Fuel pressure issue

[Dino]

I was playing around with the carb today and wanted to measure fuel pressure at idle.  I don't have what I need to install a pressure gauge and drive around with it.  I have the HF vacuum and fuel pressure gauge.

Not sure what to do I removed the fuel line on the vapor separator and stuck the gauge on.  I had my wife fire it up and keep her foot ready in case it wanted to stall.  I didn't think I''d have much time with just the fuel in the carb.

The needle on the gauge went haywire and bounced between 4 and 9 psi, in other words I still don't know what the pressure is.  I have a feeling that if I install the gauge between pump and carb and go for a drive, it'll still bounce around. 

Anyone have an idea why it's doing this?  Bad gauge, installed incorrectly, something else?

The pump is a Carter M4845.  I got it when I was doing a bunch of mods to the car and noticed the old pump looked pretty tired.  I shouldn't have done that because it didn't have the carb issues it has now.  I have a feeling pressure is too high for my TQ. 

Alternatively I could just buy a pressure regulator but where do you install it?  I run a TQ hard line to a short rubber section on the vapor separator.

Something like this may work:  www.summitracing.com/parts/qft-30-803/

[303 Mopar]

It may be a bad gauge, but I always do a fuel pressure check right by the carb.

[tan top]

I was playing around with the carb today and wanted to measure fuel pressure at idle.  I don't have what I need to install a pressure gauge and drive around with it.  I have the HF vacuum and fuel pressure gauge.

Not sure what to do I removed the fuel line on the vapor separator and stuck the gauge on.  I had my wife fire it up and keep her foot ready in case it wanted to stall.  I didn't think I''d have much time with just the fuel in the carb.

The needle on the gauge went haywire and bounced between 4 and 9 psi, in other words I still don't know what the pressure is.  I have a feeling that if I install the gauge between pump and carb and go for a drive, it'll still bounce around. 

Anyone have an idea why it's doing this?  Bad gauge, installed incorrectly, something else?

The pump is a Carter M4845.  I got it when I was doing a bunch of mods to the car and noticed the old pump looked pretty tired.  I shouldn't have done that because it didn't have the carb issues it has now.  I have a feeling pressure is too high for my TQ. 

Alternatively I could just buy a pressure regulator but where do you install it?  I run a TQ hard line to a short rubber section on the vapor separator.

Something like this may work:  www.summitracing.com/parts/qft-30-803/

pretty sure its because you have a vapor  return line  , the pressure bleeds off  ,  causing  eratic readings  , try  blocking the return line or by passing the vapor separator , just to take a pressure check ,
this is just a guess ,

mine does / done the same  , ( have a metered  return line to tank )    never jumped about before , when running just the feed line . 

[Dino]

Ahhh I didn't think about the return. Duh! 

Alright I'll get some fuel hose tomorrow so I can hook up the gauge and go for a drive with it taped to the windshield.  That way I can also stick the gauge close to the carb.   

I'll just bypass the separator to do this.   

Thanks fellas!   

[b5blue]

I'd think you want to start by reading exactly what the carb has been "seeing" all this time first, then bypass the vapor can for comparison. 

[Dino]

That's a good point, but how do I do this if the needle bounces?  Maybe just hook up the gauge close to the carb and give it a go?  It won't hurt I suppose.

[Dino]

I'm really not in the mood to spend a lot of time on this car, not now.  So is there a simple inline regulator that works well?  Anyone have any experience with them?  The hard line from separator to carb may have to go or maybe I can cut, flare and install a reg.  Not sure what the size of the hard line is, I believe it's 5/16".

Would it be a bad idea to run a rubber hose from separator to carb?

[b5blue]

  I do not have fuel pressure issues I know of but want to check readings while parts are new. So I'm in the same situation sort of.  I've extra holes in firewall not closed up yet and Test/Tune rig from vap. can to carb anyway so for me it's just a tee/hose/fitting to a real fuel pressure gauge under the dash. @ no more then 8lbs pressure max I'd think a trip to H-W store and you'd be in the same boat. 
 

[K9COP]

I just put an inline fuel pressure gauge on my car between the filter and the carb. The filter is behind the alternator. My gauge reads 5-6psi almost all the time....

FWIW...

K9

[69wannabe]

5 to 6 psi is perfect for a carb of any brand usually, I have seen a few holley's that don't run good unless they got 7 to 8 psi. That certain carter fuel pump may be rated a 8 1/2 psi and you may want to install a regulator. The best regulator for a carb that I found is made by holley and it's for carburetor's only. I had to put one on a 413 in a motor home cause the new fuel pump I put on it from the part's store was pushing 9 psi. The carter 6903 is what they call a street pump and has 6 psi pre-set and mancini racing still sell's them. I have used these pump's on several big block's with no problem's.

[Dino]

I forget what this pump is rated at but it seems that others are having high pressure issues with it as well.  So I could get the pump from Mancini or install the regulator.  I think I want to go with the regulator. 

Do you guys have pictures of how you installed them?  I'll post a pic of my setup tomorrow as I'm not sure where to put the regulator.  I just remembered I need a fuel filter as wel, I'm only running the vapor separator.

Thanks guys!

[K9COP]

OK, so here is how mine is set up at the moment. Ignore the vacuum hoses, but the fuel hose routing is valid:



My feed hose comes in along the chassis rail, and is insulated along the whole portion that's within the engine bay. It goes across to the stock type pump, and then out of the pump, up behind the alternator (to try and take the lowest temperature route) and along the top of the valve cover, via a clear filter then an inline pressure gauge. It may look a little thrown together, but I'm trying to resolve some rough running/cutting out issues myself..  

I think it is VITAL that we establish constant fuel pressure is being provided, and constant feed to the coil (I have an LED bulb on the dash fed off the coil +ve terminal) to try and establish if we are having a fuel, or an ignition issue...

I think my principal issue was a loose plug on my 'orange box' but by the time I'd discovered that, I'd done all the other stuff, such as insulating lines and a phenolic spacer on the carb....

Question for the OP, have you tried a static test to see if the situation arises at rest with the car running?

K9

[b5blue]

M4845 pump is 5lb pressure high volume pump, no need to regulate Dino. M4845 ran my 6 BBL fine for years with or without vap. can. installed.  6 BBL very picky about pressure with 3 carbs to feed. That type gauge is confused reading from air in line being compressed by pump pulse. I'd attach to return on can and burp air out of line to gauge by cranking over a bit. Then attach gauge for idle reading with no return working for a max reading, should be 5-6 max. pressure. If it is you'll be certain it can't be higher WITH vap. can. installed and can move onto other areas.

[Dino]

That sounds like a plan Neil.     I'll keep you posted.

[b5blue]

Rodger that.

[Dino]

I still didn't get to measuring pressure but while I was getting a fuel filter and some other goodies I saw a small regulator for $25 so I took a chance.  I set it to the max of 5.5 psi and problem solved, no more sputtering and flooding and the car runs way better.  I guess the pump was giving it more than what it should.  I'll still measure pressure without the regulator though, just out of curiosity...after I have the trans noise fixed.   

[b5blue]

Good news! 

[K9COP]

Any chance of a link to the regulator please?

K9

[Dino]

Mr. Gasket 9710   http://www.summitracing.com/parts/MRG-9710

It was $25 at Carquest.  Most reviews on other sites mention it leaks because the phillips screws can be loose, and they were right.  Half of mine were loose as well so before installing I tightened the screws and ran a tap through the ports to get the chrome out.  It doesn't leak and regulates pressure just fine.

This is only temporary as I want to use a hard line from pump to carb again so either I'm getting a different fuel pump or I'll be plumbing in another regulator.

[K9COP]

Thank you Sir....

K9