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Discussion Starter · #1 ·
I have a 2003 TJ with a 4.0L that will barely drive at this point. It has had an intermittent problem where it would start to cut out while driving and the speedo would go nuts. Now anything more than slight throttle and it starts bucking and cutting out violently. It will idle just fine. I made a video of the problem. Any suggestions would be greatly appreciated, especially if someone has encountered this same problem.

Video: http://youtu.be/qxV6P4Eg84c?list=UUjySIgBKORbJk2Aepx-9KsQ
 

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I had that similar issue on a 89 YJ after I had hit a deer. It shook the engine so hard that the ground wire from the engine block to the frame came lose, replaced everything electronical and it all seem to help for a while but then go back to crap. Don't know if this will help you but it's worth taking a look before dropping hundreds of dollars on it
 

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First thought Harbor Freight buy a cheap,like 48.00 OBD II code reader. Read the instuctions. Find out what up with your ride!!
 

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Discussion Starter · #4 ·
There is no check engine light on. I scanned it anyway and there are no codes. That's what makes this so frustrating, I'm kind of going in blind.
 

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mine was a misfire #3 injector, check it out and it was wet, used a tube of dielectric grease on every connection I could find. I washed mine and it did the same thing. I even pulled the coil pack off the spark plugs and coated them with dielectric grease, got it from autozone.
 

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Well although I don't know the exact cause, I am fairly certain that your issue is going to be electrical/ignition related. I have had similar issues in the past with a couple of BMW's I owned, and it was always related to the ignition system. Replacing plugs, wires, and the distributor cap/rotor would fix the issue.

This may not be the definitive answer to your issue, but it will give you a place to start looking.
 

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Start with the basics. Engine needs 3 things to run: Fuel (pressurized, clean and in the correct quantity at the correct time), Air (clean and lots of it) and Electricity (HOT spark at the right time). You can pretty much eliminate air, unless you have a serious manifold leak. Gas is easy to eliminate by shooting some into a glass jar to verify fuel rail pressure and no water in the tank. The electrical is a little harder to diagnose, but if you can verify a spark at the plugs that would help diagnose. Lame advice, but sometimes you gotta start at the bottom with the simple stuff.

Have you made any changes recently? Filled up with gas lately? (Oh, sorry. You drive a Jeep. Of course you have). Maybe got a bad batch of gas at the pump? Same symptoms as those you mentioned.
 

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A bad ground will cause you to chase your tail in circles. make sure ALL your connection are clean and tight.
 

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There is no check engine light on. I scanned it anyway and there are no codes. That's what makes this so frustrating, I'm kind of going in blind.
first thing I would do is disconnect the battery for 10 minutes. then touch the positive lead to the negative lead. Trace every chassis ground and wire, looking for poor connections or damaged wires. Then hook things back up and go for a drive again. If it's resolved, great.

If not, then I'd start by working the way down the electrical control systems....TPS sensor, MAP sensor, etc. You can use a voltmeter to test a lot of these sensors. I notice the speedo is going crazy, you definitely need to trace that down. Improperly installed speedo gear? The PCM does use the vehicle speed as engine running input.
 

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Discussion Starter · #10 ·
The only time the speedo jumps like that is when this problem occurs. The fist clip in the video was the only time the speed jumped up actually. Before hand it would always go way down, accompanied by the violent shaking, like you can see in the second clip. Now the problem is constant, and the speedo drops down as the vehicle shakes.
I was already planning on trying to test the sensors, but I'll definitely take your advice with the battery terminals and checking connections and grounds. I already looked at the connectors at the TPS and MAP, they were tight and had no corrosion. Some dirt came out when I unplugged them, but I think that was just from the plastic clip, and wasn't actually inside the connection.

Can anyone direct me to where I can get the specs on the TPS and MAP sensors so I can check them?
 

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Did this also effect your fuel gauge? The reason I ask is that I recently replaced a faulty fuel filter/check valve (on top of the fuel pump) and did it wrong.

Thought all was well until I filled up the tank. Had the big rubber gasket (under this big plastic nut that holds the fuel pump assembly into the tank) slip out and caused fuel to leak out the top. Lots of fuel. Scary I know. Anyways, on the way back home my gas gauge went down to zero and the speedo had a mind of its own.

Tore it apart and installed a new OEM fuel pump assembly (the whole nine yards top to bottom) and new gasket. Put it all back together and all is well.

I think the wires downstream of the connector above the tank got soaked with fuel and caused a short.
 

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Discussion Starter · #12 ·
The fuel gauge went from full to empty and the fuel light came on, but it only happened once while it was acting up and I was trying to get going in first gear. I chalked that one up to almost stalling. Otherwise the fuel gauge has not been affected.
 

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Discussion Starter · #13 ·
So tonight I tested my TPS, MAP, and crank sensors. All check out OK. I have a Jeep tech friend who suggested monitoring the up stream O2 sensor data. He's seen those cause similar problems. I'll have to wait until Tuesday when I can use a scan tool at work.
 

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My money is on some electrical fault between the connector and the fuel pump. Or perhaps a relay that drives it or a ground not making contact. Sounds like a fuel starvation thing. Something is shorting out the electrical intermittently to the fuel pump.

You would think that would be relatively simple for a mechanic to confirm one way or the other.
 

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So tonight I tested my TPS, MAP, and crank sensors. All check out OK. I have a Jeep tech friend who suggested monitoring the up stream O2 sensor data. He's seen those cause similar problems. I'll have to wait until Tuesday when I can use a scan tool at work.
Not sure the upstream o2 will cause that. I had an upstream o2 wire that had melded with the an evap component power wire. It would switch from absolutely no signal to max voltage if you tugged on it, and even then the engine would run okay. You'd definitely hear and feel the difference in idle while it went as lean as possible to as rich as possible. It's possible that no code is tripped, but it's doubtful. I believe it's anything over 25% fuel correction in either direction trips a lean/rich code. There's also separate codes for shorts on that circuit, and even more for the o2 sensor itself. But who knows, it could be. Hopefully your live data will lead you in the right direction.

Oh, and I 2'nd on resetting the ECM. If it won't find anything wrong now, it may do better after the monitors have been reset. Good luck.
 

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Discussion Starter · #16 ·
Update on my driveability problem. Things just keep getting weirder, and the problem is getting worse. I made another video so I could rant a little, but this you guys gotta see. I'm thinking possible ECM issue... anyone ever see anything like this?
http://youtu.be/7CWiFw05DRo
 

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Battery condition?

Hey UG Trev,

I'm sure you have already checked but what is the battery condition like? Again I'm sure you have checked but what do the battery terminals look like, are they loose?

I had a different vehicle with an old battery that would have the same issues with the gauges going haywire, replaced with a known good battery and everything cleared up. It would also explain why the engine cuts out when you give it more gas which calls for more spark, perhaps the alternator isn't proving enough current if the battery is the culprit.

-Brad
 

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Discussion Starter · #18 ·
Terminals are tight, battery has never given me any fuss, but I haven't tested it either. Now that you mention it though, I do have a squeaking noise under the hood upon cold start that I think is coming from my alternator.
I'll have to run a battery and charging system test. I tend to overlook the simple things when I get into diagnostics. I'll let you know!
 

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My TJ did the same thing when my speed sensor went bad. When I unplugged the speedo sensor wires at the transfer case tail cone my Jeep ran fine and the bucking stopped. I drove without a speedo till I got a new speed sensor. After unplugging the sensor I did get a check engine light till the new sensor was installed.

Good Luck
 

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Terminals are tight, battery has never given me any fuss, but I haven't tested it either. Now that you mention it though, I do have a squeaking noise under the hood upon cold start that I think is coming from my alternator.
I'll have to run a battery and charging system test. I tend to overlook the simple things when I get into diagnostics. I'll let you know!
I over complicate things as well if I know a lot about the subject, hope you find the culprit soon!

-Brad
 
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