: FPR Replaced - Still Runs Little Rough



mr_mr11
02-12-07, 10:08 AM
I just replaced the FPR on my 94 SLS 4.6 Liter along with new plugs and wires - I was getting a O2 rich mixture prior to FPR replacement. The FPR helped out a ton and I'm back to around 20 mpg. I'm still getting some engine roughness at lower speeds and sometimes it takes 3-4 seconds of cranking to start. Maybe a faulty injector or fuel pump issue? Any thoughts? Thanks, mr_mr11 :thehand:

Ranger
02-12-07, 11:46 AM
Next step would be to pull the fuel rail and see if any injectors are leaking. See the Tech Tips section.

eldorado1
02-12-07, 11:49 AM
Do you hear your fuel pump kick on for 2 seconds before you start it?

mr_mr11
02-12-07, 11:55 AM
Yes the fuel pump runs for 2-3 seconds before starting. mr_mr11

mr_mr11
02-12-07, 12:02 PM
Next step would be to pull the fuel rail and see if any injectors are leaking. See the Tech Tips section.

Thanks Ranger. I will check and get back to you. mr_mr11 :thehand:

eldorado1
02-12-07, 12:42 PM
Did it run rough before the FPR swap? You might have created a vacuum leak somewhere.

MonzaRacer
02-12-07, 01:21 PM
Ok so I am decoding the FPR as Fuel Pump Regulator. OK one quick check as you may another fuel problem. Get a good high preasure fuel preasure guage and hook it up. Now what you want to do is check for the proper fuel preasure BUT what you have to do is remove and block off the vaccum control to the FPR and have some one start the car. on a N/A car you should have no more than a 1.5 pound drop at the start up. If it does you mosy likely have fuel pump problem (or stopped up fuel filter) I really like to see less than 1 psi drop but some bigger engines. This means the pump cnat keep up with the engines needs.
Another thing is get a spray bottle and mix up distilled water with a drop of dish soap and a table spoon or two of ammonia and lightly mist your wires. It will show up any electrical leakage. Wynns makes a product called Hi-volt that does the same thing but you have buy it from a wynns distributor and be a contract buyer so the home made stuff does work. DONT soak your engine just mist the wires and coils.
Now you can get an injecter testor from OTC that you hook up to each injecter and you preasure up the system and it should hold steady, then you press the button after hooking it up and then write down the preasure drop. All should be with in 1 or 2 psi you really dont want them off by more than 5 psi. Doing a resistance check is another way to verify good injecters (electricly).
Hope some this helps. another thing is where you bought the wires and plugs as some plugs get rough handled or if the get damp for a long period of time it can destroy them. Most spark plugs dont completely cure or seal up till they go through several warmups and cool downs. I have had such problems especially with Champion and Autolites. especially when we built engines for boats.
A good thing to have when doing tune ups is a large tube of dielectric silicone and squeeze a good sizze drop into the ends of the wires.
A lot of people will tell you it will cause problems but I have NEVER had any problems with using it. I use so much that some have problems keeping wires on because they seal so good. BUT if they click up then they will kae connection. Lack of this will cause wires to stick AND actual carbo tracking down the side of the plug. Anotherthing is that even with AC Delco replacement wires you can have one that doesnt have the wire far enough into the boot to get to the plug properly.
another thing you can have is problems with oil, after replacement have you had the oil changed? IF your engine was over fueling your oil could be diluted and as it runs the raw fuel will slowly come through the PCV system(another thing to check as this can loosen up crud in the PCV valve) as it boils off from the crankcase oil.
also double check any connections, did you accidentally disconnect thing from the air tubes to the engine, while the fuel may be fixed an air leak in the air intake system can throw the MAF reading or lack thereof loopy and cause it to run bad yet get good mileage.
another thing is that you need either a scanner or a graphing multimeter and get a good scope reading on your O2 sensors as they need to range above 800 millivolts and below 200 milliivolts. If its in control you should actually see them range almost to zero millivolts to almost 1 volt. and it has to switch fast too.
Now after cat O2 sensors should be very close to mid range if it goes real hig or real low it can mean you have damaged the cat, or even had parts of it break off and plug up the mufflers too.
Good Luck
Lee

mr_mr11
02-12-07, 03:04 PM
Did it run rough before the FPR swap? You might have created a vacuum leak somewhere.

Yes it did run rough before I installed the new fuel pressure regulator (FPR) and was getting around 10 mpg - w/ the new FPR it's back around 20 mpg. I appreciate the comments from everyone and will check the plugs/wires, for vacuum leaks, leaking injectors, fuel pressure and the like. mr_mr11 :thehand:

mr_mr11
02-12-07, 05:19 PM
As a follow up to my problem, does the 94 SLS 4.6 liter need to have a vacuum hose hooked up to the Fuel Pressure Regulator (FPR)? I have found that the engine is still running very rich after changing the FPR. I would think that a vacuum hose is needed and mine does not have a vacuum hosed attached to the FPR which may be causing it to run rich? Any ideas on where the vacuum hose from the FPR is hooked up to? Thanks for any comments. mr_mr11

Ranger
02-12-07, 05:29 PM
Ok so I am decoding the FPR as Fuel Pump Regulator.
Fuel pressure regulator. Same thing I think.


Another thing is get a spray bottle and mix up distilled water with a drop of dish soap and a table spoon or two of ammonia and lightly mist your wires.
I have heard (an even advised others) of this procedure, but I have never heard of the soap and ammonia concoction. Can you elaborate?


A good thing to have when doing tune ups is a large tube of dielectric silicone and squeeze a good size drop into the ends of the wires.
FWIW, when I replaced the wires on my '97 Deville a few years back, the A/C Delco wires had a note in the box that said that the plug caps where precoated with something. Silicone I think, and that dielectric grease should not be used. I had to go back an wipe them all out (real men don't need instructions). Not sure what their reasoning behind this is.

Ranger
02-12-07, 05:30 PM
As a follow up to my problem, does the 94 SLS 4.6 liter need to have a vacuum hose hooked up to the Fuel Pressure Regulator (FPR)? I have found that the engine is still running very rich after changing the FPR. I would think that a vacuum hose is needed and mine does not have a vacuum hosed attached to the FPR which may be causing it to run rich? Any ideas on where the vacuum hose from the FPR is hooked up to? Thanks for any comments. mr_mr11
No. Yours is inside of the intake manifold and thus subjected to manifold vacuum. The hose is used on FPRs that are mounted externally ('95+).

dkozloski
02-12-07, 05:57 PM
Most spark plug boots are unvented. DC4 compound can emit a small amount of gas when heated and blow a boot right off. If you're bound and determined to use DC4 or some other silicon compound make a small vent hole in each boot. Darrel Waltrip mentioned during a NASCAR broadcast that this once cost him a race and ever since he vented the boots.

mr_mr11
02-12-07, 06:06 PM
No. Yours is inside of the intake manifold and thus subjected to manifold vacuum. The hose is used on FPRs that are mounted externally ('95+).

Thank you Ranger! I'll keep working on it and see what I can find out. mr_mr11 :thehand:

Ranger
02-12-07, 06:13 PM
Very interesting Koz. I never knew that or heard of the Darrel Waltrip scenario. By DC4 I assume you mean dielectric grease?

Murphyg
02-12-07, 10:08 PM
I just replaced the FPR on my 94 SLS 4.6 Liter along with new plugs and wires - I was getting a O2 rich mixture prior to FPR replacement. The FPR helped out a ton and I'm back to around 20 mpg. .................................................. ..................

Said getting rich O2 mixture ?
Was that a code you were recieving ??

Sounds as though replacing your fuel rail helped alot. Went from 13 to 20 mpg :thumbsup:

But hows bout that O2 rich mixture that got you goin in the first place.
Might want to think bout checkin and or replacin your O2 sensor/s.

Dont know if you have 1 or 2. But would be worth checkin out.

mr_mr11
02-13-07, 09:46 AM
Said getting rich O2 mixture ?
Was that a code you were recieving ??

Sounds as though replacing your fuel rail helped alot. Went from 13 to 20 mpg :thumbsup:

But hows bout that O2 rich mixture that got you goin in the first place.
Might want to think bout checkin and or replacin your O2 sensor/s.

Dont know if you have 1 or 2. But would be worth checkin out.

I was receiving P043 and P045 codes - so I replaced the Fuel Pressure Regulator (FPR) which helped some but hasn't totally solved my problem. I've noticed that I still have fuel inside the manifold area so I'm drying it out w/ a fan and will pressurize the system when it dries out to see if there are any leaks or if the FPR was the only leaking problem. Does anyone know if Cadillac upgraded from a plastic fuel rail to a newer style on a 94 SLS 4.6 Liter? mr_mr11 :thehand:

Ranger
02-13-07, 05:36 PM
There was a recall for the '95 - '97 fuel rail only. Check to see that the FPR "O" ring is not leaking. The presence of fuel leads me to think it may not be seated properly, unless of coarse the rail is leaking.

mr_mr11
02-14-07, 09:39 AM
There was a recall for the '95 - '97 fuel rail only. Check to see that the FPR "O" ring is not leaking. The presence of fuel leads me to think it may not be seated properly, unless of coarse the rail is leaking.

Ranger - There were 3 fuel injector green colored o-rings that I replaced that were leaking and I pretty well have the intake dried up now and it's running pretty decent. Now I'll work on fixing code A012 which is an AC low side temperature sensor circuit problem. Thanks for everyone's comments & Happy V Day! mr_mr11 :thumbsup: