Fuel Pressure Gauge for Renix 4.0

Guys,

I have a 88 XJ and wanted to test my fuel pressure. My buddy picked up a pressure gauge at Autozone and on the back it says it will only work on a "S" VIN 4.0, not the "M" VIN 4.0.

The M is the Renix 4.0, the S is the HO 4.0

I see in the MPI manual to use special tool J-34730-1 fuel pressure gauge. I installed the BMW check valve in the fuel line today and no improvement in starting. I am thinking I have a bad fuel pressure regulator but want to see how fast the fuel pressure bleeds off.

Just wonder what you guys with the 87-90 XJ used to test fuel pressure.

if you are concerned about fuel pressure after shutoff, just hook a pressure gauge to the fuel rail, cycle the key until you have pressure. see how long it takes to drop off. it should only drop 5 psi in about 30 minutes.(i think that is the specs). and after it drops all of the way to 0 see how long it actually takes to achieve running pressure while cranking. it should only take about 3 to 5 seconds. if it takes signifcantly longer, the check valve is bad. a new pump will improve this, but remember, the early fuel injacted xj's always took longer. that was one of the main complaints of the jeep, even when new.

Yes, I want to test my fuel pressure. I am asking "brand of tool" to use since the OEM brand does not fit the fitting on my fuel rail.

any parts storeor maybe even sears should have something, it is a pretty common fitting on the fuel rail. it is also the size of the a/c low pressure side of a r12 system.

Thanks, I'll go check this week for a R-12 fitting. The Jeep manual talks about using a R-12 fitting for the fuel pump test to verify 1 liter in 60 seconds.

I may also call Miller Special tool and see how much they want for the J-xxx gauge.

I have a Sun Pro fuel pressure gage that works on my 87xj.

Whenever I checked my fuel pressure I did it with a cold engine and used a rubber air hose with a cheap low psi pressure guage on the end. I unscrewed the valve from the fuel rail fitting and used hose clamps to keep it all together. Not the "proper" tool but it reads pressure fine. Getting fuel in a pressure guage meant for air will eventually kill it but considering many people have junk like that lying around it is a cheap alternative. I'm not saying it's ideal.....just an option.

Ron, Is your tools PN CP7818? I see sears sells that one but looking at the PDF of the manual on line shows it will fit 4.0 engines from 87-96 4.0 with VIN code S.

My buddies tool said it was just for S, not M... I'd appreciate if you could veirfy the PN.

I scrounged a fitting from an R-12 can tap and just used a 100 psia gauge from the hardware store. The fitting had a rubber check ball that I had to remove.

Martin, mine is a Sun Pro "Fuel Pressure Tester Kit" and says "CP7818" in the upper right hand corner of the backing card/instruction manual. It works on 86xj, my 87xj, my 01xj and on my daughters 91 dodge dynasty. I had to by an adapter to make it work on 89 Accord.