Topic: Car hiccups when driving at pace

[Eucalypta]

Hello Guys,

I have the following problem which is getting worse by the mile:
My car (YJ 1994, 2.5L standard powertrain with AX5, 33" tires, had his tune up a few months ago) hiccups when driving slow and especially on a bumpy road.
It always had a "sensitive" throttle but it is getting a lot worse in the last few miles.
When I pull away or drive at pace, I look like "an old woman" as the car hiccups; launching forward and dropping back when I release the throttle, then launching forward when I push the throttle just a little bit. A bumpy road makes it even worse.
I also noticed that the gearlever is violently shaking when I accelerate from standing still and there seems lacking torque on the wheels; pulling away with screaming tires is not possible.
At my latest project the engine mount rubbers and gearbox mount, including the stabilizer have been replaced.

Someone mentioned it could be the clutch or gearbox…
Some more information:
-pulling up in the right gear (1st): car hiccups (driving like “an old woman”)
-pulling up in right gear and accelerating: Car doesn’t hiccup (noticeably) but the lever does shake violently.
-pulling away in the right gear and pushing the throttle down; the car doesn’t hiccup but the gearlever is shaking. I also notice there is not much torque at the wheels; it would be impossible to pull away with screaming tires.
-Pulling away in a higher gear: car doesn’t hiccup, or unnoticeable because of the higher gear.
-Pulling away without touching the throttle: car hiccups, but it is not aggravated by pushing the throttle accidentally by every launch forward or dent in the road.

-Driving at pace without throttle: car doesn’t hiccup
-Driving at pace in the right gear: car hiccups a lot (throttle is touched more or less by every dent in the road)
-Driving in a high gear: no hiccups or you unnoticeable because of the lack of torque to the wheels.

-Clutch pushed down: no rattling; the gearbox is reasonable quiet
-Clutch up: rattling from the gearbox (or clutch)

-When idling; the engine runs smooth. When pushing the throttle, even just lightly, there seems some delay (less than a second) before the engine picks up revs.

Could these hiccup problems (so maybe not the engine delay with the revs), be caused by problems in the gearbox or clutch?
If so, how could I fix them?

I am looking forward to your opinion!

John

[sharpxmen]

doesn't sound like a clutch problem to me, more like one of the sensors (i'm thinking of TPS - throttle position sensor) or one or more of the injectors or having a bad connector at one of the injectors (for that someone here used zip-ties to secure the connectors to the injector body)

could also be an ignition problem as it seems to somehow be rpm related, so i would also check the distributor/rotor/wires/plugs and the Crankshaft Position Sensor (CPS)

do you have a check engine light on? if yes did you check the codes (look at the FAQ section for the procedure).

[95four]

Mine had the same symptoms it was the connection where CPS plugs into harness.

[aw12345]

Do all the basic stuff before you throw parts  at it. Start with engine vacuum, see where the ignition base timing is at and if the ecm advances timing when you rev it.
Good vacuum at idle and a quick drop off when you open the throttle.
If all that is good move on to the ignition system, easiest field check is still get it barely rolling in first gear then shift to third gear and floor the Jeep, if it is just chugging and slowly accelerating without a backfire you can consider the ignition system good.
From there TPS, and check the map sensor, both of those inform the ecm about engine load, which then adjusts ignition timing and fuel delivery accordingly.

[Eucalypta]

@sharpxmen: No faultcodes out of the ordinary (airco)
When I unplug an injector I can hear the engine react immediately; all injectors are working. I do not know if the amount they spray or the spray patern is ok (have no means to test it). They might have had a bang when I had water in the fueltank.
TPS is ok; exchanged it with the one from my GC; no improvement.
CPS: the connection has to be ok (see below). The problem does not occur while idling or revving it without driving.

@95four: The cable plug has been removed a long time ago; the wires are soldered (is this even english?  ) together. So there can be no problem with the connection. The CPS itself could be ofcourse but I do not know how to check it?

@AW12345: Vacuum seems ok. I have suction ad idling but more when the engines it as 2000rpm or more. It does not drop off until the revs go down (is ok?)
Ignition: need to do that including the clutch test later this week; not able to drive it at the moment. Will inform on this later on.
TPS is ok: have several spare and none take away the problem (or there are more sensors defected). Map sensor: will look into that.


My clutch might still be worn out: there is a ratling noice when the clutch is up. Whne I push it down the ratling is gone....
Probably have multiple problems; will know more after the fieldtests. 

[sharpxmen]

@sharpxmen: No faultcodes out of the ordinary (airco)

what is airco?

O2 can also cause some issues but from what you describe is less likely.

From your project thread i assume you checked the fuel pressure while under load so that's ruled out.

[aw12345]

The rattle could very well be gear clash in the transmission that or the throwout bearing is toast (druklager). vacuum near 21" at idle or atleast above 19" needs to drop near zero when goosing the throttle (vol gas) also no fluttering of the vacuum gauge needle. Match vacuum reading with map sensor voltage on the sensor wire leading back to the ecm, should be around 1 volt at idle and near 4.5 to 5 volts at WOT.
To check injectors you need a fuel pressure gauge, which you have and a contraption to pulse the injectors, a good toolplace or auto parts store should have it.
All you do is block the return line to the tank cycle the key to build fuel pressure in the rail, then pulse the injector and note the pressure drop, do the same thing for each injector, then compare results, should be fairly close.

[Jeffy]

what is airco?

O2 can also cause some issues but from what you describe is less likely.

From your project thread i assume you checked the fuel pressure while under load so that's ruled out.

Airco = Air Conditioning

[Eucalypta]

Jeffy: airconditioning indeed 

Have not yet had the chance doing the tests or look at the sensors. Been working all day in an hot office (need bigger AIRCO here    )

However I did have the time to read ALOT through this forum and found some other topics about hiccup and surging when driving slowly or on a bumpy road.
On one of them the issue seemed to be, and Jeffy you stated you seen it many times before, that a bolts turned on too tight of the springs, might give it a bucking ride.
I do not dare to jump to cunclusions but indeed the springs were bolted back on the new chassis last week. About the same time as this bucking started to aggrevate.
Could this be the problem or part of it? And how "tight" should the bolts be? First time we bolted them to FSM torque specs, this time I am unsure how tight the are. 

I also think there are many ideas of what bucking, hiccuping, surging etc is.
I put hiccup in the title but maybe the word bucking or surging is better.
To describe my problem a bit better:
At idle or revving without driving, the engine runs smooth; this makes me doubt a bit that the sensors might be bad  .
When I drive slowly and I do not touch the throttle, the car drives smoothly. At any RPM.
However when I just tough the throttle a bit the car reacts fierce; surging forward. Because of it the pedal will be pushed down a bit (my foot does not absorb the movement by the surging) and the car surges forward again.  Of course I take my foot of the pedal and the car slows down, just until I want it to go a bit faster and pushes the pedal a bit again.
When driving on a bumpy road and I want to go at a steady pace; the same thing happens. On a bump the pedal is pressed a bit down making the car surge forward, etc.
Only shifting to a high gear or not touching the pedal makes it possible to drive slow or pull away in a smooth way.
I do not know what causes this problem.  I hope this piece of information helps to find the problem.

The other thing with the shift stick shaking might have to do with the clutch been worn out or oil leaking on the clutch plates. The fieldtests of AW12345 might bring more light into this.
And I will of course pursue the sensor sugestions mentioned earlier.

[FourbangerYJ]

I never used a torque wrench when I tighten the shackle to leaf bolts. I just make sure there is a locking nut (not lock washer) either a nyloc or a all metal one. I tighten with a socket wrench until it's snug. I make sure there is a few threads sticking out of the nut to be sure there is enough engagement to make the lock nut work. It could be as little as 40# but like I said I never measured.

[Eucalypta]

It could be as little as 40# but like I said I never measured.

Did you encounter the same problems I have?

[FourbangerYJ]

Did you encounter the same problems I have?

Not really since I didn't have them to tight in the first place. If your having a harsh, stiff ride where as you did not in the past then check to see how tight those bolts are. It could be a simple cheap fix.

[sharpxmen]

poly bushings (greased) should take care of the problem

One thing i would look at is that you need to to make sure the bolts were tightened when the Jeep was on it's wheels (leaf springs, shackle and track bar bolts).

the other thing is to make sure you have the proper pinion angle at the rear driveshaft - if is wrong it will jump up and down or vibrate when you accelerate - since you mentioned you have a t-case drop - i had this problem and i needed smaller angle shims at the leafs and once i did that it stopped doing it (somewhat similar to what you describe but i can't be sure).

[Eucalypta]

the other thing is to make sure you have the proper pinion angle at the rear driveshaft - if is wrong it will jump up and down or vibrate when you accelerate - since you mentioned you have a t-case drop - i had this problem and i needed smaller angle shims at the leafs and once i did that it stopped doing it (somewhat similar to what you describe but i can't be sure).

The t-case is 1" drop and I have 2,5 degree shims under the axle. Don't know if it is enough or too much since I am not sure how much lift the springs are (second hand buy with 2,5" lift "on the label")
A buddy of mine says it is about the right angle and the SY is deep enough in the TC. Don't feel really vibration. Maybe a bit when I slow down.
What would a right angle be? (I am sure the answer is somewhere on this forum?)

[sharpxmen]

The t-case is 1" drop and I have 2,5 degree shims under the axle. Don't know if it is enough or too much since I am not sure how much lift the springs are (second hand buy with 2,5" lift "on the label")
A buddy of mine says it is about the right angle and the SY is deep enough in the TC. Don't feel really vibration. Maybe a bit when I slow down.
What would a right angle be? (I am sure the answer is somewhere on this forum?)

read this article http://www.4x4wire.com/tech/pinionangle/

on the right hand side (looks like a vertical ad banner) there are a series of images, 4th one from the top is probably what you should have with the t-case lowering kit, 3rd one is a standard setup - it is all a good read, very concise and to the subject