CPLSeraphim

New Fuel Pump did not change a thing. still zero PSI at fuel rail when off, in the On position without running, and whenever it gets to running, ~16 psi. I will look into vacuum leaks and MAP sensor. Are there any common places for vacuum leaks to occur that would cause this?


Also, I read about bad seals at the fuel pump. I can't see my mechanic missing up a seal, let alone 2, you know?


Also, After replacing the computer, is there anything I should do? or will it relearn itself? It was flashed to the VIN, but changed nothing. Guess the computer wasn't bad (at least not yet) from the flood...

dave1123

From the info you just gave us, I think you still have a fuel delivery problem, not an ECM issue. You should have at least 35 psi fuel pressure running and it should hold at least SOME pressure overnight.
It can only be leaking thru the injectors or thru the filter/pressure regulator back to tank or the pump's check valve.

CPLSeraphim

New injectors, and 2 separate fuel pumps. Like stated earlier in this thread (I think) We didn't have any issues, outside of water in the gas before causing the occasional poor idleing until it died. It depended on what angle, and if it was getting more gas than water.


When we pulled the fuel tank, and installed new fuel tank, new pump, new filter, and put it back together, it hasn't been running right. 16-18 PSI while running isn't enough to even move much.


Is it possible in any way, that the fuel filter could even be installed the wrong way, restricting flow?


I just cannot understand how replacing everything with new parts could cause it not to work. I also do not have the jeep where I am to look at it. My mechanic works part time outside of his job, so this is getting annoying. Next time I can get over there, I will try reading the codes again.


Basically, I need more fuel for it to run. This is the last thing needed before it goes on the road. everything else checks out, just needs to do that running thing. Getting it this far has been a chore, and has cost far more than buying a running jeep, granted, when this one works, It should work for a long time since its all new.

dave1123

The pressure regulator is in the filter. There are 3 fitting on it, one is pump input, one is supply to the fuel rail, and one is overpressure return to tank. It's entirely possible the regulator in the filter is leaking. I doubt it's installed incorrectly because the fittings are pretty obvious. Just for giggles, try another one.

CPLSeraphim

ok, So I cannot check codes for a while since the mechanic guy is out for the weekend, and the key is locked up.


I have read a few things after CJJ mentioned MAP sensor, which sounds plausible, except there hasn't been any mention of what would cause 16 PSI at the rail. Like I said, 2 brand new fuel pumps, new set of injectors, new fuel filter. (2nd new fuel filter as well).


If the problem is not the fuel pump, fuel filter, or injectors, where can that leave the issue? Can the relay be messed up or something? I don't get how I would get partial PSI, but that's what is happening. I will see what happens when I unplug the MAP for ****s and giggles, but can issues be in the fuel line and fuel rail?


Again, the issue I have in thinking the problem is in line has to do with the fact that it ran fine before swapping the fuel tank and stuff over. Is there a chance that in doing so, a ground may have broke or something causing the fuel pump to work enough to give 16 PSI?
0-psi off
0-psI in the on position not running
16-18 PSI when we get it running and we get it to idle.


I appreciate the help, and hope to figure this out. Thanks again for your input.

dave1123

I don't get it. That pump should be putting out over 100 psi without a regulator on it and a high volume of fuel. Could it be possible it's sucking air in the tank? I'm assuming the intake screen is clean, right? Even with a restriction in the line, you should get pressure, just minimum flow.

You are right. though. 16 psi isn't enough to supply the injectors for anything above an idle. You need high pressure to atomize the fuel in a fine spray, not just dribble in.

I think your whole problem is in the fuel system. Just where is the bugger.

CPLSeraphim

I know. Whats more confusing is that it was working fine, then we dropped the fuel tank and pump. Since then it hasn't been running right, pain to start and all, and I finally got a fuel pressure guage and discovered the issue. Prior to the change, it was drivable. I figured the issue that made me change it was because of water in the tank that clogged up the old fuel pump, because it started to run like crap, but we thought we got most of the water out. we didn't, so I swapped tanks, and cleaned the new one out really good. I just have absolutely no idea where to even look for an issue. I mean, 2 pump, 2 filters, and 2 sets of injectors. Can you hook and air hose to the fuel rail and disconnect the filter and blow air backwards to see if crap comes out? And do these have anything like a charcoal canister like my old XJ had?


I wih I had my jeep on me so I could look at it more, but this is driving me nuts. I have a month before I will be gone for 3 weeks, and I need this thing running so my wife and kids have a running vehicle, and I can't believe how much of a pain its being.


Also, via electrical, the pump would work on an all or nothing basis, right? so it would either have enough power to run or not too run, but not pump less then it should? I'm no electrician, if that question is really stupid.

dave1123

No, it's not a stupid question. If the voltage was reduced, it would run slower, but it would still build up pressure. It may not supply the volume while running slower, causing reduced pressure, but it still should hold pressure before startup.

Just for giggles, try loosening the tank cap and see if you get more pressure. It may be your tank vents are plugged. There is a carbon canister, but it's a long square box mounted on the driver's inner fender well. There is a purge solenoid just behind the windshield washer tank filler.

If that doesn't do it, the only thing I can suggest is an after market fuel pump mounted in the line before the filter, as in Summit Racing. That might be a problem because I think the filter snaps directly to the pump output.

LAREDO99

Mine's in the shop, 99 WJ, and this thread is intriguing..ANY GOOD NEWS?
I'm 200 iles from home..here's the deal..mine has had a skip, slightly at idle and here and there at hwy speeds.. changed, plugs, new TSP, coil pack, newer PCM(423AE) old one was 423AD..new one is NOT new or Reman either..no codes but check engine light is on(2months) no national part stores' scanners get any codes,.mechanic has had it all day..ruling things out, but nothing yet..ROUGH IDLE, rough acceleration, cutting out when I let off the gas..HELP??
THANKS GANG!! Chaz
p.s. Fuel pressure good, CPS good...again, no codes

CPLSeraphim

I apologize, Laredo, I am new to grand Cherokee headaches, as I was a wrangler guy before...


As for the issue, I was discussing with a couple of the people who have been around since I got this jeep 2+ years ago and going over some things. Turns out that I forgot the jeep stopped running fine shortly before I got it towed o replace the fuel pump and stuff. We are currently assuming that the line is clogged, hence no PSI when on the ON position, and when the pump is running, only getting 16-18 psi because that is all clog will allow.


I am going to disconnect pump fuel line, and check pressure coming out of pump, then at fuel filter, then after disconnecting both ends (Fuel filter and fuel rail, blow air to see if we get any crap out of it. If we do, keep blowing for a while, if not, run new fuel line. After this, I will be retesting electronics, but since the mechanic saw the nasty stuff in the tank, I am hopeful. again. lol.

dave1123

Ya know, at one point I thought of telling you to disconnect the fuel line at the rail and run the pump to check flow, but I though better about it because high pressure fuel spray is nothing to mess around with. Your method will work better anyhow.

CPLSeraphim

Yeah, but I also would have thought that a mechanic changing the fuel pump and filter and gas tank do to massive water would have blown out the lines. lol.


I am hoping to find out today if that is indeed the issue... probably just run a hole bypass line for a quick and easy.

CPLSeraphim

All right, so I got a couple things figured out today.


1st: We disconnected all the fuel lines and blew air out. between the pump and filter, we got some rust chunks out. that was good.


2nd: disconnected fuel pump from fuel lines, and turned key on to prime lines. With finger over outlet, got enough pressure to make it spray (similar to a hose with your thumb to make it spray instead of pour, except the pressure made it squirt instead of it just not having enough pressure to force past my finger.) did the same after fuel filter, and again at the end of the fuel line, going to the rail. This all seemed good, although unable to use a guage because, well, nothing else is threaded.


3rd: Read codes. Only code coming up is P1495 LDP Solenoid. Ironically enough, we looked at that vacuum, and I manually blew out the line, and it started surging. seeming like it was working. After this, it is much easier to start. See below for current starting issue.


After all this, I drove it a little, although not on the road, but it has enough power to spin gravel and to make it up a pretty steep grade from the driveway to the yard. I was afraid of messing the guys yard up.


The remaining issues are as follows.


1st: Guage still only reads 18 psi, however, I find it hard to believe since it drive, and no pressure changes when running it up to 3000 RPMs. Going to chack guage in the AM.


2: Still has a slight miss or backfire. Hard to tell, I don't notice it but occasionally.


3: to start the jeep, I have to turn key like 3 times to the on position, then off, then on, in order for it to fire up. Mech says it should just start up, but it sounds like my blazer, I am thinking the vehicle is 13 years old, but the issue has to do with almost having to triple prime the lines to get it to go.


My major concerns are the miss and the starting. I am thinking make replace the fuel rail, just in case its clogged up in there? After blowing all the lines, and the mech did spray air in fuel rail inlet while I held open bleeder. Sounds a lot better now. just need to check pressure guage and post finding.


UPDATE: Checked fuel pressure guage. It is working perfectly on my blazer, so I am still getting like 16-18 psi on the rail. How is it driving at that PSI? however, I guess I need to check the voltage at the pump. Also going to throw in a new fuel rail for ****s n' giggles because, why not? pretty much got a new jeep if we can get it running.

CPLSeraphim

Alright, Here is where I sit currently.


I checked my buddies fuel pressure. He's got a 2004 Jeep Wrangler In line 6. Same motor, same set-up, more or less. 40 PSI on the on position, 52 running. a lot different than my 0 on the on position, and 16 running.


I am currently looking online for a scrader valve since none of the auto stores carry them. Pretty much going to start at the pump and see what I have coming out. If I am unable to find a valve, I am going to hook fuel hose to the filter, and run it all the way to my fuel rail, and see if a clamp will hold for testing purposes. This will be my last check with the fuel lines. After that and volt check, I am guessing I will have to take it to a dealership.


I would really like to see if anyone has any new ideas. No matter what, I wil be posting the end result in case someone else finds themselves in this spot. Probably rename thread as well, for problem specific. Wish me luck.


Is there any chance that, running air through lines blowing good could be because it is air, and that fuel, being more viscous then air, could be getting caught up?


Also, Where would I check for the return line? is it possible it is stuck open, like the older style with a regulator on the return line? How would I check this. I no nothing of vacuum lines, so if you could explain it in laymans terms, that would be great.
I figure if the return line is clogged you have high pressure, so perhaps the return line is never blocked, giving low pressure? But I have no idea how this works in a vehicle without a pressure regulator on the rail.

dave1123

The pressure regulator/relief valve is in the filter. The return line comes off the filter and returns excess fuel to the tank. As I've said before, with the pump discharge dead-headed without the regulator, it should be developing about 100 psi or better. That's enough to pop the plastic lines or blow the connectors loose, UNLESS it's restricted internally from doing that. From the looks of the pump, it's probably a vane pump. I'm going back to my hydraulic experience for this, but if it's a new pump, it should be developing sufficent pressure.