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renix fuel pressure not holding

2stix

2stix

NAXJA Forum User
Location
fallbrook Ca.
should the fuel pressure hold a little when shut down? (89 renix.) checking fuel pressure, and when i turn to ignition to on, fuel pump cycles and i read 39psi for a couple seconds, then drops to almost nothing. turn ignition to crank and pressure comes back and it starts. pressure holds at 29psi at idle. 39psi with vacuum line removed. shut down and pressure drops to zero almost immediately.
tracking down a low idle issue, and what i thought was rich condition. but spark plugs indicate almost a lean condition. sep. issue i know, just thought i would add why i am checking fuel pres.
is my regulator not working properly?
 
Sounds like everything is working fine to me. Pressure dropping to zero almost immediately sounds a bit weird. Regulator sounds like its working properly. If its not visibly leaking and pressure goes up 9-10 psi with vacuum line removed
 
ya i was thinking the regulator was supposed to hold it longer though. i know 29psi is on the low side too.
 
I am pretty sure the Renix regulator is also the check valve, it should hold a good 25 psi or so after shut down from my experience. Sounds like it is defective. Did you see any gas coming out the vacuum nipple on the regulator with engine running and vacuum line disconnected? If yes, then it is bad.

29 psi is OK, it is the minimum.
 
didnt see or even smell fuel at the vacuum line. vacuum is 15 at idle. all vacuum lines test good. fuel pressure drops to zero or close to it almost instantly after shut down, and after pump cycles for the first couple seconds before start up. turn the key to run, pump cycles, pressure to 39, pump stops cycling and pressure drops to zero, crank engine and pressure jumps right back up to 39, engine starts and pressure drops to 29.

if one or more injectors are not completely seating after shut down, would that also mean they are not ever closing and i would be getting excessive fuel in the cylinders through all cycles? this would/could be the running rich smell i seem to get at the tail pipe, but the spark plugs look more like an almost lean condition. the pressure drops quite quickly though. more than i would have thought some leaky injectors could do. but i will not discount it, and will check this out for sure. thanks for the tip.
 
i have heard they tend to leak externally. i see no fuel leaks from them. but internally can very well be the problem. i have seen that site with the injectors and may just get some now. from what i understand, their replacement ones are better than the factory ones even if i was to get new factory style. so i can see the extra expense being a good idea by getting better quality injectors. if nothing else, having the better injectors is just another plus.
 
2stix said:
i have heard they tend to leak externally. i see no fuel leaks from them. but internally can very well be the problem. i have seen that site with the injectors and may just get some now. from what i understand, their replacement ones are better than the factory ones even if i was to get new factory style. so i can see the extra expense being a good idea by getting better quality injectors. if nothing else, having the better injectors is just another plus.
Click to expand...

It's an easily justified expense.
 
I would inspect the injectors first. How long have you had the rig? Miles since you bought it? It might already have new injectors?

Cruiser? What about the fuel pump itself, internal pump check valve on the discharge side perhaps?

Might need a clamp and hose to clamp off the line between the pump and FP regulator to see which is leaking, if it is not the fuel injector(s). Or rig up (fab) a test rig with a test port to test for leaks on each part.

I would think the FPR could be tested at 30 psi by itself (completely disconnected from the JEEP!!!) with compressed air and a cheaply built air hose, clamps and test port rig?

Also, can't the fuel rail and injectors be leak tested first off the engine, as an assembly (making sure the metal clips are on each injector to avoid firing off injector missiles, LOL), with a bump test of the ignition switch off-on-off for 1-2 seconds?

If I recall correctly on Renix, the FPR is the check valve and the regulator that keeps the injectors under pressure. When pressure gets too high it is there to leak fuel back to fuel tank to avoid overpressure.
 
IIRC the rubber hose to the fuel rail near the fire wall is the supply right?
 
did a quick check and clamped the fuel return line. no change, still lost pressure. then tried the fuel delivery line. held pressure as soon as i put the clamp on. so it looks as if the check valve inside the fuel pump itself is not working. turned the key to on to let the pump cycle and build pressure, then quickly clamped the line as soon as it stopped building. it lost a few pounds quickly untill i got the clap on, then instantly stopped loosing pressure. it is not to say that the injectors are not leaking also, but i didnt see much if not any pressure drop once i clamped the fuel delivery line.
 
Interesting. I would look for an aftermarket inline check valve, before I messed with a fuel pump swap and gas tank....

But it could also be the hose from the fuel pump to the metal bulkhead fitting going bad, or coming loose!!!! Might want to check the hose in the tank first, I have read a number of posts where it went bad after many years.

These look a bit expensive:

http://www.jegs.com/p/JEGS-Performance-Products/JEGS-One-Way-Check-Valves/1273572/10002/-1

Nice diagnostic work!!!!!
 
the last test i will do will be to crimp the fuel delivery line just after the pump itself. this should tell me if it is the line outside the tank or inside. i will need a helper for this though so i am waiting for the wife to help with turning the key. unless of course she wants to crawl under the jeep and crimp the line, but i have a feeling she will not. fortunatly if it is the pump or line inside the tank, the 89 is easy to get to. i hear the newer jeeps have the pump ontop the tank instead of toward the rear and top edge. those i hear you need to drop the tank some or cut a hole in the bed/cargo area. i do have a very nice tank and pump from the 87 parts jeep that i may be able to scrap parts from if needed. by the way, the pump on the 89 was replaced with a napa one 2 or 3 years ago.

Monster Mopar- what exactly do you mean it happened to you and was undrivable? what happened, and what was the effect? symptoms? thanks.
 
so i crimped the line right at the tank and it held pressure. so this means the problem is inside the tank. next is to remove the pump and inspect/test the check valve, lines, ect. good thing there is only 1/4 tank of fuel.
 
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