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Back to Jeeps!... YJ Fuel Injection Build


neohic
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So... my brother's VW went back to his place for his to finish up which left an open spot in my shop. Granted, I was looking forward to a little more elbow room, but I'm planning on moving this summer and this project has been pushed back for a few years now.

What I'm doing now is a little more simple than the VR6 swap: only fuel injection this time. This is my friend's 1990 YJ. Its got the carbureted 4.2 and he hates it! The main problem is the reliability... this thing is terrible and that needs to change. By no means is this project breaking new ground. There is a kit from Howell that does this same thing minus the electronic ignition... and it costs around $1300! All this kit is are the same GM 4.3 components that can be found in any junkyard. Being that I've got around $200 in it, this just seemed to be a much better choice. Lot's more research and time invested, but much, MUCH, less of a gouge in the wallet! Anyhow... pictures!

1990 YJ:


And all this stuff:



Yup, there is a carburetor under all that!


And some stuff needs to go away:


Now… you can buy an adapter plate, but I’d rather build one:



Oh, good… it fits:


Going from a mechanical fuel pump to electric. Again, made my own block off plate:




Got all the wiring mocked up so I could get it running before removing all of the original… just in case:


Should be fun!

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Ben, awesome stuff as always. You seem to keep some interesting projects going, and aren't afraid of tackling a new challenge.

 

That said, when you move, can you send your shop down to me in Illinois?

Rob :dunno:

 

Hey, thanks!

 

As far as the shop... :roll: hmm... figure out the shipping costs as we'll see what happens!

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What did you use for the ECM and did you change the programming in it??

 

ECM is the stock unit out of the donor vehicle. Part number is 1227747... same ECM that Howell sells with their kit.

 

Why not just use a junkyard setup off of an XJ and bolt that on? Would be a little more work but would be a way nicer EFI setup.

 

We thought about that, but the majority of the parts came out of a Blazer that was being scrapped... thus free. Also, the Jeep is used mostly on the trails. With the gears in it, performance gain wasn't too much of a concern. Again, going for reliability.

 

That's pretty cool making a Throttle-body injected 4.2. It were me however, I would have just got a 4.0 YJ.

 

That's what I told him! He bought it already built up and at the time he wasn't thinking about how terrible the carb would be.

 

Slight update today: found out that the starter relay was bad and chased around wiring issues with having the stock computer out of there. I had to figure out the tach and the volt gauge is still not working… maybe bad gauge? I don’t know if it worked before this whole deal started. Gonna throw the multimeter on the alternator tomorrow to see if the gauge reading nothing or if the alt is putting out nothing. :hmm:

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What did you use for the ECM and did you change the programming in it??

 

ECM is the stock unit out of the donor vehicle. Part number is 1227747... same ECM that Howell sells with their kit.

 

 

Hmmm.. I will have to go do some more reading... the FSJ guys all talk about having to get a new PROM burned. I might be confusing the 6-cyl version of the swap with the V-8 version.

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DONE!!!... pretty much. Everything works and it runs awesome! Problem is the check engine light is on. Checked the codes and it turns out that the MAP sensor is bad and there's something up with the ignition module. Otherwise, lots of power and plenty of pep!

 

Finished the wiring and put the ECM right were it was originally:

 

New underhood... so much better than it was:

 

... the diamond plate is kind of a running joke... he's already got way more on the Jeep than it needs. Why not some more?

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Now you just need a dual diaphragm booster and master from an XJ in there.

 

Must be nice having all that underhood real estate in the YJ. Plenty of room for a turbo. :D

 

:shake: Don't give the owner anymore ideas! He also has a Liberty that he's been trying to get me to think about a solid axle swap. Maybe...

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About the Check engine light, Maybe you don't have manifold vacuum to the map sensor, it's easy to get it on the wrong port. And what is the the code for the module problem, do you have a knock sensor hooked up?

 

I've got a code 24 and 42. The MAP sensor goes into the port between the fuel lines on the throttle body. It still has a GM stamp on it, so I figure it's bad. No knock sensor either but it was worked out of the wiring properly with ECM pin number B7 tied to C14 for the proper 5 volt reference. As far as the ignition module... not sure yet what to look for. Here's the diagram I used for the ignition:

 

 

Any ideas?

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Figured it out: the MAP sensor didn't have a good enough ground and the ignition just needed more advance on the timing. All in all, everything feels great on the Jeep. The owner is extremely happy with it and he'll probably get way better fuel mileage with this setup... if he can keep his foot out of the skinny pedal! My favorite part? I GOT MY SHOP BACK!!!

 

 

Oh... and I couldn't resist with all his stickers already on it:

 

 

:yes:

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Quick update on this thing: the owner was cruising around all day with it and re-fell in love with his Jeep! Lots of power... seat of the pants type of thing. Even when we took it out for the first time, he couldn't stay off the gas. Stop light? GO!!! Stop sign? GO!!! Randomly stopping on side streets without traffic? GO!!!

 

... clean shop too :brows: :brows:

 

Thanks! I finished cleaning up this morning and just hung out for a while looking at everything... even took my shoes off it was so clean!

 

Not quite sure what I'll be working on next. I should get back to my dune buggy... kicking around the idea of another MJ again.

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kicking around the idea of another MJ again.

 

:yes:

 

Can't have just one... Time to build a street ripper to give the Jetta some time off from DD use.

 

Rob :cheers:

 

I DID have two at one point... sold it to get the Jetta and I didn't want another vehicle just sitting around. I've found a 4 cyl., 5 speed '87 from Montana somewhat locally. Small lift, 32s, the guy claims he still gets around 17 mpg. Good price too... see what wifey thinks. :roll: I blame the "Family Photos" post.

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