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Unread 07-22-2014, 11:41 PM   #1
Glasssplinter
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1994 ZJ 
 
Join Date: Sep 2010
Location: Farmington
Posts: 192
Sudden intake popping / running horrible

I've done quite a bit of looking at this problem and a lot of the threads are unresolved with this issue. Here's where it started...

Started noticing it was taking longer to start after sitting. After checking some things found the most probable answer was the check valve in the pump. No biggie, just a minor annoyance but I had just filled the tank and wasn't about to drop the tank just for that. Kept running it and would just turn the key 3 times to pressurize it. Would start up pretty quick after that, run rough for a few seconds then even out. Figured that was just air in the system since I had to prime it. Read about running a bottle of cleaner through the tank might fix it if you're lucky. So I dropped a bottle of B-12 chemtool into a full tank and hoped for the best.

Progressively it was running worse and it would get up to 1st gear, then when it would shift into 2nd it would rev but lose power. It was a very noticeable feeling of accelerating okay for a 4.0 to going to a 2.0 in it. This would come and go and I thought that the B-12 might be a little too much so I topped the tank off with some 91 octane gas, think 8 gallons or so. Seemed slightly better but it depended on the day. It got to the point that it might run okay one day but not the next.

The Jeep actually died in a driveway now barely able to move. Note that it made the 15 mile trip there with almost no problems. It would barely start and when it got going had almost no power. Couldn't get above 25 mph so had to turn back and park. Started running really rough and backfiring / popping through the intake.

First thought on it was the CPS since I had replaced the original one with an Autozone one. Put what I'm assuming was a Mopar back in it and still nothing ran better. Funny thing is sometimes you can get past the coughing / popping and get to 3K+ rpms but as soon as you shift into gear, 0 power. The Jeep barely moves and gets stuck on any kind of incline. Pulled the plugs and they were heavily fouled indicating a rich running condition. Got it to move far enough with fresh plugs that it finally threw an engine code, 51 lean condition. Doesn't make any sense since the plugs are showing rich.

Step two was to pull the fuel pump and filter. Found a clogged fuel pump and heavily filled filter. Thought this was it. Found metal flakes at the bottom of the tank also indicating most likely a bad fill up. Replaced the pump and filter and still have the same conditions. I didn't replace the gas since I need to get the pump replaced with warranty. Everything was working fine just a couple of weeks ago, no problems and running strong. I'm really getting stumped on this. Could the gas be so bad from a fillup that it's causing this big of a problem? I just replaced the plug wires tonight and have to get a distributor cap and rotor tomorrow. I'm working on getting a new CPS from Kolak to make sure that's not the problem. Sorry for the long winded thread but I figure the more details hopefully some better results. Thanks!

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Unread 07-23-2014, 03:02 AM   #2
Oldfrog
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1997 ZJ 
 
Join Date: Feb 2008
Location: Louisiana/Texas
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I'd start by cleaning the throttle body and IAC.
Then I'd look at the TPS, then the upstream o2 sensor. ( unplug it and see if anything changes)

Next, I'd check the engine grounds, battery voltage, and the asd relay. Might even be a clogged cat. The fouled plugs could be from not firing very often as well as stuck injectors, fuel trim too rich, etc.

(I do know that a bad tps will cause these symptoms though.)

Also, read Zeejay's stalling thread in my sig line, below.
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Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
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Unread 07-23-2014, 08:28 AM   #3
Glasssplinter
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1994 ZJ 
 
Join Date: Sep 2010
Location: Farmington
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Thanks Oldfrog. I've swapped the TPS with another Mopar that was working during another problem I had and still didn't have any change. I have another IAC that I'll try swapping in. TB is all clean as I regularly clean that up. I've gone through a good portion of the dirty dozen list and haven't found anything odd yet. Upstream O2 was unplugged during some other testing the other night and no change in running. The worst part is this is happening in the closed and open loop of the computer so most of what could be unplugged shouldn't matter, or at least I wouldn't think it would matter. Grounds and battery are all good, not much corrosion where we live. I'll check the ASD relay and swap it out with another. I had pulled my cat in another thread about 15K ago and the thing was almost spotless but I'll see if anything is rattling around in it.
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Unread 07-23-2014, 11:46 AM   #4
Oldfrog
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1997 ZJ 
 
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Check your fuel pressue at the rail too.
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Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
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Unread 07-23-2014, 05:30 PM   #5
ZeeJay1997
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what you are describing sounds like fuel starvation. check the pressure to verify pump as old frog suggested.

grabbing at straws here... just an idea.

given the amount of crap you found in your tank, it may be that the filter failed and let fine particles into the fuel lines, plugging the injectors.

you could pull the rail, take it apart and inspect. get a set of orings before you start.
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Unread 07-23-2014, 10:24 PM   #6
Glasssplinter
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1994 ZJ 
 
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Thanks for the help guys. Almost didn't get it but got the fuel pressure kit from Autozone and hooked it up. 10 PSI at the rail. Pulled the fuel pressure regulator and only pulled out half an o ring. The other half was in the regulator itself. Replaced it with a BWD and it started after a few cranks. Acted like nothing happened and purred at idle. I didn't suspect fuel starvation because of the rich condition, anyone know why it would run rich if it barely has enough fuel? Just glad it's all fixed and there can be a solved thread on this.
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Unread 07-24-2014, 01:19 AM   #7
Oldfrog
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1997 ZJ 
 
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Because it's not hitting specified RPMs , when the TPS, etc reaches certain levels of resistance and the PCM is trying to raise them ? ( just a guess)
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Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
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Unread 07-24-2014, 04:26 AM   #8
ZeeJay1997
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mine did the same thing with weak relay contacts. idk why.
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Unread 07-24-2014, 09:45 PM   #9
Glasssplinter
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Quote:
Originally Posted by Oldfrog View Post
Because it's not hitting specified RPMs , when the TPS, etc reaches certain levels of resistance and the PCM is trying to raise them ? ( just a guess)
Yeah not sure, just seems counterintuitive that lack of fuel pressure would cause a rich condition. So much to still learn...

Either way we got her back up and going again, just hit 222222 a few miles ago and hopefully we can see that go higher
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