LT4 Help! LT4 Running Terrible!

[WantaVette]

I finally got my new clutch put in and now it is on to the engine trouble.

It all started a few months ago when I got the SES light. The code said bad O2 sensors. The car seemed to be running rich, I could smell fuel, power was down, and the idle was rough. I replaced the sensors with bosch units and everything was fine for a few days. Then the same code came up and same symptoms of the engine.

When I read the codes now, it says a bunch of O2 codes and one for a multiple cylinder misfire. My gas mileage is terrible, in the 10mpg range, there is black soot on my rear bumper and the occasional puff of black smoke. The car is way down on power, idle is rough enough to shake the car,(especially with the ac running), and the engine just doesn't run as smooth as it should.

The shop that did my clutch (Corvette Masters of Orlando) suggested changing spark plugs, wires, and buying AC Delco O2 sensors. Should this do the trick? Also, could this be a sign of a failing opti.

Basically the engine runs but just not as good as it should. (No trouble with starting either.) A few of my questions are; how many O2 sensors are there (I thought there were a total of 4, 2 pre-cat and 2 after cat), and what plugs should I buy. I plan to run nitrous in the near future so should I take this into consideration?

Also what are some tips to changing the plugs and wires? I've heard its pretty difficult. Again, my car is a 96 LT4 with 75,000 miles.

 

[LannyL81]

You are correct on the O2 sensors....four of them, all the same...AF75.

As far as changing plugs, since you want to use NO2, go with Iridium ones; no platium.

I changed plugs in my LT4 couple of weeks ago. Driver's side is easier.

On driver's side:
Disconect AIR line at the metal to rubber hose connection above #6 cylinder. Push rubber hose out of your way.
Remove the plug wire separators, two bolts each. Unclip wires from separators and just set the separators aside.
Change out plugs. I did not replace the plug wires, but expect that you have to remove the air cleaner and hose up to the throttle body to do so.
Replace the wire separators.

On Passenger's side:
Disconnect the metal AIR line out of the exhaust manifold at the exhaust manifold. This also connects to the back of the intake, remove the two long bolts on the flange. There is also a support for this hose on the rear of the head...it just slips out and in place.
Remove plug separators.
Replace plugs and wires.
Re-install in reverse order.

Can not help you with the engine running problem. Have not had my LT4 long enough yet to be familar with it.

Later,
LannyL81
Tucson, AZ

 

[regalniz]

wouldnt hurt to spray your maf sensor with some brake cleaner. i did it and got a couple of mpg. if thats dirty it might cause a rich condition.

 

[C4Tom]

When was the last time you used an injector cleaner? If the injectors are clogged or leaking it can cause O2 problems and definately MPG problems. C4C5Specialist recommends Chevron Techron injector cleaner.

I replaced half my plugs and wires and had the dealership finish the job($425). There are 4 that can be done fairly easily, but the other 4 are a bear. I used Bosch Platinum +4 plugs and Delco wires.

Have fun!

 

[SSTibet]

Sounds like you have a fuel problem. I had exact same symptoms a year ago in my 95 LT-1 which has 3 x O2 sensors. Replaced all 3 with Ac Delco's and started buying fuel from a well known gas station. Resolved the problem completely; no SES light and smooth idle since than.

Try injector cleaning fluid. If you suspect fuel quality consume the tank and fill up from a better place with the highest grade you can get. May be as easy as that.

 

[FX GS]

Another chime in: Your coolant temperature sensor is bad, put in a new one

 

[JEFNLSA]

Another chime in: Your coolant temperature sensor is bad, put in a new one

Just curious...

How did you deduce that from what he said?

I get the Random Cylinder Misfire code & an 02 code yet my car runs fine. I've been told by "some that it is because of my mods (hotcam &TB) & no PCM reprogramming.

O2 code is new (and will fix that soon)...RCM code I've had.....well...longer.(can't locate source, so can't fix)
Plugs & wires are a year old & opti checks out fine. :confused

Sorry, not trying to hijack this thread (just thought that it applies to my problem as well).

The baffling part is that the car runs perfect yat I'm throwing codes all the time. :confused

Thx in advance for any educated guesses on this,
Jeff

 

[WhalePirot]

Certainly start with the oxygen sensors before throwing other parts at it. Reset the ECM afterwards and check for more codes.

It is probably a good time to do regular tune-up things, as needed, like plugs. I have tried and will not use, plus have never had a positive recommendation on the Bosch +4s. Delco originals are fine. It the car has 75000k or so, it could be time for wires. You can check for misfires in a darkened garage, with the engine idling, and look carefully (read) each plug as you pull and number them. I drilled 8 holes in a short piece of 2x4 and put the plugs in the proper, numbered hole. This is a valuable troubleshooting tool to master.

Check: air filter condition, cleanliness of TB inlet and for a light-brownish color of the tailpipes.

Hotter cams can lower the vacuum, telling the ECM that your foot is 'in-it' more than actually true, so it adds fuel, making the car run rich. This can foul the oxygen sensor(s) and clog a cat. Codes may or may not show.

A couple of fill-ups of a quality, detergent fuel will clean the injectors just fine, per a GM study. Leakers, are another matter, but a fuel pressure drop test is simple enough.

 

[WantaVette]

I went to autozone and scanned the codes and this time I actually wrote them down.

P0151= 02 sensor Bank2 sensor 1, low voltage

P0158= Bank 2 sensor 2, high voltage

P0174= Bank 2, system too lean

P0300= multiple cylinder misfire

P1153= Manufacturer control, fuel air meter

I dont know why it says the passenger bank is lean, the engine is using way too much fuel, and there is black soot coming from the passenger tail pipe.I would think that means its too rich.

Also, what is the meaning of the fuel air meter code?