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Looking for LT-Juan HELP, Daughters LT1 (1st car) with 60k miles is missing running rich, and I'm wearing out the parts-cannon trying to fix it.
Issue: Runs great when cold, get her around 160f and she starts to stumble and is running pig fat. 3-years and counting.
New Parts:
1. Opti about 3-years ago with new plug wires.
2. New plugs 2-months ago.
3. New Bosch O2 sensors 2-months ago.
4. New Plugs 2-months ago.
5. Used Accel injectors pulled from the secondaries of my LT5.
6. New Coil and ICM with spacer mod yesterday. Found the coil wire not fully seated, got excited, wasn't an issue
7. Added a ground strap to the ECM 2-months ago.
8. Adding a ground strap to the coil bracket today, it won't do anything.
9. New MAF 2-months ago.
For the money spent on this and the wasted time, I should've swapped a 5.3 or 6.0...
AC Delco sensors seem to work better than Bosch in the LT1 system.
In my experience, Accel injectors are not the best choice. What #/HR flow rate?
Were the Opti and coil wire terminals and sockets free of corrosion?
What diagnostics have you used that led you to replace all these parts? Or does “parts-cannon” equate to “parts replacement roulette”?
Is the SES light on? Have you scanned it for codes? There are codes that do not turn on the SES light.
Sounds like it MAY relate to the coolant temp sensor in the water pump. If it is indicating a lower than actual temperature, the PCM is going to be fueling the engine in “cold start mode”, where it richens the A/F ratio, and elevates the idle speed. What transmission (affects idle speed programming)? What is the idle RPM just before things go south? Before replacing sensor, test it:
MAY also be related to the PCM transition from open loop (startup) to closed loop, which depends on coolant temperature, O2 sensors hot enough to work, and a “timer” - typically about 206-seconds from startup.
1. Probably the cheapest one on the market.
2. NGK R and I think gap is 45 or 50, whatever the manual said.
3. Ordered Delco sensors 2 hours ago, why not.
4. Think they are 24lb, normal stock replacements for the ZR-1.
5. Didn't check the coil connections, i'll clean and grease.
6. All diagnostics are by the seat of my pants. Closed loop issue, the O2 should've fixed it IMO, but it didn't. My ALDL are in my ZR-1 8 hours away in Odessa TX where my company is based, I'm on days off right now.
7. No SES light, just horrible miss at idle, and breaks up/backfires throughout the RPM range, even at WOT when warm.
8. Ordered a new CTS 2-hours ago as well.
I've read 100's of Forum posts and watched every Youtube vid that pulls up. Nada. Fearless Mods has a series of videos on the same issue for 3 years, he just replaced the OptiCrap and same issue, I think he's looking at the PCM now. Who knows...
If the PCM isn’t going into closed loop, it can be because the O2 sensors are not “ready” due to not reaching the 600°F temperature required to make them work. There are “flags” in the PCM data stream that tell you if they are ready. The other issue can be the coolant temp mentioned above. It typically takes 140°F before it can enter closed loop. And there's also a flag in the data stream telling you if it’s in closed loop, and “learning enabled”. The coolant temp thing is just a guess, but something you hadn’t checked.
The easiest way to see the PCM data stream is a free software - Scan9495 - specifically written for the 94/95 LT1 engine (and later modified to cover 93 as well). I can give you a link to info on the software. In the past I've offered a service, at no cost, reviewing the data logs to help people find the source of their problem. Unfortunately it has become too time consuming, and people don’t seem to want to provide me with all the info about their engine, won't follow through with my suggested diagnostics, or give up and never come back to tell us if their problem was solved.
But you sound like you are smart enough to dig into the data yourself, with minimal help.
Shoot dude, a smart hand would've brought the dang ALDL cable from the ZR-Juan to use that software on his days off... It'll be months before I'm back home to work on it. Wait a second, this 95 has an OBDII style diagnostic port the is pinned differently.
However, I did ground the coil bracket and applied some Arctic Silver replacing the dielectric grease I used yesterday during install; no change at all. I did notice that the car does miss cold, and gets progressively worse as warms, quickly pulled inj connectors with minimal RPM on the front 4 holes. Manipulated the inj harness wires while running looking for change, didn't find any.
If all else fails, I might pull the trigger on a Petris Enterprises pin drive, new water pump, timing gasket set and wires. $650.97
I'll be on a Perkins call all day tomorrow, so I'll OHM the coolant sensor on Tuesday, or just replace it and the Bosch O2's, they'll be in on Monday.
They already had the LT5 with waste spark distributorless ignition when the LT1 came out, why does this ignition system exist?
95 has a 16-pin OBD-2 style connector, but the PCM is still OBD-1, identical to the 1994 PCM. You can buy a 16-pin ALDL cable specifically for use on the 95. Or you can just jumper a 12-pin scanner connector.
Got the diagnostic cable and program, couldn't see anything that was causing the miss, it's missing in open and closed loop now, activating in open loop didn't change anything. Also found the fans don't turn on; however, i can activate fan 1 and 2 from Scan9495, replaced the coolant sensor, no change. Also peeked at the Opti and plug wires at night, there's a lightning show at the Opti and left bank plug wires. So at least a Cap and Wires.
In the screenshot the voltage was low with the AC on high, headlights on and both fans active. Misses at 13.8vdc too.
So the Torqhead is ordered, hopefully fix the cooling fan issue and my kid can finally enjoy her car.
Something’s causing it to pour a lot of fuel in, at least in the idle cell. Bank 1 LTFT is maxed out at 160, adding 25% extra fuel, and even more with an elevated STFT. Bank 2 is not far behind. If the misfires are that bad, might explain it. Torqhead is an expensive fix. Did you consider Bob Bailey's LTCC, removes the high voltage from the Opti, which seems to eliminate the problems with the optical cam position sensor, which is retained. Fires 8 LSx coils.
I ran a similar setup, before the LTCC was available. Started with an OEM vented Opti, Opti fed cam position to a MoTeC ECU, with their 8-channel ignition driver. Installed in 2000. Still running strong 22 years later. Just sold it after owning it 27 years. New buyer just took it for a quick drive:
03-27-2022, 11:24 AM
