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).

- 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.

Any thoughts / theories would be appreciated.

maybe clean the injectors and see if that helps

i assume you dont have access to autotap or anything. was this a pull out motor and you just put it in or has it been modded at all?

ron,

It is a stock pull out engine from a 2000 Trans Am. I had the PCM and wiring harness done by a pro and it worked fine until recently.

I don't have autotap (yet).

I know what it's not and that is the TPS. First guess based on your post would be a leaky/bad injector.

That fuel pressure looks way high to me. Is that the factory spec?

Jody

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My Cars (http://www.camcojb.com)

Billet taillights for 69 Camaros (http://www.marquezdesign.com)

That psi is about right I believe. 55-60 is stock on those engines.

Jody,

Yes, 58 psi is the factory spec for an LS1.

try checking the fuel pressur regulator. soetmes if the diaphram iside ahs a hole in it it will leak into the engine and cause it to run real rich. try getting a new one and put it on.

yeah i'd say your best bet would be autotap, hptuners, or the new efilive should have scan software included. untill you get your software i'd say check your vac. lines, electrical connections, and leaks. it could be possible you intake didnt seal properly. did you inspect the motor by tearing it apart at all before you put it in. also, did you try on www.ls1tech.com (http://www.ls1tech.com) i'm sure someone might have had the same problem and can help you out

To me it sounds like either a faulty fuel pressure regulator or an injector (or more than 1) that are stuck open....dumping fuel. In fact the loss of fuel pressure after engine shut off points to injectors being stuck open as opposed to a regulator.

Were ALL of your plugs fouled or just some of them?

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2000 Corvette hardtop black, 6 speed, Halltech Tric cold air intake w/nylon MAF ends, Corsa Touring cat back exhaust w/pro tips, Taylor wires, 1/4 mile: 12.918 @ 111.29 mph on stock EMT's 330 rwhp, 342 rwt on MTI's dyno, 3075 lbs

79 Camaro 355 CID, Edelbrock intake, Edelbrock 600 cfm carb, Edelbrock performer 64 cc alum cyl heads, comp cams extreme energy 262 cam, erson roller rockers, hooker headers, Mallory Comp 9000, 3.42 posi, 700R4 rebuilt w/ B&M kit, 2400 stall converter w/ TCI lockup kit, energy suspension f.e. rebuild, 1-1/4 front sway bar, 5/8 rear bar

67 Camaro, 327 w/ a 'glide , waiting on "funding"

Mike, I would have had to order those injectors and it would have been too much $$$ anyway. The pulse width from the computer to the injectors could be way off-but you'd need to access a fuel map to read for that. I'd put my money on the regulator too. Sounds like it's got some crap in it. -Jabin

The pressure bleed off is usually the fuel pressure regulator but could be an injector or multiple injectors.

It should hold pressure for a good amount of time. Basically no drop in a minute or two.

Mike -

You might check your MAP sensor at the rear of the intake manifold. It might be fooling the PCM into thinking the throttle is open too. I have a good used one if you need it. Got a bad tank of 93 that was mostly desiel, went crazy trying to figure that out.

The custom guy wired it up and it was running good, right? He used all the sensors and didn't mess with your fuel tables amybe?

I also have a set of shop manuals for my 99 if you need me to look anything up.



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Scott
Dallas, Tx
1975 Camaro
1999 Formula
www.74-77camaro.com

Open coolant sensor, engine looks very cold to the ECM, over enrichening during warmup? Rough idle maybe caused by severe spark retard, to control the idle speed with so much extra fuel.

Without knowing what custom programming/cals you might have in the PCM, the TPS should only be involved with fueling during transient throttles, along with MAP; steady state, injector pulse width should be basically determined by desired air/fuel ratio and MAF signal.

If you could get a Tech II or equivalent on the diag bus, even with no codes set, it might be helpful to read the spark advance, O2 signals(I assume you kept the O2 sensors, you're not just running open loop all the time), MAP, and MAF signals, and injector pulse width.

Odd all the injectors would hang open. I think there's a check ball in the fuel pump that sometimes gets stuck, which could explain why the inj rail pressure bleeds down; but I don't see why it would affect the air/fuel ratio.

Autotap would help ALOT, you can see A/F ratios and injector timings... but...

Check those injectors. If you pressure is bleeding down like that and the smoke, sounds like a lot of fuel is in the thing at startup and is continuing to allow too much fuel during running. That pressure should hold for a good while not bleed down like that. As for the popping, LS1s will do that even new and stock when cold due to the richer fuel during warmup. If it continues warm then too much gas again.

If an injector is spraying/leaking fuel all the time, it will over load that cyl with fuel and cause it to run rough and stink, just like you are describing.

Can you scrounge some spare injectors from a junkyard? Any difference in the sparkplugs that might point to the misbehaving injector?

As a thought, if you can take the injectors out and get the fuelpump on, you should see real quick if one leaks. Just point it at a bundle of rags and give the pump power. Free and might work...

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'03 Yellow S-10 4.3L - "The Bus"
'75 LT in progress again...

[This message has been edited by BusDriver (edited February 23, 2005).]

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 barometric pressure (wide open throttle, in other words). Turns out that I bent one of the pins in the electrical connector. Straightened the pin, snapped it back together. 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.

[This message has been edited by MikeM79 (edited February 26, 2005).]

Interesting. The injector on time is compensated for MAP, since the flow through the injector is a function of the square root of the pressure across it; so if the fuel pump/regulator puts out a constant pressure, the injector on time must be increased for higher MAPs, to get the same amount of fuel out of it as at lower MAPs. An interesting failure mode, worth remembering.

Yeah, what he said!