Hi guys, I hope I'm not offending anyone by pushing a question about a vehicle that isn't a Corvette, but I could really use some help with the Lt1 engine in my 96 Impala.
I installed the LTCC kit in my 96 Impala with ACDelco LS1 Coils, Taylor Magnacore wires, and ACDelco plugs (gapped at .050). I even put a new Opti on the engine just to make sure everything was "new." I took the Opti apart before installing and removed the rotor button tab. I didn't remove the entire rotor, just the metal tab on the end. I also loctite'd both screws in optical sensor disc. I started the car and it runs like a beauty. I was very happy with the cleanliness of the install and everything seemed just fine.

HOWEVER, after I took it out for a test drive today, I immediately felt like the engine was sluggish (like back to stock power), but I proceeded to drive. When I got out of my neighborhood, I decided to open it up a little... I floor the throttle and the car took off nicely, but as soon as I hit 4000rpm, the engine backfired and cut off.

It started right back up as if nothing was wrong. I got back to the shop and while sitting still, I revved the engine to right at 4000rpm and the engine backfired louder than I've heard an engine backfire before and cut off. It starts right back up though.

My LTCC kit green light is on with no flashing red light. No check engine light. As I said the engine cranks right up and runs very nicely. I did notice a little more engine vibration when idling though.

I do have a PCM tune that I had PCM4LESS tune for me about 8 years ago. Could that be the issue since I have modified the ignition by eliminated the ICM and factory coil?

Can you give me any input on this issue with my Impala?

 

Impala is NO different! LT1 is a LT1.. now you did make things complicated. Why did you replace the Opti??? what was wrong with the Original???
what brand? aftermarket Opti. New does not mean it works!! did you align the keyed splines correctly? full seated?
you no longer need your rotor. you can remove the ICM & Coil. the LTCC. actually improves & makes the engine run smoother.
the backfiring. is a strong sign something is up with the Opti.. unless you wired in the LTCC incorrectly. but you did mention you have the Green light AKA system is OK.

 

I replaced the opti because the one I had on the engine had failed. I had severe corrosion on the cap/contacts as well as the rotor button. Codes showed that no high pass resolution signal from opti had been received. That was my 4th opti over the years. Figured I would do my best to eliminate future opti problems by switching over to an LTCC kit. I put a new opti on in order to utilize a new optical sensor inside the new opti.
I removed the tab on the end of the rotor button of the new opti to prevent it from contacting/rubbing contact points inside the cap.
I removed the ICM and coil from the engine upon installing LTCC and wired the LTCC up the correct way. Only thing I did different from ltcc instructions was that instead of running the two pink wires separately all the way to the connection at original coil plug, I spliced them together at the beginning of the LTCC harness.
I do have green light in ltcc box and engine runs with no backfire until I reach 4000rpm

 

What kind of "new" opti is this and where did you get it?

 

New Optispark distributor from Carquest. Part number T1833.

 

That is more than likely your issue as parts store optisparks are hit and miss. Some are DOA and some are good for years.

 

Crap. I just got done putting all that back together
what should I purchase & where from? Hate that I have to buy a brand new opti when all I need is the optical sensor to work.

 

reading PDF there is a reference to using Taylor Spiral-pro wires. It also states MSD superconductor or similar wires cause trouble for LTCC. It also references spark retard and rev limiting adjustments both should be off. IDK if tune would be sensitive to LTCC but if you have a 96 lt1 PCM you could swap it out. and see. If you have access to a scope that does DIS systems you would be able to see ignition patterns. What does PCM data indicate?

 

Taylor Spiro Pro's are an excellent choice for the LTCC kit. The OP is using Taylor Magnecore wires which may or may not pose a problem. You want to stay away from Low Resistance MSD type wires.

For a 96' I would be trying to hunt down a genuine NOS AC Delco. It will be expensive, and possibly hard to find. However, it will last. My second choice would be a Petris Enterprises Opti:

http://petrisenterprises.com/store/#...tegory=5760095

 

I'm using Moroso Blue Max Spiral Core Spark Plug Wire Sets summit part #73210). I couldn't ever find the specific Taylor wires part number on any of the LTCC instructions. If wires are wrong style and opti was bad, why would I only be seeing issues at 4000rpm (other than the sluggishness I noticed)?

 

-Those plug wires should be okay.

-There is no specific Taylor wire part # for the LTCC kit. You make your own.

-All Opti Symptoms are different, but cutting out at the upper end of the RPM spectrum sounds timing (opti) related.

-Retrace your wiring, especially where you soldered the two pink power wires to the original coil power wire, make sure everything looks gravy.

 

Is the LTCC package new? You didn't actually mention.

I believe if I were needing an Opti- I'd be at the JY and be looking for maybe a 4.3W (L99) from a full size car. It might be an easy find OR if someone realizes what's up maybe they've all been stripped. Don't know until you've looked. If you're in a major metropolitan area some of the lesser cab companies might still have some of these things.

Any of these JY that inventory things well might off a 4.3W (L99) real inexpensively - real cheap. I did a real quick cart-par.com search and Opti- was $50 to $150 OR CALL - You would have your choice of many including the Cadillacs - search until you find one on an engine with the OE #.

 

That would be a great source to find OE opti's. I would be very careful choosing parts from cars that get driven year round. Especially on the East coast. Salt + water + O2 "Destruction"

 

I'll check the junk yards tomorrow. I'm not so sure they'll have any around here, Charlotte, NC. But 150 bucks for a used opti is sounding a little better than 450 bucks for a new AC Delco. In bound and determined to get this right. I miss driving my car.

 

Allow me to chime in...

I re-wrote the manual for Bob a number of years ago... as far as I know, that version is still going out with the kit. I installed this kit back in 2003! I did send it back once due to water intrusion, but it was ok, per Bob. It has been humming along for nearly 13 years and well over 100k miles.

The low-resistance wires problem was more related to the early coils, from what I have figured out. The later LS2 coils don't have that issue. Unless there is an electrical field issue I am unaware of.

Did you make the wires yourself or buy them to a set length? If you made them yourself, that would be a place to check. Unless they are crimped right from the get-go, they will be a problem... backfires, misfires... take your pick.

As for installing the Opti... on a 2nd get Opti, it either works or it don't. And when I say that, the timing error for aligning the pin up will not allow it to start, at all. Period, end of story, ask me how I know.

Earlier Gen 1 Optis used a splined shaft that is really impossible to screw up. I suspect with a big enough hammer... but by hand? doubtful.

The reman'd opti is a great place to start. They are suspect in the first place... The newer units are not known to use the Mitsubishi sensor. These sensors are damned near bullet proof. A friend used to work at a Dodge dealer, and a lot of Dodge badged cars had a version of that sensor in their distributors. It was not uncommon to see them last 250k or more miles. The weakness isn't in the sensor, it was in the overall design... allowed the bearings to fail, damaging the sensor.

Find a nice, clean low miles used opti... Corvette, Impala, Firebird/Camaro (LT1 only), Cadillac Fleetwood and Buick Roadmaster all had a version of the LT1. You will want one from 1995-1996.

Now, if you are brave, you might get an older one, and swap out the sensor. I haven't attempted this yet myself, but, it might work.

When you put the opti back together, pickle the damned thing in RTV. I recommend copper RTV. Then, using some rubber hose and fittings, make a bypass line for the water pump, so it drains onto the ground and not the opti... stupid stupid design.

 

The wires I used were cut-to-length wires that I had to put the terminals on myself ( only on one end though and I'm certain that I did that right). Im using new AC Delco Ls1 coils. My engine is a 96 LT1 and uses the cam pin to drive it. The car starts beautifully and runs (except above 4000rpm when it backfires and cuts off) so I have to assume that I lined up the drive pin up correctly.

I am goin to leave the lid of the LTCC box and Rev the engine up to 4000rpm again to see if the red led lights up when the engine starts to muss and backfire. Maybe that will give me a clue...

Seems like if my engine will run at all, then the LTCC wiring must be correctly connected and conducting. Inside the LTCC, I have all the ***** turned to "0" which should mean that there is no Rev limiter, no second-step, etc. I cut and capped the wires that would be hooked up to an external two-step module.

Will the check engine light still illuminate for misfires detected? Or is that a feature I no longer have since I eliminated the ICM?

 

Not having oem icm should not change OBD. ICM doesn't deal with misfire It provides initial timing until PCM take over after engine starts.
IMO before I got to the trouble of hoping it's the opti I would check everything else. This thread may help diagnosing if optic is at fault.

https://www.corvetteforum.com/forums...e-pattern.html

Myself If scope pattern was ok I would swap in used PCM before trying another opti. It's just easier to replace.

 

If the OP had an available PCM (stock FLASH preferred maybe) I'd think it a logical first move. He's in/near Charlotte so I'd think he'd have no issues putting his hands on one.

I asked if the LTCC was new or whatever and he's not mentioned but mentions GREEN LIGHT, NO RED!!

 

Sorry I forgot to mention that the LTCC is brand new. Took Bob 3 weeks to make it...

 

Update: tried to start my Impala today after it sat for 2 days over the weekend. I now have a no start issue. I pulled the lid on the LTCC and I crank, I see the red led blink on-off-on-off. I assume that is code #1 which according to t he manual means "Cylinder Decode Sequence Error." Guess its time to switch out the Opti for another one?

What about this Used ACDelco on eBay?
http://www.ebay.com/itm/172179169780?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT