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Discussion Starter #1
my buddy has a older cj with i think a 4.2l 258ci i think. we are wanting to put a modern efi system on it from a 4.0 im wondering if the tbi could just be put on his intake or the entire tbi intake on his head
 

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How "older" are we talking? As I recall, you can just swap the entire top end from any 242ci/4.0L onto 1975-up 258ci/4.2L engine, and just bring the FI and electronics over with it. However, you do have to swap over the entire top end - especially if you're going to an "HO" head - as the ports moved around a bit from the 258 to the 242, and the 242 from 1987-1990/1991-2007.
 

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Discussion Starter #3
How "older" are we talking? As I recall, you can just swap the entire top end from any 242ci/4.0L onto 1975-up 258ci/4.2L engine, and just bring the FI and electronics over with it. However, you do have to swap over the entire top end - especially if you're going to an "HO" head - as the ports moved around a bit from the 258 to the 242, and the 242 from 1987-1990/1991-2007.
so the heads interchange? he has a mid 70s i think. it has a carter carb that hes replaced a few times. is there certain years where the head wouldnt need to be swapped out and just the intake?i saw a write up where the adapt a plate for tbi off a 4.3l gm motor system.why not use a 4.0 ecu and everything?:dunno:
 

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so the heads interchange? he has a mid 70s i think. it has a carter carb that hes replaced a few times. is there certain years where the head wouldnt need to be swapped out and just the intake?i saw a write up where the adapt a plate for tbi off a 4.3l gm motor system.why not use a 4.0 ecu and everything?:dunno:
1975-up, the heads will bolt right on. You will need to swap the head to install the manifolds as well - but that's OK, because the later heads "breathe" better anyhow. Even the RENIX ones, from what I've seen (this is why I'm collecting heads.)

The later heads also have slightly smaller chambers, so you'll get a slight increase in compression. The only real issue you're likely to run into is "valve shrouding" - where the valve is close to the side of the cylinder bore. This results in an effective reduction in curtain area (the area of the cylinder of the same diameter as the valve head and height equal to the open distance of the valve,) which does reduce airflow somewhat. This can be helped by relieving the top of the cylinder bore slightly, and the fact that the ports flow better usually makes up for it anyhow.

But, don't expect to be able to bolt the later manifolds on the earlier head - they're not highly likely to fit (I can say with certainty that the 1991-up manifolds won't fit. I've not checked with the RENIX manifolds yet,) and the ports tend to be shaped somewhat differently for FI vice carburettors anyhow, since FI doesn't have to worry about "puddling" of liquid gasoline in the corners of the manifold.

So, just swap the entire head. You'll probably have to use the head gasket that goes with the head, and you'll need to use the plug "series" that will go with the head you're using (the reach is probably different.) You may have to experiment slightly to get the right heat range, but start with the plugs for your donor vehicle.
 

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Discussion Starter #5
thanks you answered pretty much everything i wanted to know.so any 4.0 head will fit? renix is the french thing right?are they tbi? im wondering how to deal with certain things like sensors the cj wont have like a 02, crank/cam shaft sensor/knock sensor.
 

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thanks you answered pretty much everything i wanted to know.so any 4.0 head will fit? renix is the french thing right?are they tbi? im wondering how to deal with certain things like sensors the cj wont have like a 02, crank/cam shaft sensor/knock sensor.
All I6-242 engines are MPFI. All of them. RENIX TBI was found on the 2.46L/150ci I4 ca. 1986-1987, before that engine went TBI as well.

RENIX 242ci engines are 1987-1990. The control system was largely spec'd by Renault (while they were partnered with AMC,) and built by Bendix/King - RENault/bendIX, thus RENIX.

Out of the three control systems found on the AMC242, the RENIX is actually my favourite, with the OBD-II 1996-2007) coming in second. I've never liked OBD-I (to 1995, 1991-1995 for us) just because it was a hodgepodge cobbled up in different ways by each manufacturer, and there were no real specified standards. Of course, it was mandated by CARB instead of SAE, which probably explains a lot (California has no farkin' clue what it's doing. I once spent a good hour stumping the directors of CARB - they tried to pass my questions off as "Federally required" - but I'd brought a highlighted copy of FMVSS and EPA automotive regs with me - nope, not Federally required. So, wanna try that again?

(I suppose the idea of my having to go to "Test Only" stations ever since is in some small way connected...)

Bendix/King are the big avionics people, and that explains the durability and flexibility of RENIX. I've yet to confirm it, but it seems that RENIX uses an "open-ended" programming scheme (with values calculated "on-the-fly" instead of looked up in a table,) which makes sense - that's the way Bendix/King does things. You can't afford to have avionics suffering from HICS (Head-In-Cement Syndrome) at 10,000MSL. Since I was a pilot years ago, I truly appreciate that!

Also, just about any test that wants doing on RENIX can be done with a simple multimeter.

RENIX still has a HEGO sensor - most electronic fuel injection setups will have one. It's a feedback sensor used to monitor (and correct) fuel trim. The HEGO is on all AMC242 engines - RENIX just used a different type (instead of the typical "air battery" voltage-generating type, it used a variable resistance to divide a +5VDC reference voltage. Why? That's the way B/K likes to do things - they run just about all sensors off of a single reference voltage, makes it easier to keep track of what's going on.)

CPS/CKP will be mounted on the engine anyhow, or close. Take the transmission out of your donor as well, since the CKP (CranKshaft Position sensor) is actually mounted on the bellhousing and reads teeth on the flywheel/flexplate. Unless you get the kit to relocate the CKP to the front of the engine, to read a modified harmonic damper - I'm fairly sure that's a HESCO kit.) CPS (Camshaft Position Sensor) is mounted in the distributor.

The MAP (Manifold Absolute Pressure) sensor on RENIX is mounted to a small bracket on the firewall - and it's a GM standard part of the vintage (most of the RENIX sensors are standard GM parts - another reason I like the system. I'm familiar with GM parts, since that's what I cut my teeth on.)

The Knock sensor (1987-1990 only, deleted for 1991-2007) is mounted to a small boss that is drilled and tapped down on the driver's side sump rail. It does not need to communicate with any fluids, and is a blind hole. It merely requires a solid mechanical connection to the block. It only picks up (and generates) a signal when something is going wrong - detonation/preignition being what it's there to measure. If it does, it advances timing (fires earlier to control combustion) until the problem goes away, then slowly retards (fires later) until its "on the line" for detonation/preignition.

Most of the sensors are going to be on the engine, and just grab the control electronics when you grab the engine (of whatever vintage.) They can be mounted fairly easily, you just have to wire everything up and see what you've got to work with in terms of room.

RENIX does have the borderline useless EGR system (I can think of a few things that would work better...) that was also deleted 1991-2007. I'm sure it can be blocked off if you're not subject to emissions controls (and I have California test results - somewhere - that show the engine actually runs cleaner without the wretched expensive thing...) without incident, I just haven't figured out the plugs. The EGR mount on the intake can be blocked off with a metal plate, and you'd just need flare bungs to block off the tube ports in the intake and exhaust manifolds. For 1991-2007, it's a non-problem - they don't have EGR.

Note also that the primary difference between sensors in the 1987-1990 and 1991-up vintages is the TPS, although it's more of a problem if you're installing an automatic. Probably an easier workaround if you're sticking in a stick behind it - in which case, I suggest a 1994-up AX-15 (external slave cylinder) or 2000-2001 NV3500 (external slave, uses the same bellhousing/clutch fork as the AX-15.) There are several donors for the AX-15, you just need to source the XJ bellhousing. Note that there are two different pilot sizes. One takes the regular "early" XJ pilot bushing (same size as the Peugeot BA-10/5, roughly 5/8". Avoid this transmission at all costs - I've been through four of them on the same truck!) and the other is somewhat larger (about 7/8"). The later one is not a problem - you'll want a 1973-1974 CJ V8-304 three-speed manual pilot bushing for that one, if you're coupling an early crank to a later AX-15 (if it's a later crank/engine assembly, just getting the later bushing should handle that.)

If you get RENIX, try to get 1989-1990, as they eliminated a bulkhead connector that causes trouble when its mounted in its original place - below the clutch master cylinder. The master can leak, and the corrosive brake fluid used to fill it can wreak havoc with the backside of the fuse panel and the bulkhead connector. I've got an 88 I've downchecked, and I plan to eliminate that connector (it's a manual,) and redo all of the pass-through wiring with CPC (Circular Plastic Connectors) or MIL-Spec Amphenols anyhow.

The aftermarket being what it is, you will probably find more performance mods available for OBD-II (1996-2007) 4.0L than any other "generation" out there - but that's entirely up to you. I still prefer RENIX, and I just wish the Air Police would get out of what's left of my hair, let me do things right, and make my XJ a ULEV or a ZEV (using the original engine!)
 

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awesome write up, very professional!
Thank you. For more information, you can check my website - that's what I'm writing books about. The Power Manual is already available, and I'm working on Swappology as of right now.
 
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