SBpunk Posted April 6, 2017 Share Posted April 6, 2017 1992 LWB 4.0 HO AX15/NP242 Ok just got my motor back from being rebuilt and installed. Double checked all the connections/vacuum hoses. Still has a rough idle. Its inconsistent and I can feel it through the steering wheel. Always most noticeable at idle but can also feel it struggling at speed. I'm going to try replacing all the sensors again but the only vacuum line that isn't connected is the one going to the heater control valve that was deleted awhile back. I'll list the replaced stuff down below but any input would be awesomeRebuilt MotorNew copper champion spark plugsNew wires from ACCELNew stock fuel injectorsNew batteryNew 63mm TBNew TB sensors (only one hasn't been changed was MAP) New exhaust from the exhaust header back to the tailpipe (no cat)New radiatorFresh antifreeze/break in oil Honestly I'm out of ideas besides trying to swap the sensors again. It hasn't backfired since I've had it back but it used to backfire out of the intake Link to comment Share on other sites More sharing options...
big66440 Posted April 6, 2017 Share Posted April 6, 2017 Check your oxygen sensor heater element, if it's not working it can't stay in closed loop at all times and you will feel a vibration. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 6, 2017 Share Posted April 6, 2017 Did you check for codes? If none, after changing all the sensors, TB, etc. you should clear the ECU residual memory and start from scratch. Clearing error codes and removing residual memory1. Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.2. Reconnect the Battery Cable3. Turn Ignition Switch to the "ON" position but DO NOT start the engine4. Turn Headlight "ON"5. Turn Headlights "OFF"6. Turn Ignition Key "OFF"The PCM Adaptive memory has now been flashed, or erased from the PCM. Link to comment Share on other sites More sharing options...
SBpunk Posted April 6, 2017 Author Share Posted April 6, 2017 Yup no codes unfortunately and it's been reset a few times. I'm going to put a map and o2 sensor in this weekend. Always thought it was the low compression cussing the idle but even when he took the motor apart he said it wasn't nearly as bad as some of the others. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 6, 2017 Share Posted April 6, 2017 New 63mm TB Where did this come from? Any exhaust mods like a header? Link to comment Share on other sites More sharing options...
SBpunk Posted April 6, 2017 Author Share Posted April 6, 2017 http://www.strokedjeep.com/ No other mods. Factory air box, new downpipe, thrush welded muffler and autozone special tail pipe. Guess the muffler would be aftermarket. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 6, 2017 Share Posted April 6, 2017 Does this throttle body have provisions for mounting the MAP sensor? Link to comment Share on other sites More sharing options...
SBpunk Posted April 6, 2017 Author Share Posted April 6, 2017 High output map sensor is mounted to the firewall. Unless you're talking about something else? Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 6, 2017 Share Posted April 6, 2017 The later TB's (96 and up) had provisions for TB mounting. I did this using a 96 MAP sensor and it really smoothed out the idle using a bored TB. http://comancheclub.com/topic/41929-installing-a-1996-throttle-body-mounted-map-sensor/ Link to comment Share on other sites More sharing options...
SBpunk Posted April 6, 2017 Author Share Posted April 6, 2017 Nice I'll check it out. 99% sure it's a 91 to 95 or whatever but meeh who knows. At this point I'd try anything already rebuilt the motor for no reason... Link to comment Share on other sites More sharing options...
Minuit Posted April 7, 2017 Share Posted April 7, 2017 I have a similar problem to you, but mine runs good at speed. I do notice a big increase in power right at 3000 rpm (4.0s aren't supposed to have VTEC!), no explanation for that one. Have you gotten a spark tester and looked at the spark? My spark is orange and kind of inconsistent, which I'm sure isn't helping. Coil and wires are in spec on mine also. This weekend probably I'll be swapping to the '96 throttle body with onboard MAP sensor. I'll let everyone know if I see improvements. Link to comment Share on other sites More sharing options...
big66440 Posted April 7, 2017 Share Posted April 7, 2017 Another thing you could check would be your intake/exhaust manifold bolts. Its not uncommon for them to loosen up causing different kinds of problems, doesn't cost anything either. Link to comment Share on other sites More sharing options...
SBpunk Posted April 7, 2017 Author Share Posted April 7, 2017 Another thing you could check would be your intake/exhaust manifold bolts. Its not uncommon for them to loosen up causing different kinds of problems, doesn't cost anything either. We just tightened them down to spec with new bolts yesterday when the motor was dropped back in. Link to comment Share on other sites More sharing options...
kryptronic Posted April 10, 2017 Share Posted April 10, 2017 Does this happen all the time, or just after the engine has reached its 190 degree operating temp? Computer doesn't kick in on Chrysler contolled motors until operating temp is reached. If you only have an issue after the engine is warm, look at the TPS, IAC, O2, Crankshaft and Camshaft sensors in that order. Link to comment Share on other sites More sharing options...
SBpunk Posted April 10, 2017 Author Share Posted April 10, 2017 Does this happen all the time, or just after the engine has reached its 190 degree operating temp? Computer doesn't kick in on Chrysler contolled motors until operating temp is reached. If you only have an issue after the engine is warm, look at the TPS, IAC, O2, Crankshaft and Camshaft sensors in that order. Its all the time. I was messing with the vacuum hoses and the only sensor I haven't messed with was the MAP. Soon as I unplug it there's a noticeable change so not thinking its the cause. There's less than 200 miles on the rebuild so maybe I'm just going crazy. Just seems like the motor is surging when I'm idle. The vibration in the steering wheel is pretty noticeable too. If the doors are open they look like they're going to shake off the hinges. Motor mounts and trans mount are brand new also. I swapped in a new O2 sensor a couple days ago along with putting in a mopar TPS / IAC. Didn't make any difference even after the reset. Not sure what else it could be. Maybe just needs to settle from the rebuild but its doing the same thing that lead me into thinking it needed a rebuild to begin with. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 10, 2017 Share Posted April 10, 2017 Does this happen all the time, or just after the engine has reached its 190 degree operating temp? Computer doesn't kick in on Chrysler contolled motors until operating temp is reached. If you only have an issue after the engine is warm, look at the TPS, IAC, O2, Crankshaft and Camshaft sensors in that order. Not quite true. You can watch the open-to-closed loop transition on an A/F meter in less than a minute after starting the engine - the temp gauge hasn't budged yet. This means the ECU is passing traffic. The cycle to closed loop is complete at about two minutes after starting depending on ambient temperature and the idle immediately smooths out. Link to comment Share on other sites More sharing options...
Jeep Driver Posted April 10, 2017 Share Posted April 10, 2017 Fuel pressure? Link to comment Share on other sites More sharing options...
SBpunk Posted April 10, 2017 Author Share Posted April 10, 2017 Haven't checked that yet. Thinking my computer might be bad. Not much else left Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 10, 2017 Share Posted April 10, 2017 It takes a good fifty miles or so of driving with several key starts along the way before the computer "learns" the new settings from changes, like sensors, throttle body, and even battery disconnects. Mine always runs like crap at first and gradually comes back to normal. The idle is usually low, and it stalls sometimes when rolling to a stop. How much have you driven it so far after the last changes you made? Link to comment Share on other sites More sharing options...
SBpunk Posted April 10, 2017 Author Share Posted April 10, 2017 It takes a good fifty miles or so of driving with several key starts along the way before the computer "learns" the new settings from changes, like sensors, throttle body, and even battery disconnects. Mine always runs like crap at first and gradually comes back to normal. The idle is usually low, and it stalls sometimes when rolling to a stop. How much have you driven it so far after the last changes you made?Not far since I put the sensors in. I'm taking down to the city this weekend about 130 miles round trip. It's just paranoia I'm sure since it's the same feel as it did prior to the rebuild. Link to comment Share on other sites More sharing options...
kryptronic Posted April 12, 2017 Share Posted April 12, 2017 Sorry, I missed that the issue happens all the time. To clear rough idle prior to reaching closed loop I would look at fuel pressure and vacuum. Test both at the fuel rail. Link to comment Share on other sites More sharing options...
omega_rugal Posted April 12, 2017 Share Posted April 12, 2017 kinda sucks having the entire thing rebuilt and get this... rough idle may be the MAP, TPS or Idle stepper motor who loves to get stuck either open or closed all the time... Link to comment Share on other sites More sharing options...
SBpunk Posted April 12, 2017 Author Share Posted April 12, 2017 Yeah it hasn't gotten any better with another 200ish miles put on it. Grabbed a new CPS to throw in later after I rent a fuel pressure tester from Orielly's. If its not any of those the only other things I have been able to think of are the Camshaft sensor/Dizzy or the computer itself is shot Link to comment Share on other sites More sharing options...
SBpunk Posted April 13, 2017 Author Share Posted April 13, 2017 OK so fuel pressure is at 31 with vacuum connected and 39 without. Got the CPS in the mail then the new distributor from a 94 to 96 is next Link to comment Share on other sites More sharing options...
SBpunk Posted April 14, 2017 Author Share Posted April 14, 2017 Ok figured out something else. So when I first start it or come to a stop it usually idles around 700rpm smooth as can be. After a few seconds it drops to 500-550ish and starts acting up. Anyone deal with anything like that? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now