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Unread 07-07-2014, 11:11 AM   #1
1984Laredo
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Just completed 4.0 swap - no power, same or less than 4.2

I just finished a 4.0 swap in my CJ7. Engine came out of a '94 Grand Cherokee, and I had it professionally rebuilt. All sensors were replaced with the swap. I'm using the E2000 pump. I also installed the Neon upgrade injectors.

Just got it on the road for the first test drive today and was not impressed AT ALL. The lack of power is depressing. About the same or less than the old 4.2. I don't even know where to begin trying to figure out what's going on. Any ideas?

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Unread 07-07-2014, 11:29 AM   #2
Mike Romain
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A new engine needs to get broken in a bit so the power should come up a little later. Did you pull the codes? That is where you have to start.

I got a nice increase when I went to a used 93 GC engine, but I kept the carb intake. Didn't want to sacrifice the gas mileage or power a carb gives for the convenience of FI.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 07-07-2014, 11:34 AM   #3
1984Laredo
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My check engine light isn't on. Will it still have codes if this hasn't come on?
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Black Diamond 3" lift, 33" tires, 4.11 gears
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Unread 07-07-2014, 11:45 AM   #4
Mike Romain
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Quote:
Originally Posted by 1984Laredo View Post
My check engine light isn't on. Will it still have codes if this hasn't come on?
It could. Does yours use the key method or do you need the scanner to check them?
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 07-07-2014, 12:25 PM   #5
1984Laredo
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I just pulled the following codes:

12 - battery disconnected within the last 50 key cycles
75 - ??? Can't find this on a code list
73 - ??? Can't find this on a code list
35 - fan control relay (no electric fan used in my application)
55 - end of codes

Any clue what the 75 and 73 codes are? I checked the codes 3 times to make sure I didn't count the flashes wrong. I can't find these codes.


Also just drove it again. It definitely accelerates slower than my 4.2 and also makes my 5th gear useless once again (like it was before I changed my gear ratio). Going up the slightest hill in 5th with the throttle held constant will result in loss of speed. My 4.2 didn't do that. Even on a flat road, acceleration in 5th gear is pretty much non-existent.
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Unread 07-07-2014, 12:57 PM   #6
1984Laredo
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I had a spare PCM with a busted case from another junkyard vehicle, so I decided to swap them to see if anything changed. The second PCM seemed to let the engine accelerate slightly faster than the first, but still no improvement over the way my stock 4.2 accelerated (I have a hill that I use to "test" the acceleration).

After I got back from that test drive, I pulled the codes from the second PCM. They were the same as the first: 12, 75, 73, 35, 55.
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Unread 07-07-2014, 01:09 PM   #7
Matt1981CJ7
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Maybe your expectations were a little too high. I think the 4.0 only had about 190 HP and the peak torque was similar to the 4.2, only at a much higher RPM.

Sounds like you're a candidate for a V8.

Matt
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Unread 07-07-2014, 01:38 PM   #8
Mike Romain
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Those codes are strange but you are not the only Jeep showing them. No one seems to know.

How old is your gas? Modern ethanol laced gas only has a 30 day shelf life....
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 07-07-2014, 02:12 PM   #9
1984Laredo
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Well, I based my expectations on all the reports of this swap being a noticeable improvement over the 4.2. Have not read any comments from anyone saying that there was no improvement over a 4.2.

The gas is a few months old.
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Unread 07-07-2014, 02:30 PM   #10
seabass1858
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you could always go back to the carbureted setup with the 4.0. sorry i kind of like working with carburetors since driving my cj7. ive seen tha setup. a nice weber 38/38 properly jetted and a fuel pressure regulator with your electric fuel pump would wake the 4.0 up but if you are not willing to go that route. here is an error code chart for odb1 cant find 73 or 75 but based off of many readings your alternator may have something to do with it. http://offroad-review.com/new/index.php?page=161 http://www.wranglerforum.com/f218/yj...tf-251402.html
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Unread 07-07-2014, 04:03 PM   #11
RenoF250
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Does it seem to run good? What are you using for exhaust? 4.0s advantage is in RPM so you need to run it up a bit before shifting or you will not see it. That is why I stroked mine, to keep the low-end torque. Mine has much better throttle response than the 4.2 and noticeably more power .
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Unread 07-07-2014, 04:18 PM   #12
firegod33
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I've never been a fan of the 4.0 swap. I've owned vehicles with the 4.0 and it's a fine engine but the 258 will out pull the 4.0 all day any day. Adding Howell injection to mine gave me nice, crisp throttle response.
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Unread 07-07-2014, 04:35 PM   #13
1984Laredo
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Quote:
Originally Posted by RenoF250 View Post
Does it seem to run good? What are you using for exhaust? 4.0s advantage is in RPM so you need to run it up a bit before shifting or you will not see it. That is why I stroked mine, to keep the low-end torque. Mine has much better throttle response than the 4.2 and noticeably more power .
It runs great, minus the power. Runs very smooth and has crisp throttle response. It's just when I'm moving, it feels like the brakes are slightly dragging (they aren't).

The current exhaust is temporary until I can get it to the exhaust shop in a couple days. I used a section of a YJ 2" downpipe connected with a 2" pipe into an old glasspack that I took off another one of my vehicles. I have a Walker 2-1/4" muffler and tailpipe to have the exhaust shop put on, along with making a new 2-1/4" downpipe.
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Black Diamond 3" lift, 33" tires, 4.11 gears
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Unread 07-07-2014, 05:44 PM   #14
hutch1200
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CJ7s are about 2 tons. My '79, 304 CJ7 was 4150#. Now compared to a little plastic (no offense) Cherokee, one could be disgruntled until 1k miles. I wouldn't even jump on a newish engine until oil changes after cam break-in, 500 miles of gentle/medium acceleration and then at 1k maybe get on it. RANT OFF!
My bro picked up speed/acceleration, just by putting a Kevlar/glass body on. Pulled so hard he threw it on its' side for awhile!
.
Seriously, you have a gorgeous CJ that I'm jealous of. Get your exhaust right, maybe a blockage somewhere is killing the power over 2k rpms? Anything fall in the muffler while it sat? That kind off back pressure could lead to catastrauphic failure! Then it is up to the code gurus or have your ECM(?) re-flashed for the injectors & exhaust?
Good Luck, & I hope to see some rubber/rooster pics when finished!
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Unread 07-07-2014, 07:14 PM   #15
RenoF250
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Quote:
Originally Posted by 1984Laredo View Post
It runs great, minus the power. Runs very smooth and has crisp throttle response. It's just when I'm moving, it feels like the brakes are slightly dragging (they aren't).

The current exhaust is temporary until I can get it to the exhaust shop in a couple days. I used a section of a YJ 2" downpipe connected with a 2" pipe into an old glasspack that I took off another one of my vehicles. I have a Walker 2-1/4" muffler and tailpipe to have the exhaust shop put on, along with making a new 2-1/4" downpipe.
The exhaust may be some of your problem. I have 2 1/4 to 2 1/2 and out. I ordered the Walker tailpipe and took it back, they smashed the crap out of that thing.

Searching a site said one of your codes is IAT too high. That may not be correct because that is supposed to be code 23 or something like that. I only mention it because if the PCM thinks the intake air temp is high you will get less power. Some on jeepstrokers relocate it to somewhere coolers to fool the PCM.

Is your throttle linkage okay? You getting WOT with the pedal to the floor?

What are you using for an air filter?

Out of my own curiosity, what oil pressure are you seeing? Mine runs 70 psi cold down to 35 psi at idle hot with Lucas SAE30 break-in oil.
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