BAWC Forums

Alot of people on the jeep forum are saying CPS, so I think I am going to test that tonight for sure.

If the CPS fails to solve my problem, I am thinking about just cutting off the exhaust before the cat and seeing what happens.

[quote=""Darkhelmet""]I fail to see how having a hole on your exhaust would cause fuel pressure to jump around. I must have been absent the day they covered the exhaust gas fuel pressure regulation system [/quote]

You must have also missed out on the presupposition lesson too. Exhaust does NOT directly regulate fuel pressure and it would be very absurd to assume that it did or that I was inquiring it does.

Fuel pressure is created by the FPR restricting the fuel lines and is controlled by vaccum. Vaccum is created from the downward travel of the piston and all the air getting burned off from combustion.

This is what I explained 2 or 3x in one of the other 50 threads on this issue. If the O2 sensor isn't getting proper reading of the exhaust (due to holes in the pipe before it), the ECU/ECM (whatever you want to call the engine computer) won't be injecting the proper fuel. Thus you get the studdering and hens the fuel pressure going bonkers.

Then to add to this, I believe I also suggested to try PATCHING the exhaust with fiberglass (as a TEMP solution) to see if the studdering goes away. It's really cheep (maybe $50 total) and anyone can do it if they don't mind getting a little dirty. If the shuddering doesn't subside, then you didn't waste your $$ on the exhaust.

Here, let me put more emphasis on PATCHING the exhaust before doing anything rash.

Duck, you're getting shamed or the mechanic is as completely clueless as Helmet's exhaust gas theories.

Ok mono. You convinced me. The only places before the O2 sensor that I noticed was bad was the part where the downpipe connects to the Manifold and the manifold itself might be bad (cracked), or the gasket is shot. How would I go about repairing that?

At Autozone they sell fiberglass patch kits. They come in a yellow box (can't remember the brand name). You may need 2 or 3 of them. The instructions are right on the packaging.

All you do is wrap the hole with aluminum foil, cut the fiberglass into 2" slits, pour the resin into a container, dip the fiberglass in it, wipe excess, apply patch over hole and allow it to dry. It really is that easy. If it doesn't work, later on you can scrape it off.

As for the leaky gaskets, there's not much you can do there other than replace them. These patch kits are only meant for fixing holes in pipes.

Did you ever go about finding if your cat was clogged?

We should have gotten together when I was out there in WI last week.

[quote=""Monochrome""]At Autozone they sell fiberglass patch kits. They come in a yellow box (can't remember the brand name). You may need 2 or 3 of them. The instructions are right on the packaging.

All you do is cut the fiberglass into 2" slits, pour the resin into a container, dip the fiberglass in it, wipe excess, apply patch over hole and allow it to dry. It really is that easy. If it doesn't work, later on you can scrape it off.

As for the leaky gaskets, there's not much you can do there other than replace them. These patch kits are only meant for fixing holes in pipes.

Did you ever go about finding if your cat was clogged?[/quote]

I wanted to, but I am not too sure how to do that, and no one has told me how yet. I bang on it, but nothing rattles that I can tell. I would have to cut the cat off since it is not bolted on.

[quote=""Monochrome""]You must have also missed out on the presupposition lesson too. Exhaust does NOT directly regulate fuel pressure and it would be very absurd to assume that it did or that I was inquiring it does.

Fuel pressure is created by the FPR restricting the fuel lines and is controlled by vaccum. Vaccum is created from the downward travel of the piston and all the air getting burned off from combustion.

This is what I explained 2 or 3x in one of the other 50 threads on this issue. If the O2 sensor isn't getting proper reading of the exhaust (due to holes in the pipe before it), the ECU/ECM (whatever you want to call the engine computer) won't be injecting the proper fuel. Thus you get the studdering and hens the fuel pressure going bonkers.

Then to add to this, I believe I also suggested to try PATCHING the exhaust with fiberglass (as a TEMP solution) to see if the studdering goes away. It's really cheep (maybe $50 total) and anyone can do it if they don't mind getting a little dirty. If the shuddering doesn't subside, then you didn't waste your $$ on the exhaust.

Here, let me put more emphasis on PATCHING the exhaust before doing anything rash.

Duck, you're getting shamed or the mechanic is as completely clueless as Helmet's exhaust gas theories.[/quote]


First of all. I was being sarcastic with my exhaust fuel pressure comment. I am a very experienced technician as well as having gone to college for this.

Second. if the car is not completely stalling out then I would assume the vaccuum level is not flucutating to the point of having a signifigant effect on fuel pressure.

Third: although he didn't state how much the fuel pressure is moving 10psi? 20psi? is assumed it was more than less which would indicate major voltage flucuation to the pump.

From personal experience, I had a DSM years ago that I was having idle problems with. It had a vaccum actuated stock fpr. the vaccum would bounce between -18 and -5 and the fuel pressure never changed.

[quote=""Darkhelmet""]From personal experience, I had a DSM years ago that I was having idle problems with. It had a vaccum actuated stock fpr. the vaccum would bounce between -18 and -5 and the fuel pressure never changed.[/quote]

It should be changing. When under vacuum, the engine is effectively "sucking" on the injector, so you'd need a lower rail pressure to get the same total flow. If it didn't, the pressure at the injector would vary thus changing the flow rate of that injector.

Think about it. 43psi in the rail at zero mm/hg in the plenum is 43psi across the injectors right?. At -10mm/hg in the plenum you'd need 10psi less in the rail (33psi in this case) to get 43psi across the injectors.

On my cars, the fuel pressure gauge mirrored the boost gauge.

Actually Dark, I may have an explanation as to why your FP never changed.

Stock DSM FPRs are prone to "over run" from the small return line orifice. If the fuel can't escape the rails fast enough, the pressure would stay constant.

Did you notice FPR "spikes" under boost?

Some of your car questions are embarassing duck go to JeepForums for your jeep and not here. Or pay someone to fix all your automotive problems.
don't wanna be an asshole but...

On my Jeep the fuel pressure is supposed to be a constant 49 psi. I don't remember what the shop said, but with it sitting at idle after a long time, they said it started to go down and back up repeatedly. When I am in Park or Neutral, I have no problem at all when I rev the engine. It is only under load after I have come to a stop. Once it starts though, if I try and accelerate slowly to moderate pace, it will sometimes continue to malfunction, and sometimes it wont. If I really slam on the accelerator hard, it will kick out of the problem and I will accelerate at a decent speed, but not like I used before the problem.

The rpm's don't move that much and it just seems like nothing is getting to the engine, it just sputters, makes loud popping sounds and feels like it is going to stall, and shakes. I keep at a constant speed though for the most part while this happens, only slow down a bit, or accelerate very slowly.

After I replaced the fuel stuff on Saturday (took me like 4 god damn hours to drop that damn tank), it drove fine on Sunday for about 30 min, but it accelerated like I was towing something. It felt like something was holding me back. Not smooth at all. Took it from 0-75 a few times, and from 0-35, and from 25-75 a few times. I then went to Wal-Mart and it was fine until my 2nd to last turn home, where it acted up again around the bend and continued to give me problems for about 50 feet, then it went back to normal (like it was before I went to wal-mart) until I got home. I put it in park, revved the engine, and it seemed fine.

That is about as descriptive as I can go without someone actually seeing/feeling it first hand.

[quote=""TajMan""]Some of your car questions are embarassing duck go to JeepForums for your jeep and not here. Or pay someone to fix all your automotive problems.
don't wanna be an asshole but...[/quote]

But what? I will admit, I don't know alot about cars, but I am learning, and I will not learn anything by bringing to a shop and having to pay out of my ass for labor. The shop I took it to was wrong about the problem. They told me that after having it all day they could find nothing wrong but bad fuel pressure. They told me they would change the pump for $500.

People on BAWC are helping me just as much as Jeepforum. They are both offering advice that I personally think is helpful.

Don't want to be an asshole, but if you are not going to try and help me then don't post here. Thank you.

Well I am repairing the exhaust (or what I can of it) this weekend. We will see if that does it.