Topic: 92 YJ 2.5 hiccuping under load

[sirchesshire]

Okay, first let me state that I've already read the other posts and changing my crankshaft position sensor did the trick...or so I thought.  I bought a new set of wheels and tires (that went into the back of my Jeep, not on yet... set of 5 AR 15x8 with 31" Cooper HT's) and almost as soon as I drove out of the guy's driveway, she started hiccuping again.  Got home, unloaded the tires and bam...good to go again.  I know my little squirrels weren't exactly designed for 31's but they were on it when I bought the jeep and haven't had a need to replace them yet.  With this newer set of 31" HT's I'm still in the green for tires.  Btw, 65 is a good speed for me as I drive back roads all the way to and from work. 

I've checked or replaced many components over the last year trying to fix this problem and thought I finally had with the cps.  Now it doesn't make sense anymore.

Plugs, wires, fuel pressure, vacuum hoses...all good.  Had the injectors and fuel rail cleaned by a local shop.  I'm out of ideas now.

My main reason for concern is that if I decided to go off road and start putting a heavy load (crawling up a mountain or such), I don't want her to start acting up on me.  That would be a very poor time for such behavior.

Any ideas?   

[sharpxmen]

tps is also known to cause hiccups, but that is just one case in many. could also be MAP sensor and also you could have some fuel delivery issues. does it throw any codes (i assume not since you didn't mention it, but who knows) - tps and/or map usually throw a code, if you lack fuel flow under load that can be w/o a code so imo i would start by monitoring the fuel pressure when that happens and go from there (not at idle or revving the engine while the vehicle is not moving, that won't require as much fuel as you would need under load - best to find a place when you can drive uphill at full throttle for a bit and see if the pressure drops). Since you mentioned that all the ignition items are sound i will leave that out, but hiccups can also be caused by spark issues so i wouldn't rule that out completely just yet. If you have a vac leak that would only cause your idle to increase but not loss of power unless it's the line that goes to the MAP sensor (i am talking at full throttle or close to that which i understand is your case since you mentioned under load).

[sirchesshire]

Under load, as I meant it, is...driving my jeep with nothing but the seats and me inside...no problems.  Add about 500 pounds (the wheels and tires I bought), it started acting up.  Take out the new shoes and it is fine again.  I had the exact same problem (without the added weight) before replacing my cps.  It acts like it is missing on 1 cyl randomly.  Sometimes only once a min, sometimes much more often.  Power is lost and the tac drops about 1000 rpm for a brief second.  Then the power is back until it happens again.  I tried revving the motor as soon as I got home that day, and she purred just fine.  It was only happening when I was trying to drive down the road, more so on grades and flat ground.

I probably have the same issues as someone else, but I've yet to be able to pin point the problem from the other questions in this forum and jeepforum.com.   And I have been reading for quite some time. 

Hope that clears up any questions I left last time. 

[sharpxmen]

Under load, as I meant it, is...driving my jeep with nothing but the seats and me inside...no problems.  Add about 500 pounds (the wheels and tires I bought), it started acting up.  Take out the new shoes and it is fine again.  I had the exact same problem (without the added weight) before replacing my cps.  It acts like it is missing on 1 cyl randomly.  Sometimes only once a min, sometimes much more often.  Power is lost and the tac drops about 1000 rpm for a brief second.  Then the power is back until it happens again.  I tried revving the motor as soon as I got home that day, and she purred just fine.  It was only happening when I was trying to drive down the road, more so on grades and flat ground.

I probably have the same issues as someone else, but I've yet to be able to pin point the problem from the other questions in this forum and jeepforum.com.   And I have been reading for quite some time. 

Hope that clears up any questions I left last time. 

this sounds familiar with couple of other threads i've seen here (tach rpm dropping) - the tach dropping points towards something electrical rather than fuel, read this thread (to the end), maybe you find your answer there http://4bangerjp.com/forums/index.php/topic,7178.0.html

there were a few things that were mentioned by some other folks: tps, cam and map sensors were mentioned in there to cause the rpm drop (although i cannot confirm that would be the case with any of them it's something to look at).

there is another thread where the guy had a issue with a bad wire that was causing somewhat the same issue, but none of these ones were related to the load (weight in vehicle) and in your case by simple logic would point to tps or map sensors (just b/c you would open the throttle more) - hope this helps and if you find the problem post an update please. good luck

[sirchesshire]

Ok....so now I'm just ticked off.  Nothing you guys did of course.

While checking the TPS, I realize one of my vacuum lines was unplugged.  Plugged it in and the idle drops a little, but everything is still working ok.

I figure...I'll put her in low 4, trug through my backyard in 1st at around 3k rpm and pull into my brother's yard.  Everything seems ok until I let off the gas to change back to 2...then she dies.  Can't crank back up.  (I've already done the stuff below, just figured I'd see if she was still acting up before replacing the TPS).    On to todays story...

I tested the TPS as the manual says....5 volts on the supply, 1 volt going up to 3.2 volts on the signal (a little low), and whoa and behold...when I check the resistance across the supply and signal (with the ign off of course) I go from .8 volts up to 1.3 at about 1/8 throttle, back down to .8 through the rest of the throttle range.  I figure....BINGO....bad tps.  So I go get another from the zone and pop it it...she's running...then she's stuttering...then she's stalling.  Check all the vacuum lines and I have one of the connectors cracked.  Gank one from my brother's 4banger (as he's putting in a V8....btw this is the same tube I found unplugged earlier) and I figure, good to go.   WRONG.  Doesn't help at all.

Just to recap....running fine...troll along in 4 low...cuts off and won't crank...replace TPS and she cranks...runs fine about 10 min...then dies and won't crank again.

One would think...maybe a fuel issue, but when she cranked back up and ran good for 10 min, there were no problems until just before she died.   Problems being that she started stumbling when the accel was pressed, started stumbling until she died.  I'm willing to bet that if I hadn't already been up 18 hours and have to be back at work in 5, she'd crank back up a little later tonight.

Any ideas??

On a positive side...I had a productive trip to the local junkyard, getting a 4.0 TB out of a TJ, along with the air tube (which I plan on cutting to adapt a K&N cone onto), got a very nice Cougar fan which looks to be the perfect size...and a few odd and end parts that I just felt like buying because they were in better shape than mine.

[sharpxmen]

how's the fuel press when it dies?

[sirchesshire]

Sent you a pm "sharp"

[Jeffy]

Since you have a spare engine sitting around, why not swap the CPS?

[sirchesshire]

Have replaced Cps and tps.

[Jeffy]

Have replaced Cps and tps.

Can you recreate the problem by adding weight to the Jeep every time?

[dwtaylorpdx]

I can't find it now, but I've been fighting a similar problem, that I've found documented on a couple other web sites.

There seems to be some gas tanks that don't play well with Alcohol and the plastic tank actually shrinks, causing the tank to push up on the fuel pickup and occasionally blocking it off. Its aggravated when you get weight in the rig and it flexes the body and skid plate.

I'm hoping to get the tank out in a week or so and check it on mine.

Dave

[sirchesshire]

Igit a new tank, pump, and filter about a year ago when my last pump melted the wires INSIDE my tank. Talk about some pucker power when I found out how close I was to being a pile of ash.

So the tank should be the problem either. 

When the tank was replaced, all injectors were checked and cleaned, fuel rail was cleaned and fuel system was checked with no probs. Just this annoying little problem.

[sirchesshire]

Sorry about the typo in the last message....Supposed to be "I got".

[sharpxmen]

let's do a recap

1. CPS and TPS replaced
2. gas tank replaced
3. fuel pump & filter replaced
3. connector replaced (dunno which one)
4. vac line reconnected (dunno which one)

Still, i would just try to identify why is dying and go with the basics to try and narrow it down

1. I would begin by having a pressure gauge on the fuel rail - it can also be too much pressure as well that can cause the problem (like a bad fuel pressure return valve or a plugged return line) and it makes me think of the melted wires you mentioned.
 
2. If that checks out ok next i would look at the spark plugs (or you can start with this one first) and see if they're wet when it fails to start - if they are wet then you'd get too much fuel or no spark. You mentioned that it starts back up if you let it sit for a while, that could be a symptom
of flooding the engine

3. Check the spark

4. check the MAP output (since you already replaced the CPS and TPS)

5. do the Camshaft position sensor test as described in the FSM

[Bounty Hunter]

If the CPS fixed it temporarily and the problem is intermittent, I suspect the CPS wiring or connector.  It's pretty common for the connector to have problems.