LS7 in a 67 Camaro - need help!

[winfield69]

I have an LS7 in my wife's 67 Camaro. I purchased the crate engine, harness and computer (stock Z06) from a reputable dealer about two years ago. It was initially up and running over a year ago and that is when the problems started.

It initially had a miss and was throwing a code that the cam and crank were not synchronized. After going through every other scenario with a local shop that specializes in late model GM cars with LS engines, we finally took off the timing chain cover and found a problem. With the crank at TDC, the cam was off by one tooth. Problem solved (or so I thought).

As long as the engine was partially apart, it seemed like a good time for a cam swap, because more power is never a bad thing. Right?

The shop was convinced that everything was great after they put the car back together. The car put 515hp to the rear wheels, and they said it ran fine. That was around March. I felt a slight miss at low throttle when I drove it home, but it did seem to run a lot better. At WOT, it would scream.

I have spent at least half this year out of the country, so I did not drive it much. My wife was pregnant, so she did not drive it at all. Over time, it has gotten worse (maybe as the temperature got hotter) to the point where it is undrivable. I'm at a loss to figure out what is wrong.

It runs good when it is cold up to about 150deg, and then it starts to run rough until it goes into what I think is closed loop operation at about 180 deg. Sometimes it gets a little better above 180, sometimes it doesn't. I initially had a colder thermostat and it never really warmed up completely. I changed to a stock thermostat with no improvement.

The engine is not throwing any codes, which is surprising as poorly as it sometimes runs.

The engine supplier has given me the finger, and said he can not help me because the problem was created by someone else (i.e. the original engine supplier, GM). I have no recourse against GM because I did not buy the engine from them. I later found out the engine is apparently a leftover from some factory backed racing program that was cancelled so it has no warranty. The stock pistons were swapped for forged ones by GM or a contracted shop, which could explain the cam being one tooth off.

I'm basically on my own and a little over my head. The only two shops in town that I know that specialize in LS engines have not been able to find out what is wrong.

The only things I can think of are:

* There is internal engine damage from the previous cam not being synchronized
* The intake air temperature is excessive from heat from the oil tank (see attached photo) and is causing problems with the programming

Does anyone have any other suggestions?

Does anyone know a shop in Texas that has the kind of experience needed to diagnose the problem?

Any assistance would be greatly appreciated.

[67 ls1 vert]

wow, sounds like a cool car. To bad your having such a bad time with the engine.

Just wondering if there could be a bad sensor or lose wire somewhere? But like you said, no code. Good luck with it and your new baby.

[Camaroholic]

There are a lot of great LSX shops in Texas. Whereabouts are you located? Has the computer been relfashed (are you sure it was stock?)?

[winfield69]

There are a lot of great LSX shops in Texas. Whereabouts are you located? Has the computer been relfashed (are you sure it was stock?)?

I'm located in Houston. The two shops I know here have not been able to fix the problem.

The computer was originally stock and was reprogrammed after the cam swap.

[James OLC]

If part of the problem seems to occur when the car is going into closed loop, perhaps you have an exhaust leak and are getting faulty O2 readings (?) I'm sure that the shops you have taken the car to have probably looked at that but it's a consideration.

[Camaroholic]

G-Force? Icon? Pavlock? LMR? Those are popular LSx based Houston shops.

Sounds like you need to drive around with a laptop collecting data, and see what happens when it goes in to closed loop. Really needs to have a lot of data collected and analyzed. A regular scan tool won't cut it.

[winfield69]

G-Force? Icon? Pavlock? LMR? Those are popular LSx based Houston shops.

Sounds like you need to drive around with a laptop collecting data, and see what happens when it goes in to closed loop. Really needs to have a lot of data collected and analyzed. A regular scan tool won't cut it.

Icon came highly recommended from a couple people, did the cam swap and identified the initial issue with the cam being one tooth off. However, that was the first LS7 they worked on and were never able to find the problem with the miss. It looks like Pavlock has actually done some LS swaps into non-LS cars.

I agree it will probably take some data logging to find the problem. The scan tool will only tell part of the problem. Then I need someone who can really interpret the data.

Thanks for the leads in Houston. Any leads outside Houston in case these don't really pan out? Austin, SA, DFW?

Anyone with any other ideas?

[68sixspeed]

LG motorsports is top notch, not cheap, but top notch. (they are in texas)

FYI, stock tune on ls7's pulls a lot of timing as intake air temp comes up, 30+hp loss on the rollers. (also what hypertech and some others use to make their products look good.) Not sure if IAT is related to your problem, but it might be possible to rule out by changing the air inlet or temp. moving the IAT sensor so it thinks it's getting cool air.

Also, You should be able to rule out a bent valve from cam timing issues by doing a compression or leak down test. -Dan

[winfield69]

LG motorsports is top notch, not cheap, but top notch. (they are in texas)

FYI, stock tune on ls7's pulls a lot of timing as intake air temp comes up, 30+hp loss on the rollers. (also what hypertech and some others use to make their products look good.) Not sure if IAT is related to your problem, but it might be possible to rule out by changing the air inlet or temp. moving the IAT sensor so it thinks it's getting cool air.

Also, You should be able to rule out a bent valve from cam timing issues by doing a compression or leak down test. -Dan

LG put me in touch with John at American Race Components last year who built my exhaust. They crossed my mind.

I believe my wiring harness does not have an intake air temp sender, it seems to be hard programmed to I believe 90F (I think).

The compression test is in my future as soon as I get back in the country. I discovered just before I left that the engine seems to have been burning oil. I just could not tell how much.

[ErikLS2]

Not sure if one tooth off on the cam is enough to cause piston to valve contact but do a running compression test, at least if a regular compression test turns up nothing. It can show things a regular compression test can't. Run the engine with a compression gauge in each cylinder one at a time. Don't know what the numbers will be for that engine but they should all be very similar. Of course, a low or high cylinder indicates a problem.

Assuming it's not a mechanical problem and igntition system is good, it's obviously either a fuel or air problem. Your injector pulse width will tell a lot. If it changes during the rough run condition you have a problem on the fuel system side. If if doesn't change, then look for an air intake system problem, vacuum leak, air flow meter, etc. If you know your fuel trim numbers and can post them that would be helpful too. The entire data list would be even better.