engine power cutting out in 10 sec. intervals

So, I've had this problem for about 3 weeks now. I drive 1/2 mile to the highway both to and from work.....and then 20+ miles on the highway at around 65 mph. The problem seems to start on the highway and lasts for about 5-8 miles of my commute and then it goes away. I found out this weekend that it happens irregardless of operating temperature though. If I shut the vehicle off and turn it back on.....even with it still warm.....the problem starts over again.

Bascially it feels like someone turned the key off for second while I'm driving down the road....and then turned it right back on. The weird thing is that it consistently happens in 10 second intervals. I can count 1...2....3....and then at 10 seconds the vehicle stalls a little and the rpm drops.....then after 1 second of this it comes right back to full power....and it continues like this for quite a few miles. The check engine light hasn't come on yet....I'm not sure if there are any codes in the system though.

I've been reading other posts as much as possible and the things I have replaced because of them are: plugs, wires, cap, and rotor. I also checked the fuel pressure and it seems to remain consistent. I bought a new CPS, but I haven't swapped it out yet because it seems that those are either bad or they aren't.....not usually in between??

My thoughts are either the CPS or an O2 sensor, but I really don't know.

Any help would be appreciated.

O2 sensor will not do that.
we need more info on your jeep - year , engine, ect.

Sorry, I dropped the ball on that part.

It's a '92 4.0L HO. with ~80k miles. It is hooked up to an AW4, but that shouldn't matter.

does this happen when u hold the throttle steady, and do u know if it clears up if u move the trottle?

It happens at steady throttle or under acceleration.

Im not sure how much a TPS is but have u considered changing that?

After reading this thread:
http://www.naxja.org/forum/showthread.php?t=85658&highlight=hesitate

And this:

Dr.Dyno said:

A bad TPS only causes the engine to buck during changes in throttle position. The engine won't buck at constant throttle so that's a clue that the problem lies elsewhere.

Click to expand...

....I figured that probably wasn't it.

Faulty TPS should show similar behaviors regardless of the vehicle it's in. I did a stand alone engine management conversion on an Audi and in order to make it work with the motor it had, I had to use a lot of parts off a 16 valve GTI. Modified throttle body and TPS were some of the parts needed. I couldn't find a TPS at the yard so I thought I'd finish the conversion and drive the thing while I kept an eye out. The car was not happy at all when driving it. It bucked all day long regardless if the throttle was steady or accelerating. I knew it was TPS and bought a brand new one...plugged it in and life was real nice. Maybe a goofy short or it's getting ready to go? I'd at least borrow one from a buddy and see if it changes anything.

Ok....I'll see if I can borrow one from a friend.

Can the fuel pump ballast resistor cause something like this? Like if it gets real hot it cuts out, then comes back?

No clue, but just another thought tossed out there.

Blue XJ said:

Can the fuel pump ballast resistor cause something like this? Like if it gets real hot it cuts out, then comes back?

No clue, but just another thought tossed out there.

Click to expand...

If it did such a thing, it would take longer to cool down.

I borrowed a TPS last night and that didn't change anything. It looks like I'm moving on to the CPS next week.....then I'm at a loss.

ASD relay...?

Digger87xj said:

ASD relay...?

Click to expand...

What is that? Where do I find it? And how do I test it?

auto shut down relay. supplies power to the injectors, coil and o2 sensors. It's in the underhood power distribution box...swap it with the a/c relay... the cover for the box has a diagram for reference.

When I bought this XJ it didn't have the cover. I'll see what I can do to figure out which one it is and swap them. Thanks for the suggestion.

I changed out the CPS two nights ago and the problem hasn't changed. It is still there and pretty consistent.

:hang:

I wonder about fuel delivery. I would be curious to see what the fuel pressure was doing when the symptom occurs.

Mudd said:

I wonder about fuel delivery. I would be curious to see what the fuel pressure was doing when the symptom occurs.

Click to expand...

I hooked up a fuel pressure gauge to it (taped to the fender and everything) and the problem didn't occur for 2 days straight. As soon as I took the gauge off it went right back to doing it. I may have to borrow another gauge again to see what is going on.

The pressure looked good when it wasn't doing it. If something were up with the fuel pump, then why would it happen every 10 seconds and then stop once the vehicle drives for more than 5 miles. You would think it would happen all the time.

I went to a friend's house this weekend. He has a live diagnostic scanner and we checked to see if it was throwing any codes. It had two...despite not giving a check engine light:

1. Lean/Rich.
2. O2 Sensor.

So, I replaced the O2 sensor. It didn't do it this morning.....we'll see how it acts over the next couple of days.

Our theory was that it was trying to adjust the air/fuel mixture while driving down the road. It may have continued to dump more fuel into the system when it wasn't getting the right readings....and then it may have figured out it was getting too much and just cut the fuel WAY back. Maybe it did this in 10 second intervals as the computer tried to figure out what was going on....and then it just gave up and closed that part of the circuit.

How's that? :eeks1: