Question about timing

So. I want to confirm something.

on the 4.0l
or I guess any engine.

At cylinder 1.
top dead center.
where should the distributor rotor be. in relation to the point on the cap for spark plug one.

Im finding conflicting things.

One set of people say 0.002th past the post for plug 1. (clockwise)

other set say 0.002th behind the post for plug one (counterclockwise)

Can someone confirm this.

When you are looking at the top of the distributor the rotor rotates clockwise, engine cranking or running. If you are looking at the front of the motor the harmonic balancer also rotates clockwise.

Most all XJ's I've looked at the rotor ends up past (mostly) number one on initial setup. The HO and the Renix end up in a little (slightly) different position, but basically the same. The only way to seriously screw it up is to have it in the wrong tooth, cam distributor drive gear or possibly the number one pole on the distributor cap wrong (wrong firing order).

I've never measured anything but the Renix. I've never had to adjust a HO, just had to get it in the right tooth on the distributor drive.

The ECU or PCM adjusts timing. So initial setup just needs to be close (not a full tooth off), not exact. The exception is some of the early Renix.

What exactly is your issue, what year XJ?

This is only for the Renix 87-90

And I think the number you are looking for is 0.020 (twenty thousandths), not 0.002 (two thousandths).

8Mud said:

When you are looking at the top of the distributor the rotor rotates clockwise. If you are looking at the front of the motor the harmonic balancer also rotates clockwise.

Most all XJ's I've looked at the rotor ends up past (mostly) number one on initial setup.

I've never measured anything but the Renix. I've never had to adjust a HO just had to get it in the right tooth on the distriubtor drive.

The ECU or PCM adjusts timing. So initial setup just needs to be close (not a full tooth off), not exact. The exception is some of the early Renix.

What exactly is your issue, what year XJ?

This is only for the Renix 87-90

And I think the number you are looking for is 0.020 (twenty thousandths), not 0.002 (two thousandths).

Click to expand...

ohhh if only it were that simple....
Had to cut the ears off the distributor to get it even close. I just want to make sure.


I have a 92 xj 4.6 stroker.
I have the comp cams cam and it advances the timing by +3 degrees.
and yella terra 1.6 roller rockers.
Ive been having roaming idle ever since I rebuilt her 8 years ago.
Recently I have had some more time to play with it. and I Want to finally fix it.
I now have all my fuel pressure issues solved. (waivered from 35-30 randomly. It was the regulator)
Spark is really good.
so that leaves timing and sensors.

I have replaced.
TPS.
CPS.
IACV.

gone through 2 engine rebuilds.

and still she waivers from 400 -700 rpm all day long.
at first I summed it up to the lobes on the comp cam. but I am not so sure. Because its not consistent. sometimes she idles fine. sometimes she is terrible.
So I want to make sure my timing is perfect.
My thinking is. Regardless of where the cam advances it. Top dead center should be the igniting point. So Im starting here. And working fowards.

Once I have checked the timing.
Next on my list is
Map sensor.
then not sure from there.

But. To confirm. Looking at the picture you are saying it is 0.02 past the post clockwise ?

blu3fan said:

I have a 92 xj 4.6 stroker.
I have the comp cams cam and it advances the timing by +3 degrees.
and yella terra 1.6 roller rockers.
Ive been having roaming idle ever since I rebuilt her 8 years ago.
Recently I have had some more time to play with it. and I Want to finally fix it.
I now have all my fuel pressure issues solved.
Spark is really good.
so that leaves timing and sensors.

I have replaced.
TPS.
CPS.
IACV.

gone through 2 engine rebuilds.

and still she waivers from 400 -700 rpm all day long.
at first I summed it up to the lobes on the comp cam. but I am not so sure. Because its not consistent. sometimes she idles fine. sometimes she is terrible.

Click to expand...

I've never had to measure an HO. I remember reading someplace that initial timing at the harmonic balancer degree marking should be around 14 degrees, never checked it myself.

Two things I've had that caused a hunting idle were a vacuum leak. Motor gets some strange O2 readings and is constantly trying to adjust. Maybe check the manifold vacuum and see what is happening? Vacuum leaks rarely happen in the center of the manifold, most of the vacuum connections that leak are off center, so some cylinders can be a little lean (to much air), seems to drive the PCM nuts trying to adjust. It can show up as different colored spark plugs, some lighter than others.

****TPS grounds. The lower the OHMs in the ground circuit the better. Wiggle the harness to see if their isn't a bad splice or a vibration fatigued wire core broken under the insulation someplace (happens more than you'd think).**** I even jumped the TPS gounds straight to my battery negative as a test, the way I found my harness issues. Stripped back a little insulation on the TPS ground and made me a jumper with a couple of alligator clips. One other issue I had was a dirty TPS connector, drove me nuts, somebody had sprayed WD 40 (I could smell it) in the connector.

Usually when your initial distributor setup is wrong, you run out of timing either top end RPM or low RPM. There is an envelope the timing is designed to operate in and the PCM adjusts.

What did the guys over on the modified board have to say? I always had enough trouble trouble trying to keep my stock XJ running well, I never had the guts to try and modify it any.

blu3fan said:

But. To confirm. Looking at the picture you are saying it is 0.02 past the post clockwise ?

Click to expand...

That is for the Renix, my 96 actually overlaps the number one pole a little but mostly past. I don't actually know if that is from a worn timing chain and/or worn cam distributor drive gears. Or it is normal, it runs fine so I haven't messed with it.

Have you checked your snyc sensor. I've never had any issues with mine, but have heard bad things happen when it is out of adjustment.

Something else to look at is the small orifice tubing from the rear of the valve cover. This feeds air to the intake and can cause issues if it is plugged (usually low idle).

That hunting at idle thing is fairly common with the Renix, not so much with the post 90 HO.

All vacuum lines are new.
no leaks.

its electrical.
or timing.
I know this much.


sync sensor ?
is it called something else ? have not seen this.
pretty sure the 92 is
map
iacv.
tps
cps
distributor
for idle.
i think thats it...

It is called the cam position sensor (sync sensor on older models). I don't think the 92 cam position sensor is adjustable, don't know or sure. The test is easy, might as well check it. At least do a good visual check and make sure the magnet isn't loose.

You might want to have a look at the purge solenoid also. If it is sticky it could cause issues.

Just some ideas.

Ill take a look.
Did some research. The sync sensor you are talking about I think is built into the distributor.
purge solenoid is the canister on the passenger side of engine bay right ?

Well that almost solved it.
Running so much smoother.
I was off by about 2-5 degrees/
Barely moved it. but it was enough
idle is a tad low still. but way way way smoother.
thanks

Meh.
Or not.
when cold she idles at 300rpm with new distributor position.
looking into sync sensor now.