Guys,

The LS1 engine in my 71Z project is not running right. No codes, that would be too easy. The problem is realtively sudden as it was running well until recently.

The symptoms:

- Cloud of black smoke upon starting the engine. Rich as hell, will water your eyes. During warmup it will idle around 1,300 rpm but the tach needle vibrates and the idle is not as smooth as it should be.

- After warmup the black smokes disappears but it still doesn't run as smoothly as it should. I propped open the throttle body so it would fast idle at about 2,500 rpm and while the tach is smoother, it is still not rock steady and a popping can be heard from the exhaust.

Other observations:

- After turning the engine off the fuel pressure bleeds off from 58 psi to zero psi over just a few minutes according to the gauge I mounted near the fuel rail. Used to be that you could come back to the car a week later and still have 20 psi or so residual pressure.

- I pulled all the plugs before starting the engine today and they were uniformly black a few were even wet and smelled of fuel. I put in a brand new set of plugs to eliminate fouled plugs as a cause of the poor idle. No difference, same cloud of smoke as soon I started the engine.

My two best guesses are:

- A faulty throttle position sensor (computer thinks throttle is further open than it is and provides too much fuel). Dunno if this would throw a code or not.

- Gunked up injectors, perhaps not closing all the way. The engine sat for three years after I bought it before I finally dropped it in the car. However, all of the plugs were black, not just some of them. Presumably at least few of the injectors would not be gunked up. I also threw a bottle of Techron injector cleaner in recently.

Any thoughts / theories would be appreciated. Thanks.

 

SLP sells new LS1 injector sets for around $100.

http://www.slponline.com/view_product.asp?P=23051

Having sat for 3 years w/ nasty old gas in them probably didn't do your old ones any favors.

 

I bought a motor from a junkyard and it had a lot of the symptoms you descirbed, but there was a wide variation cylinder to cylinder on whether the plugs were sooty.

I had the injectors cleaned and flow matched and the problem went away. It cost me more than the $100 crainholio says you can get a new set from SLP to clean them, and I'd jump at getting a set from SLP.

The guy that cleaned my injectors says they can clog in as little as six months of the motor sitting. I'd make sure the rest of my fuel system downstream of the regulator filter was squeeky clean.

 

Thanks guys.

I ordered a set of injectors from SLP. They claim that these injectors have never seen fuel and at that price it isn't worth getting the ones I have cleaned.

 

Before guessing on parts or cleaner, i'd find somebody with a scanner (efi live/hptuners/autotap) and determin whats going on besides codes, the tps could be reading 100%, maf could be way off ect.

 

If your fuel pressure is dropping at the rail you have issues with either your fuel regulator or fuel pump.

 

Have you checked your primary O2 sensors? My motor had a similar problem - alhtough it neve ran well. My O2s were fouled. It runs fine in open loop if I disconnect them. I had a small exhaust leak at the flange on one side (which wouldn't explain both sensors fouling). I fixed that, put in a 2nd set of O2s, they quickly fouled too. If I connect the O2 sensors, it runs WAY rich, idle is all over the place, plugs foul up, etc.

I hadn't thought about replacing the fuel injectors. I did replace O rings. Since the problem goes away in open loop, I'm guessing my problem is not related to the injectors. I am able to check my TPS - I have ATAP.

At any rate, I'd be curious to know what your O2s look like, or what their readings look like. I haven't really been able to solve my problem and yours seems similar.

 

I got my O2 sensor harnesses swapped and that thing really ran bad! Check there too.

 

Guys,

Thanks for all the helpful suggestions.

I got to the bottom of it. I bought a new set of injectors from SLP for $100 (cheaper than getting the old ones cleaned).

I also upgraded my Auto Xray code reader gizmo to monitor the sensors in real time. Anyway, the MAP sensor was not responsive....it always indicated "27", barometric pressure (wide open throttle, in other words). Turns out that I bent one of the pins in the electrical connector when I was hooking up the harness. Straightened the pin, snapped it back together, works now. The computer had it as a "pending" code which does not illuminate the check engine light.

It doesn't seem to matter whether you are talking about old school or new school stuff....it always seems that the bigger the problem, the simpler the solution ends up being.

Purrs like a kitten now.

Thanks again.

 

i seen a lot of people with this problem but never seen a post that actually fixed this problem....synthoms are

car starts
when warm it wont start on first try
after a few starts plugs get fouled if not driven