Newbie To Jeep Question

Have a 1989 laredo 4.0 xj automatic stock 220,000 miles

Sometimes when you crank it it takes a while to start and then shuts off
keep cranking it and it will start and shut off then it might crank up and idle fine till you touch the gas then cuts off then it may crank up and rev like 2500 rpm and stay there then you cut it of it might crank and run normal it is wierd because it is not the same thing every time i did look for vacume leaks this jeep has lots of hoses
any one had this problem before and might help me find a solution Thank you

1. Renix XJ.

2. Engine has to "spin up" to 300 RPMs before the CPS/CKP crank sensor will generate a signal to the ECU to fire the spark plugs.

3. Super sensitive to poor grounds--grounds need to be renewed periodically to keep things functioning. There is ONE single unibody ground, a POS braided strap from the rear of the head, driver's side, to the firewall. Replace it with a 4 or 2 ga cable. Clean the mounting surfaces down to bare metal, treat with an anti-corrosion material (any paint/hardware store) and make the connections TIGHT. Also, there are CRITICAL engine management grounds at the dipstick tube--yep, the dipstick tube. Make sure those are stripped to bare metal, treated, and tight.

The coil is attached to the ICM--ignition control module--with clips that become corroded. Guess what? Yep, take it apart, clean, treat with anti-corrosion and here use a little dielectric grease, reassemble.

Your battery and its cables in top-notch condition? If the system voltage drops below 9 volts the engine management goes to hell. Better clean both ends of those main cables and test the cables with an ohm meter--their resistance should be near ZERO.

Get that stuff done, post back with results.

Don't the Renix motors have a tendency for the manifold nuts coming loose? That supposedly idles them up around 2000

jbmoose said:

Don't the Renix motors have a tendency for the manifold nuts coming loose? That supposedly idles them up around 2000

Click to expand...

Common problem with all the 4.0s, not just Renix years. Generally the Belleville washers flatten out or get lost: http://www.bellevillesprings.com/

I don't think it is consistently hitting the high idle, which on the Renix (real time--no memory) usually indicates poor grounds/TPS/IAC issues. We need to hear more from the OP.

what does renix mean

RENault bendIX.

Yep, French Jeeps.

This refers to the early years RENIX fuel injection/ignition system.

Well I checked all the grounds and cleaned them even oil dip stick tube

Still doing the same I hate this Jeep

one more quetion it has o2 sensors
is there a check engine light on these

Renix XJs have a HEGO timer--a one time use box that expires at 60,000 miles if memory serves me right, then it turns on a MAINT light. Renix doesn't store codes, strictly real-time system.

The HEGO timer is under the dash, driver's side, and if memory serves me right it is a clear plastic or smoke colored plastic box with a couple wires plugged in it--just remove the plug and forget about it.

Of course, you need to remember to change the o2 sensor on occasion, about every 60k miles.

could the 02 sensors cause my problems there is no light on at all

bakerboys said:

could the 02 sensors cause my problems there is no light on at all

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should only have 1 o2 sensor on an 89. no, it should not cuase your problems.

first, check that the ground strap is in good condition or just add anoither one. sometimes the strap on the firewall looks good, but just crumbles apart when you disconnect it from the firewall.

next is to clean the throttle body and IAC.

adjust/check the tps input and output voltages.

test the MAP sensor and make sure the vacuum line is connected proporly.


a renix 4.0 has not check engine light and to diagnose problems, you need to test the electronics/sensors with a multimeter.

89xj said:

should only have 1 o2 sensor on an 89. no, it should not cuase your problems.

first, check that the ground strap is in good condition or just add anoither one. sometimes the strap on the firewall looks good, but just crumbles apart when you disconnect it from the firewall.

next is to clean the throttle body and IAC.

adjust/check the tps input and output voltages.

test the MAP sensor and make sure the vacuum line is connected proporly.


a renix 4.0 has not check engine light and to diagnose problems, you need to test the electronics/sensors with a multimeter.

Click to expand...

I agree. I would hit all the grounds and renew them--strip to bare metal, treat with anti-corrosion material, make them TIGHT, with particular attention to the grounds at the dipstick tube and the POS braided strap from the rear of the head to the firewall--replace it with a 4 or 2 ga cable.

Post back what results you get.

check the CPS. just a thought, it was giving me problems a while back.