98 Jeep Wrangler 4cyl pops misses

[njtech]

My Jeep intermittently bucks while driving and in some cases idles rough. The dilemma
is the check engine light is not triggered for any faults
making it difficult to locate the problem. Sometimes it misses
at idle either warm or cold but not bad enough to stall. However,
driving down the road it looses power completely for 5-10sec sometimes
popping though the throttle body and could be described as "bucking".

A new crank sensor and fuel pump have been installed. It also
has new plugs cap and wires. All these problems are
very intermittent and it runs perfect otherwise. I have had days go by where it ran perfectly with
no issues. The shop were I had the fuel pump installed could not experience the problem
long enough to figure out.

I was going to try changing out parts .. and wanted to
get some advise here. I was thinking about starting with the
MAP sensor.. but if that where defective the check engine light
would be on right?.. so maybe try the coil and ignition module? I suppose ignition
problems could be undetectable by the ECM?.. help!

	Crank position sensor A crank sensor is a component used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on the engine.

[Super6XJ]

i have the EXact Same problem. but my jeep is a L6 4.0.
do you get oil In your AirBox?
Try to Clean the trottle Body.. that helped me a lil bit..
I too am looking for a Solution.

[njtech]

The airbox is dry. I pretty sure the shop
looked over the throttle body.. but it won't hurt
to take another look

[Vic_The_Jeeper]

Hello NJTech,

I have a 94 Jeep Wrangler Sahara and it started the same way. It started "bucking" and running really rough all of a sudden. I would also loose power. I went through and changed the fuel pump, fuel filter, had the fuel injectors cleaned and still no fix. I replaced the spark plugs and cables and still no fix.

So I stopped messing around and went through the four steps of diagnosing a problem. The four basic elements that are needed to make an engine run are 1)fuel 2)compression 3) timing and 4) spark.

- I checked the fuel pressure by plugging in a fuel pressure gauge on the fuel rail. That was good.

- I then checked compression in the cylinders. That was good.

- So then I checked timing. Even though a little off, not enough to stop it, so in the end that was good enough. (on a side note, on my year model Jeep, only a licensed dealer mechanic can adjust the timing via their specific computer. A regular mechanic couldn't get into that function.)

- Finally I checked spark (One of the four important elements needed to make an engine do what it does). We had a weak spark. (If the spark is bright blue it's good, if it's yellow then it's not good enough to ignite every time). So that leads down to not getting enough volts to ignite a strong spark in the spark plug, thus causing the popping from the fuel not getting ignited every time and causing intermittent power loss. Tracing back the source of the problem, it could either be the distributor cap, rotor, ignition coil, or ignition module. Mine was the ignition coil! I changed that and it ran great!

My problem now lies in that the ignition coil keeps going out. I replace it and it fires up like a champ! After a while, the coil goes bad and needs to be replaced. So I have an electrical problem before the coil.

I know my alternator is good and the volts going through are ok. I'm pretty sure my voltage regulator is in the alternator. So it can either be the ignition module or there is a short somewhere in the wiring. I'm contemplating replacing ALL of the wiring since the kits now-a-days are pretty easy to install besides having to run the wires through tight places.

In the end, my suggestion to you is try the coil. This part is around $40 at your local auto parts store. It is very easy to install. If you have other questions, feel free to send me an e-mail. My contact e-mail is in this forum.

Good luck!
-Vic

[Bounty__Hunter]

Try the firepower ignition kit from 4.0 Firepower Ignition Kit if you want to get the most from your ignition system.

Consider trying a different throttle position sensor as well.

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).