What's my problem???

[Stephen Soulsby]

After much frustration in tracking down the stumble and very bad idle, I borrowed a Snap-On computer scanner. When I forst hooked it up the MAF numbers were jumping anywhere between 8 and 225 at idle. The O2 was also jumping from 75 to 1050 at idle. Also the scanner said the motor had 9-12 degrees of knock retard just idling. This is all with the stock prom chip. I swapped in a Posten 93 chip I had for the car. After that the MAF readings were steady at 6 during idle and knock retard want to 0 at idle. RPM was still jumping between 700 and 850 erratically and the O2 volts were still just as jumpy. The O2 sensor is about 5 months old, but I will change it tomorrow just in case. What is weird is when I disconnect the O2 sensor the scanner still gets jumpy O2 voltage, but not as much voltage. All other numbers check out good I think. TPS is .44 at idle and 4.72 at WOT. IAC is at about 40 at idle and around 60 in gear, but it does jump around somewimes. The IAC is new and I followed the reset procedure on GNTType.org.

I put new bearings, gaskets, high volume oil pump and lifters in the motor about 2,000 miles ago. I'm wondering if I maybe have a wiped cam lobe? What are the symptoms?

Thanks in advance.

 

[Dave85]

Your O2 #'s are going to jump at idle the only time you will get a consistant number is at WOT. My car idles rough the first couple minutes it seemed to start that after I put a cam in it. How is drivability?

Dave85

 

[Stephen Soulsby]

Drivability sucks! I can hear detonation most times on heavy throttle. Raising or lowering the fuel pressure from 40psi only makes it worse. The car feels like it lacks the power it should have. When the converter locks, you can really feel it when the motor misses. It can be a little jerky at times. When I start the car in the morning it dies after a second and then will start and run. It runs bad all the time, but it's just a little worse when the motor is cold. Is it normal for the O2 numbers to jump to such extremes at idle? To add to my frustrations my alternator died tonight! It's only six months old. Thank god for lifetime warranties.

I'm ready to drive it over a cliff

 

[Stephen Soulsby]

Update

The stumbling is much better than it was now. I also had a chance to do some other checking. O2 is fluxuating around 950 at WOT and MAF is about 225 at WOT. Are these numbers right? I do still have a detonation problem. I'm seeing as much as 10* retardwen I lay in the throttle, and sometimes I see only 2* maybe.

 

[Buick From Hell]

you might consider checking your cam sensor. It may be borderline between okay and too advanced, and depending on timing chain slack while starting it, it may be okay one time, and too advanced the next!

I changed my timing chain and gears about a year ago, and my cam sensor setting ended up advanced. It would start fine when cold, but was harder to start when warmed up. It ran okay, but felt gutless, and would audibly knock more so than before. I drove it like that for 2 weeks before I finally got tired of it and turned the cap a bit to retard the setting...bingo!

I didn't even think the engine would start with the cam sensor advanced, but I can tell you they will!

 

[Stephen Soulsby]

I set the cam sensor using the tool from Posten. It doesn't stall anymore either since I put the new chip in. Just a little stumble.

 

[Dave85]

You O2 are 950 at WOT that's a little rich. Your stumble could be caused by being to rich. I suppose your TPS/IAC is set.

Dave85

 

[Stephen Soulsby]

Yes the TPS and IAC is set. What should my O2 look like?

 

[dave84gn]

O2s should be high 700's to low 800's at WOT. Or so I'm told

Did you put in that new o2 sensor yet? Any difference? Maybe check your fuel pressure (around 40psi with the vac line off at idle is about good I think)... if you have an adjustable fuel pressure regulator, maybe play around with different settings.

Dave

 

[a.j.hogan]

Guys,how do you set your IAC.THANKS

 

[dave84gn]

http://www.gnttype.org/techarea/faq/IACreset.html