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is there a sure-fire way to check if your fuel pressure regulator is working correctly? I have heard if gas is in the vacuum line it is bad but i think I removed the line and smelled it and no gas. These things are $60 so I would rather check mine. I know I had a bad one on another caddy of mine and it made it so the car was very hard to start. Maybe I could find a used one.


* 1966 Deville Convertible

* 2007 Escalade ESV Black on Black

* 1996 Fleetwood Brougham Black on Black V4P -Gone
* 1983 Coupe Deville Street/Show Lowrider -Gone

* 1970 Calais 4dr Hardtop GONE
* 2000 Deville DTS - Silver with Black Leather and SE grille GONE
* 1999 Seville STS - Pearl Red GONE

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I have heard if gas is in the vacuum line it is bad but i think I removed the line and smelled it and no gas.

Correct, but you must check it with the fuel system pressurized (key on or engine at idle).

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I have heard if gas is in the vacuum line it is bad but i think I removed the line and smelled it and no gas.

Correct, but you must check it with the fuel system pressurized (key on or engine at idle).

Thanks, thats one thing I didnt do when I checked it before.

I also forgot to mention this "problem" with my car doesnt pester me all that much. I actually find it a fun challenge to find a solution. And I enjoy working on cars period so going and buying, say, a new TPS sensor gives me some strange joy in knowing I get to replace another part :P

Edited by CoupeDTS

* 1966 Deville Convertible

* 2007 Escalade ESV Black on Black

* 1996 Fleetwood Brougham Black on Black V4P -Gone
* 1983 Coupe Deville Street/Show Lowrider -Gone

* 1970 Calais 4dr Hardtop GONE
* 2000 Deville DTS - Silver with Black Leather and SE grille GONE
* 1999 Seville STS - Pearl Red GONE

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I have heard if gas is in the vacuum line it is bad but i think I removed the line and smelled it and no gas.

Correct, but you must check it with the fuel system pressurized (key on or engine at idle).

I turned the key on to pressurize, then removed the vacuum line and I can smell gas but not super super strong and definately not pouring out of there. Should there be any gas smell at all or is this ok?


* 1966 Deville Convertible

* 2007 Escalade ESV Black on Black

* 1996 Fleetwood Brougham Black on Black V4P -Gone
* 1983 Coupe Deville Street/Show Lowrider -Gone

* 1970 Calais 4dr Hardtop GONE
* 2000 Deville DTS - Silver with Black Leather and SE grille GONE
* 1999 Seville STS - Pearl Red GONE

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I don't believe there should be any fuel smell at all,


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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In my opinion...the only way to get fuel smell in the vacuum line, is if the diaphragm is leaking.

Otherwise it would just be AIR...with no gas smell. :)


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I don't believe there should be any fuel smell at all,

In my opinion...the only way to get fuel smell in the vacuum line, is if the diaphragm is leaking.

Otherwise it would just be AIR...with no gas smell. :)

ooooooh, this sounds promising :):bluesbrothers:

A new regulator should atleast help if nothing else.


* 1966 Deville Convertible

* 2007 Escalade ESV Black on Black

* 1996 Fleetwood Brougham Black on Black V4P -Gone
* 1983 Coupe Deville Street/Show Lowrider -Gone

* 1970 Calais 4dr Hardtop GONE
* 2000 Deville DTS - Silver with Black Leather and SE grille GONE
* 1999 Seville STS - Pearl Red GONE

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Well this would explain your poor gas mileage, maybe you are actually sucking fuel into the intake via the vacuum port on the regulator


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Just to add to and confirm what Jim and Mike said, NO fuel (nor the smell of it) should ever be present in that vacuum line. If you want to go a little farther, add vacuum to that line while at idle either with a vacuum pump or by sucking on it. If the leak is small enough that fuel pressure alone on the back side of the diaphragm will not cause a leak, the added vacuum on the vacuum side will. Another way to check is simply put a hand held vacuum pump on it (even with the engine off) and pump up the vacuum. Watch the gauge, If it falls and does not hold vacuum, the diaphragm is bad.

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Yes this makes sense. And even if its a little gas getting into the manifold it throws off all the sensors (ie o2) and screwing up the mixture. Ill order one from rock auto asap.


* 1966 Deville Convertible

* 2007 Escalade ESV Black on Black

* 1996 Fleetwood Brougham Black on Black V4P -Gone
* 1983 Coupe Deville Street/Show Lowrider -Gone

* 1970 Calais 4dr Hardtop GONE
* 2000 Deville DTS - Silver with Black Leather and SE grille GONE
* 1999 Seville STS - Pearl Red GONE

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The FPR is installed. Right away Ive noticed the car shifts into 4th at 45mph instead of 53mph. Thats where most cars shift at 45. So obviously the bad FPR was throwing alot of things off. With the earlier shifts and not sucking gas through the vacuum hose I should be getting better gas mileage now. I just filled up and my last tank I got the normal 11.2mpg. In a week or 2 I will fill up again and see how much I improve...


* 1966 Deville Convertible

* 2007 Escalade ESV Black on Black

* 1996 Fleetwood Brougham Black on Black V4P -Gone
* 1983 Coupe Deville Street/Show Lowrider -Gone

* 1970 Calais 4dr Hardtop GONE
* 2000 Deville DTS - Silver with Black Leather and SE grille GONE
* 1999 Seville STS - Pearl Red GONE

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Solved :yupi3ti:

FPR mustve been bad. This last tank I got 13mpg on the nose. Increase from 11.2 thats a big increase in percentage!

On top of that I found out why my tranny inst shifting into 4th until 51-53mph its because there is a tranny temp sensor on the cooler lines that goes bad. I dont think they sell the little sensor so people just unplug it. I did that and now it shifts like its supposed to. I think it even shifts in other gears better or more timely. So that should save some fuel also. Cant wait to see how much I get out of this tank of gas :hatsoff:


* 1966 Deville Convertible

* 2007 Escalade ESV Black on Black

* 1996 Fleetwood Brougham Black on Black V4P -Gone
* 1983 Coupe Deville Street/Show Lowrider -Gone

* 1970 Calais 4dr Hardtop GONE
* 2000 Deville DTS - Silver with Black Leather and SE grille GONE
* 1999 Seville STS - Pearl Red GONE

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Rejuvenating an old thread. For the last two years, the fuel economy of my 1995 Fleetwood with 123,000 miles on the clock has been 10 MPG around the town. It is 17-22 MPG on a long highway trip. Unfortunately, 90% of my driving is around the town. I have done all the usual checks, which has been pretty much throwing parts at the problem. Still there. New O2 sensors, new exhaust manifold bolts, fuel filter, fuel pump, FPR is fine, injectors are not leaking, fuel pressure within specs, no visible vacuum leaks. I do smell exhaust under the hood but cannot find it. MAF is clean, IAT sensor shows 3.62K at +72F, engine coolant sensor is fine, no powertrain-related codes. EGR valve is new. Ignition is fine, no misses. This is super frustrating and costly. There are some driveability issues (lack of power now and then), but this car had them since the day one and they are not really fuel mileage -related. Transmission lock-up is fine, brakes are fine, tire pressure is fine. It is OBD1 and diagnostics tools are expensive and I am not sure they would help either. Just venting out my frustration and the pain at the pump! :)

Took off the vacuum line and there IS a very, very faint smell of gas. No gas in the line or dripping from nipple of FPR. I just cannot see how that amount of gas vapor could mess things up. Obviously, there is no fuel loss through that vacuum line at all. 


The saddest thing in life is wasted talent

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It is not vapor when it leaks. What you are smelling is the leftover vapor from it leaking


GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I have connected a transparent PVC tube to the FPR and sucked the air providing around the same 20"Hg vacuum.  There was vapor and there was no gasoline in the tube whatsoever. I think nothing is wrong with FPR. No symptoms of a bad FPR either. 


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8 hours ago, adallak said:

I have connected a transparent PVC tube to the FPR and sucked the air providing around the same 20"Hg vacuum.  There was vapor and there was no gasoline in the tube whatsoever. I think nothing is wrong with FPR. No symptoms of a bad FPR either. 

With the engine running?  


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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34 minutes ago, adallak said:

Yup. Hi Mike. 

Hope you are doing well my friend!


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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good. I guess as long as there is no actual fuel coming through that line 


GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Adallak, do me a favor or confirm for me, did you REV the engine up during your test?  Typically when you REV the engine, the FPR will split fuel from its nipple if it's bad.  I usually put a white index card in front of the nipple and rev the engine, a bad regulator will spit fuel


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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2 hours ago, BodybyFisher said:

Adallak, do me a favor or confirm for me, did you REV the engine up during your test?  Typically when you REV the engine, the FPR will split fuel from its nipple if it's bad.  I usually put a white index card in front of the nipple and rev the engine, a bad regulator will spit fuel

Mike, I just did what you suggested. No fuel coming from the nipple. I am wondering what revving does to FPR if the vacuum line is taken off. 

There are FPR tests in the manual suggesting kinking return fuel line, etc, but I am a bit reluctant touching 23 years old hoses. Something tells me the FPR is fine. When I compare this LT1 with 123,000 miles to 4.9 with 175,000 in my 1991 Seville, this engine is so much cleaner and nicer, yet I never experienced lack of power, driveability problems, and terrible fuel economy with my Seville. This engine must have been tuned so that it is just too sensitive to possible exhaust, vacuum leaks, ignition, etc. 


The saddest thing in life is wasted talent

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Not sure, but the times I have found a bad FPR, it spit fuel that way.   That was the way I was taught to check them.  I thought your idea of the clear hose was good too. 

So your symptom is poor gas mileage?   Any codes?  

Did the poor gas mileage suddenly start?


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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2 minutes ago, BodybyFisher said:

Not sure, but the times I have found a bad FPR, it spit fuel that way.   That was the way I was taught to check them.  I thought your idea of the clear hose was good too. 

So your symptom is poor gas mileage?   Any codes?  

Did the poor gas mileage suddenly start?

No power-train related codes whatsoever and I never had one... There were always driveabilty issues such as sudden lack of power, hesitation, etc, but fuel economy was decent for many years. I have noticed dramatic drop two years ago.  Again, I have replaced every part , which could be responsible. Just wasted money and time, I guess. 10 MPG around the town is just way too much. or should I say too less. 


The saddest thing in life is wasted talent

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Is premium fuel required?

Could this be something odd, like a bad knock sensor?, that is retarding the ignition?

I wonder if my Autotap analyzer would help you?   Is it OBD2?   If you could monitor misfire, O2 sensor and knock sensor real time data that might give you some clues.

Have you checked to see if you have any back pressure in the exhaust system?


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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LT1 takes regular. No, it is OBD 1. Unfortunately, there are so many things , which could affect fuel economy (or intermittent lack of power) and finding them is a PITA if you do not have proper diagnostics tools. I have heard too many stories how people would take the car to a dealer and after spending $$$$$$ they would just sell the car. I do not want o go that rout.  


The saddest thing in life is wasted talent

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