Thread: trannyman can u help

97 GT is going to be a vacuum controlled trans, what vacuum code did you have?

If the car has a bad misfire it will not want to shift likely until you lift throttle as the pcm sees a greater load than it should and letting off the gas puts less load on the engine so it will allow the shift. Have you inspected plug wires, spark plugs, coil pack terminals? How does the engine itself run? Once it shifts into 3rd gear can you accelerate smoothly or does it feel like there is a power loss?

Ok, P0441 is for the EVAP, so I don't see that affecting the trans shifting. P0300 is random misfires, though, you need to get that one figured out. Being random, unfortunately, it's probably not the plugs/wires/coil packs as Dave mentioned.

Being random, unfortunately, it's probably not the plugs/wires/coil packs as Dave mentioned.

Why do you say this? I have done drivability testing and repair for a long time and ANY ignition problem can trigger this code, it isnt always a specific cylinder code that will set.

If I'm wrong, I'm wrong, but if it really is random/multiple, I don't see how a single bad plug or wire could cause it. First step would be to hook up a scan tool and watch the misfire counts, see just where it's happening.

Code P0300 can occur from several things but the easiest things to rule out first are the secondary ignition components ie the plug wires, spark plugs, and commonly corroded ignition coil plug wire ternimals. I have also ran into many bad coils that appear fine and arc internally. Some things are hard to see and without an ignition scope or scan tool to lock in on the problem it make the job that much more difficult. The GM Service manual also suggests inspecting the spark plugs wires first on the diagnostic list for this code. I am not saying I am right or wrong either and am simply offering advice to check things but nobody on a forum has access to the car except the owner and his mechanic and often problems like this can be difficult to pinpoint online so all we can do is offer suggestions to help out. You can never diagnose too much when tracking down a problem and I was always told in college never to trust anything without proving it and seeing it with my own eyes so that is what I have always gone by. I have seen a lot of things that just dont make any sense at all but hey thats what mechanics deal with every day. A brand new spark plug someone else installed with no ceramic on the center electode is a real treat to diagnose!

They likely changed the gasket because it was causing a vacuum leak which can make the engine run lean and also give the problems you had if it was a bad leak but typically you have a lean condition code to go along with it. If it had the original spark plugs with 95K miles then they were way past due. Often most vehicle manufactures rate the ignition components to go to 100K miles but that is often way past due so your spark plugs were probably very worn and also causing misfire.

You could possibly have a bad coil that is arcing internally or you could have a clogged injector that is causing that cylinder to run a bit lean. Did you check the condition of the coil terminals to the spark plug wires when you replaced them? It is very common to see rust or corrosion here and it can definately cause a misfire. An easy way to check out the injectors is to go around to each one with a stethoscope and listen to the sound they make. I have an injector pulse tool that is purpose meant to check the spray pattern and output of the fuel injectors but is not something that is too easy to come across and requires removing the fuel rail from the car. A compression test will also verify that the cylinder is mechanically sound or at least is close to the other 5 if it is then you are left with fuel and spark.

Good tip! I have also heard or using a long skinny screwdriver and that works decent also. Both save a trip to the auto store