LT1 issues

[campfire]

Wasnt there a "fix" for optispark setups (other than just replacing the LT1)? I recall something years back that was supposed to keep those distributor problems from occurring, but maybe it wasnt as much of a fix as it was being sold as, if not being mentioned here?

There are $1000+ kits to install a more standard camshaft sensor in place of the optispark. This then drives an LS1 PCM with LS-style ignition.

There are $400 kits to decode and re-encode the optispark signals to drive an LS ignition setup.

The reason I'm scratching my head is that I already have a crankshaft position sensor, fully capable of driving a waste-spark system, but I haven't yet found a GM engine that had 8 cylinders, MPFI, and waste spark ignition. I keep coming up with rear-mounted distributors (which don't fit on my engine without significant work) and COP setups that need camshaft sensors (and may not directly drive my MPFI setup).

It seems like this is the only front-mounted camshaft sensor that GM ever paired with a distributor-based ignition system on an 8-cylinder engine.

Adapting an LS camshaft sensor to my camshaft seems like the most reliable option. But by the time I get an LS PCM set up I may as well just swap in the entire LS engine.

 

[campfire]

Another reason I like points....

I know a guy who had a Camaro with that crap Opti-Spark setup,he put in more ignitions than spark plugs in that car,like 4 times in as many years...not one of GM's best inventions--why they didn't just stick with HEI when it worked reliably I dont know..

Isn't there some aftermarket "drag race" ignition that could be adapted to eliminate that setup without paying $1000+ bucks for the MSD one..?..I've seen some that use a reluctor wheel on the harmonic balancer and a MSD box like the 6AL to run the engine when guys want a cheaper way to use a newer computerized engine in a race car or pulling tractor without having to wire up a harness to use the oem computer..

Points...Ugh. You can keep 'em. And you can keep their short lifespans. The optispark may have horrible implementation, but at least the concept is sound. Points are built to fail in time, no matter how well they're implemented. And a good DIS will outlast them both.

Yes, aftermarket reluctor wheels exist for both crankshaft and camshaft. And I already have a 4-lobe reluctor wheel and sensor on my crankshaft. I just need to connect the dots...

 

[ChrisPerry]

I wasn't saying it broke after 20-30k, he either wrecked or sold the cars without ever having another issue.

 

[Blue85]

You have a trigger wheel, but is the hole combination compatible with any other standard ignition system? The big feature of Opti was the 360 degree resolution from all the tiny slots. You could spark it with Megasquirt, or run the whole engine off it. The beauty is that you could start by using the Opti(cal)Spark pickup and stock coil, then swap to another ignition system after it's running (like a GM DIS or Ford EDIS) by just changing the settings in the (free) software. Is the main failure mode exposing the active optical sensor to the EMI and ozone of the spark?
https://www.diyautotune.com/support/tech/install/chevrolet-gm/megasquirt-lt1-lt4-l99/.

My K5 sparks with a trigger wheel on the crank pulley, a Ford EDIS module, a pair of Dodge Neon coils, stock SBC plug wires and the advance signal from the Megasquirt ECU, so mixing and matching is possible.

But yeah, an LS swap could be less work than one of the conversions out there. Must be a Roadmaster wagon? I can definitely see the appeal of swapping some parts to get the Opti working well and crossing my fingers...

 

[campfire]

You have a trigger wheel, but is the hole combination compatible with any other standard ignition system? The big feature of Opti was the 360 degree resolution from all the tiny slots. You could spark it with Megasquirt, or run the whole engine off it. The beauty is that you could start by using the Opti(cal)Spark pickup and stock coil, then swap to another ignition system after it's running (like a GM DIS or Ford EDIS) by just changing the settings in the (free) software. Is the main failure mode exposing the active optical sensor to the EMI and ozone of the spark?
https://www.diyautotune.com/support/tech/install/chevrolet-gm/megasquirt-lt1-lt4-l99/.

My K5 sparks with a trigger wheel on the crank pulley, a Ford EDIS module, a pair of Dodge Neon coils, stock SBC plug wires and the advance signal from the Megasquirt ECU, so mixing and matching is possible.

But yeah, an LS swap could be less work than one of the conversions out there. Must be a Roadmaster wagon? I can definitely see the appeal of swapping some parts to get the Opti working well and crossing my fingers...

Boy-o-boy. Yes, I want to build a megasquirt system. But this is not the time nor the right vehicle for that. Yes, it's a Roadmaster wagon. The trigger wheel only has 4 lobes, so it's not as precise as what other spark-control systems use. It's just supplemental data, it's not used for spark control with this PCM. A trigger wheel would work, but developing and debugging such a system just isn't the purpose of this car.

Yes, EMI/o-zone is one of the things that's bad for the optical sensor. The other is water/oil contamination. I crawled under there today and replaced the driver-side plug wires, and the water pump weep hole is definitely wet. As is the entire front side of the distributor cap. It was wet enough to still have a drip clinging to the underside of the distributor housing. Not sure whether I somehow missed that, or if the problem has more recently developed. But a failing water pump is not a great idea. And if I hafta change that, installing a new distributor is easy.


Today I fired it up to verify the 8 new plugs & 4 new wires are correctly installed (runs like a top, so the wires are in the correct holes). While it was running I fired up Torque and found the P1371 code. Finally something to go off of, but perhaps inconclusive?

P1371 means the PCM AT SOME POINT could not find the low resolution pulse signal from the optical cam position sensor in the Opti. If the engine is running, its a "stored" code, and not an active code. When that code is "active" it shuts down the fuel system.

It isn't unusual to find P1371 as a stored code. I think it sets sometimes when the PCM has a hard time finding the pulse signal on initial cranking. Clear it and see how fast it comes back. The more frequently it appears, the more likely the optical sensor or the wiring harness has a problem.

https://www.camaroz28.com/forums/lt1-based-engine-tech-9/code-p1371-751501/

I then came back out 1/2-hr later to check codes while not running. Same code, but I also started it twice. Big billowing clouds of smoky unburned exhaust coming out both banks, and it barely would start or run even at WOT (and definitely not at idle). Same old same old.

Sounds like I definitely need to change the opti rather than trying an LTCC-style conversion.

 

[jekquistk5]

Does it look like this? I did a bunch of little stuff for my buddy a year ago. Cool car, the off idle torque of those lt1’s is nice.

 

[Blue85]

The trigger wheel only has 4 lobes, so it's not as precise as what other spark-control systems use. It's just supplemental data, it's not used for spark control with this PCM.

Well what kind of setup is it then? Optispark uses low res and high res tracks on the wheel to determine crank position. What is controlling spark timing?

 

[campfire]

Well what kind of setup is it then? Optispark uses low res and high res tracks on the wheel to determine crank position. What is controlling spark timing?

Clarification...the CRANKSHAFT trigger wheel is supplemental. I read that it is to help the PCM diagnose misfires (though it clearly isn't doing that properly, as I still have no misfire code). The tracks in the optispark unit are what control timing.

I was thinking that a 4-lobe trigger wheel doesn't offer the resolution desired for spark timing. It should work, in theory, but it's a lot fewer pulses than the EDIS or LS1 setups desire. And it's a whole lot less than the 360 slots offered by the optispark.

 

[campfire]

Does it look like this? I did a bunch of little stuff for my buddy a year ago. Cool car, the off idle torque of those lt1’s is nice.

View attachment 317359

Yes, that's the one. A rad wagon indeed.

 

[campfire]

Alright...after finding the water pump weeping onto the distributor, combined with the P1371 code (low-resolution optical sensor failure), I changed them both. The code is gone, but it seems to have made no difference. Sometimes it runs perfectly, sometimes it won't start, and it stalls out while smelling rich and belching black smoke. It left black spots on the ground, you'd think I'm playing with my diesel.

So I went back to plan B, checking the fuel pressure (as Bent and I had discussed earlier). It's all over the place. I didn't realize that this engine uses a vacuum line to mechanically throttle the fuel pressure regulator, so it really threw me off when I first measured it (fuel pressure drops as vacuum rises). But even with the compensator line disconnected, it rises to 43PSI (proper pressure), and then fluctuates +/- 4psi in an erratic manner, regardless of engine loading. Sometimes it's steady, and the engine seems to run well in that condition. So I ordered a new FPR, and we'll see how that goes.

Aaaaaaaaaaaaaaand then, while testing the fuel pressure, it threw code P0372. High-resolution optical sensor failure. Which was not present prior to the optispark change. It's possible I have a flaky (new) distributor, or it's possible that I have flaky wiring, or maybe even a flaky PCM. It can't be missing the pulses all the time, or the engine wouldn't run. The low-resolution failure code was historical, but this one was current. I cleared it out and we'll see if it comes back.

Sigh.

Is the weird engine flutter you are feeling perhaps an over fuel condition and it's blubbering? Was contemplating what you had said about the regulator also. But I believe you are on the right path

 

[Blue85]

I didn't realize that this engine uses a vacuum line to mechanically throttle the fuel pressure regulator, so it really threw me off when I first measured it (fuel pressure drops as vacuum rises).

This is normal from late 80's into mid-2000's. You get more resolution from the injectors by keeping a (nearly) constant pressure across them, then having them set to a fixed absolute pressure.

 

[campfire]

This is normal from late 80's into mid-2000's. You get more resolution from the injectors by keeping a (nearly) constant pressure across them, then having them set to a fixed absolute pressure.

Makes sense.

New regulator installed today. It now runs well enough for a 7-mile test drive, which is lots better than before. Fuel pressure stays steady at 43psi with the vacuum line disconnected, and it modulates smoothly up and down when connected. No more bouncing around on the gauge. It started fine and idles beautifully, but it's still bogging at light throttle positions. Sometimes completely stalling when I try to accelerate gently. But it's more or less driveable, as long as I avoid that one throttle position. No more smoke, and it runs more smoothly, but it's probably still short of power, with an occasional stumble. Exhaust smells slightly rich, much better than before. About 4 miles into the drive it threw code P0307 (misfire on cylinder 7). No idea why it is just now catching on to the misfires (). I reset the code and it came back half a mile later paired with P0300 (Random/Multiple cylinder misfire). I reset it again and P0307 came back again shortly thereafter.


If I'm lucky, I'll find a loose spark plug wire on #7.

But it's now running well enough that I can start test driving it and accumulating information.

 

[campfire]

No dice. Drove it 3 miles today to the gas station. It ran ok, but not great. Filled up the tank, cranked it over, and it barely started, belching black smoke and refusing to idle. As I drove back home, it would buck and stall every 30 seconds or so. Fuel pressure held steady, and it still has a dead zone just off of idle.

I think I'm exactly back where I started last month. Again it gave no error codes. I did not find a loose wire on #7 cylinder, but it's back to running poorly across the board, not just on one cylinder.

Next thing is changing the spark coil and rechecking all the wiring for the 4th time.

Oh, and the bolt holding the fuel lines next to the regulator is threaded in from the underside. Reaching up from underneath the fuel rail probably triples the amount of time & work required to change the fuel pressure regulator. Wasted time has been a running theme with this project, eh?