Fuel...my new 4 letter word

I need some serious help. I have an 87 Cherokee Laredo, 4.0, inline 6, 4x4, fuel injected, standard tranny. I had leaky injectors, didn't have a bunch of money so I ordered used injectors on ebay. Put them in, it ran great for about 20 miles, and then I let it sit. I got back in it, and it was running like it was out of gas. It was low, but not that low. I put gas in it, and it didn't get any better. Very BLACK exhaust, running rough, oil went from pretty clean to BLACK in a matter of 10 days of running it this way (my daily driver). It dies when I stop, and doesn't want to idle after restart. I have power, just not as much. I can do 60-70 on the hwy, but as soon as I stop, it dies, but restarts easily with a puff of dark exhaust. Someone told me it might be a MAP sensor, or internal injector leaking. This is what is just killing me...I changed the oil, and the oil level is rising, and I think it's getting gas in the oil, and I don't know enough about this stupid thing to figure out why. Should I buy new injectors, or could it be the fuel pressure regulator? I'm pretty strapped for cash, and can't afford a mechanic, and would really appreciate anything you all might know about this situation. I have changed these injectors out myself several times, and am actualy pretty good at figuring this kinda stuff out, but this has me over a barrel. I've also ran injector cleaner through it, thinking it might have just been clogged, and it did nothing. Thanks for any help you may have for me!

Assuming everything is hooked up correctly, it could be your map sensor or fuel pressure regulator causing the engine to run rich like you said. Its a case of fuel infection. The new injectors sound most logical since installing them caused all the problems immediately. You could have bought ones that were just bad on ebay or have the wrong injectors as they are different depending on what year XJ or you could have injectors from a completely different engine.

The general consensus is that the five-o motorsport is the place to buy oem injectors. You could also get new seals and have the old ones cleaned professionally maybe that would solve the problem.

The RENIX (1987-1990 w/4.0) injectors are notorious for leaking - and you've already replaced those. I'm assuming you put new o-rings in as well?

Black smoke typically indicates an extreme "rich" condition (too much fuel,) and the particulates that make the smoke black (the unburned carbon) will clog up the oxygen sensor in fairly short order. So, try not to run it too much, or you're going to be changing the oxygen sensor as well. (and, while relatively cheap, you still can't use a "universal" part for it - the sensor you have works on a different principle.)

What injectors did you use, anyhow? You don't mention that - and if the delivery rate is significantly different, you could get a "rich" condition that the engine controller can't correct for. The original injectors were rated for 19#/hour at (I think) 29psi - if the delivery rate for your new injectors is larger by too much (say, over 22#/hour @ 29psi,) you're going to get an uncorrectable rich condition. Note that I mention delivery rate at a certain pressure - if your new injectors are rated at a different pressure, there is a formula to correct for that.

If you don't know (the seller didn't say,) then we can take the original application and see what we can find in the Archives for that. Most small block engine fuel injectors (Ford 302/351ci, Chevvy 305/350ci) run right around 19-21#/hour @ 29psi, but there was a small variation by years.

If someone near you has a fuel rail pressure gage with a GM fitting, it should work - and you can see if you need a new regulator. You really don't want to go "shotgunning" things in the fuel system and hope you stumble upon the problem blind - that gets expensive. With a fuel pressure gage, you can check pressure (reading it off of the gage) and delivery volume (using the bypass on the gage - time how long it takes to fill a known volume - a small fuel can, for instance) - this will check both the pump and the fuel pressure regulator. Since a test gage is usually cheaper than either of those parts (~$40, last I checked,) it's a handy thing to have anyhow.

Should you need to replace your pump, changing the regulator won't do anything. And the other way around.

The fuel system depends on all the parts working - but it takes a little troubleshooting to figure out which one isn't (and one part failing can present in a number of different ways, or as something else entirely - so it does take some investigating and some thinking to save money.) You were, however, correct in replacing the leaking injectors - that's a known problem on the 1987-1990 4.0, and replacement is the only fix for it.

I did ask the NW Chaper mod to merge your other posts into this one - double posting not only makes for separate threads (taking up server space,) but it makes it entirely possible to miss getting a good answer (you try thinking about two things at once...) and, often, the answer is a synthesis of what everyone has to say. So, don't be surprised - and please don't do it again. I'd hate for you to not get a useful answer because you're running two trains of thought...

However, if you're looking for someone local to have a specific tool, or to help you work on your rig - your local chaper is a place to ask for that sort of help. For general Tech stuff, hit the large boards (OEM for original equipment, Mod Tech for modifications considered or that are failing,) since you're more likely to get a useful answer there. Just some friendly advice.

Believe me, I do understand your frustration (I've got five XJ's myself, none newer than 1990!) and I can understand what it's like to deal with a problem when you don't know much - but that's why we have clubs like this. Just be patient tho - it's rare that you get a useful answer within 10 minutes, but it's fairly rare for you to not get a useful answer within 24 hours, either. If you want an answer quickly, chances are you're going to have to pay for it locally - which you don't seem to want to do. No problem - but it does take a little patience...

I bought my injectors for my 98 from five-o motor sports, they come with a guarantee and the price was 1/3 of the OEM ones...

Thanks for all the information. I don't know what the injectors are, the seller didn't say. Then only thing different on them then the old ones is the wire clip. The ones I bought had a easy disconnect wire connector, as mine have the kind that you have to hold out the plastic clips, and then disconnect. I guess now that I think about it, It caught my attention at the time, that this might be newer, but didn't give it any more thought. Yes I changed the o-rings, fuel supply connector, and o-ring in the fuel pressure regulator.

My local auto parts store, can get reconditioned injectors for $45 a piece with a guarantee. Have you heard any success stories with reconditioned injectors?

Back to my Jeep, my fuel pump was changed right before I got it last summer. I can here it whirl when I turn on my key, and every time I manually check fuel pressure at the rail, I have a significant amount of spray. I'm working on that fuel pressure gauge, my brother in law has one, but he's just really busy.

I really appreciate everything you have told me. If it's going to cost me anymore money it's going to have to wait a bit. I'm going to try to get that pressure gauge and I will check back to report my findings. Thanks for setting me straight on the postings, I'm kinda new on here, and just got desperate! Thanks again!!!