Fuel pressre drops to near zero

[mquinn66]

My fuel pressure is 9 cold then falls to near zero when it gets hot. Tank is new, new 3/8 fuel line, new carter m6903 pump and 3/8 line with filter to carb. The line from the pump to carb is routed up between alternator and water pump and on to top of intake manifold. I only run non ethanol gas. Any wisdom from my Mopar brothers and sisters would be appreciated.

 

[ESOXER]

Fuel pressure drops when motor hot.

 

[mopar 3 B]

Vapor lock.

 

[khryslerkid]

Fuel pressure drops when motor hot.

Was there a conclusion on this thread?

 

[mquinn66]

Was there a conclusion on this thread?

Not that i can tell. Engine temp is 185ish. Shouldnt be vapor locking

 

[khryslerkid]

Does it act like its running out of gas?

 

[mopar 3 B]

Not that i can tell. Engine temp is 185ish. Shouldnt be vapor locking

Don't confuse internal engine temperature with under hood temperature. You must also consider the distance fuel lines are from the exhaust. I doubt if you are going to find 185* anywhere close to the exhaust.

 

[mquinn66]

Does it act like its running out of gas?

It runs fine around town and in the neighborhood 45 mph max. I havent taken it out on any roads for heavy load or high rpm test.

 

[khryslerkid]

I know mine looses some pressure after it's up to operating temp. Not 9lbs though. Could try another guage if you have one just to rule that out. If it has a lot of miles on it the pump might be showing some weakness. Lots of problems with aftermarket pushrods also.

Here's a thread on too much pressure on 6903s and problems with pushrods.
Mechanical Fuel Pump 101

 

[beanhead]

It runs fine around town and in the neighborhood 45 mph max. I havent taken it out on any roads for heavy load or high rpm test.

Well then it could be as simple as a faulty gauge...I'd say more troubleshooting is required here. I wouldn't start throwing internet darts at it just yet or you'll possibly do nothing but cost yourself a bunch of time and money. Get it out, get it hot, and hammer on it. Work the problem methodically to rule out any possible causes, one at a time.

 

[mquinn66]

I know mine looses some pressure after it's up to operating temp. Not 9lbs though. Could try another guage if you have one just to rule that out. If it has a lot of miles on it the pump might be showing some weakness. Lots of problems with aftermarket pushrods also.

Here's a thread on too much pressure on 6903s and problems with pushrods.
Mechanical Fuel Pump 101

Pump is new but hear mixed reviews on quality of newer pumps. Pushrod was measured and is good. I will try a different guage asap. Thanks

 

[RemCharger]

Some guages have a little pin to pull out.
Found that out breaking in a buddy's motor.
Whew.
It just kept going down

 

[mquinn66]

Maybe gauge is ok just changes with heat? I will go beat on it a little and see if its starved for fuel at high rpm when its hot.

 

[Richard Cranium]

Does the engine run ok when the gauge shows zero? If so, I would think that the gauge is the issue.

 

[Dan64]

Even a properly working gauge can lose 3 pounds when hot, best gauge to get is a Aeromotive #15632 with the equilizer valve on top. That valve will reset the gauge back to a nuetral reading after the fluid inside gets hot.

 

[mquinn66]

Does the engine run ok when the gauge shows zero? If so, I would think that the gauge is the issue.

It was starving the 750 Edelbrock but i just put a 600 back on and will have to see if it starves .

 

[mquinn66]

Update: I was able to road test today. Warmed car up to the point the gauge had dropped to near zero and took out on 55 mph road. Ran it through the gears a few times up to 5500 rpm and no starvation issues with the 600 cfm carter.
So i have concluded that the gauge reading is off due to heat in the engine bay. The 750 Edelbrock i was running had starvation issue or maybe just needs a rebuild? Or jet/ rod change? The car runs alot better with the 600 that was rebuilt last year. Onto other issues. Thank you all for your input.