I have a 2 1/16" ford racing autometer gauge.

when i first put one on my car, readings were silky smooth and awesome.
after a while i noticed the needle would shake, like 4-5 PSI of where it should be.

i was confused so i pulled the gauge off my car, and tested it on my brothers mustang. hooked it all up to his car, and started his car. it was SMOOTH on his car. so i figured that i had an issue with my car. so i was in the process of putting the gauge back on my car and i DROPPED the thing and broke it lol. so i had to buy a new FP gauge, i bought the same brand, the autometer ford racing one.

got it in, installed it on my car, started the car, the readings were silky smooth for a few days, then the readings began to shake again.
i also tried a new FPR and that didnt help anything at all. still shook.

i had small stubby rail mount gauge laying around. i hooked it up to the rail. so the fuel doenst have to travel through a long line.
the FP reading seem very stable and smooth with the little gauge right on the rail. which leads me to believe its just a gauge issue.

i took my little 1/16 NPT - -4AN adapter and restricted the fuel flow by tig welding up the pipe end of the fitting with some phosphur bronze rod, sanding it flat and drilling a #40 drill bit hole (around .030 IIRC) so the fuel flow is restricted through the tiny hole. to help smooth things out.

that seemed to help slightly but not totally cure it, i though the fitting could be leaking, so i took it back out and used some teflon tape on the pipe threads and i am pretty sure there isnt a leak at the fitting.

the car runs fine, drive alright and i dont seemed to be having a problem with that, just the needle shakes. sometimes it is fairly calm and then sometimes it will go nuts and start shaking like 10 psi back and forth lightning quick.

FWIW the gauge doesnt have the liquid filled face and the gauge is mounted on the backside of my 4" cowl hood, perhaps vibration may be doing this??

i'm still baffled as to if this is just a gauge related issue or an actual problem with the fuel system. when i first put the gauge on it was smooth and never jumped at all. now it always have a shake. the only recent fuel system change was a 255lph pump a few months ago, i doubt that would cause anything.

any ideas?

 

I had a pinched return line that made my guage do the same. It was intermittant too.

 

stupid but a clogged fuel filter?? or possibly a junk pump, i have seen that before- just because its new doesnt mean it cant be bad.. if the gauge worked fine in your bros car then i would assume there is some sort of prob in your car???

 

just an opinion, but how big of a distance is the line from rail to gauge and how secure is the mount on the hood? If its running great and just a daily driver, leave the gauge off until it starts messing up on you, just dont break this one.......

 

there is 6 ft of line going from the rail to the gauge. quite a long line.

and i am pretty sure its a gauge issue now. ive been tuning on the car some lately and as good as the car runs and as accurate i can get the AFRs i am not really convinced there is a problem with the car until something happens to tell me otherwise.

i have gotten the AFRs at WOT within .1 or so of the target AFR or so which is real close and probably wouldnt be possible is the FP was truely erratic like the gauge sometime shows.