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Hesitation Stumble Misfire

Frank Z

Frank Z

NAXJA Forum User
Location
Colorado Springs
1991 Briarwood
AW4
NP242
1999 4.0L (Approx. 200k miles)

Severe stumble/hesitation on acceleration when in gear (Drive)
No hesitation when in park and manually opening the throttle with the linkage.
No CEL

What we've done:
New TPS did not solve the problem.
Throttle body has also been cleaned, IAC pulled and leaned.
Checked fuel pressure (within FSM specs)
Disconnected Coolant Sensor...no change
Disconnected O2 sensor...no change
Replaced NSS about a week ago (yes we cleaned prior to installing it).

Anyone?
 
Any recent work BEFORE you started the troubleshooting listed above?

What is the condition of the spark?

Last time cap/rotor/plugs/plug wires were changed?
 
JJacobs said:
Which engine management system, 91 or 99?
Click to expand...
91 (OBD1)

ehall said:
does it do when the system is loaded into any gear or just 1st? what about when A/C and P/S and alternator are dragging on it
Click to expand...
Any forward gear, have not tried it in reverse.
No difference when the A/C is on or off.

joe_peters said:
Any recent work BEFORE you started the troubleshooting listed above?

What is the condition of the spark?

Last time cap/rotor/plugs/plug wires were changed?
Click to expand...
Just a new PS pump.
Plugs and wires are about a year old.
Dizzy looked pretty good....till I dropped it this evening and broke the ear off of it. :doh:
New (Reman.) going in tomorrow.
 
Well darn, I was going to ask you to check for sideways play in the distributor shaft, but now I don't get to do that.

Had you taken the distributor out before the problem started?
 
Last edited:
I had this same problem once... and did all the same things you did to try and fix it. I have a auto so my tranny wasn't shifting either. A loose ground wire on the oil dipstick tube was the cause of all the problems. Needless to say I was quite upset to know I spend months... and a lot of money.... when my problem was a loose nut..... Just one more thing to think about or check.
 
New fuel filter had no effect.

Swapped in a new MAP sensor, just cuz.....no change i re-installed the old one.

Noticed the tranny fluid was a little too dark so I Drained the pan and added some fresh ATF....no change

I jacked up the rear axle and ran the motor in gear.
Not able to duplicate the problem till the wheels are on the ground.

We did notice that the problem is noticably worse when the engine/tranny get up to N.O.T.

What say the masses?
 
More info:

I took the heep around the block a few times and noticed that the hesitation (necksnapping lurch is actually a better description) only occurs beow 20mph and when the accelarator is mashed in order to get into passing gear.

Cruising at 25-55 MPH with slight pedal movement does not cause any problems at all.

I've also checked for an open circuit/bad TCC signal and found no problems at all.

Shift solenoid failure?
 
Maybe. Unplug the TCU and drive it shifting manually and see what you get.

Should have 1st in 1-2; 3rd in 3; 4th in D; reverse, neutral, and park. No OD, no torque converter lockup.

Post back with what you find.
 
Frank Z said:
I took the heep around the block a few times and noticed that the hesitation (necksnapping lurch is actually a better description) only occurs beow 20mph and when the accelarator is mashed in order to get into passing gear.

Cruising at 25-55 MPH with slight pedal movement does not cause any problems at all.

I've also checked for an open circuit/bad TCC signal and found no problems at all.

Shift solenoid failure?
Click to expand...
sounds more like TC lockup when it shouldn't
 
just to get this in my head right....

A. acceleration from a dead stop.... ok and smooth upshifts

B. acceleration from 15-20 mph;
1. tromp the pedal and it falls on it's face; stumbles and then goes
-or-
2. tromp it and it practically slams your face in the steering wheel, straightens out and goes?
 
joe_peters said:
Maybe. Unplug the TCU and drive it shifting manually and see what you get.

Should have 1st in 1-2; 3rd in 3; 4th in D; reverse, neutral, and park. No OD, no torque converter lockup.

Post back with what you find.
Click to expand...
No change with the TCU disconnected. Tried starting out in 1st gear and the heep lurched and bucked like a mofo.

Digger87xj said:
just to get this in my head right....

A. acceleration from a dead stop.... ok and smooth upshifts

B. acceleration from 15-20 mph;
1. tromp the pedal and it falls on it's face; stumbles and then goes
-or-
2. tromp it and it practically slams your face in the steering wheel, straightens out and goes?
Click to expand...
A. No, not even close to being smooth.
B. Normal acceleration above 20 MPH is fine, rig does well. Mash the gas and it's another story altogether. RPM's are bouncing up and down (approx. 800 to 1200 RPM swing).
 
ahhh.

Have you swapped the CPS yet?

Also, check crankshaft endplay. a walking crank can mess with the CPS signal.
 
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