Fuel Pressure Test

northplainsdrifter

I think my fuel pump is not putting out enough fuel. I put on a Edelbrock 1406 with off road seats and under a long full throttle pull it sputs & sputters. I also had it run out of fuel idling and have to choke it to get fuel back in the bowl. So my question is how do you test the fuel pressure? I have a vaccum guage but just haven't figured it out yet and I just know someone here could explain it. It has the mechanical pump.

tufcj

The pump only produces pressure between the pump and carb. You can add something like this inline: http://www.jegs.com/i/Mr.+Gasket/720/1564/10002/-1 Pressure at the carb should be in the 5-7 PSI range.

The suction side, between the tank and pump really can't be reliably measured since the pump only moves liquid, not air (which is what causes vapor lock). If you're trying to fix a vapor lock problem, the best solution would be a low pressure (> 5PSI) "pusher" pump mounted near the tank. Fuel under pressure is much less prone to vapor lock that fuel under vacuum.

I ran a Carter 6906 on my CJ with good results, but finally just eliminated the mechanical pump for an electric mounted at the tank. I went to an in-tank pump when I went to EFI.

Bob
tufcj

northplainsdrifter

I know it's not a vapor lock problem. I didn't have this problem until I put the Edelbrock on and changed to the off road floats. I was thinking that there might not be enough pressure with the spring loaded floats to keep the bowl full. :-| I have a different feul pump I might throw on and see it that helps, or just put my old Holley back on, I know that will fix it!

Mudrat

Well the 6906 (stock replacement) is rated @9 psi. Do you know what is actually coming out of your pump? I have my FPR set at 6.5 PSI to feed the 1406 with off road seats, rods & jets. So far works pretty well.

ironman_gq

raise your floats up a little. Mine would do the same thing going down the highway, I raised the floats slightly and the problem went away.

Mudrat

ironman_gq wrote
raise your floats up a little. Mine would do the same thing going down the highway, I raised the floats slightly and the problem went away.

Can you define "a little"?
Was it an RCH? A twich in the wrist? 20 inch pounds on a calibrated finger? .030 or .050?? Give it up bro, we're all friends here :?

northplainsdrifter

When I hit the sand this weekend it would still stumble under full throttle :smile: , then I raised the floats AGAIN. And this time it finally quit sputtering and wound up nicely! All the way to 6000 RPM! Woo Hoo, was able to catch some air off the top of the dunes! I raised the floats till they were about perpendicular to the top plate. I have yet to go crawlin on hills to see if it will keep running under extreme angles, but for now, under WOT I'm flying! =D> That Edelbrock has been a pain in ASS to get dialed in...

rollen dean montoya

Mudrat wrote
ironman_gq wrote
raise your floats up a little. Mine would do the same thing going down the highway, I raised the floats slightly and the problem went away.

Can you define "a little"?
Was it an RCH? A twich in the wrist? 20 inch pounds on a calibrated finger? .030 or .050?? Give it up bro, we're all friends here :?

damn rat. getting technical? sounds like ironman adjusted the floats about 1/32" now you got a measurement bro :t: