awilson40

I have a slight hesitation/stumble on part throttle acceleration. Easy acel and hard acel are OK and boosting to .8bar. It doesnt hesitate at all with the O2 sensor disconnected. I've checked for vac leaks by spraying every connection, hose and gasket with starting fluid,none to be found. I've replaced the TPS, bypass valve, O2 sensor. Cleaned all grounds and connections several times even added another engine to frame ground.
I opened, cleaned and checked out the AFM.All checks fine per this site <a href="http://frwilk.com/944dme/." target="_blank">http://frwilk.com/944dme/.</a>
I'm at a loss. I hooked up a dvm to the disconnected O2 sensor and it was reading .8 v, so I adjusted to AFM CO adjustment to read .5v at which point it would start dithering from .3 to .6v. Idles OK just this slight hesitation .
Any other Ideas ??? It acts like its lean when it hesitates.

Thanks

jimbo1111

What mods do you have. Start from there.

awilson40

only mod is the ReliaBoost and it did this before I installed it.
I also hear conflicting reports as to how the DME reacts to a disconnected O2 sensor. Some say it runs only its fuel maps and that the O2 circuit is only a fine tune. Others say the DME goes full rich.
Does anyone know for sure?

Danno

"Some say it runs only its fuel maps and that the O2 circuit is only a fine tune. Others say the DME goes full rich. "

Uhhh, it will run off the chip maps without O2-sensor feedback and fine-tuning. It may just happen that the chip map may be a little rich for a stock car. However if you've got free-flowing mods like exhaust & intakes, you'll be running lean. I don't know what "full rich" means, but anything richer than 9.0:1 will probably cause clouds of black smoke and stall the engine.

awilson40

I had a new 2.5bar FPR so I went ahead and put it in, checked fuel pressure...2.1bar at idle. I checked all connections and cleaned again...just in case. Still the same thing. It doesnt hesitate in first gear or 4th or 5th. But 2nd and 3rd gear 1/2 to 3/4 throttle yelds some hesitation around 3500 and 4500 rpm. What about a bad injector ??? would a bad injector act up when in closed loop but have its problem masked when the o2 sensor is disconnected??

RJP 951

Man, it sounds like you've been taking exactly the same approach I did. I replaced O2 sensor, blow-off valve, wires, coil, plugs, air filter, TPS, DME relay, hose clamps, FPR, fuel pressure damper, cleaned AFM, scrubbed the grounds, etc.

Long story short, my problem was definitely vacuum leaks under the intake manifold. I hesitated to work that area sooner because I didn't want the down time during nice weather. When November came I pulled it all apart and replaced the vac lines, tees, hoses, the plastic "venturi", cleaned the idle control valve, cycling valve, fuel injectors, fuel rail, etc.

I finally put it all back together just before Christmas and was able to take it for one long drive before our winter weather kicked in. Bottom line, it ran great. Now I'm waiting patiently for spring to arrive!

Good luck,
Ron

awilson40

Like you, I'm trying everything else before I pull the intake. The PO had a good shop pull the cam housing in November in order to repair an oil leak and they suposedly replaced any bad hoses when they had the intake off. So thats why its last on my list. I guess my next step is to pull and clean the injectors. This being my daily driver, I cant shut it down for several days while I work on it.

RJP 951

Most of the hoses under my intake were in good condition. However, several of the clamps were loose, and you could turn the hoses on their fittings with ease. I also found that the plastic venturi leaked, and the one hose that was bad was the little rubber elbow that feeds the crankcase vent back to the intake boot.

Plan ahead and buy all new clamps, as most of the originals are the crimp style that can't be reused. If you can't afford the downtime, you might want to buy a new set of hoses and tubing beforehand, and have everything on hand that you may need.

Ron

awilson40

Ya man...When the weather warms up I may just have to take a couple days vacation and do that. BTW...what kind of gaskets/ seals are required when removing the intake?
about how long does it take to remove the intake?