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New Idle Issue Caused By Fprcv

18 posts in this topic

**UPDATE 6/23/06 - SCROLL TO LAST MSG - INSTALLED NEW FPR**

First off... had and having idle issues just like everyone else... BUT, here's where i am with this every so popular problem we seem to all be having.

(i'll post an intake diagram from the OEM service manual later on)

To cover the bases; i've cleaned MAF, IAC, & EGR, check plugs & wires, new coil pack (wasted $ on this when i didn't need a new one), new air filter, new fuel filter, new MAF (wasted $ on this again when i didn't need one), and finally, a new FPRCV (wasted $ on this again too, didn't need one). Checked the MAF, IAC, EGR, and FPRCV for electrical inconsistencies with multimeter. Everything checks out okay! Only thing i haven't done is a vacuum test (and i don't know how or where to start on doing that).

A little history, car was always having idle problems but driveable. One day it drove really well, but i got a really strong fuel smell in cabin (blower motor was blowing the fuel smell in). Looked under hood and found the hose running from FPR (fuel pressure regulator) to the FPRCV disconnected, hence fuel was being pumped by the FPR into my engine bay (so far to date, no fires... geez... i'm not driving my car with fuel spilling out!). So naturally i plugged the hose back into the FPRCV which got rid of the fuel smell but car started to idle badly and even stalling! Take hose off, and car idles beautifully, but fuel is spilling everywhere!

Long story short, i rerouted the hose from the FPR through some tubing to a resevoir (a plastic gallon container) that catches the fuel that is regulated back through the system. Bad part is that i have to empty that resevoir every so often since it does fill up, but the good is that my car idles perfect and drives perfect. I do worry about running lean (less fuel, more oxygen), but so far no signs of it. Also, just to throw a wrench into the gears, there's no codes! Yep, the CEL is black, no signs of life from that thing. I have digimoto and there are not codes popping up...

The FPRCV has 3 inlets, one comes from the intake manifold, one has an air filter on it, and the third goes to the FPR. The FPR pumps out fuel that isn't used or needed (i'm assuming that's why), the hose from the intake manifold is in constant suction, and the FPRCV is a solenoid that controls the intake either to come from the FPR or the air filter (in which case sucking air only) to the intake manifold.

So, my question is: where's the problem?! Hose on to FPRCV = rough/stall idle; hose off to resevoir = idle/running...

:blink:

I'll post some pictures later on so this will be more visual... thanks!

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I think I'm gonna need some pictures.... The FPR is a valve in itself :blink:

Anyway, it kinda sounds like you are describing the fuel return line (excess pressure is drained back to the tank). And it sorta sounds like it somehow got clogged and puts back pressure on the FPR -- but this is just a guess really....

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Pics of the intake system and FPRCV...

img-215853-1-intake.jpg

img-215853-2-prc.jpg

This should help along with my description, thanks in advance!

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ahhhh.... now I see what you're saying :P

I'm just confused on one thing.... where exactly (which hose) is leaking out fuel? To me it sounds like you're saying the hose that connects the FPR to the PRC... and AFAIK, there should be no fuel going through that line - just vacuum. ~which would be a FPR problem and explain a few thing :P

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I'm just confused on one thing.... where exactly (which hose) is leaking out fuel? To me it sounds like you're saying the hose that connects the FPR to the PRC... and AFAIK, there should be no fuel going through that line - just vacuum. ~which would be a FPR problem and explain a few thing :P

You got it! Fuel is coming from the FPR, hence leaking fuel through the hose that connects it to the PRC. You're saying that the hose is a vacuum line only?! Can someone pull theirs and check for me? If it is a vacuum line and fuel is getting in, then i suppose that could cause the car to "choke" on fuel and idle rough or stall.

Also, you may be right cause when i pulled the hose off the PRC, the PRC inlet is sucking in air... but i thought the FPR was supposed to send back fuel that isn't needed (like when u're sitting idling), or at least that what i thought. It is connected directly to the fuel line off the fuel filter, right? Or at least on the way to it...

Any more thoughts b4 i drop $130+ on a new FPR?

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There is no way that particular hose should have fuel going through it. If it does, then the diaphragm in the FPR is screwed - i.e. if it's new - take it back, 'cos it's cactus.

The vacuum fed into the back of the FPR via the PRC valve is purely there to modulate fuel pressure based on vacuum in the manifold.

If fuel hasn't destroyed the insides of the PRC then it's the pressure reg. you need to change out ... not the PRC to fix your leaking fuel problem.

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but i thought the FPR was supposed to send back fuel that isn't needed (like when u're sitting idling), or at least that what i thought. It is connected directly to the fuel line off the fuel filter, right? Or at least on the way to it...

+There's 4 lines going to/from the FPR... Fuel, Fuel Return, vaccum line, rail. The vac line changes adjusts the fuel pressure (as said).

+The Fuel return does just that... returns extra fuel back to the tank (this is one way to control pressure).

+The fuel line comes directly from the filter etc. - this is the pressure and supply side.

+The rail really isin't a line in our case as the FPR is directly connected to the rail -- but this is where regulated fuel comes out....

---

If the vac line is receiving fuel... that fuel is gonna go directly to the intake manifold... as liquid fuel (not good for much of anything) -- and that can cause your engine to run poorly (or even 'hydrolock' with a whole lot of fuel -- not possible from this tiny hose).

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Yes, your FPR diaphragm is busted, replace the FPR.

Also, the FPR control solenoid is there only to assist with hot starts, it does not actually regulate fuel pressure while the engine is running, this is done purely through engine vacuum (based on engine RPM and throttle position) with the solenoid allowing all vacuum to pass through.

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A new FPR is already ordered! Got a great deal on it! I'll install it and see how she idles, i hope this solves all the other related issues as well... we should all check the fpr lines when there is idle problems, just for the sake of it.

I'll post back with results.

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Well, just put the new FPR in and sad to say, it got WORSE! Now the car barely starts, idles so rough it shakes the whole car, the engine is squeaking loudly, and 2AM. Been troubleshooting all night to no avail...

I check all hoses to make sure there was no leak. I just don't get it... i thought maybe i got a bad FPR, so i put the old one back in and it's doing the same thing! It's not driveable as i write this.

Here's what i did:

disconnected fuel relay

started car a few time to depressurize gas

disconnected intake tubing end

removed intake filter box

removed maf

removed intake tubing between maf and tb

unscrewed 2 screws holding fpr

removed tubing from fpr

pulled fpr out, put new on in

reverse the process

start car

idle rough, car chokes, car dies, won't idle

HELP! WHAT DID I DO WRONG?! :angry:

I'M JUST GONNA JUNK THIS CAR! ANYONE WANNA BUY IT? SERIOUSLY, I COULD USE SOME ADVICE!

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I'm not sure if this is related or not. It's an issue with the idle. I don't know much about cars so I made a video and posted it to my blog. http://www.drapelyk.com/?p=17 Is that a similar problem?

DUDE! Exactly like yours! I have the high pitch squealing sounds too! Everything was all good til the new FPR went in. I think it's an air/fuel ratio problem, i'm just not sure how to go about solving or diagnosing the problem. I'll play with it some more today.

BTW, my car doesn't idle at all. I will idle for less than 30 seconds before it dies.

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We fixed it! While looking under the hood today I accidentaly found the problem. We washed under the hood yesterday, and apparently the third rubber sparkplug (plug?), on top of the engine, was somewhat loose. When we sprayed the engine water got under the edges of it and filled the tube down to the top of the sparkplug. We dried all of them out with a shop vac and a little piece of tubing. It runs a lot smoother, but it still idles really low. We're going to see if we can adjust the idle and fix it that way. I doubt that's your problem, but it could be. Good Luck!

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Glad that u r remedying the problem... i share ur problem of poor combustion, but i think mine may be bad injectors.

Cylinders 1 & 4 are charred black indicating a running rich condition (too much fuel). 2 & 3 are fine. I'm thinking my injectors are not closing or clogged.

I'm not sure how they could be affected from changing out the FPR, but the old FPR was broke and maybe the injectors were broke along with them and now are being forced to work correctly due to the new FPR?

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Glad that u r remedying the problem... i share ur problem of poor combustion, but i think mine may be bad injectors.

Cylinders 1 & 4 are charred black indicating a running rich condition (too much fuel). 2 & 3 are fine. I'm thinking my injectors are not closing or clogged.

I'm not sure how they could be affected from changing out the FPR, but the old FPR was broke and maybe the injectors were broke along with them and now are being forced to work correctly due to the new FPR?

I have a 94 Mazda 626 V6, and I have been having the same problems as you. Idle is really rough and I have an engine light. The code is 25-which is the fuel pressure regulator control soleniod which I've replaced, and still have the same problem. I have purchased an air fuel ration gauge and it tells me that I am running lean. I also think it might be the fuel injectors. I am going to replace them next week. So let me know if that was the problem if you get to it before I do.

thanks-

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I did a compression test today and cylinders 1 & 4, the ones that were running rich were 140-150 psi while 2 & 3 were very low (lower than the minimum of 119 psi) at 50 for cylinder 2 and 80 for cylinder 3.

So it's possible i have a blown head gasket... geez...

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im new to all this car stuff and i was reading the topic and im kind of comfused about what idle means. can anyone explain?

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It's the engine speed with throttle closed, sitting running and parked, that's idle, accelaration, gas pedal depressed, no idle  means the car will not run on its own.

 

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