Fuel pressure (gauge) question...

Looks like I've got to get my serious diagnostic mojo going, given nobody else seems to be able to figure out what's wrong with it.

So, starting with the basics - is it normal that a fuel pressure gauge 'flickers' on a running engine? It might be a cheap gauge after all. What I'm seeing is that once the engine is started up the fuel pressure gauge rapidly osscilates around the expected pressure - say, +/- 3 psi around 42psi. Never had a car with a fuel pressure gauge, hence the question if that's expected or if I should expect the (reasonably expensive) FPR to smooth out the pressure fluctuation caused by the injectors opening and closing?

Your gauge likley has no damping in it. That one reason to get the fliud filled units. At idle i'd except some bounce but at speed (under load) i would expect the FPR to be better.

Zombie thread resurrection time, but it starts on the question I want answered: I need a fuel pressure tester, and I only want to buy this once. Not that I'm looking to spend a zillion dollars, but I don't want to spend $50 and have a piece of crap I'm going to be unhappy (and worse, uncertain) every time I use. Recommendations?

The E28 seems a little down on power, it has some stumbles, and it bangs a little on overrun... I'm wondering whether it's a little lean everywhere. Whether the cause is FPR or pump, the first question is whether I'm even right about the pressure. (Yep, there are other things to check, but that's another several cans of worms; I've done the first 80% of vacuum leak stuff and am ordering injector O-rings, and soon I'll test the AFM's values as the door moves)

I know nobody asked but in my opinion as a tech and a boosted car owner, if you're not going to be diagnosing multiple vehicles i would just get a nice small liquid-filled gauge and find a way to adapt it permanently to your fuel rail or fuel line, and if it's a boosted car i would get an in-cab fuel pressure gauge anyway.

I have a couple of each and a regular test gauge. The test gauge is from Harbor Freight. I've owned several but they all get damaged or broken sooner or later and the one i have currently is from Harbor Freight. Good ones are kind of a lot of money for what they really are. If i 'upgrade' from here i'll probably piece something together off Amazon. I'm already using fittings from an old set of AC gauges just because they're nicer to use than what comes with most fuel pressure gauges.

My guess is something in the fuel system is causing the gauge fluctuations. On my V6 SHO engine there's a fuel dampener on the fuel rail. Not sure if yours has one. Can you block off the return line to the tank and see if the pressure steadies?

In reply to Vigo:

Thanks! I'm not boosted (though will eventually have a boosted car to deal with, and suspect I should do as you say on that one) and am totally looking for a tool I can have handy for many vehicles over time. This is not the first or last time I'll want to do a fuel-pressure-related diagnostic.

Nice to know the HF units are at least viable.

I've seen and heard of more of those fuel rail mounted gauges breaking and leaking due to vibration than I care to remember and I'd prefer to not have to worry about yet another source of fuel leaks in the engine bay.

Most fuel systems use similar fuel system test ports that the fuel pressure gauge setup I bought from Sears works just fine. The newer direct injection cars and the older CIS cars tend to require their own specialty testing sets.