Hi all, been a while since I posted here but I've had a problem for the past month or so and am at a loss of what to do next.

2000 3.8 Camaro with 4l60e and ~120,000 miles

Problem:
Problem started out as a lack of power when cruising on the freeway and accelerating hard from about 2000 RPM to pass another car. The engine would rev up to about 4000 RPM and would stay there all day long and I wouldn't go anywhere as if it wouldn't downshift. If I let off the throttle and rolled into the RPMs it would get up to speed eventually. When this happened the SES light would flash for a while until I backed off the throttle and would flash a few more times then eventually stop. This progressed to the point where a pinging/metallic fluttering would also happen during this condition which now occurs anytime when wanting to accelerate hard (eg. up a hill or from the dig). I eventually got a P0300 code to stay on and after clearing it, it will intermittently light up sometimes.

What I've done:
Using HP Tuners I would see a LTFT spike up to about 18% on both banks. This pointed me towards fuel. Had fuel injectors flow tested and cleaned by WitchHunterPerformance, all are good with about a 1% variance between injectors at both static and pulsed flow at 2500 RPM. Pressure tests good at the rails and spikes up when the fuel pressure regulator is disconnected. Fuel pump was replaced about a year ago and I put in a new fuel filter to replace the 1 year old filter the other week. Resistance on coils test good and I have 2 good spares that I've swapped around. Wires, plugs, and ICM have been replaced too. I've done a compression test and all cylinders have good pressure. Did a vacuum test by tapping into the vacuum line off the fuel pressure regulator and idle vacuum is right at 20 PSI and decreases when accelerating. MAF has been cleaned and other than visual inspection it looks good. O2 sensors bounce around from rail to rail at 0.1 to 0.9 V and rear O2 sensor is about 10 months old. Cat has been inspected by myself and my exhaust guy. Inspected the honeycomb on the outlet through the O2 sensor bung with a camera and looks good. Cut a 1" hole upstream of the cat and inspected the honeycomb block on the inlet side, looks good as well. Ran some compressed air through this hole and could feel it through the downstream O2 bung, even took it for a drive with a 1" hole upstream of the cat and still got the metallic ping/flutter when accelerating hard. I've also tried bypassing the EGR by bolting on some block off plates I made a while ago.

I'm at the point where I've tried diagnosing everything that makes sense and am close to taking it to the dealer to see if they see anything when they hook it up to their diagnostic machine. The only thing left that I can imagine it being is a slew of sensors and solenoids (TPS, camshaft position sensor, crankshaft position sensor, and any one of the solenoids in the tranny due to not downshifting at WOT).

Thanks for any and all help everyone, it's much appreciated.

 

have you taped the fuel pressure gauge to the windshield to see if pressure was dropping when problem is present?

 

Pull the plugs and see what they look like. Plugs will tell you a lot about what condition the engine is running in.

 

The P0300, random misfire, is usually the result of a lean mixture, as Craby said, check the fuel pressure with the engine under load. A fuel pump may hold the pressure at idle, but may not be able to deliver enough volume to hold the pressure as the engine demands more fuel. Also check the plugs as they also may misfire under load, especially as they are partially fouled or the gap has widened due to normal wear.

 

Taking care of the random misfire is one thing you need to look into, but can you expand on this symptom:
If the rpm's are going up, so should vehicle speed, misfire or not. Is the transmission not downshifting when it needs to be? That would dog the engine down. If rpm's are going up but the car isn't speeding up (without downshifting), then the trans is slipping. Have you tried up and down shifting manually to see if the engine acts any differently?

 

Plugs looked good, one of the first things I did was pull my TR55's and regapped them (barely out of spec), since then I've put in ACDelco copper cores. Looking at the fuel pressure gauge while driving around is a good idea. I'll have to try that out and see if it's the pump that can't deliver when there's an immediate demand. I know good fuel pressure at idle is in the range of 40 PSI. How much should I expect pressure to increase by when at different throttle positions?


Camaro 69, it just seems to have issues downshifting when immediately wanting to accelerate hard, under all other conditions it shifts normally. When I'm stuck at 4000 RPMs it will only shift okay if I back off the throttle. I've talked to a few people and they've also said that's a telltale sign of a slipping transmission. That's kind of my worst fear. I've looked around on some of the other Camaro forums and found some people reporting slipping like symptoms that turned out to be a shift solenoid, TCC solenoid, or TPS. I guess those have some control over shift points, however the total workings of an automatic transmission is still a little fuzzy to me. What would be a good way to test the transmission by manually shifting around? Putting it in 2nd and driving around then dropping to 1st before accelerating hard?

 

if it were slipping you would be reving way past 4k. not shifting down could cause knocking but at 4k it still should accelerate. did you try running through the gears manually.

 

I am not sure you need the dealership. You need someone this a portable scope so they can see way is going on in the cylinders. I would think since you car is older most shops that do injection trouble shooting would have a scope. Snap-on and mac and I am sure a lot of others make them.

A scope reading can show rich/lean, compression issue and of course any electrical issues assume the mechanic has been trained in reading the patterns. A scope and a vacuum gage can tell a mechanic just about everything that is going on inside an engine. Not what is wrong with a car but what is going on in the cylinder.

You really want to be sure the coils are not the issue. It would be nice if you had new or was just on a different car coils.

I am not big on "I had a car that did this and it was X" when it comes to issues like this. It can just be soo many different things. I have seen guys find a cracked plug, replace the plugs and wire only to have the same issue. They would all but tear the engine a part before I put it on the scope and told them one of their new wires had a bad crimp. After saying that I did have a random issue with my 96 about 4 month after replacing the MAF sensor for a low voltage code. I started getting the random misses. Maybe once week only under loan. I was about ready to take it in but I bumped the MAF wiring harness by accident and the car stumbled. When I wiggled the wire the motor RPM were all over the place. New connector and no problems since.

 

Sounds like bad upper intake gaskets that are leaking and sucking in too much air or a throttle body gasket. Get a propane torch and start the car. Open the propane and put it near your upper intake and throttle body. If the RPMs jump, then you have a leak. Leaking gaskets can cause the RPM issues and a random cylinder misfire. I'm in the process of changing the upper and lower intake gaskets on my wife's Grand AM 3.4L because of this issue. The car had the same symptoms and P0300 code too. The vacuum leak test showed a failed upper intake gasket.


RPM surges and erratic at idle can also be your MAF.

 

I've got good vacuum at 20 PSI and changed the UIM and LIM with Felpro gaskets about 2 years ago. Tested fuel pressure today and it was about 44 PSI at idle and driving around it ranged from 40-48 PSI, does this sound about right? A few other symptoms are that it will make a quick whine/shriek noise when starting up, seems to make this when accelerating too. Another thing is that it smells like exhaust gas around the EGR. Tried blocking it off and disconnecting it doesn't seem to make much of a difference. When accelerating normally up a hill it will sound muffled and dogged but bumping it up a few RPM will make it sound normal for a second.