rugbyguitargod

sorry for the low post count... i'm mainly just a lurker.

So, my 2000 Trans Am Formula has pretty much always done this the last 2 1/2 years. When I first crank it from dead cold in the morning, the car will get sideways hitting 3rd gear with crazy power. after about 2 or 3 minutes of driving and it gets around 140-160 and up, the car has a significant power lost and a very slight/intermittent miss during idle. it runs/idles smooth when cold and it always fires right up no matter if its cold or hot. it idles smoothly for the most part hot too, just an ever so slight miss though that is intermittent.

not sure at this point where to begin troubleshooting. I want to put heads/cam/intake/tune in the car later this summer, but don't wanna do it until i have this issue figured out. I was thinking it could possibly be a coil pack or fuel pump that is acting up since the car has over 200k miles. i replaced the plugs/wires (NGK TR55 IX) when i put the headers on the car about 15k miles ago and i replaced the water pump, radiator and thermostat about 10k prior to that. I also pulled the MAF and sprayed (not touch) MAF cleaner on it and cleaned the intake filter.

in short, not really sure where to begin. the car drives fine and still averages about 24-26 roughly open highway but can't pin down this issue.

conan

iTrader: (5)

Any DTC codes ? Do you or a buddy have something like HP tuner or a scan gauge you can log the computer and see if any thing is out of sorts.

Could be something like a failing inlet air temp sensor telling the computer the temps are high and then it will pull timing.

rugbyguitargod

no DTC's or MIL's, and i don't have a scan tool readily available to use at my disposal. i was thinking since it's doing it when its warm, could it possibly be a head gasket issue?

conan

iTrader: (5)

Are you loosing or burning coolant ? Pushing coolant out the overflow ?

hrcslam

Check O2's.

rugbyguitargod

nope. coolant and all fluids are normal.

will do. unfortunately, O2's are expensive to just 'swap' when they may not even be the problem.

03Sssnake

iTrader: (20)

Just take it over to autozone, they will throw the scanner on it and print out any trouble codes. I agree with you and would want to know before starting to randomly replace 02 sensors etc, as it could be a couple of things. How does you voltage look once warmed up? When my alternator started to die a slow death the car tended to run stronger when cold, voltage was a solid 13+, but as the alternator got hot the voltage dropped off significantly to 12 or little less volts, seemed to lose power...Ended up replacing the alternator with a truck alternator, no more issues and believe it or not, MPG actually increased by 1-2MPG!

hrcslam

I feel you on that one. One way to isolate it to being a sensor problem is to force the engine to stay in open loop while at operating temp. You can do this by disconnecting the O2's or MAF I believe. If the issue persists it is not a sensor. If it stops with the O2's disconnected it is a sensor. Which sensor I don't know.....

rugbyguitargod

there are no trouble codes though, and also my alternator reads a solid 14v at all times

LilJayV10

iTrader: (39)

unhook your 02's and drive it. It sounds like when it goes into closed loop it's running bad.

Unplugging the 02's will force the PCM to stay in open loop.

rugbyguitargod

that makes sense, but when i go WOT, isnt that open loop too? whether i'm cruising or have the throttle buried when it is even remotely warmed up, it does it.

Youngblood16

Pull the maf out again and Just look at the exposed part of the wire/sensor. Look for small fine particulate, matter. Even with the maf cleaner it sometimes doesn't get it all off

thunderstruck507

iTrader: (18)

This. I've also seen them develop a black film that you will need a qtip to get off. You have to be really careful but it's easily done.

Could also be the o2 sensors. If the car has a lot of miles and they are original, it would be a good idea to change them anyway. You can get them online or use an online coupon code for Advance Auto to get them very reasonable...I think I paid around $66-70 for the pair for good Denso sensors just a few weeks ago using a coupon for Advance.

Could also be the fuel pump going out. I've seen them do weird things. Easy to check with a fuel pressure gauge.


A good scan tool will be valuable to finding the problem without just replacing everything.

rugbyguitargod

i'll check those areas and see whats up. im really hoping it isn't a coil pack (which i doubt, or else id probably be getting a 'misfire cylinder x' code).

Thanks for all the good advice guys, and ill see if i can get this thing running like the animal i know it is!!

Youngblood16

Also, I just did a fuel pressure test on a v6 firebird, (same body obviously different motor) But the rubber gasket/ weatherstripping that's on the back of the hood is soft enough that you can put on the fuel pressure guage and slide it in between the hood and wiper panel then be able to the hood and actually drive it to get the "loaded/operating" fuel pressure. And slide the guage under the wiper so it doesn't scoot around and you don't have to look far for it.
Just previous experience that worked for me

thunderstruck507

iTrader: (18)

The chances of it being a coil are so slim it's barely worth considering but you can use a laser thermometer and shoot it on each header tube to see if one of them is significantly colder.

If the car has manifolds that probably won't work though, another option is to hook a timing light to the battery then clamp it on each plug wire and make sure they all cause the timing light to fire consistently.

The fact you say it runs good until it warms up makes me think it's a problem once the PCM goes into closed loop which points to a problem with the MAF or O2 sensors being the likely culprit.

rugbyguitargod

ok, so update on this topic (sorry for waiting so long, just got back from overseas), i unplugged the upstream o2 sensors and it seems like the car is staying in open loop. Runs like a scalded dog, but what is the next step in this troubleshooting procedure? clean MAF sensor and replace O2 sensors?

Fry_

I'd say clean the MAF with q-tips and rubbing alcohol, it's practically free most people have this stuff in there bathroom.