AJ-Question

[rhw1]

Thanks to all for help; I will check fuel pressure and FPR; need to get fitting for my pressure gage so it may take a few days or so.

[rhw1]

I have the following fuel pressure data:

Engine off, key on, fuel pump on, pressure = 51 psi(spec = 48-55).
When fuel pump shuts off, pressure drops immediately to 40 psi, then recovers to 48 psi in about 30 seconds. After 10 minutes, pressure = 46 psi(spec = 48-43). I don't understand this drop to 40 then return to 48; I did my best to purge air from gauge and hose. Can anyone explain?

Engine at idle and normal operating temperature, pressure bounces between 41-44 psi. While this reading is in spec(41-48), it is at the low end, should I try a new FPR?

As history, I have cleaned throttle body, IAC passages, and tried a new IAC valve. Any suggestions would be greatly appreciated.

[Ranger]

If your not having a problem, don't worry about it. Sounds normal.

[rhw1]

Originally Posted by rhw1

Would like your comment on problem below as I have read your authoratative posts on this issue.
99SLS with 72K with decel stall
Throttle body and IAC passages have been cleaned; only code is stall/near stall condition(1599).
Problem is intermittent(one or twice per week), but only happens on gradual decel when 800-900 rpm is reached; tach will drop to 400 rpm and usually recover to 1000 and then do the same thing repeatedly. It seems that engine can't run at this 800-900 rpm, but if under a more rapid decel and 700 rpm is reached engine runs fine. When the stall/near stall happens, I feel no missing or stumbling.
Thanks for your help.

I am still having the stalling problem and checked fuel pressure per my post earlier today.

[Ranger]

Those pressures are pretty normal and definitely not low enough to cause a stall. Now an intermittent fuel pump is another story.

[eldorado1]

Need more info... Does it only stall when it's hot? Both cold and hot? Can you get it to occur at speeds above 55? Does the tank have to be near E or F for it to happen?

[rhw1]

Stalls are at any gas tank level and are only during decel at 20-25 mph(at about 900 rpm). They do not happen when engine is cold. Usually it's a near stall; rpm drops from 900 to 400 with no stumbling and recovers; if A/C is on, it may not recover. The problem is intermittent, but when it happens it can go from 900 to 400 rpm and back to 900 etc. a half dozen times in succession in one minute.

[submariner409]

Let's go back to square 1. Look at the driver's door sticker, the one that lists the tire size and ratings. In the upper corner of that sticker is a date code that looks like xx/xx. What are those numbers?

Where I'm going is that if this is a late model run, some sensors could be first generation '00 stock, phased into the end of run assembly.

Which takes me back to CKP problems.........

Interested in the date code.

[AJxtcman]

I may know what is wrong with the car and it has to do with the DFCO

I had one come back to me last Friday after I put a FPR on the Friday before. I also change plug and wires for maintenance.

Anyway the POS backfire valve was leaking and throwing off the fuel trim. Then it would seal up and shoot it the other way.

Question: will a vacuum leak make a car lean?
Answer: NO

If it is a Speed density system (MAF less) it will just raise the idle RPM, because that is all you are doing when you open the throttle plate.

Now with the MAF sensor in play a vacuum leak such as the back fire valve can cause the system to subtract fuel. I vacuum leak in another location may cause the system to add fuel.

[submariner409]

In order to narrow this down, how does he go through the DFCO faults and then check out the manifold (backfire) valve?

I still want the date code........good info, No?

There are enough brains (?) in this N* forum to psyche this thing out........

[eldorado1]

Originally Posted by rhw1

Stalls are at any gas tank level and are only during decel at 20-25 mph(at about 900 rpm). They do not happen when engine is cold. Usually it's a near stall; rpm drops from 900 to 400 with no stumbling and recovers; if A/C is on, it may not recover. The problem is intermittent, but when it happens it can go from 900 to 400 rpm and back to 900 etc. a half dozen times in succession in one minute.

When it is warm, do you notice a hesitation if you slightly apply the gas?

[eldorado1]

Originally Posted by AJxtcman

I may know what is wrong with the car and it has to do with the DFCO

DFCO is not active at 20mph. Your theory on the vacuum leak may be correct, but it doesn't have anything to do with DFCO.

[AJxtcman]

Originally Posted by submariner409

In order to narrow this down, how does he go through the DFCO faults and then check out the manifold (backfire) valve?

I still want the date code........good info, No?

There are enough brains (?) in this N* forum to psyche this thing out........

If it was me I would look at fuel trim and the MAF flow rate.

[submariner409]

Would fuel trim swings set a P code?

rhw1.........did you pull the MAF when you did the IAC cleaning? Is there ANY chance you hit or moved one of the tiny wire resistors on the MAF voltage bridges? Should be 3 resistors with steel leads electro-welded to the signal and ground bridge network. They're tiny and fragile. Just another maybe.....

Click on the below pic and scroll in. These may not be your exact MAF, but they show (look carefully) the 3 resistors across the larger support wires. The little black thermistor at 1 o'clock is the IAT sensor. The pic also shows that a JET MAF is nothing more that a mechanically modified OEM DELPHI unit.

[rhw1]

Originally Posted by submariner409

Let's go back to square 1. Look at the driver's door sticker, the one that lists the tire size and ratings. In the upper corner of that sticker is a date code that looks like xx/xx. What are those numbers?

Where I'm going is that if this is a late model run, some sensors could be first generation '00 stock, phased into the end of run assembly.

Which takes me back to CKP problems.........

Interested in the date code.

Date code is 08/98