Intermittent Start Problem

I have a friend with a 96 4.0L AW4 and she is having a problem with intermittent starting. The local mechanic has really hosed her out of some serious cash so I'm taking over. OK, so when it doesnt start it just cranks and cranks and no start, so I think about the CPS being bad and replace it.. note it started fine before and after i replaced it but ran much better after i replaced it. When the jeep starts it runs wonderfully and seems perfect but then just randomly it wont start for several days in a row then one day it will just start right up. The mechanic jumped right to the fuel pump and replaced it so its a brand new pump. They also poned her for a new distributor and wiring for it and cap and rotor and plugs 2 different times now. Like I said the CPS has been replaced. Today she called me and told me it wont start again so tomorrow I'm gonna go and try to see why. I'm gonna pull a spark plug and check for spark and work my way back. I dont think they have replaced the coil but im not sure if the coil could cause an intermittent problem like this. I also plan to pull all the grounds and clean really good. I am also going to check and calibrate the TPS while I am at it. She has a whole file of maintenance records she is going to let me look through to see what else has been replaced and I will get back with an update on that and what i find tomorrow. What I need is some advice as to what else to assess when I go tomorrow to check it out. I had her hold the pedal to floor and no start. I'm also wondering about the ignition switch, obviously ground wires, I'll break all of her wire connectors apart and clean. Give me some ideas guys. BTW I have a REnix 4.0L so this wiring, although pretty much the same, is a little foreign to me.

Thanks
Rick

Thanks
Rick

Completely describe the conditions and symptoms of the no-start.

Test, whats missing, fuel or spark ? Is the Check Engine Light on ?

Is there an easy way to test fuel pressure or even that fuel is making it into cylinder

The conditions seem completely random.. I think it happens more when its wet or humid but it also happens in dryness too

Check the MIL codes.
Some less common reasons.
If it doesn't start right up, try starting with a little pedal. The IAC can stick shut and/or the battery can be a little weak and/or the grounds can be a little iffy. All of which can effect IAC function.
Some remote door unlockers are also wired into an ignition disruptor. What it does is keep the ASD relay from closing unless it gets a remote pulse. This is usually a dealer add on for a new vehicle, one of those extras you can opt for. I've also heard it is impossible to replace with the original unit, the manufacturer has gone out of business. Common on export models, also on some domestic models.
Intermittent problems can drive you nuts. It is a lot easier to troubleshoot when it craps out completely.
Check the rear O2 sensor and see if it is trying to cook onto the exhaust.
I usually check for 5 volts at the sync sensor, when a sensor starts crapping out and shorts it can suck down the 5 volt supply circuit to other sensors. It will usually show up as a stored code, but may or may not be the actual problem. I mean it may show a faulty sensor, but another sensor may be causing the faulty readings.

Ok, some quick questions, What is a MIL code, if the idle air controller sticks shut it wont start or will just idle rough and shouldnt pressing the accelerator pedal open the throttle to allow air in for it to start, weve tried holding the pedal down and it still doesnt do anything. By remote door unlockers do you mean like a key fob or wireless remote? this jeep doesnt have that and if it did the key fob is nowhere to be found and shouldnt there be a separt box or something that in the engine bay that I would see? What and where is the ASD relay, what does asd stand for. It did have the check engine light on and when i took it to scan the code (ill post the code later cause its in the jeep) it listed something about possibly a bad Cat converter and about 5 other things but the code basically said that it happended because of a poor running condition. I believe the atleast one of the o2 sensors have been replaced but I'm not sure which one, would a bad 02 sensor keep it from starting or just make it run bad? Finally what and where is the SYNC sensor, i dont recall this sensor on my renix. Where is it and what does it do, does it have another name and do you know of any procedures for testing it? Also I am having a hard time finding a PDF factory service manual for a 1996 but i have found one for a 95 or 97 will the 96 one work or should I keep searching for it or do u know of a source. Would it be worth my time to hook a computer up to it right now while it's not starting? Would it kick me some kind of code that would help me? I don't have one but I could pick one up if need be. Anyone know a really good cheap one? Thanks for your help anyone who can answer these questions or ideas let me know. Thanks
Rick

OK, so today I went and looked at the jeep and I opened the hood and had her try to start it and it stared right up and purred like a kitten (or I guess like a tiger)... again i don't have a chance to diagnose much so I decided to just clean all the grounds really good. I did find a loose spark cap to coil plug, but amazingly the thing was still running fine and I just clipped it back on there and went about finshing up cleaning all the grounds, All the wiring is in good shape, a few years ago she replaced the whole engine bay harness so it all looks in really good shape. I pulled every connector aprart and sprayed cleaner and WD40 in a plugged them back together. And again it started up fine. I encouraged her to have a back up ride and to drive it as much as possible so that we could get it to not start again and figure out the problem. So she took it to store and it started fine both ways. The she went on another errand and it started fine going there but when she came out only a few minutes after turning it off it kinda sputter started then died, then she tried again pumping and flooring the gas and was able to keep it running long enough to back it into a spot and it died again. She tried to start it again and it just cranked with no start at all. After waiting 20 minutes for her ride I her key on the ignition and wait about 10 seconds and then try to start it and it sputter started again then died. I did notice the first time she started it when I was there that i had her turn the key on and wait a sec while I did something and then it started. Is it possible that keying it on for 10 seconds or so is letting something get enough voltage to work vs just trying to start it. Do these symptoms sound familiar to anyone? Any ideas anyone please chime in. I thought about a bad or stuck IAC but I though pressing the throttle would still allow it to start every time but it just wouldnt idle but it doesnt start every time. I mean it could still be stuck but could a bad IAC keep it from starting at all? Anyway, ideas please

on another note, if she can get it started she is going to bring it to me and leave it with me, which will help me a lot as far as having it on hand to trouble shoot with.

A stuck shut IAC will keep it from starting, but if it doesn't start without the pedal (normal), giving it a little pedal will give you a start. *Unless* trying to start it the first time without pedal, you seriously flooded the motor, then it may not start until it has dried out.

ASD relay gets you power to the the coil, the alternator and maybe the fuel pump relay (I'd have to check the wiring diagram to be sure of this).

MIL codes or key codes are when you turn the key from stop to run three times and the engine or maintenance light (whichever you call it) blinks out a code stored int he PCM.

The sync sensor has other names, it is in the distributor. It is just a handy spot for me to test the 5 volt power supply to numerous sensors.

The last time I heard of a periodic no start, it turned out to be the coil. Though that one was heat related, it tended to act up when it was hot.

The door FOB module for mine was above the hump near the accelerator pedal. Mine had an anti theft circuit in it that shut down the ASD relay unless you used the key FOB. Drove me nuts, it would just randomly shut down while driving up the street. Occasionally wouldn't start. It acted much like a faulty CPS. Not all of the key FOB circuits are the same, there is nothing like mine in the FSM, my guess is it was a dealer install. I finally yanked out the module and jumped it, all is well now.

Be careful of WD-40 on sensor connectors, it works fine on 12 volt circuits but the sensors that have decimal points of voltage can have issues with WD-40. I had TPS issues once, the problem was WD-40 in the connector. I'm guessing it was WD-40, it smelled like it, felt oily. I even tried some resistance test with WD-40 out of curiosity, it does/can increase resistance enough to make a difference in very low voltage circuits. "Once burnt twice shy" I keep anything but a quality contact or electrical spray away from sensor connectors.

That loose coil to cap wire could have been your problem, it may have caused a periodic short to ground. Sounds probable. High voltage is tricky, it can be a sometimes thing, the path it takes can change.

Pumping and flooring the gas is rarely helpful with a stuck IAC, you want to give it 1/4-1/3 pedal and hold it there. It is best to give it a little pedal the first time it doesn't start, after a reasonable cranking period (3-5 revolutions). Keep holding the pedal for awhile after it starts. My IAC sticks periodically, my battery is on it's last legs and the wife makes a lot of short trips and the battery never really gets a chance to recharge completely. Probably a combination of dirt and low voltage. The starter sucks down whatever voltage is there and doesn't leave enough voltage for reliable IAC function.

Finally did last night, pictured below was the problem. I guess someone who owned this jeep before me had adjusted the stop on the throttle body because there was some threads on the adjuster screw that had a lot of corrosion then some that didnt have a whole lot. I had to adjust it almost 3/16 of an inch to get the blade to rest flush with the concave surface of the throttle body, so 3/16 of an inch vacuum leak on both ends of the blade. Once adjusted I started the bitch up and she's idlein at 650 rpm. Someone told me not to give up cause it would turn out to be right in front of my face.. so i took a step back and looked at the big picture. I had taken off the TB to clean it.. when i held it up to spray cleaner on it i noticed the light around the blade.. i emailed a buddy of mine and he saw the picture and said its normal... well for some reason i remembered taking the picture and thew it on here an within minutes several people were like dood there is your problem.. i adjusted it and the rest is History.. on to the next thing on my to do list after getting my friends problem here fixed.. I pulled my IAC since I know it's good and i have a spare battery, I feel the symptoms right now with her jeep most correlate with the weak battery/IAC sticking/failing theory. I think this is so because cleaning the grounds made a difference but not enough, i think it just let power flow more freely and helped the charging system to not be so stressed. Today I'm gonna swap out those and see if that fixes it then ill update.

I dont know if a 96 will work differentally but on my old 87 my TPS went out and it wouldnt fire up. If I disconected the TPS it would fire but not run right. If I reconected the TPS it would run good until I shut it off. And before it completely went out. It would crank and start fine. then all of the sudden it would crank and not start. Then it would crank and start again. Its something to try.

Ok, time for an update. Today i went to the non starting jeep.. I decided to take my spare battery that I know is good and to pick up a new IAC just to swap out the IAC and rule it out as the problem. Also I took the battery and tested it, then charged it and tested it and it tested as good. Changing out the IAC's basically did nothing.. But I did a few tests to see about the spark.. The fuel system is solid so I am leaning towards a spark problem since the IAC is functioning properly. So I wanted to test the spark so I pulled the wire off the distributor that connects to the coil to test if there is spark going from the coil to the distributor. I stuck my voltage tester positive lead into the boot between the connector and the boot then i took the negative and put it close to a ground and had her try to start it. I had a blue spark that i could stretch to a little over a quarter of an inch.. I read online that this spark should atleast go 1/2 an inch to indicate that it is strong enough... Then i replaced the wire and pulled a boot off of one of the plugs to test spark from distributor to the plug. As I had her start it i again held the neg close to a ground to see how far i could stretch the arc or if there was one at all. So I had her crank the engine again and i stretched the spark about the same distance and it was still blue then something happened and sll of the sudden the spark got a lot brighter and stretched to almost an inch and even with the spark plug not hooked up by the plug wire the engine immediately fired up and started running on just the five cylinders that still had the wire hooked up to them. The engine proceeded to run the rest of the evening and is parked cooling down now. My interpretation of this is that possibly the coil has a weak spark that maybe gets stronger after it energizes for a while? Im not sure if this is possible or even how a coil works for sure but i think so.. Anyhow, I think that with the weak spark and the injectors still pumping fuel in that it is flooding out and this is what is causing the no start. The first thing i did was switch out the IAC and the battery and try to start and it did start and sputtered and stalled out then wouldnt start again just like it would if it werent able to ignite all of the fuel.. If replacing the coil doesnt work maybe the ASD relay, does anyone have any feedback on any of this? Am I going down the right path? The cap, button, plugs and wires have been replaced twice and the distributor is brand new also but for some reason they did not replace the coil. Also the tab that holds the wire harness connector on to the coil is broken off like someone has unhooked the connector from the coil and broke it in the process. Please let me know if i should try anything else other than replacing the coil.. Its a $30 part so I'm replacing it regardless.

Thanks
Rick

Anyone have any other ideas?

OK, so I have been driving the jeep around for 3 days now, today it fired up great and has been running AWESOME! I drove 30 min to work parked it and when I went out 8.5 hours later it just cranked and cranked with no start. I pulled a plug wire and watched the spark, it did have spark but it looked kinda weak and blue, finally someone helped me crank while I could be in the engine bay and i removed the plug and hooked it up to the wire and held it close to the block. When I had them crank the engine, the spark started small blue and after a few sparks it Got really orange and strong and the engine started with only 5 plugs installed. I replace the coil already, also the distributor, Cap, button wires and plugs have been replaces very recently. So here are the ideas I'm having but I'm not sure, is there something that controls the amount of voltage that goes to the coil? I realize the plug screwed into the block should self ground but could sitting the electrode by the block be providing additional ground to allow the power to flow better, ie could the ground be bad somewhere in line of the ignition system that putting the electrode by the block compensates for? I'm not 100% that the fuel pressure is there although it is a new fuel pump and the problem existed before the fuel pump was replaced and after the fuel pump was replaced. I want to test the fuel pressure and I have a vacuum/fuel pressure tester but I'm not certain the best way or place to hook up the fuel pressure tester in the fuel line. What do you all think could be the issue here. Oh I mentioned this earlier but I have confirmed that the IAC valve works fine and I have replaced the CPS, I have thoroughly cleaned all the grounds and connectors. HELP!

Let me throw this out there and see what you all think. I tested the battery as one of the first things when trouble shooting this problem... It tested good but it is 6 years old.. Today when it wouldn't start, it would crank and crank and as i mentioned in my previous post the spark was there but really weak. So after cranking it for a while I could tell the batter just was getting weaker. So I got my friends car and just hooked jumpers up and let it sit for 20 min and charge. Then I when I pulled the plug to check for spark it started up on the first crank. I drove the jeep home and parked it. It sat for 2 hours then I went and tried to start it. it started and sputtered for about 5 seconds then stalled then i started it and it did same thing then I tried to start it and it just cranked over and over and over and no start. So I have a jumper box that I keep plugged in just in case I have to jump one of my vehicles I have a portable jumper ready. I hooked this up and shazaam the jeep started instantly. What is the likelyhood that this battery could test fine with an battery tester at the parts store but just not maintain enough voltage during startup to power the starter and give a nice strong charge to the spark plugs causing them to not fire strong enough to get the engine started? Has anyone had a problem like this in the past?

Ok, so I replaced the battery, started it and drove it for a week no problems... gave it back to my friend and the second day she had it she drove it somewhere and went in and then when she came back out it just cranked and sputtered and stalled twice and then just cranked utill the battery pretty much died. Then she got someone to jumpstart her and it just cranked. She waited 20 minutes then turned the key and it started right up. I am beginning to wonder if there is a problem with the wiring to the fuel pump or relay. maybe its just getting a squirt of gas then no more hint the sputtering and stalling. This is the second new replaced fuel pump she has had installed so the pump should be good but maybe a wiring or ground issue with the pump... I need to test the pressure when its not starting to rule this out. Anyone have any other ideas.

Rick

Tachometer Bounce
If this Jeep is the same as my 88 and has an OEM tachometer watch it each time you try and start it.
It will start to bounce after the third complete starting revolutions sequence. This indicates the Jeep has switch over from the cranking mode to the starting mode.
Each bounce indicates # 1 sparkplug has just received notice to fire. If this doesn’t happen the Jeep will never start.
Keep us posted as to progress

I also have an 88 and the 96 does have a more advanced computer, although I will still check out the tach.. I will have the jeep back this weekend sometime or early next week. So what if it doesnt bounce, what do you do about it?
Rick