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Discussion Starter · #1 ·
Hello!

Does anyone know what would cause a high fuel pressure problem at the injector rail on a YJ 4.0?

My ACTech tells me that it could account for my failing aircare? I've replaced the fuel regulator, and still it runs at 45-50psi, but it is supposed to run at 30?

While performance on my rig has never been better - I cann't pass air care worth a damn. And my AirCare readings are all over the place, sometimes passing, sometimes failing MISERABLY, and I've replaced the Cat and the O2 sensor, as well as the thermostat. No difference....

Axle.
 

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Superfly
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axle said:
Does anyone know what would cause a high fuel pressure problem at the injector rail on a YJ 4.0?

My ACTech tells me that it could account for my failing aircare? I've replaced the fuel regulator, and still it runs at 45-50psi, but it is supposed to run at 30?
Maybe the return line is plugged?

I'm not sure how that would increase your emissions, though. I mean, the 4.0L uses a closed-loop feedback system right? So the O2 sensor would tell the computer that it's burning too much fuel and the injectors would shorten their duration, right? (I'm not anywhere near being an EFI expert so this is more of a question than anything else)

...lars



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Discussion Starter · #3 ·
I think you may be right. I spent most of last night tracing my lines, and I couldn't see anything plugged. I traced the lines right back to the gas tank, and gas flows quite nicely - all over myself I may add :) BTW - allways FULLY depressurize your fuel rail before you start working on fuel lines. It's amazing how much will spill out even with just a tiny bit of back pressure. Mind you, it could of have been the heat, as I was working in the sun.

I didn't drop the tank, so I couldn't see if it was plugged or not internally, but I did notice that the bottom of my tank is crushed. Not much, maybe an inch in hieght, but all over the place from rock hits.

I'm going to drop the tank this weekend, and pull the pump assembly out, and see if any damage was done to it - it may be plugged there. The tank is polyuraphane (?spelling?), with a steel skid plate keeping it from harm. If the return line is steel, and the tank is crushed excessively, I could see how the plastic could plug the return line - if it's a hard line, pointing straight down. If it is - Bad Chrysler engineers - bad! :) If that is the case, time to replace with a flex line, or a rubber hose.


The fuel rail pressure thing. The way my tech explained it, and he did say he wasn't a YJ or Jeep expert is this. The computer on the truck does not actually measure the fuel pressure. It knows when it's too low, and it knows when it's too high, but it doesn't know by how much. But again, I'm guessing - it may not know at all, as you'd think an engine warning light would come on.

If it ends up that this is the case - a fuel pressure gage will be my next upgrade. It would also help to see how much fuel one really has left before it runs out.

The computer does check with the O2 sensor to make sure not too much fuel is going in, but, it regulates it, under the assumption that it's running at 30psi, not 45 - so it's adjustments are off, and it's trying to "guess" how long to open the injectors for, as it doesn't know the presure it's using - just that it's wrong.

That is where the totally erractic readings come in from. One day at AC, I recorded readings that where all roughtly 6X that of what they should of have been - but that also includes NOx, which means the car is running lean? Well, that sort of makes sense, as the fuel injectors would try to lean back the fuel, after it senses that it's too rich. Then, it senses it too lean, so it bursts in a longer duration. OK. But again, it calculated for 30psi, not 45, hense, at the next reading, it too rich (high CO), then back again.

This may explain why every single time I go to AC, my readings are all over the place. Up to this point, I've been EXTREMELY upset at AirCare, most AC techs tell you too...

Replace the Cat - Ok thats anywhere from $80 (Lordco eco), or $800 (OEM, as recommended by AC) - and lets not forget labour, I don't have a welder.

Replace the O2 - Thats not that expensive, but it's still about $100

Replace everything else (plugs, wires, caps, rotors, fuel filters, etc) that usually runns around +$100, depending on what you replace it with. I do this first of course :)

Now, I'd be really pissed off, at myself that is, if it ended up being that it should of cost me nothing, but to drop the tank, and hammer out the skid plate becuase some tech at Jeep never though the gas tank would ever be hit by a rock. This, considering how many parts I've had to upgrade - I could see.

But again, this is all just theory, and I've never taken apart a gas tank, nor did the tech that I spoke to, so it's all just guess work. But it seems logical to a small degree.

Does anyone know how the fuel return systems work once it gets to the tank? Or is there something I missed?

Axle.
 

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The fuel return line drains directly into the tank - there's nothing complicated there.

BUT, the end of the return line is very close to the bottom of the tank, so it's possible that that dent you mentioned may be blocking the line outlet.

I'd suggest dropping the tank, then putting the sender/pump assembly into a jar (or something) of gas and running it. At least this test will only cost you your time... You might want to consider cutting an access panel into the tub floor, so you can get to the sender/pump assembly without dropping the tank next time.

Lars' comment regarding the pressure affecting your emissions makes sense to me, btw. Chances are this isn't why you're having Aircare trouble.

Chris
 

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Basic Baboon
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Lars and Chris are right about the pressure not affecting emissions on an EFI. If the system can't adjust for it, it'll shut down. Carbureted engines do fall victims to running rich if the pressure is too high, but that's a different critter.

Most catalytic converters need to get some air pumped into 'em to work. Not sure on Chryslers, but the Fords I had were notorious for the air injection pump failing.

You may also want to check out your injectors; they might be dirty or clogged. You mentioned that your emissions keep changing around; that's really weird. Do you always put the same gas in?

Also, what transmission do you have? I had a lot of emission problems on my Bronco (which was running great) when a vacuum modulator in the transmission went bad, and ATF was seeping into the engine.


Seems really odd to me that an EFI engine would fail, let alone by a lot.
 

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Discussion Starter · #6 ·
I'm sorry, I had to laugh when you said same gas :)

Up until recently, I've tired everything. From Reg, to Premium to Mohawk (seems to work the best). I even ran in there once running pure Meth. Still failed Co, but my Nox! Was like at 40 or something... Won't try that again. The AC techs were also very curious to know what I was trying to pull .... hey, I was desperate and frusterated. :)

So it does feed down to the very bottom. That is @#[email protected]@@!!!! stupid. I could see why it would get plugged. Thinking about it this morning, I think the best solution is going to be to shorten the return line, and drill a hole through it just in case it gets squished again. Although I'm guessing, it won't do much for foaming, or noise. Crap, will think of something once I open it up I guess.

The fuel pressure thing. Again, I guess it does go both ways, the computer should adjust for that. Yet again, what you said also makes sense. I also called up a performance shop, and they tell me that it is a common trick for Honda's, and other MPI injected engines to raise thier pressure for more HP. But, I've also been warned that on older cars (Mine has nearly >220K on it), the injectors, while they should last pretty much the life of the car, may problems closing/opening at higher pressures. For example, it may not close every time or it may have problems opening when operating far outside the normal operating range. IE for a 30 psi system, 35 is OK, 40 is on the limit, 45-50 is too much. I'm running ~45psi +/- 1-2psi.

I'm going to take my tank apart this week, and take some pictures of what the fuel return system looks like, and measure the pressure again. I have a brand new regulator in it, so it should drop down to 30psi straight away. I'll get it AC'd afterwards, and post up a reply. Also the Skid - if this does fix the AC problems - I don't think it will, I'll let everyone know.

BTW - the air pump thing? If you do have a pre 1998? (check to see if you have 2 O2 sensors, not one), if you have problems passing AC - but just marginally, I've been advised to disconnect 1 or 2 (for balance) injectors at the rail, and try again. I havn't done it yet, and I'm guessing it would run like crap, but it is supposed to clean up your AC results, as you are now pumping clean air into the CAT. You will still fail if you have the new OEM2, or whatever it's called system that was introduced after 1998? I'm not certain the year. But again, this may be more BS. I've never heard of anyone trying that yet.

Axle.
 

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Discussion Starter · #7 ·
Actually, you mentioned another thing.

The tranny question. My truck used to ALWAYS pass when it was just idle tested. Since the put me on the treadmil, I've been failed ever since. And all over the place to boot.

Another theory is this. My truck's factory curb wieght is 1300Kg. I went down the scales, and my curb weight is now 1850Kg. It came stock with 27" tires and 3.55 geers. I've now bumped that up to 35" tires with 4.56 gears. It came with a D35 in the back running 80/90, now it runs a C-F9 with lockers and a 140W. Not to mention the noise I make at the AC center - sounds like a small plane landing - the MT tires must also cause the readings to be higher because sound=energy=fuel consumption=polution.

I asked to be classified into a different catagory, Level 9 Heavy Duty Truck - but I cann't, as I cann't adjust my GVWR (3700Kg+). I cann't adjust my GVWR because it's a class 1 vehicle (passanger, not LT). I've talked to the Burnaby AC boys (they have a research center there), and I told them about the CVW, and they said, don't let the tread mill operations know about it, as it will make your readings worse, as they have to adjust "UP" the resistence of the treadmills. Get your GVWR adjusted.

I need to reclass my vehicle first. To do that, I'll need to rip out the rear seat, seatbelts, etc. and put up a seperator between the front seat and the rear (now a box). Oh ya, did I mention that I'd need to get it government inspected, and underwritten? Although this could of been the ICBC agents BS to keep me from milking AirCare.

Anyone every try to increase the GVWR on a Jeep yet? Technically, it's GVWR far exceeds that of the stock vehicle, but how do I convince ICBC that?

axle.

ps - crap... keep missing the point. Oh ya... I wonder how much having someone who has never driven my vehicle, sure as hell never a modified one with locks (that alone adds slack to the drivetrain and could possible effect the way a tech drives it), can effect the AC readings. Forget what you do to the car, it's now up to the guy that can barely shift gears at your AC centre?

ax.
 

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Try borrowing someones street tires for AC. Turn your idle up to the limit. Maybe take your rig to a shop with a good 4 gas. I know a guy who can get just about anything to pass. Is there not the option of spending X amount of dollars to pass for this year and worry about it next year.
 

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Discussion Starter · #9 ·
Very true, and sadly, that is the path I choose (cash limit). I can only spend so much money and time driving around on permits, and temperary insurance. But dang it, I'd really like to know what the problem is, so that I don't have to do this every year, and that other's don't have to go through the same BS year after year. Argh! Frusterating.

Axle.

Hmm... 185s running at 65 psi?... hmmm.... :) Never tried that...
 

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Your fuel pressure is way too high and you need to address this problem first. It can hurt your injectors, but it will hurt your O2 and the cat. A SEFI motor like this should make 80 PSI deadhead pressure at least. I would suggest that is is a regulator related problem first, or maybe a restricted return line.
First: (with the running at idle) pull the vacuum line at the pressure regulator and put you thumb over the hose and check for vacuum, you should have a good vacuum signal at idle (roughly17-21inches, if you have a gauge).
If you do not have a good vacuum signal there's your problem, maybe the line is leaking or blocked. Remove the vacuum line from the manifold end as well, and check for vacuum at the manifold:
if yes, blow through the tube to see it is blocked
if no, clean out the passage.

At this point you should have a good signal to the reg and a new reg on the rail. You meant new as in new, not new as in new to you (used) right.

Now shut the Jeep down and relieve the fuel pressure. Unplug the return line from th fuel rail (its the smaller of the two steel line going into the rail (off the top of my head I believe it's the rear line)) anyway send some compressed air down the line (toward the tank) and your buddy that is standing beside the open gas tank filler neck should tell you that he hears the air coming out into the tank. If he hears no air sounds in the tank you definatly have blockage, if he hears some sounds, maybe you just dislodged whatever crap was in there(cross fingers now).
Hook up the fuel pressure gauge.
Reconnect the return line to the rail.
Start the motor up and watch the gauge.

If it's still too high, I would (this part could get dangerous) relieve the pressure again and disconnect the return line again and with the help of a extender hose and a jerry can make my own temporary return line (like a 10 second test temporary) and watch the gauge to see if it returns to normal. If yes you are now going to get all dirty and sweaty and cut up, swearing at the tank as you remove it for inspection. Always save this step for last, especially on a YJ.

Good luck, let us know how you make out...
 

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When you do get the pressure back to normal take it for a GOOD drive before you go through AC again, to try and clean out your cat and O2.
 

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Discussion Starter · #13 ·
Aye, not yet... went to Merritt to go fishing... discovered a lot of drunken cow girls instead... Some kind of Country Music festival is going on... Driving my rig has never been so much FUN!!! :) I'll be working on it later this week - but, I did try the return line idea, and the pressure did drop. Everything is pointing at the tank right now.

Thank you very much for everyone's help! Axle.
 
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