noisy fuel pressure regulator
Thread Starter
Cruising
Joined: Jan 2006
Posts: 10
Likes: 0
noisy fuel pressure regulator
I put a new set of Bosch 3 injectors in my 91 L98 TPI engine. All went well until I started it up.
It rattled something terrible from the fuel regulator. The fuel pressure is good. It is definitely coming from the regulator as verified with a stethoscope. It is loud enough that you can hear it with hood closed and 10 feet away. It is at same pace as the injector banks firing. Evidently, because the new injectors close more solidly, the metal disk and seat slap hard enough to make a noise. I replaced the Regulator diaphragm with no change to noise. I changed to adjustable regulator and still no change.
Having searched the forums, It appears to be somewhat of a common problem but there appears to be no solution. Before the injector change the engine would idle with absolutely no noise.
If anyone has had this problem and solved it, I love to hear how. Right now it's embarrassing to drive the car with it making so much noise.
It rattled something terrible from the fuel regulator. The fuel pressure is good. It is definitely coming from the regulator as verified with a stethoscope. It is loud enough that you can hear it with hood closed and 10 feet away. It is at same pace as the injector banks firing. Evidently, because the new injectors close more solidly, the metal disk and seat slap hard enough to make a noise. I replaced the Regulator diaphragm with no change to noise. I changed to adjustable regulator and still no change.
Having searched the forums, It appears to be somewhat of a common problem but there appears to be no solution. Before the injector change the engine would idle with absolutely no noise.
If anyone has had this problem and solved it, I love to hear how. Right now it's embarrassing to drive the car with it making so much noise.
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
I dont know what is wrong but if you need to replace the Fuel Pressure Regulator I made a how to video: http://www.youtube.com/watch?v=yG0y3bqaV7E
Its helpful as a refresher even if you know what you are doing...
Maybe the clips that holds the FPR are lose?
Its helpful as a refresher even if you know what you are doing...
Maybe the clips that holds the FPR are lose?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
On an L98 you need to take the plenum off (at least) to replace the FPR. ...And take apart the fuel rails, which you can do without removing the runners but it's a bit tight.
Mine does make some noise, but I didn't notice it until I put the stethoscope on it. I still have the original stock injectors (Bosch IIIs from FIC are waiting for me to get some time to put them on, so I have no experience with them).
I did notice many years ago that the injectors made a lot of noise after a hot autocross lap. Usually it's a pretty subtle click. I need to get close to the engine to hear them.
Mine does make some noise, but I didn't notice it until I put the stethoscope on it. I still have the original stock injectors (Bosch IIIs from FIC are waiting for me to get some time to put them on, so I have no experience with them).
I did notice many years ago that the injectors made a lot of noise after a hot autocross lap. Usually it's a pretty subtle click. I need to get close to the engine to hear them.
Last edited by Cliff Harris; Oct 7, 2012 at 11:50 PM.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
I changed injectors, same type, no noise diff that I noticed.
if not regularor, what else was changed/reinstalled? distributor, possibly. small vac leak? just a WAG. but if you changed regulator with no change in noise I would look elsewhere.
if not regularor, what else was changed/reinstalled? distributor, possibly. small vac leak? just a WAG. but if you changed regulator with no change in noise I would look elsewhere.
Thread Starter
Cruising
Joined: Jan 2006
Posts: 10
Likes: 0
Thanks Cliff but having changed many fuel pressure regulators on L98's I can attest that you only need to remove the plenum and unhook the electrical connections to move it sufficiently to access the regulator. Disassembly of the fuel rail is not needed, nor is removal of the runners. Actually I've gotten so good at it I can do it in 5 minutes flat. LOL
Thread Starter
Cruising
Joined: Jan 2006
Posts: 10
Likes: 0
Thanks Joe P. It definitely is the regulator. Stethoscope really proves it. As I said it paces the firing of the injector banks. There is quite a bit of talk of this on the third generation site as they use same engine and TPI. But no solution there either. I was hoping someone had a cure. I will probably use a external regulator and bypass the internal if I can't fix it. Thanks anyway.
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Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
Hey guys, remember the pulsator? it was put into the fuel pressure line to dampen out the fuel pressure fluctuations when the injectors are firing.
If someone removed it, the fuel pressure regulator and the fuel lines take a hit if the fuel system is tight.
On the 86, they added a fuel filter to the return line in a service letter to keep the fuel lines from banging the frame with the return line. The fuel filter acts as aair chamber to soften the pulses.
It is more pronounced when cold.
If someone removed it, the fuel pressure regulator and the fuel lines take a hit if the fuel system is tight.
On the 86, they added a fuel filter to the return line in a service letter to keep the fuel lines from banging the frame with the return line. The fuel filter acts as aair chamber to soften the pulses.
It is more pronounced when cold.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Hey guys, remember the pulsator? it was put into the fuel pressure line to dampen out the fuel pressure fluctuations when the injectors are firing.
If someone removed it, the fuel pressure regulator and the fuel lines take a hit if the fuel system is tight.
On the 86, they added a fuel filter to the return line in a service letter to keep the fuel lines from banging the frame with the return line. The fuel filter acts as aair chamber to soften the pulses.
It is more pronounced when cold.
If someone removed it, the fuel pressure regulator and the fuel lines take a hit if the fuel system is tight.
On the 86, they added a fuel filter to the return line in a service letter to keep the fuel lines from banging the frame with the return line. The fuel filter acts as aair chamber to soften the pulses.
It is more pronounced when cold.
I've ask before what the purpose was and IF this needed to be serviced or cleaned...nobody every responded. I'm assuming that nobody knew what it was/is.
So, if this is a filter on the return side, DOES it need to be serviced and has ANYONE ever encountered some fuel issues that could be traced back to this part? Being on the return side it seems like it could possibly cause spikes in the pressure and possibly effect the regulator. If the excess fuel cannot get back to tank the only other place it has to go is thru the injectors, so the pump keeps sending fuel and building pressure...I need to go take another look at this thing and its plumbing. Seems like it was more than a single steel line running in and out.
Gonna have to think about that for awhile...
I did see a fuel rail system on a C4 race car that had the return capped. ALL the fuel pressure went to the injectors and pressurized the rails at whatever the pump could push out. Seemed a little risky to me with the higher pressures trying to blow O-rings and pressure being inconsistant with rpm changes. Anyone ever done this? cap the return and run it like that? This was a 1/4 mile car where I saw this that was not on the street.
Thread Starter
Cruising
Joined: Jan 2006
Posts: 10
Likes: 0
Hey guys, remember the pulsator? it was put into the fuel pressure line to dampen out the fuel pressure fluctuations when the injectors are firing.
If someone removed it, the fuel pressure regulator and the fuel lines take a hit if the fuel system is tight.
On the 86, they added a fuel filter to the return line in a service letter to keep the fuel lines from banging the frame with the return line. The fuel filter acts as aair chamber to soften the pulses.
It is more pronounced when cold.
If someone removed it, the fuel pressure regulator and the fuel lines take a hit if the fuel system is tight.
On the 86, they added a fuel filter to the return line in a service letter to keep the fuel lines from banging the frame with the return line. The fuel filter acts as aair chamber to soften the pulses.
It is more pronounced when cold.
Thread Starter
Cruising
Joined: Jan 2006
Posts: 10
Likes: 0
My 87 also has some device mounted above the inline filter pressure side, similar in shape and size.
I've ask before what the purpose was and IF this needed to be serviced or cleaned...nobody every responded. I'm assuming that nobody knew what it was/is.
So, if this is a filter on the return side, DOES it need to be serviced and has ANYONE ever encountered some fuel issues that could be traced back to this part? Being on the return side it seems like it could possibly cause spikes in the pressure and possibly effect the regulator. If the excess fuel cannot get back to tank the only other place it has to go is thru the injectors, so the pump keeps sending fuel and building pressure...I need to go take another look at this thing and its plumbing. Seems like it was more than a single steel line running in and out.
Gonna have to think about that for awhile...
I did see a fuel rail system on a C4 race car that had the return capped. ALL the fuel pressure went to the injectors and pressurized the rails at whatever the pump could push out. Seemed a little risky to me with the higher pressures trying to blow O-rings and pressure being inconsistant with rpm changes. Anyone ever done this? cap the return and run it like that? This was a 1/4 mile car where I saw this that was not on the street.
I've ask before what the purpose was and IF this needed to be serviced or cleaned...nobody every responded. I'm assuming that nobody knew what it was/is.
So, if this is a filter on the return side, DOES it need to be serviced and has ANYONE ever encountered some fuel issues that could be traced back to this part? Being on the return side it seems like it could possibly cause spikes in the pressure and possibly effect the regulator. If the excess fuel cannot get back to tank the only other place it has to go is thru the injectors, so the pump keeps sending fuel and building pressure...I need to go take another look at this thing and its plumbing. Seems like it was more than a single steel line running in and out.
Gonna have to think about that for awhile...
I did see a fuel rail system on a C4 race car that had the return capped. ALL the fuel pressure went to the injectors and pressurized the rails at whatever the pump could push out. Seemed a little risky to me with the higher pressures trying to blow O-rings and pressure being inconsistant with rpm changes. Anyone ever done this? cap the return and run it like that? This was a 1/4 mile car where I saw this that was not on the street.
Thread Starter
Cruising
Joined: Jan 2006
Posts: 10
Likes: 0
I see coupeguy stated above that in 86 they added a filter on the return to take out some fuel line knocking problems. I may look into that more. maybe it's a way to soften the noise.
LOL