tonydepo

2000 Trans am, m6, cam, header. The car last week started pinging, like when you get some cheap gas. I figured it was the tank of gas I just got, then 3 days ago it started driving sluggish and had a small back fire. Finally burned the tank of gas and filled up with a new tank and used some stp fuel treatment in the tank. Still running sluggish (almost bucking) taking off at a light like it is missing or that. The idle is perfect and reving the engine in neutrul has no skip.

I replaced a crank sensor already too.

What could it be?

Thanks

nimrod.sixty9

iTrader: (5)

poopy CATS maybe.. any damage to exhaust
They red after driving?
Codes?

98TAjwh

iTrader: (4)

codes?

could also be clogged fuel filter or fuel pump going out

tonydepo

I have not cats on the car, just straight LT headers. I will look under the car when I get home today to check for any damage to the exhaust. Also, my buddy will be over on Saturday to check the codes on it. I just don't understand why it revs find in neutral without a hickup, but under load it bogs.

Thanks for the help all

91RS383

That's probably the key to your diagnosis. It bogs "under load".

You can get the codes read at autozone, just don't let them delete the codes, you may need them until this gets sorted out. If you go to the parts store, see if you can rent a fuel pressure test kit, so you can diagnose the fuel pump this weekend as well.

tonydepo

Changed the fuel filter and still have the same problem. We scanned it for codes and did not find any. Do you think it might be the crank sensor?

91RS383

Did you check your fuel pressure? What was it?

02pewterform

My car is doing this exact same thing. Have no idea what it could be but it is really annoying!

tonydepo

David, I haven't checked on the fuel pressure. Trying to find out if I can get something from advance to check it. I will keep you posted.

Wish I knew cars instead of computers

91RS383

I bought a fuel pressure test kit at Autozone for under $30. It's a great tool that I'm sure you'll use more than once. Just make sure it's for fuel injection as a carburated test gauge doesn't read high enough.

Here's what the kit looks like:
http://cgi.ebay.com/ebaymotors/Fuel-...motiveQ5fTools

ls1jorge

iTrader: (5)

How much is it for a fuel pump racing go for lowest budget price, & what's the cause of a fuel pump going out

tonydepo

Well, I got a fuel check gauge and hooked it up. The pressure at idle was right at 50 and keeping the revs at 3.5k it went to 60 and stayed. I guess it is not the fuel pump . Still waiting to change out the crank sensor which will happen either tonight or thursday. I will keep everyone posted.

LS6427

iTrader: (2)

A failing Crankshaft Sensor usually shuts the engines off while driving and causes hard starts...but then sometimes will run like a champ. Until it totally fails. And you won't get a SES light till it totally fails.

I've never heard of a failing Crankshaft sensor causing it to be sluggish or backfiring. But anythings possible I guess.

Your 02 sensor(s) failing WILL cause exactly that though. And you also WILL NOT get an SES light till they totally fail. I'd get a scan with a real OBDII and see what the 02 sensors are doing with the engine running. You can see if they're NOT switching properly, then you found the problem. Bad 02's rob power, cause the engine to stumble and misfire.

.

tonydepo

Quick question, I have offroad LT headers and it is my understanding I have fake out o2 sensors. would this still cause engine issues?

Thanks

LS6427

iTrader: (2)

You can turn the rear 02 sensors off but you cannot turn the front two 02 sensors off.

.

tonydepo

Sorry for the questions, I am just a noob when it comes to cars. I remember ordering o2 sims, but I think I just got them for the rear. Does that sound about right with offroad headers? If so, the front O2's might be going bad.

Thanks

spdygon

iTrader: (1)

i had a similer problem with my work van and it happen that one of the sensor in the intake was disconnected. i think it was the maf. check all connection that have to do with with intake. it might be your maf not reading correctly under load ( high velocity of air ).

tonydepo

This sounds like the same symptoms I am having. I still don't understand how it doesnt miss a beat when I rev it in neutral.

https://ls1tech.com/forums/pcm-diagn...like-crap.html

1 FMF

iTrader: (1)

revving in neutral is under zero load, and is completely different than when the engine is under a load moving the car. You can have many problems and the engine will still rev and sound fine in neutral out of gear 99% of the time, it means very little when it sounds fine in neutral.

having a cam and headers, I would first start with checking spark plugs and spark plug wires. You may be getting intermittent misfires and not all misfires throw a code. It is also common for spark plug wires to go bad from the heat being next to the headers and cause misfiring, and that would happen when under load when the most heat is generated.
Inspect the spark plugs, and wires, and look for fouling or overheating and go from there. I would do that first since it's probably easiest and free.
After that if nothing conclusive then I would go back and adjust lifter preload; you had a cam install so there's a good chance of that being the source of the problem. It's probable whoever did the work did not set one correctly and a valve is not closing fully which will cause backfiring under load but not in neutral. Or you could have the wrong valve springs or incorrect pushrod length with new cam. Worst is you might have a burnt valve which will cause what you describe, and can be diagnosed via leak-down or compression test.
I would not rule out O2's, but since you mention a cam/header install I would think valve train first. but if you have a easy cheap means to check O2's then do it to rule it out, same with fuel pressure. I doubt it's a fuel pump problem though.
And yes, it's the front O2 sensors you would be checking/replacing; those do the work of monitoring air-fuel ratio. The rear O2 sensors, which you deleted or replaced with simulators, were only there to check catalytic converter efficiency for emissions, you replace them with "sims" to fool the computer so a trouble code is not triggered.

tonydepo

Is it possible that a code would not be thrown for o2 sensor? Also, I read that o2 should be changed around 100k, and thats what i just turned on the car.

Thanks for all the help gang.