4.2l build

likeshills08 · 02-18-2010, 03:11 PM

Ok, I have an 85 cj7 with a 4.2 in it. Got a yj tub to put on it, but I need to do something with the engine.
The POS carter is on there and I did the nutter bypass so I could take it to a buddy's farm in NY and do some offroading and camping. Basically this is the ugliest thing you will ever see. My goal is to build a good mud machine on a low budget.

I want to make this 4.2 have a lot of torque with a little extra hp, be able to take a beating, stay dependable, have a strong low end and be as simple as possible. Now that you know what I am aiming for these are my questions...

1. To get the most torque out of this engine, what kind of lift and duration would I want in a cam? I know minimum duration is optimum for low end torque but how can I get that with a little hp too?
2. GM 4.3l TBI swap... is it worth it? I don't want to drop $2k on a brand new conversion system.
3. the bulkhead connector on my yj tub was cut up (junkyard). If I am going to be doing the GM 4.3l TBI swap how am I going to get the harness to work? the harness from my cj is a rats nest and not to mention i nuttered the crap out of it... (

) which leads me to my next question
4. Should I burn it to the ground? (just kidding)

Thanks for the help in advance

rusteehawk71 · 02-18-2010, 09:30 PM

Easiest to do is grab a head and intake off a TBI 4.0 and swap it onto your 4.2. Then grab the pcm and wiring harness and you should be all set. Raid a Cherokee for parts if you need be.

likeshills08 · 02-19-2010, 09:28 AM

sweet i was wondering about that if it would work but had never heard about a 4.0l tbi swap.

but what about cams, anyone had experience caming these motors?

likeshills08 · 02-19-2010, 02:39 PM

Also what years were the tbi 4.0l in the cherokees/g cherokees/wranglers? do I need to get a pcm and harness from a manual cherokee/g cherokee/wrangler since mine is a manual as well? thanks.

rusteehawk71 · 02-19-2010, 08:11 PM

I think they started running the fuel injection in '93. But you want a '94 or newer head and intake and as for the wiring harness I dont think it matters if it is from a manual or auto but you do need the pcm. It is right on the firewall and easy to get at take a 6 or 8 mm socket to get it off.

likeshills08 · 02-24-2010, 01:13 PM

Ok thanks, just what i needed to know.

No one knows cams though?

1986cj · 03-15-2010, 12:15 AM

The GM tbi never came on any Jeep factory. In 1987 Jeep put the 4.0 in the Cherokee and it has a renix fuel inj system. In 1991 Jeep move on to include the Wrangler 4.0 with fuel inj as a obd1 system and no more renix systems in any Jeep product. The 91-95 4.0 became the High output (HO) 4.0 with the new head 7120 casting. The GM is not much more than a carb with two injectors in the throttle body along with the tps and iac built in. It is a great system and works real well on a 258 but the Jeep 4.0 throttle body is just a throttle body for air intake and the intake manifold has 6 injectors. one for each cylinder. They are no way, shape, or form even similar, but for hp nothing is going to beat the Mopar obd1 system but at 2 to 3 times the cost. They both can be done as junk yards swaps. I have the GM version and looking into the Mopar one now. Look up Howell fuel inj and you can see what is TBI, great system and designed by Howell who was the engineer for GM and then Check out the Mopar system, google Herco and you can compare the difference. Howell about 1200.00 I did the junk yard version but I also let the GM coumpter contorl the timming for under 300.00 , vers the Mopar (Herso) for about 2500.00 plus 300.00 for the cps relocating system if you don't want to mod your bellhousing.