3800 series 2, when you press gas to halfway point it slows down like you took your foot off, release a little and it goes again, push it past halfway and it picks up. It has power, just bad at halfway. Replaced the gas tank, sending unit and fuel pump, fuel filter, fuel pressure regulator. The car also has all new sensors including EGR valve, 02 sensors and all of the sensors on the throttle body. New timing chain and gears, complete exhaust, complete ignition with coils, module, plugs, wires cam and crank sensors. The upper intake manifold is new and the lower intake gaskets, idles beautiful, no skips, no overheat, no check engine light yet still has same problem.
it is a project car, being restored to like new again so I am throwing parts at it. The engine only has that one issue. Also, the code was relearned a while back. Tremendous pickup up until halfway and after halfway when I hit passing gear.
What is the fuel pressure? Have the injectors been cleaned or checked out?
August, 27, 2012 AT 2:11 AM
I can't even remember how it was done but when you change a lot of sensors the check engine light comes on and says code not learned, that was set a while back, exact number for pressure I don't know but the only original parts are the 6 injectors in the entire fuel system, even the tank straps, gas cap and filler neck are new. Car had same problem with the old stuff, nothing changed when everything was replaced for the fuel system, one shop said throttle position sensor so I put in a new AC Delco sensor, another shop said MAF so that was changed with an AC Delco. All of the other sensors were done with name brand parts, nothing generic.
I had one shop tell me it was pinging when you first hit the gas because of knock sensors, sensors were changed and it turned out to be a stretched timing chain. If I go to about 1/4 throttle it picks up speed pretty quick, you can feel the pull, I hit it and catch passing gear and it takes off, only at half way, that's it.
The injectors were cleaned and they seem to be functioning ok.
August, 27, 2012 AT 2:42 AM
There is no code for re learning.
How were the injectors cleaned?
Was the cat converter back pressure checked?
August, 27, 2012 AT 3:04 AM
I pasted something below about the relearn. The CAT is a brand new magnaflow direct fit, it doesn't feel like a clogged or bad CAT.
The injectors were cleaned with 3 different brand fuel system cleaners for 3 tankfuls of gas and there was no change.
The injectors are $267 for 6 of them, they have 142000 miles on them. I am thinking that if the CAT was clogged or the injectors had issues why does it have power past the halfway point? I can go up a steep hill at 70MPH with throttle past halfway, if I let up and go to half it will die out until I go less or more.
Nothing on the 3800 series 2 is ever easy.
NOTE: If the crank sensor is bad and needs to be replaced, a special relearn procedure must be performed after the new sensor has been installed using a GM scan tool or an aftermarket scan tool with similar software. This step is necessary so the engine computer can correctly recognize the sensor's signals.
August, 27, 2012 AT 11:01 AM
Ok, what is the fuel pressure?
August, 27, 2012 AT 11:50 AM
Not sure how it matters with car acting the same even with brand new fuel components minus the injectors but 38PSI is the average so the pressure is there, is it getting through the injectors or how could all 6 be bad at the same time is another question. I can go out right now and at 1/4 or a tiny bit more throttle feel great pickup and have no problem with a hill. You don't hear it bog down like lack of fuel you just feel the engine stop pulling and go quiet at halfway and start going again 3/4 or more.
August, 27, 2012 AT 11:50 AM
P.S. I said code relearn, bad wording on my part it was case relearn.
August, 27, 2012 AT 12:02 PM
Only for crank sensor. Not other sensors and has to be done with a scan tool.
Again, the fuel pressure?
August, 27, 2012 AT 12:43 PM
August, 27, 2012 AT 1:17 PM
Try having the injectors professionally cleaned. Tank additives have very little effect. Its all pointing to this with all you have described.