More LT-1 woes

[Boulder69]

Car runs like crap. Rich with black smoke. Replaced the Opti and it runs the same. No trouble codes reported.

It runs OK when first started, but get worse as it warms up. If no trouble codes are present indicating a sensor problem, what else could it be?!?

This motor is cursed. Any suggestions would be great. Thanks. -e

[69Bbird]

Have you tried changing the O2?

[Boulder69]

Wouldn't that throw a trouble code? I already replaced the opti to no avail and don't want to play sensor roulette.

I was thinking the same thing (o2 sensors) until I came up with no codes of note.

Thanks for the input. Keep 'em coming if you got 'em.

[BRIAN]

Most complain about LT1'S running rich at idle. Try changing the temp sensor in the water pump. If it is bad the computer never gets out of cold start mode. Hard to test because it is small and it's placement. Had similar problem and it cleared it up. Also run heated 02 sensors if you are using headers. They also have to reach temp for computer to run in normal mode. Keeping terms simple here. Do not rely on the check engine light code deal. This is all considering your engine is in sound condition to start.

Brian

[Boulder69]

Replaced the ECT sensor and it runs the same. Any other ideas? Anyone?

[Samckitt]

Did you check fuel pressure?

[vintageracer]

There is a guy that does a lot of computer work with LT1's. Mine ran rich at idle also. Replaced the O2 sensors with new GM sensors per his recommendation and the car stopped running rich. He says the O2's get coated after a lot of miles. The run rich issue WILL NOT set a code on 95 and older LT1's since they are OBD I.

I have been looking for his name and number but have not found it yet. He is out of Az I believe. Do a google search on LT1 computers of something like that.

This guy can reprogram the stock computer and get 30+ more HP's with this mod. He will tell you that the first thing you will need is good O2 sensors. Throttle position sensor could be a problem.

Find this performance computer guy before spending any more money. He will help immensely!

[MonzaRacer]

first of all if you have an FI LT1 you need a good scanner to see what its doing.
Take a look at either fuel trim numbers or the block learn or fuel integrator.
fuel trims should stay within 5% +or- and if you have long ter and short term you add them or subtract them fromeach other.
If it has fuel integrator and block learn you need to be right aroung 128 counts on both.
anotherthing that can cause rich idle is a MAP being off in calibration. I have actually used extra resistors to make the engine not "SEE" its vacuum reading.
I use adding resistors in the signal line so as to cheat the computer so it gave less fuel.
As for older cars ont throwing codes well yes they will but the sensor has to be off a lot more to set a code. Again you need a scanner to read what the computer is doing.
Also if the O2 sensor has a lean bias it will make it idle rich and kill mileage.
changing the Optispark whe nyou have no misfire problems or ignition codes ,well who evertold you to do that just spent your mony for you.
Also alot of those cars HATE non AC Delco plugs. champion and Autolite seem to be the worst performers.
while a lot of people have problems with Bosch I seem to get good luck out of them.
Another trick is that Motorcraft act just like AC Delcos in most cars.
Retuning the computer if the computer isnt needing it is a waste of money. If you get it running properly then decide if it needs retuned.
I have also found that some of the LT engines have fuel pressure regulators that arent that accurate.
Good luck and if you have any diag questions email me at [email protected]
Lee

[GeoffP]

I have a suggestion to try: If the lines running to your fuel rails are long enough, pull the rail, injectors and all. Cycle the fuel pump by turning on the key to pressurize the rail. Doing this will allow you to visibly check to see if any of the injectors are leaking. Another possibility is that you simply got a new opti that was bad out of the box. It's probably not bad, but could be. Another could be a bad ignition module. Has it ever run good or has it been like this since you put it in the car?

[Boulder69]

Lee,

Thanks for the input. All of this started when a heater hose blew and spewed coolant everywhere. The drivability problems started on the way home after a quick roadside repair to bypass the hose, so the Opti replacement was logical given my past experience. Plus it gave me the excuse to switch to an F-body water pump which has better routing for my application than the Vette unit I was using before. Now I have an extra Opti that I am sure I will need sometime because well, it's an LT1....

I do have a cable and can run the diagnostics from my laptop. I get nothing really out of the ordinary and no trouble codes. Then again I am not an ASE guy, just a hobby guy so alot of that stuff I don't quite understand yet. Considering it runs OK in open loop tends to rule out the MAP and MAF. It runs OK when I stomp on it as well. The only time it runs like crap is after it goes into closed loop at part throttle. This seems to be O2 related given all of the symptoms.

If it was a bogus injector or fuel pressure regulator wouldn't it run like crap all of the time?

Thanks for all of the help guys. It does help. -e

[GeoffP]

This is good info. I would also double check all weatherpak connectors to make sure none of them have water behind them.

[ProTouring442]

You'll need to get into the datastream and watch the sensors. Go through them one at a time and see what the computer "thinks" is going on. Look at the Engine Temp and the Air Temp to start with. If the computer thinks it is doing the right thing, it won't set a code. From there, look at your O2 readings, are they saying the car is running rich? If the readings are fixed, or saying the car is lean when it's really rich, you are on the right track. If you have a grounded out O2 wire, it would drive the ECM to full rich as it would read the O2 as saying the car was running full lean. A fixed O2 reading should set a code, but it is still worth looking for. From here, continue looking at all of the sensor outputs. Something as sillt as a stuck TPS could be the issue. Finally, if all sensors look good, try grounding the O2 sensor wire (not the heater wires!), this should drive the O2 reading full lean, and after a few minutes in closed loop, it should set a code. If it doesn't you may have a faulty ECM.

Shiny Side Up!
Bill
www.FQuick.com/ProYouring442

Good Luck!

[Boulder69]

O2 Sensors fixed it. Now I need to swap out the fouled plugs and I should be all set.

[jc70chevy]

i dont know if you fixed this problem yet i had a problem like this in my 95 z28 it turned out to be the knock senor after i replaced it i ran a hell of alot better and not so rich when warmed up

[Boulder69]

Nope. It was the O2 sensors for sure. Runs better than ever now.