'90 Jeep XJ Fuel Injection Problems

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opfor
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Posts: 204
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'90 Jeep XJ Fuel Injection Problems

Post by opfor » Sat May 12, 2018 6:49 am

So for those of you who noticed and those who didn't, I haven't been driving my normal DD to Taco Tuesday (I think I did last week, but not this week).

Well, the jeep's been running like ass for about the last week, and got down and started debugging.

Symptom:

Missing, low idle, maybe misfire, fuel odor.

Debugging Steps:

New cap and Rotor
New spark plugs (looks like it needed these anyways)
Cleaned the EGR system (looking for leaks, didn't find any)
Cleaned throttle body
Cleaned IAC
Cleaned IAT (intake air temperature)
Checked and cleaned vacuum system
Checked and cleaned PCV system
Checked fuel Pressure (30 at idle vacuum on, 40PSI vacuum off) - Perfect
Mechanics stethescope on the injectors - Ruhroh

It took me a while, but eventually I got out my mechanics stethescope and after a little bit of probing the Fuel Injectors on Cylinders 1 and 3 were not making that comforting clanking noise that the other two were. It's quite possible that this vehicle was running for quite some time with a single injector down, and the drivability issues didn't get serious until the second injector failed last week.

I have been suspicious of the wiring as the connectors have a rubber boot that's more like the consistency of plaster of paris than it is like rubber, as such I didn't really want to get into these things without confirmation. But the stethescope test was really obvious and I should have done it sooner. Arguably I would have been able to start working on this during daylight.

Anyways, I happened to have some old injectors nacho gave me, and attaching those to the wiring harness gave the normal telltale "clank" of a functional injector, so, I replaced the two broken injectors with two of the injectors nacho had. I doubt this long term was a wise decision, but I'm going to get the replacements ordered next week. For the moment at least, the heep is running great.

So here's the basics of how you speed-run injector replacements:

1) With the vehicle running, pull the wiring connector off the voltage drop resistor (Big white trapezoidal thing on the front driver's side of the engine compartment) after about 15-30s the engine will die. This has now dumped the pressure of the fuel rail.
2) Remove the transmission kick-down cable from the back of the throttle body, If you turn the cable linkage straight up and down, you can pull it off the throttle-bar connection, the rest of the assembly can then be pushed out of the bracket by pushing in the tabs.
3) If you haven't already done so, remove the wiring connectors from the affected fuel injectors, on the 1990, there were little wire tabs that had to be removed, I used a pair of hemostats, a pocket knife, and a small flat-bladed screwdriver. Good news, you usually don't have to put these things back. (I didn't anyways)
4) There are 4 bolts that hold down the fuel rail, you'll see the metal feet, remove them, you'll probably need an extension, I found a few of mine to be rather tight, I would suggest using a 1/2" hex (not 12-point) socket with a 6" extension.
5) disconnect all of the throttle-body electronics (TPS, IAC) and move the wires out of the way.
6) Carefully wiggle the fuel rail backwards, the injectors should come with it, since I only had to do 1 and 3, I pulled the front out further than the back. Special Note: On my vehicle there is a vacuum manifold thinger in this area, as well as a vacuum tube that is part of the PCV system. the vacuum manifold connects to the intake manifold, and there's also a nut on top, that has a holder for the fuel return line (comes out of the Fuel Pressure Regulator which is also connected to this vacuum system) you will probably need to disconnect all of the brackets holding this stuff in place, but it's not necessary to disconnect the fuel return pipe.
7) Pop the clips off the fuel injectors
8) Wiggle the old injectors lose. Be sure to check that the fuel rail and make sure all the o-rings come out, I popped the one that stuck out with the hemostats, since I wasn't pulling the rail all the way off, using a screwdriver was a bad angle.
9) Lube the replacement fuel injectors with some kind of lubricant. I used some rem-oil on the o-rings.
10) Carefully re-insert the injectors and then snap on the clips. I found it easiest to do this with the electrical connector pointing away from me, then twisted it back to an upright config when I was done.
11) Spray some carb cleaner into the injector holes.
12) Spray some rem-oil on the O-rings
13) Re-insert the fuel injectors, re-attach the fuel rail (bolts) and put all the other vacuum shit back in place.

Took about an hour.
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dynotronix
mall ninja
Posts: 15
Joined: Sat Oct 07, 2017 6:21 pm

Re: '90 Jeep XJ Fuel Injection Problems

Post by dynotronix » Sat May 12, 2018 3:23 pm

Might as well replace all the injectors as a set, since this is a "forever" vehicle.

Replace any O-ring you remove with a new one, unless you have a low deductable comprehensive policy. They will leak if you re-use them.

I had one injector crap out on my '93 exploder, it has a built in test mode accessed by shorting two commectors with a paper clip. It tells you which injector it's deactivating by flashing the CEL that many times. So when it gets to a cylinder that doesn't make it run any worse, you know.

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opfor
tactical nylon fetishist
Posts: 204
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Re: '90 Jeep XJ Fuel Injection Problems

Post by opfor » Sun May 13, 2018 8:27 am

So far I haven't seen any leaking, but that's neither here nor there, this was quite literally a field fix I did between 1 and 2am. I have ordered new Fuel Injectors, they should be here next week. I do happen to carry 3 fire extinguishers in my vehicle.
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dynotronix
mall ninja
Posts: 15
Joined: Sat Oct 07, 2017 6:21 pm

Re: '90 Jeep XJ Fuel Injection Problems

Post by dynotronix » Sun May 13, 2018 5:28 pm

You MUST replace the rubber or it WILL burn. Have the T-shirt still from that ride.

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opfor
tactical nylon fetishist
Posts: 204
Joined: Fri Aug 25, 2017 9:19 pm

Re: '90 Jeep XJ Fuel Injection Problems

Post by opfor » Tue May 15, 2018 8:21 pm

I realize the number of Jeeps in the group is a lot thinner than it once was. I ordered new fuel injectors, and I thought I would throw out the link:

http://www.fuelinjector.citymaker.com/c ... 025237.htm

According to Rob, this is a drop-in replacement and will fit the fuel rail clips. We'll have to see once they show up.
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