90' XJ Turns over but doesn't start WTF

So my 90' XJ. Turns over fine, has over half a tank of gas. Has oil. but won't start. just keeps turning over.
Is it my CPS?
I had this problem a few months ago. and it was the CPS. and that was a PAIN to replace.
Anyone have any other suggestions?

http://www.naxja.org/forum/showthread.php?t=101119
http://ww[URL="http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm"]w.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm[/URL]

Start reading! :read:

my 1990 had bad wires going to the starter solenoid then my other 90 had a bad coil pack and cps

Another thing to check is to make sure that when you replaced the CPS a few months ago that the wiring for it is not laying on the exhaust. That is a pretty common mistake and it would make sense. Yet again, Renix rigs (87-90) make you work constantly for their love and affection. :repair:

first off - test the CPS - I beleive it should have between 250-350 ohms of resistance across the two pins on the plug (cant remember exactly but usually a bad one will read infinite resistance) ok, if thats good - do you still have the little fuel pump resistor on the inner fender next to the air box? - if so, get rid of it so you never have to worry about that - these are 2 things that haunted me and are VERY simple to get out of the way on your quest to making that renix rig run

It is possible that the crank sensor you installed a few months ago failed. It happens; called "infant mortality". Test it to be sure.

Need to see what you're missing, fuel or spark. Once you know that, much easier to isolate. Try spraying some starting fluid into the intake. If the engine starts and runs momentarily, you have a fuel delivery problem, not a spark issue.

Crankshaft Position Sensor: Common Symptoms if bad:

*Both the fuel gauge and or voltage gauge may not work/display

*You will have no spark. Fuel pressure may check okay but fuel won’t get to injectors

*Crank sensors can be intermittent; "thermal failure" is pretty common. Means that the sensor fails when engine gets hot, but works again when cooled back down. Be aware of this when testing as if you have a sensor that suffers from thermal failure, it will probably test GOOD as soon as it cools down.
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CPS TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1

Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.


Test # 2

You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

If not the CPS, the TPS, starter itself (had that one, would crank, but not at enough speed for the computer,) a Neutral safety switch - either the one on the column or in the AW4 if equipped, and don't forget the fuel pump. Check by running in the ON mode before you hit START, you should hear it pump up and stop.

As you eliminate each by proving it good, it narrows down the culprit.

Make sure the coil wire's ok - all the old school stuff needs to be right, too.

My 89 is refusing to start as well. Its been sitting for a week or so, and now its buried under 3ft of snow. I'll probably dig it out this weekend and start chasing sensors myself, starting with the CPS.

have you checked for fuel and spark? that's the first place to start.

Not yet. I hit the shraeder valve after cranking and just a little squirt, so I'm suspecting fuel pump. I just unburied it this evening and stuck it on the battery charger. Weather permitting, I'll start messing with it tomorrow. Maybe stop in town and borrow a fuel pressure guage.

Pick up a can of spray start too. If it runs on spray start, you have spark, but no gas.

I also had Thermal Failure on a new CPS. I could pour water on it to cool and the engine would keep running, stop water and the engine stopped. (but if you're buried in snow that may not be a valid test).
I tested the CPS by heating it in a 200 degree oven and checking the resistance, not working. So it got exchanged.

VDUB, what did you do with the resistor by the airbox? just splice the wires together?

Read the no start thread in the FAQ section

OZNAD said:

VDUB, what did you do with the resistor by the airbox? just splice the wires together?

Click to expand...

yeah, you just unplug the 2 orange wires and cut the ends off them strip the wire and connect them then tape em good or better yet heat shrink tubing

old_man said:

Read the no start thread in the FAQ section

Click to expand...

See post #2