MPG Gone To Crap...

[nunesjeff]

I used to be getting 19.5 mpg at first but now I went 245 miles and put 15.9 gallons in the tank on the same old routes and conditions... I don't get it... I did a tune up and EVERYTHING is topped off and looks good... I am sure the (Fuel Pressure Regulator) is going T1T$ Up I can smell fuel with the motor off pulling the vacuum line... Would that kill mileage? SLURP!!!

[londonontman]

Signs of a Bad Fuel Pressure Regulator

The vehicle engine runs rough and often stumbles and sputters.
The vehicle engine will not start after ignition. Usually, this is problem is encountered in the morning when you start your vehicle. Many a times, the engine starts, but stalls shortly after starting.
The fuel pump in the vehicle becomes noisy at times.
A bad fuel pressure regulator can also result in fouled spark plugs.
Last but not the least, the fuel mileage of the engine decreases noticeably.

[Bob Dillon]

Have you changed your LIM gaskets? They can cause an ugly vacuum leak, and vacuum leaks are very bad for MPG.

I'd put a vacuum gauge on it and see what it's pulling.

[J Wikoff]

The fuel smell in the vacuum line is a reallly good sign of a leaky regulator.

[willwren]

Don't forget I have a scantool and a fuel pressure gauge. Let me know if you want a crack at it.

[LeSabre in Buffalo]

There's a whiff of gas in the vacuum line coming from my FPR. Time to order me one...

[willwren]

Keep in mind how that system works. It's probably due to SOME reduced fuel mileage, but not all of it.

The regulator bypasses fuel back to the tank that it didn't need to maintain pressure to the rail and injectors. If the diaphragm in the regulator leaks, it'll allow SOME fuel to get back into the manifold (this can cause hard restarts in severe cases, especially in summer).

[LeSabre in Buffalo]

Keep in mind how that system works. It's probably due to SOME reduced fuel mileage, but not all of it.

The regulator bypasses fuel back to the tank that it didn't need to maintain pressure to the rail and injectors. If the diaphragm in the regulator leaks, it'll allow SOME fuel to get back into the manifold (this can cause hard restarts in severe cases, especially in summer).

I've had those for a while. They're not consistent, but happen more in warm weather when the car is stopped for a minute or two, such as at the two-minute lights. My warm idle RPM's are also starting to rise and fall from 630-710 where as before they were rock-steady at 660-670.

PS: Having real-time engine data in the car is sweet.

[willwren]

Jeff is coming over tomorrow. We'll look at everything and come up with a list, maybe a few pics too.

[LeSabre in Buffalo]

Amazon should be called Amazing. The FPR I ordered Wednesday night for $25 got here this morning. Time to jury-rig me some snap-ring pliers and install this bad boy, along with new plugs and wires.

[willwren]

Be warned, it may fight you coming out, and it won't be the snap ring that pisses you off. Fine needle-nose pliers will work for that, or a small hardened centerpunch.

The two o-rings won't want to let go. If they fight you, don't hesitate to pull the rail off for easier access.

[wjcollier07]

My FPR was replaced under recall a looong time ago. Wondering is it normal to replace it again, probably only after 50,000 miles? I do have a weird idle that I can't diagnose, it lopes and stumbles, but there is no leaking fuel in the vac line. Good insurance to just replace it I guess is the point of this.

Dave. Be sure to make it known if that fixes your lopey idle.

[LeSabre in Buffalo]

FPR, plugs and wires replaced. Putting all the O-rings back first before putting in the regulator helps a lot getting the rest back in. I had more trouble with the snap ring than the regulator.

My plugs were pretty carboned up, indicating a rich condition. Some good fuel system cleaner is going into the tank to burn off all the remaining gunk.

John, I'll report back after I've driven the car for a bit. I'm headed out right now.

[LeSabre in Buffalo]

John, here's your update: The lopey idle is gone. RPM's are back to 660-670 at warm idle. And, no strong gas smell in the vacuum line, just the faint smell of the gas vapors that had soaked in previously.

Plus, I wonder if this is related in any way to our funny KR bursts. I didn't see much KR driving around this afternoon, even in taking off under very light throttle.

[00Beast]

When I removed my FPR, the unit itself came out fine, it's the snap ring that fought me tooth and nail, and I have every snap-ring pliers imaginable.

[LeSabre in Buffalo]

The snap ring went in for me by using two screwdrivers. One was to hold the ring using the hole, the other was for pushing the ring down.

[willwren]

Jeff came by today, checked it all over. There was fuel in the vacuum line, but we kept digging. Found his pressure valve on the rail is bad, he'll need to put a new one in. Only the cap is keeping it from leaking (potentially dangerous). The NGK plugs he put in 2500 miles ago are sooted up nice and black confirming the rich condition as well (checked only the front three). The crack in his rear manifold is worse than I thought also, and may be affecting O2 readings.

O2 isn't toggling very fast, mv are a bit off, and he doesn't know how old it is either. Everything else looks good on the scan.

Things to go after:
1. New schrader valve for the rail test port
2. New fuel pressure regulator
3. Fix/replace rear exhaust manifold
4. O2 sensor

I'd do it in that order too. After that, we'll need to team up here for a myriad of odd electrical gremlins. I'll get a couple pics up tomorrow (had to work on other stuff today and haven't had time to upload yet).

[LeSabre in Buffalo]

Yowza! That list would explain why his MPG's are gone. Skewing the A/F readings would kill his mileage, and having a bad regulator pushing all the fuel it can through the injectors would make things worse.

Willwren, can you please remind me again if SII manifolds are susceptible to these same cracks?

[willwren]

S2 don't have cracking issues that I'm aware of, but only the rear on the S2 is similar to the S1. Big differences. In terms of flow, S2 didn't get it right, it was a big step in the wrong direction. S1 front and rear manifolds are tubular steel and built for flow. Notice how every runner on the S1 manifold empties into the main plenum pointing towards the direction of outward flow:


In this pic, the front is the lower manifold, rear is the upper pictured. Jeff's crack is where the far right runner on the upper manifold (rear) pictured enters the main plenum, about 3" before the outlet.

Better pic here, see the weld where the large plenum (collector) meets the #2 cylinder on the far right? His crack is there, and about 1/3 or 1/2 way around:

(these pics are the Zila's manifolds after ceramic coating)


This is a S2 front manifold (after beat blasting):

Material isn't stainless, it's cast iron. While the flow directions look great, what you can't see is just underneath the mounting flange on the cylinder head, each 'neck' of the outlet ports is severely restricted in the casting underneath. This is why it's important to build up material underneath (with nickel welding rod for cast iron) before porting. The front manifold flows less than the rear on the S2.

Rear manifold on the S2:

See how the construction looks similar to the S1? It's good in principal, but the main 'plenum' (collector) the runners dump into is smaller in volume. It's not going to be as prone to cracking due to stress as the S1 though, primarily because of the distance between the #2 and #4 ports, which is far bigger on the S1 due to the uneven port spacing.

[LeSabre in Buffalo]

Thanks for the explanation! That's a good example of heading backwards in design.

Having that giant crack in the manifold would make the pre-cat O2 lean, which would cause the PCM to command more fuel, hastening the demise of the pressure regulator as it deals with higher-than-expected fuel pressure for a sustained time. Then the regulator fails, more fuel is injected on each cycle of the injectors, and fouls the plugs. All the while the PCM is happy off in la-la land. What a crazy feedback loop that is!