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Wall of text: intermittent no start.

U

unstabl

NAXJA Forum User
Location
Arkansas
This JP is a daily driver for me. I drive 18 miles one way to work and generally about a 40 mile loop daily on the weekend. The off road park is 75 miles away if I head up there. The farm is about 35 miles one way and I’ll head over there a couple times a week as well.


Vehicle:
1991 Cherokee 4.0.


Problem:
Intermittent crank, no start. High idle and rough idle until warm. Occasionally dies while running/driving.


Things I’ve checked/replaced:
CPS is new, TPS is new, IAC is new, throttle body is new and cleaned, vacuum system is tested and good, ASD relay replaced, both temp sensors replaced, new plugs .040" Champion copper, wires, coil, 12V to coil, distributor is a few months old and looks brand new no damage or water signs, O2 sensor is new,


Background:
Running trails at the off road park one day, all day, raining, hot. Parked and went to dinner. 90 minutes after, JP would turn over but not fire and start. Left it until morning. Next morning checked for spark, none. Put on another coil (factory), fired right up and ran perfect for one month. I thought it had a bad coil/coil died.

Got gas. Went inside and bought some sweet tea, Pure Leaf brand. Not the extra sweet, that’s way too much. Back out to the JP and turns over, no fire and start. Swap another coil on (MSD), fires up and runs like a champ. Now I’m wondering why it’s burning up coils.

Drove home. Parked. Next morning turned it around in the yard to pull into the shop and troubleshoot and it dies just outside the shop. Died while driving. First time for this.

So I’m wondering why it’s burning up coils. I pull the coil plug and check for crazy voltage: 12V input. I unplug the battery and ground pos to neg for 30 seconds and leave disconnected for 10 minutes. Still no fire. I swap another coil on, fires right up and purrs.

It’s due for a new set of plug wires and plugs at this point so I pull the old. Plug wires are ohm’d at 43-45K. Champion plugs are at .045" gap. Swap out for MSD plug wires and standard Champion copper plugs at .040" gap. MSD plug wires ohm at 3k. No fire from coil.

On a weird hunch because I am thoroughly enjoying the pain so far, I grab a coil that has previously failed and install it. Fires right up and runs like a champ. Head smacking ensues. Cycle through all previously failed coils and they all work fine.

JP runs about 6 weeks through multiple off road park trips of much hard core banging and 99+ degree 100% humidity weekends and runs like a scalded ape.

I get off work one morning (graveyard) and JP turns over, no start. By now I have already relocated the coil to the fire wall and have a spare coil bolted beside it. So I swap the coil plug and the distributor wire to the other coil. Fires up and runs 10 miles.

Dies going through one of the smallest towns in existence, but fortunately it has a post office. Unfortunately for the people that get their mail there, the PO is probably only open for 7 minutes at some crazy hour that no one actually is moving around. I pull in the parking lot and disconnect the coil that is currently in use, wait 10 minutes, reconnect it. No start. Disconnect the coil, disconnect the battery, wait 10 minutes, reconnect. No start. Swap to the initially running coil. Fires up and runs fine.

At home I swap it back to the last failed coil and it continues to run fine. At this point, my high idle issues at cold start are getting worse, so I work on that. Vacuum test everything under the hood. No leaks. Pull throttle body, clean (was clean). TB gasket is new and shows no signs of leaks. Pull IAC and TPS and clean out. Connect IAC and turn on key, plunger moves in as it should. Put everything back on and it fires up like factory, no high idle, perfect.

Until I back out of the shop and as soon as I apply a load it starts coughing and missing and sputtering and will only move if I give it ¾ throttle and then it goes barely. I am thinking I killed the dang TPS so I swap a back-up (new in box) and there is no change. JP only starts with accelerator to the floor at this point and runs like it’s missing with zero power. I pull the battery cables and let it sit for an hour. No change. On a stupid hunch I swap to the other coil, fires up and runs like a champ.



That’s where I am. I think the next step is road flare and a gallon of gas. I’m up for anything at this point. I’m sure I’ve left out something somewhere. Guys, pull my head out of this hole I’ve dug and give me some direction. Thanks up front!


Steve​
 
Genuine Jeep parts, or cheap crappy Chinese clone parts ?

Note the coil/ground relationship below.

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem.

A faulty Coolant Temperature Sensor may also cause similar symptoms. Testing of the CTS is recommended as part of the diagnostics. A poor ground at the ignition coil can also cause similar symptoms.

The reboot symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will usually relearn the idle settings after a short period of driving and the engine will start and idle normally, (4) random stalling.

Begin with basic trouble shooting of the entire start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

If the symptoms reoccur, you need to have your battery and/or the alternator Load Tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Handheld testers are very inaccurate and will usually pass marginal alternators. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.
 
Tim_MN said:
Genuine Jeep parts, or cheap crappy Chinese clone parts ?

Note the coil/ground relationship below.

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem.

A faulty Coolant Temperature Sensor may also cause similar symptoms. Testing of the CTS is recommended as part of the diagnostics. A poor ground at the ignition coil can also cause similar symptoms.

The reboot symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will usually relearn the idle settings after a short period of driving and the engine will start and idle normally, (4) random stalling.

Begin with basic trouble shooting of the entire start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

If the symptoms reoccur, you need to have your battery and/or the alternator Load Tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Handheld testers are very inaccurate and will usually pass marginal alternators. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.
Click to expand...


I'm not sure if it makes a difference, but mine is a 1991, OBDI engine.

The sensors are a mix of various parts OEM and BWD, Omix Ada, etc. Each has been swapped with factory parts during the process to determine whether or not the sensor is an issue. There is no change in behavior for any part swap.

CTS has also been swapped twice as well.

After rebooting the engine never "relearns" is the best way to describe it. It never runs enough to get any better. It's a dead in the water scenario until recently, where it began the coughing/sputtering. Ran it for a good 20 minutes to see if it would "catch up" and line out but it never did.

I definitely am suspicious of my alternator and once it is back on the road under it's own power, I'm going to have that checked for voltage flow/surges. It is an "off brand" high output alternator that has gotten good reviews but is still an unknown for me.

I've refreshed all the grounds except the dipstick. I'll be doing that this evening or tomorrow and report back on my findings.

I definitely appreciate your response. I know it took a while to read and cipher my ramblings.
 
Eeyore said:
Fuel pressure good?

Sent from my SM-N920P using Tapatalk
Click to expand...


I don't have a fuel pressure reading yet, but the pump kicks on good an loud consistently throughout the starts. It has sat for days before restart as well as an attempted restart immediately after being hot/shut off 5 minutes. The pump always kicks on with no sign of fuel leaking back/losing prime. I have a fuel pressure gauge to install in the schrader valve though to confirm the level of pressure.

Thank you for the suggestion. Regardless of what the pump sounds like, I need to verify my basic three: fuel, fire and air. I'll get that done in the next day or two and report back. I appreciate your slog through the text.
 
Refreshed the dipstick ground this evening before work. Swapped distributor coil wire and plug back to the coil that was connected when it started the sputtering/etc. Let it run for an hour at idle. Idles perfect on start up. No RPM hunting. Sits at 800 RPM. Moving through the throttle range produces no stutter, lag, etc. I've seen it like this (correct) before during this saga and it goes back to its old cantankerous self within a few days usually. I'll keep updating and see how things go from here. I'll try to get a fuel reading/install a manual gauge in the rail this week. I'll have the alternator tested my next cycle off.

Thanks again guys and thanks in advance for all the help.
 
Eeyore is OBDII with coil packs so trying to picture it looking up his skirt isn't helping. Fuel pump relay is open/close, so if the pump is kicking on, maybe it's got a chunk of crud in there, but the coil swap shouldn't impact it.

Since the coil connection seems to be the common thread, what on your engine do you touch, loosen, remove (besides the coil) when swapping? Probably silly, but just thinking of what might be the simplest solution. Like maybe the coil wire isn't totally seating in the cap or coil... something one wouldn't think about because it's just a wire. If you disconnect the negative every time, maybe it's a bum terminal or cable end?

Wild guessing!

Sent from my SM-N920P using Tapatalk
 
Eeyore said:
Eeyore is OBDII with coil packs so trying to picture it looking up his skirt isn't helping. Fuel pump relay is open/close, so if the pump is kicking on, maybe it's got a chunk of crud in there, but the coil swap shouldn't impact it.

Since the coil connection seems to be the common thread, what on your engine do you touch, loosen, remove (besides the coil) when swapping? Probably silly, but just thinking of what might be the simplest solution. Like maybe the coil wire isn't totally seating in the cap or coil... something one wouldn't think about because it's just a wire. If you disconnect the negative every time, maybe it's a bum terminal or cable end?

Wild guessing!

Sent from my SM-N920P using Tapatalk
Click to expand...


I completely agree, the only thing that I have found that makes this JP run again (in five minutes or 5 days) is to swap another coil on. As soon as it fires up and runs I can kill it and swap back to the other coil and it runs just fine. I am absolutely baffled and I am frustrated because I know that the coil isn't the issue. Something is "latching" and not being released until the coil pack is removed. I can't wrap my head around that.

I unplug the coil to distributor wire from the coil and swap. Then unplug the coil input plug and swap it. Most times I've not actually done anything else. Just swap them and see what happens. Always works. No matter what I do with the battery cables, etc, it won't fire until I swap coils. I even unplugged the current coil and just left it for a while. Like all day. Would not fire at all. Plug into a different coil, fires, immediately shut down and plug into the previous one, fires fine.

It's like something loads that coil and causes it to "lock up" although I am not sure how that is possible given that it is essentially a capacitor and stepper (right?).
 
Thinking out loud, I may create a checklist of sorts for when the next failure happens. Something to work through in terms of checks/tests when it actually is dead that would eliminate each component/circuit systematically.

Something like:

Remove current coil plug/input. Wait 10 minutes. Attempt start.

Using current coil, remove pos/neg batt connections. Discharge pos to neg for 30 sec. Wait 10 minutes. Attempt start.

ETC, ETC,

Maybe unplug ECM after discharge.


I don't know. I need to brainstorm the sequence and get something on paper so that I don't cross contaminate my electricity samples. I'm open to ideas here as well. Honestly, I'm open to ideas on anything. I'd love to earn more on my investments, increase my gas mileage while at the same time increasing horse power and torque and also be more in tune to others' emotional states.
 
unstabl said:
Something like:

Remove current coil plug/input. Wait 10 minutes. Attempt start.

Using current coil, remove pos/neg batt connections. Discharge pos to neg for 30 sec. Wait 10 minutes. Attempt start.

ETC, ETC,

Maybe unplug ECM after discharge.
Click to expand...

.... Burn sage, shot of tequila in the tank, 2 double decker taco supremes consumed while walking backwards around the Jeep, etc etc 😁

The struggle is real.



Sent from my SM-N920P using Tapatalk
 
So, this morning when I crank it up to go to work it starts right up and has a crazy rough idle for about 1 second then smoothed right out. No rough idle or crazy high idle after that.
 
What are the results of having the battery and alternator load tested ? Have you completed the inspection and routine maintenance cleaning of the start and charge system wire connections and wires ?
 
Tim_MN said:
What are the results of having the battery and alternator load tested ? Have you completed the inspection and routine maintenance cleaning of the start and charge system wire connections and wires ?
Click to expand...

I didn't get a chance to load test the alternator while I was off. Farm got in the way. All of the charging system wires are clean and in good condition. They are also relatively new (<6 mos) 2 GA from Jeepwires.com.

I'll post as soon as I have the alternator load tested.
 
This morning, crank no start. Swapped to back up coil, started fine. Runs smooth. No rough idle or high idle.

I have a digital voltage display (cheap Amazon USB plug) that I pulled the cover so I can see the voltage better. It's shows1 3.8-14.2 going down the highway. My dash gauge shows the needle at the far left hand edge of the green. I've got another alternator so I may go ahead and swap it on when I pull the current one for testing. Just to see if there are changes.
 
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