ed653

What is the purpose of the vacuum port on the regulator? I know that the mid 80s Jaguar V12 has a vacuum port that conencts through a temperature controlled valve to teh intake manifold. When the rail gets too hot, the valve shunts to atmospheric pressure, which cause a 14.7 PSA increase in rail pressure and reduces the tendancy for vapor pockets to for in the rail. But the ZX regulator connects directly to the manifold (or so I'm told) so I can figure out what it does. Increases fueling when the manifold pressure goes up obviously, but why? TIA Ed

I'm trying to help a friend with what seems to be fueling problems on his '79 280ZX. He lives in a different city, which limits what I can do. Here's a recent note from him: "I connected a vacuum meter between the intake manifold and the fuel pressure regulator and hooked a pressure gauge to the fuel rail and took the Z out for a drive. For about the first five minutes the vacuum gauge read normal and the fuel pressure would vary from about 30 to 36 lbs and the car ran quite well. About a mile down the road the vacuum gauge started acting erratic and the fuel pressure also varied around 28-30lbs seeming to respond to the changes in vacuum. A few minutes later the vacuum gauge read much lower than normal and the engine ran rough. I pulled the vacuum line off the regulator and plugged it and the vacuum reading went up to normal and the car ran fine. I started back home to place an order for a regulator (which I am quite sure is faulty) when suddenly the fuel rail pressure gauge dropped to about ten lbs and the car nearly stalled. I nursed it home and when I get a little more ambition will check the fuel filter, suction hose to the fuel pump and possibly the pump itself. " Is he on the right track? I happen to have a '76 Jaguar XJ-S V12 which I believes has a very similar Bosch EFI system. What I find strange is he says there is a vacuum port on the FPR and hooked DIRECTLY to manifold vacuum. Naturally, when he disconnects it the rail pressure goes up. I know later Jag V12s had vacuum ports on the FPRs, but in this case there is a temperature controlled valve that closes when rail temperature gets high, thus venting the FRP vacuum port to atmospheric pressure, and increasing the rail pressure by about 15 PSI. Maybe someone here can tell me how it's supposed to be on the 280 ZX. Please excuse the cross-listing. I'm not sure where this belongs. TIA Ed

I'm trying to help a friend with what seems to be fueling problems on his '79 280ZX. He lives in a different city, which limits what I can do. Here's a recent note from him: "I connected a vacuum meter between the intake manifold and the fuel pressure regulator and hooked a pressure gauge to the fuel rail and took the Z out for a drive. For about the first five minutes the vacuum gauge read normal and the fuel pressure would vary from about 30 to 36 lbs and the car ran quite well. About a mile down the road the vacuum gauge started acting erratic and the fuel pressure also varied around 28-30lbs seeming to respond to the changes in vacuum. A few minutes later the vacuum gauge read much lower than normal and the engine ran rough. I pulled the vacuum line off the regulator and plugged it and the vacuum reading went up to normal and the car ran fine. I started back home to place an order for a regulator (which I am quite sure is faulty) when suddenly the fuel rail pressure gauge dropped to about ten lbs and the car nearly stalled. I nursed it home and when I get a little more ambition will check the fuel filter, suction hose to the fuel pump and possibly the pump itself. " Is he on the right track? I happen to have a '76 Jaguar XJ-S V12 which I believes has a very similar Bosch EFI system. What I find strange is he says there is a vacuum port on the FPR and hooked DIRECTLY to manifold vacuum. Naturally, when he disconnects it the rail pressure goes up. I know later Jag V12s had vacuum ports on the FPRs, but in this case there is a temperature controlled valve that closes when rail temperature gets high, thus venting the FRP vacuum port to atmospheric pressure, and increasing the rail pressure by about 15 PSI. Maybe someone here can tell me how it's supposed to be on the 280 ZX. Please excuse the cross-listing. I'm not sure where this belongs. TIA Ed

I'm trying to help a friend with what seems to be fueling problems on his '79 280ZX. He lives in a different city, which limits what I can do. Here's a recent note from him: "I connected a vacuum meter between the intake manifold and the fuel pressure regulator and hooked a pressure gauge to the fuel rail and took the Z out for a drive. For about the first five minutes the vacuum gauge read normal and the fuel pressure would vary from about 30 to 36 lbs and the car ran quite well. About a mile down the road the vacuum gauge started acting erratic and the fuel pressure also varied around 28-30lbs seeming to respond to the changes in vacuum. A few minutes later the vacuum gauge read much lower than normal and the engine ran rough. I pulled the vacuum line off the regulator and plugged it and the vacuum reading went up to normal and the car ran fine. I started back home to place an order for a regulator (which I am quite sure is faulty) when suddenly the fuel rail pressure gauge dropped to about ten lbs and the car nearly stalled. I nursed it home and when I get a little more ambition will check the fuel filter, suction hose to the fuel pump and possibly the pump itself. " Is he on the right track? I happen to have a '76 Jaguar XJ-S V12 which I believes has a very similar Bosch EFI system. What I find strange is he says there is a vacuum port on the FPR and hooked DIRECTLY to manifold vacuum. Naturally, when he disconnects it the rail pressure goes up. I know later Jag V12s had vacuum ports on the FPRs, but in this case there is a temperature controlled valve that closes when rail temperature gets high, thus venting the FRP vacuum port to atmospheric pressure, and increasing the rail pressure by about 15 PSI. Maybe someone here can tell me how it's supposed to be on the 280 ZX. Please excuse the cross-listing. I'm not sure where this belongs. TIA Ed

I'm trying to help a friend with what seems to be fueling problems on his '79 280ZX. He lives in a different city, which limits what I can do. Here's a recent note from him: "I connected a vacuum meter between the intake manifold and the fuel pressure regulator and hooked a pressure gauge to the fuel rail and took the Z out for a drive. For about the first five minutes the vacuum gauge read normal and the fuel pressure would vary from about 30 to 36 lbs and the car ran quite well. About a mile down the road the vacuum gauge started acting erratic and the fuel pressure also varied around 28-30lbs seeming to respond to the changes in vacuum. A few minutes later the vacuum gauge read much lower than normal and the engine ran rough. I pulled the vacuum line off the regulator and plugged it and the vacuum reading went up to normal and the car ran fine. I started back home to place an order for a regulator (which I am quite sure is faulty) when suddenly the fuel rail pressure gauge dropped to about ten lbs and the car nearly stalled. I nursed it home and when I get a little more ambition will check the fuel filter, suction hose to the fuel pump and possibly the pump itself. " Is he on the right track? I happen to have a '76 Jaguar XJ-S V12 which I believes has a very similar Bosch EFI system. What I find strange is he says there is a vacuum port on the FPR and hooked DIRECTLY to manifold vacuum. Naturally, when he disconnects it the rail pressure goes up. I know later Jag V12s had vacuum ports on the FPRs, but in this case there is a temperature controlled valve that closes when rail temperature gets high, thus venting the FRP vacuum port to atmospheric pressure, and increasing the rail pressure by about 15 PSI. Maybe someone here can tell me how it's supposed to be on the 280 ZX. TIA Ed

I ran across this thread from several years ago while trying to help an uncle in Yuma with his recently acquired 79 280Z (18000 miles!). He has some rough running in hot weather. As I get into this I am seeing that the EFI seems to use the same Bosch components as my 1976 Jaguar XJ-S V12! The fuel pump you posted a photo of looks just like the one in my boot, for example. I agree that "classic vapor lock" as experienced in carburated cars is probably the wrong term, but I have suffered the same problems reported in the FI vapor lock threads in the Z-car forums. I think what happens is the combination of higher rail temperature plus drooping rail pressure due to leaky injectors or check valve DOES result in vapor formation. With the "race track" (i.e., closed circuit) rail such vapor pockest are slow to clear because there are other lower resistance paths the fuel can take. meanwhile, the injectors in that section of rail are not getting supplied. I eventually replaced the race track rails (2 were used on the early Jag 5.3L V12) with the U-shaped rail used on later models. Even on this rail, which is but one of the many things Jaguar did along the way to deal with this acknowledged problem, can still suffer vaporization related problems. One of the fixes was a thermally activated vacuum valve mounted on the rail which opens the vacuum feed to one of the fuel regulators, thus raising rail pressure whne the rail is hot. Ed in Placentia, CA