Difference

[Buckey]

What is the differance between a 4.0 L and 4.0 L HO motor???Or is there any differance???

[offroader461]

there is a bunch of differences and to my recollection is all in the fuel injection system.....completley different cylinder head, intake, injectors and throttle body not to mention the wiring harness...hope that helps`

[GirsMJ86]

there is a bunch of differences and to my recollection is all in the fuel injection system.....completley different cylinder head, intake, injectors and throttle body not to mention the wiring harness...hope that helps`

 

and you can easily turn a 4.0 into an HO buy rounding all the parts up. but my 91 seems to love going through regular gas more then my 88 did with just the normal 4.0L. so i run premium in my 91 and get about 425 miles per tank, on a short bed with the tiny tank IIRC.

Alex

[Buckey]

I was just wondering cause I have a 89 comanche and the engine is runnin a little rough,and I have a 91 cherokee with 4.0 HO and I am gonna swap the engines just wanted to know what was compatible for the swap.

 

Thanks

Buckey

[GirsMJ86]

unless the engine in your 89 is really high in mileage (over 300k) it still should be good unless it was abused. what is it doing exactly? might just need a few new sensors or something.

 

Alex

[Pete M]

the engine is runnin a little rough

 

Could you expand on that? You're contemplating a huuuuuge investment in time and money when it could be as simple as replacing the TPS or cat.

[Buckey]

It only idles,nothing else.Won't rev up,won't move other then idle.I have a 91 cherokee that I am just gonna change the engine.I keep thinking maybe a fuel pump or line but not too sure.The only reason I think this is cause it idles,now when my buddy pinches off the one line the pressure gains in the line and it idles a little bit higher but like I said not too sure.

 

Buckey

[GirsMJ86]

It only idles,nothing else.Won't rev up,won't move other then idle.I have a 91 cherokee that I am just gonna change the engine.I keep thinking maybe a fuel pump or line but not too sure.The only reason I think this is cause it idles,now when my buddy pinches off the one line the pressure gains in the line and it idles a little bit higher but like I said not too sure.

 

Buckey

 

sounds like you need to test the pressure the fuel pump is putting out. i am sure there are some other things you can do to fix it but the engine does not sound ruined or needing to be replaced. i would not be sure of the other things you can do since i have not had problems. i am sure other will chime in.

 

Alex

[BIGMASS]

That is egzacaree what my 89 was doing. Would idle like a champ, but wouldn't take any revs. I'd deffinately check yer fuel pressure. I don't think the cherokee sending unit will fit in yer tank anyhow, so you might do the swap and have the same prob.

 

From 88 XJ FSM

4.0L MPFI

1) Remove cap from pressure test port in fuel rail. Connect

Fuel Pressure Gauge (J-37730-1) to pressure fitting. Start vehicle.

Pressure should be approximately 31 psi (2.7 kg/cm) with vacuum

hose connected to pressure regulator.

2) Pressure should be 39 psi (2.74 kg/cm) with vacuum

hose removed from regulator. If fuel pressure is not to

specifications, check for kinks or restricting bends in fuel supply

and return lines. Check fuel pump flow rate. Pump should deliver

minimum of 1.06 quarts (one liter) of fuel per minute with fuel

return line pinched off.

3) If flow is inadequate, check system for plugged fuel

filter or filter sock. Fuel pump flow rate can be checked by

connecting a hose to fuel test port on fuel rail and inserting other

end in clean container.

4) To operate fuel pump, install a jumper wire into

diagnostic connector terminals D1-5 and D1-6. Pinch off fuel return

line to ensure that no fuel returns to fuel tank. If fuel pressure is

still not to specifications and fuel flow is normal, replace

regulator.

[carnuck]

Check the fuel filter first. Then check the TPS and Map sensors. After that, spray ALL the underhood connectors with electronic cleaner.

 

 

Oh, one last thing: You cat's guts may be corking the muffler. (mine did that while cruising at 70. Couldn't go over 15 mph after that and I was on a 70 mph highway with no exits for 5 miles! I had to take a hammer and pound my muffler to pieces then it went like a rocket!)