Losing fuel pressure, thoughts?

[Sobek]

Hey everyone,

Slow times in the XJ world for me, lots of dramas in life putting all the fun jobs on hold... Sister in law totaled her car on christmas, mum in and out of hospital, the fun never ends! However I picked up (SCORED) a set of General Grabber AT2's 235/75/15 practically brand new for $100, so I'm itching to go to the tyre shop and get those on

Anyway, I've been having a rough start issue that's gradually got worse. At first it would fire up fine but I'd just get a come-and-go rough bog down idle until it was suitably warmed up. I had occasional check engine lights throwing codes for throttle position sensor out of range, and random injector function / failure codes. I replaced the TPS (with a quality part, not chinese trash), and that seems to have sorted that code, but I kept having injector codes. I inspected everything closely, and found a rat chewed pigtail on one that was damn near corroded through, so I figured screw it, let's just overhaul alllll of that. These injectors are 26 years old and have never been touched in the slighest.

Fast forward to last week, the set of 0280155703 injectors I ordered arriveds (as per rainman's suggestion in his awesome thread here : http://www.ausjeepoffroad.com/forum/...ad.php?t=92236 )along with a new set of EV1 connectors including wiring pigtails. I replaced the injectors and wired in all of the new connectors, heat shrink wrapped and looking good. First start was good, next few runs were alright too, still the occasional boggy cold start, but now I'm seeing extended cranking and generally sluggish performance. So I thought, gotta be the injectors... Hooked up my fuel pressure gauge, and I'm seeing 40psi running, 30psi when I yank off the fuel pressure regular vacuum line - seems good to me. But, when I shut the car off, the pressure immediately starts plummeting... within 20 seconds it's at 10psi, and will hit zero within another 20 seconds or so. So my first thought was maybe a leaking new injector. I pulled the fuel rail out with the injectors still in, hooked up the tester gauge, and shorted the fuel pump relay to build pressure. It went up to 40psi again, and plummeted back to zero, without a single drop from any of the injectors...

So I did some digging around and a lot of people talk about some return check valve on the fuel pump? I replaced my fuel pump last year (Bosch) and I don't recall seeing anything of the sort within the assembly? What about my fuel pressure regulator, could that be the culprit here? I'm not familiar with how Chrysler has plumbed all this up, but does the FPR itself act like a check valve to maintain pressure in the fuel rail and prevent it from feeding down the return line when the motor is off? At this point, the FPR is basically the only thing I HAVEN'T replaced, mostly because damn they're expensive

Within the last year or two I've put in a new fuel pump and strainer, new fuel filter and all new soft lines under the car and in the engine bay, new cam and crank sensors, o2 sensor, map sensor, TPS, cleaned the ICV / TB, replaced vacuum lines, readjusted the TV cable... I've been busy! But this fuel pressure issue is one I need your help working out.

Sorry, yep, I do rant a lot. But what do you think, fuel pressure regulator, or some mystery check valve on the fuel pump that I somehow missed. Or... both?

Also, and it hasn't done this for a while, but once in a blue moon the XJ will suddenly go like a bloody rocket, spinning the wheels going uphill... it's enough to push me right back in my seat and make me audibly go "Bloody hell!". So maybe it's just been struggling for fuel pressure for the longest time now? Whenever I get that boggy rough idle, the exhaust also smells... boaty. Lean, I suppose? Guess that's a clue too. Appreciate the input

[LuluBelle]

fuel pressure regulator more than likely on the 96 and 99 it sits on top of the fuel pump in the tank

[Sobek]

That's what I figured, just wanted to be sure I'm not missing something else potentially very obvious. I've got a new FPR coming from Rockauto in a few days, along with a one way check valve that I may install on the feed line just after the fuel filter, if need be.

Cheers

[Sobek]

It was indeed the fuel pressure regulator I put a check valve in line between the tank and filter and that did nothing, new FPR arrived today and that did the trick. Do we know what fuel pressure is supposed to be exactly for a 95? I've read around previously and people's numbers are all over the place...

I'm seeing just under 50psi at idle, no change with the FPR vacuum line disconnected, and it holds about 45psi once I shut the motor off. I see people saying 31psi, 41psi, 39, 51, 90210, who bloody knows?! I've also seen people make note that 1995 in particular might be different, which makes sense because every bloody thing is different if you have a 95

Just want to make sure before I start blowing hoses or something silly. Thanks again

*edit* I just checked and I ordered the 39psi PR210 from Standard Motor Products. That's... quite a lot less than what I'm seeing, yikes. I wonder if my cheap pressure gauge is just reading it wrong, I clearly can't have a blockage down the line if it was losing pressure almost instantly on the old regulator.

[awg]

My understanding is the '95 runs at 39PSI...BUT the '96 runs at 49PSI, and use the same pressure regulator...except (without I think) the vacuum connected

(the '96 is within the tank in an assembly that is very hard to get, but the pre-update pump and reg are used)

btw where did u get the part and how much was it ?

[Sobek]

That's what I had read mostly too. I may have to do some more assessing of my setup. Turns out, it's holding pressure now and for a VERY long time... after 2 hours I still saw almost 30psi. But I don't think it's doing it consistently. I took it out to do my horse feed run this afternoon and every time I parked it, it was HARD to get it started, cranking cranking cranking and a bunch of sputtering before finally turning over, and even then it was rough and lumpy for a bit. If I had to guess, it feels like it's simultaneously starved of fuel pressure, then suddenly is rich, it's bizarre. Exhaust smells really... smelly... once it fires up too. Not rich, and not exactly lean, just this stinky in between kind of smell. I have no cat converter so it's not that, it's just not fueling right.

I pulled my rail again, pressurized it up to over 40psi by shorting the pump, and it was still holding pressure with no obvious injector leaks (pressure seems to be higher with the motor running than by just shorting the pump manually). But I kept hearing a faint 'ticking' kind of sound, and when I listened real close, it's the number 5 injector, If I touch the pintle with my finger it'll wet it with fuel, but it's not actively pissing any fuel out. It's almost as if the injector is letting air INTO the rail? judging by the sound it makes and the fact it's not actively spilling any fuel out, but I don't know if that's even possible. After a while, as the pressure drops, that little sound stops, so I'll start with that. I'll dig out my old stock injectors tomorrow and replace just that one with one of them, see if it makes any difference.

The regulator I got from Rockauto, it was $66.59. The only more expensive one was a Delphi, but I kept hearing that people had troubles with Delphi units I'm pretty sure in the past. So I went with the Standard Motor Products to be safe. Got it from Rockauto because I also got some parts for the BMW from there, and their warehouse grouped shipping is so damn good sometimes, it was all at my door for under $100 which is awesome.

[alexbrown64]

On my 95, I am running the 4 port 777 injectors with a Delphi FP10046 49psi fpr.
Rather than point you to my XJ post on my set up and test for my 95, I thought I would just copy it in below.......

I wanted to check the health of my fuel injection system. I have upgraded my injectors from single pintle to multi pintle rebuilt units. I also upgraded the fuel pressure regulator (FPR) to a higher pressure unit. I got a lot of original info from this thread... http://www.ausjeepoffroad.com/forum/...ad.php?t=92236

Here is the procedure to check the system pressure while the Jeep is running....



My values will be different, as i have the upgraded system. Mine should look like the update Jeeps. Values should be about 41 PSI at idle with the vac hose on and 49 PSI with the vac hose off. With the vac hose off, its the equivalent of running the car at WOT as at WOT, vacuum is almost zero.

So, i needed a gauge to test my pressures. Ebay has a bunch of them, and i chose one that had a heap of adaptors and only cost $30 delivered.



Very easy to do the test. Locate the fuel rail and there is a valve. Screw in the adaptor, start the Jeep and then read the pressure. First pressure with vac hose on the FPR and second with the hose disconnected to replicate WOT (Wide Open Throttle).

My results came back surprisingly good. Pressure was spot on 41 PSI at idle with vac hose on.



Pressure at idle with vac hose off, to represent WOT was around 49 PSI, which is what the FSM for post 1995 Jeeps recommend.



Hope that helps,
Cheers,