Hello everyone, I am new to the LT1 world, but not F-bodys in genereal. I have a 1999 Trans Am Firehawk, and recently rebuilt and sold a 1991 Formula WS6.
I recently bought a 1996 WS6 Formula T56 with 85k miles on it. Even though the mileage is low, it has lived a rough life as of late. It has had 6 previous owners, and some of them didnt really know much about these cars I think, but I digress.
It is mostly stock, with the exception of a set of Pacesetter long tube headers, with off road y pipe and aftermarket muffler. AIR pump has been eliminated, and EGR pipe is blocked off. The PO said that another PO said that whenever the headers were installed, the computer was sent away for a mail order tune. The PO told me up front that he has had issues with it stumbling and setting a code when it gets warmed up. He changed 1 O2 sensor, and due to the headers, wire them into some home-made extensions. He also replaced the plugs, plug wires, opti, water pump, ECT sensor, coil, and knock sensor. Still the stumble remained.

I took a flight to pick the car up and drive it 500mi back home. The car did great, with no stumble or hesitation, but about 150 miles from home, the engine started chirping. I figured it was a pulley since the car sat for so long and would sort it out later. A few days after I got home, I pulled the serpentine belt off to isolate the chirping and could still hear it. My heart sank. I did some research and found that the noise is caused by damaged lifters/cam. So, I pulled it all apart and found one cam lobe damaged, and two lifters pretty chewed up. I put in a new JEGS Hotcam copy, new lifters, and new timing chain. One thing I noticed that was strange, is that the stock cam gear was 1 tooth away from dot to dot at #6 TDC. I put the new cam in straight dot to dot and reassembled the engine, fixing various dodgy vacuum hoses along the way. I noticed that whenever the AIR pump was removed, they neglected to plug the hole in the airbox, so the engine has been sucking unfiltered air for an unknown amount of time. Evidenced by the dirt on the inside of the air box. I am thinking dirty oil caused the death of the cam. I also noticed that the coolant was chunky like sludge. I read that if you mix Dexcool with the green stuff, they coalesce and turn to mud. SO I cleaned the radiator out, and flushed the overflow tank, the water pump, the heater core, and the block to the best of my ability.

After getting it all back together, it ren, but it ran rough. Backfiring, and a rough idle. I figured I had the valve lash too tight, so I backed that off, and also found a few ignition wires in the wrong order. After that, it ran without back firing, but still feels like it idles with more lope than it should. I put some miles on it, and a low rpm stumble started happening, and the SES light started flashing, but went off. It felt exactly like what happened to my 99 when the O2s went south. So I figured that I would replace both O2s and get proper harness extensions. No change – it still hesitates and bucks at low rpm cruise. It also gets more pronounced the longer it runs/hotter the engine bay gets. I then borrowed my friends’ Actron Scanner CP9145. No codes are stored. At hot idle, everything seems ok. MAF and MAP are both reading on the high side of the normal range according to the FSM(I am 900ft ASL). The O2s are switching, the TPS is working, the ECT is reading 180, IAT is at 90. The only thing out of whack is the bank 2 ST and LT fuel trims. LT is at 25%, and ST is around 15%.



Knowing all this, where should I start with this thing?

Thanks

 

The first thing I’d do is get the PCM re-tuned for the new camshaft.

I’m an LS guy; I’m not sure who tunes LT1s anymore.

 

The LTFT at 25% is at the maximum value limit of the stock PCM tune, and still unable to add enough fuel. So the PCM is using the STFT to add additional fuel (not the STFT primary purpose). Since they are multipliers in the fueling equation, the system is adding about 44% extra fuel to meet the system's target A/F ratio of 14.7:1 in closed loop (non-PE).

Have you checked the fuel pressure? Have you verified the injector flow capacity by checking for a part #. Stock is 24 #/HR, but who knows what a PO might have installed or had it programmed for.

What brand are the O2 sensors? Is there any indication of the Opti brand? Are there any leaks in the exhaust system BEFORE the pre-cat O2 sensors?

 

I agree with needing a tune. You said the car was mostly stock except for long tubes, does that mean the stock cam then you added a hot cam? I'm curious what valve spring and rocker you used.

 

Thanks everyone for jumping in.

The O2s are Denso, but I will be swapping those out for Delcos soon
I plan to verify the condition of the injectors today

All the parts that have been replaced by the PO look to be generic parts store parts.

 

It’s not just the condition of the injectors, it’s a matter of how well their flow rating and offsets match the data entered in the PCM program. If possible, find a brand and part #.

 

Will do, I'll keep you posted

 

No discernable part numbers, but they certainly appear stock.

 

Correct, stock except for long tubes and off road Y.
I reused the stock rockers and springs.

 

The LT4 camshafts, stock and HOT, were designed to run in the Corvette with 1.6X full roller rockers, to achieve additional lift. The LT1 rockers are 1.5X, non-roller. The HOT cam running with 1.5X rockers will still increase the gross lift by about 0.014”. Springs need to be checked for coil bind. Check pushrod length.

The LT4 cam requires a “melonized” steel oil pump drive gear. Not sure if the stock LT1 gear is steel. But it’s generally a good idea to replace the old drive gear/retainer when replacing the cam. The stock retainer is plastic.

 

What were the idle MAF and MAP readings that you feel are higher than the factory service manual? High MAP can be the result of misfires or valve adjustment problems.

I prepared a scan data guide based on what I have observed over the years, based on observing my LT1 real time data, and reviewing hundreds of LT1 data logs:

https://www.camaroz28.com/forums/com...-guide-886891/

 

Thanks.
I am not trying to go for a max effort engine, I just wanted a stock replacement cam, but stocks were more expensive than this Jegs cam. I figured it would be close enough.

The MAP and MAF readings were in range, but on the high side of the accepted range. With me being at only 900' altitude, I did not expect the pressure to be at the top of the range.

I was able to get some time with an Autel scanner today. The bank 2 is still adding fuel, the EGR valve was unresponsive when we forced it open. The knock sensor counts were in the red at about 2200. There was a few misfires on all cylinders, but #5 was particularly bad.

I have a video of the readings, but the site won't take mp4.

 

OK… was just looking for the numbers for MAP and MAF. The numbers need to be looked at in combination with things like actual RPM vs. target RPM, barometer, etc. MAF is directly related to RPM. On cold start the PCM looks at coolant temperature, and elevates the idle target RPM above the target for a fully warmed up engine. Can be as high as 1,200 RPM on a sub-zero day. At fully warmed up idle, with actual RPM matching the target RPM, I’ve seen values ranging from 6 to 10 grams per second.

MAP value at idle should be approximately 1/3 of barometer.

Not sure why the scanner would flag a knock count (not knock sensor count) of 2,200. The absolute number in this field is meaningless. The important thing is how fast it is increasing, and whether it causes knock retard. When the PCM resets, the number is “0”. The number will increase based on knock sensor activity, and PCM algorithms that detect engine operating conditions that MAY cause knock. The count normally increase by a couple thousand just from starting the engine. That is normal, and does not indicate a problem. Hence, calling out a 2,200 reading doesn’t seem to serve any purpose.

The count will increase periodically while the engine is operating. I've seen large increases in count with NO knock retard, and actual knock retard with no increases on the count. As the engine runs, the knock count can repeatedly increase, reaching as high as 65,536. That is the upper limit of a 16-bit field (2^16). Then the count resets at “0” and continues to increase.

The point with two of us asking about the cam install was not to point out you weren’t going to produce a “max effort” engine. My intent was to insure you addressed the critical issues in a cam swap - pushrod length, coil bind, oil pump drive gear.

 

Thanks. I will try to detail as much as I can remember.

At hot idle:
MAF = .02 lbs/s
BARO press - 14.5psi/4.75v
MAP = 6.96psi/2.02v
IAT = 80.6
ECT = 185
Engine Speed - 750-850 on a 800 Set

 

Ok, here is screen shots from the scanner video. Do these tell me anything other than Bank 2 is lean?