99 Jeep Wrangler TJ jerking under stress / high rpms

P

Patrick0923

New Member
Joined
Feb 18, 2020
Messages
11
Location
JAX, FL
Hello Everyone,

New member here. I've been using this site for a resource for the last 3-4 years when i picked up my 99 2.5. You all have been a great help, so i'm hoping you can help out here too! I'm stuck on this one and i don't see anyone with any similar issues, so looking for some pointers.

Car info:
- 1999
- 2.5 L
- Manual 5spd
- 135K miles
- lifted with 33's

Fist off, what i've 'touched' over last year:
* New Sparks (champions .35 spaced) / wires / cap / roter
* New battery terminal cables (custombatterycables.com)
* New Exhaust Manifold (old one had cracked, replaced by shop, cracked again within 4mo, under warrenty shop replaced)
* New Fuel Injectors (STP double platinum) ** after install reset sensors**
* New O2 sensors (NTK - upstream and downstream) ** after install i reset sensors **
* New Idle Air Controller (1st item ever replaced, done by shop, may need to revisit)


Now the issue:
Cranks up, no problem. Sitting idle, no problem. Start driving, no problem.
i get to about 40 mph, about 4th gear, between 2.5 RPMs and 3K, and it starts. Best way i can describe it is a 'bucking' or 'jerking' sensation. Happens for a split second, then levels out. But it can happen again in quick concession. My reaction has been to release the gas, dropping the accelleration, and coast until 3rd gear then try again... same results. even if i push through and try to get to 5th gear, it still happens...

Visually during the issue, no codes. Dashboard - Oil/Gas/Temp gauges remain unchanged. Mileage stays lit. Noticed Oil pressure seems on the high side, but within acceptable range. RPM and SPEEDOMETER are dying then coming back, for every jerk the needles fall and return.

So to see this issue under various scenarios i tried not driving on the highway, and i did confirm the issue doesn't happen at lower speeds.. basically if i keep her under 4th gear (-40 mph) then never see the issue. Now this is FL, and everything is flat.. so i thought i would try the same test out but on a tall bridge, trying to rule out the speed factor, which would isolate to stress?. And i was successfully able to see the issue while 'climbing' uphill. In this case the issue happened all the way from bottom to the top of the bridge even while only going 20 mph and staying around 2nd to 3rd gear. once at the top, i kept the gear engaged, took foot off gas, and let her coast to the bottom. Here i noticed no jerking or bucking, but the needles (RPM and SPD) were dying and coming back over and over.

Leads:
- Not electrical - if it was, wouldn't i have lost power to the radio and dashboard? (all needles would have fallen, mileage would have gone dark?)
- Misfire? - right before this started, i had a misfire code in cyl 3, but that was fixed after Fuel injectors replaced, issue could be stil there? but yet no codes, and no smell of gas.
- Oxygen? - new upstream and downstream O2 sensors, but maybe a vacuum leak? under stress would make it worse causing a choke, making the engine die?
- Fuel? - possible fuel pump failure? or bad Fuel pressure regulator? Needed at high speeds?

** also i have one of those OBD services (AUTOMATIC) where you can plug in and do various things. While this issue is happening, it is reporting that the car is "turning off" and "turning on" over and over. So when i drive say to work and never see/feel the issue, the dongle shows that i've taken 6 trips... but this may be a completely separate issue, so not considering it, but its information that out there.. **


Ok... i'm hoping you all can help me out on this one.. i'm an amateur with the tools, but willing to work through it if its within my skill set.. otherwise i'll take it to mech.

Thanks!
 
Just a guess...
Possible fuel delivery problem, starving for fuel?. Clogged fuel filter? What gets me is the RPM and Speedo dropping and recovering. That is deep. Possible ECM/ECU (whatever you call the computer under the hood) problem. Try getting one from a junk yard and see if problem persists?
Good luck and keep us posted.
 
76CJQuadratrac said:
Just a guess...
Possible fuel delivery problem, starving for fuel?. Clogged fuel filter? What gets me is the RPM and Speedo dropping and recovering. That is deep. Possible ECM/ECU (whatever you call the computer under the hood) problem. Try getting one from a junk yard and see if problem persists?
Good luck and keep us posted.
Click to expand...
I was also thinking the sensors on the throttle body.. but that could also point to the air intake problem.. or a leak. I don't wanna just throw parts at her.
 
Blondie70 said:
What is your fuel pressure at idle ? Test it at different engine loads, if possible.
Click to expand...
I haven't gotten that far to checking the pressure, if we think that's where I should go, then I'll go get a gauge and test for sure. At different loads? Meaning at idle then rev the engine? Problem is even if I keep it in 2nd gear and rev all the way to 4k rpms, it still won't happen.. seems the only time I can get it to happen is when I'm actually driving and at this speeds.
 
I'll have to wait until this weekend to take a peek.. I never have time during the week. I think I'm going to check for any vacuum leaks first.. then check fuel pressure.. and if not that then I'll look at replacing the sensors around the throttle body.

Unless anyone has any better suggestions..
 
Since there are a number of other threads about wiring at the moment, I wonder if you have a short in the wiring harness somewhere and it's causing the wiring to ground on whatever it's rubbing against, thus causing this issue. The faster you go, the more the engine moves, thus moving the wiring with it, thus causing it to short out.

It's worth looking, of course it's going to take a lot of time and patience to figure out if there is a short in the wiring, as there is a lot of wiring to go around, and way more than just one area where this could be happening.
 
Chris said:
Since there are a number of other threads about wiring at the moment, I wonder if you have a short in the wiring harness somewhere and it's causing the wiring to ground on whatever it's rubbing against, thus causing this issue. The faster you go, the more the engine moves, thus moving the wiring with it, thus causing it to short out.

It's worth looking, of course it's going to take a lot of time and patience to figure out if there is a short in the wiring, as there is a lot of wiring to go around, and way more than just one area where this could be happening.
Click to expand...
Very true.. I have noticed a lot of electrical tape wrapping from the previous owner on some of the wires.. I'll add it to the list to look at this weekend.. thanks for the suggestion
 
Patrick0923 said:
Very true.. I have noticed a lot of electrical tape wrapping from the previous owner on some of the wires.. I'll add it to the list to look at this weekend.. thanks for the suggestion
Click to expand...

No problem, that's definitely something to check out in depth.
 
Seems to point to electrical problem. Intermittent contacts in key cylinder in steering column? Check under center console to make sure PO didn't leave any wires that are being moved around by gear shifter?
How about a rev limiter malfunction? Either a bad sensor or ECM issue that is shutting the engine down to early, thinking it is at its rev limit?
Just some guesses...
 
Ok an update:

Saturday, i started with Electrical. Started in exhaust, moved my way to engine bay, and back to fuel, wrapping anything 'open' or 'free' in either heat wrap or electrical wrap.
Electrical Findings:
- Upstream O2 sensor wire and Temp/Charge Sensor wire were bouncing around like crazy. Possibly touching against inner frame at high speeds (wind). Wrapped em up, zip tied.
- Main electrical hosing (contains the wires for fuel injectors, o2, throttle body sensors etc was resting on the back of the block. It was wrapped in that plastic shielding, so shouldn't be a problem. However, i noticed that the clip that holds it steady was missing, and the bolt that it clips to was impaling that plastic shielding. lifted it, twisted the shielding, placed some electrical tape to hold in place.

Next up = possible leaks. Followed the same process (exhaust > engine bay > fuel) and torqued everything down.
leak findings:
- O2 sensors had been hand tightened, but not torqued
- Intake manifold - needed torquing
- exhaust manifold to exhaust pipe - needed torquing


put her all back together and reset the sensors again.
drove her around, no problems. But i knew i needed to "stress" her out in order to check fully.
So Sunday, i drove at high RPMs in all gears, issue never happened.
Just to confirm i took her to work this morning, which requires crossing the bridge i mentioned previously, issue still didn't show itself....

I'm hopeful, but really curious what the issue was related to. and if it will return.
I already ordered the replacement sensors for the throttle body. I think i'll replace them anyways just to say i did.

but what are ya'll's thoughts?
- O2 sensors not torqued?
or
- Electrical shorts fixed with wrappings and tie downs?

Thanks again for all the suggestions, by the way, super helpful as always.
-Patrick
 
  • Like
Reactions: Chris
I had the EXACT same issue last June. O2 sensors were my fix. Replaced both and ran smooth again. I had cleaned IAC, replaced a couple other sensors, had new ignition wires, etc. nothing helped until the O2s.

My 2c...
 
David Valentine said:
I had the EXACT same issue last June. O2 sensors were my fix. Replaced both and ran smooth again. I had cleaned IAC, replaced a couple other sensors, had new ignition wires, etc. nothing helped until the O2s.

My 2c...
Click to expand...

He said he replaced the O2 sensors in the original post (with NTK sensors), so I suspect that isn't the issue.

Patrick0923 said:
Electrical shorts fixed with wrappings and tie downs
Click to expand...

Ummm, yes. Electrical shorts would absolutely cause the symptoms you are describing, 100%.
 
It sounds like you may have it solved but if it continues I would definitely do a running fuel pressure test to rule that out. If the fuel pressure is dropping when the symptoms occur it would indicate something is preventing adequate fuel flow for those higher loads.
 
Chris said:
He said he replaced the O2 sensors in the original post (with NTK sensors), so I suspect that isn't the issue.



Ummm, yes. Electrical shorts would absolutely cause the symptoms you are describing, 100%.
Click to expand...

Thanks again, Chris for the hint to look to wiring! I agree I was leaning that direction after looking at so many fixes I needed to do regarding the wiring.
 
  • Like
Reactions: Chris
freedom_in_4low said:
It sounds like you may have it solved but if it continues I would definitely do a running fuel pressure test to rule that out. If the fuel pressure is dropping when the symptoms occur it would indicate something is preventing adequate fuel flow for those higher loads.
Click to expand...

Yeah with the money I've saved from this little project I think I'm going to invest it in a fuel overhaul. My gas gauge is broken anyways, so I think I'll go the route of a new pump and sending unit. And have them check the pressure regulator while they making the effort.
 
Patrick0923 said:
Thanks again, Chris for the hint to look to wiring! I agree I was leaning that direction after looking at so many fixes I needed to do regarding the wiring.
Click to expand...

Wiring is one of the last things people think to check, but often times it ends up being the issue. There was a good thread about this here recently and how wiring can cause all sorts of faults / drivability issues.
 
Patrick0923 said:
Hello Everyone,

New member here. I've been using this site for a resource for the last 3-4 years when i picked up my 99 2.5. You all have been a great help, so i'm hoping you can help out here too! I'm stuck on this one and i don't see anyone with any similar issues, so looking for some pointers.

Car info:
- 1999
- 2.5 L
- Manual 5spd
- 135K miles
- lifted with 33's

Fist off, what i've 'touched' over last year:
* New Sparks (champions .35 spaced) / wires / cap / roter
* New battery terminal cables (custombatterycables.com)
* New Exhaust Manifold (old one had cracked, replaced by shop, cracked again within 4mo, under warrenty shop replaced)
* New Fuel Injectors (STP double platinum) ** after install reset sensors**
* New O2 sensors (NTK - upstream and downstream) ** after install i reset sensors **
* New Idle Air Controller (1st item ever replaced, done by shop, may need to revisit)


Now the issue:
Cranks up, no problem. Sitting idle, no problem. Start driving, no problem.
i get to about 40 mph, about 4th gear, between 2.5 RPMs and 3K, and it starts. Best way i can describe it is a 'bucking' or 'jerking' sensation. Happens for a split second, then levels out. But it can happen again in quick concession. My reaction has been to release the gas, dropping the accelleration, and coast until 3rd gear then try again... same results. even if i push through and try to get to 5th gear, it still happens...

Visually during the issue, no codes. Dashboard - Oil/Gas/Temp gauges remain unchanged. Mileage stays lit. Noticed Oil pressure seems on the high side, but within acceptable range. RPM and SPEEDOMETER are dying then coming back, for every jerk the needles fall and return.

So to see this issue under various scenarios i tried not driving on the highway, and i did confirm the issue doesn't happen at lower speeds.. basically if i keep her under 4th gear (-40 mph) then never see the issue. Now this is FL, and everything is flat.. so i thought i would try the same test out but on a tall bridge, trying to rule out the speed factor, which would isolate to stress?. And i was successfully able to see the issue while 'climbing' uphill. In this case the issue happened all the way from bottom to the top of the bridge even while only going 20 mph and staying around 2nd to 3rd gear. once at the top, i kept the gear engaged, took foot off gas, and let her coast to the bottom. Here i noticed no jerking or bucking, but the needles (RPM and SPD) were dying and coming back over and over.

Leads:
- Not electrical - if it was, wouldn't i have lost power to the radio and dashboard? (all needles would have fallen, mileage would have gone dark?)
- Misfire? - right before this started, i had a misfire code in cyl 3, but that was fixed after Fuel injectors replaced, issue could be stil there? but yet no codes, and no smell of gas.
- Oxygen? - new upstream and downstream O2 sensors, but maybe a vacuum leak? under stress would make it worse causing a choke, making the engine die?
- Fuel? - possible fuel pump failure? or bad Fuel pressure regulator? Needed at high speeds?

** also i have one of those OBD services (AUTOMATIC) where you can plug in and do various things. While this issue is happening, it is reporting that the car is "turning off" and "turning on" over and over. So when i drive say to work and never see/feel the issue, the dongle shows that i've taken 6 trips... but this may be a completely separate issue, so not considering it, but its information that out there.. **


Ok... i'm hoping you all can help me out on this one.. i'm an amateur with the tools, but willing to work through it if its within my skill set.. otherwise i'll take it to mech.

Thanks!
Click to expand...
Idk about the 2.5 but in my 4.0 it was the camshaft position sensor. I tried everything and nothing worked, swapped the sensor and instantly fixed it. I have a thread on it
 
[Update]

So I replaced all the sensors around the throttle body including the temperature/charge sensor. While I do feel the issue is fixed from the wiring adjustments, I do feel the ride is better with the new sensors... However I ran into the good ole IAC issue.

Put in new IAC, reset the sensors, started her up. She ran at 3k rpms at idle. Driving was no prob, but in neutral or at idle 3k. Scary and embarrassing..

I thought leak like I've seen in so many other posts about this, especially from Jerry and Chris in the past, so with it still idling, I through some carb cleaner all around listening for change in rpms.. nothing.. I had just cleaned my TB recently but to cross it off with it running I sprayed a hefty amount down the throat, and it did sputter, but i actually couldn't get it to cut off entirely..

After all that, placed the old IAC in.. runs like a champ..

Not gonna bother with it. I'll enjoy what I have for as long as I have it.
 
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