WannaBeCherokee

I just replaced all 6 of my fuel injectors on my 97 Cherokee. After I put it all back together (properly...I think), It ran pretty rough. I checked out some other stories of changing injectors, and it seems that's typical for it to run rough for the first few minutes or so. However, now I'm idling a bit low, and it's choppy. From idle, when I give it gas via foot pedal, it skips a bit before totally revving up. When I hit the throttle under the hood however, there is no lag. Also, around 2000 RPMs the whole thing shakes, but once I get past that it stops. New injectors are stock, and there are no visible leaks running or not. I tried resetting the computer by disconnecting the battery for a half hour, reconnecting, turning the lights on and off while the key was on (without running), and that didn't help much. What the hell did I do?!

Bustedback

How did it run before replacing the injectors? Why did you replace the injectors?

WannaBeCherokee

It ran good. I replaced the injectors because that was the top diagnosis for fuel getting into my oil.

DFlintstone

So before....the fuel pressure was dropping too fast after shutdown? It would miss a second upon starting hot, after sitting a bit?

Your description is a bit tough....opening the throttle plate with the hood open, it acts different then with the hood closed? I might check that somehow the hood isn't touching something. Also changing injectors it's easy to bump something like a vacuum line or maybe a connector for some wire.

The first time I did it I got a lower O ring boogered up on #6. Found that vacuum leak spraying starting fluid. (Upper O ring would leak fuel)

WannaBeCherokee

The hood had nothing to do with it. I hit the gas pedal with the hood open and it didn't respond as well as when I manually opened the throttle. That's also the second time I've heard about vacuum lines, so I'm going to check that out as well. Another note to add that I should've added before...When I replaced the injectors, I didn't remove the fuel line (for lack of a quick release tool), and I also input the injectors into the rail first, then the head. That may have been a wrong move.

"So before....the fuel pressure was dropping too fast after shutdown? It would miss a second upon starting hot, after sitting a bit?" - I never had that problem.

WannaBeCherokee

And sorry for the rough description...I'm still learning a lot about how engines and cars work. This Jeep has kinda been my crash test, so bear with me. Thank you in advance.

DFlintstone

Fuel pump pressurizes the rail to your pressure. After you turn it off it should hold pressure a bit. There are specs for what is normal for it to bleed down. It's slow though, like there is still respectable pressure in 20 minutes. If it doesn't hold, either the line itself, an injector, the regulator, or some have a check valve in the pump is letting the pressure drop.

I'm at a loss as to why pulling it open with your hand is different than using the throttle cable.

You could use a dish soap bottle with just water, or a hose turned down very low, to apply water to the area to where the bottom of the injector(s) goes into the head. Or listen for a hiss with a section of tube to your ear...or I just use little shots of starting fluid, to search for vacuum leaks. Water, or anything you spray from a can should not change the sound of the engine. If it does, of course you have a vacuum leak.

Btw, small amount of water is fine, done on purpose sometimes to remove carbon deposits and other reasons. (I'd run it after a bit so it doesn't rust something)...if it DID suck it in.

WannaBeCherokee

Perfect potential solutions. Thank you! I'll be testing some things out tomorrow and I'll be sure to update the progress.

DFlintstone

The pressure bleed down would have been a check before changing injectors....(if one or more leaked, the pressure would drop too fast

I'm clueless what your current issue might be. Honesty is the best policy, as we try to help through Email. (it's like trying to tie your shoes with chopsticks) I mean be pretty sure.....The throttle cable, basically attached to your foot, opens the throttle plate in the TB, normally done with your foot on the petal. Maybe have someone else press the petal while you watch the linkage to the TB? I don't get why there is a difference from when you do that by hand.

Often "special" fun comes up when there is more than one problem. Vacuum leaks are common with some line leaking or even on the wrong place. Cruiser gives us a great list of things, including making sure the sensors feeding info to your puter' are grounded well. That link is in my sig, if you hadn't seen it everywhere!

I'm better at 87-90 Jeeps. If you re-state your current symptoms clearly, hopefully someone better with the HO's will chime in.

DFlintstone

Had a thought. I couldn't find right off how much the plug gap increases every mile, but it does. Cleaning the cap/rotor and wires, and making sure the plug gap is .035 is "101" before chasing other problems.

WannaBeCherokee

I'm about to go in and change the plugs, so I'll clean it up good as well. Any special substance I should use to clean?

DFlintstone

I take the cap, rotor and wires right to the kitchen sink and clean with Dawn dish soap and a brush, like any other greasy pot. (then clean the sink!).

The rotor and cap are high temp plastic..anyway getting it all good and dry needs to happen. Time in the sun or a hair dryer...even a low (200* oven)...

Of course if anything looks funky buy new...depending on your budget. The 30 thousand volt secondary spark, that can jump 1/2 an inch isn't gonna care much if it's not spanking new. The game is to not give a path to get to ground without jumping the plug gap. You can't see a carbon track on a black cap. Even with others that can be tough to see.

Anyway that is stuff to do as maintenance. I recently had one I'd let go a bit and found .055 plug gaps...

OH! I just saw "changing" Check the gap of the new! Likely, but not always fine.

Do keep them in order and note the color of the porcilin. That tells allot.

Roler

A throttle cable with some slack in it could be one explanation, D...

WannaBeCherokee

Success!!!! I changed the plugs (checked the gap the night before), and the old plugs were all (except #1 which was spot on), anywhere from .045 - .050. After I changed the plugs, I took it for a nice long ride after filling the tank and after I went about five miles or so, I stopped at a Wawa, and it was perfect. Idling around 750 consistently, smooth, no drops or rises. I'm thinking there may have been an air pocket in the fuel line/rail from when I changed the injectors. That, or the system needed to adjust to the new injectors. The new plugs probably helped a bit too.

My only concern is the MPG has dropped a bit. It seems like I'm running through fuel a bit faster than before. I noticed a leak as well. Looks and smells like oil. I may have fudged something when changing the oil (perhaps the filter isn't tight enough), but aside from that, all is well. Still have to check the oil for gas odor though...

Again, thanks for all the help, I appreciate it immensely.

DFlintstone

Hey there Roler. Maybe if I hang upside down from a rafter like a bat, I'd be able to see clearly like you?

Cold, engine off you can do "key on" key off, (to pressurize the rail), a few times and look close at the fuel line connectors and the upper O ring seals on the injectors. A small leak on a hot engine with the fan running might be hard to spot. I'd use a really good light. You don't normally smell an oil leak. A fuel leak after messing with the rail and changing injectors could happen.

Sliding a piece of cardboard under the Jeep parked hot, overnight should tell you if you have an oil leak, if you can't see it. If you have a few drops, join the club! It takes me at least a couple fill-ups to get a meaningful mileage figure Btw...Glad if I helped!