• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Surging when just start driving.

R

Renegade360

NAXJA Forum User
Location
SW FL
99xj, 4.0, AW4, 69k miles
Replaced TPS Still surging. Pulled the IAC at same time and cleaned it.
Cap, Rotor, plugs & wires changed around 50K miles.
Radiator recently replaced.

Condition
When I just starting driving after startup, The jeep will surge with moderate throttle at low speeds. Like it has no power, trys to stall. It stops surging when I mash the throttle and let back off, then drives normally the rest of the trip. Shut down for 30minutes start back up and the surging repeats until I mash the throttle again. What do you think, Vacume? Fuel Pressure? Clogged Cat? Map? IAC? Bad replacement TPS? Computer program? Transmission? CTS? What would you check next? Thanks. Tried search but didn't find anything that went away with high throttle.
 
Maybe crank position sensor (CPS)? When mine was bad, it was OK at idle and light throttle, terrible at 20% to 80% throttle, and OK at 100% throttle.
 
Well Now I have a spare CPS. Bought one from Napa. Still same problem. Old one tested fine on the multi meter. I'm thinking this is a fuel issue. It's acting like there is air in the fuel line. After driving a 1/2 mile or just putting the throttle to the floor, it runs fine the rest of the trip. Any thoughts? Could the fuel be leaking down? Also tried the code reader with no codes reported.
 
Talyn said:
Have you checked your fuel pressure?
Click to expand...

I agree that fuel pressure should be ruled in or out with testing with a gauge.

For a 99, you should have 49 psi, plus or minus 5 psi.

Test it when the engine is cold and symptomatic. You may have a marginal fuel pump that starts to work better when it has run for a little while.
 
Replaced fuel pump module. Still same problem. All I can come up with now is air leaking into the fuel line at one of the quick connect junctions.
 
You might want to test things before you up and replace them.

Surging to me would mean unwanted acceleration or RPM increases. Is that what you mean ?

Weak or faulty O2 sensors and weak/faulty Coolant Temperature Sensor or TPS can cause misfires or diminished power. They can and should be tested before you replace them.

Did you test/monitor the fuel pressure while these symptom occur ?
 
Have you washed the engine lately? If so you may have gotten the TPS wet. Another think could be a leaky vacuum hose over to the MAP (on Renix).
 
Map sensor tested low voltage. Unplugged map sensor and problem went away, though Idle sucked. Replaced Map Sensor and now all is great. In the trouble shooting I now have a new CPS, TBS and Fuel pump module on the 12 year old Jeep, so they should be good for another 12 years and I have spare parts incase something goes wrong. Probably still cheaper than taking to a shop to have fixed. Now I'm ready for those couple of thousand of mile trips to the hunting lodge this fall. Thanks for the help guys.
 
Surging it usually caused by fuel or ignition timing. Since the timing is non adjustable, I suspected fuel. The MAP sensor is the major contributor to fuel control. However, if the fuel pressure checked OK I wouldn't had replaced the fuel pump.
 
OK So I was wrong about the MAP sensor fixing this. It is still occuring.

Fuel Pressure reading is constant 49PSI from start, Through the Bogging down of the engine and surging. So it is not Fuel related.

There are still no Codes on my OBDII Scanner.
My Scanner shows live data. What my scanner also shows me when the vehicle is in open loop and closed loop. I've never paid attention to this when runnig it before, but the symptoms begin at the exact same moment that the system switches from Open Loop to Closed loop.

The 02 sensors test fine on the diagnostics, but all symptoms point to the 02 sensor. Especially since the symptoms clear when you open the throttle all the way. Will take them out and try to clean the contacts and see if that helps.
 
Renegade360 said:
.... the symptoms begin at the exact same moment that the system switches from Open Loop to Closed loop.
Click to expand...

Test the Coolant Temperature Sensor.

You are inspecting the wires and wire connectors to all the sensors for corrosion, damage, and chafed or melted insulation, right ?
 
Last edited:
It's the O2 sensor. Mine was doing this EXACT thing last week. Searched and read for a couple hours and everything I read pointed to the O2 sensor. Replaced it and she runs like a champ again.
 
Did you replace the front or rear o2 sensor or both?

Will check the Coolant temp sensor, though it appears to be functioning correctly and mirrors the reading on the dash gauge with the OBD scanner. I've paid attention to all connections. No Rust/corrosion or Frayed wires on any connection.
 
Coolant Temp sensor is fine. Took off the front o2, it was pretty clean, no buildup and reinstalled, haven't gotten the back one out yet. Drove it, Still same problem. Wish these o2 sensors were the same part number.
 
It was the up stream sensor. Sorry about my box being full when you pm'ed, its empty now.
 
Also there was no visible sign of damage or problems, not even a check engine light.
 
You must log in or register to reply here.

Similar threads

I
High idle, smells like gas, running out of things to replace
Replies
2
Views
2K
Inverhyt
I
G
1997 Sport running rough after warming up
Replies
8
Views
2K
Gilpine
G
M
96 XJ stumbles then shuts off when warmed up. P0171
4 5 6
Replies
113
Views
11K
Unclewolverine
U
B
Jeeper needs Help !!
2
Replies
22
Views
3K
denverd1
denverd1
M
New to my XJ & wrenching - How to choose parts and what to prioritize?!
2
Replies
28
Views
4K
flyin_ryan
F
Back
Top