How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Amedee Your Own Question
Amedee
Amedee, Jeep Technician
Category: Jeep
Satisfied Customers: 25607
Experience:  ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
279429
Type Your Jeep Question Here...
Amedee is online now
A new question is answered every 9 seconds

I have a 1998 jeep 4.0 at 4x4 240'000 miles on it runs

Customer Question

I have a 1998 jeep 4.0 at 4x4 240'000 miles on it runs smooth up till 2000 rpm than no power and spark knocks things I have done ,replaced distributor and complete tune up replaced timing chain also all needed did a vacuum test to see if exhaust was,plugged up vacuum stayed up did a compression test before started good you can drive a while as long no hurry all so replaced fuel pump no check engine light tested the looks good need help before I set fire to it thanks
Submitted: 8 months ago.
Category: Jeep
Expert:  Amedee replied 8 months ago.

Hello and welcome!

My name isCustomerand I can assist you with your question.

Expert:  Amedee replied 8 months ago.

What is the engine vacuum at idle?

Customer: replied 8 months ago.
Around 18
Expert:  Amedee replied 8 months ago.

Excellent! And what about at 2500 rpm?

Customer: replied 8 months ago.
About the same
Expert:  Amedee replied 8 months ago.

Thats good. I would say by those readings the exhaust is not plugged up.

Expert:  Amedee replied 8 months ago.

What is the fuel pressure at under a load when this happens?

Customer: replied 8 months ago.
That I haven't checked but I just allow replaced pump with the hole kit
Customer: replied 8 months ago.
I did that because no fuel filter to change
Expert:  Amedee replied 8 months ago.

The reason I ask is because it is possible that the fuel pressure is low. There is more to the fuel delivery system than just a fuel pump that can cause low fuel pressure. Low power to the fuel pump, restricted fuel supply line etc..

I would start by checking that and watch the oxygen sensor readings under a load to see if the engine is running rich or lean. That way you will know if the problem is a fuel delivery issue or not.

Customer: replied 8 months ago.
Okay that i can do I a few minutes I will get back with you
Expert:  Amedee replied 8 months ago.

Sounds good

Customer: replied 8 months ago.
It houses back and forth like it should did notice it runs good till about 2300 rpm so everything I replaced has helped some
Expert:  Amedee replied 8 months ago.

I am taking under a load. WIDE OPEN THROTTLE WHEN THE ENGINE HAS THE NO POWER PROBLEM

Customer: replied 8 months ago.
Okay
Customer: replied 8 months ago.
Good catch it stays rich so I have a fuel problem I guess
Expert:  Amedee replied 8 months ago.

If the oxygen sensor was reading lean, .1 or so under a load, then I would suspect a fuel delivery concern. If the oxygen sensor is reading rich .8 or .9 under a load, then the engine has enough fuel.

Which one do you have?

Customer: replied 8 months ago.
It reads rich .98
Expert:  Amedee replied 8 months ago.

Ok, thank you for that information. Either the oxygen sensor is bad, or the engine is simply has enough fuel under a load. If this is the case, then I would suspect an ignition timing issue. How did you set the distributor in place and how did you time the engine?

Customer: replied 8 months ago.
I set it on number one plus before i pulled it I marked old one
Expert:  Amedee replied 8 months ago.

Do you know what the distributor sync or indexing is set at?

Customer: replied 8 months ago.
You can,t adjust timing it goes in one way Plus it ran the same after I replaced it
Expert:  Amedee replied 8 months ago.

Right. I understand that. However, sometimes the distributor needs to be modified to get the reading in specs.

Expert:  Amedee replied 8 months ago.

Let me send you the procedure.

Turn the balancer clockwise to Top Dead Center. (The rotor will be turning clockwise also)

The trailing edge of the metal part of the rotor needs to be 0.020" past the #1 terminal in the cap.

Customer: replied 8 months ago.
Okay give me a few
Expert:  Amedee replied 8 months ago.

If the fuel pressure checks out good under a load, then here are some other possible causes.

MAP sensor

TPS sensor

Oxygen sensor

Crankshaft position sensor

Broken/cracked flex plate

Customer: replied 8 months ago.
Its hard to tell anyway to check it with a timing light
Expert:  Amedee replied 8 months ago.

That is why it needs to be checked using a scan tool reading live data. There is a PID for distributor sync or indexing

Customer: replied 8 months ago.
Okay I will check
Expert:  Amedee replied 8 months ago.

Sounds good

Customer: replied 8 months ago.
I could not find dist index but i did see advance at idle is 14 jumps to 40 right before i hit 2300 than spark knock and it starts messing up and my.jumps to much what should advance be at idle
Expert:  Amedee replied 8 months ago.
The manufacture does not provide that information. If the distributor in on fact installed correctly, then I would suspect a bad crank sensor or flex plate issue.
Customer: replied 8 months ago.
Okay thanks I will go from their. Thanks to r your help
Expert:  Amedee replied 8 months ago.
You're welcome! I'm glad I could help! Please don't forget to honor your good faith deposit by reading my answer as excellent service. It is been a pleasure working with you. Have a great day!
Expert:  Amedee replied 8 months ago.

Hello! It'sCustomerfrom just answer.

I am just checking in to see if you need any further assistance?

Let me know!