Hey guys,

Mystery problem I've been fighting for months now. Just thought I'd see if anyone has some ideas, as I've seen similar posts but not quite the same enough to run by.

Starting engine: I HAVE to start it right away, no priming the lines, or it may give me trouble, and when it runs will run realllllly high idle, 2500+. Start right away, runs fine. Note: I tested the fuel regulator, it seems to work ok, as the line pressure changes when the vac line is unplugged.

Idle: Idles fine most of the time, however the odd time i start it its kinda hesitating until i drive away, then its fine again.

Running: sometimes it drives fine for a while, a few hours, a day, whatever. Sometimes it likes to bog down, missfire at SPECIFICALLY 2000 rpm, and shoot down to about 1500, 1200 ish, pick back up and do it all over again. If i was able to get it to go past it, it would drive fine, except that specific rpm.

TODAY, its a lot worse. I went wheeling yesterday, only minor, got a lot of dirt all over the place etc. Now, it wont even get out of the driveway as i cannot get it to run past 1500 rpm before it bogs down, and wont go past it. Missfire as well this time.


What ive done to try and fix it..

Changed EVERY sensor, except the CAM position sensor.

that is, Ive changed..
- o2
- Crank sensor
- map
- tps
- idler
- knock sensor
- coolant temp sensor

- ign coil
- dist/cap/wires
- plugs
- injectors
- ecu (ran even worse with the other ecu)

Oh, and I did do a fuel pressure test.

40 without regulator, 32 with. drops down to zero over night, but that shouldnt make this issue quite this bad, should it..?




Anyone got any other ideas?

thanks a lot for the time.

 

Grounds need to be cleaned, dirty injectors, water in the distributor? Just look at every wire and plug and make sure there connected.

 

Changed the injectors, theyre brand new. It idles fine though most of the time, then wont run high rpm, thats the part that throws me off. Checked the other things you mentioned, all is in check. Brand new grounds & connections!

 

change your fuel filter recently? if so, is it in the right way? (you sure?)

try do a compression test. see what results you get.

any funk in your oil? (like coolant?)

ALL vacuum line are good? done a CLOSE inspection of them?

just putting ideas out there sir!

cpnwrench

 

Fuel filter was done recently. I removed half the vac lines permenantly to eliminate a lot of possible leakage areas, however have not yet checked the rest thoroughly - would that really affect high rpm and not the idle? Im not sure?? New head gasket as of 2 months ago as well. However, this issue only came up when I did an engine swap recently - old head, replacement used bottom end. I heard another possible is slack in the timing chain?

Oh, and another thing i noticed..

When I go full throttle, it will occasionally BACKfire, and also seems as if its only properly firing on the first 3 cylinders, missing 3, then firing 3, maybe a backfire, etc.

 

could also be distributor is going bad.


cpnwrench

 

First off, did you adjust your TPS when you installed it?

Secondly, have you checked the fuel rail pressure?

 

how do you adjust the tps this is what my cherokee is doing

 

Check your TPS wiring to and from the ECU. Look in the Haynes or Chilton manuals for adjusting you need a voltmeter to read the voltage during throttle changes from the TPS. The manuals will tell you the proper voltage reading for the wiring in the TPS circuit.

 

courtesy of cruiser54....
------------------------

RENIX TPS ADJUSTMENT

Before attempting to adjust your TPS be sure the throttle body has been recently cleaned.
It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

IMPORTANT NOTE: Using one lead of your ohmmeter, probe the B terminal of the flat 3 wire connector
of the TPS . The letters are embossed on the connector itself.
Touch the other lead of your meter to the negative battery post.
If you see more than 1 ohm of resistance some modifications to the sensor ground harness will be
necessary. The harness repair must be performed before proceeding.
I can provide an instruction sheet for that if needed.

MANUAL TRANSMISSION:

RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body.
This manual transmission vehicle TPS provides data input to the ECU. The manual transmission
TPS has three wires in the connector and they're clearly embossed with the letters A,B, and C.

Wire "A" is positive.
Wire "B" is ground.

Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors..
Note the voltage reading--this is your REFERENCE voltage.

Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your
OUTPUT voltage.
Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For
example: 4.82 volts X .17=.82 volts. Adjust the TPS until you have achieved this percentage. If
you can't achieve the correct output voltage replace the TPS and start over.

AUTOMATIC TRANSMISSION:

RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a three-
wire connector, same as the manual transmission vehicles have, and it is tested the same as the
manual transmission equipped vehicles--FOR ENGINE MANAGEMENT RELATED ISSUES.

However, the automatic TPS also has a four-wire connector clearly embossed with the letters
A,B,C, and D.. For the automatic transmission equipped vehicles the four-wire connector
provides data to the TCU.

Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your
REFERENCE voltage.

Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT
voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage.
For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage.
If you can't, replace the TPS and start over.

So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and
the other side feeds the TCU. If you have TRANSMISSION issues check the four-wire
connector side of the TPS. If you have ENGINE issues check the three-wire connector side of
the TPS.

For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is
stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.

 

Be sure to use the Manual Trans procedure for diagnosing driveability issues.

Most other procedures recommend the trans side to check/adjust the tPS. Ain't worth a hoot if the engine side of the TPS is bad.....

 

Tps was installed and adjusted properly to begin with, so that is out. Fuel rail has good pressure as mentioned earlier, 32 at idle 40 before crank, 40 also if I disconnect the regulator.

Cpn you mentioned distributor-- what's the likelihood of that? Possible defective component in it? Sensor? Why will it idle fine-- perhaps the advance is failing??

 

yassir,, componentry wears down, even in sealed environs.

might be cam sensor, could be ign module, dist could be worn out..

might want to take it apart see whats what.....(meaning cam sensor)

1989 though...hmmm, might get bashed by the other guys, not 100% if you have cam sensor.

but its something to check, to make sure!

You look at your injectors? see if there is corrosion/sticking/melted at pintle ends?

just suggestions sir, open frame of mind .......

cheers!

cpnwrench

 

I had the dist cap off the other night and all appears ok, but you know how that is, always can appear fine, sensors are hard to really tell. I have a friend whos bringing me a replacement distributor, whole unit - gonna slap it in and see what happens.

apparently the sensor in the dist. is the cam sensor, I could be researching bad sources though.

The injectors are all brand new, so thats not likely a problem. Its particularely funny when the pedal is WOT, it misses on 3, fires 3, misses 3... or so it sounds like its 3 at a time.

In the meantime, thanks for the ideas. Il be doing lots of wrenching this weekend to find the problem!

 

The camshaft position sensor (also known as the stator or synch generator depending on the vintage of XJ) is inside of the distributor.

00-01 don't have a distributor, but do have a cam sensor where the distributor normally is.