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View Full Version : Check engine Misfire cyl 1 with a/c off runs fine with a/c on


Alopanec
October 24th, 2017, 08:30
I have a 98 with a 4.0 ax 15 and its white I can drive a month with the air conditioning on and I won't get a cel but if I drive with it off I can hear and if I put my hand on the exhaust I can feel my hand get sucked in indicating a miss and ill get a cel after 2 or 3 starts and I have tested my theory about the a.c. multiple times it holds true every time I have replaced plugs wires cap rotor fuel pump and i.a.c I plan on changing 02 sensors this weekend just because I'm sure they are old and have never been changes and I have a smog coming up I've ran multiple bottles of sea foam in the fuel and a can of the spray for the intake I've also did a compression test and everything was between 80 and 95 I know it's low as factory says 120 I think but its got 200k miles on her plus I don't think it would be a intermittent issue if it was low compression I really think it's a vaccume issue but not sure I've checked vaccume and everything seemed good but one really wierd thing was that one of the vaccume lines was full of water I thought that was strange and if I blow in it I can hear bubbles from somewhere

90xj06
October 24th, 2017, 09:48
80-95 is really low. double check to make sure the gauge was good. i have close to 300,000 on mine and its up at 120's.

if the compression is good. and its got new spark plugs and is constantly getting a spark i would have to say its fuel related. under load the PCM will run the injectors with a longer duration so it may just be enough to fire and not have the misfire detected.

Water in a vacuum line??? is the vacuum canister full of water? there should be no liquid in the vacuum system.

Alopanec
October 24th, 2017, 10:59
I will try another gauge as the one I used is probably older than I am

I'll try swapping injectors to another cyl to see if its the injector causing the issue the misfire seems to always be cyl 1 so ill swap it with number 6 and see if it follows

I'll check the vaccume canister today after work and post what I find I've only owned the jeep for 3 months now and seeing all the Jerry Rigged crap the P.O. did to it I wouldn't be surprised if it is full of water its amazing what you find behind panels and trim

Alopanec
October 24th, 2017, 20:28
Wasn't able to get a hold of a new compression gauge but I did swap the number 1 injector with the number 6. so I'm just waiting for the cel to come on to see if the misfire code jumped to that cylinder. i also learned that i have the 4 hole injectors i may just go back to the oem ones if i discover the injector to be the issue. And appearantly that the P.O. decided to delete the vaccume canister as I was not able to locate it. I checked the passenger side front bumper and just found a vaccume line that had been capped. I checked the other known area by the brake booster as i read people sometimes relocate them there I cant remember why though. so ill try to find one at a pick a part or something maybe car quest will have one. I hope I am on the right track your guy's input is much appreciated.

Alopanec
October 28th, 2017, 10:29
Swapped Injector 1 with 6. No luck with that still have misfire on cyl 1. Installed new vaccume canister., Vaccume gauge read 17 in vaccume at idle.

Alopanec
November 5th, 2017, 17:59
Checked compression and starting from num 1 to 6 ot was 120,110,110,110,120 110 fuel pressure is at 50lbs spark was verified. Hopefully I'll get someone to respond

Runnin'OnEmpty
November 5th, 2017, 21:07
I have a 98 with a 4.0 ax 15 and its white I can drive a month with the air conditioning on and I won't get a cel but if I drive with it off I can hear and if I put my hand on the exhaust I can feel my hand get sucked in indicating a miss and ill get a cel after 2 or 3 starts and I have tested my theory about the a.c. multiple times it holds true every time.......
I would disconnect the A/C clutch wire and see if this has any effect. Also pull the A/C fuse. I have no idea why the A/C would cause a miss, but this might isolate the problem...

Alopanec
November 6th, 2017, 22:45
Ok thanks ill try that

Alopanec
November 9th, 2017, 09:10
Drove for a couple hours with the ac disconnected amd was pretty low on fuel so iDecided to just start runing 87 octane fuel instead of the 91 (i know it was dumb to run 91) any way the misfire went away and has gotten better as in it doesnt misfire as much every now and then it misfire but i noticed if i run the jeep kinda hard it will go away but comes back on the next start then i run it hard and it goes away again also i know the battery is a cheap brand from mexico i was thinking of changing that and the alternator as well as the cps and distributor after that its going to the shop

N8N_99xj
November 9th, 2017, 15:59
OK shot in the dark time. If you run with the A/C on the engine compartment might be cooler due to the e-fan. This usually only shows up on precat vehicles but is it possible your fuel pump is getting weak and you're vapor locking? Does it miss real bad if you shut it off and then start it 10 minutes later?

Alopanec
November 9th, 2017, 21:28
No usually its pretty constant if anything its not as bad when its warmed up my scan tool is saying the catalyst systems arent clearing as in showing ready so i paid real close attention to the 02 sensor reading and sensor 2 is basicly reading same voltage as sensor 1 usually minus .040 volts could that mean that my catalytic converter is shot or i have an exaust leak somewhere im just throwing out as much info as possible i appretiate everyone's help regarding this issue its definatly a head scratcher

Alopanec
November 21st, 2017, 22:52
Still fighting this thing i replaced cat last weekend. I also found a article about weak valve springs will try that in a few weeks. Still refusing to take it to a shop. Here is a little backround info about me since i have nothing important to post. Im 23 this is my first jeep ive owned ive grown up around them and have a decent mechanical knowledge ive rebuilt dirt bike motors with some help from my dad but still have a long ways to go knowledge and experiene wise if anything i can say ive learned alot in these past months working on this thing and with your guys and my dads help ill learn even more. Im not asking to be spoon fed but any input good or bad is appreciated