Hey guys, I've read Tim Weaver's excellent article on installing a 4.0 head on a 4.2 block (
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) and am preparing to do the same to my 84 CJ7. I'm wondering if anyone in this group has swapped a factory Cherokee 4.0 fuel injection system into an earlier model vehicle. I know I'm going to need the wiring harness, the computer (ECM), as well as the manifold with the MAF, Temp sensor, TPS, etc., etc.. Other than installing an O2 sensor in the exhaust is there anything I'm overlooking? I will not be running a catalytic converter. This seems to be a pretty heads up swap and I really would like to avoid a $2,000.00 bill for a fuel injection system. While I'm at it I'll probably change the ignition to the later model computer controlled ignition. Any and all input is greatly appreciated. Thanks, Charles E.
84 CJ7
92 Cherokee
81 DJ5L
Be advised the Cherokees have two totally different computer systems with different heads and manifolds. As I recall there's even differences in different years of the "HO" heads.
Well.... it is a shaky conversion. You have to rely on glue or JB Weld to seal up big voids in the water jacket....
Not for me thanks.
And yes, if you get everything from one donor vehicle, you shouldn't have issues.
The problem is all the folks that do the FI conversion only boast about a 25% boost in power with a drop in gas mileage. Well you get that for free by just killing the computer via a Nutter bypass and as a bonus, you get an 'increase' in gas mileage.....
All the 4.0's that wheel with me and my BBD 'nuttered' carb engine burn a lot more gas than me on the same trails....
I always get a nice 23 mpg loaded on the highway and my CJ7 goes like a scalded cat. It will spin up my 33's too easy in first with 3.31 gears even, 2nd hits 50+ mph at 4400 rpm, 3rd pulls fast to 75 mph, 4 buries the speedo and I have 'no' freakin' urge to find out how fast 5th goes....
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Mike, Tell me more about this neutered computer! My CJ is pure stock, well, it's got a header and no catalytic converter. My fuel mileage is poor, probably about 14-16 mpg. 258 cid, T5. 31" tires and the engine lacks power. This is basically a street Jeep. No big hills in S. Louisiana, no rocks and I've little time to go muddin! I'm more than willing to fart around with the current set up to make the Carter BBD useable or driver friendly. Worse case scenario... Drivability gets worse and then I convert to F.I. So if you don't mind, elaborate on the 'killing of the computer' . Can I keep the Carter or do I need to replace it with a Holly
Basically the 'Nutter' bypass just connects the ignition module directly to the distributor as it was before the failed excuse for a Ford emissions computer was stuck in in 82.
I add 2 new wires rather than mess inside the harness like the author, John Nutter does. The orange and purple wires at the ignition module get connected to the orange and purple at the distributor.
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Then the timing and carb mix get set manually. The BBD is a nice carb and it does have the manual mix screws under caps to set. A carb kit for the BBD is about $20.00 and is highly recommended as well as a clean/ream of the idle tubes to make it just purr.... The tool to clean the idle tubes can be obtained from any welding supply shop. Doing this first makes the idle mix set 'soooo' much easier. The end of the tubes are crimped and crimped slightly too small. Reaming them was even recommended as a factory fix.
Here is a link on the idle tube job. I can do it on the trial in 15 minutes if it gets crap in it. The venturi will come out from the top with a twist.
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I added an Accel 'SuperCoil' for a hot spark and OEM wires from the $tealer to give me great power and mileage. I also went manual cable for choke.
I do only get 15 or so if I now use regular, but with 91 octane, I get a sweet 11L/100 KM or 23 mpg and it just flies.
It will not stall on sand pit wall climbs, get too steep at 400 rpm and it just starts digging holes. I did the nutter in 98 and love it.
I also passed the last emissions with a straight pipe and dynomax superturbo muffler with 15 ppm HC, 0.16% CO and even though I 'don't' need to pass NOx, got 589!
There are 'mechanics' or better said 'techs' because I don't think any of them have a real license on this group that have a shit fest when I post these numbers because they don't think anything 'manually' set up can be even close to what a computer can tell them to do. They forget that 'real' mechanics actually knew how to tune engines before computers. LOL! Sorry for the obvious troll, but they are just sooo funny with their squawks....
Like the "real" mechanic said, you'll have to tune it manually to get it right. And even then don't expect to get 23mpg in a cj. Unless your in a different country using kilometers or something.
Well, I am not a 'real' mechanic, but I sure can tune a 258 CJ engine to get consistently better than 20 mpg and that is not just on my engine alone. One of our tenants had an 85 automatic and we used within a couple liters the same amount on a 200 mile run and every other time we compared. Conversions get fun, but we get 11L/100 km or 23 mpg.
Our Cherokee 4.0 gets 10L/100km.
Now if we try to run gasohol or any 'ol' mixes like the owners manual warns 'not' to do, then the mileage and performance sucks the big one and we only get 17 or 18 mpg.
Maybe we have better gas? LOL.
Naw, we just don't need no stinking computer to tell us how to tune them properly.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
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