89 Cherokee Laredo fuel system problem?

[osiris151]

Just bought a jeep that seems to be having a bit of a problem. It's and 89 Cherokee Laredo 4.0L Straight-6 w/ Auto Trans.

Okay, so this beast starts up fine and drives at a low speed just fine, but once I get going and try to kick a few rpms into it it wants to sputter, miss, and occasionally backfire. When it does this it has no acceleration and just rolls slowly until you get the rpms back under 2k. I wanna say it's fuel related, but I'm not sure. Anybody have any ideas before I make the mistake of replacing things that aren't part of the problem?

Any help is much appreciated.

[easy151]

u must have cloned my jeep i have the same exact problem....
i have changed...
1. spark plugs, the wires look ok
2. fuel filter
3. air filter

i have and just need to replace valve cover gasket causing it's leaking like a race car and i read somewhere that a leaky cover can cause oil to get in the chamber and cause hesitation. i ordered the rear vacumm harness cause mine is duck tape and home rigged back together. Next i will be moving to the egr valve or crank position sensor.

[Saudade]

There is a port on the forward end of the fuel rail for testing fuel pressure. Get a gauge and attach it. Next to the port, on the very end, is the fuel pressure regulator. There is a vacuum line attached.

Connect the gauge, start the Jeep. The fuel pressure should read about 31 psi. While the Jeep is still running, remove the vacuum line and hold your finger over it to plug it, the fuel pressure should jump to about 39psi. Put the vacuum line back on and the fuel pressure should drop back to 31 psi. If not, you have a fuel pressure problem.

Search the site (or even Google) for Renix Sensor Diagnostics. You'll find out how to test the various sensors as well.

[osiris151]

kthx... I'll give it a look.

[discnik]

If it is all origonal exhaust, you may want to take a look at your catalytic converter.

Just a thought

[ironman2712]

what is rpm when idle?oil presure when cold starded and after 2-3 min when warm?it may be injectors jammed or at least one of them-you cold try to add "fuel add"cleaner into your tank, but you would have to drive like senior until you empty the gas tank, also check air filter and breather lines (vacum lines arround valve cover-esspecially the one at the back going to intake jams often with oil vapour) and cat.converter may have broke arart-simply disconect it
If all these won't help-prepare manual, tools and a lot of tea.....

[gtmud]

Could be fuel related, like Saude advised, also with the gauge attached, drive it, under hard acceleration the pressure should go up to about 40 psi, if it drops, then you found your problem, also check the fuel filter, replace it if it looks old, could be stopped up. AS far as the leaky V-cover causing it, NO, not unless you have crappy plug wires and its running oil over them and shorting them out. Also check your CPS sensor, make sure its mounted securely to the tranny housing, and the wires aren't contacting the exhaust manifold. You can also ohm this sensor out.