96 Tahoe Fuel Pressure Regulator

[av8r4golf]

My 96 Tahoe with a 5.7L motor and auto transmission has 122K on it. I had a 100K check done at which time the plugs, wires, rotor and cap were replaced. Rececently the fuel pump failed and the dealership wanted to replace the Fuel Pressure Regulator as an add on sale. I declined and am now experiencing a check engine light, and rough start. Autozone checked the pcm and said the truck was running rich.

any ideas?

[maxwedge]

What codes? Check for fuel in the fuel press. reg vacuum hose if so reg. is bad if not post codes and check fuel pressure with a gage, how does it run/start, need lots more info, question is way too non specific.

[Riche]

The fuel press regulator is inside the intake manifold for this year. He can't check the hose.
try getting a gage and checking for blead off. This might point the finger at the regulator. or take a shot in the dark if you just replaced the fuel pump and go ahead and replace the regulator. it may not fix the problem but seems like it could be the culprit.
If it is the culprit then that is why it runs rich... b/c the regulator is inside the intake the gas is dumpin strait in there. You can tell it is leaking when you get the upper intake off. The aluminum under the regulator will be clean and the rest will be "crudded" up...

[av8r4golf]

Originally Posted by av8r4golf

My 96 Tahoe with a 5.7L motor and auto transmission has 122K on it. I had a 100K check done at which time the plugs, wires, rotor and cap were replaced. Rececently the fuel pump failed and the dealership wanted to replace the Fuel Pressure Regulator as an add on sale. I declined and am now experiencing a check engine light, and rough start. Autozone checked the pcm and said the truck was running rich.

any ideas?

Autozone Good Guy did another check. Here are the codes:
P0172, P0175, P0300

[av8r4golf]

Here are the codes:

P0172, P0175, P0300

Thanks

[Riche]

That is weird... 172 & 175 If it is the regulator should it be rich on both sides?

[av8r4golf]

What about an O2 sensor?

[Riche]

If you think it is the o2 then swap the "pre" cat o2's the code should change to 0171 & 0174.
I am not sure Just guessing here but since it is running rich on bank2, the computer is trying to lean the motor out to compensate. The question is why is it running rich on bank 2, The f.p. regulator is on the bank 2 side of the engine. but an injector could have taken a dump... If I had access to a good scanner I would check the injector pulse width and see if Bank 1 & 2 match. if they do then all the injectors are either rich or lean. I would guess lean b/c you can't have a rich bank 1 if it is throwing a lean code. so the gas would have to be coming from somewere else... Maybey someone will chime in and set me strait b/c I am guessing at this

[Jeremy-WI]

Originally Posted by Riche

If you think it is the o2 then swap the "pre" cat o2's the code should change to 0171 & 0174.
I am not sure Just guessing here but since it is running rich on bank2, the computer is trying to lean the motor out to compensate. The question is why is it running rich on bank 2, The f.p. regulator is on the bank 2 side of the engine. but an injector could have taken a dump... If I had access to a good scanner I would check the injector pulse width and see if Bank 1 & 2 match. if they do then all the injectors are either rich or lean. I would guess lean b/c you can't have a rich bank 1 if it is throwing a lean code. so the gas would have to be coming from somewere else... Maybey someone will chime in and set me strait b/c I am guessing at this

It is running rich on banks 1 and 2, P0172 Rich Bank1, P0175 Rich Bank 2. P0171 and P0174 are the lean codes

[Crasen]

How long ago was the fuel pump changed? Did this occur imediately after it was changed or has it been awhile? Any way you look at it you either have high fuel pressure, leaking injectors, or the pcm is opening the injectors for too long. If you have high fuel pressure you either have a bad regulator, a restricted fuel return line from the regulator to the pump, or a poor source of manifold vacuum at the pump ( I am assuming this year uses a vacuum controlled regulator) If both sides are showing rich I would not expect it to be leaking injectors, as long as the Check engine light hasn't been on for a long time, because that would mean more than one injector started leaking at once. Many things could cause the PCM to open the injectors for too long. I would not suspect O2 sensors being that it is on both sides, but it is possible. At that point you can either start checking every sensor you can think of for correct reference voltage and resistance values or bring it to a shop so they can use a scantool,(not a code reader), they can see all the sesnor values as the PCM sees them and may be able to see wich sesnor may be causeing it to run rich. I would get a fuel pressure gauge and check fuel pressure, that would be my first guess since you only have the bank1 and bank 2 rich codes, and an intermittent misfire code

[Jeremy-WI]

I would do a fuel pressure test. The fuel pressure should get to 60-66 psi with key on, engine off. If the pressure drops rapidly after the fuel pump quits, I would suspect a bad regulator.

Another cause for your problem could be a worn distributor gear(or someone trying to time the engine like a pre-96 vehicle). To fix this you would need to have someone with a scan tool that will check the cam retard(or camshaft offset), it is the difference between the pulses the PCM receives from the crankshaft position sensor and the camshaft position sensor. The cam retard is supposed to be 0 degrees +/- 2 degrees, if it is too far off it will cause misfire/crossfire conditions that could result with rich and misfire codes without giving the CKP/CMP correlation code which tells you the distributor is not placed correctly. The misfire caused by distributor gear wear should be most apparent during light throttle high speed cruise(45+ mph) as this is when the PCM will advance the timing the most

[Riche]

Awww.... I missed that. It is running rich on both banks!!! That makes me think it is the F.P. regulator. I got my codes messed up... It may be easier just to pull the upper intake and check the F.P.R. for leaks?

[av8r4golf]

Merry Christmas to All.

I appreciate your insight. I am going to replace the regulator tomorrow. Any thoughts on the procedure!

Steve

[av8r4golf]

Just a quick update. I wimped out on the install but found a great mechanic who did it with the regulator I bought. Total price with gasket was $170. No more check engine light, no more rough start. Another local company in Frisco Tx, tried the oldest trick in the book. Replace fuel filter, new cap, rotor, wires, diagnostic fee, and of course the regulator. All for $420. Only problem was that I had replaced all but the regulator 1 year ago.

Thanks for all of your help.

God Bless You