fbrown540

First a brief History.

I bought a GM LS3 430HP crate engine in 2008. Installed and started in my 68 GTO clone in early 2009. I had intended to drive the car a few hundred miles before starting on the body restoration. I cranked and idled the engine for a few minutes a couple of times but was unable to drive the car after the rear end locked up. . . . removed the engine and started the body restoration . . . life got in the way . . . didn't complete the car until summer 2014. Put 55 miles on car between then and August of this year. I been fighting many problems, transmission failed at 55 miles, brake pedal soft, and other numerous startup problems.

I now have 166 miles on the car and have started to address the engine, which I will describe as having a slightly rough idle, power seems low, not nearly as quick as my 2006 GTO was. Sometimes backfires at moderate throttle and does not rev in park smoothly.

Compression test 170,200,155,180,175,160,170,165

These numbers don't look real good, I found a couple magazine tests measuring the cranking compression of a stock LS3 of 200 and 205 PSI.

I don't really know where to go from here as I am more of a body man than an engine mechanic. Any suggestions would be appreciated.

Description of powertrain - Stock LS3 430 HP crate engine, Speartech harness and PCM (E67), Superematic 4L70E, stock 2006 GTO converter (2300 stall ?) Moser 12 bolt 3.42 Truetrac.

Here's a picture of the car.

As Ebay purchase - looks much better here than in real life. Much rust under bondo and paint.

booboo37

iTrader: (43)

Take a close look at your valve springs and if they look good then put a new set of NGK BR7EF plugs and gap them at 33 and go for a ride and report back...

gofastwclass

iTrader: (2)

Was your compression test with the engine cold or warm? I'm told you want to do a compression test with the engine warm for most realistic results. A cold engine may not have good oil pressure or the oil will be thicker which will have an effect on ring seal.

If the engine sat between 2009 and now without running more than a couple hundred miles I would check several things:

• check fuel rail / fuel pressure for 58 PSI. See if the pressure holds 58 PSI while sitting (engine off) and see if it maintains 58 PSI while running.
• As mentioned, I would check / replace spark plugs which may have corroded during this time
• check injector spray pattern (fuel pressure first)
• if necessary soak the injectors in cleaner to remove old fuel deposits from sitting.

If you get 58 PSI at the rail with the engine off, but the pressure drops off after a few minutes, you likely have a bad regulator. If the pressure doesn't make 58 PSI or won't hold 58 PSI while running, you have poor fuel delivery (kinked line, clogged filter, bad pump, etc.)

fbrown540

The compression was tested cold. Fuel pressure is 59 PSI on my gauge. The fuel system bleeds to only a few PSI after 12 hours. I wonder if the right most injector in the left bank is maybe leaking a little. Engine RPM flares to around 2000 rpm after cranking and then goes to normal. Plugs are wires were changed out about 50 miles ago.

Maybe the regulator should be changed, but after it was removed, the gas was drained out before I stored it.

The PCM only runs the fuel pump long enough to reach about 50 PSI after the car sits for 12 hours. Then reaches 59 immediately after the engine cranks.

Agreed the injectors need to be cleaned. Other than sending the injectors to a cleaning service I don't know how I could check spray pattern.

One other thing is the care stinks like crazy with a fine mist like black smoke at idle. The smoke is not visible in the mirror and can only be seen when looking at the exhaust pipes

My guess all along was the injectors are most likely the problem and should be cleaned and flow tested. Since I have no way to test the injectors, I figure to eliminate everything but the injectors, but got side tracked with a bad compression gauge.

I went to squirt some oil in one of the cylinders last night and found that I couldn't get a repeatable reading. Then I was able to see the gauge drop between 20-40 PSI after turning starter off. It's hard to see the gauge when sitting in the car. I bought a new gauge tonight and ran the tests again.

Much better this time.

220,205,203,204,203,195,205,203

The 220 was the cylinder I squirted last night

The 195 improved to 200 after a shot of oil.

Here are shots of the spark plugs. The plugs and wires were changed out about 50 miles ago. MSD wires were installed since the GM wires didn't clear the headers good enough.

The PCM is almost certain to need tuning, but I figure I need to get at least 500 miles on the engine before subjecting the engine to a dyno. The base tune was based on a Trailblazer SS.

Opinions are welcome.

Right Bank



Left Bank

BLKMGK

One plug looks awful dark. What size injector's did the trailblazer have compared to what you have now? Do you have a wideband installed? Might be s good idea to find out what the A/F is.

DW SD

I would suspect the tune, also. Would be a real surprise if a trailblazer tune works well in LS3.
Glad to hear the compression issues seem to be resolved.

Doug

gofastwclass

iTrader: (2)

You're using a crate LS3 ending with a Trailblazer SS calibration????
That my friend is your problem.

Just digging through my saved tunes, a stock 2007 Trailblazer SS is a 6.0 liter engine and has 29.4 lb injectors. A 2010 LS3 from a manual transmission Camaro is a 6.2 with better flowing heads and 42 lb injectors. The MAP (Manifold Absolute Pressure) sensors are different between the two engines as are the MAF (Mass Air Flow) sensors. The incorrect injector information (flow rate, voltage offset, etc.) will make the engine miss the mark dramatically even if the other sensors are calibrated properly. There are a host of other things that could be different but those come to mind initially as potential problems.

You don't need a dyno tune, you need someone with HP Tuners or similar to update your calibration with stock LS3 parameters. Until you have a good baseline with proper sensor data, trying to get the car running properly on a dyno is a waste of time and money.

Any of these things alone will create a poor running engine, but all of them together makes me amazed it ran and drove at all.

fbrown540

The PCM settings were modified by Speartech. Speartech supplied a new harness and PCM and TCM. The tune was to have modified for my engine. I have HPT Tuners and have looked at the settings. The injector size was changed. The MAF table was modified and a few other things, when compared with a stock Trailblazer SS tune. I just not sure everything is right. The MAF table doesn't look like it came from any stock tune. It was to have been setup for a 2005-2006 GTO MAF, which looks like the same one that is used in the Trailblazer. The MAF table in my tune is different.

gofastwclass

iTrader: (2)

I'm told Speartech is good, but they are human and make mistakes.

Have you tried to scan the engine with HP Tuners? Do you see anything odd?

What are the settings for the MAP sensor? Is it right? Are the injector settings right for your engine? Etc.

fbrown540

I'm new to HP tuners and don't know what to look for. The injector size looks like it has been changed. The only thing that I'm not sure about is the MAF table. It doesn't look like it came from any stock tune that I could find. Not having a good Log file to look at, I don't know what a good log file should look like. Here is a dump of my PCM and a scan..

MAF was from a 2006 GTO (new) and cross reference in Rock Auto shows this MAF was used in Trailblazer SS.

VCM scan gto scan 3.hpl

PCM file 1968 GTO LS3 - Trailblazer ECU.hpt

While I don't think everything is right with the PCM base tune, I don't see how the tune would cause one cylinder to have a miss. Since I have eliminated ignition and compression, it would seem that injectors are the only thing left.

When the engine was reinstalled, new gas tank (Ricks) and all new lines were installed. Only the FPR was reused and of course gas in the injector lines for four + years. I do remember that the engine idled very smooth with no miss when it was first fired in 2009.

Maybe it's time to get a set of injectors. Even if I soak the injectors in a solvent, I still won't know if they all have equal flow after cleaning.

fbrown540

Here is a picture of how the MAF in mounted.

cpd004

iTrader: (13)

What is the fuel pressure at the rail?

Also, your MAF should be somewhere in the straight part of the tube. Here's what GM recommends:

"Ensure the MAF sensor is oriented correctly in the induction (it will
only read correctly in the proper direction). An arrow is located on the
sensor indicating correct flow direction. Verify this before welding the
mounting boss, as the sensor will mount only one way in the boss.

Ensure the MAF Sensor is mounted in the middle of a minimum 6 inch
length of 4 inch diameter tube, and is a minimum of 10 inches from
the throttle body."


Placing it at the elbow like that doesn't look like the best possible location.

I'd start with moving the MAF, ensuring proper fuel pressure and double checking that you have enough grounds and that they are tight down to clean metal.

Pop N Wood

iTrader: (1)

As suggested by many the car sat for awhile and probably gummed up the fuel system.

Pretty easy to pull the injectors and squirt some carb cleaner through each. Use a 9V battery to open each injector. I hooked some alligator clips to a 9V battery connector just for this purpose. Power up each injector and use your fingers to "seal" the carb cleaner hose to the inlet. This will pressurize the injector enough to do a poor man's spray test. I would consider replacing the injector O rings and other seals while they are off. Than do a standard vacuum leak test by your favorite method. I use starter fluid. Be sure to check all hoses for cracks /leaks.

So many times people dive into the computer and forget the basics. Computers do a pretty poor job of telling you when an injector is sticking or leaking.

And if you haven't done so already get a fresh tank of gas. I would consider dropping and flushing the tank as well. Replace the fuel filter when all that is done.

You might want to check the O2 sensors as well. They can gunk up if left to sit without ever getting to full operating temperature.

I wouldn't be surprised if some of your issues went away from just normal driving. Maybe a can or two of sea foam in the tank.

fbrown540

I appreciate all the suggestions.

Fuel system. Installed new lines twice during the body off restoration. Second time around because the line I first used is no longer approved for fuel use. It was at the time I installed it. Went with a nylon OEM type hose.

A can of Sea Foam in tank can't hurt. Gas is fresh since I usually only put a gallon or two in at a time. I did however fill the tank a few weeks ago, since I was planning to put some miles on.

MAF location, air intake system. It needs some improvement. When stopped, IAF goes up 40-50 degrees over outside temp. Returns fairly quickly once moving. Something to address.


I changed in injectors tonight. Can't tell how well the car will run since the PCM was disconnected during the compression test. I can't detect a idle miss but the PCM needs to relearn.

Pressure measures 56 at rail, however my gauge is old and may not be too accurate. Probably time to replace the FPR, since pressure drops 6 PSI after 30 minutes.

I will try and drive the car some during the weekend and see if the new injectors make a difference.

fbrown540

I changed the FPR today. (WIX brand). No change, reads 56 PSI and bleeds off about 10 PSI in 30 minutes. How long should the FPR hold pressure ? I looked at all the joints in the system about 2 years ago and gave up because I couldn't see any leaks and assumed the pressure was bleeding back to the tank.

ls1nova71

iTrader: (4)

Could be leaking back through the pump, but if it's only losing 10psi in half an hour, I wouldn't think that would be any problem at all. Most of this sounds like you have an injector gummed up from sitting. If it ran fine and didn't miss when you first started it, I don't see how it could be much else, lines and tunes don't go bad in 4 years. LOL! I agree with Pop N Wood, I wouldn't be surprised it a lot of it went away after you've driven it some more.

Project GatTagO

iTrader: (7)

This is a long shot, but do you have the large ground loops bolted to the back of the heads? There should be one on each side. Those are coil grounds and are critical. Is the engine grounded well? Big cable directly from the battery to the engine?

I suspect this is a tune or an electrical issue, not fuel related.

Andrew

gofastwclass

iTrader: (2)

I think that is pretty good. I agree, I'm still thinking injectors are a potential problem.

After that bit is sorted, I would dive into the calibration and make sure things are good for a stock LS3. A tune can not fix a hardware issue, but an improper tune can make it look like you have a hardware issue.

I admit I am NOT a tuning expert, so this is only advice from personal experience and not a guarantee to resolve your problem.

I looked at your tune. If you are using an LS3 intake manifold with the stock LS3 MAP sensor, the calibration is incorrect.

There are a pair of fields that control what the PCM expects from the MAP sensor under Engine, Airflow, General. On that tab there will be two fields under MAP called: MAP Sensor Linear and MAP Sensor Offset. Yours is setup for a typical GEN III MAP sensor with 94.43 kPa and 10.34 kPa. An LS3 MAP sensor will read 128.13 kPa and -0.31 kPa respectively.

The injector data isn't quite right for a stock LS3 and the VE table is different but I really haven't gone much farther.

One problem is you can't straight compare the two because the TBSS PCM is built on an E67 controller while an LS3 is on an E38 controller. This means having two HP Tuners windows open at the same time and going field by field. Some fields don't exist in the TBSS file while others aren't in the Camaro file I was comparing.

Just the few things I mentioned could make your car drive like crap - if it runs at all.

Before you make any tune changes, save your original file and NEVER edit it. Then save the previous running (even if it was poorly) file and make changes to the copy. I use a date system and always copy off my original and save it in a different folder called "xyz original" so I know that is the very first read. This way if you really muck things up you have the previous version or worst case, the original to fall back on.

I added a link to a stock LS3 file from a 2010 Camaro LS3 (manual) if you're interested. The automatic cars are L99 (Displacement On Demand) and use a completely different calibration.

ls1nova71

iTrader: (4)

Just curious, but have you talked to Speartech about this? And if so, what did he say?

gofastwclass

iTrader: (2)

Excellent point, ls1nova71.