4-cylinder engines: upgrades through the years

[yellowta]

I've got a spare cylinder head I've been contemplating having shaved and port matched. You don't really want to have it ported, as increased volume means less air velocity. That means less torque at lower rpm's. What we need with our little motors is as high of an air velocity through the head as possible, so you want to smooth out the runners, take out any sharp edges in the valve bowls, and a good three angle valve job. I may also shave the head a bit to bump up the compression, but my 2000 stock is supposed to be at 9.5:1 stock, and I don't want to have to run more expensive fuel.

 

[xj92]

I'm just going off what the guy at the machine shop told me, so I can't argue the details, but he ports it differently based on the desired effect, i.e. horsepower, torque, etc. I had him do the same thing to the head on my 4.0L and it made night and day difference on the low-end torque. It had a lot more afterwards, pulled hills better, great in the low-rpm rockcrawling, etc. By looking at it, it appears that he opened the intake ports up a little bit where they connect to the manifold, but not all the way through, and then he smoothed them all out.

 

[alex22]

Its all about the shape of the short side radius. Well maybe not all about the short side, that and the valve job / choke have a big impact on the flow curve. Generally speaking the flatter the short side is the better high end flow. For low end power a steeper, wider short side and IIRC about an 88% choke before a good multi angle valve job and unshrouding the valve. Sometimes a backcut valve will help too.

~Alex

 

[xj92]

I'm in the middle of this MPI swap still. Now I need to put in a body harness. I thought I had bought one from a junkyard, but evidently it was pre 91 cause it doesn't match up to the loom that comes through the firewall from the '93 engine harness. Here is the loom I'm referring to. Anybody know what this loom controls?

 

[Mr_Random]

I probably wont be doing any porting, but I'm doing the same swap with my 86 and a 1994 YJ, you got a freaking steal at the junkyard... I wish I could do that well!

$100 Intake manifold/fuel rail/Air temp sensor (check)
$130 Body/engine harness and ECU from 94 YJ (deal pending)
I HOPE $50 for an XJ tank and Fuel pump (can talk down JY guys)
~$100 for brand new sensors and t-stat housing (could be as low/high as $80/$130, I'll try to stay with the same brand to be consistant).

I also want a cheap 4.0 TB and new exhaust mani, but could just plug up the EGR tube on current mani and run it.

I'm sure there will be other problems to find along the way, but first I've got to get everything together!

 

[xj92]

My FSM shows the MJ body harness part #'s, and each year, '91-'93, has a different part #. Hopefully they at least have the same connector for that loom of mine coming through the firewall, which is from a '93 XJ. I'm not quite sure how they have a '93 MJ part # since they were only made through '92. I called the dealer, and the part #'s below are all valid, but none are available anymore, they're considered obsolete.

2.5 & 4.0 Eng., Body Harness Part #'s:
5601 6869 MJ 1991
5601 7509 MJ 1992
5601 9161 MJ 1993

If I put in a later body harness, will it still connect to all the radio controls, heater, etc. etc.? or will I have to splice all of those over anyways?

 

[Ghost]

I can help you but nto right this second... PM me a number and I'll call you . I just pulled the mpi stuff from my 84 xj. That is part of the body harness IIRC in that picture. All of the switches and the other stuff on the 84 pluged into the 94 harness I got. I think I may have changed a few things like the hvac and brake switch but that was about it. I have all that sitting in a box.

 

[REDXJ4FUN]

A few more tricks that work great for a 2.5 are a 4.0 TB witch does require just a little bit o cleaning up on the intake(about .5mm) and a flywheel weight( it realy helps the little motor pull) another great upgrade is good plugs and wires and coil like the DUI live wire setup. A header works ok but not needed. and real biggie is an electric fan. the Taurus fan works great and can be found cheap on ebay or a good pick and pull. If you do go with a TB spacer make sure ita a stock bore that for a 4'0 to match the TB. I have seen people use TB spacers as big as 62mm on the stock intake and it is worse than leaving it stock. if you have all of that the next best thing is a good cam but you will be happy witht the basics here.

 

[Ghost]

A few more tricks that work great for a 2.5 are a 4.0 TB witch does require just a little bit o cleaning up on the intake(about .5mm) and a flywheel weight( it realy helps the little motor pull) another great upgrade is good plugs and wires and coil like the DUI live wire setup. A header works ok but not needed. and real biggie is an electric fan. the Taurus fan works great and can be found cheap on ebay or a good pick and pull. If you do go with a TB spacer make sure ita a stock bore that for a 4'0 to match the TB. I have seen people use TB spacers as big as 62mm on the stock intake and it is worse than leaving it stock. if you have all of that the next best thing is a good cam but you will be happy witht the basics here.

All good sugestions too. The 4.0 tb really is a difference. But not a 4.0 bored it actually does make it worse. As for the cam I actually have a mopar stage 3 in the box that was going in my 2.5L but when it blew a head gasket I scratched the idea and found a 4.0 for cheap!

 

[BarracudaBlueXJ]

would you want to sell that cam?

 

[xj92]

I have a '94 XJ chassis harness that is about halfway in now. I had to cut off the back half that goes to the fuel pump, rear doors, & tail lights because it's all different on the comanche, and I'm in the process of splicing some of those wires. I believe I have all the wires hooked up for the engine harness and for the fuel pump (I spliced two wires, left ground the same). When trying to start it I'm not building any fuel pressure though. I tested it using the bleeder valve on the fuel rail, and no gas comes out at all. Is something more required than just splicing the two wires from the fuel pump to the new chassis harness? Even if it had a different psi than the tbi it replaced, it should still build some pressure. The only things I can think to check at the moment are my fuses and make sure that I didn't switch the two fuel lines. I was fairly thorough when doing the fuel lines, but you never know. Does anybody have any other suggestions?

The break switch thing is also different between '88 & '93. It looks like I'll have to get the metal plate to mount the later model switch thing to, since the new one has 4 or 5 wires vs. 2 on the '88 model.

 

[Ghost]

I have a '94 XJ chassis harness that is about halfway in now. I had to cut off the back half that goes to the fuel pump, rear doors, & tail lights because it's all different on the comanche, and I'm in the process of splicing some of those wires. I believe I have all the wires hooked up for the engine harness and for the fuel pump (I spliced two wires, left ground the same). When trying to start it I'm not building any fuel pressure though. I tested it using the bleeder valve on the fuel rail, and no gas comes out at all. Is something more required than just splicing the two wires from the fuel pump to the new chassis harness? Even if it had a different psi than the tbi it replaced, it should still build some pressure. The only things I can think to check at the moment are my fuses and make sure that I didn't switch the two fuel lines. I was fairly thorough when doing the fuel lines, but you never know. Does anybody have any other suggestions?

The break switch thing is also different between '88 & '93. It looks like I'll have to get the metal plate to mount the later model switch thing to, since the new one has 4 or 5 wires vs. 2 on the '88 model.

Now that you mention it I think I had to do something to mountthat switch. As for the fuel problem Is it the renix pump? If so swap it out, iirc it suns on a much lower pressure. I could be wrong though. Maybe someone who knows more of those tow systems will chime in.

 

[xj92]

Yeah, it's still the '88 renix pump. Guess I'll swap it out. Come to think of it, I heard the fuel pump the first couple times I tried to start it before I had every wire connected, but haven't heard it in a while, so a new pump might be in order anyways.

 

[Mr_Random]

So the big fat fuse plug will work, but not that smaller one?

Should I go get the full harness, or just the pieces (I have great electrical skills anyways) that don't work?

I have a 94 YJ engine harness right now... it was too hard to find an XJ 2.5 anyways...

WAIT! I have the YJ body harness too, could I splice any needed connectors on to mine?

wow I make no sense...

Basically I have the FULL harness from a 94 YJ, every connector and everything, so could I just hack it up enough to fit onto my current (86) harness?

 

[xj92]

Should I go get the full harness, or just the pieces (I have great electrical skills anyways) that don't work?

I'm not that great with electrical stuff if it gets complex, so I think it's better to just use the harness. If I could have easily bought an MJ harness, I would have done that also since the splicing is taking too much time now. That's just me though.

 

[Mr_Random]

I'm not that great with electrical stuff if it gets complex, so I think it's better to just use the harness. If I could have easily bought an MJ harness, I would have done that also since the splicing is taking too much time now. That's just me though.

I'm still having too much trouble tracking down exactly what I need, mind you I've only really done a couple hours' research studying the various diagrams for the YJ's and XJ's, but dang...

Anyways, I took a peek under the dash of my XJ, minus all the stupid splices the previous owner did, it looks like everything should go together rather well if I can find what couple plugs I need to splice over to my old harness from the YJ's.

I think I'm gonna leave these problems for later, or sort them out while I make more money and buy more conversion parts.

I still need;
Fuel pump/tank (probably pull it all off a junk yard XJ)
t-stat housing (JY 4.0 will work, plus CTS)
Crank PS
Cam PS
Newer distributer
4.0 TB
TPS
(missing any sensors there?)

I need to research;
More on how I will make my A/C (very important, as you know) work with the engine harness (YJ didn't have A/C).
Which plugs need to be spliced over
Whether I can just weld my current exhaust manny's EGR tube shut and whether the O2 sensor will fit in it for now.
... and probably some other things...

Since my power steering pump is dying, I think I may get the following;
Upgraded alternator
New power steering pump
New A/C condensor
4.0/2.5 timing chain and cover
4.0/2.5 water pump
... and whatever else is needed to change to the newer (smaller) pulleys, so I can then run an electric fan and not worry about clearance.

Wow... and that's only the list for electrical/engine things I want/need...

Oh, and if I get this done before your MJ is done, I'll gladly (test) drive up to scottsdale to help you wire the MJ up! At not even 18, I have basically six years of extensive wiring experience... my dad's an electrician and I can do just about everything he can, plus some other odd specialized things that I picked up in electronics classes in high school.

 

[xj92]

As far as the hole in the exhaust manifold for the EGR tube, I just cut a small plate out of 1/8" metal, drilled 2 holes, and bolted it on with the existing gasket to seal up that hole. Time will tell if that works good or not.

 

[Mr_Random]

As far as the hole in the exhaust manifold for the EGR tube, I just cut a small plate out of 1/8" metal, drilled 2 holes, and bolted it on with the existing gasket to seal up that hole. Time will tell if that works good or not.

well that's a relief! I didn't think about that as a solution!

Is my sensor list looking good to you?

 

[xj92]

I don't remember all the sensors, I just tried to grab everything attached to the harness when I bought it. Some things to remember:

• Speedometer? If you're converting the gauge cluster and all that, you'll also need the electronic speedometer thing that replaces the speedo cable in the transfer case or transmission housing.

• Temperature sending unit at the back of the head. Not sure if it's a different plug or not. I had to get a new one cause the top is plastic and breaks easily when trying to get to the valve cover bolts, fuel rail, etc.

• If you want to hook up the funky sensor in the power steering line, make sure you get the right line from a 4-banger with the threaded part.

I figured out why I wasn't getting fuel pressure. I had the lines switched . Now fuel is leaking out through the fuel pressure regulator o-ring. Gotta love junkyard builds. Time for a new o-ring kit on that. I still need the 91+ fuel pump too. It sounds like it's going to start now but doesn't quite make it. Maybe due to not enough fuel pressure? I haven't checked anything electrically yet to make sure I have spark, etc.

 

[Ghost]

I don't remember all the sensors, I just tried to grab everything attached to the harness when I bought it. Some things to remember:

• Speedometer? If you're converting the gauge cluster and all that, you'll also need the electronic speedometer thing that replaces the speedo cable in the transfer case or transmission housing.

• Temperature sending unit at the back of the head. Not sure if it's a different plug or not. I had to get a new one cause the top is plastic and breaks easily when trying to get to the valve cover bolts, fuel rail, etc.

• If you want to hook up the funky sensor in the power steering line, make sure you get the right line from a 4-banger with the threaded part.

I figured out why I wasn't getting fuel pressure. I had the lines switched . Now fuel is leaking out through the fuel pressure regulator o-ring. Gotta love junkyard builds. Time for a new o-ring kit on that. I still need the 91+ fuel pump too. It sounds like it's going to start now but doesn't quite make it. Maybe due to not enough fuel pressure? I haven't checked anything electrically yet to make sure I have spark, etc.

Have you priced them? I do have mine left I thought I had sold it. I guess it was the 96 one that I sold. Pm me an offer if you want the whole unit.