Fuel Pressure Guage Tip

[Argess]

A fuel pressure guage can be a handy item to have installed. I happen to have a fuel distribution sytem which came with a guage....sort of a "Y" type affair for feeding two carbs.

Went for a test drive the other day and when I got back the fuel pressure was reading a little under 5.5. Usually reads 8.5 starting from 1.5 with no pressure (so I figure about 7 psi normal). I took a rag and wet it with cold water and wrapped the guage. After a few minutes, guage was reading almost 7 ...up from the 5.5 reading. Next, took a dry rag and put it over the guage....spread out so engine heat would heat the guage again. After a few minutes, guage had dropped to almost 6 psi.

Apparently, a cheapie guage that is sensitive enough to read from 0 to 15 is strongly affected by ambient temperature. I suspect most of these under-hood guages are the same, the slightly more expensive ones being oil-filled for damping, but the basic mechanism (bourden tube) remains the same.

So, before you go changing fuel filters, fuel pumps, fuel line hoses, cleaning gas tank, etc, re-check your pressure with a proper test guage that isn't permanently installed.

Oh......small tip on Fuel Pumps.......inlet vacuum should be a min of 6 inches Hg according to Ford. On my Carter pump, I actually measured 17 in Hg. Just an easy test vs a volume test where you measure the quantity of fuel pumped out in 30 seconds or so.....at least a pint in 30 seconds is a fair test.

[cdnus]

That is a common problem when using a oil filled gauge under the hood of a Cobra.
You are better off with a good quality non-filled gauge. It will give accurate readings under all temp conditions. (Don't ask--Been there done that.)

Craig

[vector1]

interesting, i have an electric dash mounted gauge that does the same thing, starts at around 6.5, then will drop to 6 when everything has been running for awhile, electric fuel pump also, probably the regulator heating up which is in the engine compartment.