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Amedee
Amedee, ASE Master Tech
Category: Car
Satisfied Customers: 21846
Experience:  ASE Master Tech advanced level specialist. Wisconsin certified emissions state inspector
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95 land rover discovery, 3.9l..running rough..cap..rotor

Customer Question

95 land rover discovery, 3.9l. running rough once warm. new plugs, new wires, new cap and rotor. started doing this after a can of seafoam. also new fuel filter
Submitted: 2 years ago.
Category: Car
Expert:  Amedee replied 2 years ago.
Hello!

Is the engine misfiring or bogging down when this happens?

Does this happen at idle or under a load?
Customer: replied 2 years ago.

it idles fine, it feels like it is misfireing on one or more cylinders. kinda skipping like its running out of gas. once it is warm and normal driving is when this happens, but the idle stays good the whole time

Expert:  Amedee replied 2 years ago.
Is the check engine light on?

Are there any codes in the computer?
Customer: replied 2 years ago.
no, no lights and no codes, and i have verified the obd is working
Expert:  Amedee replied 2 years ago.
So it does not misfire when cold?

Do you know which cylinder is misfiring?
Customer: replied 2 years ago.
no it feels like a misfire but all the plugs are dry and burning perfect, also no smell of gas in exhaust
Expert:  Amedee replied 2 years ago.
I would remove one spark plug wire at a time to see what cylinder is misfiring. Each cylinder should cause the engine rpm to drop when doing this test. The cylinder that does not affect the engine rpm when this happen is the cylinder that is misfiring.

Once you have found this, then you need to double check the tune up parts, fuel delivery and engine mechanical to find out what is going on.
Customer: replied 2 years ago.
i have done that and unplugging each plug boot causes stumble, it only feels like a misfire but it is not, has to be on fuel delivery. if the temp sensor is faulty can it send an incorrect signal to the ecm which will incorrectly delivery fuel to the injectors once the car is hot
Expert:  Amedee replied 2 years ago.
You bet it could be!

You could try adding some propane to the intake it is running rough to see if it smooths out.
Expert:  Amedee replied 2 years ago.
Also, be sure that the fuel pressure regulator is not leaking and that the fuel pressure checks out within specs.
Customer: replied 2 years ago.
hey sorry i have been stuck at work and have not got to work on land rover rover,i have checked the fuel reg and its not leaking, also fuel pressure holds at 29-31 psi at idle. ran fine today for about 15 minutes and started skipping again. any thoughts?
Expert:  Amedee replied 2 years ago.
So this problem only happens off idle?

Have you tried to spray carb cleaner into the intake or propane to see if it improves the condition at all when this happens?
Customer: replied 2 years ago.
it idles perfect at 750, it does not jump around at all, only when driving the land rover it starts bucking like its running out of gas, even then when you stop the idle is perfect. it will not do it with it just sitting only under normal driving load
Expert:  Amedee replied 2 years ago.
If you can get it to do this under a load, try spraying some starting fluid into the intake while doing a brake stand (ever so lightly) and see if the problem clears up. If so, then you just have a fuel delivery concern. THe fuel injectors may not be opening up enough causing this condition. If this does not help, then chances are we have a primary ignition system issue that needs to be dealt with.
Customer: replied 2 years ago.

i have changed the fuel injectors a few weeks ago, (sorry i didnt mention that) and they have been working fine untill this started, not saying thats not it, but not likely. is there any resistence checks on the coil or any checks i can do there

Expert:  Amedee replied 2 years ago.
Honestly, I do not use resistance checks on ignition components. As long as the engine is running, it does no good. I will tell you why. You need to check the voltage in the ignition components WHEN they are in use... or under a load. That is when they break up. This means it has to be done with the engine running when it is acting up using a lab scope. Hands down, this is going to be the beast way. Unfortunately, I understand you do not have a lab scope. You can use try and ohm out all of the secondary ignition components, but it will take a long time and my experience has been that you will not get good results.
Customer: replied 2 years ago.

no i dont have a lab scope

Expert:  Amedee replied 2 years ago.
So then your only option would be to replace the suspect ignition parts or pay someone to scope your ignition system.
Customer: replied 2 years ago.
what would be your best guess on what to change first?
Expert:  Amedee replied 2 years ago.
I would go after the crankshaft position sensor on the lower right hand side of the engine.
Customer: replied 2 years ago.
the 95 disco does not have a crankshaft position sensor
Expert:  Amedee replied 2 years ago.
According to my references, it is located on the right hand side of the engine. It has to have a engine speed sensor for spark timing.
Customer: replied 2 years ago.
not sure what your looking at but it does not have crank position sensor. it has the rpm reference sensor
Expert:  Amedee replied 2 years ago.
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