Stumble

[whiner]

Ok so I just installed the LS1 MAF sensor and MAF translater and the car does run better when driving. The biggest problem I have is when the engine is cold the car idles bad. When driving and acclerate from a stop either
hot or cold there is stumble like it cuts out for a second, unless I very slowly push the gas pedal. I just replace the idle air control motor and still get the same thing. I checked the fuel pressure, since I have not checked it since I put the injectors and fuel pump in. The fuel pressure is at 56psi with line off. I had it set to 43psi with line off. How come it jumped up so much. Also I cannot lower it more then 2psi, no matter how much I turn the adjustment screw. So you think I have a bad fuel pressure regulator. Will that caust the off idle stumble. Any ideas???

 

[jasjamz]

Yep a sign of a regulator going south. Check your return line for kinks first.

 

[whiner]

What do you suggest.
Rebuild fuel pressure regulator or replace ir. I do not know what brand I have.

 

[turbo nasty]

Make sure your fuel psi gauge is good. The fixed ones mounted on the end of the fuel rail go bad due to the vibrations

 

[whiner]

No mine is not a fixed one and has only been used once. Hopefully it is still good.

 

[turbo nasty]

Put the gauge where you can see it going down teh road (tape to windsheild/cowl/etc) and see if the rising rate is working correctly.

I.e. Fuel psi is 43 line off then at 5 psi of boost it should 48 10 psi 53 etc.

LAso, Post up your parameters from your scantool:
TPS idle and WOT (engine off)
IAC in gear and park with the engine fully heated
MAF counts at Idle
Batt volt at idle, just off idle and WOT with and w/o headlights on.

Vac at idle
Exh leaks?
O2 sensor age and brand?

As soon as it goes into closed loop does it go away?

 

[sam87]

clean contacts

Agree with above steps. Just went thru a lengthy off-idle stumble diagnosis & while I did replace a couble sensors the very first step should have been to unplug & clean the electrical contacts - starting with ECU. With any little bit of corrosion this cold weather will alter the voltage.

 

[whiner]

So I have replaced the Idle air control and the fuel pressure regulator.
When I hook up the fuel pressure guage, I can still only adjust the fuel
pressure about 5 psi, its up around 58psi at idle. It will not adjust any lower. When I turn the key off the fuel pressure drops to zero right away. I know I have a fuel related issue, I just don't know what to check next. I am going to try a different fuel pressure guage just to make sure.
This car still stumbles off the line, idles like crap, and sometimes stumbles when getting into the boost. I have no knock though according to the scanmaster and all my numbers on the scanmaster are within range as far as I can tell.
Any other ideas? I really need your help, I have been fighting this condition for a long time.

 

[jasjamz]

Trace the return line look for kinks. Also if it loses pressure right away it could be the check valve in the pump or the feed line from the pump to the sender is busted.

 

[whiner]

Are they having problems with the Walbro pumps. I only have about 200 miles on it since installing. I will also check the lines.
The only rubber lines I remember is the ones going to the pump, so I will have to drop the tank again.
When I did install the pump I could adjust my fuel pressure and I think the car was running a little better.