Not Using The Crank Position Sensor

Hello.... I am current,y running the Accel Gen 6 engine management system.... bought the car with it already installed.... it is a very archaic system but it does the job.... the interface is DOS and not Windows and it has very poor data logging. I have the opportunity to get my hands a Accel Thruster system... cheap!! My son works for Leash Electronics, and is going to convert the harness to work with my LT1.

I am currently not using the crank position sensor.... I never have. I also sonveretd to electric water pump and double row chain and I removed the reluctor wheel when I did that.

does the Opti provide a "crank trigger" where the CPS is no longer needed when running an aftermarket engine management system??

thank you for any input!!

Depends whether the Accel Thruster ECU is designed to process the Opti's pulse signals, that identify the position of each cylinder. Typically the aftermarket units that accept the Opti signals are units that can operate full sequential injection. Thruster is discontinued, can’t find much info. What I did find is that you need a dual-synch distributor to run full sequential.

With the stock LT1 PCM, the crank sensor was only added to meet the OBD-2 misfire detection requirements. It is not used to run the engine.

Thanks for the reply Injuneer!!.... I did some additional research and the Thruster is Opti compatible with a supporting harness part number ACL77653..... no longer available:-(..... I think my son get make one for me.

Not sure if my ATI damper can mount a MSD trigger, but that me be an option as well.... not sure.

There is some interesting info on that sensor for those still using the GM computer with the OPTI.

About 8 years ago I had an issue where the car just slowed down. Nothing was wrong as it drove perfect but it just didn't have the power it use to. I checked everything and couldn't find anything wrong and that's the worst problem to have. Easy to fix something that stops working!! What I did notice was you could see the #6 cylinder dropout went the engine went above 3000 RPM's on the wideband. Change the plug, changed the plug wire, changed the dist, cap, put a new injector in the port, changed the injector box, Changed the computer and still the same thing. No check engine codes or anything that's showed anything wrong other then my eight channel wide band showing #6 dropping out, even though you couldn't feel it or hear a miss. Could be about the only time, since I have been playing with this stuff, where I was ready to change to a FAST system or something else as I was out of ideas why this was happening and couldn't fix it.

I'm lucky as I know two guys that either work at GM in Detroit or with GM as a vendor. So I called in a favor to see if they could ask around after telling them the story. About a day later an engineer called me from Detroit and starting telling me what some of the electric/electronic engineering was for the OBD's. The one thing he said was the 96's were to be OBD1's and were changed to OBD2's at the last minute. He also talked about the timing wheel in the OPTI and why they put the crank sensor in there for 1996 and OBD2. He stated that the ODB1's without the crank sensor were having issues above 3000 because of the speed of the timing marks on the OPTI wheel. So they changed in 96 to the crank sensor which helped above 3000. It also told me the crank sensor was designed for the ODB1's so it was there in the program even though a 95 or earlier never had the sensor.

He never came out and told me what he thought my problem was but I had heard enough and now knew an issue in the crank sensor could cause a problem. Replaced the crank sensor and the engine ran on all eight again, problem gone!! It never crossed my mind a bad crank sensor, with no check fault, could drop a single cylinder.

To this day I run the crank sensor as it's there for a reason which helps the timing above 3K.

Now thats info thats hard to come by. Thank you for posting this!

My statement is based on GM's statement. 1996 factory service manual on troubleshooting P0335 and P0336 codes for the CPK sensor states "This sensor is not used for spark or fueling." The issue is also clarified in manual "Corvette Fuel Injection & Electronic Engine Management" by Charles Probst. That manual bears a GM Part #12497977. "So in the LT1 and LT4, Opti-Spark provides the distributor reference signals for timing of fuel injection and ignition. And in the 96 LT1 and LT4, the CKP provides misfire detection."

The Society of Automotive Engineers technical paper #920673, Kulkarni, A., "New Generation Small Block V8 Engine," describes the extremely high accuracy of the optical cam position sensor, and shows the results of actual testing that confirm a significant reduction in spark scatter compared to the previous L98 distributor system. GM attributes the LT1's ability to run aggressive spark timing, and the resulting gains in torque and HP to the reduced spark scatter. GM also attribues the engine's reduced emissions to the reduced spark scatter. I run the optical sensor (but not the factory PCM) with redline in excess of 7,000 RPM, with no problems. Others have run LT1 engines closer to 8,000 RPM with the stock GM optical sensor. Rick Abare, often cited by Advanced Induction for the extreme performance of his LT1 was running a Dynatech Opti and Holley ECU above 7,000 RPM, to the best of my knowledge.

Over the course of 20+ years helping people with their LT1 problems, I have accumulated close to 1,000 PCM data logs showing critical PCM sensor readings and parameters, I have never detected a difference in performance between systems with and without the CKP. Nor have I ever seen a misfire problem solved by adding or replacing the CKP sensor. Not to say it hasn't happened in the case described above. I have found numerous problems caused by faulty Opti's - including the recent problem with the erratic RPM readings from the MSD Optis, a problem MSD confirmed by reviewing my analysis of the problematic data from the optical module they were using. All this is documented in posts on this forum, since a member here worked for MSD and passed the documentation back and forth.

I'm not pulling this info out of my rectal orifice.

I never doubted you and thanks again for the input.... I'm still looking into how I can wire the Thruster into my OPTI.... I thought a crank trigger was an option but that damn OPTI looks like it would be in the way for thE sensor.. LOL

I ran an Electromotive SDI/Opti-Eliminator for a while with my stock PCM. For crank input, it used a 60-tooth wheel bolted to the front of the crank damper/pulley. The disadvantage of that system (with NO cam position input) was that the sequential injection could synch incorrectly with the wrong crank revolution. No problem with ignition, because the system used a waste spark, dual-tower coil system. But the injector sequence got screwed up 1/2 of the time. Main place the problem was noticed was on cold start, where the fuel injected against a closed valve wouldn't vaporize. Once the engine got hot enough, it was not really affected any more that a batch fire/bank-to-bank injection strategy would be.

But, the Electromotive system was not compatible with an OBD-2 PCM, because the incorrect sequence of the injectors would trip the misfire detection, picked up by the CKP sensor. The "engineer" at Electromotive, a guy named JC Hyde, bought his own OBD-2 Camaro to try and develop the Electromotive system to the extent it would work with OBD-2. The owner of Electromotive died in the meantime, and Hyde was diverted to keeping the company running. I had a "sudden cutout" problem with my system, and he dropped me like a hot potato. I had given him all kinds or info/photos on my install, since it was one of the first ones done, and even drove my Formula to Electromotive in Manassas VA to show him my install.

Eventually Hyde left and started Delteq. We all know where that went.... the first system was not really any different than the Electromotive SDI/Opti-Eliminator, except he used the Opti for the trigger, and the waste spark ignition components from the GM Northstar engine. He promised everyone who bought the initial Delteq system they would get first chance and reduced price on the "advanced" Delteq system that totally eliminated the Opti, and was OBD-2 compatible. One day he disappeared from the face of the earth and was never heard from again. No tech support for the Delteq owners, no replacement parts, etc.