LS1LT1 Forum banner
1 - 4 of 4 Posts

· Registered
Joined
·
11 Posts
Discussion Starter · #1 ·
Sorry this is going to read like a book. I was a diesel mechanic in the late 1980’s and OBD systems were out while I was in school, so I have some tech skills. Lol
**My son US ARMY has a stock 1994 Firebird TA GT auto trans - 58,000 miles,.We bought the car in 2021 from a mechanic with a new water pump installed. After driving car for 500 miles we heard ignition detonation knock under hard throttle. After reading this forum I thought Opti was bad and replaced it. I got from Autozone with lifetime warranty car ran perfect with new one. Because of Covid no good ones you guys spoke of were available (Petris) 3 months after replacing I got email from Petris saying they were available, just a bit late. Kid took the car DEC 2021 to North Carolina from Wisconsin with no problems.
**May 2022 Son was discharged to go to West Point so I drove car home for him. North Carolina to Wisconsin, car ran great 25mpg and no problems. A 2 weeks later he’s driving & engine started loosing power after it warmed up, car was Non Operable at this point. I took it out for a drive a few times after it sat overnight multiple times. Car started and ran great for a few minutes then a couple blocks from my house the thing just lost all power 15mph max and goes funny shifting. I've read 100+ posts, watched YouTube videos but can’t seem to find issue.
**OK so the story changed a bit - things got worse -Car did runs great when cold, could spin wheels. Even when car is warmed up it did idle perfect, when in park you could rev engine. It did not miss or backfire.
**SEPT 2022 OK so a little change in problem, I just fired up the car after 2 months of sitting. It started fine but 2 minutes into running it won't go over 1800rpms and stinks out the tailpipe. It sounds like a diesel - not like rod knock just a bit out of time and doesn’t idle good - bad miss firing.
**I put in new Opti July 2021 which was 2500 miles ago, and I did replace Opti again OCT 2022 with wire harness pigtail up to plug next to intake. Again Autozone because of lifetime warranty.
**I tested O2 sensors- (they tested fine but out of caution put in 2 new AC Delco sensors), Tested tps, maf, fuel pressure is 43psi and held 30psi for hours after. Fuel injectors all 12.4 ohms, also Noid lite on all injectors was solid pulse. I did test engine running and disconnected each injector and there was no change in RPMs from passenger side, but Driver side definitely could tell drop in RPMs, I took out the PCM and checked all the pins to see if there was corrosion also. I checked EGR and fuel pressure regulator,
**When we got car I replaces OPTI, fuel filter, intake gasket, ground strap,rad coolant sensor. no spark plug wire light show
**SINCE problem began NEW knock sensor, water pump coolant sensor, ICM, coil,
**OCT 2022 Got the OBD1 cable and downloaded Scan9495 for PC it had 2 DCT codes 16 & 18
**NOV 2022 new spark plugs - the old ones looked good.
**12/5/22 Now again today tested voltage and ohms at pins for Opti and ICM all normal 5v 12.3v and continuity. Injectors raised fuel rail and battery tested each one Spray was perfect and no leaks. Barely idles now and hard to start. I did smell oil to be sure there isn’t a stench of gas in oil. It seems ok.
**I saw today in a post about oscilloscope testing- I will buy one but I'm not sure if the car runs (be it badly) that I need to test Opti with it. And I don’t even know how to use one (but I can look it up if needed)
**The answer may be here on forum I just haven’t seen it, Any help would be appreciated, My son is home in 2 weeks for Holidays from West Point and I would like to have Car repaired if possible for him. Thank you guys
 

· Registered
Joined
·
93 Posts
Code 16 indicates that you may have an opti problem. Low Resolution Signal not found. I know you addressed the Optispark, however, the parts store units have been known to be a bit of a crap shoot.

Code 18 indicates that there is a problem with the injector circuit. It could be a bad connection, loose ground. Further diagnostics can be found in the service manual.

Service manual downloads

Good luck!
 

· Registered
Joined
·
4,116 Posts
Injector code may be from disconnecting while running. Normally heat related issue I'd suspect icm, but looks like you put a new one on.

Not on LT1s but on other cars I've seen cats get damaged and not cause problems until they get hot, then they act like a huge restriction.

May not be heat though, could just be open loop vs closed loop.

Probably not your problem but first thing I always do is unplug the MAF and see if it runs better.

You've mentioned a bunch of testing you are doing, you might want to only do your testing when it's running bad in case it's an intermittent problem
 

· Registered
Joined
·
11 Posts
Discussion Starter · #4 ·
OK so problem solved, Bad Catalytic converter. I downloaded and used the SCAN9495 which you can Google or search on here. Doug did a great job with this PC reader and even explains how to make a USB cable for under $20. It showed all the operating systems and an Admin saw my screen shot and saw MAP pressure was to high. He thought Catalytic converter may be plugged. It was actually on my list of things to check way back in October but somehow got sidetracked. I drilled a hole thru the pipe in front of converter and put a camera in and saw the converter had collapsed (it looked like Lego's) I even looked back at text messages to my son and sent him pics of a good and bad one. Terrible of me to not have followed my gut. Well after running all those tests it just happened to be a simple fix. The admin also said you can buy a back pressure tester and remove O2 sensor and check that way. All fixed now, Thank you guys for responding
 
1 - 4 of 4 Posts
Top