running ritch, low power

the 89 is running not so great.

Starts, runs, idles fine. Just uses lots of gas and the tailpipe is black as coal inside.

Figured O2 sensor is the first stop, darn thing is gonna be a booger to get out!

What else should I look into?

Probably the 02 Sensor. It tells the comp what amount of fuel to dump in. Look for fuel fouled plugs too, maybe all the fuel isn't getting burned too great.

Map, MAT, coolent temp, egr,cat plugged up.

Look for vacuum leak in the map sensor vacuum line. That's where mine was. Of course if you've been running rich you need to change the O2 sensor anyway.

Does the Renix system read coolant temp?
Will check the map vac.
No cat on this rig.

andyr354 said:

the 89 is running not so great.

Starts, runs, idles fine. Just uses lots of gas and the tailpipe is black as coal inside.

Figured O2 sensor is the first stop, darn thing is gonna be a booger to get out!

What else should I look into?

Click to expand...

The O2 sensor is the most likely culprit. Check the voltage coming from the signal wire. Since the engine's running rich, it should be close to 1.0v. If it's close to 0.0v instead, that means the sensor's giving false information to the ECU and therefore needs replacing.
Other sensors that could go south, causing the engine to run rich but otherwise run well, are the coolant temp. sensor (lower part of radiator on driver's side in Renix 4.0) and the manifold air temp. sensor. Check the resistance across these sensors (backprobe the wires going to them) when the engine's hot. If it's more than 1000ohm, the sensor's knackered.
Another thing you need to check is the voltage across the TPS with the throttle fully closed and again when fully open (engine off). You may need to adjust it.
A bad MAP sensor would also cause difficult starting (or no start at all) and poor running.
If you still don't have any joy after checking all these items, check the fuel pressure at the injector rail. It should be ~30-32psi with the vacuum attached to the fuel pressure regulator. If it's much higher than that, you've probably got a break in the regulator diaphragm in which case, you'll need to replace the regulator.

Found my renix service manual last night and did some reading. It has test procedures for all the sensors. Now just to get to work on troubleshooting them.

BTW the sensor in the radiator controls the electric fan. The computer temp sensor is in the block on the drivers side. This according to the FSM.

Any tips on getting a stuck O2 sensor out. Might heat the header with the torch is my best guess. Thing doesn't want to budge.

before you go taking it out check with the dealer about an 02 sensor recall. It had never been done on my 87, and even though it's that old they did the recall. Free 02 sensor, and I didn't have to deal with pulling it.

That would be nice.

But its an hour drive to the closest dodge/jeep dealer and I already have a sensor I bought for another project a few years ago.

click here and enter in the last 8 characters of your Jeeps VIN to see if the recall has been performed on your Jeep yet.

tested the sensors according to FSM

ambient temp right around 70 deg with engine cold:
intake air temp sensor 3800ohms
engine coolant temp 3800ohms

Map sens:
with engine off 4.8v
with engine running cool at idle 1.9v, after a couple of minutes it was reading 1.7
If I goosed the throttle it would jump up to 4v or so (hard to see without a peak hold on my meeter.

So it seems those all look pretty spot on. FSM says 1.0-1.5 on the map though? I didn't have a vac meeter to check the manifold though.

All those numbers are within spec so that leaves the O2 sensor and the fuel pressure regulator as the most likely culprits. Check the O2 sensor voltage and the fuel pressure.

WobblesXJ said:

Look for vacuum leak in the map sensor vacuum line. That's where mine was.

Click to expand...

ok so where is the map sensor vacuum line?? mine is burning fuel at an expontial rate. ( i already replaced the o2 sensor)

When i lifted it expected bad gas milage but 10 mpg sucks. i only put 33's on it. it has 3.55's.

and where is the fuel pressure regulator?

I don't have a guage to put on the rail.

Switched out the 02 sensor the other night though and it is running better... at least I think it is, could just be the placebo effect.

Starts quicker and has better power. Temp guage also reads slightly warmer, to me would point towards getting a leaner burn.

Just throwing this out there, but maybe check to CPS too. I know the big sign is for the Jeep to completely die, but there was a thread last year on another board where the CPS (CKP), which tells the timing, was off and created a little idle/hesitation. May affect richer conditions?? Most likely not a issue. Also, someone stated after 100,000 it should be changed anyway as it is magnetic or something. Hope you find it. I have heard of people getting bad O2 sensors from parts...