Engine Runs Better When It Rains???

Some_Anchovies · Jun 11, 2009

So I've got a 4.0L, and it's got that weird rough idle that won't seem to go away.

But, is it just my engine, or does anyone else's run much smoother when it's raining or extremely humid? I noticed today that my jeep almost didn't vibrate at all when I came to a stoplight, and start up didn't have as many vibrations. It has always ran better when its wet outside.

what would cause this? I've got pinpoint steady vacuum, but could I just have a slight leak and cause a slight lean mix, and the humid air providing a slightly richer mix? my idle is about 5-600 when warm, so I figured I didn't have a leak. I've cleaned the throttle body many times, and replaced the IAC. I still can't figure out why it idles like it's got a slight misfire but nothing shows up in vacuum testing. new plugs and wires didn't help, air filter is clean, throttle body is clean, IAC is new, CCV orifice is clear. I've seafoamed it a few times, and it seems nothing besides wet weather can get it to run smooth (besides a very slight vibration, but it's so little it's nearly gone).

I'm stumped

jeep95xj · Jun 11, 2009

the 4.0 will never run smooth as glass its just the nature of the engine. Im having a rough idle issue that i believe is being caused by one or both of the o2 sensors. Ill be replacing them both soon. May want to give that a shot. If they are orig or have over 100K its time anyway. Lucky for you, you only have 1

Some_Anchovies · Jun 12, 2009

my friend's 99 WJ 4.0 runs smooth as glass.

I have a loud ticking coming from what I think is one of the injectors. I used a screwdriver and they all tick, but 1 was extremely loud. could I just have a bad injector?

jgorm · Jun 12, 2009

Some_Anchovies said:
my friend's 99 WJ 4.0 runs smooth as glass.

I have a loud ticking coming from what I think is one of the injectors. I used a screwdriver and they all tick, but 1 was extremely loud. could I just have a bad injector?

you could. do you have any codes. humid air will slow down the burn, but probably won't effect a lean misfire. It might make a rich misfire better, but you'd probably be smoking if it was that rich. There may be some carbon deposits that are causing mild detonation or preignition that gets quenched with the humid air. I'd pull the injectors and see if they are plugged up. Also look at all the plugs to see what the combustion is like.

georgem · Jun 13, 2009

I can't suggest any solutions, but I noticed mine doing the exact same thing. 1995 4.0 with 95000ish miles, no codes. I have a lot of rattle which I think is the catalytic converter. It's quiet under the hood, but really idles rough sometimes. It was wet and humid the last few mornings and i really noticed a lack of the usual noise and roughness in the idle.

Some_Anchovies · Jun 13, 2009

No, I've tried to pull codes. There are none besides 55, which is end of codes. I've got 143,000 miles on the engine.
I'm checking compression tomorrow, and hopefully I'll get something. If not, there's a few things that I'm thinking it could be.

Cap and rotor gunky with carbon.
Catalytic Converter ruined
spark plugs gunky
bad injector
MAF/MAP sensor faulty/dirty
O2 sensor needs replaced

Also one thing to note, my exhaust smells funny. no smoke, just smells different than other cars. (though I've smelled it many times on older cars, and seemed to smell like that for most 90's car's I've been around). Which makes me believe I'm burning a very small amount of oil, the CAT is messed up, or the burn is not right.

But Of all the things, vacuum is extremely good. If I did have a misfire, it should show up on the vacuum gauge when it does misfire, but there's nothing. That's why I'm scratching my head and going to do a compression check. also if the o2 sensor were bad, I'd think my gas mileage would be bad wouldn't it? I average 23mpg.

Some_Anchovies · Jun 17, 2009

Ok, so here it is.

Did compression check. Jeep's got worn piston rings, because the compression would be weak on the first crank, then raise on the next, up until it hit about 180

Compression was 170, 170, 180, 180, 165, 180. Leads be to believe there is excessive carbon buildup in the combustion chamber.

Things I did prior to the compression check. I replaced the Distributor Cap and Rotor. Then, the o2 sensor got replaced. Did compres ion check, and then put new, Copper plugs in. Runs rough still, even more rough than lately.

What I figure happens is when it's very wet outside, a sort of decarbonization takes place, where the water vapor is actively steamcleaning the cylinder, causing a smoother idle.

I'm gonna see what I can do about that. Maybe the mist water thing?

Some_Anchovies · Jun 18, 2009

alright, so I tried it. I took a spray bottle and filled it with water. Then, I disconnected the CCV vacuum hose and, with the spray bottle on mist, sprayed water into the vacuum hose. I did it until I noticed the engine start to slightly drop in RPM's and then let off till it went back up, and sprayed again. I didn't use all of the water, but I made sure it was in a mist, while the engine was hot so that the water quickly turned to steam, which can be compressed (So as to not hydrolock the engine). The engine began to run rough, and at the tail pipe steam was puffing out.

So then I took it on a drive. I let it idle for a while, taking it down a hill first. Then, I took it out on some back roads. At first, I was very careful not to hyrolock. I didn't take the rpm's over 1000 at first, as the engine would run really rough once I hit 1000. So, I slowly but steadily rose rpm's, until I got it up to 1250rpm without running rough. I continued to drive the back roads at about 25-30mph, till I got back to a main road, where I stopped, turned around, and the parked the jeep on a side road. I then again sprayed the mist into the vacuum line like before, then, repeated the same procedure on the way back home.

Results? Well the engine definitely runs smoother! I couldn't believe it. Coast down is better now, rough Idle is almost gone, and it definitely makes less noise. i'll have to confirm this with more driving and testing, but so far so good. :thumbsup: I'll probably do this procedure again. But I want to test it out on my Jeep first, and make SURE that it's safe. So use at your own risk.

Also note, that I have done much to tune my engine with no avail until this. I've cleaned the CCV orifice, fixed all oil leaks, replaced the IAC, and has new spark plugs (switched from platinum to copper, with no results), new plug wires, new oxygen sensor, New distributor cap and rotor, Tested Vacuum (good), ran injector cleaner in many events, cleaned throttle body, ran seafoam, lucas, new fuel filter and all sorts of things. The thing has a new water pump, and has never pulled up any codes.

So the engine has had it's own tune up, and had no results, and this was a last resort. Make sure it's not something else before trying this!!:2thumbsup:

jgorm · Jun 18, 2009

Sometimes vehicles can benifit from a "ghetto" tune up. Just drive the piss out of it for a while, wot redline shifts, and it will blow out all the crud caused by driving like a grandma. also it takes a LOT of water to hydrolock an engine. You could pump a spray bottle into a vacuum line as fast as you could pump without worrying about hydrolock.

Some_Anchovies · Jun 19, 2009

^ I've tried the drive it hard technique. Only thing I got was...well, an engine that ran worse than before.

gmp211 · Jun 19, 2009

It rained today in Jersey and I was thinking...maybe its because you drive it easier. Like don't womp on the throttle at a light cause you'll peel out.

Just a thought.

Some_Anchovies · Jun 20, 2009

I drive it the same as I do everyday. The RPM's never go above 1800.

And that got by thinking about driving it hard, so I took it mudding, got it stuck, got it really hot, smoked the tires and everything, and didn't do jack for the situation.

And the thing is, It's only at idle. If it's dry one day and I start it up, Idle can be horrendous, and if it rains and I go and start it up while it's raining, the idle is smoother.

So far, the water in the vacuum line has worked the best. once it clears out, the engine is much quieter, and shakes much less.

Could my Cat cause it to run like crap? I figured that would only hurt emissions, not make the thing idle like it's on it's deathbed.

andrew383 · Jun 20, 2009

or you could have put some 93 in it and beat on it a few times,that will do the same cleaning...
beatin on it is not getting it stuck in mud either.The reason you have buildup is you dont go over 1800 rpm.
Now this is beatin on it :teehee:

and here

i love driving this thing by the way :wave:

RavenCorax · Jun 20, 2009

that wot redline driving is called an italian tune up. back in the 70's th e hot ferraris hasindividual carberators per cylinder. they ewere3 meant to run fast all day autobahn and twisties being bombed on. well you take a high rpm carbed sports car and idle it through traffic all day they get funky. so the mechanics learned that just taking em out and flogging on em the way they were meant to be driven fixed the problem. sometimes it can glaze the deposits tho then you have other issues

i love the water trick i use a glallon jug and a pair of flat vicegrips and a vacuum hose. the vise grips let me have more control over the flow. works great love it

Saltydawg1 · Jun 20, 2009

jeep95xj · Jun 21, 2009

Rather than removing a vacuum line is it ok to spray the water in through the throttle body? Slowly of course but wont that do the same thing?

Some_Anchovies · Jun 21, 2009

well, usually you put any type of thing like that through the vacuum lines because of the injection type. MPFI usually gets cleaners and stuff through the vacuum line.

Plus, the vacuum line literally sucks the mist out of the air.

andrew383 said:
beatin' on it is not getting it stuck in mud either.

I said I got it stuck in the mud, got it real hot, and smoked the tires. I'm thinkin you gotta take the RPM's pretty high to get the tires smokin.

andrew383 · Jun 21, 2009

Some_Anchovies said:
I said I got it stuck in the mud, got it real hot, and smoked the tires. I'm thinkin you gotta take the RPM's pretty high to get the tires smokin.

high like 2500rpm of 4500rpm :rofl:
and no it doesnt take high rpm to smoke tires

Some_Anchovies · Jun 21, 2009

High like... my Minimum RPM was 4k? or are you guys sayin' I need to take the RPM's past 8???? :rantscream: :brickwall:

God, sorry, but damn I'm not retarded.

jeep95xj · Jun 22, 2009

high means redline. do it while driving not in park. if there is no load on the engine its going to do more harm than good.

Engine Runs Better When It Rains???

Some_Anchovies

jeep95xj

Some_Anchovies

jgorm

georgem

Some_Anchovies

Some_Anchovies

Some_Anchovies

jgorm

Some_Anchovies

gmp211

Some_Anchovies

andrew383

RavenCorax

Saltydawg1

jeep95xj

Some_Anchovies

andrew383

Some_Anchovies

jeep95xj

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