cherokee timing????
- Thread starter mburian02
- Start date
1077106
As far as I know the timing is controlled by the ECU (computer) and can not be adjusted. If you try to move the CPS one way or the other the advance on the distributor is going to go way out as the ECU tries to adjust it. I would not recomend trying this. There are some after market ECU's that will change the performance if that is what you are trying to do.[addsig]
As far as I know the timing is controlled by the ECU (computer) and can not be adjusted. If you try to move the CPS one way or the other the advance on the distributor is going to go way out as the ECU tries to adjust it. I would not recomend trying this. There are some after market ECU's that will change the performance if that is what you are trying to do.[addsig]
MudderChuck
New member
1077283
There is a way to adjust the timing on an 87, initial timing that is. But it is pretty much a pain and rarley necessary.
On my 88, what was really acting like timing issues, turned out to be, a combination of things. Plugs, wires, distributor cap, filters, dirty electrical connectors and slightly plugged injectors, with a partially plugged exhaust and a possible loose timing chain.
If your getting a serious cross fire, at mid RPM´s (around 2000) with a steady pedal (moderate vacuum). It may be crossfire, but is probably something else.
One major improvemnet I had, was to clean all the die electric grease out of the distributor pick up plug. really made a noticibale improvement.
A new air filter, was also a major improvement.
You can check your initial timing fairly easily. All you need is an old distributor cap. Cut a hole after the number one electrode in the cap, so you can see the rotor. Set the motor up for TDC, number one cylinder, align the timing marks. The rotor should be past the electrode, with the trailing edge of the rotor about .020 past the electrode. The timing mark for the 4.0 is hard to see, on the inside of the main pulley, I usually move the mark to the outside (chisel) and mark it with nail polish (my daughters not mine :roll: ).
If my explanation is hard to understand, I can try a better explanation.[addsig]
There is a way to adjust the timing on an 87, initial timing that is. But it is pretty much a pain and rarley necessary.
On my 88, what was really acting like timing issues, turned out to be, a combination of things. Plugs, wires, distributor cap, filters, dirty electrical connectors and slightly plugged injectors, with a partially plugged exhaust and a possible loose timing chain.
If your getting a serious cross fire, at mid RPM´s (around 2000) with a steady pedal (moderate vacuum). It may be crossfire, but is probably something else.
One major improvemnet I had, was to clean all the die electric grease out of the distributor pick up plug. really made a noticibale improvement.
A new air filter, was also a major improvement.
You can check your initial timing fairly easily. All you need is an old distributor cap. Cut a hole after the number one electrode in the cap, so you can see the rotor. Set the motor up for TDC, number one cylinder, align the timing marks. The rotor should be past the electrode, with the trailing edge of the rotor about .020 past the electrode. The timing mark for the 4.0 is hard to see, on the inside of the main pulley, I usually move the mark to the outside (chisel) and mark it with nail polish (my daughters not mine :roll: ).
If my explanation is hard to understand, I can try a better explanation.[addsig]
1077302
On the new distributor caps there is a small plug after the #1 contact point. I will assume this is so the rotor is visible at or near TDC. Now that you can see it and have the marks on the pulley lined up. How do you make any sort of change to advance or retard the timing? I thought that the ECU would continue to pick up rotor position from the sensor in the distributor and TDC position from the CPS and adjust it on it's own.[addsig]
On the new distributor caps there is a small plug after the #1 contact point. I will assume this is so the rotor is visible at or near TDC. Now that you can see it and have the marks on the pulley lined up. How do you make any sort of change to advance or retard the timing? I thought that the ECU would continue to pick up rotor position from the sensor in the distributor and TDC position from the CPS and adjust it on it's own.[addsig]
1077343
never thought the nail polish was yours but if it is i guess that is your business.... :lol:
and yes it makes perfect sense,is what happened is the guy that owned it before me had pulled the distributor out , not a smart move if you don't know what you are doing, i think i finally got it buy dropping the distributor about 50 times (toothe by toothe)
man that was one long day.....thanks for all the input[addsig]
never thought the nail polish was yours but if it is i guess that is your business.... :lol:
and yes it makes perfect sense,is what happened is the guy that owned it before me had pulled the distributor out , not a smart move if you don't know what you are doing, i think i finally got it buy dropping the distributor about 50 times (toothe by toothe)
man that was one long day.....thanks for all the input[addsig]
MudderChuck
New member
1077458
I havn´t removed the distributor in a 4.0 for awhile, but one thing I´ve managed not to forget, after the last time. Was don´t move anything with the distributor removed. Been there done that. Getting the oil pump drive and the gear teeth lined back up and having the distributor drop in at an angle is sure enough a pain.
I´m not absolutly positive of this, but at a guess, initial timing, allows the computer to advance and retard the timing, from a known starting point and maybe between max advance and max retard. Using imput from the throttle position sensor, the MAP sensor. 02 sensor and the knock sensor. The CPS probably also figures in there as a reference point.
The book says, the only way to adjust initial timing, is to cut, the positioning tabs off of the distributor shaft housing. There is a recall, on the 88 XJ, that talks of cutting the positioning tab, to adjust initial timing. if I ever decide to cut the positioning tab off of the distributor, I´m sure gonna put a couple of notches, in the shaft housing and the block, so I can get it back where it was, if needed.
I can hear alot of slap in my timing chain, I think, before I´d change initial timing, I´d replace the chain (and gear to an adjustable) and degree the cam.[addsig]
I havn´t removed the distributor in a 4.0 for awhile, but one thing I´ve managed not to forget, after the last time. Was don´t move anything with the distributor removed. Been there done that. Getting the oil pump drive and the gear teeth lined back up and having the distributor drop in at an angle is sure enough a pain.
I´m not absolutly positive of this, but at a guess, initial timing, allows the computer to advance and retard the timing, from a known starting point and maybe between max advance and max retard. Using imput from the throttle position sensor, the MAP sensor. 02 sensor and the knock sensor. The CPS probably also figures in there as a reference point.
The book says, the only way to adjust initial timing, is to cut, the positioning tabs off of the distributor shaft housing. There is a recall, on the 88 XJ, that talks of cutting the positioning tab, to adjust initial timing. if I ever decide to cut the positioning tab off of the distributor, I´m sure gonna put a couple of notches, in the shaft housing and the block, so I can get it back where it was, if needed.
I can hear alot of slap in my timing chain, I think, before I´d change initial timing, I´d replace the chain (and gear to an adjustable) and degree the cam.[addsig]
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