Cylinder Misfire code when floored

[2001 RED XJ]

Re: TRANSMISSION PROBLEM

Wouldn't it buck and jerk from fuel starvation. It feel like when it gets to 4500 and someone is holding the gas and brake at the same time. Motor sounds good just something holding it back. I've head camshaft timing at high RPM's can stall the motor too.

 

[2001 RED XJ]

Re: TRANSMISSION PROBLEM

It throws a misfire code when I leave it there for awhile. Sometimes the jeep runs really bad after this. Like a plug is fouled. Let it sit and disconnect the battery then it runs better.

 

[Digger87xj]

Re: TRANSMISSION PROBLEM

Rail has 45 PSI what should it be when engine is off, while running, and under load.

engine off.. really the only thing that matters during engine off is that the fuel remains in the line, priming to 45psi or close to it when the key is turned on. all other times: 45 psi.

Wouldn't it buck and jerk from fuel starvation. It feel like when it gets to 4500 and someone is holding the gas and brake at the same time. Motor sounds good just something holding it back. I've head camshaft timing at high RPM's can stall the motor too.

no, fuel starvation can act just like driving into a massive headwind, similar to plugged exhaust.

 

[DieselSJ]

Re: TRANSMISSION PROBLEM

Define "high performance with bigger cam and ported heads."

Cam specs?

Extent of porting?

Did you change injectors or make any other modifications?

 

[DieselSJ]

I think the misfire is because it won't go past 65. It's like its hitting a brick wall.

You left out the part of the engine mods. It is entirely possible that your fuel requirements are exceeding what the injectors can supply.

List up cam specs and full list of engine mods.

 

[DieselSJ]

Fuel injector wires mixed up?

That wouldn't do it. Above 2K rpm the injectors are open longer than the intake valve anyway so sequence doesn't matter at that point.

 

[Digger87xj]

Re: TRANSMISSION PROBLEM

Could this be camshaft timing being off. This is a High Performance Motor with a bigger cam ported heads. This motor screams until it hits 65.

yeah... totally missed this post.

Has it acted up ever since you got it back or is it something that has cropped up?

 

[2001 RED XJ]

Re: TRANSMISSION PROBLEM

http://indianapolis.craigslist.org/ptd/5176601736.html

 

[2001 RED XJ]

Re: TRANSMISSION PROBLEM

Yes it has been doing this ever since I brought it home.

 

[2001 RED XJ]

Re: TRANSMISSION PROBLEM

I haven't changed injectors.

 

[ValveMachinist]

You already answered your question of the problem !!! With the fuel pressure at 45 p.s.i.!!! Fuel pressure on a 2001 Jeep Cherokee should be at 49.2 psi 22.5 lb./hr. 236.5cc/min.on 04854181 factory blue tip injector. Look up of a chart of change in fuel flow from change in fuel pressure and you will find that a original pressure of 49.2 psi to 45 psi will reduce your flow from 22.5 lb/hr. to 21.518 lb/hr. or 236.5 cc/min. to 226.16 cc/min.! You definitely have a reduction of fuel flow and would probably notice it most at 65mph.Your problem is a very weak fuel pump or pressure regulator at top of tank. That is if I read it right and you have a 2001 Jeep Cherokee?

 

[DieselSJ]

Re: TRANSMISSION PROBLEM

I haven't changed injectors.

And you said in the other thread that your fuel pressure was like 45? Problem is becoming obvious.

 

[2001 RED XJ]

Yes it a 2001. I thought fuel pressure had tolerances. I was told that this was still in spec. It does drop down to 43 when it floored.

 

[2001 RED XJ]

Re: TRANSMISSION PROBLEM

I thought fuel pressure had tolerances. I was told that is was still in spec. It does drop down to 43 when floored.

 

[DieselSJ]

Yes it a 2001. I thought fuel pressure had tolerances. I was told that this was still in spec. It does drop down to 43 when it floored.

You were misinformed. The later models want 49. You have a weak pump or a restriction somewhere.

 

[Digger87xj]

You were misinformed. The later models want 49. You have a weak pump or a restriction somewhere.

I knew it sounded like a fuel starvation problem. I missed the 45psi red flag wagging in my face.

 

[Talyn]

45 psi shouldn't cause this problem. Stock spec is 49 psi +/- 5 psi. It is borderline with in spec. However, just testing at curb idle and/or with the engine off tells nothing. Pressure could be fine there, but fuel volume could be failing. Retest fuel pressure when the problem is happening. You will have to rid up a way to mount the gauge and watch it when driving. Jugging from the description of hitting a brick wall I do agree it is fuel related.

 

[1993 Red XJ]

It drops to 43 when the problem is happening.

 

[DieselSJ]

45 psi shouldn't cause this problem. Stock spec is 49 psi +/- 5 psi. It is borderline with in spec. However, just testing at curb idle and/or with the engine off tells nothing. Pressure could be fine there, but fuel volume could be failing. Retest fuel pressure when the problem is happening. You will have to rid up a way to mount the gauge and watch it when driving. Jugging from the description of hitting a brick wall I do agree it is fuel related.

He has engine mods - cam and head work. I'll bet lunch that he is starving the engine.

 

[1993 Red XJ]

Do I need to get bigger injectors?