97pontta

iTrader: (10)

I've been trying to get my car running well again after it has been sitting for about 2 years. The car had developed some minor issues during this time. So far I've replaced the O2 sensors with new Delco units and spark plugs with NGK TR6 plugs. Opti seems fine and my problem seems to be fuel related. Still running the stock fuel pump and injectors. Have a CC305 cam with ported heads, and the usual bolt ons.

After I replaced the O2 sensors with delco units I had one go bad after only after a few miles. It has been replaced with a new unit so I have two new O2 sensors right now. I have have driven the car about 400 miles, most of these miles were HWY miles with little or no aggressive driving, just cruising. During this time I had monitored the O2 sensors and fuel trims to make sure everything was OK, which it was.

Today I was on a back road with no traffic and was doing some WOT runs from a stop thru 4th gear, a 1/4 mile run pretty much. I had done about 3 of these in 4-5 minutes. Immediately afterwards I continued driving down the road at 55MPH and noticed the car was starting to miss/stumble under light load. I drove the car home which was about 15 miles away. I shut the car off for about 25 minutes and then grabbed my Snap-On scanner and went for another drive to check into the stumble. Drove for 30 minutes at regular speeds, not WOT or aggressive driving. The car drove fine, no stumbling or missing at all. No trouble codes stored either.

I then drove to an area where I could do some 1/4 mile runs to see if the stumble would return, this time with the scanner. I did 3 runs just like I had done in the previous drive, with the same missing/stumbling results again. I checked the O2 readings and they seemed to be frozen in place. Normally they are reading high/low very quickly. Now the readings on both bank 1 and 2 were moving very little. Short term fuel trims were split very badly, 110/205 and the injector pulse width showed this as well. Long term fuel trims looked good, 132/136.

I pulled the car over and shut it off and let it sit for 5 minutes. Started the car and drove it normally down the road checking the O2's and fuel trims. Now everything was back to normal, O2's reading good, Short term fuel trims were at 134/133 and injector pulse widths readings were even between banks.

I repeated this same sequence of events two more time with the same results. The car would begin to stumble/miss only after the WOT runs and would go away when shutting the engine off for about 5 minutes.

I have no idea where to look, the car drives very smooth with no stalling what so even until after I do WOT runs. It runs very well at WOT, pulls hard all the way to my shift point of 6200 RPM.

Is it possible that the TR6 plugs are too cold for my setup causing the O2's to foul when the engine is at WOT? I've been running the same PCM tune for 5 years and it has been fine. The only thing I have changed recently is the O2's and spark plugs.

Looking for any help or a direction to start looking.

96autoformula

You're thinkin your OPTI is fine, but that's what I'm screamin. The weakest link always goes first...my money says it's a bad OPTI. . I mean I've only had to replace two of them myself, and my dad had to replace one on his old bird.

AChotrod

iTrader: (17)

Clean your MAF

97pontta

iTrader: (10)

MAF was just cleaned with MAF cleaner from AutoZone, for got to mentoin that. Unless the MAF is going bad, I may see if I still have my spare lying around to swap and test.

I thought it might be a OPTI at first, but the problem doesn't feel like a ignition problem, and the problem goes away when I shut the engine off and restart 5 min later. The OPTI in the car right now has about 45K on it, I replaced it druing the cam swap. I still have the origional that had 50K on it, it was working fine when I pulled it.

Still can't figure out why my O2 sensor readings freeze up after the WOT runs and work fine after restarting the engine.

RamAir95TA

iTrader: (2)

At WOT, you will always see the O2s freeze. That is normal, as the PCM enters "power enrichment" mode.

Make sure and double sure that you aren't burning any plug wires (look at the engine running while it's dark out, look for arcing).

You've done many diagnostics, but nowhere do you mention that you performed a simple fuel pressure test. Pick up a fuel pressure gauge and do some preliminary readings.

Rocky70304

iTrader: (4)

I'm curious to know what your o2s are reading when the freeze up, just a possibility that pops into my head is that when you are pulling these WOT pulls before the problem it is sucking an intake gasket or something down and causing a vacuum leak that sticks the o2s lean, then after letting sit for a bit (and cool down) the vacuum leak goes away, just a thought, but o2s would show this, and fuel trims would go crazy.

97pontta

iTrader: (10)

I wasn't aware that the O2 readings did this under WOT, thanks for the info Ramair.

I will check for burn't wires. I do need to do a fuel pressure test also, will have to find a tester.

When the O2's freeze the values vary, once I seen them both frozen around 10, the other time 740.

I don't think the problem is heat related becasue I drove the car for 45 minutes straight with the scanner on my lap watching reading from the O2, injectors and fuel trims and everything looked fine. I then slowed down and ran the car thur the first four gears 2-3 times in a row and then the problem starts and continues until I shut the car off. Shutting the car off for 5 minutes wouldn't be enough time for it to cool donw would it?

Thanks for the pointers guys.

97pontta

iTrader: (10)

OK, I just did a fuel pressure test. 34-36 while idling and 42 under load and WOT. I ran the car hard until it developed the problem described in my first post. Fuel pressure still remained the same, so I wouldn't imagine its no a fuel pressure problem.

Can some one explain a little more in depth to me about "power enrichment" mode?
What values is the PCM using in this mode?


While driving tonight just a few WOT runs and bank 1 goes rich and will not return to normal until the engine is shut off and restarted, then the problem is gone and fuel trims are back to normal.

Example, I had a hard time making it up the hill to my house with the engine stumbling. With the scanner still on the BLM's were 210/134 with bank 1 being rich. Shut the car off for 2 minutes and restarted. Checked the BLMs and they were at 133/134.

Bank 1 O2 sensor has about 700 miles on it and Bank 2 sensor has about 400 miles on it. Bank 1 is the one giving me problems, I'm going to stick a used O2 I have lying around in to see what happens.

GIVE EM' THE BIRD

iTrader: (1)

I like your thinking there. Its kinda far fetched but with the many intake leaks on lt1's, you never know. It would be really hard to test this theory though b/c if it is only happening after heavy load, you arent going to be able to just pop the hood and figure it out. Maybe take some carb cleaner while watching the ST fuel trims and spray around the intake. Just a thought.

good luck
Derek

97pontta

iTrader: (10)

Well I was up late last night messing with the car and it appears my other new Delco O2 is bad. I replaced the new bank 1 sensor with an old used Bosch that was on the car. Took it out and beat the snot out of it with the scanner on my lap the whole time. After about 20 minutes of hard running the car continued to run well, no stumbling issues like before and my fuel trims were dead even the whole time 133/135 plus/minus a few. Injector pulse widths were nearly exactly the same and the bank 1 Bocsh O2 sensor continued to work correctly after the heavy load, unlike the new Delco sensor.

What would cause two new Delco O2 sensors to crap out in 700 miles? First bank 2 went around 300 miles, I replaced it, now bank 1 is bad around 700 miles. When bank 2 went out it just completely stopped working, this time with bank 1 the problem threw me because it drove fine until I put load on it.
The reason I changed O2s in the first place is during my header install I spliced longer lengths of wire in my O2s instead of buying extensions, and the car has ran fine for the last 5 years this way. I though I would be nice to have the proper extensions so I bought a set and new Delco O2 sensors to replace the Boschs.

I don't want to be driving around with a Bosch sensor on bank 1 and a Delco on bank 2 so I guess I will buy another new Delco.

myltwon

iTrader: (1)

factory defect, happens from time to time. or it was some how damaged physically