Help! 95 wrangler 4.0 shakes/revs when idling

[Guymancouch]

Hello, I have a problem with my 95 wrangler. It shakes when it is in idle also in first gear (automatic trans). I had the engine replaced hoping it would solve this problem but it still exists just not as bad, before the engine replacement it would shake to the point that it would shut off. Almost everything is new inside, engine, thermostat, water pump, distributor, wires and plugs, fuel pump and injectors, o2 sensor, map sensor, pretty much all the sensors; the only thing that hasn't been replaced in it is the computer.

The mechanic who installed the new motor saw the problem on the 500 mile check up and then ran tests and said that there is no error that is coming up on any of the testing equipment. His advice was to run it, the jeep, until the problem gets bad enough and hopefully they can catch the error on a diagnostic machine. Has anyone had this problem or similar problem? It also seems to get worse after it has been driven for a while. The first start up and drive is fine but after 20 minutes or multiple turn offs and turn on (going to a store and turning it off then hoping back in and cranking the engine) seems to make the shaking worse. At speed, 30 plus mph, it runs smooth but sometimes I feel it shake as if gas is not being sent into the engine.

Any advice would be appreciated

Thanks.

 

[Jackson LeBlanc]

Check your air system. I had a similar problem with my jeep very recently where it wouldn’t get enough air and the revs would drop and it would start shaking. It could take a quick replacement of the air filter to cleaning your fuel injectors. Even call someone who can maybe give you a tune up if needed. Hope this helps, keep us posted.

 

[DOWNS]

Holy crap man you replaced the whole engine because it shook? How much troubleshooting was done prior to the engine replacement?

What fuel pressure are you getting? A pinched return line can cause your pressures to spike to 80-90 PSI which basically floods the engine. Too low can cause similar feeling issues. Doesn't matter if the pump is new get a fuel pressure reading. Normal Fuel pressure is around 30 psi with the vacuum line connected to the pressure regulator. 40ish if you unhook that line.

 

[Guymancouch]

Holy crap man you replaced the whole engine because it shook? How much troubleshooting was done prior to the engine replacement?

What fuel pressure are you getting? A pinched return line can cause your pressures to spike to 80-90 PSI which basically floods the engine. Too low can cause similar feeling issues. Doesn't matter if the pump is new get a fuel pressure reading. Normal Fuel pressure is around 30 psi with the vacuum line connected to the pressure regulator. 40ish if you unhook that line.

A lot of trouble shooting. All the diagnostics came back normal. The fuel pressure is within the normal range. I replaced my fuel injectors so considering the engine was close to 300,000 miles It would of been replaced eventually. It also was not a "shake", the shaking literally would shut the car off. So in the long run its not a bad idea. That being said I will have the mechanic double check the fuel line and bring up the ideas you mentioned. Thank you for the advice and I will let you know if that is the problem

 

[Guymancouch]

Holy crap man you replaced the whole engine because it shook? How much troubleshooting was done prior to the engine replacement?

What fuel pressure are you getting? A pinched return line can cause your pressures to spike to 80-90 PSI which basically floods the engine. Too low can cause similar feeling issues. Doesn't matter if the pump is new get a fuel pressure reading. Normal Fuel pressure is around 30 psi with the vacuum line connected to the pressure regulator. 40ish if you unhook that line.

Check your air system. I had a similar problem with my jeep very recently where it wouldn’t get enough air and the revs would drop and it would start shaking. It could take a quick replacement of the air filter to cleaning your fuel injectors. Even call someone who can maybe give you a tune up if needed. Hope this helps, keep us posted.

Thank you for the ideas. I am bringing it in soon and I will have the mechanic look into the air system. I let you know how that goes

 

[DOWNS]

I mean at this point if the only thing not replaced is the ECU then what's the cost of that compared to a whole engine?

Also when's the last time the battery cables have been replaced? Grounds cleaned? All of these sensors run on a 5 volt reference signal so clean grounds and good cables are very important. I've seen what externally looked like good cables be so corroded internally they wouldn't pass enough power to turn the engine over. Probably a lot of sensors have been replaced over the decades due to bad grounds.

I replace mine on a 5 year cycle as preventative maintenance.

 

[T-Rex Jeepster]

I've brought this up before....Many...MANY times I have found "Misses" By putting the vehicle in a very dark place, Garage etc. Lift the hood with it running and look for dead shorts via arching though what looks like perfectly good insulation on plug wires, Connections on ignitions etc .You'll be shocked what shows in the dark that you cannot see even in low light......