How to find find #1 TDC

90 XJ 4.0

I know this is a pretty stupid question, but how can I find TDC on the #1 cylinder by myself. I dont have a buddy to crank the engine while I plug the spark plug hole and wait for the compression stroke. My timing is off because I tried to advance the timing one day and screwed up. I got it to where it will start and run, but really shi**y. When its cold, it sputters real bad like I am dropping cylinders while I am trying to accelerate. Once it warms up, its doesnt do it. It will also continuously have a rough idle, warm or cold. I really need to get this fixed. My Emissions Maint. light is on constantly. I dont know if it is because of this, or if it is something totally different. I think the o2 sensor is original w/214,000 miles on it. I know I need to change it, but those things arent cheap. New plugs, wires, rotor, cap, TPS, IAC, clean throttle body, new throttle body gasket, 0 vacuum leaks. The timing is my main concern right now. Any and all help is greatly appreciated.

90red

i think you should really do the O2 sensor before everything else... some important things do cost a few$$.... it made a world of difference in the way my 87 ran at idle..... TDC is easy to find by yourself.. pull all the plugs and put a big socket on the balancer bolt and turn it over with your finger in the hole... you will not mistake the exhaust stroke for compression at all.... i also use the oil dipstick as a "feeler" when it gets at the top of the stroke to find the exact point of transition... mark your distributor with a sharpie marker on the body to mark the #1 spot... the "emmision maint" light is just a milage timer that comes on at 82,000 mile increments. its not triggered by the ECU.. good luck
mike

You go to the auto parts store of your choice and you buy something called a remote starter switch. It's a hand-held push (momentary contact) switch with wire leads and battery clamps. You use that to jump from the battery to your starter solenoid and you can crank the engine from under the hood -- without turning on the ignition.

I think in your case you don't need to find TDC.

You are obviously close to proper distributor indexing, since it runs (albeit roughly when cold) and doesn't backfire.
I *think* your distributor is off by ONE gear tooth.

SOOO, mark where your rotor is now and remove/reinstall one tooth advanced and see if that helps.
(Erring to the side of 'advance' has less potential for backfire than retarding).
If not, then remark rotor position and r/r TWO teeth the other way.
Etc.
Keep the aircleaner on in case of major backfire.

-Rick

PS: If it's been awhile, go ahead and replace the O2 sensor since it makes a world of difference and prolly needs replacing soon anyway.

Thanks Guys

Thanks for all your suggestions guys. I really appreciate the help. I will be working on it tonight and hopefully with your tips I can fix it. Thank Goodness for

90red

Okay, I found #1 TDC. Now how do I figure out what 5 degrees BTDC is. I have the rotor pointing just past the #1 plug on the cap. It does run better, but stills misses at high RPM's, but not nearly as bad. When you say to advance the timing, rather than retard, does that mean move the distributor clockwise, or counter-clockwise past the #1 plug on the cap.

Thanks again for all the help.

the timing on a 4.0L is not adjustable.... its all computer controled... the hold-down tab on the distributor housing has a single hole in it to mount it securley... it's a pain to get it right but when i did this i marked the #1 pole on the housing body then i moved it one tooth in each direction to make suree i got it the closest it could be.. you cant "time" it like an old v-8 where you could just twist the dist one way or the other to fine-tune it with a light..
mike

My guess is that if it runs but misses at high rpms, the problem is not distributor indexing. As sdriptide notes, the computer sets the running timing, and if it's out of range it won't run at all. When I "experimented" with this on my 87, I found that it would not run at all more than a tooth off either way. When it was one tooth retarded, it started perfectly but backfired and wouldn't rev. When it was a tooth advanced, it ran very well but started badly (long cranks, and acting sometimes as if hydrolocked).

when my 89 4.0L got old (around 305K miles ), I had to cut the locating tabs off the distributor and move it a hair to keep it properly indexed.

maybe this is an indication of the timing chain being stretched or having jumped a tooth or something.

you could try a new distributor if it has excessive play in the shaft.

Thanks Guys

I appreciate all the help guys. I think that I am right on with the distributor. I probably need to start looking elswhere for the problem. I am also considering cutting the tabs off of the distributor so I can move it a little bit and see if that helps. I would be stuck if it werent for you guys. Thanks again.

90red