Could SHOnut FPR cure low RPM studdering & bogging?

[morebhp]

Actually, I replaced mine a few years ago... just as a "hope so" fix. It didn't make me any difference. But that's a good thought. It does affect A/F ratio a good bit.

I'm still leaning towards a fuel pressure issue. I'm having trouble finding a fuel pressure gauge around here. I should just order one online.

I've tried everything else. At 62K miles and relatively gentle driving, I can't imagine my timing is off or any of my cams are that worn. I'm a religious 3K mile oil changer.

If I can't find a fuel pressure issue, I may break down and take it to Doug down at FPS and have him put his "stethoscope" to it and see if he can figure out what's wrong. This one appears to be beyond me.

It's doing it again pretty bad today. Half throttle in first and second gear feels like someone has my car's ****** in a vice. Once 4K comes... zoom. (whatever)

 

[F-22 Raptor SHO]

Go to your local autoparts place...they should have a pressure gauge.

 

[hawkeye18]

I know bad timing will cause a backfire. Have you checked to see if your timing belt is loose? It may have skipped a few teeth. This is not a "might happen" thing with our SHOs. It will happen unless you replace it. It's just a fact of life with timing belts.

 

[morebhp]

Wouldn't I be experiencing more than just a minor loss of low range power and an occasional intake backfire if my timing had jumped a few teeth?

It idles smoothly. Starts realitively easily and gets 18mpg in town. I think I'd be having other issues wouldn't I?

 

[Off Road SHO]

Mike,

The temp guage reads from the single wire sensor that is to the left of the thermostat. The computer reads from the two wire unit (Engine Coolant Temp sensor ECT ) that is to the right of the thermostat. The ECT tells the warm-up story to the PCM constantly so that the PCM can control the richness of the fuel air mix during warm up. Both are cheap to buy and easy to replace. Drain a 1/2 gallon of coolant out of the radiator if you don't want a little spillage.

If the sensor is putting out a false "story", the PCM might be thinking that the engine is very cold all the time and giving you a rich mixture all the time. At low rpms the secondaries would be closed and give you a rich burn. When the secondaries dump in more air, the mixture is closer to normal ratios.

Maybe some of the other more experienced SHO gear heads will chime in with their ideas.

Tom

 

[F-22 Raptor SHO]

you just saved me 2 days of shipping and 14.99. They showed me the 2 pronged sensor and I was swearing it was the other one pronged sensor. now I know what is up. going to buy the 2 pronger now.

Mike,

The temp guage reads from the single wire sensor that is to the left of the thermostat. The computer reads from the two wire unit (Engine Coolant Temp sensor ECT ) that is to the right of the thermostat. The ECT tells the warm-up story to the PCM constantly so that the PCM can control the richness of the fuel air mix during warm up. Both are cheap to buy and easy to replace. Drain a 1/2 gallon of coolant out of the radiator if you don't want a little spillage.

If the sensor is putting out a false "story", the PCM might be thinking that the engine is very cold all the time and giving you a rich mixture all the time. At low rpms the secondaries would be closed and give you a rich burn. When the secondaries dump in more air, the mixture is closer to normal ratios.

Maybe some of the other more experienced SHO gear heads will chime in with their ideas.

Tom

 

[F-22 Raptor SHO]

Ok, it is a daily battle as I need to officially test every change in the morning as I go to work. When the car gets warm, the problem is not as apparent. Today I

Replaced the ECT Same
cleaned the IAC and added an extra ground wire to the motor (per another post)...nothing.

Finally I changed out the ACT sensor (I had a new one hanging around). Hmmm......after all these test drives, the car was warm again, but it seemed like it was, uhh, better a bit. I will see in the morning.

 

[morebhp]

So, How was it with the new ACT sensor? That would be cool if it were that simple!

 

[F-22 Raptor SHO]

Wasnt any better.....there is no greater frustration than having zero confidence that a change will fix the problem you have.

Fuel pump arrived today....I will know tomorrow night if the car is fixed.

Funny thing is my wife has seen me working on this 1 sensor at a time and saying "But the car runs and drives and gets you there and back, so this is like a level 4 problem (1 being DOA and 10 being a new paint job)...She fails to realize that I think it is a level 1 problem as it ****** me off when the car doesnt run in tip top condition. I've had more racing opportities than ever that I have turned down cause its not 100%

 

[morebhp]

Wasnt any better.....there is no greater frustration than having zero confidence that a change will fix the problem you have.

Fuel pump arrived today....I will know tomorrow night if the car is fixed.

Funny thing is my wife has seen me working on this 1 sensor at a time and saying "But the car runs and drives and gets you there and back, so this is like a level 4 problem (1 being DOA and 10 being a new paint job)...She fails to realize that I think it is a level 1 problem as it ****** me off when the car doesnt run in tip top condition. I've had more racing opportities than ever that I have turned down cause its not 100%

Dude... I coudn't have said it any better myself with week's worth of preparation.

 

[morebhp]

Get that new pump installed Michael? I'm anxious to hear...

 

[F-22 Raptor SHO]

Get that new pump installed Michael? I'm anxious to hear...

Figured you would be. Good News, bad news

The good news is a new walbro pump arrived yesterday and I installed it tonight after work. Better news: it only took me 2 hours to do the job from start to finish and cutting a hole in the back seat using the SHOPP instructions at shophoenix. Took it for a spin and of course, its too warm for me to notice. I will know in the morning. Codes were clear after the drive. I had one before the project started which was a 542...ground to fuel pump is bad. I cleaned up everything and installed a very nice pump...quiet too.

Bad news: Test drive was not what I thought it would be, I will know more tomorrow.

Other thoughts are:

Timing could be off? I have to change my water pump gasket anyways, so I will double check that.

Cats clogged? we shall see.

Compression test.

Barimetric sensor? How would the car know it isnt reading correctly?

I have all weekend for this.

 

[Shoaz]

...Better news: it only took me 2 hours to do the job from start to finish and cutting a hole in the back seat using the SHOPP instructions at shophoenix...

Oh, dang, dude, you could have taken the seat bottom out and just cut a hole in the floor of the unibody.

I know where there's an extra seat bottom lying around if you want to replace yours now...

 

[F-22 Raptor SHO]

Oh, dang, dude, you could have taken the seat bottom out and just cut a hole in the floor of the unibody.

I know where there's an extra seat bottom lying around if you want to replace yours now...

I covered it with brown tape, you can hardly tell it is there.

 

[blue2ndgen]

I really hope someone figures this out. I have had the same problem for almost 2 years now and have replaced almost every sensor on the car including the fuel pump.I get that same pop through the intake at low rpm and the hesitation until 4k. I have more trouble when the car is warm trying to restart it though so I am leaning towards coil pack or DIS module.

 

[F-22 Raptor SHO]

I really hope someone figures this out. I have had the same problem for almost 2 years now and have replaced almost every sensor on the car including the fuel pump.I get that same pop through the intake at low rpm and the hesitation until 4k. I have more trouble when the car is warm trying to restart it though so I am leaning towards coil pack or DIS module.

Welcome to the fold. I will have this fixed before the convention, so dont you worry.

I'm not replacing sensors all willy nilly as I have not had any codes. I have however done a fair number of swaps from my wifes car. The car doesnt think there is anything wrong.

 

[hawkeye18]

lack of power only below 4K rpm is almost always the IMRC, the module that controls the butterflies. Make sure the butterflies open at 4k rpm. The easiest way to do this is to rev the engine at the throttle body and look for the little tabs at the butterflies to move. If they do, you'll know what I'm talking about. There are two vacuum hoses and an electrical connector that need to be hooked up.

And for some reason almost all SHOs don't like to start or run after sitting for ~15-30 minutes when it's still warm. Mine doesn't. I know at least 40 other people who say theirs doesn't. I wouldn't worry about that too much.

 

[F-22 Raptor SHO]

lack of power only below 4K rpm is almost always the IMRC, the module that controls the butterflies. Make sure the butterflies open at 4k rpm. The easiest way to do this is to rev the engine at the throttle body and look for the little tabs at the butterflies to move. If they do, you'll know what I'm talking about. There are two vacuum hoses and an electrical connector that need to be hooked up.

And for some reason almost all SHOs don't like to start or run after sitting for ~15-30 minutes when it's still warm. Mine doesn't. I know at least 40 other people who say theirs doesn't. I wouldn't worry about that too much.

IMRC is ok....butterflies are operating properly. At 4k is just doesnt suck as bad, but still sucks.

 

[F-22 Raptor SHO]

UPDATE:

Swapped out the DIS>>>nothing
Removed Y-PIPE and checked for flow using shop vac: No clogs.
I did swap out a single plug wire at a time using one I had. Trouble was, the extra one I had has a resistance of 17...the ones on the car had resistances in the neighborhood of 10.

 

[morebhp]

Gosh. I can't believe what a riddle this has turned out to be. Someone else mentioned timing on this thread. I'm leaning away from that because it just seems that I'd be having more serious problems than sluggishness under 4k and an occasional intake backfire. I reserve the strong possibility that I'm wrong but I'd be utterly shocked if that's what ends up being the problem.

Have you checked your fuel injectors? I imagine that's a pain. I don't even know how to do it. This really seems like a fuel thing to me. I was sure the pump would do it.

Crap... I'm soooooooo sick of this nagging problem. I've put up with it for years...

PLEASE keep me posted on your progress or lack thereof. :type: