RPM dips/engine stalls at idle (intermittent), 99 4.0
- Thread starter Mercury
- Start date
JPNinPA
Active member
Hunting down a miss is difficult. It could be expensive if like yourself you change things before verifying they are bad.
How bad is the miss? Post up a video recording of the running engine driver side of the engine capturing the miss.
No if its past the CAT it should not be an issue. Before the CAT it gives the CAT wrong O2 readings and changes the O2 mixture.
This is something you should be able to see with a OBDII reader.
The 99 and earlier exhaust manifolds tend to crack on first or last cylinder
Replacementl like the below correct it. Is your miss a exhaust leak or an intake leak?
Never look down on anyone unless you are helping them up - Jesse Jackson
How bad is the miss? Post up a video recording of the running engine driver side of the engine capturing the miss.
No if its past the CAT it should not be an issue. Before the CAT it gives the CAT wrong O2 readings and changes the O2 mixture.
This is something you should be able to see with a OBDII reader.
The 99 and earlier exhaust manifolds tend to crack on first or last cylinder
Replacementl like the below correct it. Is your miss a exhaust leak or an intake leak?
Never look down on anyone unless you are helping them up - Jesse Jackson
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I'm not sure what kind of miss this is. I only know it's a miss because I asked a few people to listen to it. It just sounds like a fast "puh" sound, it's not regular at all. It could happen a few times a second, or go a several seconds without one.
I don't mind changing the exhaust manifold, I've done it three times already. The mechanic who worked on it recently smoked the exhaust and the only leak that showed up was the one behind the muffler. If I can get my little smoke machine to work right I'm going to try and see if there are any leaks at the bottom of the intake.
JPNinPA
Active member
Im not saying change your intake. I will always say prove out what is wrong before swapping. Im just saying the stock is known to crack.
There are plenty other reasons for the pum pum sound that is not tripping a misfire code 0300 thru 0306.
These are difficult to track down. Post up a video of the. Noise.
Never look down on anyone unless you are helping them up - Jesse Jackson
There are plenty other reasons for the pum pum sound that is not tripping a misfire code 0300 thru 0306.
These are difficult to track down. Post up a video of the. Noise.
Never look down on anyone unless you are helping them up - Jesse Jackson
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Oh, I was just thinking out loud mostly. No one has smoked the intake other than me, and I've only viewed it from the top, I'll need to smoke it and crawl under just to check.
That's part of my problem, most of the time the "miss" is light, especially after fixing the TB vacuum leak, and I can't capture it on recording. I'll try again tomorrow, maybe if I move my phone around the engine compartment it'll register. When I ask someone to listen they have to get close to the Jeep and then they'll notice it, especially if they're touching the Jeep and feel the little impacts.
JPNinPA
Active member
With the engine running very carefully take the longest screwdriver and place it on the back of each injector. No long hair, hoodie strings or lanyards chains or anything dangling from your body. Lean in and place your ear on the back of the screwdriver. You should hear clicking. The clicks are the injectors firing. If any are not this could be a stuck injector.
https://youtu.be/tA_E6X4ISgQ?si=oo55ylEUng3SqSMU
Never look down on anyone unless you are helping them up - Jesse Jackson
https://youtu.be/tA_E6X4ISgQ?si=oo55ylEUng3SqSMU
Never look down on anyone unless you are helping them up - Jesse Jackson
JPNinPA
Active member
Another cheap if not near free thing is to sea foam the engine or steam it to clean carbon off of the cylinders and valves. This goes along with changing spark plugs, cleaning grounds, and TB +IAC every 30k miles.
Once cleaned every few thousand miles drive s quarter mile with the engine up at 3300 rpm or just higher. This knocks off carbon and gives the valvs a chance to spin in their seat farther reducing buildup.
Never look down on anyone unless you are helping them up - Jesse Jackson
Once cleaned every few thousand miles drive s quarter mile with the engine up at 3300 rpm or just higher. This knocks off carbon and gives the valvs a chance to spin in their seat farther reducing buildup.
Never look down on anyone unless you are helping them up - Jesse Jackson
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Okay, I've got a mechanic's stethoscope, so I'll try that tomorrow. Been raining all week
I take it you mean Seafoam the crank case? I ran some through the gas recently, but never tried in the oil. With Seafoam you just run it for a few hundred miles and then change the oil, right?
JPNinPA
Active member
NOPE! I mean seafoam through the intake. The aerosol seafoam bottle with the thin straw applicator in the pic goes into either the TB or a vacuum line to the intake. Heat engine up and follow directions.
Ran the Seafoam through the intake. No smoke out the back, apparently things were already pretty clean. If it weren't for that misfire it's running like a top.
Tried a timing light just to see if there were spark issues, everything looks fine.
Forgot to do the stethoscope; if it isn't raining too bad tomorrow I'll give that a shot. I need more things to try.
Tried a timing light just to see if there were spark issues, everything looks fine.
Forgot to do the stethoscope; if it isn't raining too bad tomorrow I'll give that a shot. I need more things to try.
Did that. Ran the whole can, let the Jeep sit for 20 minutes, drove it hard as heck for about 30 minutes. No smoke. Or it was so minor I didn't notice it.
The stethoscope says all injectors are clicking, and at the same rate. Tried with the probe against pretty much every surface of that engine that I could reach and I can't hear the miss from anywhere, but it's there.
Discovered that one of the ears that the distro cap bolts to on the distributor is broken and the cap has been loose. I reattached with a longer bolt and a nut, still missing.
I tried to get an audio recording but the forum won't let me post them here. Seeing what I can do.
I'm not sure what else to do at this moment other than getting my fuel injectors cleaned.
Discovered that one of the ears that the distro cap bolts to on the distributor is broken and the cap has been loose. I reattached with a longer bolt and a nut, still missing.
I tried to get an audio recording but the forum won't let me post them here. Seeing what I can do.
I'm not sure what else to do at this moment other than getting my fuel injectors cleaned.
JPNinPA
Active member
Terry might be able to help with video uplink.
You could upload to 3rd party cloud and link from there like photo-bucket.
Never look down on anyone unless you are helping them up - Jesse Jackson
Okay, took it to a guy who rebuilds 4.0s, as well as race cars and vintage cars. He listened, said it doesn't sound like it's from the engine failing in any way, he said it sounds electrical or ignition. He suggested replacing the distributor, which is something I probably need to do anyways because it's stock.
I'm going to order one, though I'm nervous as all heck about doing it. Such a finnicky replacement, and the idea of messing with timing worries me.
I'm going to order one, though I'm nervous as all heck about doing it. Such a finnicky replacement, and the idea of messing with timing worries me.
Guesswork based on experience, but no testing on-site, so all with a grain of salt.
Ordered an automotive smoke machine. I hooked my vacuum tester to the intake the other day and the vacuum leak was back, and I'm done chasing it with starter fluid. I found the throttle body leak is still present. Ordered a new one, it'll be in Friday. I'll install that first, and if the miss goes away I'll return the distributor; if not, then I may as well throw that in, too.
