that problem early in the spring or in the winter months if there is an abnormally hot day. The winter fuel here is formulated to light off easier for better cold starts but is prone to vapor lock and percolation in hot temps. The changeover to summer fuel seems to be in mid to late May judging by the way my car acts. After the engine is warm and shut off the fuel boils in the lines and the air in the bubbles lowers the fuel pressure untill the engine runs for a minute or so. Sound familiar? Quote Link to comment Share on other sites More sharing options...
R0N Posted August 20, 2002 Share Posted August 20, 2002 I'm not sure if I'm having that problem. Haven't drove the car enough. I do know when I fill up the tank my fuel pressure goes up 1 psi, I also have a malpassi fpr. Come to think of it I may have the same problem as you Pete. It does seem different everytime I start it. I either have to lean it out or richen it with the SDS lean / rich knob. I'm starting to think it's the fpr. Hey Pete, it's been long time but I'm the one who bought your carb turbo setup a couple of years ago. Well I never put it on but instead when with a full FI setup. Quote Link to comment Share on other sites More sharing options...
z-ya Posted August 20, 2002 Author Share Posted August 20, 2002 Hi Ron, You made the right decision going with EFI and a programmable computer. I have my FPR mounted on the passenger side firewall, which is one of the cooler areas under the hood. It may be that the fuel is getting too hot in the fuel rail, which is causing the fuel pressure to drop. I'm running a nonwebbed manifold, but I have the turbo heat sheild installed. It does seem to get much hotter around the fuel rail with this manifold. I did not have this problem last year with the turbo intake manifold. But I have changed a lot of other things since last summmer (injectors, TB, downpipe, etc). I'm leaning towards the fuel getting too hot in the manifold. Ron, what manifold are you running? Pete Quote Link to comment Share on other sites More sharing options...
R0N Posted August 21, 2002 Share Posted August 21, 2002 Unfortunately I using the stock l28et manifold. I do notice my steel braded is no longer steel looking - looks like dull braded line. With my fuel line looking like that,one would think the fuel is getting to hot. Quote Link to comment Share on other sites More sharing options...
turbobluestreak Posted November 1, 2002 Share Posted November 1, 2002 Correct me if I'm wrong but if you run a z31 ecu and have the fuel temp sensro working shouldn't teh z31 ecu compensate for the extra fuel heat?? Sleeper what do you think? tbs Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted November 1, 2002 Share Posted November 1, 2002 Originally posted by turbobluestreak:Correct me if I'm wrong but if you run a z31 ecu and have the fuel temp sensro working shouldn't teh z31 ecu compensate for the extra fuel heat?? Sleeper what do you think? tbs I'm fairly sure you cannot compensate for a fuel pressure increase or decrease with the fuel temp sensor. The issue here I think is the pressure regulator itself is being affected by temperature, not mixture temperature differences that can be compensated wuth fuel temperature information. Quote Link to comment Share on other sites More sharing options...
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