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Unread 12-03-2011, 06:14 PM   #1
1SASjeepster
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1992 YJ Wrangler 
 
Join Date: Apr 2010
Location: Smith,TN, Tennessee
Posts: 720
Zj fuel injector swap for 5.2

I have recently replaced the fuel pump/ sending module in my wife’s 1998 ZJ Grand Cherokee. This module comes with the fuel pump, sending unit, fuel pump regulator and “one way” check valve. All located on top of the fuel tank. About one month later, the vehicle was hard to start in the morning. It was very intermittent... . The engine spun nicely but it wasn’t catching until ten-fifteen seconds later. I ran a fuel line pressure test and she tested fine. The vehicle has the 5.2 engine and it has over 160,000 miles on it. Sometimes it would bog down on acceleration, sometimes it was low on power. I wasn’t sure what was going on. I suspected it had something to do with the previous repair but it all tested great.

I searched the forum and found articles on swapping out the fuel injectors off of the 4.0 engine to the better Ford fuel injectors. I didn’t see anything about doing this on a 5.2 engine though, plus most of the articles were conjecture without any details on what to do. Now, there were three or four articles which were superb and the writers went out their way to document it. One even listed a source for the injectors. I decided (after watching the YouTube video on comparing the injectors) that I was going to do this upgrade. I didn't know if this was my problem or not.

I contacted Rob at Motor Man Fuel Injection (989) 644-2695. He rebuilds injectors and he knew just what I wanted. His rebuilt fuel injectors were BOSCH # 0280155703 and sold them for $ 24.99 a piece. I ordered eight of them and they arrived in three days.

The job will take about two hours. You will smell like gasoline when you are finished, so keep that in mind with clothes and safety glasses. Also ONLY DO THIS UPGRADE WITH A COLD ENGINE!

REPLACING THE FUEL INJECTORS

FIRST, disconnect the negative battery cable and tuck it down on the side of the battery with a rag keeping it there. This job will have gasoline fumes throughout the engine compartment. You must make sure that the battery cable cannot touch the negative post whatsoever. Remember sparks ignite gasoline fumes easily.

SECOND, remove the air cleaner assembly. Since I don’t have a stock one, you have to do this on your own.

THIRD, remove the “A” bracket at the rear of the air compressor. All you have to do is loosen it so that it can pivot out of the way. Remove the top “A” bolt and the lower right corner “A” bolt... from the perspective of looking directly at it with your knees leaning on the front bumper. Loosen the lower left corner. Now pivot the bracket towards the passenger side as far as it will go. That’s it. It prevents you from getting full access to the driver’s side fuel rail.

FOURTH, unplug the three sensor plugs on the throttle body. There is one in front, one on the driver’s side and one at the rear. All three plugs are removed by gently pressing down the tabs while pulling. These plugs get very brittle. BE GENTLE. You do not want to damage them.

FIFTH, unbolt the throttle body. Do not remove or disconnect any of the throttle cables are linkages. It is not necessary. All that has to be done is that the throttle body needs to swing out of the way of each fuel fuel rail as you are lifting it. There are four bolts on top of the throttle body that hold it to the intake manifold. Remove these bolts and be careful lifting up the throttle body because you don’t want to damage the thin gasket underneath it.

SIXTH, release the fuel line pressure at the driver’s side fuel rail. The fuel line pressure port is at the midpoint of the rail, next to the throttle body. It has a cap on it. (If your vehicle does not have this “pressure port” you need to find out how to relieve the pressure before you do anything.) I just used a small baby food jar and put it under the port. With my safety glasses on and my baseball hat, I used a large Phillips screwdriver and pressed down on the nipple. The gas flowed out of the nipple into the jar. When it stops flowing, you’re done, but remember there is more fuel in the line, just not under pressure. (Whenever I suspect gasoline might "shoot out" I wear safety glasses and a baseball hat. I have had gas in my eyes before. It isn't pleasant.)

SEVENTH, now remove the driver's side fuel rail, BUT BEFORE YOU DO... you need to realize a few things. (1) There is a vinyl/ plastic tube connecting both fuel rails which runs around the rear of the throttle body. DO NOT KINK THIS LINE, DO NOT DAMAGE THIS LINE. DO NOT PUT HOSE CLAMPS ON THIS LINE. This is considered a “non serviceable” item. If you damage it, it has to be replaced in its entirety. It is OK because you have just enough clearance to get the injectors out. Just be careful. (2) There is a fuel line connecting to the driver’s side fuel rail. (This is the "feed line" coming from the gas tank.) You do not have to remove this. Just be careful when you start handling the fuel rail. (3) Remaining gasoline will run out of the rail every time you pull out an injector. Have rags ready to wipe this up.
The fuel rails are held onto the intake manifold by two bolts. Remove the two bolts on the driver’s side fuel rail. Now grab the fuel rail and gently move the rail left and right, and to and fro. The idea is to do this gently. Once loose, pull the rail straight up. The injectors are vertical. Pull straight up. (Now, the rear of the fuel rails will not pull far up because of the vinyl fuel line connecting both rails. That is OK. You will have more than enough clearance. If you can’t pull them straight up, use a large, flat bladed screwdriver and pry up. Be careful what you rest the screwdriver on before you pry. You can break things like this, so be careful and think it through.
Once the fuel rail is up, you have four injectors connected to the fuel rail by thin sheet metal clips. Use a flat bladed screwdriver to remove the clip. The clip is shaped like a “square U” so work it off and then the injector pulls out. Notice how the clips come out because that is how you need to put them back during installation. The fuel injector holes in the intake manifold are tapered and mine were very clean.

EIGHTH, Remove all of the injectors from the driver’s side rail. Put them aside and get four of the replacement injectors. Use some oil to lubricate both “O” rings on the injector. This makes is a lot easier to get the injectors back in.

NINTH, Now the fun part... the only problem I had with this swap was getting the new injectors into the fuel rail. They were a PITA... but doable with patience. I found out that once you press the injector in a certain amount, that it just snaps in... but getting to that point is something else. I tried twisting them, pushing while twisting, etc., etc. If you find a great technique, LET ME KNOW!! Anyway, you will do better starting at the rear of the fuel rail. Once the injector is in, put the clip on. The clip fits in a thin groove cut into the injector body. It just presses on with finger pressure. Once you finish putting in the four injectors with their clips, start pushing down the fuel rail so the injectors go back into the holes in the intake manifold. You need to gently manipulate the injectors so each line up perfectly in the holes. You do not want to tear the “O” rings on the bottom. Once you have them in the holes, push the fuel rail down and they should center on their own. Now install the two bolts that hold the fuel rail to the intake manifold. You are now finished with one side. Go to the passenger’s side and repeat.

TENTH, Once this is all done, hook up the “A” bracket to the air compressor again. Install the throttle body, install the plugs for the three throttle body sensors, put on the air cleaner assembly and make sure there are no puddles of gasoline on your engine, intake manifold, exhaust manifold, etc., etc., Reconnect the negative cable to your battery. Now turn the key “on” but don’t start your engine yet. This will get the fuel pump to pressurize the fuel rails. (I gave it five seconds.) Now start the motor. My motor was idling rough at first, due to the fuel that was dumped into the holes in the intake manifold when I pulled the injectors. However, once the engine settled down, IT WAS GREAT!!! The computer had to "learn" again, so I took it for short run (20 minutes). There were no more sluggish response and the engine was running great. I was at 70 mph and punched it. Usually there is a sluggish response. Now it pulled unbelievably. I took my foot off the pedal at 90 mph, but I had plenty more to go. (Oh. please note... NOBODY WAS ON THE ROAD WITH ME ON THIS STRETCH OF HIGHWAY.) I drove it around some more on errands, and my starting problem was gone. It idles more smoother and the engine’s response is so much better. My fuel consumption was 15 mpg. Now it is 21 mpg. This swap worked for me.

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Unread 12-04-2011, 09:55 AM   #2
98BlackZJ
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Thanks for the detailed write up. I picked up some FMS 24lb injectors a few months ago but haven't gotten around to installing them yet.
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Unread 12-04-2011, 11:39 AM   #3
JrMechanic
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Petroleum Jelly on the O rings makes them slide into the fuel rail like butter, if you still have trouble you can put the Petroleum Jelly on the injector ports and lube the O rings with oil.
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Unread 12-04-2011, 02:17 PM   #4
1SASjeepster
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JrMechanic,

Petroleum Jelly... what a great idea!! That would have worked so much better than a drop of oil. Thank you.

Take care,
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Unread 12-26-2011, 03:49 PM   #5
extrememarine
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thanks for the detailed write up. This is on my list of upgrades now. I've got a new intake manifold on the way (Mopar Performance MPI), and I may just do the injectors while I've got it apart.

For the MPG numbers you listed - are those from the trip computer or actual calculated at fill up? I'd be happy to get a bump in MPG, but it's not bad right now at 15-17.5 on my commute.
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Unread 12-26-2011, 04:24 PM   #6
zander21510
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I recently made the super-detailed write up for the 4.0...can I quote this so we can consolidate the injector swap write-ups? I wanted to make one thread possibly added into the FAQ so it would be easy for people to find. Of course I will give you credit for it
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Unread 12-27-2011, 05:58 AM   #7
1SASjeepster
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"Extrememarine",

My MPG figures came from the trip computer. It was pretty consistently going from 13-15mpg. Now it is going from 21-23 mpg. Again, I can't promise anything. All I can tell you is this swap worked excellent for me.

"Zander21510",

You are welcome to quote me and use any information I gave out. I am not out for "glory" but just to help fellow jeepers. Use whatever you can. I hope you do well with your project. And I hope it helps a lot of jeepers!

Take care,
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Unread 12-28-2011, 06:17 PM   #8
extrememarine
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thanks

Thanks. I've got about 8 weeks of MPG data now (calculated from gas reciepts), so we'll see...


Quote:
Originally Posted by 1SASjeepster View Post
"Extrememarine",

My MPG figures came from the trip computer. It was pretty consistently going from 13-15mpg. Now it is going from 21-23 mpg. Again, I can't promise anything. All I can tell you is this swap worked excellent for me.
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